Yun Jung Park

Inhibitory Effect of mTOR Activator MHY1485 on Autophagy: Suppression of Lysosomal Fusion

Autophagy is a major degradative process responsible for the disposal of cytoplasmic proteins and dysfunctional organelles via the lysosomal pathway. During the autophagic process, cells form double-membraned vesicles called autophagosomes that sequester disposable materials in the cytoplasm and finally fuse with lysosomes. In the present study, we investigated the inhibition of autophagy by a synthesized compound, MHY1485, in a culture system by using Ac2F rat hepatocytes. Autophagic flux was measured to evaluate the autophagic activity. Autophagosomes were visualized in Ac2F cells transfected with AdGFP-LC3 by live-cell confocal microscopy. In addition, activity of mTOR, a major regulatory protein of autophagy, was assessed by western blot and docking simulation using AutoDock 4.2. In the result, treatment with MHY1485 suppressed the basal autophagic flux, and this inhibitory effect was clearly confirmed in cells under starvation, a strong physiological inducer of autophagy. The levels of p62 and beclin-1 did not show significant change after treatment with MHY1485. Decreased co-localization of autophagosomes and lysosomes in confocal microscopic images revealed the inhibitory effect of MHY1485 on lysosomal fusion during starvation-induced autophagy. These effects of MHY1485 led to the accumulation of LC3II and enlargement of the autophagosomes in a dose- and time- dependent manner. Furthermore, MHY1485 induced mTOR activation and correspondingly showed a higher docking score than PP242, a well-known ATP-competitive mTOR inhibitor, in docking simulation. In conclusion, MHY1485 has an inhibitory effect on the autophagic process by inhibition of fusion between autophagosomes and lysosomes leading to the accumulation of LC3II protein and enlarged autophagosomes. MHY1485 also induces mTOR activity, providing a possibility for another regulatory mechanism of autophagy by the MHY compound. The significance of this study is the finding of a novel inhibitor of autophagy with an mTOR activating effect.

Design and synthesis of 5-(substituted benzylidene)thiazolidine-2,4-dione derivatives as novel tyrosinase inhibitors.

In continuing our search for novel tyrosinase inhibitors, a series of 5-(substituted benzylidene)thiazolidine-2,4-diones were rationally designed and synthesized, and their inhibitory effects on mushroom tyrosinase activity were evaluated. Twelve target compounds 2a-2l were designed and synthesized based on the structural characteristics of N-phenylthiourea, a tyrosinase inhibitor, and tyrosine and L-DOPA, the natural substrates of tyrosinase. Among them, (Z)-5-(4-hydroxybenzylidene)thiazolidine-2,4-dione (2a) and (Z)-5-(3-hydroxy-4-methoxybenzylidene)thiazolidine-2,4-dione (2f) exhibited much higher tyrosinase inhibitory activities, with IC(50) values of 13.36 and 9.87 μM, respectively, than kojic acid (IC(50) = 24.72 μM). Kinetic analysis of tyrosinase inhibition revealed that 2a and 2f are competitive inhibitors of mushroom tyrosinase. In addition, through prediction of the potato catechol oxidase tertiary structure and simulation of docking with compounds 2a and 2f using DOCK6, we found that these inhibitors likely bind to the active site of the enzyme. Docking simulation results suggested that 2a and 2f have high binding affinities with potato catechol oxidase. In addition, compounds 2a and 2f effectively inhibited tyrosinase activity and reduced melanin levels in B16 cells treated with α-melanocyte-stimulating hormone (α-MSH). These data strongly suggest that compounds 2a and 2f suppress the production of melanin via the inhibition of tyrosinase activity.

Evaluation of in vitro and in vivo anti-melanogenic activity of a newly synthesized strong tyrosinase inhibitor (E)-3-(2,4 dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP).

