What changed in this filing

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Item 1. Business

2026-03-19 compared with 2025-03-20 · 165 added, 198 removed, 1224 unchanged (23% of the section changed)

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The next and final analysis will be conducted once 80 events (deaths) are reached.

We anticipate that 80 events will be reached this year.

In December 2025, we announced that our contract research organization informed us that the pooled number of events was 72 as of December 26, 2025.

We remain blinded to all efficacy and survival data outcomes and, as no outcomes analyses were performed and no statistical penalty has been incurred, this one-time update on the aggregate number of events does not impact future statistical analyses.

Because the final analysis is event driven, it is difficult to predict with any certainty and it may occur at a different time than currently expected.

We will announce the 80th event when it occurs.

In December 2020, we entered into an exclusive license agreement, or the 3D Medicines Agreement, with 3D Medicines Inc., or 3D Medicines, a China-based biopharmaceutical company developing next-generation immuno-oncology drugs, for the development and commercialization of GPS, as well as the Company’s next generation heptavalent immunotherapeutic GPS+, which is at preclinical stage, across all therapeutic and diagnostic uses in mainland China, Hong Kong, Macau and Taiwan, which we refer to as Greater China.

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The timing of such participation and patient enrollment by 3D Medicines, if at all, cannot be predicted with certainty.

As of March 15, 2025, we have received an aggregate of $10.5 million in upfront and milestone payments under our license agreement with 3D Medicines, or the 3D Medicines Agreement, and a total of $191.5 million in potential future development, regulatory and sales milestones, not including future royalties, remains under the license agreement, which milestones are variable in nature and not under our control.

In December 2023, we announced that we had commenced a binding arbitration proceeding against 3D Medicines to resolve a dispute regarding, among other things, the trigger and payment of relevant milestone payments due to us under the 3D Medicines Agreement.

As of December 31, 2025, we have received an aggregate of $10.5 million in upfront and milestone payments under our license agreement with 3D Medicines, or the 3D Medicines Agreement, and a total of $191.5 million in potential future development, regulatory and sales milestones, not including future royalties, remains under the license agreement, which milestones are variable in nature and not under our control.

In December 2023, we announced that we had commenced a binding arbitration proceeding against 3D Medicines to

resolve a dispute regarding, among other things, the trigger and payment of relevant milestone payments due to us under the 3D Medicines Agreement.

Legal Proceedings .

GPS was granted Orphan Drug Designations, or ODD, from the FDA, as well as orphan medicines designations from the European Medicines Agency, or EMA, in AML, malignant pleural mesothelioma, or MPM, and multiple

myeloma, or MM, as well as Fast Track designations for AML, MPM, and MM from the FDA.

In October 2024, the FDA granted Rare Pediatric Disease, or RPD, designation to GPS for the treatment of pediatric AML.

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We completed a Phase 1 dose-escalating clinical trial in the United States and China for SLS009 in mid-2023 and reported positive safety and efficacy data for both patient cohorts, that is relapsed and/or refractory AML and refractory lymphoma.

We also established in the trial a recommended Phase 2 dose, or RP2D, of 60 mg once weekly for AML and 100 mg once weekly for lymphomas.

We also established in the trial a recommended Phase 2 dose, or RP2D, of 60 mg once weekly or 30 mg twice weekly for AML and 100 mg once weekly for lymphomas.

In the second quarter of 2023, we commenced an open label, single arm, multi-center Phase 2a clinical trial with SLS009 in combination with venetoclax and azacitidine, or aza/ven, in patients with AML who failed or did not respond to treatment with venetoclax-based therapies.

The trial is evaluating safety, tolerability, and efficacy at two dose levels of SLS009, 45 mg once weekly, and 60 mg once weekly or 30 mg twice a week, in combination with aza/ven.

In addition to safety and tolerability of SLS009 in combination with aza/ven, the efficacy endpoints are complete response composite rate and duration of response.

Additional endpoints include event free survival, overall survival, and pharmacokinetic and pharmacodynamic assessments.

In the fourth quarter of 2023, we completed enrollment in the 45 mg (safety) dose cohort in the Phase 2a study and reported positive initial topline data.

At that time, we also commenced enrollment in the 60 mg dose cohort with patients randomized to one of two groups, 60 mg fixed dose once weekly or 30 mg fixed twice weekly.

Each group was planned to enroll five to 10 patients.

During the trial we identified 30 mg fixed twice weekly as our optimal dose level.

During the trial, we identified potential biomarkers currently undergoing testing as predictive markers in the most recent portion of the study.

In May 2024, we announced additional preliminary data from the Phase 2a trial of SLS009 in r/r AML and successful filing of a provisional patent application around the ASXL1 mutation and SLS009, including all CDK9 inhibitor drugs.

ASXL1 mutations are associated with poor prognosis in all myeloid diseases, owing to the reduced response to the current treatment options.

We observed a high rate of responses in patients with myelodysplasia-related molecular mutations (AML MRC), as defined by the World Health Organization, and patients with the ASXL1 gene mutation accounted for the most responders across all dose cohorts.

We expanded the ongoing study to include two additional cohorts, one with ASXL1 mutated AML patients and one with patients with myelodysplasia-related molecular abnormalities other than ASXL1 at the optimal dose level of 30 mg fixed twice weekly.

A summary of the positive data from the first 3 cohorts in the Phase 2a trial is as follows as of the December 2024 follow-up, which we announced in December 2024:

Dose Level Evaluable Patients ORR AML MRC ORR mOS AML MRC mOS

45 mg QW 10 10% 17% 5.1 months 5.8 months

60 mg BIW 9 33% 33% 3.9 months 3.9 months

30 mg BIW 9 46% 60% 7.7 months + 8.3 months +

Overall 28 31% 40% 5.1 months + 5.7 months +

leukemia-free status that includes complete response, complete response with incomplete hematologic recovery, and morphologic leukemia-free state.

median overall survival

Additionally, we announced that, as of the December 2024 follow-up, in the expansion cohorts 4 and 5, in patients with AML-myelodysplasia-related changes (AML-MRC) with ASXL1 mutation (cohort 4) and mutations and cytogenic changes other than ASXL1 (cohort 5), the ORR was 56% in 9 patients evaluable for efficacy.

SLS009 was well-tolerated with no new safety signals observed to date as the regimen remains safe in additional patients enrolled to date.

The trial evaluated safety, tolerability, and efficacy at two dose levels of SLS009, 45 mg once weekly, and 60 mg once weekly or 30 mg twice a week, in combination with aza/ven.

In December 2024, we announced positive data from the first 3 cohorts in the Phase 2a trial.

In July 2025, we announced that the Phase 2 trial of SLS009 in r/r AML met all primary endpoints and received FDA guidance to advance into a first-line therapy study.

The overall response rate, or ORR, in 54 evaluable patients was 33% across all cohorts and dose levels, 40% for the 30 mg BIW dose level, and 44% in the 30 mg BIW dose among patients with myelodysplasia-related molecular mutations, or AML MR, all exceeding the pre-specified ORR threshold of 20%.

The highest efficacy was observed among patients with ASXL1 mutations, with an ORR of 50% (9/18) at 30 mg BIW dose levels, and AML MR with Myelomonocytic/Myelomonoblastic markers, or M4/M5 per FAB classification, patients with an ORR of 50% (6/12).

The median overall survival, or mOS, reached 8.9 months in patients with AML MR and 8.8 months in patients r/r to venetoclax-based regimens at a 30 mg BIW dose level, surpassing the historical benchmark of ~2.4 months.

SLS009 was well-tolerated with no new safety signals observed.

No dose-limiting toxicities were observed across all dose levels.

Following a productive end of Phase 2 meeting, the FDA recommended that we proceed into a clinical trial to include newly diagnosed, first-line AML patients eligible for aza/ven therapy, where the FDA noted clinical benefit might be greatest.

The randomized 80-patient Phase 2 clinical trial is currently ongoing and began enrollment in the first quarter of 2026.

The clinical trial will include two groups:

predictive biomarker cohort (newly diagnosed patients unlikely to benefit from standard aza/ven therapy based on molecular profiling) and early venetoclax resistance cohort (patients who initiate treatment with aza/ven, but demonstrate confirmed lack of any response after two treatment cycles).

In January 2026, we announced that we entered into an agreement with IMPACT-AML, a European collaborative initiative dedicated to advancing innovative treatments for patients with AML.

