SELLAS Life Sciences to Present In Vivo Preclinical Data Demonstrating Statistically Significant Survival Benefit of SLS009 in T-Cell Prolymphocytic Leukemia at the European Society for Medical Oncology (ESMO) Congress 2025

Preclinical data support SLS009 as a monotherapy or in combination with venetoclax for the treatment of T-PLL, a rare and highly aggressive form of mature T-cell leukemia

NEW YORK, Oct. 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 announced that preclinical efficacy of its highly selective CDK9 inhibitor, SLS009 (tambiciclib), as a monotherapy and in combination with venetoclax in T-cell prolymphocytic leukemia (T-PLL), will be presented at the European Society for Medical Oncology (ESMO) Congress 2025, being held October 17 – 21, 2025, in Berlin, Germany.

The results highlight an in vivo patient-derived xenograft (PDX) model of relapsed/refractory T-PLL that reproduced key human clinicopathological features of the disease. In this model, SLS009 demonstrated meaningful single-agent activity as well as in combination with the BCL2 inhibitor venetoclax. Both SLS009 monotherapy and the combination prolonged overall survival (7.4 weeks and 7.9 weeks, respectively) compared to venetoclax alone (4.4 weeks), a difference that was statistically significant (p<0.05), and SLS009 achieved better control of circulating T-PLL cells in the peripheral blood relative to other treatments. The combination regimen was also well tolerated in the study.

“These results are highly encouraging and provide important preclinical evidence that selective CDK9 inhibition with SLS009 may play a critical role in the treatment of T-PLL, an aggressive leukemia with very limited treatment options,” said Dr. Dragan Cicic, Senior Vice President, Chief Development Officer at SELLAS. “Notably, SLS009 alone and in combination with venetoclax prolonged survival more effectively than venetoclax monotherapy, while demonstrating favorable tolerability. This reinforces the potential of SLS009 to improve outcomes in T-PLL and broadens its therapeutic relevance across additional hematologic malignancies that require novel treatment approaches.”

“The T-PLL patient-derived xenograft model we developed is highly robust and closely mirrors the behavior and progression of the disease in humans,” said Dr. Francisco Vega, Professor and Head of the Lymphoma Section in the Department of Hematopathology at the University of Texas MD Anderson Cancer Center (MDACC) and lead author of the study. “This breakthrough allows for more rapid and meaningful translation into the clinic, greatly accelerating drug development by enabling us to evaluate novel therapies with strong clinical potential, such as SLS009, without waiting years for early clinical trial results.”