Tambiciclib

– Announced Positive Overall Survival in Cohort 3 from the Ongoing Phase 2 Trial of SLS009 (tambiciclib) in Relapsed/Refractory (r/r) Acute Myeloid Leukemia (AML) Demonstrating 8.9 mOS in AML-MRC and 8.8 mOS in All r/r to Venetoclax-Based Regimens Patients – – SLS009 Shows Promising Efficacy in Pediatric Acute Lymphoblastic Leukemia (ALL) Xenograft Models – – Final Analysis of Pivotal Phase 3 REGAL Trial of Galinpepimut-S (GPS) in AML Anticipated in 2025 – – $28.4 million in Cash and Cash Equivalents as of March 31, 2025; Additional $4.0 million Proceeds received in April 2025 through Warrant Exercises – NEW YORK, May 13, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS” or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today reported financial results for the first quarter ended March 31, 2025, and provided a corporate update. “We are very encouraged by the strong momentum across our pipeline,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The positive overall survival data in cohort 3 from the ongoing Phase 2 trial of SLS009 in r/r AML, showing a median OS that exceeds all historical benchmarks by over 3 times, further underscores the transformative potential of SLS009 for many underserved patients. In parallel, our new preclinical findings demonstrating the ability of SLS009 to overcome TP53-driven resistance, along with the promising clinical efficacy from the ongoing Phase 2, give us renewed optimism for patients across different genetic AML mutations. We look forward to presenting further data on SLS009 at ASCO, highlighting its preclinical efficacy in ASXL1-mutated colorectal cancer lines. With the full topline Phase 2 data of SLS009 anticipated soon, and the final analysis of our Phase 3 pivotal REGAL trial of GPS in AML expected later this year, we are well-positioned for an exciting and meaningful 2025.” Recent Corporate Highlights: Announced Positive Overall Survival in Cohort 3 from the Ongoing Phase 2 Trial of SLS009 in r/r AML: The data demonstrated that patients with AML-Myelodysplasia-Related Changes (AML-MRC) achieved a mOS of 8.9 months, while all relapsed or refractory to venetoclax-based regimens patients receiving 30 mg BIW achieved a mOS of 8.8 months, far surpassing the historical benchmark of 2.5 months. In addition, the therapy demonstrated a 67% ORR in patients with AML-MRC and 46% in all evaluable patients, significantly exceeding the targeted 20% ORR. The trial continues with full data and FDA regulatory path feedback expected in 1H 2025. Presented Preclinical Data Highlighting Efficacy of SLS009 in TP53 Mutated AML at the 2025 AACR Conference: Preclinical data suggest that SLS009 can induce apoptosis downstream of p53 by targeting critical proteins such as MCL-1 and survivin, regardless of p53 status. Immunoblot analysis reveals near-complete removal of these proteins in treated cells within 8 hours of exposure to SLS009. Furthermore, the treatment reduced TP53-mutated leukemia cell populations by up to 97% in combination with azacitidine–venetoclax, and by up to 80% as monotherapy. Preclinical Efficacy of SLS009 in ASXL1 Mutated Colorectal Cancer to be Showcased at ASCO 2025: The poster, entitled, In vitro efficacy of CDK9 inhibitor tambiciclib (SLS009) in ASXL1 mutated colorectal cancer cell lines, will be presented on Monday, June 2, 2025, 1:30 PM-4:30 PM CDT. Announced Positive Outcome of Interim Analysis for Phase 3 REGAL Trial of GPS in AML: The interim futility, efficacy, and safety analysis was designed to assess whether the therapy is safe, demonstrates potential efficacy, and merits continuation. The IDMC’s review supports the continuation of the study according to its original protocol. Based on this positive evaluation, GPS has shown preliminary signals of effectiveness, allowing the trial to advance toward completion. Fewer than 50% of enrolled patients were confirmed deceased after the median follow-up of 13.5 months, indicating a median survival of over 13.5 months in the trial vs. a historical median survival of 6 months for conventional therapy, as reported in a similar Phase 2 study. 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. SELLAS anticipates that 80 events will be reached this year. Announced Promising Data from Phase 2a Trial of SLS009 in Combination with Zanubrutinib in DLBCL: The trial, conducted and funded by GenFleet Therapeutics (Shanghai), Inc. (“Genfleet”), was an open-label single-arm multicenter Phase 2a study in China evaluating SLS009 in combination with BTK inhibitor, Brukinsa® (zanubrutinib) in r/r DLBCL. The results showed an overall response rate (ORR) of 67%, more than double the expected ORR of zanubrutinib alone. Among responders, one achieved complete response (CR), 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, median overall survival (OS) was not reached, and 6 out of 9 patients were alive. GenFleet will determine the