Regulation of p53 expression to overcome cisplatin rsistance

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The p53 tumor suppressor gene product is an important participant in the cellular response to DNA damage. This response results in either Gl cell cycle arrest or cell death by apoptosis. Therefore, the status of p53 can be expected. to affect the cellular response to DNA-damaging cytotoxic agents. The present study was performed to investigate whether introduction of the wild-type p53 gene into human osteosarcoma cells could change growth rates and enhance the cytocidal effect of cisplatin and the synergistic antitumor effect of caffeine. Three human osteosarcoma cell lines, OST (wild p53 alleles) , Saos2 (both p53 alleles deleted) , and HOS, (both mutant p53 alleles) were used. Wild-type p53 expression plasmid was transfected into each of the osteosarcoma cell lines by using the lipofection method. The transfected cells, Saos2/p53 and HOS/p53, showed a reduction in growth rate compared with the parent cells. WST-1 assay, performed to assess the cytocidal effect of cisplatin and the sy … More nergistic antitumor effect of caffeine, showed that Saos2/p53 cells were twice as sensitive to cisplatin alone in 1C50 than were Saos2 cells. The synergistic antitumor effect of caffeine also enhanced in the Saos2/p53 cell line. The other two transfected cells revealed no significant differences from their respective parent cells. Furthermore, TUNEL assay used to analyze apoptotic events in Saos2 cells and Saos2/p53 cells that were treated either with cisplatin alone or with cisplatin and caffeine revealed that compared with the parent Saos2 cell line, Saos2/p53 become most sensitive to cisplatin alone and to cisplatin with caffeine. OST/p53 and HOS/p53 cell lines did not show any significant increase in sensitivity to either cisplatin alone or to cisplatin with caffeine. These results demonstrate that the cytocidal effect of cisplatin and the synergistic antitumor effects of caffeine are enhanced by introduction of the wild-type p53 gene in a human osteosarcoma cell line with deleted p53 alleles, indicating the possibility of gene therapy using the p53 gene for human osteosarcomas with abnormal p53 status. Less