Mesenchymal stem cells as cellular vehicles for prodrug gene therapy against tumors

Gene-directed enzyme prodrug therapy (GDEPT) consists of targeted delivery to tumor cells of a suicide gene responsible for the in situ conversion of a prodrug into cytotoxic metabolites. One of the major impediments of GDEPT is to target specifically the tumor cells with the suicide gene. Among gene delivery methods, mesenchymal stem cells (MSCs) have emerged recently as potential cellular vehicles for gene delivery. MSCs are particularly suited for gene transduction. They exhibit remarkable migratory property towards tumors and their metastases and they are weakly immunogenic. This review will summarize the current knowledge about MSCs engineered to express different suicide genes (cytosine deaminase, thymidine kinase, carboxylesterase, cytochrome P450) to elicit a significant antitumor response against brain tumors, ovarian, hepatocellular, pancreatic, renal or medullary thyroid carcinomas, breast or prostate cancer and pulmonary metastases. The potential side effects of these MSC-based tumor therapies will also be considered to highlight certain aspects that need to be improved prior to clinical use.