Radiosensitization of rat glioma with bromodeoxycytidine and adenovirus expressing herpes simplex virus-thymidine kinase delivered by slow, rate-controlled positive pressure infusion

Infection of rat RT2 glioma cells in vitro with an adenovirus (ADV-TK) expr essing herpes simplex virus (HSV) thymidine kinase (TK) and subsequent expo sure to 5-bromo-2 '-deoxycytidine (BrdC), which is specifically incorporate d into ADV-TK-infected cell DNA as 5-bromo-2'-deoxyuridine (BrdU), results in significant radiosensitization (sensitizer enhancement ratio: 1.4-2.3) c ompared with Ad beta gal-infected cells. Cell killing correlated well with increased BrdU DNA incorporation and with apoptosis. Whereas radiation (4 G y) alone was relatively ineffective in inducing apoptosis, treatment with H SV-TK/BrdC resulted in BrdC dose- (10-100 mu M) and time-dependent (24-48 h ours) increases, and the combination of the two treatments produced a syner gistic response (1.5- to 2-fold). To investigate the effects of the ADV-TK/ BrdC treatment in vivo, RT2 cells were grown as soft tissue tumors in Fisch er 344 rats and conditions for virus infusion were optimized by altering th e volume and rate of infusion using a rate-controlled positive pressure dev ice. We found that relatively large volumes (100-150 mu L) of virus deliver ed at rates of less than or equal to 1 mu L/minute were optimal and gave un iform and reproducible results. Using these optimal infusion conditions, we were able to achieve 90% adenovirus infection in the tumor. Infection of R T2 tumors with ADV-TK and continuous administration of BrdC from an osmotic pump resulted in significant (.001 < P < .009) tumor regression 6 days aft er radiation (30 Gy delivered as 2 x 5 Gy over 3 days) compared with contro ls. In situ staining of sectioned tumors with anti-BrdU antibody or by high -performance liquid chromatography analysis of extracted and hydrolyzed tum or DNA confirmed that we obtained efficient and specific incorporation of B rdU into tumor cells. These results suggest that adenovirus-mediated delive ry of HSV-TK in combination with BrdC and radiation can potentially be an e fficient combination modality for the treatment of gliomas.