Under the agreement, the IMPACT-AML network will conduct a clinical study evaluating SLS009, enabling access to multiple European clinical sites and patients.

IMPACT-AML is a pan-European project and builds an inclusive clinical network (STREAM platform)

that connects patients, clinicians, and researchers to test novel AML therapies and improve patient outcomes.

It is part of the prestigious EU Mission Cancer program and a top-tier scientific cluster.

The IMPACT-AML project is led by a consortium of major research and clinical institutions in Europe, including IRST (IRCCS Istituto Romagnolo per lo Studio dei Tumori “Dino Amadori”), the University of Bologna, IIS LA FE (Health Research Institute Hospital La Fe), several European AML collaborative groups, and supranational organizations under the umbrella of the European Leukemia Net (ELN), as well as various university hospitals across Europe.

By leveraging IMPACT-AML’s existing infrastructure and expertise, we expect to expand European patient access to SLS009 in a highly cost-efficient manner while supporting broader participation across the clinical program.

In November 2024, we announced data from preclinical studies identifying ASXL1 mutation as key predictor of SLS009 in response to solid cancers.

SLS009 is also currently being evaluated in pediatric solid tumors and leukemia models through the NCI Pediatric Preclinical in Vivo Testing, or PIVOT, program.

Studies are supported through cooperative agreement grants from the NCI to the PIVOT research centers performing the testing in pediatric tumor models and a centralized coordinating center.

We expect to report relevant data from the program in the first half of 2025.

Our partner, GenFleet, is focusing on lymphoma indications with SLS009 in its Greater China market.

In March 2024, we announced that GenFleet initiated a study of SLS009 in combination with zanubrutinib (Brukinsa®), a BTK inhibitor, in r/r diffuse large B-cell lymphoma, or DLBCL, and the first patient was dosed in the trial.

The study is funded and sponsored by GenFleet and is being conducted in China only.

In February 2025, we announced positive data from the Phase 2a study evaluating SLS009 in combination with zanubrutinib.

The results showed an overall response rate of 67%, more than double the expected ORR of zanubrutinib alone.

In May 2025, we announced data for pediatric acute lymphoblastic leukemia, or ALL, patients derived xenografts, or PDX.

The experiment conducted and funded by the National Institute of Health, or NIH, through the NCI Pediatric Prelinical in Vivo Testing, or PIVOT, program, included 27 patient-derived ALL tumors from pediatric patients.

Tumors were xenografted in mice in two groups, vehicle control arm and SLS009 arm.

Mice were treated with a fractionated dose once per week for six consecutive weeks.

Treatment was well tolerated.

For all models, median survival was approximately tripled in the SLS009 arm, compared to vehicle control arm.

SLS009 demonstrated delayed progression in 25/27 (93%) models and more than two times longer time to progression in 15/27 (56%) of ALL models.

In addition, there were complete responses, or CR, in two models and in one of the two models CR was maintained after the treatment had been completed until the end of the study (four months).

Among seven KMT2A rearranged models, time to progression was extended in all seven models, and in six out of seven (86%) time to progression was more than doubled.

For SLS009, the FDA granted Orphan Drug Product designations in AML and peripheral T-cell lymphoma, or PTCL, and Fast Track designations for r/r AML and r/r PTCL.

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• Phase 1 clinical trial of 3D189 (GPS) in China (our licensee, 3D Medicines is the sponsor)

Enrollment completed;

final results pending

final data report pending

• Phase 1 clinical trial in patients with hematologic and thoracic malignancies with no demonstrable residual/recurrent disease after debulking therapy

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The next and final analysis will be conducted once 80 events (deaths) are reached, further determining the potential of GPS in addressing the needs of AML patients.

We anticipate that 80 events will be reached this year.

In December 2025, we announced that our contract research organization informed us that the pooled number of events was 72 as of December 26, 2025.

Because the final analysis is event driven, it is difficult to predict with any certainty and it may occur at a different time than currently expected.

We will announce the 80th event when it occurs.

We have agreed with our partner in China, 3D Medicines, for 3D Medicines to participate in the REGAL study through the inclusion of approximately 20-25 patients from mainland China.

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In the second quarter of 2022, we received a $1.0 million milestone payment which was triggered by the NMPA’s approval of the IND.

Enrollment in this study has been completed.

The study has been completed and the final data report is pending.

Expanded Access Program

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Ovarian cancer was chosen as a target indication for the following reasons:

• ovarian cancer presents a clinical setting whereby MRD status can be achieved with standard upfront therapy both immediately after first line therapy, but also after effective debulking of the “first relapse.” The latter subgroup of patients (after successful second line treatment/first salvage, lacking demonstrable macroscopic residual disease) would be optimal candidates for GPS therapy, as no standard maintenance therapy exists for such patients and the subsequent relapse patterns and metrics are known and predictable;

latter subgroup of patients (after successful second line treatment/first salvage, lacking demonstrable macroscopic residual disease) would be optimal candidates for GPS therapy, as no standard maintenance therapy exists for such patients and the subsequent relapse patterns and metrics are known and predictable;

• the high levels of expression of WT1 in ovarian cancer cells.

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GPS Combination Therapy with Nivolumab for MPM

initiated in February 2020 at MSK in patients with MPM who have previously received treatment with pemetrexed-based chemotherapy and have measurable disease on imaging, either due to residual disease after prior treatment or recurrent disease.

A single-center, open-label, single-arm, non-randomized investigator-sponsored Phase 1 trial of concomitant administration of GPS in combination with Bristol-Myers Squibb’s anti-PD-1 therapy, nivolumab (Opdivo) was initiated in February 2020 at MSK in patients with MPM who have previously received treatment with pemetrexed-based chemotherapy and have measurable disease on imaging, either due to residual disease after prior treatment or recurrent disease.

We provided GPS and Bristol-Myers Squibb provided nivolumab for this study.

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, age and functional status).

approximately three years (from time of initial treatment) in patients with MM who achieve less than partial response, or PR, after ASCT.

Consequently, median survival can vary from up to at least 15 years in non-high-risk patients who achieve complete remission, as defined by the International Myeloma Working Group, or IMWG, criteria, to approximately three years (from time of initial treatment) in patients with MM who achieve less than partial response, or PR, after ASCT.

There are patients with MM who fare even more poorly than described above.

For example, those in the immediately aforementioned group who also have high-risk cytogenetics at baseline may survive on average less than three years.

For example, those in the immediately aforementioned group who also have high-risk cytogenetics at baseline may

survive on average less than three years.

Similarly, patients who are ineligible for ASCT and are managed only with chemotherapy and long-term IMiD maintenance (with up to nine cycles of lenalidomide) who also achieve less than complete remission and remain MRD-positive demonstrate a three-year OS rate of only about 55%;

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Information on the primary endpoint of this clinical trial, which was the safety of repeated GPS administrations, for a total of six doses, in combination with seven infusions of nivolumab was presented at the American Society of Clinical Oncology, or ASCO, 2018 annual meeting (O’Cearbhaill RE, et al).

The secondary endpoint of the study was immune response, and the exploratory endpoints included landmark one-year PFS rate compared to historical controls and correlative analyses between clinical and

immune responses.

Exploratory efficacy interim data from this pilot trial showed that GPS, when combined with a PD-1 inhibitor, in this case nivolumab, demonstrated PFS of 64% at one year in an intent to treat the group of 11 evaluable patients with WT1+ ovarian cancer in second or greater remission.

Among patients who received at least three doses of GPS in combination with nivolumab, PFS at one year was 70% (7/10).

Among patients who received at least

three doses of GPS in combination with nivolumab, PFS at one year was 70% (7/10).

The historical rates with best standard treatment do not exceed 50% in this disease setting.

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No new serious adverse events were noted during the longer follow-up period.

SLS009 (Tambiciclib):

Highly Selective Next Generation CDK9 Inhibitor

SLS009 is a next generation highly selective CDK9 inhibitor which we in-licensed from GenFleet in March 2022.

SLS009, or tambiciclib, is a next generation highly selective CDK9 inhibitor which we in-licensed from GenFleet in March 2022.

We have worldwide development and commercialization rights, except for Greater China.

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The preclinical data below is a comparison of SLS009 and an exact molecular copy of enitociclib (VIP152) (shown in the graphs as GFC002).

The top table shows the maximal inhibitory concentration, which is the amount of drug that is needed to inhibit survival of cancer cells, across different cell lines of cancer in

The top table shows the maximal inhibitory concentration, which is the amount of drug that is needed to inhibit survival of cancer cells, across different cell lines of cancer in vitro.

