Sellas Pipeline

Acute Myeloid Leukemia (AML)

PHASE 2 TRIAL IN AML PATIENTS, IN FIRST COMPLETE REMISSION (CR1)
PHASE 2 TRIAL IN AML PATIENTS IN SECOND COMPLETE REMISSION (CR2)
PHASE 3 TRIAL (REGAL STUDY) IN AML PATIENTS IN CR2

Phase 2 trial results in AML patients in their first complete remission (CR1) showed a median OS of 67.6 months (all ages) for patients receiving GPS in the maintenance setting, which represents a substantial improvement compared to best standard therapies. The patients’ median age was 63 years old. The results also showed a trend in improved clinical outcomes in patients who mounted an immune response with GPS compared to those patients who did not (Maslak PG, et al. Blood Adv. 2018;2:224-34). Broadly similar results were obtained in a pilot study of GPS in a more advanced setting, i.e., in AML patients who had relapsed, received standard second line therapy and were able to achieve their second complete remission (CR2). In that study, the patients’ median age was 74 years old. Initial data showed that administration of GPS in the maintenance setting resulted in a median OS of 16.3 months (all ages) versus 5.4 months in post-hoc matched, contemporaneously treated patients (P = 0.0175) (Brayer J, et al. Am J Hematol. 2015;90:602-7). Final data from the study shows a median OS of 21.0 months, at a median follow-up of 30.8 months, in patients receiving GPS therapy versus 5.4 months OS for those AML CR2 patients being treated with best standard care, a statistically significant difference (p-value < 0.02) for the patients treated with GPS. In both studies, serial active immunization with GPS showed a well-tolerated safety profile. In addition, GPS elicited immune responses in patients, including CD4+ and CD8+ T cell responses.

Based on the above data and following review by the FDA, a pivotal Phase 3 clinical trial, the REGAL study, for AML patients in CR2 was commenced in January 2020. The REGAL study is a 1:1 randomized, open-label study comparing GPS monotherapy in the maintenance setting to investigators’ choice best available treatment in AML patients who have achieved hematologic complete remission, with or without thrombocytopenia (CR2/CR2p), after second-line antileukemic therapy and who are deemed ineligible for or unable to undergo allogeneic stem-cell transplantation. The primary endpoint is the overall survival (OS) from the time of study entry. Secondary endpoints include leukemia-free survival, antigen-specific T-cell immune response dynamics, measurable residual disease by multigene array, and assessments of AML clonal evolution and inflammasome molecular signatures in the tumor microenvironment in bone marrow biopsy samples. The study is expected to enroll approximately 116 patients across approximately 50 clinical sites in the United States and Europe.

GPS IN COMBINATION WITH KEYTRUDA® (PEMBROLIZUMAB) BASKET STUDY (5 INDICATIONS)

PHASE 2 TRIAL IN MULTIPLE INDICATIONS

In October 2017, SELLAS entered into a Clinical Trial Collaboration and Supply Agreement for the conduct of a combination clinical trial targeting multiple cancer types with Merck & Co., Inc., Kenilworth, N.J., USA (known as MSD outside the United States and Canada). GPS is being administered in combination with MSD's anti-PD-1 therapy KEYTRUDA® (pembrolizumab) in a Phase 1/2 trial and is currently enrolling patients in two indications, ovarian cancer (second or third line) and colorectal cancer (third or fourth line), to be followed by AML (patients unable to attain deeper morphological response than partial on hypomethylating agents and who are not eligible for allogeneic hematopoietic stem cell transplant), triple negative breast cancer (second line) and small cell lung cancer (second line). The Phase 1/2 trial utilizes a combination of GPS plus KEYTRUDA in patients with WT1-positive relapsed or refractory tumors. This study will assess the efficacy and safety of the combination, comparing overall response rates (ORRs) and immune response markers achieved with the combination versus prespecified rates based on those seen with KEYTRUDA alone in comparable patient populations. The trial was initiated in December 2018 (ClinicalTrials.gov Identifier: NCT03761914). The study is planned to enroll approximately 90 patients at up to 20 centers in the United States.

Malignant Pleural Mesothelioma (MPM)

RANDOMIZED, DOUBLE-BLIND, PLACEBO-CONTROLLED PHASE 2 STUDY IN A TOTAL OF 41 MPM PATIENTS ENROLLED AT MSKCC AND M.D. ANDERSON CANCER CENTER.

According to the final analysis of the Phase 2 MPM study data of GPS with a median follow up of 17.2 months, median OS of 22.8 months was observed for GPS-treated MPM patients, compared to a median 18.3 months OS for patients in the control arm (Zauderer M et al, Clin Cancer Res. 2017;23:7483-9). In the datasets from both these analyses, GPS induced CD8+ and CD4+ T cell activation. GPS also demonstrated a well-tolerated safety profile in MPM patients.

