Interruption of p38MAPK-MSK1-CREB-MITF-M pathway to prevent hyperpigmentation in the skin.

Background: Melanocortin 1 receptor (MC1R), a receptor of α-melanocyte-stimulating hormone (α-MSH), is exclusively present in melanocytes where α-MSH/MC1R stimulate melanin pigmentation through microphthalmia-associated transcription factor M (MITF-M). Toll-like receptor 4 (TLR4), a receptor of endotoxin lipopolysaccharide (LPS), is distributed in immune and other cell types including melanocytes where LPS/TLR4 activate transcriptional activity of nuclear factor (NF)-κB to express cytokines in innate immunity. LPS/TLR4 also up-regulate MITF-M-target melanogenic genes in melanocytes. Here, we propose a molecular target of antimelanogenic activity through elucidating inhibitory mechanism on α-MSH-induced melanogenic programs by benzimidazole-2-butanol (BI2B), an inhibitor of LPS/TLR4-activated transcriptional activity of NF-κB. Methods: Ultraviolet B (UV-B)-irradiated skins of HRM-2 hairless mice and α-MSH-activated melanocyte cultures were employed to examine melanogenic programs. Results: Topical treatment with BI2B ameliorated UV-B-irradiated skin hyperpigmentation in mice. BI2B suppressed the protein or mRNA levels of melanogenic markers, such as tyrosinase (TYR), MITF-M and proopiomelanocortin (POMC), in UV-B-exposed and pigmented skin tissues. Moreover, BI2B inhibited melanin pigmentation in UV-B-irradiated co-cultures of keratinocyte and melanocyte cells and that in α-MSH-activated melanocyte cultures. Mechanistically, BI2B inhibited the activation of cAMP response element-binding protein (CREB) in α-MSH-induced melanogenic programs and suppressed the expression of MITF-M at the promoter level. As a molecular target, BI2B primarily inhibited mitogen-activated protein kinase (MAPK) kinase 3 (MKK3)-catalyzed kinase activity on p38MAPK. Subsequently, BI2B interrupted downstream pathway of p38MAPK-mitogen and stress-activated protein kinase-1 (MSK1)-CREB-MITF-M, and suppressed MITF-M-target melanogenic genes, encoding enzymes TYR, TYR-related protein-1 (TRP-1) and dopachrome tautomerase (DCT) in melanin biosynthesis, and encoding proteins PMEL17 and Rab27A in the transfer of pigmented melanosomes to the overlaying keratinocytes in the skin. Conclusion: Targeting the MKK3-p38MAPK-MSK1-CREB-MITF-M pathway was suggested as a rationale to inhibit UV-B- or α-MSH-induced facultative melanogenesis and as a strategy to prevent acquired pigmentary disorders in the skin.

Marliolide Derivative Induces Melanosome Degradation via Nrf2/p62-Mediated Autophagy.

Nuclear factor erythroid 2-related factor 2 (Nrf2), which is linked to autophagy regulation and melanogenesis regulation, is activated by marliolide. In this study, we investigated the effect of a marliolide derivative on melanosome degradation through the autophagy pathway. The effect of the marliolide derivative on melanosome degradation was investigated in α-melanocyte stimulating hormone (α-MSH)-treated melanocytes, melanosome-incorporated keratinocyte, and ultraviolet (UV)B-exposed HRM-2 mice (melanin-possessing hairless mice). The marliolide derivative, 5-methyl-3-tetradecylidene-dihydro-furan-2-one (DMF02), decreased melanin pigmentation by melanosome degradation in α-MSH-treated melanocytes and melanosome-incorporated keratinocytes, evidenced by premelanosome protein (PMEL) expression, but did not affect melanogenesis-associated proteins. The UVB-induced hyperpigmentation in HRM-2 mice was also reduced by a topical application of DMF02. DMF02 activated Nrf2 and induced autophagy in vivo, evidenced by decreased PMEL in microtubule-associated proteins 1A/1B light chain 3B (LC3)-II-expressed areas. DMF02 also induced melanosome degradation via autophagy in vitro, and DMF02-induced melanosome degradation was recovered by chloroquine (CQ), which is a lysosomal inhibitor. In addition, Nrf2 silencing by siRNA attenuated the DMF02-induced melanosome degradation via the suppression of p62. DMF02 induced melanosome degradation in melanocytes and keratinocytes by regulating autophagy via Nrf2-p62 activation. Therefore, Nrf2 activator could be a promising therapeutic agent for reducing hyperpigmentation.

