Reversal of lactate and PD-1-mediated macrophage immunosuppression controls growth of PTEN/p53-deficient prostate cancer
Purpose: PTEN loss-of-function occurs in ~50% of metastatic, castrate-resistant prostate cancer (mCRPC) patients, and associated with poor prognosis and responsiveness to standard-of-care therapies and immune checkpoint inhibitors. While PTEN loss-of-function hyperactivates PI3K signaling, combinatorial PI3K/AKT pathway and androgen deprivation therapy (ADT) has demonstrated limited anti-cancer efficacy in clinical trials. Here, we aimed to elucidate mechanism(s) of resistance to ADT/PI3K-AKT axis blockade, and to develop rational combinatorial strategies to effectively treat this molecular subset of mCRPC.  Experimental design: Prostate-specific PTEN/p53-deficient genetically engineered mice (GEM) with established 150-200 mm3 tumors, as assessed by ultrasound, were treated with either ADT (degarelix), PI3K inhibitor (copanlisib), or anti-PD-1 antibody (aPD-1), as single agents or their combinations, and tumors were monitored by MRI and harvested for immune, transcriptomic and proteomic profiling, or ex vivo co-culture studies. Single-cell RNAseq on human mCRPC samples was performed using 10X Genomics platform.  Results: Co-clinical trials in PTEN/p53-deficient GEM revealed that recruitment of PD-1-expressing tumor-associated macrophages (TAM) thwarts ADT/PI3Ki combination-induced tumor control. The addition of aPD-1 to ADT/PI3Ki combination led to TAM-dependent ~3-fold increase in anti-cancer responses. Mechanistically, decreased lactate production from PI3Ki-treated tumor cells suppressed histone lactylation within TAM, resulting in their anti-cancer phagocytic activation, which was augmented by ADT/aPD-1 treatment and abrogated by feedback activation of Wnt/ß-catenin pathway. Single-cell RNA-sequencing analysis in mCRPC patient biopsy samples revealed a direct correlation between high glycolytic activity and TAM phagocytosis suppression.   Conclusions: Immunometabolic strategies that reverse lactate and PD-1-mediated TAM immunosuppression, in combination with ADT, warrant further investigation in PTEN-deficient mCRPC patients. Overall design: Pb-Cre; PTENfl/fl Trp53fl/fl mice with established prostate tumors were treated with degarelix (0.625 mg/mouse, sc, single dose) + copanlisib (14 mg/kg, iv, every alternate day) + aPD-1 (200 µg/mouse, ip, every alternate day) combination for 28 days Grant information: This work was supported by 16CHAL12 (Prostate Cancer Foundation Challenge Award to *A. Patnaik*) and P30CA014599 (National Cancer Institute grant to *E. Markiewicz, M. Zamora, X. Fan*). Schürer and Khurana were supported by grants P30CA240139 (National Cancer Institute), U54HL127624 (National Institutes of Health), U24TR002278 (National Institutes of Health), 9BC13 (Bankhead Coley State of Florida Biomedical Research Program), 16CHAL12 (Prostate Cancer Foundation Challenge Award to *A. Patnaik*) and P30CA014599 (National Cancer Institute grant to *E. Markiewicz, M. Zamora X. Fan*).