Cindy Yeoh Shin Ly, Anil Philip Kunnath.
Gene-directed enzyme prodrug therapy (GDEPT) is an advanced cancer therapy that has potential use against localized and metastasized cancer. This strategy aims to improve the limitations of chemotherapy and existing cancer treatments by specific gene delivery, which allows the conversion of systemically administered nontoxic prodrugs to active chemotherapeutic drugs inside the target tumor cells, thereby resulting in a significant therapeutic index by introducing high concentrations of cytotoxic compounds to the tumor cells while limiting the systemic toxicity. The main attraction of GDEPT is by expanding the toxicity to adjacent non-expressing target cancer cells through local and distal bystander effects, leading to tumor regression. This review focused on the application of the six main GDEPT systems for treating cancer, including herpes simplex virus thymidine kinase
(HSV-TK) with ganciclovir (GCV), cytosine deaminase (CD) from bacteria or yeast with 5-fluorocytosine (5-FC), E. coli nitroreductase (NfsB) with 5-(aziridin-1-yl)-2,4- initrobenzamide (CB1954), hepatic cytochrome P4l50 (CYP450) with cyclophosphamide (CPA), purine nucleoside phosphorylase (PNP) from E. coli with 6-methylpurine deoxyriboside (MEP), and bacterial carboxypeptidase G2 (CPG2) with 4-[(2-chloroethyl)(2-mesloxyethyl)amino] benzoyl-L-glutamic acid (CMDA). In each system, the mechanism of action, clinical trials for the past decades, limitations, and areas that need improvement are discussed.