Stem Cell Factor-Inducible MITF-M Expression in Therapeutics for Acquired Skin Hyperpigmentation.

Rationale: Microphthalmia-associated transcription factor M (MITF-M) plays important roles in the pigment production, differentiation and survival of melanocytes. Stem cell factor (SCF) and its receptor KIT stimulate MITF-M activity via phosphorylation at the post-translation level. However, the phosphorylation shortens half-life of MITF-M protein over the course of minutes. Here, we investigated novel hypotheses of (i) whether SCF/KIT can regulate MITF-M activity through gene expression as the alternative process, and (ii) whether chemical inhibition of KIT activity can mitigate the acquired pigmentation in skin by targeting the expression of MITF-M. Methods: We employed melanocyte cultures in vitro and pigmented skin samples in vivo, and applied immunoblotting, RT-PCR, siRNA-based gene knockdown and confocal microscopy. Results: The protein and mRNA levels of MITF-M in epidermal melanocytes and the promoter activity of MITF-M in B16-F0 melanoma cells demonstrated that SCF/KIT could trigger the expression of MITF-M de novo, following the phosphorylation-dependent proteolysis of pre-existing MITF-M protein. SCF/KIT regulated the transcription abilities of cAMP-responsive element-binding protein (CREB), CREB-regulated co-activator 1 (CRTC1) and SRY-related HMG-box 10 (SOX10) but not ß-catenin at the MITF-M promoter. Meanwhile, chemical inhibition of KIT activity abolished SCF-induced melanin production in epidermal melanocyte cultures, as well as protected the skin from UV-B-induced hyperpigmentation in HRM2 mice or brownish guinea pigs, in which it down-regulated the expression of MITF-M de novo at the promoter level. Conclusion: We propose the targeting of SCF/KIT-inducible MITF-M expression as a strategy in the therapeutics for acquired pigmentary disorders.

Nuclear Entry of CRTC1 as Druggable Target of Acquired Pigmentary Disorder.

Rationale: SOX10 (SRY-related HMG-box 10) and MITF-M (microphthalmia-associated transcription factor M) restrict the expression of melanogenic genes, such as TYR (tyrosinase), in melanocytes. DACE (diacetylcaffeic acid cyclohexyl ester) inhibits melanin production in α-MSH (α-melanocyte stimulating hormone)-activated B16-F0 melanoma cells. In this study, we evaluated the antimelanogenic activity of DACE in vivo and elucidated the molecular basis of its action. Methods: We employed melanocyte cultures and hyperpigmented skin samples for pigmentation assays, and applied chromatin immunoprecipitation, immunoblotting, RT-PCR or siRNA-based knockdown for mechanistic analyses. Results: Topical treatment with DACE mitigated UV-B-induced hyperpigmentation in the skin with attenuated expression of MITF-M and TYR. DACE also inhibited melanin production in α-MSH- or ET-1 (endothelin 1)-activated melanocyte cultures. As a mechanism, DACE blocked the nuclear import of CRTC1 (CREB-regulated co-activator 1) in melanocytes. DACE resultantly inhibited SOX10 induction, and suppressed the transcriptional abilities of CREB/CRTC1 heterodimer and SOX10 at MITF-M promoter, thereby ameliorating facultative melanogenesis. Furthermore, this study unveiled new issues in melanocyte biology that i) KPNA1 (Impα5) escorted CRTC1 as a cargo across the nuclear envelope, ii) SOX10 was inducible in the melanogenic process, and iii) CRTC1 could direct SOX10 induction at the transcription level. Conclusion: We propose the targeting of CRTC1 as a unique strategy in the treatment of acquired pigmentary disorders.

