The androgen receptor (AR) signaling is the most prominent signaling pathway driving tumorigenesis in prostate cancer. As a result, androgen-deprivation therapy (ADT) is often used to treat prostate cancer, aimed to lower testosterone levels and block AR action. However, despite initial treatment response, patients inevitably relapse due to AR signaling restoration, with the tumor acquiring features that enable it to survive and ultimately proliferate despite low circulating testosterone levels. However, over the last years, other androgenic steroids such as 11-ketotestosterone and 11-keto-dihydrotestosterone have been reported to exhibit significant AR activation potential. Importantly,  the adrenal-derived steroid 11-KT is considered the predominant circulating active androgen in patients with castration-resistant prostate cancer (CRPC), suggesting that may contribute to AR (re)activation following ADT. Although these steroids have been reported to act as potent AR agonists and henceforth drive the receptor’s activation, their biological mechanism of action on AR remains fully elusive.

Our study focused on comparing the effect of 11-Ketotestosterone and Testosterone in hormone-sensitive prostate cancer cells, LNCaP. Using extensive genomics, proteomics and computational analyses, we successfully illustrated the direct biological impact of 11-Ketotestosterone in AR action and prostate cancer growth. These studies show, for the first time, the critical impact of a thus-far largely ignored -yet predominant testosterone variant in castrated men following prostate cancer treatment. Finally, in a randomized phase II clinical trial of prostate cancer patients, treated with AR-targeted therapy versus chemotherapeutics, we directly assessed the clinical implications of this largely overlooked testosterone variant in prostate cancer care.