Across multiple cancer cell line histologies, a smaller concentration of SLS009 is needed to achieve the same inhibitory effect as compared to the exact molecular copy of enitociclib (VIP152).

In a mouse AML xenograft model, the lowest tumor growth and the highest AML cell killing was achieved by SLS009.

In a mouse AML xenograft model,

the lowest tumor growth and the highest AML cell killing was achieved by SLS009.

In this mouse model, there was significantly more toxicity, including weight loss, observed with enitociclib (VIP152) treated mice.

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The duration of the CR was eight months.

Historic, best available therapy median OS for patients relapsed after aza/ven is estimated at 2.5 months.

Historically, best available therapy median OS for patients relapsed after aza/ven is estimated at 2.5 months.

Lymphomas cohort:

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In the second quarter of 2023, we commenced an open label, single arm, multi-center Phase 2a clinical trial of SLS009 in combination with aza/ven in AML patients who failed or did not respond to treatment with venetoclax-based therapies.

The trial is designed to evaluate safety, tolerability, and efficacy at two dose levels of SLS009, 45 mg QW, and 60 mg QW or 30 mg BIW, in combination with aza/ven.

In addition to safety and tolerability of SLS009 in combination with aza/ven, the primary endpoints are complete response composite rate and duration of response.

Additional endpoints include event free survival, OS, and PK assessments.

The trial includes several sites in the United States, designed to enroll a minimum of 20 patients and based on initial results, may be expanded into a registrational trial.

In the fourth quarter of 2023, we completed enrollment in the 45 mg QW dose cohort in the Phase 2a study and reported positive initial topline data.

We also commenced enrollment of the 60 mg dose cohort with patients randomized to one of two groups, 60 mg fixed dose QW or 30 mg fixed dose BIW.

Each group will enroll approximately five to 10 patients.

In March 2024, we announced positive topline data from the Phase 2a study of SLS009 in combination with aza/ven in r/r AML.

As of March 15, 2024 data cutoff, 21 patients were treated.

All patients were diagnosed with AML refractory to or relapsed after venetoclax containing regimens.

20 out of 21 (95%) enrolled patients had adverse/high-risk cytogenetics and 1 patient (5%) had intermediate cytogenetics.

Median age was 70 and 19/21 (90.5%) of patients were older than 60.

In May 2024, we announced additional preliminary data from the Phase 2a trial of SLS009 in r/r AML.

As of the April 19, 2024 data cutoff, a 57% overall response rate had been achieved in the 30 mg BIW cohort, far surpassing the targeted 20% rate.

4/4 (100%) r/r AML patients with ASXL1 truncating mutations at the selected dose level achieved an overall response (CR/CRi/MLFS) and were alive.

5/8 (63%) of r/r AML patients, across all dose levels, with ASXL1 truncating mutations treated with SLS009 achieved an overall response.

A review of the mutational status of the patient in the Phase 1 trial with SLS009 monotherapy, who achieved a CR lasting 8+ months, revealed that the patient also harbored an ASXL1 mutation.

The ASXL1 mutation was found in both hematological malignancies as well as solid tumors.

In June 2024, we announced the completion of enrollment and additional positive data in the Phase 2a study.

A total of 30 patients were enrolled in the study as of May 25, 2024:

10 in the 45 mg QW safety cohort, 9 in the 60 mg QW cohort, and 11 in the 30 mg BIW cohort.

Among 27 evaluable patients,

• 10% response rate in the 45 mg QW safety cohort

• 33% response rate in the 60 mg QW cohort

• 50% response rate in the 30 mg BIW cohort

• Observed strong anti-leukemic activity, defined as 50% or more bone marrow blast reduction in 67% of patients across all dose levels.

• Median survival rate had not been reached at the time of analysis in any of the dose levels.

• The first patient enrolled in the study who achieved a complete response (CR) continued on the study and remained leukemia-free 9 months after enrollment.

• During the trial, we identified potential biomarkers currently undergoing testing as predictive markers in the most recent portion of the study.

• Patients with the identified biomarkers exhibited significantly higher response rates:

• 100% response rate at the optimal dose level (30 mg BIW).

• 57% response rate across all dose levels.

• Furthermore, we have clarified the proposed biological basis and mechanism of action for SLS009 activity in patients with these biomarkers.

• The relevant biomarkers are present in multiple hematologic and solid cancer indications, with a substantial proportion of patients exhibiting them in additional indications, ranging up to ~50% of patients in some indications.

• SLS009 in combination with aza/ven has been well-tolerated at all tested dose levels.

• No DLTs at any of the studied dose levels and no treatment-related high-grade (≥G3) toxicities were observed.

• Hematologic toxicities profile was consistent with aza/ven standalone treatment.

In December 2024, we announced additional data from the expansion cohorts in the Phase 2a clinical trial of SLS009 in r/r AML.

As of the December 4, 2024 data cutoff date, 14 patients were enrolled in the 30 mg BIW cohort and 14 patients were enrolled in cohorts 4 (ASXL1 mutated AML patients) and 5 (patients with myelodysplasia-related molecular abnormalities other than ASXL1), of which 9 were evaluable at the time of analysis.

At latest follow-up, the median overall survival, or mOS, had not been reached yet but had exceeded 7.7 months in the 30 mg BIW cohort.

This is particularly significant as the expected mOS for patients in this setting is typically 2.5 months.

In expansion cohorts 4 and 5, in patients with AML-myelodysplasia-related changes (AML-MR) with ASXL1 mutation (cohort 4) and mutations and cytogenic changes other than ASXL1 (cohort 5) the ORR was 56% in 9

evaluable for efficacy patients.

SLS009 was well-tolerated with no new safety signals observed to date as the regimen remains safe in additional patients enrolled to date.

The trial was designed to evaluate safety, tolerability, and efficacy at two dose levels of SLS009, 45 mg QW, and 60 mg QW or 30 mg BIW, in combination with aza/ven.

In addition to safety and tolerability of SLS009 in combination with aza/ven, the primary endpoints were overall response rate and duration of response.

Additional endpoints included event free survival, OS, and PK assessments.

The trial included several sites in the United States and was designed to enroll a minimum of 20 patients.

Patients with AML that fail venetoclax-based therapies have limited treatment options and a poor prognosis with a median OS of approximately 2.5 months.

See Current AML Treatment Therapies for more information on the AML treatment landscape.

Phase 1b/2 in PTCL

The first patient in a Phase 1b/2 trial evaluating SLS009 in r/r PTCL was dosed in the fourth quarter of 2023.

The open-label, single-arm trial will enroll up to 95 patients to evaluate safety and efficacy.

This initial PTCL study was fully funded by GenFleet and was conducted in China.

Phase 1b/2 in Combination with Brukinsa ® in Diffuse Large B-Cell Lymphoma (DLBCL)

In March 2024, we announced that GenFleet initiated a combination study of SLS009 and Brukinsa (zanubrutinib), a BTK inhibitor, in r/r DLBCL and the first patient was dosed in the trial.

The open-label, single-arm multi-center trial will be conducted in two parts.

This study is funded by GenFleet and is being conducted in China.

In February 2025, we announced positive data from the Phase 2a study evaluating SLS009 in combination with zanubrutinib.

The results showed an overall response rate of 67%, more than double the expected ORR of zanubrutinib alone.

Among responders, one achieved complete response, while three had partial response (PR) with target lesion shrinkages of 89%, 78%, and 56%, respectively.

As of the last follow-up, after the median of 4.6 (range:

1.4 - 7.4) months follow-up, mOS was not reached, and six out of nine patients were alive.

GenFleet will determine the next steps on development around lymphoma as our focus remains on AML and spliceosome–chromatin mutations, including ASXL1 mutations.

Efficacy and Safety

• Among six non-GCB DLBCL (ABC DLBCL) patients, four had an objective response and one patient achieved stable disease (SD) for the disease control rate (DCR) of 5/6 (83%)

• Overall response rate was 4/6 (67%), more than double the expected ORR with zanubrutinib alone

• One patient achieved complete response (CR), and three patients had PR with target lesion shrinkages of 89%, 78%, and 56%, respectively

• As of the last follow-up, after the median of 4.6 (range:

1.4 - 7.4) months follow-up, mOS was not reached

• Six patients were alive as of the last follow-up, including five non-GCB DLBCL and 1 GCB DLBCL.

