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Figure 3.15 4-[(2-Chloroethyl)[2-(mesyloxy)ethyl]amino]benzoic acid (a) and CMDA (b).

activation. The only notable difference between the two strategies is that GDEPT uses nonviral vectors for intracellular delivery of genes, whereas VDEPT uses viral vectors for achieving the same purpose. The trans-fected tumor cells express the enzyme protein, which is further converted to active enzyme and selectively catalyzes intracellular activation of inactive prodrug to the active drug (toxic), resulting in cell death. Another variation of GDEPT is genetic prodrug activation therapy (GPAT), which involves the use of transcriptional differences between normal and tumor cells to induce the selective expression of drug-metabolizing enzymes to convert nontoxic prodrug into the active toxic moiety.

Examples of GDEPT include irinotecan (CPT-11), a prodrug of 7-ethyl-10-hydroxy-camptothecin activated by carboxylesterase; 5-fluorocytosine, a prodrug of 5-FU activated by cytosine deaminase; and cyclophosphamide, a prodrug of 4-hydroxycyclophosphamide activated by cytochrome P450, which degrades into acrolein and phospho-ramide mustard.112-115

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