Adenovirus-mediated p16(INK4a) gene expression radiosensitizes non-small cell lung cancer cells in a p53-dependent manner

We examined the influence of adenovirus-mediated wildtype p16(INK4n) (Ad/p1 6) expression on the radiation sensitivity of NSCLC cell lines, all of whic h lacked constitutive p16(INK4n) but each of which varied in p53 status: A5 49 (- p16(INK4n)/+pRb/wt-p53), H322 (- p16(INK4n)/ + pRb/mt-p53), and H1299 (- p16(INK4a)/ +pRb/deleted-p53). The in vitro clonogenic survival results indicate that Ad/p16 enhanced the radiosensitivity of A549 but not H322 or H1299. Further analysis indicated that the apoptosis induced by combinatio n therapy using Ad/p16 plus irradiation was dependent on the endogenous p53 status of the cancer cells. We performed Western blotting to analyst the p 53 protein expression of A549 cells treated with either Ad/p16 or Ad/Luc. E ndogenous p53 protein levels were higher in A549 cells transfected with Ad/ p16 than in those transfected with Ad/Luc. Furthermore, when wt-p53 protein expression was restored in H1299 using Ad/ p53, Ad/p16 stabilized p53 prot ein expression and radiosensitized the cells. These results suggest that Ad / p16-induccd stabilization of p53 protein may play an important role in Ad /p16 mediated radiosensitization by enhancing or restoring apoptosis proper ties. Thus, Ad/p16 plus radiation in combination may be a useful gene thera py strategy for tumors that have wt-p53 but nonfunctional p16(INK4n).