Therapeutic Efficacy of Prodrug Activator Gene Therapy Using Retroviral Replicating Vectors for Human Ovarian Cancer.

BACKGROUND/AIM: Retroviral replicating vectors (RRV) have exhibited efficient tumor transduction and improved therapeutic benefits in a variety of cancer models. In this study, we validated two RRV created from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV), which use different cell receptors for virus entry, in human ovarian cancer (OC) cells. MATERIALS AND METHODS: Expression levels of the receptors for AMLV (PiT-2) and GALV (PiT-1) in human OC cell lines (A2780, Caov3, RMG-1, SKOV-3), fibroblasts and HEK293 cells were evaluated using quantitative RT-PCR. In vitro RRV-GFP replication was monitored using flow cytometry, and cytotoxicity quantitated using AlamarBlue assay after 5-fluorocytosine treatment of OC cells transduced with RRV expressing the yeast cytosine deaminase prodrug activator gene. In vivo antitumor effect of RRV-mediated prodrug activator gene therapy was investigated in a SKOV-3 subcutaneous tumor model. RESULTS: Quantitative RT-PCR analysis revealed high expression levels of PiT-2 (AMLV receptor) and PiT-1 (GALV receptor) in the RMG-1 and SKOV3 OC cell lines, compared with their levels in non-malignant cells. In RMG-1 and SKOV3 cells, both RRV showed highly efficient RRV replication and spread leading to over 90% transduction by Days 10-13. Additionally, both RRV that express the yeast cytosine deaminase gene demonstrated effective cell killing of RMG-1 and SKOV-3 cells upon treatment with the prodrug 5-fluorocytosine. Notably, RRV-mediated prodrug activator gene therapy showed significant inhibition of subcutaneous SKOV-3 tumor growth in nude mice. CONCLUSION: RRV-mediated prodrug activator gene therapy may be used for treating PiT-expressing human OC.

Retroviral Replicating Vectors Mediated Prodrug Activator Gene Therapy in a Gastric Cancer Model.

Retroviral replicating vectors (RRVs) selectively replicate and can specifically introduce prodrug-activating genes into tumor cells, whereby subsequent prodrug administration induces the death of the infected tumor cells. We assessed the ability of two distinct RRVs generated from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV), which infect cells via type-III sodium-dependent phosphate transporters, PiT-2 and PiT-1, respectively, to infect human gastric cancer (GC) cells. A quantitative RT-PCR showed that all tested GC cell lines had higher expression levels of PiT-2 than PiT-1. Accordingly, AMLV, encoding a green fluorescent protein gene, infected and replicated more efficiently than GALV in most GC cell lines, whereas both RRVs had a low infection rate in human fibroblasts. RRV encoding a cytosine deaminase prodrug activator gene, which converts the prodrug 5-flucytosine (5-FC) to the active drug 5-fluorouracil, showed that AMLV promoted superior 5-FC-induced cytotoxicity compared with GALV, which correlated with the viral receptor expression level and viral spread. In MKN-74 subcutaneous xenograft models, AMLV had significant antitumor effects compared with GALV. Furthermore, in the MKN-74 recurrent tumor model in which 5-FC was discontinued, the resumption of 5-FC administration reduced the tumor volume. Thus, RRV-mediated prodrug activator gene therapy might be beneficial for treating human GC.