Inhibition of insulin-like growth factor 1 receptor by CP-751,871 radiosensitizes non-small cell lung cancer cells

Purpose: Therapeutic strategies that target the insulin-like growth factor I receptor (IGF-1R) hold promise for a wide variety of cancers. We have now investigated the effect of CP-751,871, a fully human monoclonal antibody specific for IGF-IR, on the sensitivity of human non-small cell lung cancer (NSCLC) cell lines to radiation. Experimental Design: The radiosensitizing effect of CP-751,871 was evaluated on the basis of cell death, clonogenic survival, and progression of tumor xenografts. Radiationinduced damage was evaluated by immunofluorescence analysis of the histone γ-H2AX and Rad51. Results: A clonogenic survival assay revealed that CP-751,871 increased the sensitivity of NSCLC cells to radiation in vitro. CP-751,871 inhibited radiation-induced IGF-IR signaling, and potentiated the radiation-induced increases both in the number of apoptotic cells and in the activity of caspase-3. Immunofluorescence analysis of the histone γ-H2AX and Rad51 also showed that CP-751,871 inhibited the repair of radiationinduced DNA double-strand breaks. Finally, combination therapy with CP-751,871 and radiation delayed the growth of NSCLC tumor xenografts in nude mice to a greater extent than did either treatment modality alone. Conclusions: These results show that CP-751,871 sensitizes NSCLC cells to radiation both in vitro and in vivo, and that this effect of CP-751,871 is likely attributable to the inhibition of DNA repair and enhancement of apoptosis that result from attenuation of IGF-IR signaling. Combined treatment with CP-751,871 and radiation thus warrants further investigation in clinical trials as a potential anticancer strategy.