Abstract 2853: VPAC antagonism as potential therapeutic for prostate cancer

Abstract Background: Tumor-associated macrophages (TAM) within prostate cancer (PC) microenvironment correlates with poor clinical outcomes and with acquired resistance to androgen-deprivation therapy (ADT). Our preclinical work has established that macrophage phagocytosis can partially restrain PC growth at both castration-sensitive and -resistant stages; however, this response remains incomplete. We therefore hypothesized that activating phagocytosis by targeting androgen-regulated checkpoints on macrophages empowers ADT and provides a combinatorial therapeutic strategy to control PC via anti-tumor immunity. Methods: Bone marrow-derived macrophages (BMDM) profiled using RNA sequencing and Western blot to identify androgen-regulated immune checkpoints, followed by functional validation in polarization and phagocytosis assays. In vivo anti-tumor efficacy of candidates was tested using syngeneic TrampC1, Myc-CAP, cMyc-Rb-knockout (KO) models in both wildtype (WT) and immune checkpoint-knockout mice. Treatment with androgen receptor (AR) and immune checkpoint blockade alone and the combination arms with relevant untreated controls. Results: Transcriptomic and proteomic profiling revealed selective upregulation of VIP receptor 1 (VPAC1) on immunosuppressive M2-like BMDM vs anti-tumor M1-like. Functional assays revealed an increased IL-12 expression in BMDM following AR and VPAC co-blockade. Enzalutamide upregulated VPAC1 on both M1/M2-like BMDM. It also increased phagocytosis of PC cells in VIP-KO BMDM relative to untreated control, but not in WT, indicate that VPAC1 serves as an androgen-regulated macrophage-suppressive checkpoint. Bioinformatic analysis showed positive correlations between 1) VPAC1 and AR, and 2) VIP and synaptophysin (SYP) in prostate adenocarcinoma samples. Furthermore, degarelix improved the survival of syngeneic TrampC1 tumor (harboring both adenocarcinoma and neuroendocrine phenotypes)-bearing mice, particularly in VPAC1-KO mice, compared to VIP or VPAC2-KO and WT controls, with corresponding benefits in prostate tumor growth control. In the androgen-sensitive Myc-CAP syngeneic model, a potent VIP receptor antagonist, ANT308, increased degarelix-mediated tumor control. ANT308 treatment yielded similar effects in androgen-independent Myc-Rb-KO PC model, highlighting the synergy of co-blocking VIP/VPAC and AR pathways for controlling PC. Conclusions: VPAC1 is an androgen-regulated macrophage checkpoint. VPAC inhibition with ANT308 leads to anti-tumor phagocytosis and enhances ADT-mediated control of prostate tumors in both adenocarcinoma and mixed adeno-neuroendocrine diseases. Further mechanistic investigation is needed to elucidate the intrinsic versus extrinsic role of VIP/VPAC at those stages, informing the design of clinical trials for ANT308 in PC patients. Citation Format: YuJie Chen, Tuisha Gupta, Kiranj Chaudagar, Edmund K. Waller, . VPAC antagonism as potential therapeutic for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2853.