Furthermore, in an exploratory toxicology assessment in mice, no toxicity was observed in animals treated systemically with EPI: no loss of body weight, no changes in behavior, and no pathologic changes in the histology of internal organs [91, 93]. shortcomings of current hormonal therapies by inhibiting all forms of GIII-SPLA2 AR-mediated transcriptional activity, and as a result, may affect a broader AR population including mutational and splice variant ARs. Indeed, the first clinical trial of an AR NTD inhibitor is now underway. Implications for Practice: Because of emerging resistance mechanisms Ureidopropionic acid that involve the ligand-binding domain of the androgen receptor (AR), there is currently no effective treatment addressing tumor escape mechanisms related to current AR-targeted therapies. Many patients still demonstrate limited clinical response to current hormonal agents, and castration-resistant prostate cancer remains a lethal disease. Intense research efforts are under way Ureidopropionic acid to develop therapies to target resistance mechanisms, including those directed at other parts of the AR molecule. A novel small-molecule agent, EPI-506, represents a new pharmaceutical class, AR N-terminal domain inhibitors, and shows preclinical promise to overcome many known resistance mechanisms related to novel hormonal therapies. sp., were identified through a screening of marine natural extracts and show inhibition of AR activity as measured by reporter gene-based assays . In addition, sintokamides effectively blocked proliferation of LNCaP prostate cancer cells but not PC3 prostate cancer cells, which do not express AR, indicating that the inhibitory effect of sintokamides on cell proliferation was likely caused by its effect on the AR and not via cell cytotoxicity. Further characterization of sintokamides will be useful in assessing these agents as a potential AR-targeted therapy. Agents directed at preventing the AR NTD from properly initiating transcription Ureidopropionic acid are also currently being explored. At least four compounds (GSK525762, GS-5829, OTX015, and JQ1) are in development for CRPC that target bromodomain-containing protein 4 (BRD4), a member of the bromodomain extraterminal (BET) family of proteins. BRD4 is a coregulator of the AR and interacts with the AR NTD to facilitate transcriptional activity . BRD4 inhibitors have been shown to block BRD4-AR interactions and prevent binding of both full-length and splice variant AR to chromatin, thereby impairing transcription of downstream genes [87, 88]. BRD4 inhibition also induced apoptosis and cell-cycle arrest in AR-driven prostate cancer cell lines (VCaP, LNCaP, and 22Rv1), but not in cell lines that are negative for AR signaling (PC3, DU145) . In vivo, BRD4 blockade was Ureidopropionic acid shown to significantly reduce tumor volume and weight in VCaP xenograft mice compared with enzalutamide. In addition, BRD4 inhibitors can suppress the transcription of . The transcriptome of AR splice variants may have some overlap with that of full-length AR, but splice variants also regulate expression of a distinct set of genes . AR splice variants, such as AR-V7, preferentially increase the manifestation levels of genes such as . Consistent with upstream blockade of both full-length and splice variant AR transcriptional activities, EPI treatment inhibits gene manifestation that is controlled by both full-length and AR-V7 in LNCaP95 and VCaP cells, whereas enzalutamide and bicalutamide experienced no effect, respectively [93, 94]. Notably, both LNCaP95 cells and VCaP cells endogenously communicate the full-length AR and AR-V7 protein . An adaptive shift to AR-V7 signaling is definitely suggested to occur in androgen-depleted environments and with antiandrogen treatment . Therefore, LNCaP95 and VCaP cells represent an important population of combined full-length and splice variant ARs that may be reflective of human being CRPC. Consistent with focusing on the AR NTD without reliance within the LBD for AR inhibition, EPI did not compete with androgen inside a competitive ligand-binding assay . Increasing concentrations of unlabeled synthetic androgen, bicalutamide, and EPI were used to compete with fluorescent-labeled androgen for binding to the AR LBD. Increasing concentrations of both synthetic androgen and bicalutamide displaced the fluorescent-labeled androgen and competed for the ligand-binding pocket. By contrast, EPI did not affect binding of the fluorescent-labeled androgen, no matter androgen concentration . In another study, elevated androgen levels were shown to compete for, and reverse, the inhibitory effect of enzalutamide . Therefore, the reversible binding of antiandrogens to the AR may indicate the reason behind their possible failure when intratumoral androgen becomes elevated in CRPC. In contrast, EPI neither focuses on the AR LBD nor will it compete for binding to the LBD. Therefore, EPI compounds possess a unique mechanism of action and don’t depend on the presence of the LBD. The potential therapeutic benefits of EPI have been demonstrated using a variety of human being prostate malignancy cell lines and xenograft models in castrated male mice. The EPI compounds have been shown to block AR-dependent proliferation of human being prostate malignancy cells, but have no effect on the viability of cells that.