Quercetin and sulforaphane in combination suppress the progression of melanoma through the down-regulation of matrix metalloproteinase-9

Malignant melanoma is one of the most common types of cancer in the US and worldwide. The epidemiological data suggest that dietary modification may reduce the incidence of this disease. Quercetin (3,5,7,3',4'-tetra-hydroxyflavone), a flavonoid isolated from onion, exhibits anti-oxidant, anti-inflammatory and anti-cancer effects. D,L-sulforaphane [1-isothiocyanato-4-(methylsulfinyl)butane], a cruciferous vegetable-derived isomer isolated from broccoli, is highly effective in protection against cancer. Matrix metalloproteinases (MMPs), extracellular matrix degrading enzymes, are involved in embryogenesis, inflammation, angiogenesis and cancer. MMP-9 in particular plays a crucial role in the regulation of invasion, tumor growth and metastasis. Previous studies have reported that both quercetin and sulforaphane independently reduce tumor growth and metastasis in breast, prostate, lung and other types of cancers. However, the combined effects of quercetin and sulforaphane on the regulation of tumor growth and the mechanism(s) of actions underlying this process have not yet been investigated. In the present study, we report for the first time that quercetin and sulforaphane in combination inhibit the proliferation and migration of melanoma (B16F10) cells more effectively than either compound used alone. Moreover, these compounds in combination significantly suppressed melanoma growth as compared to their individual use in a mouse model. This combined effect was predominantly due to a decrease in MMP-9 expression in the mouse tumors. Taken together, our findings revealed that the administration of quercetin and sulforaphane in combination rather than alone may be a more effective approach for the treatment of malignant melanoma.