Androgen Receptor Gene Aberrations in Circulating Cell-Free DNA: Biomarkers of Therapeutic Resistance in Castration-Resistant Prostate Cancer

Abstract

Purpose: Although novel agents targeting the androgen–androgen receptor (AR) axis have altered the treatment paradigm of metastatic castration-resistant prostate cancer (mCRPC), development of therapeutic resistance is inevitable. In this study, we examined whether AR gene aberrations detectable in circulating cell-free DNA (cfDNA) are associated with resistance to abiraterone acetate and enzalutamide in mCRPC patients. Experimental Design: Plasma was collected from 62 mCRPC patients ceasing abiraterone acetate (n = 29), enzalutamide (n = 19), or other agents (n = 14) due to disease progression. DNA was extracted and subjected to array comparative genomic hybridization (aCGH) for chromosome copy number analysis, and Roche 454 targeted next-generation sequencing of exon 8 in the AR. Results: On aCGH, AR amplification was significantly more common in patients progressing on enzalutamide than on abiraterone or other agents (53% vs. 17% vs. 21%, P = 0.02, χ2). Missense AR exon 8 mutations were detected in 11 of 62 patients (18%), including the first reported case of an F876L mutation in an enzalutamide-resistant patient and H874Y and T877A mutations in 7 abiraterone-resistant patients. In patients switched onto enzalutamide after cfDNA collection (n = 39), an AR gene aberration (copy number increase and/or an exon 8 mutation) in pretreatment cfDNA was associated with adverse outcomes, including lower rates of PSA decline ≥ 30% (P = 0.013, χ2) and shorter time to radiographic/clinical progression (P = 0.010, Cox proportional hazards regression). Conclusions: AR gene aberrations in cfDNA are associated with resistance to enzalutamide and abiraterone in mCRPC. Our data illustrate that genomic analysis of cfDNA is a minimally invasive method for interrogating mechanisms of therapeutic resistance in mCRPC. Clin Cancer Res; 21(10); 2315–24. ©2015 AACR.

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.…”

“…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).…”

“…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). To gain a better understanding of the therapeutic potential of CYP17 inhibitors in antiandrogen-resistant CRPC, we assessed the ability of CYP17 inhibitors and benchmark AR antagonists to inhibit mutant AR …”

“…The most recent studies have attributed such resistance to continued AR overexpression, increased adrenal or intratumoral androgen synthesis, expression of constitutively active AR splice variants (AR-V7), glucocorticoid receptor (GR) expression, and AR mutations (5,(19)(20)(21)(22). AR point mutations are rare in early, untreated prostate tumors but commonly arise in treated CRPC tumors (23).…”

“…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).…”