Pharmacological inhibition of EGFR tyrosine kinase affects ILK-mediated cellular radiosensitization in vitro

Abstract

Purpose: Integrin-linked kinase (ILK) mediates signals from β integrins and links integrins to epidermal growth factor receptor (EGFR). Previous studies have identified an antisurvival effect of ILK in irradiated cells. The aim of this study was to evaluate the role of EGFR tyrosine kinase (tk) activity for ILK-mediated radiosensitization.Materials and methods: Human FaDu squamous cell carcinoma (SCC) cells stably transfected with hyperactive ILK (ILK-hk) and ILKfl/fl and ILK−/− mouse fibroblasts were treated with the pharmacological EGFR-tk inhibitor BIBX1382BS without or in combination with single doses of X-rays. Clonogenic radiation survival, protein expression and phosphorylation (EGFR, v-akt murine thymoma viral oncogene homolog 1 (Akt), p42/44 mitogen-activated protein kinase), DNA-double strand break (DSB) repair measured by γH2AX foci, cell morphology and cell cycle distribution were examined.Results: Expression of ILK-hk or ILKfl/fl status resulted in significant radiosensitization relative to vector controls or ILK−/−. Following BIBX1382BS, clonogenic survival of normal fibroblasts and vector controls remained unaffected while ILK-hk-related radiosensitization was significantly diminished. In contrast to BIBX1382BS, which did not affect DNA-DSB repair, ILK-hk-mediated radiosensitization was associated with reduced DNA-DSB repair. At 10 days after BIBX1382BS treatment, FaDu transfectants, in contrast to fibroblasts, showed reduced cell size, accumulation of G1 phase cells and reduced Akt-serine(S)473 phosphorylation.Conclusions: Our findings confirm ILK as a cell type-independent antisurvival factor in irradiated cells, which actions in terms of radiosensitization critically depend on proper EGFR-tk activity.