Activity of oral VT-464, a selective CYP17-lyase inhibitor, in the LNCaP prostate cancer xenograft.

4671 Background: With the FDA approval of abiraterone acetate, inhibition of CYP17 (17α hydroxylase/C17, 20-lyase) is now a validated approach to the treatment of castration-resistant prostate cancer. VT-464 is a novel, selective CYP17-lyase inhibitor with decreased activity against CYP17 hydroxylase (less mineralcocorticoid and glucocorticoid effects). The study objectives were to observe the effects of VT-464 in a prostate cancer xenograft model and to compare its activity to abiraterone acetate and surgical castration. Methods: SCID mice were implanted subcutaneously with LNCaP cells. When tumors reached 100 mm3, mice were randomized to receive vehicle (0.5% CMC in saline, 5 mL/kg), VT-464 at 15, 50, or 100 mg/kg p.o. b.i.d. A second cohort of LNCaP tumor-bearing mice received vehicle, surgical castration, or VT-464, or abiraterone acetate at 100 mg/kg p.o. b.i.d. for 28 days. Terminal blood and tumor concentrations were analyzed on day 28, four hours after the last dose. Results: In the first LNCaP xenograft cohort, percent growth inhibition (± S.E.) of 9.6 (±15.6), 38.5 (±12.4), and 73.9 (±13.2) was observed on day 21 of treatment for VT-464 doses of 15, 50, and 100 mg/kg, respectively. Growth reduction at 100 mg/kg was statistically significant compared to vehicle control from day 7 to 28. VT-464 was well tolerated with insignificant weight loss at all doses. In the second cohort, VT-464-treated (100 mg/kg) mice had significantly reduced tumor volumes on day 28 compared to control and abiraterone acetate (p<0.05, p<0.01, respectively). Reduction in tumor volumes were similar between VT-464-treated (100 mg/kg) and castrate animals. Plasma and tumor analyses revealed much greater plasma and tumor exposure of VT-464 compared to abiraterone acetate. Conclusions: VT-464 exhibited dose-dependent growth inhibition with significantly reduced tumor volumes at the highest dose compared to abiraterone acetate. The activity in VT-464-treated animals was similar to that of castrate animals. These preclinical results show promising activity of VT-464 in the treatment of prostate cancer.