Background: Interstitial flow in and around tumour tissue not only has particular importance in delivering anticancer agents to tumour tissue, but also affects the microenvironment to modulate tumour cell growth and metastasis. We investigated the roles of flow-induced shear stress in modulating radiosensitivity in two colon cancer cell lines and the underlying mechanisms. Materials and Methods: T84 and SW480 colon cancer cells were trypsinized and seeded onto glass slides (75?38 mm) pre-coated with fibronectin (10 mg/ml). A parallel-plate flow chamber system was used to impose fluid shear stress. Irradiation was delivered using 160kV RS 2000 X-ray irradiator (Rad Source Technologies, Inc.). Cell proliferation, apoptosis and colony assay were measured after various combinations between shear stress and radiation. Cell cycle analysis and immunoblots of integrin b1/FAK/Akt signal molecules were evaluated. The combination effect of shear stress was reversed by neutralizing integrin b1 or using FAK overexpressed cell lines. Results: In both cell lines, incubation under shear stress (12 dynes/cm2) for 24 hours enhanced radiation induced cytotoxicity. Protein expression of integrin b1 was moderately while FAK was significantly suppressed. FAK down-regulation was mainly due to ubiquitin-dependent proteasomal pathway but not transcriptional suppression. The amount of ILK, GSK3b was not affected. Using FAK overexpressed cell lines, we demonstrated that shear stress enhanced colon cancer cell radiosensitivity by regulating FAK expression. On the other hand, incubation under shear stress for 3 hours did not revealed radiosensitizing effect in both cell lines. Using integrin b1 neutralizing antibody, we suppressed FAK/Akt activation by 3-hr shear stress and enhanced radiation related cytotoxicity in both colon cancer cell lines. Conclusions: Shear stress of 24 hours provides radio-sensitization to colon cancer cell through proteosomal degradation of FAK via integrin b1. Our findings provide insights into the mechanism by which shear stress modulates colon cancer cell cytotoxicity in response to radiation. The results impact rationale combination between radiation and strategy in modulating tumour interstitial fluid pressure.
