Abstract 6111: OBI-3424, an AKR1C3-activated prodrug, exhibits in vivo synergistic anti-tumor effect in combination with pembrolizumab by induction of immunogenic cell death

Abstract Immunogenic cell death (ICD) involves the activation of cytotoxic T lymphocyte-driven adaptive immunity with long-term immunological memory. OBI-3424 is a highly selective prodrug that is activated by AKR1C3 to release a potent bis-alkylating agent. This study aims to investigate whether OBI-3424 can induce ICD and create a tumor microenvironment that benefits the combination therapy of OBI-3424 with immune checkpoint inhibitors. OBI-3424 induced ICD was examined in vitro by incubation of the prodrug with AKR1C3 positive cells followed by the detection of damaging-associated molecular patterns (DAMPs). The ICD-related immunity was assessed in vivo using advanced severe immunodeficient mice that were engrafted with human peripheral blood mononuclear cells (PBMCs). Anti-tumor effect of OBI-3424 in combination with pembrolizumab was evaluated in a xenograft model using PBMC-humanized mice. Incubation of OBI-3424 with AKR1C3 positive cells H460 and HepG2 induced the release of DAMPs including calreticulin, HMGB1, and ATP, in dose- and time-dependent manners. The detection of the DAMPs indicated that OBI-3424 induced ICD in vitro. The OBI-3424-induced ICD and its related immunity were also assessed in vivo. PBMC-humanized mice were immunized with OBI-3424- or PBS-treated HepG2 cells and then challenged with live HepG2 cells. No tumor growth was noted in mice that were immunized with OBI-3424-treated cells, indicating that the dying HepG2 cells induced by OBI-3424 elicited an adaptive, tumor-specific immune response. Furthermore, OBI-3424 showed a synergistic anti-tumor effect in combination with pembrolizumab in HepG2 xenograft model using PBMC-humanized mice. OBI-3424 plus pembrolizumab exhibited significantly stronger inhibition on tumor growth (TGI 77.2%) when compared with the treatment of OBI-3424 (TGI 27.8%) or pembrolizumab (TGI -15.3%) alone. Analysis of tumor-infiltrating lymphocytes (TILs) showed that OBI-3424 treatment induced the populations of activated cytotoxic CD8 T-cells (CD45+/CD8+/CD69+ and CD45+/CD8+/Granzyme), activated helper CD4 T-cells (CD45+/CD4+/CD69+), and mature dendritic cells (CD11b+/CD86+). In addition, OBI-3424 treatment also increased PD-1 expression on CD8 and CD4 cells, which in turn potentiated the anti-tumor effect of pembrolizumab. We demonstrated that OBI-3424 was able to induce ICD as shown by the release of DAMPs in vitro and tumor-specific immunity in vivo. OBI-3424 also created a tumor microenvironment that enhances the function of pembrolizumab, supported by the synergistic effect in animals with the cotreatment of the two drugs. The results suggest that a combination therapy of OBI-3424 and anti-PD-1 in human clinical study is warranted. OBI-3424 is currently in Phase 1/2 clinical trials for solid tumor and acute lymphoblastic leukemia (NCT03592264 and NCT04315324). Citation Format: Chun-Chung Wang, Wan-Fen Li, Chih-Chan Lee, Lu-Tzu Chen, Jhih-Jie Yang, Jiann-Shiun Lai, Ming-Tain Lai. OBI-3424, an AKR1C3-activated prodrug, exhibits in vivo synergistic anti-tumor effect in combination with pembrolizumab by induction of immunogenic cell death [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 6111.