Inhibition of melanogenesis as a radiation sensitizer for melanoma therapy

Copper in melanoma: At the crossroad of protumorigenic and anticancer roles

Copper is an essential micronutrient that is a cofactor for various enzymes involved in multiple cellular processes. Melanoma patients have high serum copper levels, and elevated copper concentrations are found in melanoma tumors. Copper influences the activity of several melanoma-related proteins involved in cell survival, proliferation, pigmentation, angiogenesis, and metastasis. Targeting these processes with copper chelators has shown efficacy in reducing tumor growth and overcoming drug resistance. In contrast, excessive copper can also have detrimental effects when imported into melanoma cells. Multiple distinct cellular effects of copper overload, including the induction of different types of cell death, have been reported. Cuproptosis, a novel type of copper-dependent cell death, has been recently described and is associated with the metabolic phenotype. Melanoma cells can switch between glycolysis and oxidative phosphorylation, which are crucial for tumor growth and drug resistance. In this respect, metabolic plasticity might be exploited for the use of copper-delivery strategies, including repurposing of disulfiram, which is approved for the treatment of noncancer patients. In addition, the development of nanomedicines can improve the targeted delivery of copper to melanoma cells and enable the use of these drugs alone or in combination as copper has been shown to complement targeted therapy and immunotherapy in melanoma cells. However, further research is needed to explore the specific mechanisms of both copper restriction and excess copper-induced processes and determine effective biomarkers for predicting treatment sensitivity in melanoma patients. In this review, we discuss the dual role of copper in melanoma biology.

Prognostic significance of melanogenesis pathway and its association with the ultrastructural characterisation of melanosomes in uveal melanoma

BACKGROUND

Pigmentation could be a relevant prognostic factor in uveal melanoma (UM) development. Microphthalmia-associated transcription factor (MITF) regulates melanin synthesis by activating tyrosinase-related protein 2 (TYRP2) and silver protein (SILV) that induce the melanogenesis pathway. Although their oncogenic potential has been observed in various malignancies but has not been investigated in UM Asian population. Our aim is to study the ultrastructure of melanosomes and the prognostic significance of pigmentation markers such as TYRP2, MITF and SILV in UM.

METHODS

Transmission electron microscopy was performed to compare the ultrastructure of melanosomes in the normal choroid and UM cases. Immunoexpression of TYRP2, SILV and MITF was analysed in 82 UM samples. The mRNA expression level of all genes was measured in 70 UM cases. A statistical correlation was performed to determine the prognostic significance of all markers.

RESULTS

Premelanosomes and mature melanosomes undergoing dedifferentiation were observed in high-pigmented UM cases as compared with low-pigmented UM cases. Seventy per cent of UM cases showed high SILV expression while TYRP2 and MITF expression was present in 58% and 56% of cases, respectively. At the mRNA level, upregulation of TYRP2, SILV and MITF markers was seen in around 50% of UM cases, which was statistically significant with high pigmentation. Reduced metastatic-free survival was statistically significant with the MITF protein expression.

CONCLUSION

Our results demonstrated that ultrastructural changes in melanosomes and high expression of TYRP2, MITF and SILV could dysregulate the melanogenesis pathway and might be responsible for the aggressive behaviour of UM.

Small-Molecule Tyrosinase Inhibitors for Treatment of Hyperpigmentation

Increasing attention is being focused on skin health currently, especially the excessive deposition of melanin in the skin. Tyrosinase, the rate-limiting enzyme in melanin biosynthesis, is a crucial enzyme in melanin synthesis. However, existing tyrosinase inhibitors pose some degree of toxicity to humans. Therefore, the development of more efficient and low-toxicity tyrosinase inhibitors is urgently needed. This review briefly depicts the melanin biosynthesis process and the crystal structure and catalytic mechanism of tyrosinase. The latest research progress regarding small-molecule tyrosinase inhibitors is also reviewed. Moreover, the structure-function relationships are analyzed and summarized. This is expected to provide new and more scientific insights to enable researchers to explore safer and more potent tyrosinase inhibitors.

Inhibitory Effect on the Tyrosinase Activity and Low Cytotoxicity of Monounsaturated Long-Chain Chelating Fatty Ester

In the present study, 5-Hydroxy-2-(Oleoyloxymethyl) -4H-pyran-4-one (KMO 3), and their chelated with Cu(II) and Fe(III) ions were synthesized to explore their inhibitory activity against tyrosinase and cytotoxicity. To this end, the structures of the obtained compounds were confirmed by ATR/FT-IR, 13C and 1H-NMR, and UV-vis techniques. The results show that chelating fatty ester presents the bands at 1567m, 1511w cm-1 attributed to the coordinated carbonyl (Cu(II)←[O=C]2), and the bands at 1540m, 1519m cm-1 which were attributed to the coordinated carbonyl (Fe(III)←[O=C]3). The inhibitory effect of chelating Oleic acid 2 (inhibition 68.3% ± 4.5) showed a factor of 19 times higher than free fatty acid (3.6% ± 3.2). IC50 Anti-tyrosinase activity of the Kojic acid 1 and KMO 3 compounds were 62.8 ± 6.6 µM and 77.6 ± 4.3 µM. The IC50 and IC90 values for tyrosinase inhibitory activity for chelating fatty ester and their complexes are values > 400 µM. Finally, the assay with the series showed no hemolytic activity (EC50> 250 μg mL-1), and not cytotoxic to B16F10, ACP-02, and human dermal fibroblast cells at 100 µM and showed no hemolytic potential at the concentration of IC50 250 µM.

