Targeting IRE1α reprograms the tumor microenvironment and enhances anti-tumor immunity in prostate cancer [scRNA-seq2]

Unfolded protein response (UPR) is a central intracellular stress response pathway that is hijacked by tumor cells for their survival. However, how activation of UPR in cancer cells may shape the tumor microenvironment (TME) remains largely unexplored. Here, we investigated the potential role of IRE1α signaling on modulation of TME dynamics in prostate cancer (PCa). We found that IRE1α is increased in PCa patient tumors and genetic inhibition of IRE1α in syngeneic mouse PCa models, as well as in an orthotopic model, dramatically reduced tumor growth. Multiomics analysis suggested that IRE1α ablation in cancer cells significantly potentiated interferon (IFN) response and activation of immune system related pathways in the TME. Single-cell RNA-sequencing (scRNA-seq) revealed that the abundance of immunosuppressive cells, such as tumor-associated macrophages (TAMs), were markedly reduced in the IRE1α deficient tumors. Geneset Enrichment Analysis demonstrated that IFN response was significantly enriched in TAMs, cancer cells, and dendritic cells. Notably, the small molecule IRE1α inhibitor MKC8866 (ORIN1001), currently in clinical trials, reprogrammed the TME and enhanced the response to anti-PD-1 blockade therapy in syngeneic PCa mouse models. Furthermore, a novel scRNA-seq-derived TAM gene signature is strongly associated with poor PCa survival, which is reduced by the MKC8866 + anti-PD-1 combination therapy. Our findings indicate that activation of IRE1α signaling not only promotes cancer cell growth and survival, but it also interferes with anti-tumor immunity in the TME. Thus, IRE1α targeting could present a novel approach for improving anti-PD-1 immunotherapy in PCa.