α-Viniferin Improves Facial Hyperpigmentation via Accelerating Feedback Termination of cAMP/PKA-Signaled Phosphorylation Circuit in Facultative Melanogenesis.

Rationale: cAMP up-regulates microphthalmia-associated transcription factor subtype M (MITF-M) and tyrosinase (Tyro) in the generation of heavily pigmented melanosomes. Here, we communicate a therapeutic mechanism of hyperpigmented disorder by α-viniferin, an active constituent of Caragana sinica. Methods: We used cAMP-elevated melanocyte cultures or facial hyperpigmented patches for pigmentation assays, and applied immunoprecipitation, immunobloting, RT-PCR or reporter gene for elucidation of the antimelanogenic mechanism. Results:C. sinica or α-viniferin inhibited melanin production in α-melanocyte-stimulating hormone (α-MSH)-, histamine- or cell-permeable cAMP-activated melanocyte cultures. Moreover, topical application with C. sinica containing α-viniferin, a standard in quality control, decreased melanin index on facial melasma and freckles in patients. As a molecular basis, α-viniferin accelerated protein kinase A (PKA) inactivation via the reassociation between catalytic and regulatory subunits in cAMP-elevated melanocytes, a feedback loop in the melanogenic process. α-Viniferin resultantly inhibited cAMP/PKA-signaled phosphorylation of cAMP-responsive element-binding protein (CREB) coupled with dephosphorylation of cAMP-regulated transcriptional co-activator 1 (CRTC1), thus down-regulating expression of MITF-M or Tyro gene with decreased melanin pigmentation. Conclusion: This study assigned PKA inactivation, a feedback termination in cAMP-induced facultative melanogenesis, as a putative target of α-viniferin in the treatment of melanocyte-specific hyperpigmented disorder. Finally, C. sinica containing α-viniferin was approved as an antimelanogenic agent with topical application in skin hyperpigmentation.

Melanogenesis inhibitory pregnane glycosides from Cynanchum atratum.

Bioassay-guided fractionation of the methanolic extract from the roots of Cynanchum atratum has resulted in the isolation of three new pregnane glycosides (1-3) along with four known compounds (4-7). Their structures were identified by analysis of the spectroscopic data including extensive 2D NMR. All of the isolates were evaluated for their potential to inhibit the melanin production in α-melanocyte stimulating hormone (α-MSH)-activated B16 melanoma cells. Of these, compounds 4-7 dose-dependently inhibited the melanin production with the IC50 values ranging from 4 µM to 33 µM.

Sesquiterpenes from fruits of Torilis japonica with inhibitory activity on melanin synthesis in B16 cells.

Melanin, a dark macromolecular pigment, protects skin from harmful damage. However, abnormal accumulation is responsible for hyperpigmentation disorders. Melanogenesis inhibitors have therefore become important constituents in cosmetic products for depigmentation. Torilis japonica Decandolle (Umbelliferae) is a biennial plant which is distributed in East Asia. Fruits of this plant have been used for the treatment of skin disease and inflammation. In our previous study, torilin, a major sesquiterpene of T. japonica, showed an inhibitory effect on melanin production in α-melanocyte stimulating hormone (α-MSH)-activated B16 melanoma cells. Further extensive chromatographic separation resulted in thirteen compounds. On the basis of spectroscopic analysis, the structures of the compounds isolated were determined to be three new sesquiterpenes, viz. a guaiane-type, epoxytorilinol (1), a eudesmane-type, elematorilone (2) and a cadinane-type, cardinatoriloside (3), together with ten known sesquiterpenes (4-13). Of the compounds isolated, compounds 4-6 and 11-13 inhibited α-MSH-activated melanin production in B16 melanoma cells with IC50 values from 72.9 to 191.0 µM.