Investigating the Local Effectiveness of Carbon Ion Radiotherapy for Unresectable Female Genital Tract Melanomas: A Preliminary Real-World Study

Background/Objectives: Primary gynecological melanomas are rare malignancies with lower survival rates compared to cutaneous melanomas. Both preclinical and clinical data support the evidence that mucosal melanomas are photon-radioresistant but responsive to carbon ion radiotherapy (CIRT). The aim of this study is to assess, in a real-world cohort, the effectiveness and tolerability of radical CIRT in patients with inoperable gynecological mucosal melanoma. Methods: This is a real-world study aimed to assess the effectiveness and the safety of CIRT in this setting. We defined as the primary endpoints the objective response rate (ORR) and the clinical benefit (CB). The secondary endpoints included the actuarial local control rate (LC) assessed after 1 year and 2 years and the toxicity scored according to CTCAE v.5. Actuarial outcomes were analyzed using the Kaplan-Meier method, while potential predictors were investigated through the Log-rank test. Results: Between 2017 and 2023, eleven Caucasian patients underwent pelvic CIRT (total dose 68.8 GyRBE) for mucosal malignant melanoma of the vulva or the vagina. With a median follow-up of 18 months, we observed an ORR of 82% and a CB of 100%. LC at 1 and 2 years was 100% and 86%, respectively, and among the factors analyzed for their potential impact on LC, age < 60 years seems to be a potential predictor (p = 0.014). The treatment was well tolerated, with only one case of acute grade 3 erythema and, in the late phase, one case of grade 3 erythema and grade 3 urethral toxicity. Conclusions: CIRT was effective and safe for gynecological melanomas. Larger collaborative cohort studies and longer follow-ups are needed to take a step forward in comprehending the correct management of this disease.

Vaginal Mucosal Melanoma Cell Activation in Response to Photon or Carbon Ion Irradiation

Purpose

Primary gynecological melanomas are uncommon with lower survival rates compared to cutaneous melanomas. Although melanocytes have been identified in a variety of mucosal membranes, little is known about their interactions or roles inside the mucosa layer. Melanin is a common pigment in nature and is endowed with several peculiar chemical, paramagnetic, and semiconductive characteristics. One of its latest explored functions is its interaction with ionizing radiation as a protective mechanism as well as its implication in the metastatic cascade of tumor cells.

Materials and Methods

In this work, we analyzed in vitro the effects of different doses of photon and carbon ion irradiation on dendrite formation, pigmentation, migration, and invasion abilities of human mucosal melanoma cells of the vagina. We evaluated the morphology and melanin production of HMV-II cells exposed to photon and carbon ion beams with single doses between 0.5 and 10 Gy.

Results

Our results showed that irradiation induces dendrite formation or elongation and pigmentation in HMV-II cells in a dose-type-dependent and radiation-type-dependent way but also a decrease in cell motility.

Conclusion

The present study describes for the first time an induction of dendritic formation, melanin production, and alterations in migration and invasion abilities by low-linear energy transfer and high-linear energy transfer radiation in human mucosal melanoma cells, suggesting a radioprotective response to further possible exposures increasing the radioresistance of these cells.

Complex Inhibitory Activity of Pentacyclic Triterpenoids against Cutaneous Melanoma In Vitro and In Vivo: A Literature Review and Reconstruction of Their Melanoma-Related Protein Interactome

Pentacyclic triterpenoids (PTs) are a class of plant metabolites with a wide range of pharmacological activities, including strong antitumor potential against skin malignancies. By acting on multiple signaling pathways that control key cellular processes, PTs are able to exert complex effects on melanoma progression in vitro and in vivo. In this review, we have analyzed the works published in the past decade and devoted to the effects of PTs, both natural and semisynthetic, on cutaneous melanoma pathogenesis, including not only their direct action on melanoma cells but also their influence on the tumor microenvironment and abberant melanogenesis, often associated with melanoma aggressiveness. Special attention will be paid to the molecular basis of the pronounced antimelanoma potency of PTs, including a detailed consideration of the pathways sensitive to PTs in melanoma cells, as well as the reconstruction of the melanoma-related protein interactome of PTs using a network pharmacology approach based on previously published experimentally verified protein targets of PTs. The information collected on the primary targets of PTs was compiled in the Protein Interactome of PTs (PIPTs) database, freely available at http://www.pipts-db.ru/, which can be used to further optimize the mechanistic studies of PTs in the context of melanoma and other malignancies. By summarizing recent research findings, this review provides valuable information to scientists working in the fields related to the evaluation of melanoma pathogenesis and development of PTs-based drug candidates.

Recycled melanoma-secreted melanosomes regulate tumor-associated macrophage diversification

Extracellular vesicles (EVs) are important mediators of communication between cells. Here, we reveal a new mode of intercellular communication by melanosomes, large EVs secreted by melanocytes for melanin transport. Unlike small EVs, which are disintegrated within the receiver cell, melanosomes stay intact within them, gain a unique protein signature, and can then be further transferred to another cell as "second-hand" EVs. We show that melanoma-secreted melanosomes passaged through epidermal keratinocytes or dermal fibroblasts can be further engulfed by resident macrophages. This process leads to macrophage polarization into pro-tumor or pro-immune cell infiltration phenotypes. Melanosomes that are transferred through fibroblasts can carry AKT1, which induces VEGF secretion from macrophages in an mTOR-dependent manner, promoting angiogenesis and metastasis in vivo. In melanoma patients, macrophages that are co-localized with AKT1 are correlated with disease aggressiveness, and immunotherapy non-responders are enriched in macrophages containing melanosome markers. Our findings suggest that interactions mediated by second-hand extracellular vesicles contribute to the formation of the metastatic niche, and that blocking the melanosome cues of macrophage diversification could be helpful in halting melanoma progression.

Drug design of tyrosinase inhibitors

This copper-containing enzyme catalyzes the rate-limiting step for the melanin skin pigment bioproduction. Tyrosinase inhibitors can be exploited as skin whitening agents and food preservatives, opening new scenarios in food, cosmetics, agriculture and medicine. Despite the availability of natural inhibitors (hydroquinone, α-arbutin, kojic acid, retinoids, azelaic acid, resveratrol, caftaric acid, valonea tannin, chrysosplenetin and phenylethyl resorcinol), several synthetic compounds were proposed to overcome side effects and to improve the efficacy of natural agents. This chapter will gather the recent advances about synthetic tyrosinase inhibitors from the MedChem perspective, providing new suggestions for the scaffold-based design of innovative compounds.

