FDA Fast Track for SLS009 in Relapsed/Refractory AML with Phase 2a Study Update

On January 9, 2024, SELLAS Life Sciences Group (NASDAQ: SLS) announced that the U.S. Food and Drug Administration (FDA) has granted Fast Track Designation to its novel CDK9 inhibitor, SLS009 (formerly GFH009), aimed at treating relapsed/refractory acute myeloid leukemia (r/r AML). This designation is intended to expedite the development and review process of drugs that address serious medical conditions and fulfill significant unmet medical needs.

Angelos Stergiou, MD, ScD h.c., President and CEO of SELLAS, emphasized that the Fast Track Designation for SLS009 supports its potential in treating r/r AML, a condition with a grim prognosis due to its aggressive nature. According to Dr. Stergiou, recent data from a Phase 2a study revealed positive outcomes at a 45 mg safety dose level when SLS009 was combined with venetoclax and azacitidine (aza/ven). These results showed notable anti-leukemic effects and a promising safety profile among AML patients who were resistant to venetoclax combination therapies.

Notably, out of nine patients enrolled in the 45 mg cohort, eight were alive at the last follow-up. The first patient treated experienced a complete response (CR) and remained on study in the seventh month, showcasing full peripheral blood recovery. The second patient enrolled was in the sixth month of treatment, indicating the potential benefits of incorporating CDK9 inhibition into the aza/ven regimen. The ongoing cohorts have now included patients receiving the 60 mg dose as well.

Dr. Stergiou highlighted that SLS009 is emerging as a potentially effective treatment for hematologic cancers, underscored by the FDA’s recognition through Fast Track and Orphan Drug Designations for AML. These designations enable accelerated clinical development, aiming to deliver a groundbreaking treatment to patients with urgent needs.

In the 45 mg safety dose cohort, nine patients have been enrolled, with eight (89%) still alive. One patient succumbed to sepsis after contracting COVID-19. Furthermore, six patients continue to receive treatment, with durations ranging from two to seven months. Interestingly, significant anti-leukemic effects, such as a 50% or greater reduction in bone marrow blasts, were observed in seven out of eight (87.5%) evaluable patients, without significant safety concerns to date. No dose-limiting toxicities were reported among the patients.

Previously, in a Phase 1 study where SLS009 was administered as monotherapy, one AML patient who had not responded to prior aza/ven therapy achieved a durable complete response with no minimal residual disease, remaining alive 16 months after treatment began.

The Phase 2a clinical trial of SLS009 is an open-label, single-arm, multi-center study assessing its safety, tolerability, and efficacy in combination with aza/ven at two dose levels: 45 mg and 60 mg. In the 60 mg cohort, patients are randomized into two groups with different dosing schedules to analyze various safety and efficacy parameters, such as composite complete response rate (CRc) and duration of response (DOR). Additional assessments include event-free survival (EFS), overall survival (OS), and pharmacokinetic (PK) and pharmacodynamic (PD) evaluations.

Detailed results from the 45 mg cohort and preliminary data from the 60 mg cohort are expected in the first quarter of 2024, with further analysis of the 60 mg cohort anticipated in the second quarter of 2024.