Piperidylmethyloxychalcone improves immune-mediated acute liver failure via inhibiting TAK1 activity.

Mice deficient in the toll-like receptor (TLR) or the myeloid differentiation factor 88 (MyD88) are resistant to acute liver failure (ALF) with sudden death of hepatocytes. Chalcone derivatives from medicinal plants protect from hepatic damages including ALF, but their mechanisms remain to be clarified. Here, we focused on molecular basis of piperidylmethyloxychalcone (PMOC) in the treatment of TLR/MyD88-associated ALF. C57BL/6J mice were sensitized with D-galactosamine (GalN) and challenged with Escherichia coli lipopolysaccharide (LPS, TLR4 agonist) or oligodeoxynucleotide containing unmethylated CpG motif (CpG ODN, TLR9 agonist) for induction of ALF. Post treatment with PMOC sequentially ameliorated hepatic inflammation, apoptosis of hepatocytes, severe liver injury and shock-mediated death in ALF-induced mice. As a mechanism, PMOC inhibited the catalytic activity of TGF-ß-activated kinase 1 (TAK1) in a competitive manner with respect to ATP, displaced fluorescent ATP probe from the complex with TAK1, and docked at the ATP-binding active site on the crystal structure of TAK1. Moreover, PMOC inhibited TAK1 auto-phosphorylation, which is an axis in the activating pathways of nuclear factor-κB (NF-κB) or activating protein 1 (AP1), in the liver with ALF in vivo or in primary liver cells stimulated with TLR agonists in vitro. PMOC consequently suppressed TAK1-inducible NF-κB or AP1 activity in the inflammatory injury, an early pathogenesis leading to ALF. The results suggested that PMOC could contribute to the treatment of TLR/MyD88-associated ALF with the ATP-binding site of TAK1 as a potential therapeutic target.

Caffeic Acid Cyclohexylamide Rescues Lethal Inflammation in Septic Mice through Inhibition of IκB Kinase in Innate Immune Process.

Targeting myeloid differentiation protein 2 (MD-2) or Toll-like receptor 4 (TLR4) with small molecule inhibitor rescues the systemic inflammatory response syndrome (SIRS) in sepsis due to infection with Gram-negative bacteria but not other microbes. Herein, we provided IκB kinase ß (IKKß) in innate immune process as a molecular target of caffeic acid cyclohexylamide (CGA-JK3) in the treatment of polymicrobial TLR agonists-induced lethal inflammation. CGA-JK3 ameliorated E. coli lipopolysaccharide (LPS, MD-2/TLR4 agonist)-induced endotoxic shock, cecal ligation and puncture (CLP)-challenged septic shock or LPS plus D-galactosamine (GalN)-induced acute liver failure (ALF) in C57BL/6J mice. As a molecular basis, CGA-JK3 inhibited IKKß-catalyzed kinase activity in a competitive mechanism with respect to ATP, displaced fluorescent ATP probe from the complex with IKKß, and docked at the ATP-binding active site on the crystal structure of human IKKß. Furthermore, CGA-JK3 inhibited IKKß-catalyzed IκB phosphorylation, which is an axis leading to IκB degradation in the activating pathway of nuclear factor-κB (NF-κB), in macrophages stimulated with TLR (1/2, 2/6, 4, 5, 7, 9) agonists from Gram-positive/negative bacteria and viruses. CGA-JK3 consequently interrupted IKKß-inducible NF-κB activation and NF-κB-regulated expression of TNF-α, IL-1α or HMGB-1 gene, thereby improving TLRs-associated redundant inflammatory responses in endotoxemia, polymicrobial sepsis and ALF.

The serum/PDGF-dependent "melanogenic" role of the minute level of the oncogenic kinase PAK1 in melanoma cells proven by the highly sensitive kinase assay.

