SELLAS Life Sciences’ Highly Selective CDK9 Inhibitor, GFH009, Demonstrates Cancer Cell Growth Inhibition in Preclinical In Vitro Model of Neuroendocrine Prostate Cancer Cell Line

– Neuroendocrine Prostate Cancer is Growing Unmet Medical Need –

NEW YORK, Aug. 24, 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 new preclinical in vitro study for its highly selective CDK9 inhibitor, GFH009, in neuroendocrine prostate cancer (NEPC). The data shows that GFH009 demonstrated significant anti-tumor effects in the selected cell line at nanomolar concentrations and, in certain samples, complete growth inhibition with no viable cancer cells.

NEPC, an aggressive variant of prostate cancer, is a rapidly growing indication which arises as a result of otherwise successful treatment of advanced prostate cancer. In up to 15 to 20 percent of patients treated with hormonal therapies for prostate adenocarcinoma, small-cell prostate cancer may develop in later stages of prostate cancer progression. This histologic transformation occurs as a mechanism of treatment resistance. Aggressive NEPC represents a lethal endpoint in the progression of prostate cancer from prostate adenocarcinoma to castration-resistant prostate cancer (CRPC) to NEPC. Median survival for NEPC patients whose cancer arose from prior prostate adenocarcinoma is estimated at only 5.4 months. 

The conversion to NEPC is associated with recurrent genetic lesions including mutation or deletion of RB1 and TP53 as well as the overexpression and genomic amplification of MYCN. SELLAS believes that all forms of MYC may be susceptible to CDK9 inhibition and the data from the in vitro study, conducted at an independent, third-party contract research organization, Translational Drug Development (TD2), supported this supposition, resulting in 38 nM median IC50 value.

“We are very excited with this first confirmation of our hypothesis that GFH009 could address NEPC, a rapidly growing indication,” said Dragan Cicic, MD, Senior Vice President, Clinical Development, of SELLAS. “About one in eight men will be diagnosed with prostate cancer during his lifetime and any significant change in the course of treatment for this cancer has potential for outsized consequences.”

About Translational Drug Development (TD2)  
TD2 is an oncology development organization that provides innovative services for oncology-focused companies. Using a dedicated team of professionals with broad experience and understanding in drug development, TD2 is uniquely positioned to support improved and accelerated development of medicines for life-threatening oncology diseases. TD2 applies rigorous and high-throughput translational preclinical development, combined with regulatory affairs expertise, to customize clinical trial design and execution. TD2’s suite of capabilities encourages the timely selection of patient populations who are most likely to benefit from a new agent, and the rapid identification of clinically significant endpoints. TD2 is committed to reducing the risks and uncertainty inherent in the drug development process and to the acceleration of patient access to promising treatments. For more information, visit www.TD2inc.com. 

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
Allison Soss
KCSA Strategic Communications
Email: SELLAS@kcsa.com
Phone: 212.896.1267

Media Contacts
Raquel Cona / Michaela Fawcett
KCSA Strategic Communications
Email: SELLAS@kcsa.com
Phone: 212.896.1276