Combating Resistance to Anti-IGFR Antibody by Targeting the Integrin 3-Src Pathway

Several phase II/III trials of antiinsulin-like growth factor 1 receptor (IGF-1R) monoclonal antibodies (mAbs) have shown limited efficacy. The mechanisms of resistance to IGF-1R mAb-based therapies and clinically applicable strategies for overcoming drug resistance are still undefined. IGF-1R mAb cixutumumab efficacy, alone or in combination with Src inhibitors, was evaluated in 10 human head and neck squamous cell carcinoma (HNSCC) and six nonsmall cell lung cancer (NSCLC) cell lines in vitro in two- or three-dimensional culture systems and in vivo in cell line or patient-derived xenograft tumors in athymic nude mice (n 69 per group). Cixutumumab-induced changes in cell signaling and IGF-1 binding to integrin 3 were determined by Western or ligand blotting, immunoprecipitation, immunofluorescence, and cell adhesion analyses and enzyme-linked immunosorbent assay. Data were analyzed by the two-sided Student t test or one-way analysis of variance. Integrin 3Src signaling cascade was activated by IGF-1 in HNSCC and NSCLC cells, when IGF-1 binding to IGF-1R was hampered by cixutumumab, resulting in Akt activation and cixutumumab resistance. Targeting integrin 3 or Src enhanced antitumor activity of cixutumumab in multiple cixutumumab-resistant cell lines and patient-derived tumors in vitro and in vivo. Mean tumor volume of mice cotreated with cixutumumab and integrin 3 siRNA was 133.7mm(3) (95% confidence interval [CI] 57.6 to 209.8mm(3)) compared with those treated with cixutumumab (1472.5mm(3); 95% CI 1150.7 to 1794.3mm(3); P < .001) or integrin 3 siRNA (903.2mm(3); 95% CI 636.1 to 1170.3mm(3); P < .001) alone. Increased Src activation through integrin ?3 confers considerable resistance against antiIGF-1R mAb-based therapies in HNSCC and NSCLC cells. Dual targeting of the IGF-1R pathway and collateral integrin 3Src signaling module may override this resistance.