On May 26, 2022 SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) ("SELLAS" or the "Company"), a late-stage clinical biopharmaceutical company focused on the development of novel therapies for a broad range of cancer indications, reported top-line clinical data from its Phase 1/2 trial of galinpepimut-S (GPS), the Company’s Wilms Tumor-1 (WT1)-targeting peptide immunotherapeutic, in combination with Merck’s anti-PD-1 therapy, KEYTRUDA (pembrolizumab), in patients diagnosed with WT1(+) relapsed or refractory platinum resistant advanced metastatic ovarian cancer (Press release, Sellas Life Sciences, MAY 26, 2022, View Source [SID1234615101]).
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Data from 15 patients enrolled in the study, conducted under a Clinical Trial Collaboration and Supply Agreement with Merck & Co., Inc., Rahway, N.J., USA (known as MSD outside the United States and Canada), has been preliminarily analyzed with final data for all 17 patients enrolled in the clinical trial expected by the end of 2022. All enrolled patients were resistant to standard of care platinum-based therapy and 78.5 percent of evaluable patients were refractory to or had failed their first- or second-line therapies with 21.5 percent having failed three or more lines of therapy, including one patient who failed five previous lines of therapy. Of the 15 patients, 13 received at least three doses of GPS, the last of which was in combination with pembrolizumab, and were evaluable for response outcomes.
Summary of Top-Line Clinical Data
The overall response rate (ORR) of the trial is (7.7 percent), similar to the response to checkpoint inhibitors.
An ad hoc analysis of clinical outcomes in this cohort shows a disease control rate (DCR), the sum of overall response rate and rate of stable disease, of 53.9 percent at a median follow-up of 43.1 weeks. In a checkpoint inhibitor single agent study in a similar platinum-resistant ovarian cancer patient population treated with a checkpoint inhibitor alone, the observed DCR was 37.2 percent, consistent with a DCR rate increase of 45 percent in the GPS combination with pembrolizumab over that seen for checkpoint inhibitors alone.
Median progression-free survival (PFS) was 12 weeks compared to 8.4 weeks for checkpoint inhibitors alone seen in studies with similar patient populations, a 43 percent increase in the GPS combination with pembrolizumab. Patients with fewer previous lines of chemotherapy experienced a more favorable median PFS than those with more than two previous lines: for patients with two or fewer previous lines of therapy treated with GPS in combination with pembrolizumab, median PFS was 24 weeks.
With 43.1 weeks of follow-up the median overall survival has not been reached.
The safety profile of GPS in combination with pembrolizumab was similar to pembrolizumab alone, with the only addition of low-grade rapidly resolving local reactions at the GPS injection site, consistent with observations from other GPS clinical studies.
"These early data are an example of a new direction in development of immunotherapy for platinum-refractory ovarian cancer," commented Jeffrey S. Weber, M.D., Ph.D.; Deputy Director of the Perlmutter Cancer Center at New York University (NYU)-Langone Health; Co-Director of its Melanoma Research Program Center; and Chair of SELLAS’ Scientific Advisory Board. "In patients who failed as many as five lines of previous therapy, with small numbers of patients, the disease control rate and progression free survival that were observed merit further study. The GPS combination with checkpoint blockade, such as pembrolizumab, should be further explored, both in active disease as well as potentially in the setting of maintenance therapy after patients reach minimal residual disease post salvage therapies," added Dr. Weber.
"GPS has been primarily designed as maintenance therapy in order to provide an overall survival benefit after patients reach the minimal residual disease state or complete remission. However, in this very difficult to treat patient population with active disease, who underwent intensive chemotherapies with no apparent clinical benefit and a severe toxicity toll, the combination of GPS and pembrolizumab seems to be effective in the active disease state by halting or slowing down progression without significant further side effects," said Angelos Stergiou, M.D., Sc.D. h.c., President and CEO, SELLAS.
"As we continue to do further analyses, including immune response and correlative analyses, which will be presented at an upcoming medical conference, we are also considering how to best pursue development of GPS in combination with PD1 inhibitors in this patient population and we are excited about the path ahead. I would like to wholeheartedly thank all patients for participating in the study as well as their physicians, nurses and study teams as well as collectively our teams at SELLAS and Merck," concluded Dr. Stergiou.
About Ovarian Cancer
Ovarian cancer is one of the most common gynecologic malignancies and the fifth most frequent cause of cancer death in women in the United States. Over 22,000 cases are diagnosed annually, and there are an estimated 15,500 deaths per year. The majority of patients have widespread disease at presentation. The 5-year survival for advanced-stage disease remains less than 30 percent. Combining GPS with the checkpoint inhibitor pembrolizumab, which beneficially and profoundly alters the tumor microenvironment (TME) is hypothesized to increase the proportion of patients who develop an immune response against their cancer and potentially improve their clinical outcome over checkpoint inhibitors monotherapy, without the burden of additional toxicities in macroscopically measurable malignancies.