SELLAS Announces Positive Initial Topline Phase 2a Data of SLS009 in Acute Myeloid Leukemia

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 positive initial topline data at the 45 mg (safety) dose level from its ongoing Phase 2a clinical trial of its novel and highly selective CDK9 inhibitor, SLS009, in combination with venetoclax and azacitidine (aza/ven) in patients with relapsed/refractory (r/r) acute myeloid leukemia (AML) who did not respond or stopped responding to venetoclax-based therapies. Topline data for the recommended Phase 2 dose (60 mg) is expected later this quarter.

A total of five patients with r/r AML who failed venetoclax-based therapies have been enrolled to date at the 45 mg dose level. The first patient enrolled in the study achieved a complete response, remains alive and is currently in the fifth month of treatment after relapsing on venetoclax, and the second patient is alive and in the fourth month of treatment. All patients enrolled were alive at the time of their last follow-up and four continue treatment. Anti-leukemic effects have been observed in all patients without any significant safety issues to date. Patients with AML that fail venetoclax-based therapies have limited treatment options and a poor prognosis with a median overall survival (mOS) of approximately 2.5 months.

“This outcome may represent a long-awaited breakthrough in treating patients refractory to venetoclax combination therapies after multiple lines of treatment,” said Dr. Omer Jamy, a principal investigator in the study and Assistant Professor of Medicine at the O’Neal Comprehensive Cancer Center at the University of Alabama at Birmingham (UAB) and Associate Director of the Bone Marrow Transplant Program at UAB. “Almost all older AML patients in the United States are treated with venetoclax combinations at some point during their course of treatment and, unfortunately, the majority of them become resistant to venetoclax with limited options thereafter. Survival of those patients with currently available treatment options is approximately 2.5 to 3 months. Based on what we have seen to date in this Phase 2a study of SLS009, we have managed to reverse this resistance to therapy and, equally important, extend survival in addition to a very good safety profile and quality of life. I hope to see continuation of this pattern in other patients enrolled later.”

“This initial outcome that includes a complete response, anti-leukemic activity in all patients, good safety profile across the patients and indications of extended survival for our enrolled patients still continuing treatment, we believe opens multiple registrational opportunities for SLS009. We will be exploring these options in the coming weeks as we treat patients with the recommended Phase 2 dose, 60 mg, in this study,” said Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS. “While these results are early, they are extremely encouraging and consistent with the Phase 1 study results, and further strengthen our initial proposition that the addition of CDK9 inhibition in combination with BCL-2 inhibition and hypomethylating agents could provide patients with a triple hit to increase response rates and survival outcomes without sacrificing safety and tolerability due to the specificity of SLS009. We look forward to providing additional updates this quarter from this study.”

The Phase 2a clinical trial of SLS009 is an open label, single arm, multi-center study that is designed to evaluate safety, tolerability, and efficacy at two dose levels, 45 mg and 60 mg, in combination with aza/ven. In addition to safety and tolerability of SLS009 in combination with aza/ven, the primary endpoints are composite complete response rate (CRc) and duration of response (DOR). Additional endpoints include event free survival (EFS), overall survival (OS), and pharmacokinetic (PK) and pharmacodynamic (PD) assessments.

SLS009 was recently granted orphan drug designation by the U.S. Food and Drug Administration in AML supported by the data from the Phase 1 study of SLS009 as a monotherapy that met all key study objectives. In the Phase 1 study one patient with AML achieved a complete response, making SLS009 the first CDK9 inhibitor to achieve a complete response in r/r AML as a monotherapy and remained alive for 11 months as of the last follow up. Among the 31 Phase 1 AML patients, 29 out of 31 (94%) patients were alive as of their May 2023 follow-up.