Abstract
Retroviral replicating vectors (RRVs) have been shown to achieve efficient tumor transduction and enhanced therapeutic benefits in a variety of cancer models. In the present study, we evaluated a possible combinatorial effect of prodrug activator genes delivered by two different RRVs derived from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV) on human hepatocellular carcinoma Hep3B cells. Both RRVs showed efficient replicative spread in culture and can overcame superinfection resistance each other. Notably, the replication and spread of each RRV in culture remained unaffected by pretransduction with the counterpart RRV. We further transduced cells with RRVs which individually possessed the prodrug activator genes yeast cytosine deaminase (CD) and herpes simplex virus thymidine kinase (TK) alone or in combination, and evaluated the cytotoxic effects of RRV-mediated gene therapy with CD and TK in the presence of the respective prodrugs, 5-fluorocytosine and ganciclovir. All combinations of the two prodrug activator genes produced synergistic cytocidal effects, but the combined effects of the different genes were significantly greater than those of the same genes when delivered by two different vectors. The present findings indicate the potential utility of dual-vector gene therapy using two different RRVs carrying different prodrug activator genes.
Highlights
Advances in gene transfer technologies have opened the way toward cancer treatment by gene therapy
We have developed two different retroviral replicating vectors (RRVs) derived from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV) [12, 13]
We have shown that two different RRVs, AMLV and GALV, utilizing different cellular receptors can overcome superinfection resistance
Summary
Advances in gene transfer technologies have opened the way toward cancer treatment by gene therapy. Using RRVs that express yeast cytosine deaminase (CD), which converts the prodrug 5-fluorocytosine (5FC) to the toxic metabolite 5-fluorouracil, we showed highly efficient killing of a wide variety of cancer cells in vitro and in vivo following 5FC administration [10,11,12, 16,17,18,19] Based on these promising preclinical results, a phase 1 clinical trial for RRV-mediated prodrug activator gene therapy in patients with recurrent glioblastoma was recently conducted in the United States and Europe, resulting in long-term survival and systemic antitumor immunity mediated by memory T cells [20]. RRVs are currently under evaluation in an international phase III trial for recurrent high-grade glioma
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