Object. Multiple gene replacements have been examined as a potential treatment modality for malignant gliomas. Nevertheless, no reports are available that detail the synergy, additivity, or antagonism of multiple genes. The aim of this study was to assess the interaction between p53 and p16 genes in the growth of glioma cell lines.
Methods. The human glioma cell lines U87MG and U373MG were transduced using an adenoviral vector with Ad-p53, Ad-p16, or both. Western blotting was performed to determine the expression of the protein products of the transduced p53 and p16 genes. To establish whether the combination of Ad-p53 and Ad-p16 would be beneficial, the effects of gene combinations at the median inhibitory concentration level were analyzed using the isobologram method. Annexin assays and cell cycle analyses were performed on the transduced cells. Western blotting demonstrated the expression of p53 and p16 in transduced cells. Simultaneous exposure to Ad-p53 and Ad-p16 produced additive effects in both glioma cell lines. Experimental data points in U373MG lay near the Mode I line, indicating that the vectors had a different mode of action. The restoration of normal p53-encoded protein in the mutant cell lines induced apoptosis, whereas in the wild-type p53 cell lines, the overexpression of wild-type p53 resulted in a moderate degree of apoptosis and G1 arrest. Furthermore, Ad-p16 induced more marked G1 arrest than Ad-p53 in cells with wild-type p53.
Conclusions. The results show that interaction between Ad-p53 and Ad-p16 is additive, regardless of p53 gene status.