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

Design and synthesis of 4-amino-2',4'-dihydroxyindanone derivatives as potent inhibitors of tyrosinase and melanin biosynthesis in human melanoma cells

Melanogenesis inhibition constitutes a privileged therapeutic solution to treat skin hyperpigmentation, a major dermatological concern associated with the overproduction of melanin by human tyrosinase (hsTYR). Despite the existence of many well-known TYR (tyrosinase) inhibitors commercialized in skin formulations, their hsTYR-inhibition efficacy remains poor since most of them were investigated over mushroom tyrosinase (abTYR), a model with low homology relative to hsTYR. Considering the need for new potent hsTYR inhibitors, we designed and synthesized a series of indanones starting from 4-hydroxy compound 1a, one of the two most active derivatives reported to date against the human enzyme, together with marketed thiamidol. We observed that analogues featuring 4-amino and 4-amido-2',4'-dihydroxyindanone motifs showed two-to ten-fold increase in activity over human melanoma MNT-1 cell lysates, and a ten-fold improvement in a 4-days whole-cell experiment, compared to parent analogue 1a. Molecular docking investigation was performed for the most promising 4-amido derivatives and suggested a plausible interaction pattern with the second coordination sphere of hsTYR, notably through hydrogen bonding with Glu203, confirming their impact in the binding mode with hsTYR active site.

Significance of melanin distribution in the epidermis for the protective effect against UV light

Melanin, the most abundant skin chromophore, is produced by melanocytes and is one of the key components responsible for mediating the skin's response to ultraviolet radiation (UVR). Because of its antioxidant, radical scavenging, and broadband UV absorbing properties, melanin reduces the penetration of UVR into the nuclei of keratinocytes. Despite its long-established photoprotective role, there is evidence that melanin may also induce oxidative DNA damage in keratinocytes after UV exposure and therefore be involved in the development of melanoma. The present work aimed at evaluating the dependence of UV-induced DNA damage on melanin content and distribution, using reconstructed human epidermis (RHE) models. Tanned and light RHE were irradiated with a 233 nm UV-C LED source at 60 mJ/cm2 and a UV lamp at 3 mJ/cm2. Higher UV-mediated free radicals and DNA damage were detected in tanned RHE with significantly higher melanin content than in light RHE. The melanin distribution in the individual models can explain the lack of photoprotection. Fluorescence lifetime-based analysis and Fontana-Masson staining revealed a non-homogeneous distribution and absence of perinuclear melanin in the tanned RHE compared to the in vivo situation in humans. Extracellularly dispersed epidermal melanin interferes with photoprotection of the keratinocytes.

Transglutaminase Type 2-MITF axis regulates phenotype switching in skin cutaneous melanoma

Skin cutaneous melanoma (SKCM) is the deadliest form of skin cancer due to its high heterogeneity that drives tumor aggressiveness. Melanoma plasticity consists of two distinct phenotypic states that co-exist in the tumor niche, the proliferative and the invasive, respectively associated with a high and low expression of MITF, the master regulator of melanocyte lineage. However, despite efforts, melanoma research is still far from exhaustively dissecting this phenomenon. Here, we discovered a key function of Transglutaminase Type-2 (TG2) in regulating melanogenesis by modulating MITF transcription factor expression and its transcriptional activity. Importantly, we demonstrated that TG2 expression affects melanoma invasiveness, highlighting its positive value in SKCM. These results suggest that TG2 may have implications in the regulation of the phenotype switching by promoting melanoma differentiation and impairing its metastatic potential. Our findings offer potential perspectives to unravel melanoma vulnerabilities via tuning intra-tumor heterogeneity.

Melanogenesis Is Directly Affected by Metabolites of Melatonin in Human Melanoma Cells

Melatonin (N-acetyl-5-methoxytryptamine, MEL), its kynurenic (N1-acetyl-N2-formyl-5-methoxykynurenine, AFMK) and indolic derivatives (6-hydroxymelatonin, 6(OH)MEL and 5-methoxytryptamine, 5-MT) are endogenously produced in human epidermis. Melatonin, produced by the pineal gland, brain and peripheral organs, displays a diversity of physiological functions including anti-inflammatory, immunomodulatory, and anti-tumor capacities. Herein, we assessed their regulatory effect on melanogenesis using amelanotic (A375, Sk-Mel-28) and highly pigmented (MNT-1, melanotic) human melanoma cell lines. We discovered that subjected compounds decrease the downstream pathway of melanin synthesis by causing a significant drop of cyclic adenosine monophosphate (cAMP) level, the microphthalmia-associated transcription factor (MITF) and resultant collapse of tyrosinase (TYR) activity, and melanin content comparatively to N-phenylthiourea (PTU, a positive control). We observed a reduction in pigment in melanosomes visualized by the transmission electron microscopy. Finally, we assessed the role of G-protein-coupled seven-transmembrane-domain receptors. Obtained results revealed that nonselective MT1 and MT2 receptor antagonist (luzindole) or selective MT2 receptor antagonist (4-P-PDOT) did not affect dysregulation of the melanin pathway indicating a receptor-independent mechanism. Our findings, together with the current state of the art, provide a convenient experimental model to study the complex relationship between metabolites of melatonin and the control of pigmentation serving as a future and rationale strategy for targeted therapies of melanoma-affected patients.

Aspacochioside C from Asparagus cochinchinensis attenuates eumelanin synthesis via inhibition of TRP2 expression

Aspacochioside C (ACC) is a steroidal saponin isolated from Asparagus cochinchinensis. Steroidal saponins, such as pseudoprotodioscin and dioscin, are known to inhibit melanogenesis, but the role of ACC in melanogenesis remains unknown. Due to the toxic effect of the commonly used skin whitening agents like arbutin, kojic acid and α-lipoic acid alternative plant products are recentlybeen studied for their anti-hypergmentation effect. This study explores the role of ACC in melanogenesis in both in vivo and in vitro models. Here, we for the first time demonstrate that ACC attenuated α-MSH- and UVB-induced eumelanin production by inhibiting tyrosinase-related protein (TRP)-2 protein expression in both murine B16F10 and human melanoma MNT1 cells. However, ACC had no significant effect on pheomelanin concentration. ACC also decreased the pigmentation density in zebrafish embryos, which indicates that ACC targets TRP2 and inhibits eumelanin synthesis. Our results demonstrate that ACC inhibits TRP2, thereby attenuating eumelanin synthesis both in in vitro and in vivo zebrafish model. Therefore, ACC can potentially be used as an anti-melanogenic agent for both aesthetic and pharmaceutical purposes.

