RESUMO
AIMS: Gene therapy is a candidate approach for treating cancer patients whose tumors have developed resistance to some drugs. Our study aims to examine possible alteration in Ad5RSVßgal-mediated transgene expression in a vincristine-resistant cells (VK2) derived from the human laryngeal carcinoma cell line HEp2, and the underlying mechanism(s) thereof. MAIN METHODS: Adenovirus-mediated transgene expression in HEp2 and VK2 cells was measured by ß-gal staining. Semiquantitative PCR was used to evaluate attachment of adenovirus to the cell surface and adenovirus internalization into cells. After transfection of cells with plasmid DNA, promoter activity was measured by semiquantitative RT-PCR. KEY FINDINGS: We show here that VK2 cells exhibited increased Ad5RSVßgal-mediated transgene expression, despite moderately decreased Ad5RSVßgal attachment and internalization, as compared with HEp2 cells. The increased transgene expression was also observed with a virus (Ad5FbΔ639RSVßgal) that does not use the coxsackie-adenovirus receptor (CAR), suggesting that increased transgene expression is independent of CAR. Upon transfection of VK2 cells with a plasmid expressing a reporter gene under the control of the RSV promoter or a plasmid containing the complete Ad5RSVßgal genome, RSV promoter activity was 33- and 4.7-fold higher, respectively, than in HEp2 cells. SIGNIFICANCE: The increased Ad5RSVßgal-mediated transgene expression in the VK2 cells is due to the increased RSV promoter activity in VK2 cells. Our results point out that (i) drug-resistance may be accompanied with an alteration in promoter activity; (ii) the proper choice of promoter could contribute to a decrease in the vector dose required to achieve a therapeutic effect during gene therapy.