We previously demonstrated that the oncogenic kinase PAK4, which both melanomas and normal melanocytes express at a very high level, is essential for their melanogenesis. In the present study, using the highly sensitive "Macaroni-Western" (IP-ATP-Glo) kinase assay, we investigated the melanogenic potential of another oncogenic kinase PAK1, which melanoma (B16F10) cells express only at a very minute level. After transfecting melanoma cells with PAK1-shRNA for silencing PAK1 gene, melanin content, tyrosinase activity, and kinase activity of PAK1 were compared between the wild-type and transfectants. We found that (i) PAK1 is significantly activated by melanogenic hormones such as IBMX (3-isobutyl-1-methyl xanthine) and α-MSH (melanocyte-stimulating hormone), (ii) silencing the endogenous PAK1 gene in melanoma cells through PAK1-specific shRNA reduces both melanin content and tyrosinase activity in the presence of both serum and melanogenic hormones to the basal level, (iii) the exogenously added wild-type PAK1 in the melanoma cells boosts the α-MSH-inducible melanin level by several folds without affecting the basal, and (iv) α-MSH/IBMX-induced melanogenesis hardly takes place in the absence of either serum or PAK1, clearly indicating that PAK1 is essential mainly for serum- and α-MSH/IBMX-dependent melanogenesis, but not the basal, in melanoma cells. The outcome of this study might provide the first scientific basis for explaining why a wide variety of herbal PAK1-blockers such as CAPE (caffeic acid phenethyl ester), curcumin and shikonin in cosmetics are useful for skin-whitening.

p21-activated kinase 4 critically regulates melanogenesis via activation of the CREB/MITF and ß-catenin/MITF pathways.

p21-activated kinase 4 (PAK4) regulates a wide range of cellular events, including cytoskeletal remodeling, cell growth, and survival. Our previous study identified PAK4 as a key regulator of cAMP-response element-binding protein (CREB) that acts upstream of microphthalmia-associated transcription factor (MITF), a master transcription factor in melanogenesis. We therefore investigated the role of PAK4 in melanogenesis. Melanocytes express both PAK2 and PAK4 isoforms, but only RNA interference knockdown of PAK4 significantly influenced α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis in B16 melanoma cells. Consistent with this result, PAK4 inhibition by PF3758309, a potent ATP-competitive inhibitor of PAKs, suppressed not only α-MSH-induced melanogenesis in B16 melanoma and human epithelial melanocyte cells but also UVB-induced melanogenesis in the skin of melanin-possessing hairless mice (HRM-2) in a dose-dependent manner. Inhibition of PAK4 over several days markedly decreased the levels of CREB, MITF, and tyrosinase in both HRM-2 mice and B16 melanoma cells. Moreover, PAK4 knockdown and inhibition suppressed α-MSH-stimulated ß-catenin phosphorylation at serine 675 (S675) but enhanced phosphorylation at S33/37, an indicator for ubiquitination-dependent proteolysis. Together, our results provide evidence that PAK4 promotes α-MSH/UVB-induced melanogenesis via the CREB and Wnt/ß-catenin signaling pathways and suggest that PAK4 may be a potential therapeutic target in pigmentation disorders.

Non-muscle myosin II regulates neuronal actin dynamics by interacting with guanine nucleotide exchange factors.