Adverse events (AEs) grade ≥ 3 AEs were reported in 55.6% of patients, comparable to safety outcomes expected with Zanubrutinib alone.

• Genetic data of six out of nine enrolled patients showed that none of the patients carried MYD88 or CD79B mutations predictive of better response to BTK inhibitors.

The patient who achieved complete response (CR) by CT had MYC amplification, which is expected, but interestingly also harbored TP53 mutations, indicating that CDK9 inhibition with SLS009 could circumvent TP53 mutated cancers drug resistance.

In July 2025, we announced that all primary endpoints were met in the Phase 2 clinical trial of SLS009 in r/r AML.

54 evaluable r/r AML patients who previously failed venetoclax-based therapies were enrolled and treated with SLS009, and venetoclax/azacitidine.

Among the 54 treated patients, 47 had AML MR (87%) and 23 had ASXL1 mutations (43%).

Among the AML MR patients, 17 had myelomonocytic/myelomonoblastic subtype of AML (M4 and M5), representing 31% of all patients.

• The results exceeded the pre-specified ORR threshold of 20%, demonstrating robust clinical activity and supporting advancement into late-stage development.

• The ORR in all evaluable patients was 33% across all cohorts and dose levels and 40% for the 30mg BIW dose level.

• At the 30 mg BIW dose, among AML MR patients, the ORR was 44%.

• The highest efficacy was observed among patients with ASXL1 mutations, with an ORR of 50% (9/18) at 30 mg BIW dose levels and M4/M5 patients with 50% (6/12) ORR.

• The mOS surpassed the historical benchmark of best available therapy of 2.4 months for patients who received one prior line of therapy and 1.8 months for those who received more than one prior line of therapy.

• The mOS for patients treated with 30mg BIW, with a median of 1 prior line of therapy, was 8.8 months, while the mOS in AML MR patients reached 8.9 months vs.

2.4 months with best available therapy.

• The mOS for cohorts with a median of 2 prior lines of therapies was 4.1 months vs.1.8 months with best available therapy.

The addition of SLS009 to the venetoclax/azacitidine regimen was well tolerated and did not result in increased toxicities compared to ven/aza alone.

No DLTs were observed across all dose levels.

In addition, following a productive end of Phase 2 meeting, the FDA recommended that we proceed into a trial to include newly diagnosed, first-line AML patients eligible for aza/ven therapy, where the FDA noted clinical benefit might be greatest.

The randomized 80-patient trial is currently ongoing and began enrollment in the first quarter of 2026.

The trial will include two groups:

Preclinical Studies

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All cell lines were analyzed for presence of ASXL1 mutations and other genetic markers.

High efficacy was prespecified as IC50 < 100 nM, significantly lower than the standard threshold definition for an effective compound (IC50 < 1,000 nM).

High efficacy was prespecified as IC50 < 100 nM, significantly lower than the standard threshold definition for an effective compound

(IC50 < 1,000 nM).

This threshold was chosen based on the observed long-lasting concentrations of SLS009 observed in patients, which were ~400 nM.

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In the second phase, tolerability of the dose and route of administration selected from the PK phase will be determined.

In the last phase, monotherapy in vivo efficacy testing for SLS009 will be performed by PIVOT

investigators.

In the last phase, monotherapy in vivo efficacy testing for SLS009 will be performed by PIVOT investigators.

Studies will be supported through cooperative agreement grants from the NCI to the seven PIVOT research programs performing the testing and a centralized coordinating center.

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The first and second phases of the program, pharmacokinetics and tolerability, respectively, have been successfully completed and dosing regimens have been developed.

The final phase of the program, efficacy, is in progress and we expect to report relevant data from the program in the first half of 2025.

In May 2025, we announced data from this PIVOT program, which included 27 patient-derived ALL tumors

from pediatric patients.

Tumors were xenografted in mice in two groups, vehicle control arm and SLS009 arm.

Mice were treated with a fractionated dose once per week for six consecutive weeks.

Treatment was well tolerated.

For all models, median survival was approximately tripled in the SLS009 arm, compared to vehicle control arm.

SLS009 demonstrated delayed progression in 25/27 (93%) models and more than two times longer time to progression in 15/27 (56%) of ALL models.

In addition, there were complete responses, or CR, in two models and in one of the two models CR was maintained after the treatment had been completed until the end of the study (four months).

Among seven KMT2A rearranged models, time to progression was extended in all seven models, and in six out of seven (86%) time to progression was more than doubled.

Strategic Collaborations and License Agreements

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Under the terms of the current amended and restated MSK license agreement, we agreed to pay minimum royalty payments in the amount of $0.1 million each year commencing in 2015 and research funding costs of $0.2 million in each year and for three years commencing in January 2016.

We also agreed to pay MSK a mid-six digit amount over a one year period in exchange for MSK’s agreement to further amend and restate the MSK license agreement

in October 2017.

We also agreed to pay MSK a mid-six digit amount over a one year period in exchange for MSK’s agreement to further amend and restate the MSK license agreement in October 2017.

In addition, to the extent certain development and commercial milestones are achieved, we also agreed to pay MSK up to $17.4 million in aggregate milestone payments for each licensed product, and for each additional patent licensed product, up to $2.8 million in additional milestone payments.

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3D Medicines also agreed to pay tiered royalties based upon a percentage of annual net sales of GPS Licensed Products in the 3DMed Territory ranging from the high single digits to the low double digits.

from the receipt of marketing authorization for such GPS Licensed Product in such region and (ii) the date that is 10 years from the expiration of the last valid claim of a licensed patent covering or claiming such GPS Licensed Product in such region.

The royalties are payable on a GPS Licensed Product-by- GPS Licensed Product and region-by-region basis commencing on the first commercial sale of a GPS Licensed Product in a region and continuing until the latest of (i) the date that is 15 years from the receipt of marketing authorization for such GPS Licensed Product in such region and (ii) the date that is 10 years from the expiration of the last valid claim of a licensed patent covering or claiming such GPS Licensed Product in such region.

The royalty rate is subject to reduction under certain circumstances, including when generic competition for a GPS Licensed Product exists in a particular region.

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A joint development committee has been established between 3D Medicines and us to coordinate and review the development, manufacturing and commercialization plans with respect to the GPS Licensed Products in the 3DMed Territory.

We and 3D Medicines also agreed to negotiate in good faith the terms and conditions of a clinical supply agreement, a commercial supply agreement, and related quality agreements pursuant to which we will manufacture or have manufactured and supply 3D Medicines with all quantities of the GPS Licensed Product necessary for 3D Medicines to develop and commercialize the GPS Licensed Products in the 3DMed Territory until 3D Medicines has received all approvals required for 3D Medicines or its designated contract manufacturing organization to manufacture the GPS Licensed Products in the 3DMed Territory.

We and 3D Medicines also agreed to negotiate in

good faith the terms and conditions of a clinical supply agreement, a commercial supply agreement, and related quality agreements pursuant to which we will manufacture or have manufactured and supply 3D Medicines with all quantities of the GPS Licensed Product necessary for 3D Medicines to develop and commercialize the GPS Licensed Products in the 3DMed Territory until 3D Medicines has received all approvals required for 3D Medicines or its designated contract manufacturing organization to manufacture the GPS Licensed Products in the 3DMed Territory.

The 3D Medicines Agreement will expire on a GPS Licensed Product-by-GPS Licensed Product and region-by-region basis on the date of the expiration of all of 3D Medicines’ payment obligations to us.

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We also agreed to pay GenFleet tiered royalties based upon a percentage of annual net sales of CDK9 Licensed Products in the SLS009 Territory ranging from the low to high single digits.

The royalties are payable on a CDK9 Licensed Product-by-CDK9 Licensed Product and region-by-region basis commencing on the first commercial sale of a CDK9 Licensed Product in a region and continuing until the later of (i) the date that is 10 years following the date of first commercial sale for such CDK9 Licensed Product in such region and (ii) the date of the expiration of the last valid claim of a licensed patent covering or claiming such CDK9 Licensed Product in such region.

The royalties are payable on a CDK9 Licensed Product-by-CDK9 Licensed Product and region-by-region basis commencing on the first commercial sale

of a CDK9 Licensed Product in a region and continuing until the later of (i) the date that is 10 years following the date of first commercial sale for such CDK9 Licensed Product in such region and (ii) the date of the expiration of the last valid claim of a licensed patent covering or claiming such CDK9 Licensed Product in such region.

