Involvement of Up-Regulation of DR5 Expression and Down-Regulation of c-FLIP in Niclosamide-Mediated TRAIL Sensitization in Human Renal Carcinoma Caki Cells.

Niclosamide is used to treat intestinal parasite infections, as being an anthelmintic drug. Recently, several papers suggest the niclosamide inhibits multiple signaling pathways, which are highly activated and mutated in cancer. Here, niclosamide was evaluated for identifying strategies to overcome tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance. Although niclosamide (100⁻200 nM) alone did not bring about cell death, combinations of niclosamide and TRAIL led to apoptotic cell death in carcinoma cells, but not in normal cells. Niclosamide markedly increased DR5 protein levels, including cell-surface DR5, and decreased c-FLIP protein levels. Down-regulation of DR5 by specific small interfering RNA (siRNA) and ectopic expression of c-FLIP markedly blocked niclosamide plus TRAIL-induced apoptosis. Our findings provide that niclosamide could overcome resistance to TRAIL through up-regulating DR5 on the cell surface and down-regulating c-FLIP in cancer cells. Taken together, niclosamide may be an attractive candidate to overcome TRAIL resistance.

Plumbagin Suppresses α-MSH-Induced Melanogenesis in B16F10 Mouse Melanoma Cells by Inhibiting Tyrosinase Activity.

Recent studies have shown that plumbagin has anti-inflammatory, anti-allergic, antibacterial, and anti-cancer activities; however, it has not yet been shown whether plumbagin suppresses alpha-melanocyte stimulating hormone (α-MSH)-induced melanin synthesis to prevent hyperpigmentation. In this study, we demonstrated that plumbagin significantly suppresses α-MSH-stimulated melanin synthesis in B16F10 mouse melanoma cells. To understand the inhibitory mechanism of plumbagin on melanin synthesis, we performed cellular or cell-free tyrosinase activity assays and analyzed melanogenesis-related gene expression. We demonstrated that plumbagin directly suppresses tyrosinase activity independent of the transcriptional machinery associated with melanogenesis, which includes micropthalmia-associated transcription factor (MITF), tyrosinase (TYR), and tyrosinase-related protein 1 (TYRP1). We also investigated whether plumbagin was toxic to normal human keratinocytes (HaCaT) and lens epithelial cells (B3) that may be injured by using skin-care cosmetics. Surprisingly, lower plumbagin concentrations (0.5-1 µM) effectively inhibited melanin synthesis and tyrosinase activity but do not cause toxicity in keratinocytes, lens epithelial cells, and B16F10 mouse melanoma cells, suggesting that plumbagin is safe for dermal application. Taken together, these results suggest that the inhibitory effect of plumbagin to pigmentation may make it an acceptable and safe component for use in skin-care cosmetic formulations used for skin whitening.