Inhibition of nuclear factor-[kappa]B and nitric oxide by curcumin induces G2/M cell cycle arrest and apoptosis in human melanoma cells

Curcumin (diferuloylmethane) inhibits tumour cell growth by inducing apoptosis in many tumour types, including melanoma, via complex and ill-defined pathways. Recent studies have shown that curcumin is both a nitric oxide scavenger and an inhibitor of inducible nitric oxide synthase (iNOS) expression, low levels of which correlate with antiapoptotic function and poor survival and which may be regulated by inhibition of nuclear factor-κB (NFκB) activation. To elucidate the mechanisms by which curcumin inhibits melanoma proliferation, we tested the in vitro effects of curcumin on specific cell cycle pathways and melanoma cell survival, including NFκB activation. Curcumin induced melanoma cell apoptosis and cell cycle arrest, which is associated with the downregulation of NFκB activation, iNOS and DNA-dependent protein kinase catalytic subunit expression, and upregulation of p53, p21^Cip1, p27^Kip1 and checkpoint kinase 2. Curcumin also downregulated constitutive iNOS activity in melanoma cells. Our results demonstrate that curcumin arrested cell growth at the G₂/M phase and induced apoptosis in human melanoma cells by inhibiting NFκB activation and thus depletion of endogenous nitric oxide. Therefore, curcumin should be considered further as a potential therapy for patients with melanoma.