Efficacy of the combined use of bevacizumab and irinotecan as a postoperative adjuvant chemotherapy in colon carcinoma

We evaluated the efficacy of anti-human VEGF antibody (bevacizumab) with or without irinotecan (CPT-11) against lung metastases in which neovascularization was already induced, as a postoperative adjuvant therapy using orthotopically implanted colon cancer in rat. The high VEGF productive KM12SM human colon cancer cells were injected into the cecal wall. At 5 weeks after the injection, the cecum was removed including the tumor. Then, 5 mg/kg of bevacizumab and 40 mg/kg of CPT-11 were administered, alone or in combination, intravenously once a week for 3 weeks, from day 15 after the cecal removal. The results show that the incidences of macroscopic and/or microscopic lung metastases in the bevacizumab-alone group (B) and in the combination group (C) were significantly lower (B, p=0.001 and C, p=0.037) than that in the control group at day 35 after the cecal removal. The number of lung metastases in B was 0.8±0.8 (p=0.024) and in C 2.4±1.8 (p=0.060), each value lower than the 12.4±4.2 of the control group. The growth of a subcutaneously implanted tumor was significantly inhibited in the combination group compared to either the CPT-alone (p=0.003) or the bevacizumab-alone groups (p=0.027). Apoptosis was significantly (p<0.001) induced in the combination group. In conclusion, a beneficial effect of bevacizumab against postoperative lung metastases may be expected even after the establishment of neovascularization in metastatic foci in nude rat. The results from the present subcutaneously implanted tumor model suggested that a higher efficacy may be expected when bevacizumab is combined with the cytotoxic agent CPT-11, compared to bevacizumab alone, against tumors with a variety of VEGF production levels in clinical situations.