IGF-1R inhibition enhances radiosensitivity and delays double-strand break repair by both non-homologous end-joining and homologous recombination

Abstract

Inhibition of type 1 insulin-like growth factor receptor (IGF-1R) enhances tumor cell sensitivity to ionizing radiation. It is not clear how this effect is mediated, nor whether this approach can be applied effectively in the clinic. We previously showed that IGF-1R depletion delays repair of radiation-induced DNA double-strand breaks (DSBs), unlikely to be explained entirely by reduction in homologous recombination (HR) repair. The current study tested the hypothesis that IGF-1R inhibition induces a repair defect that involves non-homologous end-joining (NHEJ). IGF-1R inhibitor AZ12253801 blocked cell survival and radiosensitized IGF-1R over-expressing murine fibroblasts but not isogenic IGF-1R null cells, supporting specificity for IGF-1R. IGF-1R inhibition enhanced radiosensitivity in DU145, PC3 and 22Rv1 prostate cancer cells, comparable to effects of ATM inhibition. AZ12253801-treated DU145 cells showed delayed resolution of γH2AX foci, apparent within 1hr of irradiation and persisting for 24hr. In contrast, IGF-1R inhibition did not influence radiosensitivity or γH2AX focus resolution in LNCaP-LN3 cells, suggesting that radiosensitization tracks with the ability of IGF-1R to influence DSB repair. To differentiate effects on repair from growth and cell survival responses, we tested AZ12253801 in DU145 cells at sub-SF50 concentrations that had no early (≤48hr) effects on cell cycle distribution or apoptosis induction. Irradiated cultures contained abnormal mitoses, and after 5 days IGF-1R inhibited cells showed enhanced radiation-induced polyploidy and nuclear fragmentation, consistent with the consequences of entry into mitosis with incompletely repaired DNA. AZ12253801 radiosensitized DNA-PK proficient but not DNA-PK deficient glioblastoma cells, and did not radiosensitize DNA-PK-inhibited DU145 cells, suggesting that in the context of DSB repair, IGF-1R functions in the same pathway as DNA-PK. Finally, IGF-1R inhibition attenuated repair by both NHEJ and HR in HEK293 reporter assays. These data indicate that IGF-1R influences DSB repair by both major DSB repair pathways, findings that may inform clinical application of this approach.

Activation of insulin-like growth factor receptor signaling mediates resistance to histone deacetylase inhibitors

“…DNA damage and enhanced DNA repair [41]. Inhibition of IGF-1R resulted in the delayed repair of radiation-induced DNA doublestrand breaks, potentiating the antiproliferative effect of radiation therapy [42,43]. IGF-1R signaling was also involved in resistance to conventional chemotherapy [44,45].…”

Dsh Homolog DVL3 Mediates Resistance to IGFIR Inhibition by Regulating IGF-RAS Signaling

“…S1B). Primary screens were performed to deplete approximately 1,000 targets; given our interest in the involvement of IGFIR kinase in the DNA damage response (12,18), we selected siRNA libraries targeting kinase-related and DNA repair-associated proteins, with positive (siPLK1) and negative (Allstars) control siRNAs, as described (13,14). Forty-eight hours after siRNA transfection to allow target depletion, cells were treated with solvent or AZ12253801 at the GI 50 , and viability was assayed 5 days later.…”

“…Western blotting, immunoprecipitation, and pulldown assays were performed using reagents described in ref. 12, Supplementary Methods, and Supplementary Table S1.…”

Trabectedin Efficacy in Ewing Sarcoma Is Greatly Increased by Combination with Anti-IGF Signaling Agents

“…cycle regulators (53). The importance of trabectedin and IGF system inhibitors in DNA-damage response and repair pathways, which have implications on the therapeutic efficacy and potential toxicity of this combined therapy in the clinic, deserve further research to better elucidate the molecular mechanisms and protein interactions.…”