Abstract CT035: Safety, preliminary efficacy and pharmacodynamic (PD) analysis of maveropepimut-S, intermittent low-dose cyclophosphamide and pembrolizumab in patients with advanced, metastatic bladder cancer

Abstract Background: Maveropepimut-S (MVP-S) is a novel immunotherapeutic that educates a specific CD8 T cell response to the cancer antigen, survivin, to orchestrate immune-mediated elimination of survivin-expressing cancer cells. Specifically, MVP-S is a lipid-in-oil formulation of the DPX delivery platform, incorporating five survivin-specific immunogenic peptides, the innate immune stimulant, polydIdC, and a CD4 T cell helper peptide. In prior clinical studies, MVP-S and intermittent low-dose cyclophosphamide (CPA) elicited confirmed clinical responses (both partial and complete by RECISTv1.1) and induced a robust, durable survivin-specific CD8 T cell response. Moreover, the combination with pembrolizumab appeared to be well tolerated in solid tumors and lymphomas. The purpose of this phase 2 study is to explore whether this combination may be safe and effective in advanced, metastatic bladder cancer patients, both naïve to, and previously treated with, immune checkpoint inhibitors. Results: Seventeen (17) subjects were treated with the combination of MVP-S, CPA and pembrolizumab. Subjects received an average of 3 prior lines of therapy with 13/17 (76.4%) having previously received an anti-PD1/L1. Seven subjects progressed on or after anti-PD1/L1 as last line of therapy prior to entering the trial. The combination was well-tolerated, with majority of AEs being grade 1 or grade 2. Five (5) out of 17 subjects showed response: 3 subjects with PR (unconfirmed) and 2 with CR (confirmed). Three of these, including the 2 CRs, had progressed on anti-PD-1/L1. Long-term clinical benefit has been observed in several subjects (one patient is still on treatment after 17 months) and coincides with an increase in detectable survivin-specific T cells in peripheral blood. Conclusion: Preliminary data suggest that MVP-S/CPA and pembrolizumab is a well-tolerated combination and shows encouraging preliminary clinical activity in the treatment of advanced or metastatic bladder cancer patients, including patients who have progressed on prior anti-PD-1/L1 therapy. Citation Format: Olivier Rixe, Vincent Castonguay, Henry Conter, Eva Chalas, Pratibha Desai, Christian Squillante, Lisa A. MacDonald, Rebekah Conlon, Yogesh Bramhecha, Heather Hirsch, Jeremy R. Graff, Stephan Fiset. Safety, preliminary efficacy and pharmacodynamic (PD) analysis of maveropepimut-S, intermittent low-dose cyclophosphamide and pembrolizumab in patients with advanced, metastatic bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT035.