SELLAS Life Sciences’ CDK9 Inhibitor GFH009 Demonstrates Tumor Growth Inhibition in Small Cell Lung Cancer Murine Model

GFH009 exhibits robust activity against small cell lung cancer xenografts, both as monotherapy and in combination with PARP inhibitor olaparib

Results support designating small cell lung cancer as first indication in planned solid cancer basket trial for GFH009

NEW YORK, Dec. 01, 2022 (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 results from a preclinical in vivo study for its highly selective CDK9 inhibitor, GFH009, that demonstrate robust inhibition of tumor growth in a mouse xenograft model of small cell lung cancer (SCLC).

GFH009 was tested against NCI-H209 SCL xenografts in athymic nude mice in four treatment groups of eight mice each (n=32) consisting of GFH009 alone, olaparib (a PARP inhibitor) alone, a combined regimen of GFH009 and olaparib, and a vehicle control. Treatments were initiated after tumor xenograft volumes exceeded 120 mm³ in each animal group and mice were subsequently sacrificed after mean tumor volume exceeded 1,500 mm³ in the control group.

GFH009 treated mice exhibited a 40.4% decrease in mean tumor growth compared to the control group in this very aggressive cancer model which had a tenfold increase in average tumor volume over 20 days. Strongest effects were observed with GFH009 in combination with olaparib, with mean tumor growth decreased by 72.3%. Treatment with olaparib alone resulted in a 30.2% mean decrease in tumor growth. No significant toxicity or safety concerns were observed in any of the treatment groups.

“We are looking forward to expanding use of GFH009 into solid cancers and these results indicate CDK9 can be an actionable target not only in the apoptotic pathway but also the DNA damage response pathway,” said Dragan Cicic, MD, Senior Vice President, Clinical Development, of SELLAS. “This opens up additional avenues for the use of GFH009 in an expanding array of difficult to treat cancers based on their genomic and proteomic traits, moving another step towards truly personalized medicine.”

Olaparib is a commercially available targeted oncology drug that acts as a PARP inhibitor and induces synthetic lethality in BRCA mutated cancer cells via DNA damage and response (DDR) pathways. Recently published clinical trials have demonstrated early signals of efficacy for olaparib both as a single agent and in combination with agents targeting DDR, specifically ATR pathways in refractory SCLC patients. CDK9 is known to bind with cyclin K, forming a complex that plays a key role in the DDR pathway which could enhance synthetic lethality of olaparib.

About SELLAS Life Sciences Group, Inc.
SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) 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, galinpepimut-S (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 potential as a monotherapy or in combination with other therapies to address a broad spectrum of hematologic malignancies and solid tumor indications. The Company is also developing GFH009, a small molecule, highly selective CDK9 inhibitor, which is licensed from GenFleet Therapeutics (Shanghai), Inc., for all therapeutic and diagnostic uses in the world outside of Greater China.

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 preclinical data for GFH009, plans for further development of GFH009, and the potential for GFH009 as a drug development candidate. 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 associated with the COVID-19 pandemic and its impact on the Company’s clinical plans and business strategy, risks and uncertainties associated 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 31, 2022 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