BACKGROUND Tyrosinase inhibitors have become increasingly important because of their ability to inhibit the synthesis of the pigment melanin. A search for new agents with strong tyrosinase activity led to the synthesis of the tyrosinase inhibitor (E)-3-(2,4-dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP). METHODS The inhibitory effect of 3-DBP on tyrosinase activity and melanin production was examined in murine melanoma B16F10 cells. Additional experiments were performed using HRM2 hairless mice to demonstrate the effects of 3-DBP in vivo. RESULTS The novel compound, 3-DBP, showed an inhibitory effect against mushroom tyrosinase (IC50=0.53 μM), which indicated that it was more potent than the well-known tyrosinase inhibitor kojic acid (IC50=8.2 μM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), 3-DBP also inhibited murine tyrosinase activity, which in turn induced a decrease in melanin production in these cells. The anti-melanogenic effect of 3-DBP was further verified in HRM2 hairless mice. The skin-whitening index (L value) of HRM2 hairless mice treated with 3-DBP before irradiation with UVB was greater than that of UVB-irradiated mice that were not treated with 3-DBP. GENERAL SIGNIFICANCE The newly synthesized 3-DBP has a potent inhibitory effect on tyrosinase. In addition to an in vitro investigation of the effects of 3-DBP on tyrosinase, in vivo studies using an HRM2 hairless mouse model demonstrated the anti-melanogenic potency of 3-DBP. Our newly synthesized 3-DBP showed efficient tyrosinase inhibitory effect in vivo and in vitro. Our finding suggests that 3-DBP can be an effective skin-whitening agent.

Analogs of 5-(substituted benzylidene)hydantoin as inhibitors of tyrosinase and melanin formation

BACKGROUND Many tyrosinase inhibitors find application in cosmetics and pharmaceutical products for the prevention of the overproduction of melanin in the epidermis. A series of 5-(substituted benzylidene)hydantoin derivatives 2a-2k were prepared, and their inhibitory activities toward tyrosinase and melanin formation were evaluated. METHODS The structures of the compounds were established using (1)H and (13)C NMR spectroscopy and mass spectral analyses. All the synthesized compounds were evaluated for their mushroom tyrosinase inhibition activity. RESULTS The best results were obtained for compound 2e which possessed hydroxyl group at R(2) and methoxy group at R(3), respectively. We predicted the tertiary structure of tyrosinase, simulated its docking with compound 2e and confirmed that this compound interacts strongly with mushroom tyrosinase residues as a competitive tyrosinase inhibitor. In addition, we found that 2e inhibited melanin production and tyrosinase activity in B16 cells. CONCLUSIONS Compound 2e could be considered as a promising candidate for preclinical drug development in skin hyperpigmentation applications. GENERAL SIGNIFICANCE This study will enhance understanding of the mechanism of tyrosinase inhibition and will contribute to the development of effective drugs for use hyperpigmentation.

Characterization of a novel tyrosinase inhibitor, (2RS,4R)-2-(2,4-dihydroxyphenyl)thiazolidine-4-carboxylic acid (MHY384)

BACKGROUND We synthesized (2RS,4R)-2-(2,4-dihydroxyphenyl)thiazolidine-4-carboxylic acid (MHY384) as a potential tyrosinase inhibitor and investigated its antityrosinase activity. METHODS The structure of MHY384 was established using (1)H and (13)C NMR spectroscopy and mass spectral analyses. To investigate dual mechanisms of action of MHY384 for the inhibition of melanin synthesis, we confirmed the inhibitory effect of tyrosinase catalytic activity of MHY384. Then, we confirmed the inhibitory effect of MHY384 on transcription of tyrosinase mRNA through alpha-MSH-induced cAMP-PKA-MITF signaling. In addition, we supported the inhibitory mechanism of MHY384 against tyrosinase using a kinetic study and docking programs. RESULTS To determine how MHY384 regulates melanogenesis, we measured melanin levels and expression of the genes for microphthalmia-associated transcription factor (MITF) and tyrosinase in α-melanocyte-stimulating hormone (α-MSH)-induced B16F10 melanoma cells. MHY384 potently inhibited tyrosinase activity and melanin production in B16F10 melanoma cells. Through docking models, we were able to construct the tertiary structure of mushroom tyrosinase and simulate its docking with MHY384. The result supports that MHY384 strongly interacts with tyrosinase residues in the active site and it can directly inhibit tyrosinase. To investigate additional mechanisms of action of MHY384, we confirmed that the inhibition of tyrosinase activity was found to be due to the modulation of the expression of tyrosinase and its transcription factor, MITF, through cAMP, which regulates protein kinase A. CONCLUSIONS This study strongly indicates that the depigmenting effect of MHY384 results from the down-regulation of MITF and tyrosinase through direct tyrosinase inhibition. GENERAL SIGNIFICANCE Our findings suggest that MHY384 can be an effective skin-whitening agent.

