Redifferentiation of human hepatoma cell induced by 6-(p-chlorophenyl)-3- [1-(p-chlorophenyl)-5-methyl-1H,1,2,3-triazol-4-yl]-s-triazolo[3,4-b]-1,3, 4-thiadiazole (TDZ)

6-(p-Chlorophenyl)-3-[1-(p-chlorophenyl)-5-methyl-1H-1,2,3-triazol-4-yl] -s-triazolo[3,4-b]-1,3,4-thiadiazole (TDZ) is a derivative of various substituted s-triazolo[3,4-b]-1,3,4-thiadiazoles, which are associated with diverse pharmacological activities. However, the antitumor activity of TDZ is not well understood. To evaluate its role on tumor cell lines, we have examined the effect of TDZ on two tumor lines: human hepatoma cell (SMMC-7721) in vitro and Sarcoma180 tumor (S180) in vivo. The cytotoxicity of TDZ on human hepatoma cells was assessed using the MTT assay. The inhibition on tumor growth was evaluated by means of trypan blue exclusion test in vitro, and using a Sarcoma180 tumor (S180) animal model in vivo. A scanning electronic microscope was used to discover the morphological changes on cell surface, cell electrophoresis was employed to determine the changes of cell surface negative charges, and α-fetoprotein was applied as a biomarker of hepatoma. The effect of TDZ on DNA synthesis was determined by a [³H]-thymidine incorporation assay, and cell cycle distribution by flow cytometry. The IC ₅₀ value of TDZ on SMMC-7721 cells was 52.9 αg/ml (48 h). However, TDZ could inhibit the growth of SMMC-7721 cells at concentrations far lower than the IC₅₀ value. Treated with the same low concentrations of TDZ, microvilli on the surface of SMMC-7721 cells decreased obviously, electrophoresis rate of cells reduced from 2.14 μm · s^-1 · V^-1 · cm^-1 of control to 1.54 and 1.56μm · s^-1 · V^-1 · cm ^-1, the content of AFP dropped from 205.14 ± 6.41 ng · mg^-1 Pr to 115.68 ± 3.47 and 78.57 ± 2.35 ng · mg^-1 Pr, and the DNA replication was inhibited by 26.8% and 45.2%. These results indicated that TDZ may inhibit proliferation of cancer cells by reversing SMMC-7721 cells malignant phenotypic characteristics and inducing redifferentiation. Flow cytometry showed that TDZ-treated cells resulted in a higher proportion of cells in S phase compared with untreated cells, and only when the concentration reached 64 μg/ml, the apoptosis could happen at the rate of 4.2%. Detection of the inhibition of Sarcoma 180 tumor growth in vivo showed that TDZ reduced the tumor weight and 69.08% of the growth was inhibited. TDZ could inhibit the proliferation of tumors in vitro and in vivo; the possible antitumor mechanism might be inducing redifferentiation at a lower dosage in vitro.