The royalty rate is subject to reduction under certain circumstances, including when generic competition for a CDK9 Licensed Product exists in a particular region.

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Patents and patent applications covering GPS and WT1-targeting peptides:

• Patent application co-owned by us and MSK:

◦ Patent applications covering a heptavalent (7-peptide) immunotherapy composition and methods of use for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer pending in the United States, Australia, Canada, China, European Patent Office, or EPO, Hong Kong, India, Israel, Japan, South Korea, Mexico and Russia, which, if granted, are expected to expire in 2040.

• Patents and patent applications co-owned by us and MSK:

◦ Patent applications covering a heptavalent (7-peptide) immunotherapy composition and methods of use for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer pending in the United States, Australia, Canada, China, European Patent Office (or EPO), Hong Kong, India, Japan, South Korea, and Mexico, which, if granted, are expected to expire in 2040.

◦ Patents covering a heptavalent (7-peptide) immunotherapy composition and uses thereof for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer in Israel and Russia, which are expected to expire in 2040.

• Patents and patent applications in-licensed from MSK:

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and a composition-of-matter patent covering additional WT1-targeting peptides and methods of use in the United States, which is expected to expire in 2035;

◦ Composition-of-matter patents covering certain WT1-targeting peptides and methods of use in Australia, China, Hong Kong, several countries in Europe, and Japan, which are expected to expire in 2034;

◦ Composition-of-matter patents covering certain WT1-targeting peptides and methods of use in Australia, Canada, China, Hong Kong, several countries in Europe, and Japan, which are expected to expire in 2034;

◦ Patent applications covering certain WT1-targeting peptides and methods of use pending in the United States, Australia, the EPO, Canada, China, and Hong Kong, which, if granted, are expected to expire in 2034;

◦ Patents covering methods for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer, using the peptides of GPS in combination with anti-PD-1 antibody checkpoint inhibitors in the United States, Australia, China, Hong Kong, several countries in Europe and Japan, which are expected to expire in 2037 (United States) and 2036 (Australia, China, Hong Kong, Europe and Japan);

◦ Patents covering methods for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer, using the peptides of GPS in combination with anti-PD-1 antibody checkpoint inhibitors in the United States, Australia, China, Hong Kong, several countries in Europe, South Korea, and Japan, which are expected to expire in 2037 (United States) and 2036 (Australia, China, Hong Kong, Europe and Japan);

◦ Patent applications covering methods for treating, reducing the incidence of, or inducing an immune response against a WT1-expressing cancer, using the peptides of GPS in combination with immune checkpoint inhibitors pending in the United States, Australia, Canada, China, Hong Kong, the EPO, South Korea, and Japan, which, if granted, are expected to expire in 2036;

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◦ Composition-of-matter patent covering the WT1-427 long and WT1-331 long peptides of GPS issued in the United States, which is expected to expire in 2031, and patents covering the methods of use in the United States, which are expected to expire in 2026;

a patent covering nucleic acids encoding the WT1-427 long and WT1-331 long peptides of GPS and methods of use thereof in the United States, which are expected to expire in 2026;

a patent covering peptide conjugates of the WT1-427 long peptide or WT1-331 long peptide in the United States, which is expected to expire in 2027;

a patent covering nucleic acids encoding peptide conjugates of the WT1-427 long peptide or WT1-331 long peptide and methods of use thereof in the United States, which is expected to expire in 2029;

and a patent application covering peptide conjugates of the WT1-427 long peptide or WT1-331 long peptide pending in the United States, which, if granted, is expected to expire in 2026;

◦ Composition-of-matter patents covering the WT1-427 long peptide of GPS and WT1-331 long peptide of GPS, and methods of use, in Australia, Canada, and several countries in Europe, which are expected to expire in 2026;

◦ Composition-of-matter patents covering the WT1-427 long peptide of GPS and WT1-331 long peptide of GPS, and methods of use, in Australia, Canada, several countries in Europe, and Hong Kong, which are expected to expire in 2026;

◦ Composition-of-matter patent covering a WT1-specific peptide in the United States, which is expected to expire in 2026;

◦ Composition-of-matter patent covering the WT1-122A1 long peptide of GPS in the United States which is expected to expire in 2033;

patent covering the WT1-122A1 long peptide of GPS and methods of use in the United States, which is expected to expire in 2029;

and patent application covering the WT1-122A1 long peptide of GPS and methods of use pending in the United States, which, if granted, is expected to expire in 2027;

◦ Composition-of-matter patent covering the WT1-122A1 long peptide of GPS and methods of use in several countries in Europe, which is expected to expire in 2027, and patent applications covering the WT1-122A1 long peptide of GPS and methods of use pending in the EPO, Hong Kong and Canada, which, if granted, are expected to expire in 2027.

patent covering methods of using the WT1-122A1 long peptide of GPS in the United States, which is expected to expire in 2029;

and patent application covering the WT1-122A1 long peptide of GPS and methods of use thereof pending in the United States, which, if granted, is expected to expire in 2027;

◦ Composition-of-matter patent covering the WT1-122A1 long peptide of GPS and methods of use in several countries in Europe, which is expected to expire in 2027, and patent applications covering the WT1-122A1 long peptide of GPS and methods of use pending in the EPO and Canada, which, if granted, are expected to expire in 2027.

Patents and patent applications covering SLS009:

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◦ Composition-of-matter patents covering SLS009 and use thereof in the treatment or amelioration of cancer in the United States, Australia, Brazil, Canada, Japan, Russia, South Korea, and several countries in Europe, which are expected to expire in 2038;

and a patent application covering SLS009 and use thereof in the treatment or amelioration of cancer pending in Brazil, which, if granted, is expected to expire in 2038;

◦ Patents covering maleate and fumarate crystal salts and polymorphs of SLS009, syntheses thereof, and use thereof in prevention or treatment of CDK9-related diseases, including cancer, in Australia and Japan, which are expected to expire in 2040;

patent applications covering maleate and fumarate salt forms and polymorphs of SLS009, syntheses thereof, and use thereof in prevention or treatment of CDK9-related diseases, including cancer, pending in the United States, Brazil, Canada, South Korea, the EPO, and the Eurasian Patent Office, which, if granted, are expected to expire in 2040.

◦ Patents covering maleate and fumarate polymorphs of SLS009 and uses thereof in prevention or treatment of CDK9-related diseases, including cancer, in the United States, Australia, Canada, Eurasian Patent Office, South Korea, and Japan, which are expected to expire in 2042 (United States) and 2040 (Australia, Canada, Eurasian Patent Office, South Korea, and Japan);

patent applications covering maleate and fumarate salt forms and polymorphs of SLS009, syntheses thereof, and use thereof in prevention or treatment of CDK9-related diseases, including cancer, pending in the United States, Brazil, the EPO, and the Eurasian Patent Office, which, if granted, are expected to expire in 2040.

• Patents and patent applications owned by us:

◦ Patent applications covering methods of treating cancer in a subject having an ASXL1 mutation using CDK9 inhibitors in the Patent Cooperation Treaty (PCT) and Taiwan, which, if granted, are expected to expire in 2045.

Oncology in general, and specifically, cancer immunotherapy, is a significant growth area for the biopharmaceutical industry, attracting large pharmaceutical companies as well as small niche players.

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Companies developing novel products with similar indications to those we are pursuing and may pursue are expected to influence our ability to penetrate and maintain market share.

Principal competitors for AML broadly include companies with currently marketed products, such as AbbVie/Genentech (Venclexta), Pfizer (Mylotarg), Daiichi-Sankyo (Vanflyta), Rigel Pharmaceuticals (Rezlidhia) and Bristol Myers Squibb (Vidaza), among others.

There are also companies developing therapies to treat AML in the r/r setting, which are in earlier stages of clinical development, including emavusertib, which is in a Phase 1/2 trial in AML and being developed by Curis, and later-stage clinical development candidates which may enter the market before our potential products, such as Delta-Fly Pharma (DFP-10917) and AROG Pharmaceuticals (crenolanib).

Actinium Pharmaceuticals, which previously announced in late 2022 / early 2023 positive results in its Phase 3 trial of Iomab-B in adults aged 55 and above with r/r AML, has since announced that the FDA determined that its Phase 3 trial is not adequate to support a BLA filing for Iomab-B.

With respect to WT1-targeting therapies, we do not believe GPS has direct competition in AML in the maintenance setting after CR2 at this time.

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With respect to SLS009, we anticipate competition from companies who have been engaged in the clinical development of selective CKD9-targeting therapies.

