Growth inhibitory effect on glioma cells of adenovirus-mediated p16/INK4a gene transfer in vitro and in vivo

The tumour suppressor gene p16/INK4a encodes a specific inhibitor of the cy clin D-dependent kinases CDK4 and CDK6. p16/INK4a prevents the association of CDK4 with cyclin D1, and subsequently inhibits phosphorylation of retino blastoma tumour suppressor protein (pRb), thus preventing exit from the G1 phase. In human cancers, the estimated frequency of genetic alteration invo lving the p16/INK4a locus is believed to be second only to alteration of p5 3. A high frequency (greater than 50%) of homozygous p16/INK4a gene deletio n has been demonstrated in glioblastoma tissues and p16/INK4a is altered in 80% of glioma cell lines. Therefore, restoration of p16/INK4a would suppre ss cell proliferation and induce cell growth arrest. We showed here that re storation of p16/INK4a expression in p16 negative U87MG, U251MG and partial ly deleted U373MG by Ad-CMV-p16/INK4a induced growth suppression in vitro a nd in vivo. Expression of p16 transferred by Ad-CMVp16/INK4a in glioma cell s was highly efficient and maintained for more than seven days. In addition , we found that the endogenous status of p16 and Rb might affect the expres sion of exogenous p16/INK4a gene and inhibitory effect of cell proliferatio n. Even though, there were several factors affecting the efficiency of Ad-C MV-p16/INK4 gene transfer, our results suggest that Ad-CMV-p16 gene therapy strategy is potentially useful and warrants further clinical investigation for the treatment of gliomas.