Synergistic cytotoxic effects of recombinant human adenovirus p53 and radiation at various time points in A549 lung adenocarcinoma cells.

The aim of this study was to evaluate the effects of recombinant human adenovirus p53 (rAd-p53; Gendicine) transfection and radiation at various time points following transfection. Cytotoxic effects and p53 protein expression levels were analyzed. rAd-p53 containing the human wild-type p53 gene was introduced into the human lung adenocarcinoma cell line A549, and cells were irradiated with a single dose of 6 MeV 4 Gy β rays. According to the time interval between rAd-p53 transfection and radiotherapy (RT), A549-transfected rAd-p53 cells were divided into 5 groups: radiation administered immediately after transfection (0 h-RT) group, after 3 h group (3 h-RT), after 6 h group (6 h-RT), after 24 h group (24 h-RT) and after 48 h group (48 h-RT). Cells with rAd-p53 transfection alone (Ad-p53) and with empty adenovirus (Ad) were included as the two control groups. Following 72 h of transfection, cell viability and growth were analyzed using MTT assays and flow cytometry, and p53 protein expression was analyzed using western blot analysis. From 0 h-RT to 48 h-RT, cell viability gradually decreased, while percentage of apoptotic cells and p53 protein expression gradually increased. The cell viability suppression rates in the 6 h-RT, 24 h-RT and 48 h-RT groups were 56.7±5.4, 60.8±6.0 and 68.9±6.6, respectively, which were significantly greater compared to that of the Ad-p53 (40.8±4.7), 0 h-RT (45.0±3.5) and 3 h-RT groups (47.0±4.3). No statistically significant differences were observed in the cell viability suppression rates among the 6 h-RT, 24 h-RT and 48 h-RT groups (P>0.05). Similar changes were observed in the percentage of apoptotic cells. The p53 protein expression level in the 6 h-RT group (0.856±0.092) was higher compared to that in the 3 h-RT group (0.643±0.089) (t=2.882; P=0.045), but not significantly different from that of the 24 h-RT group (1.193±0.202). The cell viability suppression rate and percentage of apoptotic cells was positively correlated with p53 protein expression in the A549 cells (P<0.05). Radiation may inhibit or damage p53 protein expression at the early stage of rAd-p53 transfection. To sensitize tumor cells to irradiation and achieve maximal cytotoxic effects, it is recommended to conduct RT at least 6 h following transfection with rAd-p53.