Inhibitors of the human enzyme dimethylarginine dimethylaminohydrolase-1 (DDAH-1) can raise endogenous levels of asymmetric dimethylarginine (ADMA) and lead to a subsequent inhibition of nitric oxide synthesis. Herein, N5-(1-imino-2-chloroethyl)-L-ornithine (Cl-NIO) is shown to be a potent time- and concentration-dependent inhibitor of purified human DDAH-1 (KI = 1.3 ± 0.6 μM; kinact = 0.34 ± 0.07 min−1), with > 500-fold selectivity against two arginine-handling enzymes in the same pathway. An activity probe is used to measure the “in cell” IC50 value (6.6 ± 0.2 μM) for Cl-NIO inhibition of DDAH-1 artificially expressed within cultured HEK293T cells. A screen of diverse melanoma cell lines reveals that a striking 50 / 64 (78 %) of melanoma lines tested showed increased levels of DDAH-1 in comparison to normal melanocyte control lines. Treatment of the melanoma A375 cell line with Cl-NIO shows a subsequent decrease in cellular nitric oxide production. Cl-NIO represents a promising tool for the study of methylarginine-mediated nitric oxide control and a potential therapeutic lead compound for other indications with elevated nitric oxide production such as septic shock and idiopathic pulmonary fibrosis.

Melanoma is the most aggressive form of skin cancer. The rising incidence of melanoma and its poor prognosis in advanced stages are compelling reasons to identify novel therapeutic agents. Though isolated dietary components such as lycopene, resveratrol, and isothiocyanate compounds have been shown to provide limited protection against cancer development, the use of whole herbs and herbal extracts for the treatment of cancer remains of great interest. As suggested by earlier studies, the antiinflammatory activity of many plants available as intact products or as extracts has long been considered for supplemental therapeutics for cancer. Zyflamend, a unique multiherbal extract preparation, is a promising antiinflammatory agent that has also been suggested to regulate multiple pathways in cancer progression. As Zyflamend contains ingredients that can suppress tumor cell proliferation, invasion, angiogenesis, and metastasis through regulation of inflammatory pathway products, we hypothesized that this preparation might inhibit melanoma proliferation. To test this hypothesis, we studied the effect of Zyflamend on melanoma proliferation. Here, we present that Zyflamend inhibits melanoma growth by regulating the autophagy-apoptosis switch. Based on the responsible molecular mechanisms of Zyflamend, our study highlights the importance of the use of herbal preparations for the prevention and treatment of cancer.