The folate pathway inhibitor pemetrexed pleiotropically enhances effects of cancer immunotherapy via immunogenic tumor cell death and T cell-intrinsic mechanisms

Combination strategies leveraging chemotherapy and immunotherapy have held the promise as a method to improve benefit to cancer patients. However, most chemotherapies have detrimental effects on immune homeostasis and do not induce immunogenic cell death. The positive phase III trial of pemetrexed/carboplatin with the PD-1 antibody pembrolizumab in NSCLC (Keynote-189) lead to the first chemotherapy/immunotherapy combination ever approved. While this suggests a positive interaction between pemetrexed-based chemotherapy and PD-1 therapy, the underlying mechanism is unknown. Therefore, it is important to understand the role of pemetrexed in modulating antitumor immune response to assure application of this therapy to the appropriate patients. To characterize the effects of pemetrexed on intra-tumor immune response, murine tumor models which were sensitive to pemetrexed and known to be sensitive to PD-L1, were treated with pemetrexed with or without carboplatin, or anti-mouse PD-L1. In MC38 tumors, pemetrexed monotherapy demonstrated a trend towards an increased frequency of intra-tumor leukocytes that was accompanied by immune-related gene expression changes indicative of enhanced T cell infiltration and/or activation. Gene expression induced by pemetrexed was largely unaffected by carboplatin. Treatment of both MC38 and Colon26 tumor cells in vitro with pemetrexed induced release of HMGB1, indicative of immunogenic cell death. Although proliferation of primary human T cells was slightly reduced by pemetrexed, at clinically relevant concentrations, treatment lead to an enhanced T cell activation phenotype, including upregulation of multiple interferon gamma-induced genes, and increased mitochondrial respiration. This correlated with improved antigen specific in vitro cytotoxic activity of OT-1 TCR transgenic CD8 T cells when treated with pemetrexed during priming with OVA peptide. Treatment with pemetrexed and PD-L1 demonstrated a combination benefit compared to either monotherapy in both tumor models. Pathway Analysis of gene expression data revealed that improved antigen presentation, enhanced T cell and cytokine signaling and an engagement of CD4+ T cell-mediated immunity during the combination. This correlated with upregulation of MHC-I & II on monocytes, macrophages and tumor cells, suggesting increased immune priming. Accordingly, treatment with S1P1R antagonist (FTY720, preventing T cell LN egress) after initiation of therapy resulted in a loss of combination efficacy. This data suggests that pemetrexed promotes intra-tumor T cell-mediated immune response through immunogenic tumor cell death and increased activation and metabolic fitness of T cells. The combination of these effects results in enhanced T cell function leading to an improved anti-tumor efficacy in combination with PD-L1 antibody Citation Format: David A. Schaer, Nelusha Amaladas, Zhao Hai Lu, Erik Rasmussen, Andreas Sonyi, Darin Chin, Andrew Capen, Yanxia Li, Catalina Meyer, Bonita Jones, Xiaodong Hong, Shuang Luo, Carmine Carpenito, Kenneth Roth, Alexander Nikolayev, Bo Tan, Manisha Brahmachary, Krishna Chodavarapu, Frank Charles Dorsey, Jason Manro, Thompson Doman, Greg Donoho, David Surguladze, Gerald Hall, Sandaruwan Geeganage, Michael Kalos, Ruslan Novosiadly. The folate pathway inhibitor pemetrexed pleiotropically enhances effects of cancer immunotherapy via immunogenic tumor cell death and T cell-intrinsic mechanisms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3945.