207 ENGINEERED HUMAN AMNIOTIC FLUID-DERIVED STEM CELLS BY EXPRESSING CYTOSINE DEAMINASE (CD) AND THYMIDINE KINASE (HSV-TK) MEDIATE TARGETING KILLING EFFECT IN BREAST CANCER CELLS

Genetically engineered stem cells (GESTECs) expressing suicide genes which can convert non-toxic prodrugs to toxic metabolites have been shown to reduce tumour growth. In this sudy, we employed human amniotic fluid-derived stem cells (hAFSCs) as a source of cells for suicide gene transfer. hAFSCs were engineered to express multiple suicide genes, a bacterial cytosine deaminase (CD) and herpes simplex virus thymidine kinase (HSV-TK) genes. Thus, AF2.CD-TK cells were generated to express CD and HSV-TK genes simultaneously, which can convert 5-fluorocytosine (5-FC) and monophosphorylate ganciclovir (GCV-MP) into 5-fluorouracil (5-FU) and active form of triphosphate ganciclovir (GCV-TP), respectively. Combination of CD and HSV-TK suicide genes in AF2.CD-TK cells resulted in enhanced antitumour activity in vitro and in vivo xenograft models. AF2.CD-TK cells significantly inhibited the growth of MDA-MB-231 human breast cancer cells in the presence of the prodrugs, 5-FC and GCV, by MTT assay. MDA-MB-231 cells were implanted into the right mammary fat pad of female BALB/c nude mice and CM-DiI-labelled AF2.CD-TK cells were injected into the circumtumoral site with 5-FC (500 mg kg–1 day–1) and GCV (10 mg kg–1 day–1). Treatment of the mice with AF2.CD-TK cells significantly reduced tumour volumes in MDA-MB-231 xenografted mice. We further evaluated tumour progression by histopathological and fluorescent staining. Taken together, these results indicate that AF2.CD-TK cells can serve as a vehicle for a novel therapeutic approach enzyme/prodrug system to selectively target breast malignancies. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0015385).