BACKGROUND: Non-muscle myosin II (NM II) regulates a wide range of cellular functions, including neuronal differentiation, which requires precise spatio-temporal activation of Rho GTPases. The molecular mechanism underlying the NM II-mediated activation of Rho GTPases is poorly understood. The present study explored the possibility that NM II regulates neuronal differentiation, particularly morphological changes in growth cones and the distal axon, through guanine nucleotide exchange factors (GEFs) of the Dbl family. PRINCIPAL FINDINGS: NM II colocalized with GEFs, such as ßPIX, kalirin and intersectin, in growth cones. Inactivation of NM II by blebbistatin (BBS) led to the increased formation of short and thick filopodial actin structures at the periphery of growth cones. In line with these observations, FRET analysis revealed enhanced Cdc42 activity in BBS-treated growth cones. BBS treatment also induced aberrant targeting of various GEFs to the distal axon where GEFs were seldom observed under physiological conditions. As a result, numerous protrusions and branches were generated on the shaft of the distal axon. The disruption of the NM II-GEF interactions by overexpression of the DH domains of ßPIX or Tiam1, or by ßPIX depletion with specific siRNAs inhibited growth cone formation and induced slender axons concomitant with multiple branches in cultured hippocampal neurons. Finally, stimulation with nerve growth factor induced transient dissociation of the NM II-GEF complex, which was closely correlated with the kinetics of Cdc42 and Rac1 activation. CONCLUSION: Our results suggest that NM II maintains proper morphology of neuronal growth cones and the distal axon by regulating actin dynamics through the GEF-Rho GTPase signaling pathway.

Melanogenesis inhibitory daphnane diterpenoids from the flower buds of Daphne genkwa.

Two new daphnane-type diterpene esters, daphneresiniferins A (1) and B (2), along with seven known diterpenes, yuanhuacine (3), yuanhuadine (4), yuanhuahine (5), genkwadaphnin (6), genkwanine A (7), genkwanine F (8), and genkwanine H (9), were isolated from the methanol extract of the flower buds of Daphne genkwa. Their structures were elucidated on the basis of spectroscopic methods, especially 2D NMR spectra such as HMQC, HMBC, and NOESY. All the isolates were evaluated for their inhibitory effects of the melanogenesis against α-melanocyte stimulating hormone (α-MSH)-activated B16 melanoma cells.

cAMP-binding site of PKA as a molecular target of bisabolangelone against melanocyte-specific hyperpigmented disorder.

Microphthalmia-associated transcription factor (MITF) is inducible in response to cAMP and has a pivotal role in the melanocyte-specific expression of tyrosinase for skin pigmentation. Here we suggest that the cAMP-binding site of protein kinase A (PKA) is a target in the inhibition of the melanogenic process in melanocytes, as evidenced from the molecular mechanism of small molecules such as bisabolangelone (BISA) and Rp-adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS). BISA is a sesquiterpene constituent of Angelica koreana, a plant of the Umbelliferae family, whose roots are used as an alternative medicine. BISA competitively inhibited cAMP binding to the regulatory subunit of PKA and fitted into the cAMP-binding site on the crystal structure of PKA under the most energetically favorable simulation. In α-melanocyte-stimulating hormone (α-MSH)-activated melanocytes, BISA and Rp-cAMPS nullified cAMP-dependent PKA activation, dissociating catalytic subunits from an inactive holoenzyme complex. They resultantly inhibited cellular phosphorylation of the cAMP-responsive element-binding protein (CREB) or another transcription factor SOX9, thus downregulating the expression of MITF or the tyrosinase gene with decreased melanin production. Taken together, this study defined the antimelanogenic mechanism of BISA or Rp-cAMPS with a notable implication of the cAMP-binding site of PKA as a putative target ameliorating melanocyte-specific hyperpigmented disorder.

Melanogenesis inhibitory bisabolane-type sesquiterpenoids from the roots of Angelica koreana.

Bioactivity-guided isolation of the methanolic extract of the roots of Angelica koreana led to the isolation of four new bisabolane-type sesquiterpenoids, osterivolones A-D (1-4) together with four known compounds, bisabolangelone (5), decursinol angelate (6), psoralen (7), and falcarindiol (8). Their structures were elucidated on the basis of spectroscopic data interpretation, especially 2D NMR spectra such as HMQC, HMBC, and NOESY. All compounds were evaluated for their inhibitory effects of the melanogenesis against α-melanocyte stimulating hormone (α-MSH)-activated B16 melanoma cells.

Hypopigmenting activity of bisabolangelone isolated from Angelica koreana Maxim. in α-melanocyte stimulating hormone-activated B16 or melan-a cells.

