Co-targeting of two distinct androgen receptor-regulated signaling pathways as a therapeutic approach in prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed cancer in men and the second leading cause of cancer-related deaths in the United States. Androgen deprivation therapy (ADT) is initially effective; however, most patients eventually relapse and progress to castration-resistant prostate cancer (CRPC), where tumor growth persists despite being exposed to extremely low levels of androgens. In probing the molecular determinants of androgen receptor (AR) pharmacology in PCa, we made the unexpected observation that PCa cells can recognize and respond differently to different levels of androgens. Notably, we demonstrated that low levels of androgens, functioning through an AR monomer, facilitate a non-genomic activation of the mammalian target of rapamycin (mTOR) signaling pathway to drive proliferation. Conversely, we found that eugonadal levels of androgens (high dose; HD) promote AR dimer formation, which actively suppress c-MYC expression, inhibit proliferation, and drive a transcriptional program associated with a differentiated phenotype. To elucidate the mechanism(s) by which AR activates mTOR signaling, we dissected the molecular events initiated by androgens in validated cellular models of PCa. These studies revealed that androgens, acting through AR, induce AKT phosphorylation at S473, an early and previously unrecognized regulatory node in AR-driven pathways. Prior studies have established that AKT S473 phosphorylation is mediated by mTOR complex 2 (mTORC2) and can be stimulated by insulin-like growth factor-1 (IGF-1). Indeed, we demonstrated that IGF-1 signaling was absolutely required for androgen-dependent mTOR activation and cell proliferation. These results suggest that androgens/AR act upstream of mTOR to amplify the activity of the IGF-1-AKT signaling axis rather than directly engaging mTOR pathway components. While we have established that AR-driven mTOR activation occurs through the IGF-1-AKT axis, our data also revealed a distinct AR-regulated growth program centered on c-MYC. Notably, inhibition of the IGF-1-AKT-mTOR pathway suppresses PCa cell proliferation in vitro but fails to reduce c-MYC expression, indicating that targeting this axis alone is unlikely to achieve durable control of the disease. It is significant, therefore, that we determined that HD androgens downregulate c-MYC expression while maintaining mTOR activation. Leveraging these insights, we evaluated the utility of combining AKT inhibition with HD androgen treatment in a xenograft model of PCa. This combination strategy was superior to either treatment alone, resulting in robust suppression of tumor growth. Together, these findings establish a mechanistic framework for the dose-dependent effects of androgens on PCa biology and highlight the potential clinical utility of dual-targeting approaches to overcome resistance to standard of care treatments in PCa.