Targeting the androgen receptor signaling pathway in advanced prostate cancer

Purpose This article summarizes current androgen receptor (AR)-directed therapies that have received regulatory approval for the treatment of advanced prostate adenocarcinoma (herein referred to as prostate cancer, PC). PC is an androgen-dependent malignancy in which ligands including testosterone and dihydrotestosterone bind to AR, initiating androgen-AR complex translocation to the nucleus followed by AR-mediated transcription of target genes. Androgen deprivation therapy (ADT), including gonadotropin hormone-releasing hormone (GnRH) agonists with or without AR antagonists (antiandrogens), GnRH antagonists, or bilateral orchiectomy, forms the backbone of treatment for patients with metastatic castration-naive PC and/or castration-resistant PC (CRPC). ADT is also an option for high-risk, early-stage PC after prostatectomy and/or radiation. While ADT is often very effective as initial therapy, resistance ultimately develops despite suppression of gonadal and/or adrenal androgens, leading to CRPC, which is characterized by mechanisms such as reactivation of the AR signaling pathway, AR gene overexpression, and mutations in the ligand-binding domain of AR that lead to disease progression, resulting in increased symptom burden and ultimately death. However, disease in patients with CRPC is still dependent on androgen signaling, and these patients continue on ADT to maintain a castrate level of serum testosterone. Novel hormonal therapies including agents that target AR directly (eg, AR antagonists) are often added to ADT in this setting. Targeting the AR signaling pathway led to the development of second-generation AR antagonists, examples of which include enzalutamide, apalutamide, and darolutamide. These agents do not exhibit partial agonism, possess a higher affinity for AR, and are postulated to improve survival outcomes relative to their first-generation counterparts for patients with CRPC. Lastly, the emergence of ADT, including second-generation AR antagonists, has led to the development of supportive care for treatment-related adverse effects. Conclusion Major advances have been made in targeting the AR signaling pathway in patients with advanced PC. Further studies are warranted to identify the optimal sequencing of therapies to maximize treatment benefit. Mitigation of treatment-related adverse effects presents new opportunities to advance clinical pharmacy practice.