Structure-Based Virtual Screening of Furan-1,3,4-Oxadiazole Tethered N-phenylacetamide Derivatives as Novel Class of hTYR and hTYRP1 Inhibitors

Human tyrosinase (hTYR) is a key and rate-limiting enzyme along with human tyrosinase-related protein-1 (hTYRP1), which are among the most prominent targets of inhibiting hyper pigmentation and melanoma skin cancer. In the current in-silico computer-aided drug design (CADD) study, the structure-based screening of sixteen furan-1,3,4-oxadiazole tethered N-phenylacetamide structural motifs BF1-BF16 was carried out to assess their potential as hTYR and hTYRP1 inhibitors. The results revealed that the structural motifs BF1-BF16 showed higher binding affinities towards hTYR and hTYRP1 than the standard inhibitor kojic acid. The most bioactive lead furan-1,3,4-oxadiazoles BF4 and BF5 displayed stronger binding in affinities (-11.50 kcal/mol and -13.30 kcal/mol) than the standard drug kojic acid against hTYRP1 and hTYR enzymes, respectively. These were further confirmed by MM-GBSA and MM-PBSA binding energy computations. The stability studies involving the molecular dynamics simulations also provided stability insights into the binding of these compounds with the target enzymes, wherein it was found that they remain stable in the active sites during the 100 ns virtual simulation time. Moreover, the ADMET, as well as the medicinal properties of these novel furan-1,3,4-oxadiazole tethered N-phenylacetamide structural hybrids, also showed a good prospect. The excellent in-silico profiling of furan-1,3,4--oxadiazole structural motifs BF4 and BF5 provide a hypothetical gateway to use these compounds as potential hTYRP1 and hTYR inhibitors against melanogenesis.

Recent Advances and Progress on Melanin: From Source to Application

Melanin is a biological pigment formed by indoles and phenolic compounds. It is widely found in living organisms and has a variety of unique properties. Due to its diverse characteristics and good biocompatibility, melanin has become the focus in the fields of biomedicine, agriculture, the food industry, etc. However, due to the wide range of melanin sources, complex polymerization properties, and low solubility of specific solvents, the specific macromolecular structure and polymerization mechanism of melanin remain unclear, which significantly limits the further study and application of melanin. Its synthesis and degradation pathways are also controversial. In addition, new properties and applications of melanin are constantly being discovered. In this review, we focus on the recent advances in the research of melanin in all aspects. Firstly, the classification, source, and degradation of melanin are summarized. Secondly, a detailed description of the structure, characterization, and properties of melanin is followed. The novel biological activity of melanin and its application is described at the end.

Resorcinol-based hemiindigoid derivatives as human tyrosinase inhibitors and melanogenesis suppressors in human melanoma cells

Human tyrosinase (hsTYR) catalyzes the key steps of melanogenesis, making it a privileged target for reducing melanin production in vivo. However, very few hsTYR inhibitors have been reported so far in the literature, whereas thousands of mushroom tyrosinase (abTYR) inhibitors are known. Yet, as these enzymes are actually very different, including at their active sites, there is an urgent need for new true hsTYR inhibitors in order to enable human-directed pharmacological and dermocosmetic applications without encountering the inefficiency and toxicity issues currently triggered by kojic acid or hydroquinone. Starting from the two most active compounds reported to date, i.e. a 2-hydroxypyridine-embedded aurone and thiamidol, we combined herein key structural elements and developed new nanomolar hsTYR inhibitors with cell-based activity. From a complete series of thirty-eight synthesized derivatives, excellent inhibition values were obtained for two compounds in both human melanoma cell lysates and purified hsTYR assays, and a promising improvement was observed in whole cell experiments.

The expression pattern of pyroptosis-related genes predicts the prognosis and drug response of melanoma

Cutaneous melanoma (CM, hereafter referred to as melanoma) is a highly malignant tumor that typically undergoes early metastasis. Pyroptosis, as a special programmed cell death process that releases inflammatory factors and has been widely studied in tumors, but its role in melanoma has not been fully elucidated. In this study, we examined the relationship between pyroptosis and the prognosis of melanoma through bioinformatic analysis of RNA-sequencing data. Our results demonstrated that pyroptosis is a protective factor associated with melanoma prognosis. A higher pyroptosis score was associated with a more favorable overall survival. We used weighted gene co-expression networks analysis (WGCNA) to establish an effective prognosis model based on 12 pyroptosis-related genes. We then validated it in two independent cohorts. Furthermore, a nomogram combining clinicopathological characteristics and a pyroptosis-related gene signature (PGS) score was designed to effectively evaluate the prognosis of melanoma. Additionally, we analyzed the potential roles of pyroptosis in the tumor immune microenvironment and drug response. Interestingly, we found that the elevated infiltration of multiple immune cells, such as CD4⁺ T cells, CD8⁺ T cells, dendritic cells, and M1 macrophages, may be associated with the occurrence of pyroptosis. Pyroptosis was also related to a better response of melanoma to interferon-α, paclitaxel, cisplatin and imatinib. Through Spearman correlation analysis of the 12 pyroptosis-related genes and 135 chemotherapeutic agents in the Genomics of Drug Sensitivity in Cancer database, we identified solute carrier family 31 member 2 (SLC31A2) and collagen type 4 alpha 5 chain (COL4A5) as being associated with resistance to most of these drugs. In conclusion, this PGS is an effective and novelty prognostic indicator in melanoma, and also has an association with the melanoma immune microenvironment and melanoma treatment decision-making.

Melanosomal targeting via caveolin-1 dependent endocytosis mediates ZN(II) phthalocyanine phototoxic action in melanoma cells

Melanosomes have been considered crucial targets in melanoma treatments. In this study we explored the role of melanosomes in photodynamic therapy (PDT), employing the synthetic Zn(II) phthalocyanine Pc13, a potent photosensitizer that promotes melanoma cell death after irradiation. Phototoxic action is mediated by reactive oxygen species increase. The internalization mechanism of Pc13 and its consequent subcellular localization were evaluated in melanotic B16-F0 cells. Pharmacological inhibitors of dynamin or caveolae, but not of clathrin, decreased Pc13 cellular uptake and phototoxicity. Similar results were obtained when cells over-expressed dominant negative mutants of dynamin-2 and caveolin-1, indicating that Pc13 is internalized by caveolae-mediated endocytosis. Confocal microscopy analysis revealed that Pc13 targets melanosomes and damage of these structures after irradiation was demonstrated by transmission electron microscopy. Treatment of pigmented B16-F0 and WM35 melanoma cells with the melanin synthesis inhibitor phenylthiourea for 48 h led to cell depigmentation and enhanced cell death after irradiation, whereas a 3-h period of inhibition did not modify melanin content but produced a marked reduction of Pc13 phototoxicity, together with a decrease of oxidative melanin synthesis intermediates. In contrast, the effect of Pc13 in amelanotic A375 cells was not altered by phenylthiourea treatment. These results provide evidence that melanosomes have a dual role in the efficacy of PDT. While melanin antagonizes the phototoxic action of Pc13, the release of cytotoxic synthetic intermediates to cytosol after irradiation and melanosome damage is conducive to the phototoxic response. Based on these findings, we demonstrate that melanosome-targeted PDT could be an effective approach for melanoma treatment.