Benzylidene-linked thiohydantoin derivatives as inhibitors of tyrosinase and melanogenesis: importance of the β-phenyl-α,β-unsaturated carbonyl functionality

Based on the structural characteristics of the heterocyclic scaffolds of substituted benzylidene-hydantoin, -pyrrolidinedione, and -thiazolidinedione derivatives with potent tyrosinase inhibitory activity, substituted benzylidene derivatives with a 2-thiohydantoin heterocyclic scaffold were synthesized by modified Knoevenagel condensation between benzaldehydes and 2-thiohydantoin with a view toward producing more potent, safer tyrosinase inhibitors capable of being utilized in the agricultural, food, cosmetics, and pharmaceutical industries. Of the twelve compounds synthesized, three compounds, 2c, 2d and 2i, exhibited even more potent inhibitory activities against mushroom tyrosinase than kojic acid or resveratrol, which are well-known potent tyrosinase inhibitors. The inhibitory pattern of compounds with a thiohydantoin template differed from that of compounds with a hydantoin, pyrrolidinedione, or thiazolidine scaffold, probably because of the loss of the hydrogen bonding ability of the thiocarbonyl group of thiohydantoin. Considering the high tyrosinase inhibitory activities of 5-(substituted benzylidene)thiohydantoin derivatives, the thiohydantoin template is considered a near perfect surrogate for hydantoin, pyrrolidinedione, and thiazolidinedione scaffolds. (Z)-5-(2,4-Dihydroxybenzylidene)-2-thiohydantoin (2d, IC50 = 1.07 ± 2.30 μM) had 24 times the inhibitory effect of resveratrol (IC50 = 26.63 ± 0.55 μM) and 18 times that of kojic acid (IC50 = 19.69 ± 4.90 μM) against mushroom tyrosinase and showed anti-melanogenesis through the inhibition of tyrosinase activity in B16 cells with no appreciable cytotoxicity, which suggests that 2d is a promising candidate for the development of safer and more potent fruit and food browning preventatives and skin-lightening medicines. This result and our previous data indicate that it is the “β-phenyl-α,β-unsaturated carbonyl” group that is essential for potent anti-tyrosinase activity.

Synthesis and biological activity of hydroxy substituted phenyl-benzo[d]thiazole analogues for antityrosinase activity in B16 cells

In this study, we synthesized hydroxy and/or alkoxy substituted phenyl-benzo[d]thiazole derivatives using substituted benzaldehydes and 2-aminothiophenol in MeOH. The structures of these compounds were established by (1)H and (13)CNMR and mass spectral analyzes. All synthesized compounds were evaluated for their mushroom tyrosinase inhibition activity. Out the 12 generated compounds, 2a and 2d exhibited much higher tyrosinase inhibition activity (45.36-73.07% and 49.94-94.17% at 0.01-20 μM, respectively) than kojic acid (9.29-50.80% at 1.25-20 μM), a positive control. The cytotoxicity of 2a and 2d was evaluated using B16 cells and the compounds were found to be nontoxic. Compounds 2a and 2d were also demonstrated to be potent mushroom tyrosinase inhibitors, displaying IC(50) values of 1.14±0.48 and 0.01±0.0002 μM, respectively, compared with kojic acid, which has an IC(50) value of 18.45±0.17 μM. We also predicted the tertiary structure of tyrosinase, simulated the docking with compounds 2a and 2d and confirmed that the compounds strongly interact with mushroom tyrosinase residues. Kinetic plots showed that 2a and 2d are competitive tyrosinase inhibitors. Substitutions with a hydroxy group at R(3) or both R(3) and R(1) of the phenyl ring indicated that these groups play a major role in the high binding affinity to tyrosinase. We further found that compounds 2a and 2d inhibit melanin production and tyrosinase activity in B16 cells. These results may assist in the development of new potent tyrosinase inhibitors against hyperpigmentation.

