BackgroundThe androgen receptor (AR) is a pivotal drug target for the treatment of prostate cancer, including its lethal castration-resistant (CRPC) form. All current non-steroidal AR antagonists, such as hydroxyflutamide, bicalutamide, and enzalutamide, target the androgen binding site of the receptor, competing with endogenous androgenic steroids. Several AR mutations in this binding site have been associated with poor prognosis and resistance to conventional prostate cancer drugs. In order to develop an effective CRPC therapy, it is crucial to understand the effects of these mutations on the functionality of the AR and its ability to interact with endogenous steroids and conventional AR inhibitors.ResultsWe previously utilized circulating cell-free DNA (cfDNA) sequencing technology to examine the AR gene for the presence of mutations in CRPC patients. By modifying our sequencing and data analysis approaches, we identify four additional single AR mutations and five mutation combinations associated with CRPC. Importantly, we conduct experimental functionalization of all the AR mutations identified by the current and previous cfDNA sequencing to reveal novel gain-of-function scenarios. Finally, we evaluate the effect of a novel class of AR inhibitors targeting the binding function 3 (BF3) site on the activity of CRPC-associated AR mutants.ConclusionsThis work demonstrates the feasibility of a prognostic and/or diagnostic platform combining the direct identification of AR mutants from patients’ serum, and the functional characterization of these mutants in order to provide personalized recommendations regarding the best future therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0864-1) contains supplementary material, which is available to authorized users.

The human androgen receptor (AR) is a proven therapeutic target in prostate cancer. All current antiandrogens, such as Bicalutamide, Flutamide, Nilutamide, and Enzalutamide, target the buried hydrophobic androgen binding pocket of this protein. However, effective resistance mechanisms against these therapeutics exist such as mutations occurring at the target site. To overcome these limitations, the surface pocket of the AR called binding function 3 (BF3) was characterized as an alternative target for small molecule therapeutics. A number of AR inhibitors directly targeting the BF3 were previously identified by us ( J. Med. Chem. 2011 . 54 , 8563 ). In the current study, based on the prior results, we have developed structure-activity relationships that allowed designing a series of 2-((2-phenoxyethyl)thio)-1H-benzimidazole and 2-((2-phenoxyethyl)thio)-1H-indole as lead BF3 inhibitors. Some of the developed BF3 ligands demonstrated significant antiandrogen potency against LNCaP and Enzalutamide-resistant prostate cancer cell lines.

Background:The androgen receptor (AR) is a transcription factor regulating progression of prostate cancer. Results: Developed compounds inhibit AR transcriptional activity in vitro and in vivo by selective targeting of the AR-DNAbinding domain (DBD). Conclusion: By targeting the DBD, the compounds differ from conventional anti-androgens. Significance: Anti-androgens with a novel mechanism of action have the potential to treat recurrent prostate cancer.

There has been a resurgence of interest in the development of androgen receptor (AR) inhibitors with alternative modes of action to overcome the development of resistance to current therapies. We demonstrated previously that one promising strategy for combatting mutation-driven drug resistance is to target the Binding Function 3 (BF3) pocket of the receptor. Here we report the development of a potent BF3 inhibitor, 3-(2,3-dihydro-1H-indol-2-yl)-1H-indole, which demonstrates excellent antiandrogen potency and anti-PSA activity and abrogates the androgen-induced proliferation of androgen-sensitive (LNCaP) and enzalutamide-resistant (MR49F) PCa cell lines. Moreover, this compound effectively reduces the expression of AR-dependent genes in PCa cells and effectively inhibits tumor growth in vivo in both LNCaP and MR49F xenograft models. These findings provide evidence that targeting the AR BF3 pocket represents a viable therapeutic approach to treat patients with advanced and/or resistant prostate cancer.

Based on misinterpretation of the NMR spectra provided by our chemical vendor, the structure of VPC-14449 should be corrected. VPC-14449 (4-(4-(4,5-bromo-1H-imidazol-1-yl)thiazol-2-yl)morpholine) should be replaced with VPC-14449 (4-(4-(2,4-dibromo-1H-imidazol-1-yl)thiazol-2-yl)morpholine). In Fig. 1A, the graphical representation of VPC-14449 should be changed to the correct structure. Our industry partner synthesized the published VPC-14449 structure (4,5-bromo) and noticed that its NMR spectrum was different from that of our VPC-14449 stock synthesized by our chemical vendor. Upon synthesizing the correct structure (2,4-bromo), it was found that the NMR spectrum of the newly synthesized 2,4-bromo compound superimposed with the NMR spectrum of the compound supplied by our chemical vendor, establishing that the original compound used in this article was the 2,4-bromo version. In conclusion, our stock of VPC-14449 supplied by our chemical vendor and used in this article is (4-(4-(2,4-dibromo-1H-imidazol-1-yl)thiazol-2-yl)morpholine). This error does not affect the results or conclusions of this work, as we simply reported the incorrect structure of our compound.