Ingenol-3-Angelate Suppresses Growth of Melanoma Cells and Skin Tumor Development by Downregulation of NF-κB-Cox2 Signaling

BACKGROUND: A recent focus in skin cancer prevention intervenes though modulating molecular links between inflammation and cell growth signaling, such as NF-κB. This study elucidates the effect of a non-tumor promoting phorbol ester, ingenol-3-angelate (I3A), on the growth of human melanoma cells and on the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin inflammation and 7,12-Dimethylbenz(a)anthracene (DMBA)-induced skin carcinoma in mice. MATERIAL/METHODS: Cell viability was assessed by MTT assay, cell proliferation by clonogenic assay, apoptosis and cell cycle arrest was analyzed by flow cytometry, protein expression was studied by IHC and Western blotting, and gene expression by qPCR. RESULTS: I3A suppressed the survival and proliferation of human melanoma cells with estimated IC50 values around 38 and 46 μM for A2058 and HT144 cell, respectively. I3A activated the protein levels of PKCδ and PKCɛ, which induced apoptosis by activating caspase-9 and caspace-3 followed by lowering of mitochondrial membrane potential and enhancing DNA fragmentation. I3A induced G1 phase cell cycle arrest as well as G2/M phase arrest in both cell lines. I3A inhibited the levels of NF-κB p65 protein as well as phosphorylation of p65 and its nuclear translocation. I3A suppressed the gene expression of NF-κB, COX-2 and iNOS. I3A inhibited TPA-induced inflammation and epidermal hyperplasia in female ICR mice by downregulating NF-κB and iNOS. I3A suppressed the growth of skin tumor in DMBA-induced mice in dose-dependent manner. CONCLUSIONS: The mechanism of I3A induces apoptosis in human melanoma cells and suppresses skin inflammation and carcinoma via downregulation of NF-κB-iNOS-COX-2 signaling.