Novel regimens of capecitabine alone and combined with irinotecan and bevacizumab in colorectal cancer xenografts.

BACKGROUND Xenograft and mathematical models have shown that the antitumor activity of capecitabine can be increased by modifying the schedule from 14 days on, 7 off (14/7) to 7/7. MATERIALS AND METHODS Capecitabine at two-thirds maximum tolerated dose (MTD) administered using 14/7 (267 mg/kg) and 7/7 (467 mg/kg) schedules, alone and in doublet and triplet combinations with irinotecan (40 mg/kg intraperitoneally) and bevacizumab (5 mg/kg intraperitoneally) were studied in mice bearing HT29 colorectal xenografts. RESULTS Tumor growth inhibition was >100% in doublet and triplet regimens with capecitabine 7/7 compared with 70% and 98%, respectively, with 14/7. Increase in lifespan was significantly greater with the 7/7 triplet than the corresponding doublet without bevacizumab (288% versus 225%, respectively). CONCLUSION Addition of bevacizumab to capecitabine and irinotecan significantly improved tumor growth inhibition and lifespan in the HT29 xenograft model. Modifying the capecitabine schedule from 14/7 to 7/7 improved the efficacy of doublet and triplet combinations without toxicity.