Targeting gene expression to tumor cells with loss of wild-type p53 function

The tumor suppressor protein p53 is a transcription factor thai can positiv ely regulate the expression of critical target genes involved in negative c ontrol of cell growth or induction of apoptosis; p53 is also able to suppre ss the transcription of other genes by virtue of its ability to bind compon ents of the basal transcription machinery. Over 50% of human tumors are cha racterized by p53 mutations that result in a loss of wild-type p53 (wtp53) function in the transcriptional control of these target genes. We have expl oited this loss of p53 function in the regulation of gene transcription to develop a novel gene therapy strategy that maximizes expression of the pote ntial therapeutic gene in tumors while simultaneously down-regulating the s ame gene in normal cells. In one construct (unit I), the potential therapeu tic gene (in this case represented by a luciferase reporter) is placed unde r the control of a promoter such as the heat shock protein 70 gene promoter , which is repressed by wtp53 but overexpressed in many tumor cells with de fective p53 function. Residual expression of the reporter in normal cells i s repressed by cotransfection of another construct (unit II) consisting of a repressor of unit I under the control of a promoter that is activated by wtp53 expression. Unit II contains a promoter with a consensus wtp53 bindin g sire driving a transcriptional repressor or an antisense construct for th e gene in unit I. Our results suggest that this dual control approach may r epresent a strategy with wide applications in the field of cancel gene ther apy.