Hepatoma-specific gene therapy through retrovirus-mediated and targeted gene transfer using an adenovirus carrying the ecotropic receptor gene.

Tissue-specific transcriptional regulatory sequences have been inserted in retrovirus vectors for therapeutic gene expression in cancer gene therapy. However, the transcriptional activity of these sequences is generally low, and the proviral DNA integration appears to increase the possibility of genomic DNA alteration in nontarget cells. Therefore, retrovirus-mediated targeted gene transduction into human hepatoma cells was evaluated using transient expression of an ecotropic receptor gene, mouse cationic amino acid transporter-1 (MCAT-1). Two recombinant adenoviruses, AxCAMCAT and AxAFMCAT, carrying the MCAT-1 gene under the control of the CAG and human alpha-fetoprotein (AFP) promoter, respectively, were generated. The preinfection with AxCAMCAT allowed highly efficient ecotropic retroviral infection of human cells. In addition, after AxAFMCAT infection, retroviral infection occurred only in AFP-producing hepatoma cells, resulting in selective cytotoxicity induced by the herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir (GCV) system. Transient expression of the MCAT-1 gene under the control of the AFP promoter permits ecotropic retrovirus-mediated gene transduction specifically in AFP-producing human hepatoma cells, resulting in selective induction of the suicide killing effect while the therapeutic gene is driven from ubiquitously expressed promoters.