Synthesis and biological activity of hydroxybenzylidenyl pyrrolidine-2,5-dione derivatives as new potent inhibitors of tyrosinase

In this study, we describe the synthesis and tyrosinase inhibitory activity of a new family of hydroxybenzylidenyl pyrrolidine-2,5-dione compounds. Among them, compound 3f (HMP) exhibited the highest inhibition, 83.87%, at a concentration of 20 μM, on the L-DOPA oxidase activity of mushroom tyrosinase. We also predicted the tertiary structure of tyrosinase, simulated its docking with HMP and confirmed that HMP strongly interacts with tyrosinase residues. This result suggested that the binding activity of HMP with tyrosinase could be high. Based on these results, we determined the IC50 value for HMP inhibition of mushroom tyrosinase activity. HMP inhibited mushroom tyrosinase with an IC50 value of 2.23 ± 0.44 μM, which is more potent than the anti-tyrosinase activity of kojic acid (IC50 = 20.99 ± 1.80 μM), a well-known tyrosinase inhibitor. Kinetic analysis of tyrosinase inhibition revealed that HMP is a competitive inhibitor (Ki = 4.24 × 10−7 M at 1.25 μM and Ki = 1.82 × 10−6 M at 20 μM). HMP also inhibited melanin production and tyrosinase activity in B16F10 melanoma cells (B16 cells). These data strongly suggest that HMP can suppress the production of melaninvia the modulation of tyrosinase activity.

Design, synthesis, and evaluation of (E)-N-substituted benzylidene–aniline derivatives as tyrosinase inhibitors

We attempted to design and synthesize (E)-N-substituted benzylidene-hydroxy or methoxy-aniline derivatives and to evaluate their inhibitory effect on tyrosinase activity and anti-melanogenesis activity in murine B16F10 melanoma cells. Derivatives with a 4-methoxy- or 4-hydroxy-anilino group exerted more potent inhibition against mushroom tyrosinase than those with a 2-hydroxyanilino group. (E)-4-((4-Hydroxyphenylimino)methyl)benzene-1,2-diol exhibited the most potent and non-competitive inhibition on mushroom tyrosinase showing an IC(50) of 17.22 ± 0.38 μM and being more effective than kojic acid (51.11 ± 1.42 μM). This compound decreased melanin production stimulated by the alpha-melanocyte-stimulating hormone and inhibited murine tyrosinase activity in a dose-dependent manner. Therefore, we propose (E)-4-((4-hydroxyphenylimino)methyl)benzene-1,2-diol as a new candidate of potent tyrosinase inhibitors that could be used as therapeutic agent with safe skin-whitening efficiency.

De novo tyrosinase inhibitor: 4-(6,7-Dihydro-5H-indeno[5,6-d]thiazol-2-yl)benzene-1,3-diol (MHY1556)

In this study, we have synthesized and studied de novo tyrosinase inhibitor, MHY1556, which showed significantly better efficacy than other pre-existing tyrosinase inhibitors in vitro experiments. The IC50 value of MHY1556 was 0.50μM which was significantly lower than that of kojic acid (IC50=53.95μM), which is a well-known tyrosinase inhibitor and was used as a positive control in this study. We predicted the tertiary structure of tyrosinase, simulated the docking with compound MHY1556 and confirmed that the compound strongly interacts with mushroom tyrosinase residues. Substitutions with a hydroxy group at both R1 and R3 of the phenyl ring indicated that these groups play a major role in the high binding affinity to tyrosinase, especially through the hydrogen bonding interaction of the hydroxyl group at R1 with GLY281. In addition, MHY1556 showed concentration-dependent inhibitory effects in melanin content assay where B16F10 melanoma cells were treated with α-melanocyte stimulating hormone (α-MSH), and also there is no significant cytotoxicity of this compound in cell viability assay conducted in B16F10 melanoma cells. The tyrosinase activity assay results with MHY1556 also support its potent inhibitory effects. Therefore, our data strongly suggest MHY1556 suppresses the melanogenesis via a tyrosinase inhibitory effect.