Therapeutic effects of cantharidin analogues without bridging ether oxygen on human hepatocellular carcinoma cells

Previous research indicates that cantharidin, norcantharidin and their analogues exhibit anticancer activity due to their inhibition of cancer cell lines such as HL60, HT29 and L1210. The anticancer activities of cantharidin, norcantharidin and their analogues involve the suppression of serine/threonine protein phosphatases (PPs) activity. However, cantharidin is not suitable for cancer therapy because of its high cytotoxicity in vitro (IC(50) = 21 microM in primary cultured rat hepatocytes). In this study, synthetic cantharidin analogues with a structure of aminothiazole compounds 3-9 and a structure of anhydride compounds 10-12 were screened for anticancer activities and cytotoxic effects on human hepatocellular carcinoma cell (HCC) lines HepG2, Sk-Hep1, and primary cultured rat hepatocytes. Experimental results indicated that compounds 3-9 did not perform as expected with regard to anticancer activity and exhibited lower cytotoxicity. Compound 10 promoted apoptosis in HepG2 (IC(50) = 62 microM) and SK-Hep1(IC(50) = 151 microM) cell lines. Compounds 11 and 12 had anticancer potential similar to that of compound 10. After treatment with compounds 3-12, primary cultured rat hepatocytes exhibited no cytotoxicity (IC(50) > 200 microM). By investigating the structure-activity relationship (SAR) of these analogues as a whole, this study suggests that the anhydride ether oxygen such as in cantharidin, norcantharidin and compounds 10-12 may be correlated with HCC survival suppression. The results further suggest that the elimination of bridging ether oxygen on the ring, such as in compounds 10-12, can decrease cytotoxicity.