OBJECTIVETo study the gap junction mechanisms for synergistic effects of liuwei di-huang pill (LDP) containing serum on HSV-tk/GCV suicide gene therapy of mouse malignant melanoma B16 cells.

METHODSThe LDP containing serum (2.5% LDP serum group, 5.0% LDP serum group, and 10.0% LDP serum group) and the control serum group were set up. The effects of LDP on mRNA expressions of Cx26 and Cx43 in mouse malignant melanoma B16 cells were detected by RT-PCR assay. The effects of LDP on protein expressions of Cx26 and Cx43 in B16 cells were detected using Western blot and indirect immunofluorescence assay. The interference efficiencies of Cx26-309, Cx26-337, Cx26-367, Cx26-2098 SiRNA on Cx26 gene in B16 cells were detected using RT-RCR technique. Cx26-2098 SiRNA, due to the optimal interference efficiency, was chosen to interfere Cx26 gene, and the bystander effect of LDP + HSV-tk/GCV was observed. The effects of the gap junctional intercellular communication (GJIC) inhibitor glycyrrhetinic acid on the killing of LDP + HSV-tk/GCV system to B16 cells were detected by MTT assay. In this experiment, the control serum group, 2.5% LDP serum group, 5. 0% LDP serum group, 10.0% LDP serum group, the control serum combined GCV group, 2.5% LDP serum combined GCV group, 5.0% LDP serum combined GCV group, 10.0% LDP serum combined GCV group, 2.5% LDP serum combined GCV + glycyrrhetinic acid group, 5.0% LDP serum combined GCV + glycyrrhetinic acid group, 10.0% LDP serum combined GCV + glycyrrhetinic acid group were set up. The final concentration of GCV was 20 micromol/L. The final concentration of glycyrrhetinic acid was 50 micromol/L.

RESULTSLDP containing serum could increase the protein and mRNA expressions of Cx43 in B16 cell in a dose-dependent manner. It had bi-directional regulation on the Cx26 protein and mRNA expressions. The low dose LDP had inhibition while high dose LDP could up-regulate its expression. After SiRNA interfered Cx26 gene, there was no obvious change in the bystander effect of LDP combined suicide gene therapy between before and after interference. There was significant reduction in the inhibition rate between before (48.75%, 59.39%, and 69.28%) and after blockage (29.14%, 38.71%, and 58.13%) of glycyrrhetinic acid in the 2. 5%, 5.0%, 10.0% LDP serum combined GCV groups (P <0.01).

CONCLUSIONThe synergistic effects of LDP containing serum on HSV-tk/GCV suicide gene therapy in mouse malignant melanoma B16 cells were correlated with the gap junction mechanisms, which might be achieved through increasing the expressions of Cx26 and Cx43.