Tocagen Inc (TOCA)

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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.

In conclusion, our results demonstrated AMLV and GALV can coinfect and replicate independently in cultured cells, suggesting their ideal combination for dual-vector gene therapy. The dual RRV-mediated CD/5FC and TK/GCV combinatorial gene therapy achieved synergistic cytotoxic efficacy compared with single-vector gene therapy. Thus, coinfection of cancer cells with AMLV and GALV vectors supplied with different prodrug activator genes may be employed for combination intracellular chemotherapy, leading to enhanced cytotoxic effects while avoiding drug resistance.

https://www.nature.com/articles/s41417-018-0051-0