Most anti-angiogenic agents target vascular endothelial growth factor-A (VEGF) or the VEGF receptor-2 (VEGFR-2). To investigate the effects of combining these two approaches, we evaluated the in vivo anti-tumor efficacy of bevacizumab, a highly specific monoclonal antibody directed against VEGF, and AZD2171, an oral, highly potent and selective VEGF signaling inhibitor of all VEGFR tyrosine kinases (VEGFR-1, -2 and -3). Investigations were performed using a VEGF-secreting human head and neck tumor cell line, CAL33, injected in the flank of 6-week-old female nude mice. When mean tumor volume reached 250 mm3, mice received bevacizumab (5 mg/kg/day i.p.), AZD2171 (2.5 mg/kg/day p.o.) or the combined regimen for 12 days. The drug interaction on tumor growth was analyzed using the combination ratio (CR): CR=FTvAZD2171x FTvbevacizumab/FTvAZD2171+bevacizumab, where FTv is the fractional tumor volume. Both AZD2171 and bevacizumab strongly inhibited tumor growth and the combination of both drugs produced an additive effect (CR=0.8±0.09). Tumor growth was measured in animals (n=5/treatment group) that were not sacrificed at the end of treatment period. The effects were longer lasting post treatment with bevacizumab with or without AZD2171 compared with AZD2171 alone. The results on tumor growth were paralleled by immunohistochemical data with an increase in tumor necrosis and the number of necrotic tumor vessels, and an inhibition of tumor cell proliferation (Ki67). Time-dependent changes in these parameters were influenced more rapidly and strongly by AZD2171 than bevacizumab, with the combination producing greater than additive effects. As AZD2171 showed direct anti-proliferative effects on tumor cells at concentrations that were 20,000 fold higher than that required for comparable inhibition of VEGF-stimulated HUVEC proliferation(IC50=8 µM on CAL33 in vitro), such a direct effect on tumor cell could not explain the observed in vivo effect. In summary, the combination of bevacizumab and AZD2171 showed additive and greater than additive effects on tumor growth inhibition and tumor/vessel necrosis, respectively. These preclinical data suggest that combining these two anti-angiogenic agents may be of interest in the clinical setting.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA