Monosubstituted Acetophenone Thiosemicarbazones as Potent Inhibitors of Tyrosinase: Synthesis, Inhibitory Studies, and Molecular Docking

A set of 12 monosubstituted acetophenone thiosemicarbazone derivatives (TSCs) were synthesized and their inhibitory properties toward tyrosinase activity were tested. Moreover, their ability to inhibit melanogenesis in the B16F10 murine melanoma cell line was studied. In order to investigate the nature of interactions between the enzyme and the inhibitors, molecular docking to the active site was performed. TSCs 5, 6, 8, and 9 revealed a half maximal inhibitory concentration (IC50) below 1 µM. Compound 6 turned out to be the most potent tyrosinase inhibitor. All investigated compounds showed reversible inhibition of competitive or mixed type. The para-substituted TSCs had higher affinity for the enzyme as compared to their ortho- and meta-analogues. All investigated compounds inhibited melanin production in B16F10 cells at the micromolar level. Molecular docking showed that the sulfur atom of the thiourea moiety penetrates the active site and interacts with copper ions. The above outcomes might be helpful in the design of new tyrosinase inhibitors in the food and cosmetic industries.

Synthesis of Novel Cinnamides and a Bis Cinnamate Bearing 1,2,3-Triazole Functionalities with Antiproliferative and Antimetastatic Activities on Melanoma Cells

The present investigation describes the synthesis of novel cinnamides and a bis cinnamate bearing 1,2,3-triazole functionalities and investigation of their antiproliferative and antimetastatic effects on melanoma cells. The necessity for the development of new chemotherapeutic agents for melanoma treatment motivated this work. Sixteen derivatives were obtained with yields ranging from 23-81% and fully characterized by spectroscopic (1H and 13C nuclear magnetic resonance, infrared) and spectrometric high resolution mass spectrometry (HRMS) techniques. The derivatives were in vitro evaluated against B16-F10 murine melanoma cell line. The most effective compound (a bis cinnamate) (6b) reduced the melanoma cell viability, generated cell cycle arrest, and influenced the metastatic behavior of melanoma cells by decreasing migration, invasion, and colony formation. Based on these findings, it is believed that compound 6b may represent an interesting scaffold to be explored toward the development of new antimelanoma agents.

Inhibitory Effects of Polyphenol-Rich Plant Extracts on Melanogenesis in B16F10 Murine Melanoma Cell Line

Objectives Polyphenol compounds have been demonstrated to exhibit melanin inhibitory activities in previous studies. We studied 4 extracts of polyphenol-rich plants—rose petal (Rosa centifolia), pomegranate (Punica granatum L.), red orange (Citrus sinensis (L.) Osbeck), and acai berry (Euterpe oleracea Mart.)—for their inhibitory effects on melanogenesis as potential skin whitening agents. Methods Four plant extracts were supplemented into the culture of B16F10 murine melanoma cell line respectively to study their influences on the cell viability using CCK-8 assay and optimal concentrations were determined for the following melanogenesis inhibitory experiments. Thereafter, melanin concentration in the co-cultured B16F10 cells was measured by the NaOH lysis method. Arbutin and kojic acid were used as positive controls. Results Plant extracts showed different effects on cell viability. To achieve cell viability higher than 80%, the concentration of rose and pomegranate extracts should be lower than 1.56 and 3.12 μg/mL, respectively; whereas acai and red orange extracts should be within 50 and 100 μg/mL, respectively. In the range of concentrations adopted in this study, 1.56 μg/mL rose petal extract, 25 μg/mL red orange fruit extract and 25 μg/mL acai berry polyphenol extract showed a melanogenesis inhibitory effect of 33.29%, 29.13%, and 24.09%, respectively, which were greater than that of 50 μg/mL arbutin (10.27%, P < 0.05), but had no difference with 50 μg/mL kojic acid (29.96%). Pomegranate juice powder exhibited a similar inhibitory effect with arbutin, but weaker than kojic acid (P < 0.05). Conclusions Four polyphenol-rich plant extracts were studied for their melanin inhibitory activity in B16F10 melanoma cells in the current study. Red orange fruit extract and acai berry polyphenol extract exhibited stronger inhibitory activity on melanogenesis but milder influence on cell viability compared to the extracts of rose petal and pomegranate, therefore they could be used as potential candidates for developing new skin whitening agents. Funding Sources As a joint project, this research was cofounded by Heilongjiang Feihe Co., Ltd. and Beijing Technology and Business University.

Optical control of MAP kinase kinase 6 (MKK6) reveals that it has divergent roles in pro-apoptotic and anti-proliferative signaling

The selective pressure imposed by extrinsic death signals and stressors adds to the challenge of isolating and interpreting the roles of proteins in stress-activated signaling networks. By expressing a kinase with activating mutations and a caged lysine blocking the active site, we can rapidly switch on catalytic activity with light and monitor the ensuing dynamics. Applying this approach to MAP kinase 6 (MKK6), which activates the p38 subfamily of MAPKs, we found that decaging active MKK6 in fibroblasts is sufficient to trigger apoptosis in a p38-dependent manner. Both in fibroblasts and in a murine melanoma cell line expressing mutant B-Raf, MKK6 activation rapidly and potently inhibited the pro-proliferative extracellular signal–regulated kinase (ERK) pathway; to our surprise, this negative cross-regulation was equally robust when all p38 isoforms were inhibited. These results position MKK6 as a new pleiotropic signal transducer that promotes both pro-apoptotic and anti-proliferative signaling, and they highlight the utility of caged, light-activated kinases for dissecting stress-activated signaling networks.

Vitamin A Enhances Macrophages Activity Against B16-F10 Malignant Melanocytes: A New Player for Cancer Immunotherapy?

Background and objectives: The incidence of cutaneous melanoma has been increasing. Melanoma is an aggressive form of skin cancer irresponsive to radiation and chemotherapy, rendering this cancer a disease with poor prognosis: In order to surpass some of the limitations addressed to melanoma treatment, alternatives like vitamins have been investigated. In the present study, we address this relationship and investigate the possible role of vitamin A. Materials and Methods: We perform a co-culture assay using a macrophage cell model and RAW 264.7 from mouse, and also a murine melanoma cell line B16-F10. Macrophages were stimulated with both Escherichia coli lipopolysaccharides (LPS) as control, and also with LPS plus vitamin A. Results: Using B16-F10 and RAW 264.7 cell lines, we were able to demonstrate that low concentrations of vitamin A increase cytotoxic activity of macrophages, whereas higher concentrations have the opposite effect. Conclusion: These findings can constitute a new point of view related to immunostimulation by nutrients, which may be considered one major preventive strategy by enhancing the natural defense system of the body.

Nanoemulsion Strategy for Ursolic and Oleanic Acids Isolates from Plumeria Obtusa Improves Antioxidant and Cytotoxic Activity in Melanoma Cells

Background: Triterpenoids are an important class of natural bioactive products present in many medicinal plants. Objective: The aim of present study is to investigate the antioxidant and anticarcinogenic potential of Oleanolic Acid (OA) and Ursolic Acid (UA) on B16 murine melanoma cell line isolated from Plumeria obtusa, free and loaded in a nanoemulsion (NEm) system. Methods: The nanoemulsion was characterized by dynamic light scattering, transmission electron microscopy. The viscosity was also evaluated. The antioxidant activity was determined by the reduction of 2,2-diphenyl-2- picrylhydrazyl (DPPH) free radical. In vitro proliferation studies were determined using the sulforhodamine-B method. Results: OA/UA natural mixture exhibited high percentage of inhibition of DPPH (86.06% and 85.12%, with and without irradiation). Percentages of inhibition higher than 85% in samples with and without ultraviolet irradiation were recorded when loaded in the NEm system. The natural mixture incorporated into the NEm showed cytotoxic activity from 2.9 µM, whereas the free compounds from 17.4 µM. Conclusion: We conclude that these pentacyclic triterpenes loaded in a NEm system could be considered as a new potential tool for further investigation as anticancer agents.