Targeting Melanin in Melanoma with Radionuclide Therapy

Nearly 100,000 individuals are expected to be diagnosed with melanoma in the United States in 2022. Treatment options for late-stage metastatic disease up until the 2010s were few and offered only slight improvement to the overall survival. The introduction of B-RAF inhibitors and anti-CTLA4 and anti-PD-1/PD-L1 immunotherapies into standard of care brought measurable increases in the overall survival across all stages of melanoma. Despite the improvement in the survival statistics, patients treated with targeted therapies and immunotherapies are subject to very serious side effects, the development of drug resistance, and the high costs of treatment. This leaves room for the development of novel approaches as well as for the exploration of novel combination therapies for the treatment of metastatic melanoma. One such approach is targeting melanin pigment with radionuclide therapy. Advances in melanin-targeting radionuclide therapy of melanoma can be viewed from two spheres: (1) radioimmunotherapy (RIT) and (2) radiolabeled small molecules. The investigation of mechanisms of the action and efficacy of targeting melanin in melanoma treatment by RIT points to the involvement of the immune system such as complement dependent cytotoxicity. The combination of RIT with immunotherapy presents synergistic killing in mouse melanoma models. The field of radiolabeled small molecules is focused on radioiodinated compounds that have the ability to cross the cellular membranes to access intracellular melanin and can be applied in both therapy and imaging as theranostics. Clinical applications of targeting melanin with radionuclide therapies have produced encouraging results and clinical work is on-going. Continued work on targeting melanin with radionuclide therapy as a monotherapy, or possibly in combination with standard of care agents, has the potential to strengthen the current treatment options for melanoma patients.

CYP11A1‑derived vitamin D hydroxyderivatives as candidates for therapy of basal and squamous cell carcinomas

Hydroxyderivatives of vitamin D3, including classical 1,25(OH)2D3 and novel CYP11A1‑derived hydroxyderivatives, exert their biological activity by acting as agonists on the vitamin D receptor (VDR) and inverse agonists on retinoid‑related orphan receptors (ROR)α and γ. The anticancer activities of CYP11A1‑derived hydroxyderivatives were tested using cell biology, tumor biology and molecular biology methods in human A431 and SCC13 squamous (SCC)‑ and murine ASZ001 basal (BCC)‑cell carcinomas, in comparison with classical 1,25(OH)2D3. Vitamin D3‑hydroxyderivatives with or without a C1α(OH) inhibited cell proliferation in a dose‑dependent manner. While all the compounds tested had similar effects on spheroid formation by A431 and SCC13 cells, those with a C1α(OH) group were more potent in inhibiting colony and spheroid formation in the BCC line. Potent anti‑tumorigenic activity against the BCC line was exerted by 1,25(OH)2D3, 1,20(OH)2D3, 1,20,23(OH)3D3, 1,20,24(OH)3D3, 1,20,25(OH)3D3 and 1,20,26(OH)3D3, with smaller effects seen for 25(OH)D3, 20(OH)D3 and 20,23(OH)2D3. 1,25(OH)2D3, 1,20(OH)2D3 and 20(OH)D3 inhibited the expression of GLI1 and β‑catenin in ASZ001 cells. In A431 cells, these compounds also decreased the expression of GLI1 and stimulated involucrin expression. VDR, RORγ, RORα and CYP27B1 were detected in A431, SCC13 and ASZ001 lines, however, with different expression patterns. Immunohistochemistry performed on human skin with SCC and BCC showed nuclear expression of all three of these receptors, as well as megalin (transmembrane receptor for vitamin D‑binding protein), the level of which was dependent on the type of cancer and antigen tested in comparison with normal epidermis. Classical and CYP11A1‑derived vitamin D3‑derivatives exhibited anticancer‑activities on skin cancer cell lines and inhibited GLI1 and β‑catenin signaling in a manner that was dependent on the position of hydroxyl groups. The observed expression of VDR, RORγ, RORα and megalin in human SCC and BCC suggested that they might provide targets for endogenously produced or exogenously applied vitamin D hydroxyderivatives and provide excellent candidates for anti‑cancer therapy.

Antimelanoma Potential of Cladonia mitis Acetone Extracts - Comparative in Vitro Studies in Relation to Usnic Acid Content

In this study, the cytotoxic activity of acetone extracts of Cladonia mitis was assessed with respect to the content of usnic acid, a secondary metabolite commonly present in this species. Following quantitative HPLC analysis of the extracts, usnic acid was isolated by preparative chromatography. The study of cytotoxic activity was performed using the MTT test on three melanoma cell lines - HTB140, A375 and WM793. The selectivity of action was also assessed by comparing the effect towards normal human keratinocytes HaCaT. The results showed a dose-dependent cytotoxic activity of the extracts tested and usnic acid itself, but no relationship was found between the content of usnic acid and the activity of the extracts. Furthermore, the extracts showed varied, but rather low anti-tyrosinase activity. Other in vitro and in vivo studies are necessary to demonstrate that C. mitis extracts may be useful in the adjuvant external treatment of skin melanoma.

