Studies on the combination therapy of radiation and p53 gene transfer

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DNA damage can cause cell cycle arrest or apoptosis, and both responses contribute to tumor suppression by p53. In response to DNA damage, cells with wild-type p53 genes exhibit a rapid increase in p53 protein levels. We studied the relation between individual cellular p53 level and apoptosis, and also tried to detect the induction of apoptosis on X-irradiated cells with mutant p53 in purpose to cancer therapy.Human leukemic MOLT-4 cells undergo apoptosis after X-irradiation through p53-dependent pathway. In MOLT-4 cells, p53 (wild type) is stabilized and increased after X-irradiation. We have studied to measure p53 accumulation by flow cytometry. Irradiated cells were fixed and permeabilized, stained, and analyzed on FACSClibur (Becton Dickinson). MOLT-4 cells exposed to 0.05-9.1 Gy were anlayzed for p53 at 1-6 h after the irradiation by flow cytometory. The p53 protein level was increasing by 4-5 h after the irradiation, and then decrease gradually. In the case of cells exposed to D10 or lower than, cellular p53 protein level showed that in unirradiated control cells after 24 h of postirradiation. In the other hand, cells exposed to high dose rapidly underwent apoptosis, and the cellular p53 reached the low level than control cells after 24h of postirradiation. These results show that there is the significant correlation among radiosensitivity (by colony formation), apoptosis and the amount of individual cellular p53.We also evaluated the effect of wild p53 transfer to mutant p53 expressing cells. When survival was determined by the dye-exclusion test at 24 h after irradiation, the percentage of X-ray-induced dead cells was increased.