SUPPRESSION OF HUMAN GLIOMA GROWTH BY ADENOVIRUS-MEDIATED RB GENE-TRANSFER

Objective: This study was conducted to obtain evidence that restoratio n of the retinoblastoma protein function may have therapeutic applicat ion for gliomas. Background: The development of glioblastoma multiform e involves progressive inactivation of several tumor suppressor genes. Abnormalities of the retinoblastoma tumor suppressor gene are found i n the majority of cancers, including at least 30% of malignant gliomas . No final evidence has been produced about the role of Rb in suppress ing glioma growth. Methods: To address this question, the Ad5CMV-Rb ad enovirus carrying a 3.2-kb cDNA of the Rb gene was constructed. Expres sion of the exogenous protein was assessed by immunoblot and immunohis tochemistry analyses. Growth curve assays were used to evaluate the ef fect of the Rb protein on glioma cell growth. Flow-cytometry analyses were used to analyze the phenotype of the cell cycle after the transfe r of Rb. Human glioma xenografts implanted subcutaneously in nude mice were used for the tumorigenicity assay. Results: After the transfer o f Rb, 80% of the treated cells expressed high levels of the retinoblas toma protein for at least 7 days. Within 5 days of treatment, the cell s lost the neoplastic morphology and showed marked growth suppression. The majority of the Rb-expressing cells were arrested in the G(1) pha se of the cell cycle. In addition, the restoration of the retinoblasto ma activity rendered the human glioma cells unable to form tumors in n ude mice. Conclusions: These findings provide direct evidence that ina ctivation of the retinoblastoma protein is a critical event in gliomas , and suggest that the restoration of wild-type retinoblastoma activit y in these tumors may have therapeutic utility.