PHASE 1 OPEN LABEL STUDY OF GPS IN COMBINATION WITH NIVOLUMAB IN MPM PATIENTS

In February 2020, an investigator-sponsored clinical trial (IST) of GPS in combination with Bristol-Myers Squibb’s anti-PD-1 therapy, nivolumab (Opdivo®), in patients with malignant pleural mesothelioma (MPM), which is being conducted at MSKCC, was commenced. Study drug is being provided by both SELLAS and Bristol-Myers Squibb for this Phase 1 open-label clinical study of GPS in combination with nivolumab in patients with MPM who harbor relapsed or refractory disease after having received frontline standard of care multimodality therapy. The purpose of the trial is to determine if the administration of GPS in combination with nivolumab has the potential to demonstrate antitumor immune responses and meaningful clinical activity in the presence of macroscopic disease in MPM patients. The study will also investigate the tolerability of the combination, evaluate the immunogenicity of the two agents administered together, by CD4+ and CD8+ T-lymphocytes (both peripherally and at the tumor site), and gauge the degree of clinical benefit by assessment of the overall response rate with the combination in comparison with that reported with nivolumab alone in historical comparable patient populations. In a randomized, controlled, blinded Phase 2 clinical trial in MPM patients completed in 2017, GPS monotherapy, given as maintenance after first line tumor-debulking multimodality treatment, demonstrated meaningful clinical activity with median survival of 22.8 months vs. 18.3 months in the control group (N=41) and with associated sustained immune responses (both CD4+ and CD8+) against the WT1 antigen while adverse events were mainly comprised of low grade reactions at the site of the injection.

Multiple Myeloma (MM)

OPEN-LABEL PHASE 2 STUDY IN HIGH-RISK MULTIPLE MYELOMA (MM) PATIENTS.

High-risk MM patients typically relapse within 12 months after frontline induction therapy, followed by successful ASCT, even when they receive maintenance therapy with IMIDs. SELLAS reported updated positive Phase 2 data showing 88% actuarial OS at the 18-month landmark in 18 evaluable patients (median follow-up at 18 months for survivors). All patients had evidence of MRD after ASCT and 15 had high-risk cytogenetics at diagnosis. Combined, these characteristics typically result in low PFS rates that do not exceed 12 months following ASCT, even while on maintenance therapy with IMIDs or proteasome inhibitors. Current median PFS is 23.6 months, while median OS has not been reached. Administration of GPS in the post-ASCT maintenance setting (along with lenalidomide) also resulted in cross-epitope reactivity in the majority of patients, whereas strong correlations were observed between immune response to WT1 antigens and clinical response (achievement of complete response/very good partial response [CR/VGPR]) at the time of completion of the inoculation series (Koehne G, et al. 44th Ann. Meeting of the European Society for Blood and Marrow Transplantation (EBMT), 2018; Abstr. # O132). GPS demonstrated a 2.5-fold increase in median PFS, as well as a 2.6-fold increase in the PFS rate at 18 months versus a historical cohort of MM patients with high-risk cytogenetics published by the Spanish PETHEMA group from the PETHEMA Network No. 2005-001110-41 trial, which included MM patients with high-risk cytogenetics and MRD+ status post-ASCT and on continuous thalidomide maintenance.

Ovarian Cancer

OPEN-LABEL, NON-RANDOMIZED PHASE 1/2 CLINICAL STUDY EVALUATING THE SAFETY AND EFFICACY OF GPS IN COMBINATION WITH NIVOLUMAB (OPDIVO®), A PD-1 IMMUNE CHECKPOINT INHIBITOR, IN PATIENTS WITH RECURRENT OVARIAN, FALLOPIAN TUBE OR PRIMARY PERITONEAL CANCER WHO ARE IN SECOND OR GREATER CLINICAL REMISSION.

This Phase 1/2 study enrolled 11 patients with recurrent ovarian cancer who are in second or greater clinical remission at MSKCC. Patients enrolled in the study received the combination therapy during the study’s 14-week treatment period. Individuals who have not progressed by the end of this period also received a maintenance course of the GPS. Repeated vaccination with GPS for a total of 6 inoculations in combination with 7 infusions of nivolumab was shown not to add toxicity burden above and beyond what would be expected with nivolumab alone; therefore, the primary endpoint of the study (safety of the combination) was met. Moreover, the 1-year landmark progression-free survival (PFS) rate was 70% for patients who received >2 doses of GPS and nivolumab (n=10), which compared favorably with a historical rate of 43-50% in this setting (O’Cearhaill RE, et al. J Clin Oncol. 2018;36[15; Suppl], 5553). Median follow-up of 33 months showed 30% of patients being progression free at 2 years (historical controls are 3-10%); WT1-specific IgG observed in 86% of patients (weeks -27) as well as CD4 and CD8 T cell responses. These data have supported the rationale for further study of GPS in combination with PD1 inhibitors in patients with advanced ovarian cancer.