Androgen-mediated TGFβ expression suppresses anti-tumor neutrophil response in bone metastatic prostate cancer

Prostate Cancer (PCa) bone metastases are associated with spinal cord compression, fracture, bone pain and death. Despite advances in the medical therapy for localized disease, metastatic disease is incurable and osseous progression is largely dictated by tumor-stromal interactions in the bone microenvironment. We showed previously that tumor bone neutrophils are tumoricidal to PCa but lose their cytotoxic potential as the tumor progresses. However, there have been no studies to date to clinically define and characterize neutrophils throughout the prostate cancer disease spectrum to determine their biomarker potential. Using patient peripheral blood polymorphonuclear neutrophils (PMNs), we identify that PCa progression dictates PMN properties, including viability, cell surface markers and gene expression. However, the majority of PMNs elicited an anti-tumor response ex vivo demonstrating that PMN cytotoxicity is cell autonomous and independent of PCa disease stage. In fact, we identify a novel role for androgen regulation, i.e., androgen deprivation therapy (ADT), in suppressing PMN cytotoxicity via altered transforming growth factor beta receptor I (TβRI). Using preclinical models, we found that high dose testosterone/bipolar androgen therapy (BAT) and genetic or pharmacologic TβRI inhibition combined with standard ADT rescued the androgen-associated suppression and restored PMN anti-tumor immune response. This combination provided a therapeutic strategy more impactful than ADT alone, in bone metastatic prostate cancer (BM-PCa). These studies: 1) highlight a necessity for both molecular and functional characterization of PMNs per cancer type and 2) reveals the ability to program PMN immune response for successful targeting of BM-PCa.