On June 4, 2018 SELLAS Life Sciences Group, Inc. (NASDAQ:SLS) ("SELLAS" or "the Company") reported that interim Phase 1 data of GPS in combination with nivolumab in patients with WT1+ ovarian cancer in second or third remission after salvage chemotherapy at the 2018 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting (Press release, Sellas Life Sciences, JUN 4, 2018, View Source [SID1234527155]). The presentation, "A phase I study of concomitant galinpepimut-S (GPS) in combination with nivolumab (nivo) in patients (pts) with WT1+ ovarian cancer (OC) in second or third remission," is being delivered by Roisin E. O’Cearbhaill, M.D., Gynecologic Medical Oncology Service, Memorial Sloan Kettering Cancer Center, during the "Gynecologic Cancer" session from 1:15 to 4:45 p.m. CT. The primary endpoint of the study is safety and assessment of toxicity, and treatment is continued until disease progression or toxicity. The secondary endpoint is immune response, and the exploratory endpoints include landmark 1-year PFS rate compared to historical controls and correlative analyses between clinical and immune responses.

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Exploratory efficacy interim data from this open-label Phase 1 investigator-sponsored trial showed that GPS, when combined with a PD-1 inhibitor, demonstrated PFS of 64% at one year in an intent to treat (ITT) group of 11 evaluable patients with WT1+ ovarian cancer in second or greater remission. Among patients who received at least three doses of GPS in combination with nivolumab, PFS at one year was 70% (7/10). The historical rates with best standard treatment do not exceed 50% in this disease setting. The most common adverse events were Grade 1 or 2, including fatigue and injection site reactions. Dose limiting toxicity was observed in one patient, following the second dose of the combination. No additional adverse event burden was observed for the combination as compared to nivolumab monotherapy. WT1 is a tumor antigen that is expressed in about half of ovarian cancers. The combination induced a high frequency of T- and B-cell immune responses.

Based on these safety, clinical activity and immunogenicity data, SELLAS expects to initiate a Phase 1/2 clinical study of GPS in combination with the PD-1 inhibitor pembrolizumab in a variety of tumor types, including WT1+ ovarian cancer in the third quarter of 2018.

"Patients with advanced relapsed ovarian cancer, in which WT1 is highly expressed, have few treatment options with limited efficacy," said Angelos Stergiou, MD, ScD h.c., President & Chief Executive Officer of SELLAS. "The interim data being presented today further support the therapeutic potential of GPS in high-risk cancer populations, including ovarian cancer. In this Phase 1 trial, the combination of GPS and nivolumab showed promising clinical and immune response activity with no additional adverse event burden as compared to nivolumab monotherapy, warranting further evaluation. These data bolster our commitment to developing GPS, alone and in combination, across a wide range of cancers, and we look forward to initiating our Phase 1/2 basket trial investigating the combination of GPS with pembrolizumab in five WT1+ tumor types, including ovarian, small cell lung, colorectal and triple negative breast cancer and acute myeloid leukemia."

Of the 11 patients evaluated:

7 patients were in second remission and 4 patients were in third remission
10 patients received six total doses of GPS (800 mcg) over 12 weeks in combination with seven infusions of I.V. nivolumab (3 mg/kg) over 14 weeks
all underwent toxicity assessments with each dose of GPS, and three weeks after the completion of therapy at Week 15. Non-progressors at Week 15 were permitted to receive four additional GPS doses, administered every eight weeks.
With regard to clinical and immune responses:

in 11 evaluable patients, the landmark 1-year PFS rate was 64% in the ITT group and 70% in the ten patients who received at least three doses of GPS + nivolumab. Historical rates do not exceed 50% in this disease setting
serum levels of antigen-specific IgG, against both individual WT1 peptides within GPS and the full-length WT1 protein, were induced in 86% of patients
achievement of high titers of WT1-specific IgG post-GPS results from Immunoglobulin (Ig) M to IgG class switching, the latter being a surrogate marker of induction of activated T-helper (Th) cells after vaccination
antigen-specific T-cell responses to individual WT1 peptides were observed between Weeks 6-15, primarily CD4 T-cells and, to a smaller extent, CD8 T-cells
"Effective consolidation or maintenance strategies are needed to prevent further recurrence or to prolong remission in patients with ovarian cancer after successful salvage from a previous relapse. In this setting, immune-directed therapy with a combination of blocker nivolumab and GPS, a multivalent, heteroclitic peptide vaccine targeting WT1, an antigen expressed in about half of ovarian cancers, led to high rates of antigen-specific immunization. We anticipate that this enhanced immunogenicity will translate into a reduction in relapses in larger studies," mentioned Dr. O’Cearbhaill. She added "these encouraging interim data suggest that the combination of GPS plus PD-1 inhibitors deserves further study in WT1+ ovarian cancer."

About Galinpepimut-S (GPS):
GPS is a heteroclitic multivalent, multi-peptide cancer immunotherapeutic agent composed of four peptides, addressing over 20 epitopes, and derived from the WT1 protein, which has been ranked by the National Cancer Institute as a top priority among cancer antigens for immunotherapy. Importantly, because the WT1 antigen is overexpressed in many malignancies, and is not found in most normal tissues, GPS has the potential to be a broad immunotherapy, effective across a multitude of diverse cancer types and patient populations.