Amelanotic Uveal Melanomas Evaluated by Indirect Ophthalmoscopy Reveal Better Long-Term Prognosis Than Pigmented Primary Tumours-A Single Centre Experience

(1) Background: There is a constant search for new prognostic factors that would allow us to accurately determine the prognosis, select the type of treatment, and monitor the patient diagnosed with uveal melanoma in a minimally invasive and easily accessible way. Therefore, we decided to evaluate the prognostic role of its pigmentation in a clinical assessment. (2) Methods: The pigmentation of 154 uveal melanomas was assessed by indirect ophthalmoscopy. Two groups of tumours were identified: amelanotic and pigmented. The statistical relationships between these two groups and clinical, pathological parameters and the long-term survival rate were analyzed. (3) Results: There were 16.9% amelanotic tumours among all and they occurred in younger patients (p = 0.022). In pigmented melanomas, unfavourable prognostic features such as: epithelioid cells (p = 0.0013), extrascleral extension (p = 0.027), macronucleoli (p = 0.0065), and the absence of BAP1 expression (p = 0.029) were statistically more frequently observed. Kaplan−Meier analysis demonstrated significantly better overall (p = 0.017) and disease-free (p < 0.001) survival rates for patients with amelanotic tumours. However, this relationship was statistically significant for lower stage tumours (AJCC stage II), and was not present in larger and more advanced stages (AJCC stage III). (4) Conclusions: The results obtained suggested that the presence of pigmentation in uveal melanoma by indirect ophthalmoscopy was associated with a worse prognosis, compared to amelanotic lesions. These findings could be useful in the choice of therapeutic and follow-up options in the future.

The Dark Side of Melanin Secretion in Cutaneous Melanoma Aggressiveness

Skin cancers are among the most common cancers worldwide and are increasingly prevalent. Cutaneous melanoma (CM) is characterized by the malignant transformation of melanocytes in the epidermis. Although CM shows lower incidence than other skin cancers, it is the most aggressive and responsible for the vast majority of skin cancer-related deaths. Indeed, 75% of patients present with invasive or metastatic tumors, even after surgical excision. In CM, the photoprotective pigment melanin, which is produced by melanocytes, plays a central role in the pathology of the disease. Melanin absorbs ultraviolet radiation and scavenges reactive oxygen/nitrogen species (ROS/RNS) resulting from the radiation exposure. However, the scavenged ROS/RNS modify melanin and lead to the induction of signature DNA damage in CM cells, namely cyclobutane pyrimidine dimers, which are known to promote CM immortalization and carcinogenesis. Despite triggering the malignant transformation of melanocytes and promoting initial tumor growth, the presence of melanin inside CM cells is described to negatively regulate their invasiveness by increasing cell stiffness and reducing elasticity. Emerging evidence also indicates that melanin secreted from CM cells is required for the immunomodulation of tumor microenvironment. Indeed, melanin transforms dermal fibroblasts in cancer-associated fibroblasts, suppresses the immune system and promotes tumor angiogenesis, thus sustaining CM progression and metastasis. Here, we review the current knowledge on the role of melanin secretion in CM aggressiveness and the molecular machinery involved, as well as the impact in tumor microenvironment and immune responses. A better understanding of this role and the molecular players involved could enable the modulation of melanin secretion to become a therapeutic strategy to impair CM invasion and metastasis and, hence, reduce the burden of CM-associated deaths.

Development and Validation of a Novel Survival Model for Cutaneous Melanoma Based on Necroptosis-Related Genes

Background

Necroptosis is crucial for organismal development and pathogenesis. To date, the role of necroptosis in skin cutaneous melanoma (SKCM) is yet unveiled. In addition, the part of melanin pigmentation was largely neglected in the bioinformatic analysis. In this study, we aimed to construct a novel prognostic model based on necroptosis-related genes and analysis the pigmentation phenotype of patients to provide clinically actionable information for SKCM patients.

Methods

We downloaded the SKCM data from the TCGA and GEO databases in this study and identified the differently expressed and prognostic necroptosis-related genes. Patients’ pigmentation phenotype was evaluated by the GSVA method. Then, using Lasso and Cox regression analysis, a novel prognostic model was constructed based on the intersected genes. The risk score was calculated and the patients were divided into two groups. The survival differences between the two groups were compared using Kaplan-Meier analysis. The ROC analysis was performed and the area under curves was calculated to evaluate the prediction performances of the model. Then, the GO, KEGG and GSEA analyses were performed to elucidate the underlying mechanisms. Differences in the tumor microenvironment, patients’ response to immune checkpoint inhibitors (ICIs) and pigmentation phenotype were analyzed. In order to validate the mRNA expression levels of the selected genes, quantitative real-time PCR (qRT-PCR) was performed.

Results

Altogether, a novel prognostic model based on four genes (BOK, CD14, CYLD and FASLG) was constructed, and patients were classified into high and low-risk groups based on the median risk score. Low-risk group patients showed better survival status. The model showed high accuracy in the training and the validation cohort. Pathway and functional enrichment analysis indicated that immune-related pathways were differently activated in the two groups. In addition, immune cells infiltration patterns and sensitivity of ICIs showed a significant difference between patients from two risk groups. The pigmentation score was positively related to the risk score in pigmentation phenotype analysis.

Conclusion

In conclusion, this study established a novel prognostic model based on necroptosis-related genes and revealed the possible connections between necroptosis and melanin pigmentation. It is expected to provide a reference for clinical treatment.

Interaction mechanism of pelargonidin against tyrosinase by multi-spectroscopy and molecular docking

The interaction mechanism of pelargonidin (PG) with tyrosinase was investigated by multi-spectroscopy and molecular docking. As a result, PG had strong inhibitory activity on tyrosinase with the IC₅₀ value of 41.94×10^-6 mol·L^-1 . The inhibition type of PG against tyrosinase was determined as a mixed mode. Meanwhile, the fluorescence of tyrosinase was quenched statically by PG, and accompanied by non-radiative energy transfer. The three-dimensional (3-D) fluorescence, ultraviolet-visible spectroscopy (UV-Vis) and circular dichroism spectroscopies (CD) indicated that PG decreased the hydrophobicity of the micro-environment around tryptophan (Trp) and tyrosine (Tyr), which resulted in the conformational change of tyrosinase. In addition, fluorescence and molecular docking analysis indicated that PG bound to tyrosinase via hydrogen bonds (H-bonds) and van der Waals force (vdW force). We herein recommended that PG might be a potential candidate drug for the treatment of melanin-related diseases.

