APOPTOSIS INDUCTION MEDIATED BY WILD-TYPE P53 ADENOVIRAL GENE-TRANSFER IN SQUAMOUS-CELL CARCINOMA OF THE HEAD AND NECK

Cancer gene therapy strategies for inducing apoptosis in solid tumors may allow contemporary medicine to reassess its management of these ca ncers. We demonstrated previously that overexpression of the wild-type p53 gene in squamous cell carcinoma of the head and neck cell lines v ia adenovirus-mediated gene transfer suppressed growth both in vitro a nd in vivo. Here, we characterize the mechanism of the growth suppress ion by the exogenous p53 gene as a consequence of programmed cell deat h (apoptosis). One of the cell lines used in this study, Tu-138, harbo rs a mutated p53 gene, whereas the other cell line, MDA 686LN, possess es a wild-type p53 gene. DNA fragmentation was detected by electrophor esis in both cell lines after infection with the wild-type p53 adenovi rus, Ad5CMV-p53, With the use of the terminal deoxynucleotidyl transfe rase-mediated dUTP-biotin nick end-labeling method, 4.4% of the remain ing viable Tu-138 cell population was identified as apoptotic as early as 15 h after inoculation with Ad5CMV-p53, The percentage of apoptoti c cells increased to 31% at 22 h, In contrast, only 10% of the viable MDA 686LN cells (wt-p53) had undergone apoptosis 30 h after Ad5CMV-p53 infection, although the percentage of apoptotic cells rapidly increas ed to 60% at 48 h after infection, For in vivo analysis of apoptosis, nude mice in which squamous cell carcinoma of the head and neck cell l ines had been implanted s.c. had exogenous wt-p53 transiently introduc ed to the tumor cells via Ad5CMV-p53 2 days later. In situ end labelin g clearly illustrated apoptosis in the tumor cells. These results sugg est that wt-p53 plays an important role in the induction of apoptosis in human head and neck cancer cell lines and that selective induction of apoptosis in cancer cells can be further explored as a strategy for canter gene therapy.