On June 28, 2023 SELLAS Life Sciences Group, Inc. (NASDAQ: SLS) ("SELLAS" or the "Company"), a late-stage clinical biopharmaceutical company focused on developing novel therapies for a broad range of cancer indications, reported topline clinical data from a Phase 1 investigator-sponsored clinical trial of its lead clinical candidate, galinpepimut-S (GPS), combined with the checkpoint inhibitor nivolumab (Opdivo) in patients with malignant pleural mesothelioma (MPM) who were either refractory to or relapsed after at least one line of the standard of care therapy (Press release, Sellas Life Sciences, JUN 28, 2023, View Source [SID1234632967]).
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Nine of the ten patients enrolled received at least three doses of GPS, with the third GPS dose given in combination with nivolumab. All enrolled patients had either received and progressed with or were refractory to frontline pemetrexed-based chemotherapy. Additional immune response data from all ten patients is expected by Q4 2023.
The study details are as follows:
70.3 weeks (17.6 months) median overall survival (OS) in patients who received the combination therapy (9/10 patients) and 54.1 weeks (13.5 months) for all ten patients (nine patients with combination therapy and one GPS only patient). Median overall survival for patients who entered the study as Stage IV patients was 62.3 weeks (15.6 months). OS was calculated as the time from cessation of the most recent previous therapy until confirmed death or most recent data update for patients who are still alive (40 percent of patients)
11.9 weeks median progression-free survival (PFS) for all patients
30% disease control rate (DCR) with three patients achieving stable disease per RECIST criteria with the tumor volume decrease of up to 17%. DCR is the sum of overall response rate and rate of stable disease.
As expected in this high-risk advanced cancer population, all patients experienced adverse events, unrelated and related. Seven out of ten patients (70%) had treatment related toxicities and six (60%) had nivolumab related toxicities. Grade 3 (G3) and higher toxicities were observed in three patients (30%). None of the G3 and higher toxicities were related to GPS. GPS related toxicities were observed in three patients (30%), all were Grade 1 (G1) and included G1 skin induration at the site of injection/injection site reaction and/or fatigue in two patients and G1 dizziness and non-cardiac chest pain, each in one patient.
Of the ten evaluable patients, eight were male and two were female, with a median age of 69 years. Sixty percent of entered the study as Stage III or IV patients. Initial tumor stages were I (one patient), II (three patients), III (two patients) and IV (four patients).
All patients had MPM epithelioid and/or sarcomatoid variant, a tumor which universally expresses Wilms Tumor 1 (WT1), one of the most widely expressed cancer antigens, ranked by the National Cancer Institute as the top priority among cancer antigens for immunotherapy.
"In our GPS trials completed in previous years we have observed and reported increased survival in the maintenance therapy setting, which is the primary setting for our GPS therapy. This year, we have seen in two studies where GPS appears to increase the survival benefit in active disease when combined with checkpoint blockade drugs, one with relapsed/refractory WT1 positive ovarian cancer and now in relapsed/refractory WT1 positive mesothelioma. We believe that these observed survival benefits in the active disease setting further confirms strong biological effect of GPS in even the most challenging settings," said Angelos Stergiou, M.D., Sc.D. h.c., President and CEO, SELLAS. "This is demonstrated by a very promising disease control rate where GPS seems to contribute to stopping progression of extremely aggressive cancers."
"It is important to note that the positive survival outcomes seen in this study are accompanied with a safety profile which is similar to that of the checkpoint inhibitor alone," commented Dragan Cicic, MD, SVP Clinical Development, SELLAS. "It is rare for a drug used to treat advanced cancers to result in no toxicities higher than Grade 1. Interestingly, patients in this trial in whom low toxicities were observed all had survival at the median or higher."
About MPM
With approximately 3,300 cases in the United States each year, accompanied by a rising incidence in developing countries, MPM is notoriously difficult to treat and can lead to poor clinical outcomes with respect to both OS and PFS, especially for those patients with the sarcomatoid variant who show a median OS of approximately 4.0 to 5.0 months. In relapsed and refractory patients who progressed after the first line standard of care pemetrexed, a similar patient population to that in the GPS nivolumab combination trial, the common treatment regimen is vinorelbine and OS in those patients is reported to be between 4.5 and 6.2 months. In patients treated with other chemotherapy regimens, such as carboplatin and irinotecan, median OS is reported to be approximately 7.0 months.