Abstract 1603: The imipridone ONC212 cooperates with MEK and immune checkpoint inhibition to elicit <i>in vivo</i> regression in KPC T cell-low mouse pancreatic tumors

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with limited therapeutic options. ONC212 is a second-generation imipridone with antitumor effects in human PDAC cell lines. ONC212 has been shown to agonize the mitochondrial protease ClpP/ClpX complex, thereby impairing oxidative phosphorylation. Further data has suggested that ONC212 acts by heterogeneously activating other pathways, notably the inhibition of autophagy. MEK inhibitors have been shown to increase pancreatic cancer cells' dependence on autophagy for survival and synergistically induce cell death when combined with autophagy inhibitors. In addition, inhibition of autophagy has been shown to increase MHC class I presentation of neoantigens and increase efficacy of immune checkpoint inhibitors (ICI) in preclinical pancreatic models. Our group has previously shown that ONC212, trametinib, and ICI are synergistically effective in immunocompetent mice bearing KrasLSL.G12D/+; Tp53LSL.R172H/+; Pdx1Cretg/+ (KPC) T cell-high murine PDAC tumors. We sought to assess the efficacy of this combination in a KPC T cell-low model to determine if it similarly enhances the tumor cell death in a model with greater resistance to immunotherapy. Methods: We determined in vitro sensitivity of the T cell-low cells to ONC212 alone and in combination with trametinib using CellTiter-Glo® luminescent cell viability assays. Results were analyzed after 72 hours of incubation using Combenefit. In vivo experiments involved C57BL/6 mice that were injected subcutaneously with 3x105 T cell-low cells in 100 mL of matrigel. Treatment was terminated once tumor volumes reached 2,000 mm3 or if ulceration occurred. Mouse weight and tumor size was measured every four days. ONC212, trametinib, and ICI (anti-PD-1 mAb) alone and all possible doublet/triplet combinations were evaluated in KPC tumor-bearing C57BL/6 mice. Once mice were sacrificed, tumors were harvested and processed for GeoMx proteomics analysis, specifically looking at immune cell profiling/activation, MAPK signaling, PI3K/AKT signaling, and cell death pathways. Results: We found that the combination of ONC212 and trametinib exhibited synergy in the T cell-low cell line in vitro. Our in vivo experiments revealed that, similar to the T cell-high cell line, the triple therapy containing ONC212, trametinib, and ICI (anti-PD-1 mAb) effectively slowed T cell-low tumor growth. However, differences were observed in these two KPC models. Notably, mice bearing T cell-low tumors had more aggressive tumors with more frequent ulcerations. We attribute the rapid tumor growth to the reduced T cell population within these tumors, likely diminishing the effectiveness of the ICI used; however, combining ICI and MEK/autophagy inhibitors was able to overcome this barrier. RNA sequencing and spatial proteomic evaluation is ongoing. Citation Format: Jasper Chan, Alexis J. Lannigan, Leiqing Zhang, Archana Saxena, Lanlan Zhou, Varun V. Prabhu, Wafik S. El-Deiry, Alexander G. Raufi. The imipridone ONC212 cooperates with MEK and immune checkpoint inhibition to elicit in vivo regression in KPC T cell-low mouse pancreatic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1603.