THERAPEUTIC POTENTIAL OF RECOMBINANT P53 OVEREXPRESSION IN BREAST-CANCER CELLS EXPRESSING ENDOGENOUS WILD-TYPE P53

Reconstitution of the p53-dependent apoptotic pathway by gene transfer of a recombinant wild-type p53 minigene leads to rapid apoptotic cell death in breast and other cancer cell types expressing null or mutant p53. Tumour cells expressing wild-type p53 have been reported to be m ore resistant to this treatment strategy, presumably as a result of mu tations in downstream regulators of p53-dependent apoptotic signalling . The MCF-7 breast cancer cell line is representative of this class of tumour cell. Our recent observation of a p53-dependent apoptotic resp onse following adenovirus-mediated HSV thymidine kinase gene transfer and gancyclovir treatment led us to reexamine recombinant p53 cytotoxi city in MCF-7 cells. Infection with a recombinant adenovirus expressin g wild-type p53 resulted in a dramatic increase in p53 protein levels and was accompanied by an increase in p21(WAF1/CIP1) protein levels an d G1 arrest within 24 hours post-infection. A significant decrease in MCF-7 cell viability was first observed at 5 days post-infection and c oincided with the appearance of morphological and biochemical changes consistent with apoptotic cell death. By day 7 post-treatment, cell vi ability decreased to 45% and clonogenic survival was reduced to 12% of controls. The results demonstrate that persistent, high level express ion of recombinant p53 can induce programmed cell death in MCF-7 cells . While the mechanism by which p53 overexpression overcomes the defect in downstream apoptotic signalling is not clear, our data suggests th at this treatment strategy may be beneficial for the class of tumour c ells represented by the MCF-7 cell line.