Multi-mechanistic inhibitors of androgen action for the treatment of prostate cancer

Abstract

Prostate cancer (PC) is a major cause of mortality among males in the USA. The prominent treatment strategy for advanced cases involves inhibition of the effects of androgens through orchidectomy, LHRH agonists/antagonists, anti-androgens, and inhibitors of androgen synthesis. Despite these treatments, nearly all patients will experience recurrence, in which they fail to satisfactorily respond to endocrine-based treatments. However, recent evidence increasingly implicates a continued role of the androgen receptor (AR), in all disease stages. Therefore, improved strategies for targeting the AR signaling axis are needed. On this basis, we are developing novel agents with the ability to block multiple targets within the androgen signaling pathway. The major targets are androgen biosynthesis, ligand-AR binding, and AR expression. The rationally designed compounds VN/125-1, VN/124-1, VN/85-1, VN/87-1, VN/108-1 and VNLG/82-1 were evaluated for inhibition of CYP17 (a key enzyme in androgen biosynthesis), and compared with the clinically used ketoconazole. For these studies, we utilized our cell-based radiometric acetic acid releasing assay. Among the effective compounds, IC50 values ranged from 0.5 to 112 nM. In competitive binding and transactivation studies, VN/124-1, VN/125-1, and VN/85-1 prevented binding of radiolabeled ligand to both the mutant LNCaP AR and the wild-type AR, and reduced AR mediated transactivation by 90-99% at 10 muM. In proliferation studies, VN/124-1, VN/125-1 and VN/85-1 inhibited the growth of DHT-stimulated LNCaP and LAPC4 cells with IC50 values in the low micromolar range (i.e., <10 muM). They also inhibited AR-negative PC3 cell proliferation, suggesting mechanisms additional to modulation of androgen signaling. Through western blot technique and immunofluorescence microscopy, the effects of VN/124-1 on AR expression and translocation were observed. VN/124-1 dramatically down-regulated AR expression, both in vitro and in vivo, which corresponded to its superior anti-tumor activity previously observed in our LAPC4 xenograft model. VN/124-1 also induced apoptosis in LNCaP cells as shown by annexin/FITC staining and caspase 3/7 activity assays. These finding suggest that combined inhibition of androgen biosynthesis, AR-mediated transactivation, and AR expression represents a new class of agents with exciting potential for PC treatment.