next steps in development around lymphoma as SELLAS’ focus remains on AML and spliceosome–chromatin mutations, including ASXL1 mutations. PIVOT - Received Preliminary Data for Pediatric Acute Lymphoblastic Leukemia (ALL) Patients Derived Xenografts (PDX): The experiment conducted and funded by the National Institute of Health (NIH) through the 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 6 consecutive weeks. The treatment was well tolerated. For all models, median survival was approximately tripled in the SLS009 arm compared to the vehicle control arm. SLS009 demonstrated delayed progression in 25/27 (93%) models and more than 2 times longer time to progression in 15/27 (56%) of ALL models. In addition, there were complete responses (CR) in 2 models, and in one of the two models, CR was maintained after the treatment had been completed until the end of the study (4 months). Among 7 KMT2A rearranged models, time to progression was extended in all 7 models, and in 6/7 (86%) time to progression was more than doubled. Raised $25.0 Million of Gross Proceeds from a Registered Direct Offering Priced At-the-Market under Nasdaq Rules: On January 28, 2025, SELLAS announced the closing of a $25 million registered direct offering with a single healthcare-focused institutional investor before deducting placement agent’s fees and related offering expenses. The net proceeds from the offering strengthens the Company’s financial position and will be used for working capital purposes and general corporate procedures, including the purchase of any pending or future acquisitions. Financial Results for the First Quarter 2025: R&D Expenses: Research and development expenses for the quarter ended March 31, 2025, were $3.2 million, compared to $5.1 million for the same period in 2024. The $1.9 million decrease was primarily due to decreases in clinical trial expenses, manufacturing costs, and clinical drug supply purchases, and clinical and regulatory consulting costs primarily driven by the completion of enrollment in the REGAL study in the first quarter of 2024. G&A Expenses: General and administrative expenses for the first quarter of 2025 were $2.9 million, as compared to $4.5 million for the same period in 2024. The $1.6 million decrease was primarily attributable to a decrease in personnel related expenses driven by the initial recognition of a one-time severance charge during the three months ended March 31, 2024, and a decrease in headcount, and decreases in professional fees and other general and administrative expenses. Net Loss: The net loss was $5.8 million for the first quarter of 2025, or a basic and diluted loss per share of $0.07, as compared to a net loss of $9.6 million for the first quarter of 2024, or a basic and diluted loss per share of $0.21. Cash Position: As of March 31, 2025, cash and cash equivalents totaled approximately $28.4 million. Subsequent to March 31, 2025, the Company received $4.0 million in proceeds from the exercise of warrants. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact Bruce Mackle Managing Director LifeSci Advisors, LLC SELLAS@lifesciadvisors.com

NEW YORK, April 28, 2025 (GLOBE NEWSWIRE) -- SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) (“SELLAS” or the “Company”), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, today announced that preclinical efficacy of SLS009 in TP53 mutated Acute Myeloid Leukemia (AML) cells are being presented in a poster session at the American Association for Cancer Research (AACR) taking place from April 25th – 30th at McCormick Place Convention Center, Chicago, IL. Patients with TP53–mutated AML continue to face extremely poor outcomes, even with intensive chemotherapy or the addition of stem cell transplantation. Preclinical data suggest that SLS009, a highly selective CDK9 inhibitor, can induce apoptosis downstream of p53 by targeting critical proteins such as MCL-1 and survivin, regardless of p53 status. Immunoblot analysis reveals near-complete removal of these proteins in treated cells within 8 hours of exposure to SLS009. Furthermore, the treatment reduced TP53-mutated leukemia cell populations by up to 97% in combination with azacitidine–venetoclax, and by up to 80% as monotherapy. “These findings are an exciting step forward in addressing one of the most challenging subsets of AML,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “The ability of SLS009 to overcome TP-53 driven resistance in preclinical models, combined with the positive data we have seen in our ongoing Phase 2 AML program, including a response in a patient with a TP53 mutation, gives us hope that we may one day offer an effective therapeutic option to patients with AML who have long been underserved.” SLS009 is currently in Phase 2 clinical trials in patients with relapsed or refractory (r/r) AML following venetoclax-based regimens, including patients with TP53-mutated leukemia. Recently