Xanthorrhizol inhibits 12-O-tetradecanoylphorbol-13-acetate-induced acute inflammation and two-stage mouse skin carcinogenesis by blocking the expression of ornithine decarboxylase, cyclooxygenase-2 and inducible nitric oxide synthase through mitogen-activated protein kinases and/or the nuclear factor-kappa B.

Xanthorrhizol is an active component isolated from Curcuma xanthorrhiza Roxb. (Zingiberaceae) that is traditionally used in Indonesia for medicinal purposes. In the present study, we found that the topical application of xanthorrhizol before 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment significantly inhibits TPA-induced mouse ear edema and TPA-induced tumor promotion in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated ICR mouse skin. The topical application of xanthorrhizol following the induction of papillomas with TPA-induced hyperplasia and dysplasia also reduced tumor multiplicity and incidence in DMBA-initiated mouse skin. To further elucidate the molecular mechanisms underlying the antitumor-promoting activity of xanthorrhizol, its effect on the TPA-induced expression of ornithine decarboxylase (ODC), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) and the upstream signaling molecules controlling these proteins were explored in mouse skin. The pre-treatment with xanthorrhizol inhibited the expression of ODC, iNOS and COX-2 proteins and nuclear factor-kappaB (NF-kappaB) activation in both mouse skin with TPA-induced acute inflammation and DMBA-initiated mouse skin promoted by TPA for 19 weeks. When mouse skin was treated after TPA-induced production of papillomas, xanthorrhizol remarkably suppressed the expression of ODC, iNOS and COX-2 and inhibited the activation of NF-kappaB. Furthermore, western blot analysis showed that xanthorrhizol suppressed the activation of extracellular signal-regulated protein kinase, p38, c-Jun-N-terminal kinase and Akt in mice after topical application for 6 weeks following the induction of papillomas. Taken together, the present study demonstrates that xanthorrhizol not only delays or inhibits tumor formation, but also reverses the carcinogenic process at pre-malignant stages by reducing the protein levels of ODC, iNOS and COX-2 regulated by the NF-kappaB, mitogen-activated protein kinases and/or Akt.