In this study, in vitro cytotoxic effects of seven adamantyl isothiourea derivatives were evaluated against five human tumor cell lines using the MTT assay. Compounds 5 and 6 were found to be the most active derivatives particularly against hepatocellular carcinoma (HCC). To decipher the potential mechanisms involved, in vivo studies were conducted in rats by inducing HCC via chronic thioacetamide (TAA) administration (200 mg/kg, i.p., twice weekly) for 16 weeks. Compounds 5 and 6 were administered to HCC rats, at a dose of 10 mg/kg/day, for further 2 weeks. In vitro and in vivo antitumor activities of compounds 5 and 6 were compared to those of the anticancer drug doxorubicin (DOXO). In the HCC rat model, compounds 5 and 6 significantly reduced serum levels of ALT, AST with ALP and α-fetoprotein. H & E and Masson trichrome staining revealed that both compounds suppressed hepatocyte tumorigenesis and diminished fibrosis, inflammation and other histopathological alterations. Mechanistically, compounds 5 and 6 markedly decreased protein expression levels of α-SMA, sEH, p-NF-κB p65, TLR4, MyD88, TRAF-6, TNF-α, IL-1β and TGF-β1, whereas they increased caspase-3 expression in liver tissues of HCC rats. In most analyses, the effects of compound 6 were more comparable to DOXO than compound 5. These findings suggested that the compounds 5 and 6 displayed in vitro and in vivo cytotoxic potential against HCC, probably via inhibition of TLR4-MyD88-NF-κB signaling.
Keywords: Adamantyl isothiourea; MyD88; NF-κB; TLR4; epoxide hydrolase; hepatocellular carcinoma.
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