announced data revealed that r/r AML patients receiving 30 mg of SLS009 BIW achieved a mOS of 8.8 months for all patients, while the mOS in AML myelodysplasia-related-changes (MRC) patients reached 8.9 months - far surpassing the historical benchmark of 2.5 months. Among patients with mutation ASXL1, 4/6 (67%) responded; among those with RUNX1 3/5 (60%) responded, and among those with TP53 1/3 (33%) responded. In addition, there were 3 patients with adverse karyotypes, and 1 responded. “Over the past decade we’ve seen significant progress in the treatment of AML, particularly with the introduction of the venetoclax/azacitidine regimen, the use of targeted agents, and safer application of haploidentical stem cell transplants,” said Dr Phillip Amrein, MD, Clinical Investigator, Massachusetts General Hospital, Assistant Professor of Medicine Harvard Medical School, the senior author of the study. “Yet, leukemias characterized by TP53 remain a major area of unmet need, with poor outcomes even with bone marrow transplantation. The preclinical findings suggest that CDK9 inhibition might have the potential to overcome this resistance and restore sensitivity to existing therapies, offering a promising new path forward for high-risk patient populations.” Poster presentation details: Title: CDK9 inhibition enhances apoptosis of TP53 mutated AML when combined with standard chemotherapy Session Date and Time: Monday, April 28, 20025, 9:00 AM to 12:00 noon Session Title: CDK9 inhibition enhances apoptosis of TP53 mutated AML when combined with standard chemotherapy Location: Poster Section 17 Poster Board #: 1626 The poster will be available on SELLAS websites following the session. SLS009 is currently being investigated in a Phase 2 open-label, single-arm, multi-center study designed to evaluate the safety, tolerability, and efficacy of SLS009 in combination with venetoclax and azacitidine, including AML patients with ASXL1 mutations. Initial clinical safety and efficacy data are available. In addition, the study aims to identify biomarkers for the target patient population and enrichment for further trials. For more information on the study, visit clinicaltrial.gov identifier NCT04588922. About SELLAS Life Sciences Group, Inc. SELLAS is a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, GPS, is licensed from Memorial Sloan Kettering Cancer Center and targets the WT1 protein, which is present in an array of tumor types. GPS has the potential as a monotherapy and combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing SLS009 (tambiciclib) - potentially the first and best-in-class differentiated small molecule CDK9 inhibitor with reduced toxicity and increased potency compared to other CDK9 inhibitors. Data suggests that SLS009 demonstrated a high response rate in AML patients with unfavorable prognostic factors including ASXL1 mutation, commonly associated with poor prognosis in various myeloid diseases. For more information on SELLAS, please visit www.sellaslifesciences.com. Forward-Looking Statements This press release contains forward-looking statements. All statements other than statements of historical facts are “forward-looking statements,” including those relating to future events. In some cases, forward-looking statements can be identified by terminology such as “plan,” “expect,” “anticipate,” “may,” “might,” “will,” “should,” “project,” “believe,” “estimate,” “predict,” “potential,” “intend,” or “continue” and other words or terms of similar meaning. These statements include, without limitation, statements related to the GPS clinical development program, including the REGAL study and the timing of future milestones related thereto. These forward-looking statements are based on current plans, objectives, estimates, expectations, and intentions, and inherently involve significant risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks and uncertainties with oncology product development and clinical success thereof, the uncertainty of regulatory approval, and other risks and uncertainties affecting SELLAS and its development programs as set forth under the caption “Risk Factors” in SELLAS’ Annual Report on Form 10-K filed on March 20, 2025 and in its other SEC filings. Other risks and uncertainties of which SELLAS is not currently aware may also affect SELLAS’ forward-looking statements and may cause actual results and the timing of events to differ materially from those anticipated. The forward-looking statements herein are made only as of the date hereof. SELLAS undertakes no obligation to update or supplement any forward-looking statements to reflect actual results, new information, future events, changes in its expectations, or other circumstances that exist after the date as of which the forward-looking statements were made. Investor Contact Bruce Mackle Managing Director LifeSci Advisors, LLC SELLAS@lifesciadvisors.com