The effects of naturally occurring compounds on the proliferation of human malignant melanoma cells

Malignant melanoma is a prevalent skin cancer and the leading cause of death from cutaneous malignant tumors in the United States. This study investigates the anti-proliferative effect of some naturally occurring substances on human malignant melanoma cells. Ginkgo biloba leaf extract standard preparation EGb761 and its flavonoid constituents kaempferol and quercetin significantly decreased the proliferation of melanoma cells at relatively low concentrations, and exhibited selective toxicity to some extent. The anti-proliferative effects are both time- and dose-dependent. Bilobalide and ginkgolide B, the two main terpenoid constituents of EGb761, did not show inhibitory effect on the melanoma cells. Instead, they promoted the growth of melanoma cells. No evidence of apoptosis was shown in melanoma cells treated by EGb761, kaempferol or quercetin. DNA microarray analysis showed that EGb761 (500 mug/m1) upregulated 251genes and downregulated 63 genes in melanoma cells, and its flavonoid kaempferol upregulated 355 genes and downregulated 640 genes. Many of kaempferol-regulated genes are involved in cell cycle, apoptosis, cell adhesion and metastasis, signal transduction, transcription regulation, inflammatory response, tumor necrosis factor-mediated signaling pathway, angiogenesis, which are all important in tumor progression and senescence. Selected kaempferol-regulated genes were validated by qRT-PCR, and the results were consistent with those obtained from DNA microarray analysis. Bacterium ZYD4 isolated from soil samples was a strain of Brevibacillus laterosporus and produced a substance in the supernatant that exhibited a strong anti-proliferative effect on melanoma cell. The activity of the anti-melanoma substance was acid- and alkali-stable, but significantly attenuated by treatment with heat or proteinase K. The anti-tumor activity could be precipitated by the saturation of ammonium sulfate, and be extracted by ethanol but not ethyl acetate, which suggested the hydrophilicity of the substance.