Sensitization and caffeine potentiation of cisplatin cytotoxicity resulting from introduction of wild-type p53 gene in human osteosarcoma

The present study was performed to investigate whether the introduction of a wild-type p53 gene into human osteosarcoma cells could alter the growth r ate and enhance the cytocidal effect of cisplatin (CDDP) and the synergisti c antitumor effect of caffeine. The lipofection method was used to transfec t a wild-type p53 expression plasmid into the human osteosarcoma cell line, Saos2, which has both p53 alleles deleted. The transfected cells, Saos2/p5 3, had a reduced growth rate compared with the parental cell line. The colo rimetric WST-1 assay demonstrated that Saos2/p53 cells were twice as sensit ive to CDDP alone at a 50% inhibition concentration than the parental Saos2 cells. Caffeine significantly potentiated the cytocidal effect of CDDP in the Saos2/p53 cells. Furthermore, the TUNEL assay revealed that following t reatment both with CDDP alone and with CDDP combined with caffeine, a highe r percentage of the Saos2/p53 cells underwent apoptosis than did the parent al Saos2 cells. Therefore the cytocidal effect of CDDP and the synergistic antitumor effect of caffeine are enhanced by the introduction of a wild-typ e p53 gene into a human osteosarcoma cell line null for p53. This raises th e possibility that gene therapy using the p53 gene may prove efficatious fo r human osteosarcomas lacking p53 and which are resistant to standard chemo therapy.