MYC and p53 Alterations Cooperate through VEGF Signaling to Repress Cytotoxic T-cell and Immunotherapy Responses in Prostate Cancer.

Patients with castration-resistant prostate cancer (CRPC) are generally unresponsive to tumor-targeted treatments and immunotherapies. Genetic alterations acquired during the evolution of CRPC may affect antitumor immunity and immunotherapy responses, which could inform personalized therapeutic strategies. Using our innovative electroporation-based mouse models, we generated distinct genetic subtypes of CRPC found in patients and uncovered unique immune microenvironments. Specifically, mouse and human prostate tumors with MYC amplification and p53 disruption had weak cytotoxic lymphocyte infiltration and an overall dismal prognosis. MYC and p53 cooperated to induce tumor-intrinsic secretion of VEGF, which signaled through VEGFR2 expressed on CD8+ T cells to directly inhibit T-cell migration and effector functions. Targeting VEGF-VEGFR2 signaling in vivo remodeled the immunosuppressive prostate tumor microenvironment, leading to CD8+ T-cell-mediated primary tumor and metastasis growth suppression and significantly increased overall survival in MYC- and p53-altered CRPC. VEGFR2 blockade also led to the induction of PD-L1 in tumors and produced antitumor efficacy in combination with PD-L1 immune checkpoint blockade in multiple preclinical CRPC mouse models. Thus, these results identify a genetic mechanism of immunosuppression through VEGF signaling in prostate cancer that can be targeted to reactivate immune and immunotherapy responses in an aggressive subtype of CRPC. SIGNIFICANCE: VEGFR2 blockade inhibits VEGF-mediated T-cell suppression and potentiates the effects of PD-L1 immune checkpoint blockade to treat castration-resistant prostate cancer driven by MYC and p53 alterations.