An F876L Mutation in Androgen Receptor Confers Genetic and Phenotypic Resistance to MDV3100 (Enzalutamide)

Abstract

Castration-resistant prostate cancer (CRPC) is the most aggressive, incurable form of prostate cancer. MDV3100 (enzalutamide), an antagonist of the androgen receptor (AR), was approved for clinical use in men with metastatic CRPC. Although this compound showed clinical effi cacy, many initial responders later developed resistance. To uncover relevant resistant mechanisms, we developed a model of spontaneous resistance to MDV3100 in LNCaP prostate cancer cells. Detailed characterization revealed that emergence of an F876L mutation in AR correlated with blunted AR response to MDV3100 and sustained proliferation during treatment. Functional studies confi rmed that AR F876L confers an antagonist-to-agonist switch that drives phenotypic resistance. Finally, treatment with distinct antiandrogens or cyclin-dependent kinase (CDK)4/6 inhibitors effectively antagonized AR F876L function. Together, these fi ndings suggest that emergence of F876L may (i) serve as a novel biomarker for prediction of drug sensitivity, (ii) predict a "withdrawal" response to MDV3100, and (iii) be suitably targeted with other antiandrogens or CDK4/6 inhibitors. SIGNIFICANCE:We uncovered an F876L agonist-switch mutation in AR that confers genetic and phenotypic resistance to the antiandrogen drug MDV3100. On the basis of this fi nding, we propose new therapeutic strategies to treat patients with prostate cancer presenting with this AR mutation. Cancer Discov; 3(9); 1030-43.

Androgen receptor antagonism drives cytochrome P450 17A1 inhibitor efficacy in prostate cancer

“…The AR-W741C mutation enabled an antagonist-to-agonist switch with bicalutamide but was effectively antagonized by the other antiandrogens tested and with seviteronel, galeterone, and abiraterone. The AR-F876L mutation appears to be associated with enzalutamide resistance, and we have confirmed that this mutation enables this antiandrogen to manifest agonist activity (21,24,25). This mutation did not affect the antagonist activity of hydroxyflutamide or bicalutamide, and, further, its activity was inhibited by seviteronel, galeterone, and abiraterone.…”

“…The data were subjected to exponential growth-curve analysis constrained to share an initial value and to 2-way ANOVA analysis followed by Bonferroni's multiple comparisons test. Significant differences as compared with the vehicle-treated control group (P < 0.05) were detected only for seviteronel at a dose of 100 mg/kg (days [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

“…This group of CYP17 inhibitors was as effective as enzalutamide in preventing the interaction of the AR with DNA and inhibiting AR target gene transcription in cells engineered to overexpress the receptor. These drugs also demonstrated efficacy against those AR mutations (enzalutamide, F876L; flutamide, T877A; bicalutamide, W741C) that are associated with resistance to endocrine therapy (6,21,(24)(25)(26)(27). Importantly, the ability of seviteronel and abiraterone to inhibit the growth of enzalutamide-resistant xenografts through direct antagonism of AR-F876L activity provides compelling evidence that the antiandrogenic activity of CYP17 inhibitors is manifest in vivo.…”

“…In addition to enhanced AR expression, there is considerable evidence to suggest that mutations in the AR that alter its response to pharmacological agents may also be important in CRPC (6,21,23). Specifically, treatment failure in patients progressing while on antiandrogens has been attributed to point mutations in the AR: flutamide, T877A; bicalutamide, W741C; and enzalutamide, F876L (6,21,(24)(25)(26)(27). There is also recent evidence that the T877A mutation may be causally involved in resistance to abiraterone (21,28,29).…”

“…These mutations occur most frequently in the AR ligand-binding domain (LBD) and lead to altered ligand pharmacology, such that antiandrogens function as agonists and drive the outgrowth of cells expressing the gain-of-function resistance mutation. Examples of clinically relevant mutations include T877A, W741C, and F876L, which are found in prostate tumors resistant to flutamide, bicalutamide, and enzalutamide/ ARN-509, respectively (6,21,(24)(25)(26)(27). T877A mutations have also recently been identified in tumor biopsies and circulating cell-free DNA from patients with CRPC progressing on, or previously treated with, abiraterone (21,28,29).…”