Novel C-17-Heteroaryl Steroidal CYP17 Inhibitors/Antiandrogens:  Synthesis, in Vitro Biological Activity, Pharmacokinetics, and Antitumor Activity in the LAPC4 Human Prostate Cancer Xenograft Model

Abstract

New chemical entities, steroidal C-17 benzoazoles (5, 6, 9 and 10) and pyrazines (14 and 15) were rationally designed and synthesized. The key reaction for synthesis of the benzoazoles involved the nucleophilic vinylic "addition-elimination" substitution reaction of 3beta-acetoxy-17-chloro-16-formylandrosta-5,16-diene (2) and benzoazole nucleophiles, while that for synthesis of pyrazines involved palladium-catalyzed cross-coupling reaction of 17-iodoandrosta-5,16-dien-3beta-ol (13) with tributylstannyl diazines. Some of the compounds were shown to be potent inhibitors of human CYP17 enzyme as well as potent antagonist of both wild type and mutant androgen receptors (AR). The most potent CYP17 inhibitors were 3beta-hydroxy-17-(1H-benzimidazole-1-yl)androsta-5,16-diene (5, code named VN/124-1), 3beta-hydroxy-17-(5(1)-pyrimidyl)androsta-5,16-diene (15) and 17-(1H-benzimidazole-1-yl)androsta-4,16-dien-3-one (6), with IC(50) values of 300, 500 and 915 nM, respectively. Compounds 5, 6, 14 and 15 were effective at preventing binding of (3)H-R1881 (methyltrienolone, a stable synthetic androgen) to both the mutant LNCaP AR and the wild-type AR, but with a 2.2- to 5-fold higher binding efficiency to the latter. Compounds 5 and 6 were also shown to be potent pure AR antagonists. The cell growth studies showed that 5 and 6 inhibit the growth of DHT-stimulated LNCaP and LAPC4 prostate cancer cells with IC(50) values in the low micromolar range (i.e., <10 microM). Their inhibitory potencies were comparable to that of casodex but remarkably superior to that of flutamide. The pharmacokinetics of compounds 5 and 6 in mice were investigated. Following s.c. administration of 50 mg/kg of 5 and 6, peak plasma levels of 16.82 and 5.15 ng/mL, respectively, occurred after 30 to 60 min, both compounds were cleared rapidly from plasma (terminal half-lives of 44.17 and 39.93 min, respectively), and neither was detectable at 8 h. Remarkably, compound 5 was rapidly converted into a metabolite tentatively identified as 17-(1H-benzimidazol-1-yl)androsta-3-one. When tested in vivo, 5 proved to be very effective at inhibiting the growth of androgen-dependent LAPC4 human prostate tumor xenograft, while 6 was ineffective. Compound 5 (50 mg/kg/twice daily) resulted in a 93.8% reduction (P = 0.00065) in the mean final tumor volume compared with controls, and it was also significantly more effective than castration. To our knowledge, this is the first example of an antihormonal agent (an inhibitor of androgen synthesis (CYP17 inhibitor)/antiandrogen) that is significantly more effective than castration in suppression of androgen-dependent prostate tumor growth. In view of these impressive anticancer properties, compound 5 is a strong candidate for development for the treatment of human prostate cancer.

Synergistic effect of a novel antiandrogen, VN/124-1, and signal transduction inhibitors in prostate cancer progression to hormone independence in vitro

“…Additionally, recent clinical findings indicate the success of other androgen synthesis inhibitors in hormone-resistant prostate cancer patients using PSA response as a measurable endpoint (48). Our potent novel androgen synthesis inhibitor with antiandrogenic activity, VN/124-1, has potential as treatment in hormone-dependent prostate cancer and possibly hormone-resistant prostate cancer, providing further clinical benefit over pure antiandrogens (7).…”

“…We have described previously a novel potent CYP-17 inhibitor, VN/124-1, which is also an androgen receptor antagonist (7 -9). This lead compound is the first to show superior efficacy compared with castration in prostate cancer xenograft models (7). Here, we describe its effects in combination with inhibitors of signal transduction pathways in hormone-sensitive and hormone-refractory disease.…”

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

“…However, seviteronel was found to be as effective as enzalutamide in preventing androgen-mediated target gene expression ( Figure 1E), while galeterone and abiraterone were less effective on a subset of AR target genes (e.g., N-Myc downstream-regulated 1 [NDRG1], diazepam-binding inhibitor, acyl-CoA-binding protein [DBI], and hydroxyprostaglandin dehydrogenase [HPGD]), likely reflecting their lower binding affinity for the T877A mutation. Individual graphs for the kallikrein-related peptive inhibition of CYP17 lyase activity could negate the need for concomitant administration of glucocorticoids by sparing CYP17 hydroxylase activity (16)(17)(18).…”

Identification of Novel Steroidal Androgen Receptor Degrading Agents Inspired by Galeterone 3β-Imidazole Carbamate

“…As an androstene core alternate, estrogen was selected, where three derivatives, including C-3 hydroxy (22), C-3 methylcarboxylate (27), and C-3 carboxy (28) were designed and synthesized (Scheme 2). Synthesis of these compounds was achieved by slightly modifying our routine method for synthesis for galeterone and related compounds.…”

“…Synthesis and purity check for the compounds 6−7 and 14 was reported previously. 22 To determine whether our new compounds modulate f-AR transcriptional activation, we performed a luciferase experiment utilizing LNCaP cells dual-transfected with the probasin luciferase reporter construct AAR2-luc and the Renilla luciferase reporting vector pRL-null as we previously described 22, 27 and reported in the Supporting Information. As shown in Figure 2A, luciferase expression was significantly increased after 10 nM DHT treatment for 24 h. The ability of the novel compounds (10 μM, each) to modulate DHT-induced AR transactivation was assessed, using enzalutamide (4) and galeterone (5) as positive controls.…”