Melanoma, Melanin, and Melanogenesis: The Yin and Yang Relationship

Melanin pigment plays a critical role in the protection against the harmful effects of ultraviolet radiation and other environmental stressors. It is produced by the enzymatic transformation of L-tyrosine to dopaquinone and subsequent chemical and biochemical reactions resulting in the formation of various 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI) oligomers-main constituents of eumelanin, and benzothiazine and benzothiazole units of pheomelanin. The biosynthesis of melanin is regulated by sun exposure and by many hormonal factors at the tissue, cellular, and subcellular levels. While the presence of melanin protects against the development of skin cancers including cutaneous melanoma, its presence may be necessary for the malignant transformation of melanocytes. This shows a complex role of melanogenesis in melanoma development defined by chemical properties of melanin and the nature of generating pathways such as eu- and pheomelanogenesis. While eumelanin is believed to provide radioprotection and photoprotection by acting as an efficient antioxidant and sunscreen, pheomelanin, being less photostable, can generate mutagenic environment after exposure to the short-wavelength UVR. Melanogenesis by itself and its highly reactive intermediates show cytotoxic, genotoxic, and mutagenic activities, and it can stimulate glycolysis and hypoxia-inducible factor 1-alpha (HIF-1α) activation, which, combined with their immunosuppressive effects, can lead to melanoma progression and resistance to immunotherapy. On the other hand, melanogenesis-related proteins can be a target for immunotherapy. Interestingly, clinicopathological analyses on advanced melanomas have shown a negative correlation between tumor pigmentation and diseases outcome as defined by overall survival and disease-free time. This indicates a "Yin and Yang" role for melanin and active melanogenesis in melanoma development, progression, and therapy. Furthermore, based on the clinical, experimental data and diverse effects of melanogenesis, we propose that inhibition of melanogenesis in advanced melanotic melanoma represents a realistic adjuvant strategy to enhance immuno-, radio-, and chemotherapy.

In Situ Nanotransformable Hydrogel for Chemo-Photothermal Therapy of Localized Tumors and Targeted Therapy of Highly Metastatic Tumors

Metastasis is one of the predisposing factors for cancer-related mortalities worldwide. Patients with advanced cancers (stage IV) receive palliative care with minimal possibility of achieving complete remission. Antibody-based therapeutic modalities are capable of targeting tumors that are confined to a particular location but are ineffective in targeting distant secondary tumors. In the current study, we have developed a smart nano-transforming hydrogel (NTG) that transforms in situ to polymeric nanoparticles (PA NPs) of 100-150 nm when injected subcutaneously. These nanoparticles targeted the primary and secondary metastatic tumors for up to ∼5 and ∼3 days, respectively. The in situ-formed PA NPs also demonstrated a pH-responsive drug release resulting in about ∼80% release within 100 h at 5.8 pH. When tested in vivo, substantial inhibition of lung metastases was observed compared to chemotherapy, thus demonstrating the efficiency of nanotransforming hydrogels in targeting and inhibiting primary and secondary metastatic tumors.

A Comparative Survey of Anti-Melanoma and Anti-Inflammatory Potential of Usnic Acid Enantiomers-A Comprehensive In Vitro Approach

Usnic acid (UA) is a chiral lichen metabolite with an interesting pharmacological profile. The aim of this study was to compare the anti-melanoma effect of (+)-UA and (−)-UA in an in vitro model by studying their impact on the cells as well as the processes associated with cancer progression. The effect of UA enantiomers on the viability, proliferation, and invasive potential of three melanoma cell lines (HTB140, A375, WM793) was evaluated. Their interaction with a chemotherapeutic drug—doxorubicin was assessed by isobolographic analysis. Anti-inflammatory and anti-tyrosinase properties of (+)-UA and (−)-UA were also examined. Both UA enantiomers dose- and time-dependently decreased the viability of all three melanoma cell lines. Their synergistic effect with doxorubicin was observed on A375 cells. (+)-Usnic acid at a sub-cytotoxic dose strongly inhibited melanoma cells migration. Both UA enantiomers decreased the release of pro-inflammatory mediators. The cytotoxic effect of (+)-UA and (−)-UA depends greatly on the melanoma cell type; however, the overall anti-melanoma potential is perspective. Our results indicate that the strategy of combining usnic acid enantiomers with cytostatic drugs may be an interesting option to consider in combating melanoma; however, further studies are required.

Melanization as unfavorable factor in amelanotic melanoma cell biology

The biology of three amelanotic melanoma cell lines (Ab, B16F10, and A375) of different species origin was analyzed during in vitro induced melanization in these cells. Melanin production was induced by DMEM medium characterized by a high level of L-tyrosine (a basic amino acid for melanogenesis). The biodiversity of amelanotic melanoma cells was confirmed by their different responses to melanogenesis induction; Ab hamster melanomas underwent intensive melanization, mouse B16F10 darkened slightly, while human A375 cells did not show any change in melanin content. Highly melanized Ab cells entered a cell death pathway, while slight melanization did not influence cell biology in a significant way. The rapid and high melanization of Ab cells induced apoptosis documented by phosphatidylserine externalization, caspase activation, and mitochondrial energetic state decrease. Melanoma cell type, culture medium, and time of incubation should be taken into consideration during amelanotic melanoma cell culture in vitro. L-tyrosine, as a concentration-dependent factor presented in the culture media, could stimulate some amelanotic melanoma cell lines (Ab, B16F10) to melanin production. The presence of melanin should be considered in the examination of antimelanoma compounds in vitro, because induction of melanin may interfere or be helpful in the treatment of amelanotic melanoma.

D-Penicillamine: The State of the Art in Humans and in Dogs from a Pharmacological and Regulatory Perspective

Chelant agents are the mainstay of treatment in copper-associated hepatitis in humans, where D-penicillamine is the chelant agent of first choice. In veterinary medicine, the use of D-penicillamine has increased with the recent recognition of copper-associated hepatopathies that occur in several breeds of dogs. Although the different regulatory authorities in the world (United States Food and Drugs Administration-U.S. FDA, European Medicines Agency-EMEA, etc.) do not approve D-penicillamine for use in dogs, it has been used to treat copper-associated hepatitis in dogs since the 1970s, and is prescribed legally by veterinarians as an extra-label drug to treat this disease and alleviate suffering. The present study aims to: (a) address the pharmacological features; (b) outline the clinical scenario underlying the increased interest in D-penicillamine by overviewing the evolution of its main therapeutic goals in humans and dogs; and finally, (c) provide a discussion on its use and prescription in veterinary medicine from a regulatory perspective.

