Adenovirus-mediated gene transduction of truncated IκBα enhances radiosensitivity in human colon cancer cells

Nuclear factor kappa B (NF-kappaB) is a transcription factor that is known to regulate apoptosis when cells are exposed to DNA-damaging agents such as ionizing radiation and cytotoxic drugs. We sought to determine if inhibition of NF-kappaB could enhance radiosensitivity in human colon cancer cells in vitro and in vivo. To inhibit NF-kappaB activation specifically, we constructed a recombinant adenovirus vector expressing a truncated form of the inhibitor protein IkappaBalpha (IkappaBalphaDeltaN) that lacks the phosphorylation sites essential for activation of NF-kappaB, and transfected two human colon cancer cell lines (HT29 and HCT15) with this vector. In vitro colony-forming assays revealed that the overexpression of the stable IkappaBalpha by AxIkappaBalphaDeltaN infection significantly suppressed cell growth after irradiation in both cell lines as compared to infection with a control vector, AxLacZ. Treatment with AxIkappaBalphaDeltaN and irradiation successfully inhibited the growth of HT29 xenografted subcutaneous tumors in nude mice with an 83.8% volume reduction on day 38 as compared to the untreated tumors. Furthermore, it was demonstrated that apoptosis was increased by adenovirus-mediated gene transduction of IkappaBalphaDeltaN in vitro and in vivo. These results indicated that inhibition of NF-kappaB could enhance radiosensitivity through an increase in radiation-induced apoptosis. We believe that radio-gene therapy using adenovirus-mediated gene transduction of IkappaBalphaDeltaN could be an attractive candidate as a treatment strategy for colorectal cancer.