Vincerx Pharma may be a potential competitor in our other indication, PTCL, with enitociclib, its CDK9 inhibitor, as a monotherapy and in combination with venetoclax.

are other companies which are in early development stages for their CDK9 inhibitors and targeting other hematologic malignancies or solid tumors, including Sumitomo Dainippon Pharma (TP-1287), Cothera Bioscience (zotiraciclib), and Prelude Therapeutics (PRT2527).

There are other companies which are in early development stages for their CDK9 inhibitors and targeting other hematologic malignancies or solid tumors, including Sumitomo Dainippon Pharma (TP-1287), Cothera Bioscience (zotiraciclib), and Prelude Therapeutics (PRT2527).

With regard to both GPS and SLS009, many of our competitors, either alone or with their strategic partners, may have substantially greater resources and expertise in research and development, manufacturing, preclinical testing, obtaining regulatory approvals, and marketing approved products than we have.

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We believe our relationship with our employees is good.

We are committed to creating and maintaining a diverse, inclusive and safe work environment which encourages collaboration and integrity and inspires high performance and achievement.

Our employees have various backgrounds, experience, and perspectives.

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In addition, two of our six Board of Director members are women.

We believe we have built and continue to build a strong culture of cooperation, respect and acceptance.

We also invest in our employees and are able to recruit talented individuals through our competitive benefits, compensation packages and health and wellness initiatives, which are based on peer company benchmarks.

We believe we have built and continue to build a strong diverse and inclusive culture of cooperation, respect and acceptance.

We are committed to identifying, retaining, and incentivizing highly skilled employees, and we are able to recruit talented individuals through our competitive benefits, compensation packages and health and wellness initiatives, which are based on peer company benchmarks.

Government Regulation

The FDA and other regulatory authorities at federal, state, and local levels, as well as in foreign countries, extensively regulate, among other things, the research, development, testing, manufacture, quality control, import, export, safety, effectiveness, labeling, packaging, storage, distribution, record keeping, approval, advertising, promotion, marketing, post-approval monitoring, and post-approval reporting of drugs and biologics such as those we are developing.

wish to conduct studies or seek approval or licensure of its current or future product candidates.

Along with our third-party contractors, we will be required to navigate the various preclinical, clinical and commercial approval requirements of the governing regulatory agencies of the countries in which we wish to conduct studies or seek approval or licensure of its current or future product candidates.

The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local, and foreign statutes and regulations require the expenditure of substantial time and financial resources.

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• preparation of and submission to the FDA of an NDA or BLA, after completion of all pivotal clinical trials;

• satisfactory completion of an FDA Advisory Committee review, if applicable;

• a determination by the FDA within 60 days of its receipt of an NDA or BLA to file the application for review;

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• potential audit of selected clinical trial sites to assess compliance with GCP and the integrity of the clinical data submitted in support of the NDA or BLA;

• satisfactory completion of an FDA Advisory Committee review, if applicable;

• FDA review and approval of the NDA or BLA to permit commercial marketing of the product for particular indications for use in the United States.

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Before testing any drug or biological product candidate, including our product candidates, in humans, the product candidate must undergo rigorous preclinical testing.

Nonclinical studies during the preclinical development stage

include laboratory evaluation of product chemistry and formulation and typically include in vitro and animal studies to assess the potential for adverse events and in some cases to establish a rationale for therapeutic use.

Nonclinical studies during the preclinical development stage include laboratory evaluation of product chemistry and formulation and typically include in vitro and animal studies to assess the potential for adverse events and in some cases to establish a rationale for therapeutic use.

The Consolidated Appropriations Act for 2023, signed into law on December 29, 2022, (P.L.

117-328) amended the Food, Drug, and Cosmetic Act, or the FDCA, and the Public Health Service Act to specify that nonclinical testing for drugs and biologics may, but is not required to, include in vivo animal testing.

According to the amended language, a sponsor may fulfill nonclinical testing requirements by completing various in vitro assays (e.g., cell-based assays, organ chips, or microphysiological systems), in silico studies (i.e., computer modeling), other human or nonhuman biology-based tests (e.g., bioprinting), or in vivo animal tests.

According to the amended language,

a sponsor may fulfill nonclinical testing requirements by completing various in vitro assays (e.g., cell-based assays, organ chips, or microphysiological systems), in silico studies (i.e., computer modeling), other human or nonhuman biology-based tests (e.g., bioprinting), or in vivo animal tests.

The conduct of preclinical studies is subject to federal regulations and requirements, including GLP regulations for safety/toxicology studies.

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Our Phase 3 REGAL trial of GPS for AML patients who have achieved CR2 was initiated before this requirement became effective, but for any future Phase 3 trials we plan to conduct, we must submit a diversity action plan to the FDA by the time we submit plans for such Phase 3, or pivotal study, protocol to the agency for review as part of an IND, unless we are able to obtain a waiver for some or all of the requirements for a diversity action plan.

It is unknown at this time how the diversity action plan may affect Phase 3 trial planning and timing, but if FDA objects to a sponsor’s diversity action plan and requires the sponsor to amend the plan or take other actions, it may delay trial initiation.

If FDA objects to a sponsor’s diversity action plan and requires the sponsor to amend the plan or take other actions, it may delay trial initiation.

Phase 1, Phase 2 and Phase 3 testing may not be completed successfully within a specified period, if at all, and there can be no assurance that the data collected will support FDA approval or licensure of the product.

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The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things, must incorporate methods for testing the identity, strength, quality and purity of the final product, or for biologics, the safety, purity and potency.

Additionally, appropriate packaging must be selected and tested, and

stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

Additionally, appropriate packaging must be selected and tested, and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

Marketing Application Submission and Review by the FDA

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Before approving an NDA or BLA, the FDA will typically inspect the facility or facilities where the product is manufactured.

The FDA will not approve an application unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product

within required specifications.

Additionally, before approving an NDA or BLA, the FDA will typically inspect one or more clinical trial sites to assure compliance with GCP and integrity of the trial data.

If the FDA determines that the application, manufacturing process or manufacturing facilities are not acceptable, it will outline the deficiencies as part of the review process and often will request additional testing or information.

Notwithstanding the submission of any requested additional information, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval.

Notwithstanding the submission of

any requested additional information, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval.

Under the Pediatric Research Equity Act, or PREA, amendments to the FDCA, an NDA or BLA or supplement to such applications must contain data that are adequate to assess the safety and efficacy of the product candidate for the claimed indications in all relevant pediatric populations and to support dosing and administration for each pediatric population for which the product is safe and effective.

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The FDA may delay or refuse approval of an NDA or BLA if applicable regulatory criteria are not satisfied, require additional testing or information and/or require post-marketing testing and surveillance to monitor safety or efficacy of a product.

In September 2025, the FDA began publishing CRLs soon after issuing them to the respective sponsors, breaking with long standing agency tradition of publishing CRLs with approval documentation after the product is approved.

If a CRL is issued, the applicant may either resubmit the NDA or BLA, addressing all of the deficiencies identified in the letter, or withdraw the application.

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Once approved, the FDA may withdraw the product approval if compliance with pre- and post-marketing regulatory standards is not maintained or if problems occur after the product reaches the marketplace.

The FDA may require one or more Phase 4 post-market studies and surveillance to further assess and monitor the product’s safety and

effectiveness after commercialization and may limit further marketing of the product based on the results of these post-marketing studies.

The FDA may require one or more Phase 4 post-market studies and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization and may limit further marketing of the product based on the results of these post-marketing studies.

After approval, some types of changes to the approved product, such as adding new indications, manufacturing changes and additional labeling claims, are subject to further testing requirements and FDA review and approval.

In addition, new government requirements, including those resulting from new legislation, may be established, or the FDA’s policies may change, which could delay or prevent regulatory approval of our products under development.

In addition, new government requirements, including those resulting from new legislation,

may be established, or the FDA’s policies may change, which could delay or prevent regulatory approval of our products under development.

Fast Track, Priority Review, and Breakthrough Therapy Designations

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If criteria are not met for priority review, the application is subject to the standard FDA review period of ten months after FDA accepts the application for filing.

In addition, a sponsor may seek FDA designation of its product candidate as a Breakthrough Therapy, if the product candidate is intended, alone or in combination with one or more other drugs or biologics, to treat a serious or life-threatening disease or condition and preliminary clinical evidence indicates that the therapy may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development.

