Induction of wild-type p53 activity in human cancer cells by ribozymes that repair mutant p53 transcripts

Several groups have attempted to develop gene therapy strategies to treat c ancer via introduction of the wild-type (wt) p53 cDNA into cancer cells. Un fortunately. these approaches do not result in regulated expression of the p53 gene and do not reduce expression of the mutant p53 that is overexpress ed in cancerous cells. These shortcomings may greatly limit the utility of this gene replacement approach. We describe an alternative strategy with tr ans-splicing ribozymes that can simultaneously reduce mutant p53 expression and restore wt p53 activity in various human cancers. The ribozyme accompl ished such conversion by repairing defective p53 mRNAs with high fidelity a nd specificity. The corrected transcripts were translated to produce functi onal p53 that can transactivate p53-responsive promoters and down-modulate expression of the multidrug resistance (MDR1) gene promoter. The level of w t p53 activity generated was significant, resulting in a 23-fold induction of a p53-responsive promoter and a 3-fold reduction in MDR1 promoter expres sion in transfected cancer cells. Once efficient delivery systems are devel oped, this strategy should prove useful for making human cancers more respo nsive to p53 activity and more sensitive to chemotherapeutic agents.