Androgen deprivation therapy allows for effective anti-TIGIT immunotherapy in murine model of castration resistant prostate cancer.

Abstract Prostate cancer is the second leading cause of cancer associated mortality in men, and for reasons that remain unclear, immunotherapy treatments have largely failed in patients with advanced prostate cancer. Standard of care therapy for these patients relies on androgen deprivation therapies (ADT) to block testosterone production combined with small molecules that inhibit androgen synthesis and/or the function of the androgen receptor (AR). Importantly, androgens are reported to be immunosuppressive; therefore, we postulated that androgen axis blockade might promote response to immunotherapy. In the recent years, the co-inhibitory receptor TIGIT has emerged as a promising immunotherapy target, and we observed that TIGIT is highly expressed on tumor infiltrating T cells and NK cells in metastatic castration resistant prostate cancer (CRPC) patients treated with the AR antagonist enzalutamide. Likewise, in a mouse model of CRPC, we show that tumor infiltrating T cells express TIGIT and that treatment with enzalutamide increases its expression. In this model, neither treatment with anti-TIGIT alone nor with chemical castration and enzalutamide affects tumor growth. Remarkably, the combination of anti-TIGIT with chemical castration and enzalutamide leads to delayed tumor growth and long-term cures in about 60% of the animals. Taken together, our data suggest that androgen receptor blockade sensitizes immune cells in the tumor to respond to anti-TIGIT immunotherapy. This work was largely supported by an OHSU Foundation grant and a sponsored research agreement with AstraZeneca to A.E.M. Additional funding was provided by Collins Medical Trust and Prostate Cancer Foundation.