Abstract: Described are methods and compositions for inhibiting undesired cells by expression of one or more exogenous enzymes in the cells and administration of a prodrug which is a substrate for at least one of the enzymes to produce a cytotoxic compound. Inventive methods and compositions are active to inhibit cells expressing the exogenous enzymes as well as bystander cells. Tumor cells are a particular target for inhibition using methods and compositions detailed according to the present invention. Provided are methods and compositions for improved anti-tumoral effects by overexpression of adenine phosphoribosyltransferase (APRT) to produce cytotoxins which inhibit the cells overexpressing the APRT as well as bystander cells. Overexpression of APRT in conjunction with expression of E. coli PNP and administration of a substrate for E. coli PNP provides particularly effective anti-tumoral effects.

Abstract: Compounds having the structure: 1