A sponsor may seek FDA designation of its product candidate as a Breakthrough Therapy, if the product candidate is intended, alone or in combination with one or more other drugs or biologics, to treat a serious or life-threatening disease or condition and preliminary clinical evidence indicates that the therapy may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development.

Breakthrough Therapy designation provides all the features of Fast Track designation in addition to intensive guidance on an efficient development program beginning as early as Phase 1, and FDA organizational commitment to expedited development, including involvement of senior managers and experienced review and regulatory staff in a proactive, collaborative, cross-disciplinary review, where appropriate.

A drug designated as Breakthrough Therapy is also eligible for accelerated approval if the relevant criteria are met.

In 2025, the FDA created a new voucher program called the Commissioner’s National Priority Voucher (“CNPV”) with the goal of radically expediting the drug and biological product review and approval process.

The agency may award a CNPV to a company or a specific product candidate that demonstrates alignment with certain national health priorities.

The FDA aims to take action on a marketing application for which a CNPV is used within one to two months after the filing date.

Even if a product qualifies for one or more of these programs, the FDA may later decide that the product no longer meets the conditions for qualification or decide that the time period for FDA review or approval will not be shortened.

Fast Track, priority review and Breakthrough Therapy designations do not change the scientific or medical standards for approval or the quality of evidence necessary to support approval but may expedite the development or approval process.

None of these programs changes the scientific or medical standards for approval or the quality of evidence necessary to support approval but may expedite the development or approval process.

Accelerated Approval

In addition, products studied for their safety and effectiveness in treating serious or life-threatening illnesses and that provide meaningful therapeutic benefit over existing treatments may receive accelerated approval from the FDA and may be approved on the basis of adequate and well-controlled clinical trials establishing that the drug product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit.

The FDA may also grant accelerated approval for such a drug or biologic when it has an effect on an intermediate clinical endpoint that can

be measured earlier than an effect on irreversible morbidity or mortality, or IMM, and that is reasonably likely to predict an effect on IMM or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments.

The FDA may also grant

accelerated approval for such a drug or biologic when it has an effect on an intermediate clinical endpoint that can be measured earlier than an effect on irreversible morbidity or mortality, or IMM, and that is reasonably likely to predict an effect on IMM or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments.

As a condition of approval, the FDA may require that a sponsor of a drug or biologic receiving accelerated approval perform post-marketing clinical trials to verify and describe the predicted effect on IMM or other clinical endpoint, and the product may be subject to expedited withdrawal procedures.

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After the FDA grants Orphan Drug Product Designation, the generic identity of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA.

orphan product exclusivity, which means that the FDA may not approve any other applications, including a full NDA or BLA, to market the same drug or biologic for the same indication for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan product exclusivity or if FDA finds that the holder of the orphan product exclusivity has not shown that it can assure the availability of sufficient quantities of the orphan product to meet the needs of patients with the disease or condition for which the drug or biologic was designated.

If a drug or biologic product that has Orphan Drug Product Designation subsequently receives the first FDA approval for a particular active ingredient for the disease for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications, including a full NDA or BLA, to market the same drug or biologic for the same indication for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan product exclusivity or if FDA finds that the holder of the orphan product exclusivity has not shown that it can assure the availability of sufficient quantities of the orphan product to meet the needs of patients with the disease or condition for which the drug or biologic was designated.

Orphan product exclusivity does not prevent the FDA from approving a different drug or biologic for the same disease or condition, or the same drug or biologic for a different disease or condition.

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Biosimilarity to an approved reference product requires that there be no differences in mechanism of action for the conditions of use, route of administration, dosage form, and strength, and no clinically meaningful differences between the follow-on biological product and the reference product in terms of safety, purity, and potency.

Biosimilarity is demonstrated in steps beginning with rigorous analytical studies or “fingerprinting,” in vitro studies, in vivo animal studies, and generally at least one clinical study, absent a waiver from the FDA.

Biosimilarity is demonstrated in steps beginning with rigorous analytical studies or “fingerprinting,” in vitro studies, in vivo animal studies, and for some biosimilar products, at least one clinical study, absent a waiver from the FDA.

The biosimilarity exercise tests the hypothesis that the investigational product and the reference product are the same.

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In order to meet the higher hurdle of interchangeability, a sponsor must demonstrate that the biosimilar product can be expected to produce the same clinical result as the reference product, and for a product that is administered more than once, that the risk of switching between the reference product and biosimilar product is not greater than the risk of maintaining the patient on the reference product.

Complexities associated with the larger, and often more complex, structures of biological products, as well as the process by which such products are manufactured, pose significant hurdles to implementation that are still being evaluated by the FDA.

Complexities associated with the larger,

and often more complex, structures of biological products, as well as the process by which such products are manufactured, pose significant hurdles to implementation that are still being evaluated by the FDA.

Under the BPCIA, a reference biological product is granted 12 years of data exclusivity from the date of first licensure of the product, which means that the FDA is barred from approving biosimilar applications for 12 years after the reference biological product receives initial marketing approval.

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The cGMP regulations include requirements relating to organization of personnel, buildings and facilities, equipment, control of components and drug product containers and closures, production and process controls, packaging and labeling controls, holding and distribution, laboratory controls, records and reports and returned or salvaged products.

The manufacturing facilities for our product candidates must meet applicable cGMP requirements to the FDA’s or comparable foreign regulatory authorities’ satisfaction before any product is approved and our commercial products can be manufactured.

We rely, and expect to continue to rely, on third parties for the

production of clinical and commercial quantities of our products in accordance with cGMP regulations.

The manufacturing facilities for our product candidates must meet applicable cGMP

requirements to the FDA’s or comparable foreign regulatory authorities’ satisfaction before any product is approved and our commercial products can be manufactured.

We rely, and expect to continue to rely, on third parties for the production of clinical and commercial quantities of our products in accordance with cGMP regulations.

These manufacturers must comply with cGMP regulations that require, among other things, quality control and quality assurance, the maintenance of records and documentation and the obligation to investigate and correct any deviations from cGMP.

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Furthermore, the Drug Supply Chain Security Act, or DSCSA, was enacted with the aim of building an electronic system to identify and trace certain prescription drugs distributed in the United States, including most biological products.

The DSCSA mandates phased-in and resource-intensive obligations for pharmaceutical manufacturers, wholesale distributors, and dispensers over a ten-year period, which culminated in November 2023.

After an additional one-year stabilization period to give entities subject to the DSCSA additional time to finalize interoperable tracking systems and to ensure supply chain continuity, the applicable requirements under the DSCSA became fully enforceable as of November 27, 2024.

The DSCSA mandates resource-intensive obligations for pharmaceutical manufacturers, wholesale distributors, and dispensers.

From time to time, new legislation and regulations may be implemented that could significantly change the statutory provisions governing the approval, manufacturing and marketing of products regulated by the FDA.

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This calculation is made on a product-by-product basis and the amount of the rebate owed to the federal government is directly dependent on the volume of a drug product that is paid for by Medicare Parts B or D.

Additionally, starting in payment year 2026, CMS will negotiate drug prices annually for a select number of single-source Part D drugs without generic or biosimilar competition.

Additionally, CMS will negotiate drug prices annually for a select number of single-source Part D drugs without generic or biosimilar competition.

CMS will also negotiate drug prices for a select number of Part B drugs starting for payment year 2028.

If a drug product is selected by CMS for negotiation, it is expected that the revenue generated from such drug will decrease.

CMS has begun to implement these new authorities and entered into the first set of agreements with drug and biologic manufacturers for negotiated prices of 10 products, which will become applicable for payment year 2026.

CMS has begun to implement these new authorities, announcing the first round of negotiated prices for the first 10 drug products in August 2024, which will become applicable for payment year 2026.

The second round of negotiated prices for 15 drug products was announced in November 2025.

However, the IRA’s impact on the pharmaceutical industry in the United States remains uncertain, in part because multiple large pharmaceutical companies and other stakeholders (e.g., the U.S.

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Those lawsuits are currently ongoing.

Separately, the Trump Administration announced the creation of a government website called TrumpRx, which will allow consumers to purchase certain drugs at reduced prices as negotiated between the drug manufacturers and the administration.

As of December 2025, the Trump Administration secured deals with five major drug manufacturers to offer certain drugs at most-favored-nation prices.

At the state level, legislatures have increasingly passed legislation and implemented regulations designed to control drug and biological product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure and transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing.

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Coverage policies and third-party reimbursement rates may change at any time.

