2122

MMTV-neu transgenic mice express an activated form of the rat neu (erbB2) gene under the control of the MMTV promoter (Muller et al. Cell 1988:54;105) and spontaneously develop mammary gland tumors. This study examined mice bearing a tumor of ≥0.4 cm3 volume and treated with once-daily oral administration of vascular endothelial growth factor receptor (VEGFR) and/or epidermal growth factor receptor (EGFR) signaling inhibitors: AZD2171 (6 mg/kg/day; a highly potent inhibitor of VEGFR tyrosine kinases); gefitinib (100 mg/kg/day; an inhibitor of EGFR tyrosine kinase); or vandetanib (ZD6474; 100 mg/kg/day; an inhibitor of both VEGFR and EGFR tyrosine kinases). AZD2171 induced profound and durable regression of tumors and comparable tumor regression was observed following vandetanib treatment. Gefitinib inhibited tumor growth significantly compared with tumors from vehicle-treated mice. Analysis of tumor blood vessels (CD31 staining) indicated that 1-3 days of treatment with AZD2171 induced a progressive reduction in vessel density and area (56% and 81% reduction, respectively, by day 3) and similar reductions in vessel density and area were evident following 5 days of vandetanib treatment. Gefitinib treatment had no effect on vessel parameters over a 5-day period. A high proportion (86%) of CD31-positive vessels within MMTV-neu tumors were associated with cells that stained positive for α-smooth muscle actin (α-SMA), although some heterogeneity was observed in the extent of endothelial-mural cell contact. Co-staining verified that following 3 days of AZD2171 treatment the mean number of α-SMA/CD-31-positive structures was reduced by 88%. Tumors treated with AZD2171 (for 4 days), vandetanib or gefitinib (both for 5 days) were analyzed at a genomic level. Following removal of probe sets of low expression (which reduced the total number from 45,000 to 12,000), remaining probe sets from treated samples were assigned significance using a cut-off of P<0.005 versus vehicle treatment. The number of probe sets satisfying these criteria was 451 for AZD2171, 689 for vandetanib and 425 for gefitinib. The degree of overlap between AZD2171 and gefitinib significant gene lists was extremely low (2%). In contrast, 29% of the AZD2171 gene set, and 16% of the gefitinib gene set were also contained within the vandetanib gene set. Collectively these data suggest that vascular regression and progressive shrinkage of MMTV-neu tumors is mediated by inhibition of VEGF signaling. Comparative analysis of genomic changes in tumors following treatment also indicates that independent changes are induced by AZD2171 and gefitinib, which are mechanistically distinct therapies, and that each have overlap with gene changes induced by vandetanib, which has activity versus both VEGFR and EGFR signaling.

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