Synthesis and Evaluation of Cantharidinimides on Human Cancer Cells

Background: Cantharidin isolated from the blister beetle is used as a traditional Chinese medicine. The anticancer activity of thiadizolyl and some known N-substituted thiazolyl of cantharidin has been reported. We obtained a novel type of cantharidinimides for testing their cytotoxicity in human carcinoma cell lines. The structural modification of cantharidin to cantharidinimide might lead to the discovery of a novel class of antitumor compounds. Methods: We synthesized more than 34 cantharidinimide derivatives from heating the cantharidin (compound 1) to ca. 200°Cin toluene and triethylamine along with primary amine, aniline derivatives, and aminopyridines, respectively. These imide derivatives contain aryl, pyridyl, azolyl, thiadiazolyl, diaminophenyl, aminosulfanyl, sulfamethoxazolyl, or sulfadiazine cantharidinimides (compounds 2-34). All of these synthetic compounds were tested for their capability to suppress growth of the human carcinoma cell lines such as HepG2, HL-60, 59T, HONE-1, DLD-1, SCM-1 NUGC, and Hep3B cells. Results: The 3-(4, 5-dimethylthiazol-2-yl)2, 5-diphenyltetrazolium bromide (MTT) viability assay was used to evaluate the cytotoxic effect of newly synthesized cantharidinimides against the previously mentioned carcinoma cell lines. The current results indicate that compounds 2, 3, 4, 6, 8, 11, 12, 13, 14, 15, 17, 29, 30, and 31 were somehow effective and some of them were more potent than the parent compound cantharidin. Compounds 4, 13, 14, and 15, which were thiazol- and thiadiazol-containing cantharidinimides, caused cytotoxic effects on 59T, SCM-1, HONE-1, Hep3B, and NUGC human carcinoma cell lines. Compounds 11 and 16 with a planar side chain had medium cytotoxicity on hepatoma cell lines. Compounds 6 and 8 were bromine-containing aromatic cantharidinimide that produced significant cytotoxic effects on HONE-I and NUGC in high concentrations, but only compound 6 inhibited the growth of 59T and SCM-1 cell lines. Conclusions: The current results indicate that the cytotoxic effects on several cancer cells were produced by many different structural domains of the cantharidinimide compounds. The current in vitro results suggest that decreasing electron negativity on the substituent-donating group might increase their cytotoxicity to cancer cells.