PIK3CG Is a Potential Therapeutic Target in Androgen Receptor-Indifferent Metastatic Prostate Cancer

The prostate epithelium consists of predominantly luminal cells that express androgen receptor and require androgens for growth. As a consequence, the depletion of testicular androgens in patients with prostate cancer results in tumor regression. However, it eventually leads to a castration-resistant disease that is highly metastatic. In this report, a mouse model of metastatic prostate cancer was generated through the deletion of the tumor-suppressor gene Trp53 in conjunction with oncogenic activation of the proto-oncogene Kras. These mice developed early-onset metastatic prostate cancer with complete penetrance. Tumors from these mice were poorly differentiated adenocarcinoma, characterized by extensive epithelial-mesenchymal transition. With no or a very low level of androgen receptor expression, the tumor cells were resistant to androgen receptor inhibition. Pik3cg, encoding phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit γ (Pi3kγ), was highly expressed in these tumors, and pharmacologic inhibition of Pi3kγ blocked tumor cell growth in vitro, reversed epithelial-mesenchymal transition, and abated tumor metastasis in vivo. Immunohistochemistry analysis in human prostate cancer specimens showed that the expression of PIK3CG was significantly associated with advanced clinical stages. Taken together, these results suggest that PIK3CG plays an important role in the progression and metastasis of prostate cancer, and may represent a new therapeutic target in the metastatic castration-resistant prostate cancer.