Curcumin-induced antiproliferative and proapoptotic effects in melanoma cells are associated with suppression of IκB kinase and nuclear factor KB activity and are independent of the B-Raf/mitogen-activated/extracellular signal-regulated protein kinase pathway and the Akt pathway

Background. Nuclear factor-kappa B (NF-kappa B) plays a central role in cell survival and proliferation in human melanoma; therefore, the authors explored the possibility of exploiting NF-kappa B for melanoma treatment by using curcumin, an agent with known, potent, NF-kappa B-inhibitory activity and little toxicity ill humans. Methods. Three melanoma cell lines (C32, G-361, and WM 266-4), all of which had B-raf mutations, were treated with curcumin, and the authors assessed its effects on viability ((3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide assay) and apoptosis (flow-cytometric analysis of annexin V/propidium iodide-stained cells). Curcumin-treated cells also were examined for NF-kappa B binding activity (electrophoretic mobility shift assay) and for the activity of its upstream regulator, I kappa B kinase (IKK (immune complex kinase assay). In addition, relevant signaling, as reflected by B-Raf kinase activity (kinase cascade assay), and steady-state levels of activated, downstream effectors, as reflected by mitogen-activated signal-regulated protein kinase (MEK), extracellular signal-regulated protein kinase (ERK), and Akt phosphorylation levels (immunoblots), were assessed. Results. Curcumin treatment decreased cell viability of all 3 cell lines in a dose-dependent manner (50% inhibitory concentration=6.1-7.7 mu M) and induced apoptosis. NF-kappa B and IKK were active constitutively in all melanoma cell lines examined, and curcumin, under apoptosis-inducing conditions, down-regulated NF-kappa B and IKK activities. However, curcumin did not inhibit the activities of B-Raf, MEK, or ERK, and Akt phosphorylation was enhanced. Furthermore, in the presence of curcumin, the Akt inhibitor 1L-6-hydroxymethyl-chiro-inositol 2-[(R)-2-O-methyl-3-O-octadecylcarbonate] no longer suppressed Akt phosphorylation. Conclusions. Curcumin has potent antiproliferative and proapoptotic effects in melanoma cells. These effects were associated with the suppression of NF-kappa B and IKK activities but were independent of the B-Raf/MEK/ERK and Akt pathways.