2473: VEGFR-2 Tyrosine Kinase Inhibitor AZD2171 and Radiotherapy in Mouse Models of Lung Cancer

Abstract

The VEGF receptor tyrosine kinases are being explored as targets for anti-angiogenic cancer therapy. Radiotherapy also inhibits tumor growth and affects vasculature. We investigated the combination of the potent VEGFR-2 tyrosine kinase inhibitor AZD2171 and ionizing radiation in cell culture and mouse models of lung cancer, as the combination of this promising agent with radiation remains unexplored. Radiation sensitivity of human umbilical vein endothelial cells (HUVEC) and H460 human lung cancer cells was determined by clonogenic assay. The ability of treated HUVEC cells to form vascular tubules was examined by Matrigel assay. H460 cells were used for a xenograft model in nude mice. Tumors were grown for 6 to 8 days until average tumor volume reached 0.14 cm3. Mice in the treatment group were treated with AZD2171 (0.75 mg/kg/day) for 7 days, and the tumors were irradiated with 2 Gy/day for days 3–7 of drug treatment. In order to determine vascular density, tumors were resected and paraffin fixed, and an antibody for von Willebrand factor (vWF) was used to stain for blood vessels. To determine whether AZD2171 enhances radiation-induced tumor volume regression, the tumor volume was measured at various time points in similarly treated nude mice. Both HUVEC and H460 cells became more sensitive to radiation after treatment with AZD2171 as shown by clonogenic assay. Matrigel assay showed an additive decrease in in vitro tubule formation with combination treatment with 20 nM AZD2171 and 3 Gy irradiation. No treatment control had 28 (SD=0.9) tubules per microscopic field, radiation alone had 21 (SD=1.0) tubules, AZD2171 alone had 20 (SD=0.9) tubules, and AZD2171/radiation combination had 12 (SD=0.9) tubules. vWF staining of xenograph tumors showed a large decrease in tumor vascular density after combination treatment. The control group had 15 (SD=0.6) vessels per microscopic field, radiation alone had 11.3 (SD=0.9) vessels, drug alone had 6 (SD=0.6), and combination had 2.3 (SD=0.9). H460 tumor growth delay was also greatly enhanced in the combination treatment group versus treatment with drug or radiation alone. For a 5-fold increase in tumor volume, the delay was 1 day with AZD2171 alone, 4 days with radiation alone, and 7 days with AZD2171/radiation combination. For a 10-fold increase in volume, the growth delay was 1 day for AZD2171 alone, 7 days with radiation alone, and 11 days for combination treatment. AZD2171 sensitizes lung tumor xenografts to radiation and inhibits angiogenesis in both in vitro and in vivo models. When used as a radiation enhancer, AZD2171 has the potential to improve tumor growth delay. Further in vivo studies and clinical trials are needed to determine the potential of AZD2171 as a radiation enhancer.