Axitinib Improves Radiotherapy in Murine Xenograft Lung Tumors

A third of patients with non-small cell lung cancer (NSCLC) present with un-resectable stage III locally advanced disease and are currently treated by chemo-radiotherapy but the median survival is only about 21 months. Using an orthotopic xenograft model of lung carcinoma, we have investigated the combination of radiotherapy with the anti-angiogenic drug axitinib (AG-013736, Pfizer), which is a small molecule receptor tyrosine kinase inhibitor that selectively targets the signal transduction induced by VEGF binding to VEGFR receptors. We have tested the combination of axitinib with radiotherapy in nude mice bearing human NSCLC A549 lung tumors. The therapy effect was quantitatively evaluated in lung tumor nodules. The modulation of radiation-induced pneumonitis, vascular damage and fibrosis by axitinib was assessed in lung tissue. Lung irradiation combined with long-term axitinib treatment was safe resulting in minimal weight loss and no vascular injury in heart, liver and kidney tissues. A significant decrease in the size of lung tumor nodules was observed with either axitinib or radiation, associated with a decrease in Ki-67 staining and a heavy infiltration of inflammatory cells in tumor nodules. The lungs of mice treated with radiation and axitinib showed a complete response with no detectable residual tumor nodules. A decrease in pneumonitis, vascular damage and fibrosis were observed in lung tissues from mice treated with radiation and axitinib. Our studies suggest that axitinib is a potent and safe drug to use in conjunction with radiotherapy for lung cancer that could also act as a radioprotector for lung tissue by reducing pneumonitis and fibrosis.