Even if favorable coverage and reimbursement status is attained for one or more products for which we receive regulatory approval, less favorable coverage policies and reimbursement rates may be implemented in the future.

Even if favorable coverage and reimbursement status is attained for one or more products

for which we receive regulatory approval, less favorable coverage policies and reimbursement rates may be implemented in the future.

In some foreign countries, proposed pricing for drug and biological products must be approved before the product may be lawfully marketed.

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Some countries provide that drug and biological products may be marketed only after agreement on a reimbursement price has been reached.

Some countries may require additional studies that compare the cost-effectiveness of our

product candidate to currently available therapies (so called health technology assessment, or HTA) in order to obtain reimbursement or pricing approval.

Some countries may require additional studies that compare the cost-effectiveness of our product candidate to currently available therapies (so called health technology assessment, or HTA) in order to obtain reimbursement or pricing approval.

For example, the EU provides options for its member states to restrict the range of medicinal products for which their national health insurance systems provide reimbursement and to control the prices of medicines.

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Other national and EU-wide regulatory requirements may also apply.

Currently, the extent to which clinical trials will be governed by the Clinical Trials Regulation will depend on when the clinical trial is initiated or on the duration of an ongoing trial.

As of January 2023, all new clinical trials must comply with the Clinical Trials Regulation.

In addition, any clinical trial that was already under way as of January 1, 2023, and continues for more than three years from the day on which the Clinical Trials Regulation becomes applicable (i.e., January 31, 2025), the Clinical Trials Regulation will apply to the clinical trial.

The requirements and processes governing the conduct of clinical trials, product licensing, pricing and reimbursement in Europe vary from country to country, even though there is already some degree of legal harmonization in the EU member states resulting from the national implementation of underlying EU legislation.

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The centralized procedure is compulsory for human medicines that are:

(i) derived from biotechnology processes, such as genetic engineering, (ii) contain a new active substance indicated for the treatment of certain diseases, such as HIV/AIDS, cancer, diabetes, neurodegenerative diseases, autoimmune and other immune dysfunctions and viral

diseases, (iii) officially designated as orphan medicinal product and (iv) advanced-therapy medicines, such as gene-therapy, somatic cell-therapy or tissue-engineered medicines.

(i) derived from biotechnology processes, such

as genetic engineering, (ii) contain a new active substance indicated for the treatment of certain diseases, such as HIV/AIDS, cancer, diabetes, neurodegenerative diseases, autoimmune and other immune dysfunctions and viral diseases, (iii) officially designated as orphan medicinal product and (iv) advanced-therapy medicines, such as gene-therapy, somatic cell-therapy or tissue-engineered medicines.

The centralized procedure may at the request of the applicant also be used for human medicines which do not fall within the above mentioned categories if the medicinal product contains a new active substance which has not been previously authorized in the EEA, the product constitutes a significant therapeutic, scientific or technical innovation, or where the granting of authorization in the centralized procedure is in the interests of public health in the EEA.

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Once renewed, the marketing authorization is valid for an unlimited period, unless the European Commission, or the applicable competent authority, decides, on justified grounds relating to pharmacovigilance, to proceed with one additional five-year renewal.

Any marketing authorization which is not followed by the actual placing of the drug on the market in the EU (in case of centralized procedure) or on the market in the authorizing member state within three years after authorization ceases to be valid (the so-called sunset clause).

Any marketing authorization which is not followed by the actual placing of the drug on the market in the EU (in case of centralized procedure) or on the

market in the authorizing member state within three years after authorization ceases to be valid (the so-called sunset clause).

In the EU, new chemical entities, sometimes referred to as new active substances, qualify for eight years of data exclusivity upon marketing authorization and an additional two years of market exclusivity.

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We have obtained Orphan Medicinal Product Designations from the EMA for GPS in AML, MPM and MM.

In April 2023, the European Commission issued a proposal that will revise and replace the existing general pharmaceutical legislation.

In April 2023, the European Commission issued a proposal to revise and replace the existing general pharmaceutical legislation.

As of January 2026, the three EU institutions, the European Commission, the European Parliament and the Council of the EU are in the process of negotiating the final content of the new Directive and Regulation.

Once negotiations are complete, the European Parliament and the Council of the EU will vote on whether to approve the Directive and Regulation.

If adopted and implemented as currently proposed, these revisions will significantly change several aspects of drug development and approval in the EU.

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In the United States and some foreign jurisdictions, there have been, and continue to be, several legislative and regulatory changes and proposed changes regarding the health care system that could prevent or delay marketing approval of product and therapeutic candidates, restrict or regulate post-approval activities, and affect the ability to profitably sell product and therapeutic candidates that obtain marketing approval.

The FDA’s and other regulatory authorities’ policies may change and additional government regulations may be enacted that could prevent, limit or

delay regulatory approval of our product and therapeutic candidates.

The FDA’s and other regulatory authorities’ policies may change and additional government regulations may be enacted that could prevent, limit or delay regulatory approval of our product and therapeutic candidates.

In addition, future legislative and regulatory proposals may materially impact the ability of the FDA and other regulatory agencies to operate as they have historically operated.

We cannot be sure whether additional legislative changes will be enacted, or whether any of the FDA’s regulations, guidances or interpretations will be changed, or what the impact of such changes on the agency and its scientific review staff, if any, may be.

For example, the next FDA user fee reauthorization package is expected to enter stakeholder negotiations beginning in mid-2025, with any agreement sent to Congress in early 2027 for purposes of initiating the legislative process.

Reauthorization of the prescription drug user fee program would need to be finalized by Congress by the end of September 2027 in order to avoid a disruption in FDA’s review goals for NDAs and other activities supported by user fees assessed against industry.

For example, negotiations on the next FDA user fee reauthorization package began in mid-2025, and the resulting agreement is expected to be sent to Congress in early 2027 for purposes of initiating the legislative process.

Reauthorization of the prescription drug user fee program must be finalized by Congress by the end of September 2027 in order to avoid a disruption in FDA’s review goals for NDAs and other activities supported by user fees assessed against industry.

As previously mentioned, the primary trend in the US health care industry and elsewhere is cost containment.

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116-94) included a piece of bipartisan legislation called the Creating and Restoring Equal Access to Equivalent Samples Act of 2019, or the CREATES Act.

The CREATES Act aims to address the concern articulated by both the FDA and others in the industry that some brand manufacturers have improperly restricted the distribution of their products, including by invoking the existence of a REMS for certain products, to deny generic and biosimilar product developers access to samples of brand products.

Because generic and biosimilar product developers need samples to conduct certain comparative testing required by the FDA, some have attributed the inability to timely obtain samples as a cause of delay in the entry of generic and biosimilar products.

To remedy this concern, the CREATES Act establishes a private cause of action that permits a generic or biosimilar product developer to sue the brand manufacturer to compel it to furnish the necessary samples on “commercially reasonable, market-based terms.” Although lawsuits have been filed under the CREATES Act since its enactment, those lawsuits have settled privately;

The CREATES Act was enacted to address the concern articulated by both the FDA and industry stakeholders that some brand manufacturers improperly restrict the distribution of their products, including by invoking the existence of a REMS for certain products, to deny generic and biosimilar product developers access to samples of the brand products.

Because generic and biosimilar product developers need samples to conduct certain comparative testing required by the FDA, some attributed the inability to timely obtain samples as a cause of delay in the entry of generic and biosimilar products.

To remedy this concern, the CREATES Act established a private cause of action that permits a generic or biosimilar product developer to sue the brand manufacturer to compel it to furnish the necessary samples on “commercially reasonable, market-based terms.” Although lawsuits have been filed under the CREATES Act since its enactment, those lawsuits have settled privately;

therefore, to date no federal court has reviewed or opined on the statutory language and there continues to be uncertainty regarding the scope and application of the law.

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Our website address is www.sellaslifesciences.com.

We do not incorporate the

information on our website into this Annual Report on Form 10-K, and you should not consider such information part of this Annual Report on Form 10-K.

We do not incorporate the information on our website into this Annual Report on Form 10-K, and you should not consider such information part of this Annual Report on Form 10-K.

We were incorporated on April 3, 2006 in Delaware as Argonaut Pharmaceuticals, Inc.

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Compared sentence by sentence after normalising whitespace, quotation marks, case and digits, so re-formatting and restated figures do not read as changed language. Wording changes appear as one removal and one addition. The current filing and the prior one are authoritative.

What changed 10-K

Item 1. Business