A window of opportunity phase II study of enzastaurin in chemonaive patients with asymptomatic metastatic colorectal cancer.

BACKGROUND: Preclinically, protein kinase C and AKT activation can be inhibited by enzastaurin and reduce tumor growth of colorectal cancer cells. In asymptomatic patients with metastatic colorectal cancer (mCRC), enzastaurin activity was evaluated by measuring the 6-month progression-free survival (PFS) rate in a window study design. PATIENTS AND METHODS: Chemonaive patients with asymptomatic mCRC who did not require immediate chemotherapy-induced tumor reduction received a 400-mg thrice daily loading dose of enzastaurin on day 1 of cycle 1, followed by 500 mg once daily for the remaining 28-day cycles. Progression was assessed on the basis of radiographic imaging, rise in carcinoembryonic antigen or lactate dehydrogenase (LDH) levels or by appearance of clinical symptoms. RESULTS: Twenty-eight patients received daily enzastaurin. The 6-month PFS rate was 28% [95% confidence interval (CI) 13%-45%] and median PFS was 1.9 months (95% CI 1.8-4.5 months). Twelve (43%) patients had stable disease with a median duration of 6.1 months. The survival rate at 20 months was 77% (95% CI 47%-92%). No grade 4 toxicity was reported and grade 3 toxic effects were observed in three patients with one patient showing probable drug-related elevation of liver transaminases. CONCLUSION: The window design in asymptomatic patients with mCRC can be safely applied to assess the activity and safety of novel cytostatic agents like enzastaurin.

Cytochrome P450 3A inhibition by ketoconazole affects prasugrel and clopidogrel pharmacokinetics and pharmacodynamics differently.

Prasugrel and clopidogrel inhibit platelet aggregation through active metabolite formation. Prasugrel's active metabolite (R-138727) is formed primarily by cytochrome P450 (CYP) 3A and CYP2B6, with roles for CYP2C9 and CYP2C19. Clopidogrel's activation involves two sequential steps by CYP3A, CYP1A2, CYP2C9, CYP2C19, and/or CYP2B6. In a randomized crossover study, healthy subjects received a loading dose (LD) of prasugrel (60 mg) or clopidogrel (300 mg), followed by five daily maintenance doses (MDs) (15 and 75 mg, respectively) with or without the potent CYP3A inhibitor ketoconazole (400 mg/day). Subjects had a 2-week washout between periods. Ketoconazole decreased R-138727 and clopidogrel active metabolite Cmax (maximum plasma concentration) 34-61% after prasugrel and clopidogrel dosing. Ketoconazole did not affect R-138727 exposure or prasugrel's inhibition of platelet aggregation (IPA). Ketoconazole decreased clopidogrel's active metabolite AUC0-24 (area under the concentration-time curve to 24 h postdose) 22% (LD) to 29% (MD) and reduced IPA 28% (LD) to 33% (MD). We conclude that CYP3A4 and CYP3A5 inhibition by ketoconazole affects formation of clopidogrel's but not prasugrel's active metabolite. The decreased formation of clopidogrel's active metabolite is associated with reduced IPA.