Radiosensitization of human tumor cell lines induced by the adenovirus-mediated expression of an anti-Ras single-chain antibody fragment

The expression of activated ras genes has been implicated as a contributing factor to the radioresistance of tumor cells. As a strategy for compromisi ng Ras protein activity and potentially enhancing the radiosensitivity of t umor cells, we have investigated the application of the AV1Y28 adenovirus, which expresses a single-chain antibody fragment directed against p21 Ras p roteins. The ability of AV1Y28 transduction to modulate radioresponse was i nvestigated using four human tumor cell lines-U251 glioblastoma, MIA PaCa-2 pancreatic carcinoma, and the colon carcinomas SW620 and HT29, Cultures we re exposed to sufficient levels of AV1Y28 to transduce more than 90% of the cells; 24 h later, cultures were exposed to ionizing radiation, and clonog enic cell survival was determined. Tumor cell survival was reduced by 40-50 % when the tumor cell lines were exposed to AV1Y28 only. In addition, for e ach tumor cell line, AV1Y28 exposure enhanced the level of radiation-induce d cell killing. Dose enhancement factors at a surviving fraction of 0.1 ran ged from 1.3 to 1.5. Furthermore, for each of the cell lines, the surviving fraction at 2 Gy was significantly reduced by AV1Y28 exposure. In contrast to the results seen in tumor cells, the radiosensitivity of a normal human fibroblast cell line was not affected by AV1Y28. These data indicate that this anti-Ras adenovirus enhances the radiosensitivity of tumor cells but d oes not affect the radiosensitivity of normal cells.