Tyrosinase is a key enzyme in the biosynthetic pathway of melanin pigments. Abnormal accumulation of melanin pigments causes melasma, freckles, and senile lentigo, which can be substantially ameliorated by treatment with arbutin or other tyrosinase inhibitors. In this study, roots of Angelica koreana Maxim. (Umbelliferae) inhibited melanin production in α-melanocyte stimulating hormone ( α-MSH)-activated B16 melanoma cells or melan-a melanocytes. To elucidate the hypopigmenting principle of A. koreana, the plant extracts were subjected to bioassay-guided phytochemical analysis, resulting in the identification of bisabolangelone. Bisabolangelone dose-dependently inhibited α-MSH-induced melanin production in B16 or melan-a cells with IC(15) values of 9-17 µM. The positive control arbutin also inhibited melanin production in B16 cells with an IC(50) value of 317 µM. Bisabolangelone suppressed α-MSH-inducible protein levels of tyrosinase in B16 cells but could not significantly inhibit the catalytic activity of cell-free tyrosinase. Taken together, this study indicates that bisabolangelone is the primary hypopigmenting principle of A. koreana and may have pharmacological potential in the melanin-associated hyperpigmentation disorders.

Refinement of the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity.

In order to define the structural requirements of quinazoline-2(1H)-thiones 1 for their inhibitory activity on melanogenesis, a novel series of 3,4-dihydroquinazoline-2(1H)-thiones (3a-h) were prepared and screened for their melanogenesis inhibition on melanoma B16 cell line under the stimulant of alpha-MSH. The anti-melanogenesis activity of 3 is mainly mediated by the hydrogen bonding ability of thioamide unit in addition to complexation ability of thione and the hydrophobic binding power of side chain substitutions at 3-position. Thus, the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity could be refined as 3-hydrophobic substituted quinazolinethione.

Novel benzo[d]imidazole-2(3H)-thiones as potent inhibitors of the alpha-melanocyte stimulating hormone induced melanogenesis in melanoma B16 cells.

In order to determine the optimum size of heterocycle of lead compound 1 (6-methyl-3-phenethyl-3,4-dihydro-1H-quinoline-2-thione; IC(50)=0.8 microM) for inhibition of melanogenesis, we have synthesized and evaluated some benzimdazole-2(3H)-thiones 5a-e. The preliminary bioassay has shown that the benzimdazole-2(3H)-thione motif of 5 is essential structural unit for their inhibitory activity. Among all thiones 5a-e, the compound 5d strongly inhibited the formation of melanin with IC(50) value of 1.3 microM.

Structural requirement(s) of N-phenylthioureas and benzaldehyde thiosemicarbazones as inhibitors of melanogenesis in melanoma B 16 cells.

In order to define the structural requirements of phenylthiourea (PTU), a series of thiourea and thiosemicarbazone analogs were prepared and evaluated as inhibitors of melanogenesis in melanoma B16 cells. The most potent analog was 2-(4-tert-butylbenzylidene)hydrazinecarbothioamide (1u) with an IC(50) value of 2.7 microM in inhibition of melanogenesis. The structure for potent inhibitory activity of these derivatives are required with the direct connection of pi-planar structure to thiourea without steric hinderance in PTU derivatives and the hydrophobic substituent at para position in case of semicarbazones.

Evaluation of 3,4-dihydroquinazoline-2(1H)-thiones as inhibitors of alpha-MSH-induced melanin production in melanoma B16 cells.

Novel 3,4-dihydroquinazoline-2(1H)-thiones (QNTs) 1 were found to be potent inhibitors of alpha-MSH-induced melanin production. The effect of QNTs to inhibit melanin formation in B16 melanoma cells was screened in the presence of alpha-MSH. In defining the mechanism of activity, the effects on tyrosinase activity, on tyrosinase synthesis and on the depigmentation of melanin were evaluated. QNTs did not affect the catalytic activity of tyrosinase, but rather acted as an inhibitor of tyrosinase synthesis.