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.