Transcriptional targeting in cancer gene therapy using the p21/WAF1 promoter

Lack of target cell specificity is the main limitation with gene therapy. Tissue-specific receptors (Kashara et al. 1994) and enhancers (Manome et al. 1994) have been used to localise therapy to the desired area. However low levels of gene expression are often associated with these methods. There has been a great deal of interest in the use of exogenous inducible promoters that operate at the transcriptional level, such as the Egr-1 promoter (Manome et al. 1998). This investigation focuses on the promoter for the x-ray inducible gene, p21/WAF1 (wild type p53 activated fragment). The WAF1 promoter has a p53 binding site which has been shown to confer p53 dependent inducibility upon the gene (El-Deiry et al. 1993). However a p53 independent activation pathway also exists (Wu et al. 2000). The current study examines the radiation and hypoxia inducibility of the WAF1 promoter in several human tumour cell lines of which the p53 status is known. Using the pEGFP reporter gene, we have established that the promoter is induced by radiation at clinically relevant doses (Worthington et al, 2000) and also by hypoxia. Results indicate that the WAF1 promoter is not leaky in normal human cells but is leaky in human tumour cells regardless of p53 status, indicating a level of tumour specificity not yet fully explored. This observation, coupled with its hypoxia and radiation inducibility at clinically relevant radiation doses, suggest that the WAF1 promoter could have significant advantages in overcoming the target specificity associated with gene therapy