SLS009 Generates Positive Topline Data in R/R AML and REGAL Trial Completes Enrollment

Sellas has announced positive topline findings from the phase 2a portion of a phase 1/2 trial (NCT04588922) of SLS009 (formerly GFH009) in patients with relapsed/refractory acute myeloid leukemia (AML). The company simultaneously announced that the phase 3 REGAL trial (NCT04229979) of galinpepimut-S (GPS) in patients with AML has completed enrollment, and that an interim analysis guided by the trial’s steering committee is expected soon.¹

In the phase 2a portion of the phase 1/2 study, at the March 15, 2024, data cutoff, SLS009 in combination with azacitidine (Vidaza) and venetoclax (Venclexta) elicited an overall response rate (ORR) of 50% in patients with relapsed/refractory AML who received the agent at the selected optimal dose of 30 mg twice weekly. This ORR exceeded the targeted 20% rate.

The open-label, single-arm, multicenter trial was designed to investigate the safety, tolerability, and efficacy of SLS009 plus azacitidine and venetoclax in patients with AML that was relapsed/refractory to venetoclax-containing regimens. This trial enrolled a total of 21 patients, 10 who received SLS009 at 45 mg once weekly in a safety cohort, and 11 who received the agent at either 30 mg twice weekly or 60 mg once weekly. Ninety-five percent of patients had adverse or high-risk cytogenetics, and 5% had intermediate cytogenetics. Patients had a median age of 70 years, and 90.5% of patients were older than 60 years of age.

The primary end points of the trial are safety and tolerability, namely the incidence of dose-limiting toxicities (DLTs) and the incidence and severity of all adverse effects, with pharmacokinetics, complete response (CR), duration of response, progression-free survival, and overall survival (OS) serving as key secondary end points.² The trial will also identify biomarkers in the target patient population to use for further study enrichment.¹

The ORR was 10% in the 45 mg cohort, and this dose level was determined to be below the recommended phase 2 dose. Additionally, the ORR was 20% in the 60 mg once weekly cohort.

The median OS with SLS009 was not yet reached at any dose level. The target median OS is over 3 months. SLS009 elicited strong anti-leukemic activity, defined as bone marrow blast reduction of at least 50%, in approximately 67% of patients across all dose levels. The first patient to achieve CR is continuing on the study and remains leukemia free at 9 months since enrollment.

Furthermore, the agent exhibited a favorable safety profile at all tested dose levels. Investigators observed no DLTs at any of the dose levels, and no treatment-related toxicities of grade 3 or higher were seen. The hematologic toxicities profile of SLS009 was consistent with that of azacitidine/venetoclax standalone treatment.

To date, all patients with identified potential predictive biomarkers who received the SLS009 at the optimal dose level have responded. The ORR was 57% in patients with identified biomarkers who received the agent across all dose levels. Based on these findings, Sellas has described the proposed biological basis and mechanism of action of SLS009 in patients with these biomarkers. These biomarkers are present in several hematologic and solid cancers, and many patients exhibit them in additional indications.

“We are extremely excited to share positive topline data from the phase 2a trial of SLS009 in [patients with] AML resistant to venetoclax combination therapies,” Angelos Stergiou, MD, ScD, hc, president and CEO of Sellas, said in a press release. “These compelling results from the phase 2a [portion of the trial] reinforce our belief that SLS009 represents a potential breakthrough for [patients with] relapsed and/or refractory AML, addressing 1 of the most urgent unmet medical needs.”

In 2023, SLS009 received orphan drug designation from the FDA for the treatment of patients with AML.³

Regarding REGAL, the trial’s steering committee met on March 22, 2024, to discuss the study and noted that the interim analysis, which requires 60 events, may begin soon because of the high number of patients who completed trial participation.¹

“Completion of enrollment in the phase 3 REGAL trial represents an important milestone in our goal to deliver GPS to [patients with] AML,” Stergiou added. “We are extremely grateful to the patients, their families, and investigators who have helped us achieve this significant milestone.”

Stergiou noted that the steering committee reviewed REGAL as of the March 1, 2024, data cutoff, at which point 123 patients had been enrolled and 66 patients had discontinued the study treatment because of relapse, intolerable toxicity, death from any cause, or treatment completion.

“Regarding the GPS arm, we are pleased to report that we have not observed any intolerable toxicities in any patient population across all our clinical studies thus far, although toxicities are commonly observed with therapies used in the control arm,” Stergiou concluded. “Therefore, almost all patients who are off treatment may have most likely either relapsed or passed away. The most frequent cause of death in this patient population is relapse. As the study sponsors, we lack specific information on the outcomes of these 66 patients, hindering our ability to confirm whether the required number of events for interim analysis – 60 – has been reached. The determination of such outcomes, the primary end point of the trial, lies within the purview of the IDMC, which is now scheduled to meet by the end of April.”

References

1. Sellas announces positive topline data from the phase 2a study of SLS009 in r/r AML and provides steering committee update on phase 3 REGAL study. News release. Sellas Life Sciences Group, Inc. March 26, 2024. Accessed March 26, 2024. https://ir.sellaslifesciences.com/news/News-Details/2024/SELLAS-Announces-Positive-Topline-Data-from-the-Phase-2a-Study-of-SLS009-in-rr-AML-and-Provides-Steering-Committee-Update-on-Phase-3-REGAL-Study/default.aspx
2. A study of GFH009 in patients with hematologic malignancies. ClinicalTrials.gov. Updated September 1, 2023. Accessed March 26, 2024. https://classic.clinicaltrials.gov/ct2/show/NCT04588922
3. SELLAS receives FDA orphan drug designation for SLS009 for treatment of acute myeloid leukemia. News release. SELLAS. October 11, 2023. Accessed March 26, 2024. https://www.sellaslifesciences.com/investors/news/News-Details/2023/SELLAS-Receives-FDA-Orphan-Drug-Designation-for-SLS009-for-Treatment-of-Acute-Myeloid-Leukemia/default.aspx