Positive Phase 2a Results for SLS009 in r/r AML and REGAL Phase 3 Steering Committee Update

March 26, 2024--SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) announced key data from their Phase 2a trial of SLS009 and provided an update on their Phase 3 REGAL Study of GPS in Acute Myeloid Leukemia (AML). The company also hosted a webinar to discuss these findings.

Angelos Stergiou, MD, ScD h.c., President and Chief Executive Officer of SELLAS, expressed the significance of completing enrollment for the Phase 3 REGAL trial, marking a step forward in providing GPS to AML patients. Dr. Stergiou extended gratitude towards participants and investigators involved in reaching this milestone. The Steering Committee reviewed the study up to March 1, 2024, where 123 patients were enrolled, and 66 discontinued. The reasons for discontinuation include death, relapse, intolerable toxicity, or treatment completion. Interestingly, no intolerable toxicities were observed in the GPS arm across all clinical studies, although they are common in the control arm. Most patients discontinuing treatment likely relapsed or succumbed. The Steering Committee will meet at the end of April to determine whether the trial has met its primary endpoint for interim analysis.

The REGAL Steering Committee met on March 22, 2024, to evaluate the study and noted the high number of patient completions, suggesting that the interim analysis with 60 events might soon be met. The Committee praised SELLAS for its clinical management and for addressing a significant unmet need, given that no drugs are currently approved in the AML CR2 maintenance setting.

Dr. Stergiou also highlighted positive topline data from the Phase 2a trial of SLS009 for AML patients resistant to venetoclax combination therapies. The optimal dose regimen of 30 mg BIW achieved an impressive 50% response rate, surpassing the target of 20%. Promising biomarkers were identified with a remarkable 100% response rate at the optimal dose level and a 57% response rate across all levels tested. The SLS009 aza-ven treatment showed tolerable side effects and demonstrated anti-leukemic effects in 67% of patients. The first patient to achieve complete response remains leukemia-free nine months post-enrollment. These results suggest SLS009 could be a breakthrough for relapsed and/or refractory AML patients.
Summary of Topline Data from Phase 2a study of SLS009 in AML:

Patient Characteristics:
1.As of March 15, 2024, 21 patients were treated.
2.All patients had AML resistant to or relapsed after venetoclax-based regimens.
3,20 (95%) had adverse/high-risk cytogenetics, and 1 (5%) had intermediate cytogenetics.
4.Median age was 70; 90.5% were older than 60.
Safety:
1.SLS009 with aza/ven was well-tolerated across all dose levels.
2.No dose-limiting toxicities (DLT) or high-grade (≥G3) treatment-related toxicities were observed.
3.Hematologic toxicity was consistent with standalone aza/ven treatment.
Efficacy:
1,21 patients were enrolled by March 15, 2024, in the study: 10 in the 45 mg safety cohort and 11 in the 60 mg cohort (either 2 x 30 mg BIW or 60 mg QW).
2,10% response rate in the 45 mg QW safety cohort.
3,20% response rate in the 60 mg QW cohort.
4,50% response rate in the 60 mg, 2 x 30 mg BIW cohort.
5,67% of patients showed a significant anti-leukemic effect, with bone marrow blast reduction of 50% or more.
6,The median survival rate has not yet been reached.
7,The first patient to achieve a complete response remains leukemia-free nine months post-enrollment.
Biomarkers:
1.Potential biomarkers were identified and are currently being tested as predictive markers.
2,100% response rate at the optimal dose level (30 mg BIW) and a 57% response rate across all dose levels were observed in patients with identified biomarkers.
3.The proposed biological basis and mechanism of SLS009 were clarified.
4.Relevant biomarkers are present in multiple hematologic and solid cancer types, with up to 50% prevalence in some indications.
The Phase 2a trial is an open-label, single-arm, multi-center study evaluating the safety, tolerability, and efficacy of SLS009 in combination with aza/ven at 45 and 60 mg doses. The study aims to identify biomarkers for patient selection and further trials.