Pigmentation Levels Affect Melanoma Responses to Coriolus versicolor Extract and Play a Crucial Role in Melanoma-Mononuclear Cell Crosstalk

Melanoma, the malignancy originating from pigment-producing melanocytes, is the most aggressive form of skin cancer and has a poor prognosis once the disease starts to metastasize. The process of melanin synthesis generates an immunosuppressive and mutagenic environment, and can increase melanoma cell resistance to different treatment modalities, including chemo-, radio- or photodynamic therapy. Recently, we have shown that the presence of melanin pigment inhibits the melanoma cell response to bioactive components of Coriolus versicolor (CV) Chinese fungus. Herein, using the same human melanoma cell line in which the level of pigmentation can be controlled by the L-tyrosine concentration in culture medium, we tested the effect of suppression of melanogenesis on the melanoma cell response to CV extract and investigated the cell death pathway induced by fungus extract in sensitized melanoma cells. Our data showed that susceptibility to CV-induced melanoma cell death is significantly increased after cell depigmentation. To the best of our knowledge, we are the first to demonstrate that CV extract can induce RIPK1/RIPK3/MLKL-mediated necroptosis in depigmented melanoma cells. Moreover, using the co-culture system, we showed that inhibition of the tyrosinase activity in melanoma cells modulates cytokine expression in co-cultured mononuclear cells, indicating that depigmentation of melanoma cells may activate immune cells and thereby influence a host anticancer response.

From Proteomic Mapping to Invasion-Metastasis-Cascade Systemic Biomarkering and Targeted Drugging of Mutant BRAF-Dependent Human Cutaneous Melanomagenesis

Simple Summary

Despite the recent advances in human malignancy therapy, metastasis and chemoresistance remain the principal causes of cancer-derived deaths. Given the fatal forms of cutaneous metastatic melanoma, we herein employed primary (WM115) and metastatic (WM266-4) melanoma cells, both obtained from the same patient, to identify novel biomarkers and therapeutic agents. Through state-of-the-art technologies including deep proteome landscaping, immunofluorescence phenotyping, and drug toxicity screening, we were able to describe new molecular programs, oncogenic drivers, and drug regimens, controlling the invasion-metastasis cascade during BRAF^V600D-dependent melanomagenesis. It proved that proteomic navigation could foster the development of systemic biomarkering and targeted drugging for successful treatment of advanced disease.

Abstract

Melanoma is classified among the most notoriously aggressive human cancers. Despite the recent progress, due to its propensity for metastasis and resistance to therapy, novel biomarkers and oncogenic molecular drivers need to be promptly identified for metastatic melanoma. Hence, by employing nano liquid chromatography-tandem mass spectrometry deep proteomics technology, advanced bioinformatics algorithms, immunofluorescence, western blotting, wound healing protocols, molecular modeling programs, and MTT assays, we comparatively examined the respective proteomic contents of WM115 primary (n = 3955 proteins) and WM266-4 metastatic (n = 6681 proteins) melanoma cells. It proved that WM115 and WM266-4 cells have engaged hybrid epithelial-to-mesenchymal transition/mesenchymal-to-epithelial transition states, with TGF-β controlling their motility in vitro. They are characterized by different signatures of SOX-dependent neural crest-like stemness and distinct architectures of the cytoskeleton network. Multiple signaling pathways have already been activated from the primary melanoma stage, whereas HIF1α, the major hypoxia-inducible factor, can be exclusively observed in metastatic melanoma cells. Invasion-metastasis cascade-specific sub-routines of activated Caspase-3-triggered apoptosis and LC3B-II-dependent constitutive autophagy were also unveiled. Importantly, WM115 and WM266-4 cells exhibited diverse drug response profiles, with epirubicin holding considerable promise as a beneficial drug for metastatic melanoma clinical management. It is the proteome navigation that enables systemic biomarkering and targeted drugging to open new therapeutic windows for advanced disease.

Mitochondrial function is controlled by melatonin and its metabolites in vitro in human melanoma cells

Melanoma is a leading cause of cancer deaths worldwide. Although immunotherapy has revolutionized the treatment for some patients, resistance towards therapy and unwanted side effects remain a problem for numerous individuals. Broad anti-cancer activities of melatonin are recognized; however, additional investigations still need to be elucidated. Herein, using various human melanoma cell models, we explore in vitro the new insights into the regulation of melanoma by melatonin and its metabolites which possess, on the other side, high safety profiles and biological meaningful. In this study, using melanotic (MNT-1) and amelanotic (A375, G361, Sk-Mel-28) melanoma cell lines, the comparative oncostatic responses, the impact on melanin content (for melanotic MNT-1 melanoma cells) as well as the mitochondrial function controlled by melatonin, its precursor (serotonin), a kynuric (N¹ -acetyl-N² -formyl-5-methoxykynuramine, AFMK) and indolic pathway (6-hydroxymelatonin, 6(OH)MEL and 5-methoxytryptamine, 5-MT) metabolites were assessed. Namely, significant disturbances were observed in bioenergetics as follows: (i) uncoupling of oxidative phosphorylation (OXPHOS), (ii) attenuation of glycolysis, (iii) dissipation of mitochondrial transmembrane potential (mtΔΨ) accompanied by (iv) massive generation of reactive oxygen species (ROS), and (v) decrease of glucose uptake. Collectively, these results together with previously published reports provide a new biological potential and make an imperative to consider using melatonin or its metabolites for complementary future treatments of melanoma-affected patients; however, these associations should be additionally investigated in clinical setting.

Advances in the Design of Genuine Human Tyrosinase Inhibitors for Targeting Melanogenesis and Related Pigmentations

Human tyrosinase (hsTYR) is the key enzyme ensuring the conversion of l-tyrosine to dopaquinone, thereby initiating melanin synthesis, i.e., melanogenesis. Although the protein has long been familiar, knowledge about its three-dimensional structure and efficient overexpression protocols emerged only recently. Consequently, for decades medicinal chemistry studies aiming at developing skin depigmenting agents relied almost exclusively on biological assays performed using mushroom tyrosinase (abTYR), producing a plethoric literature, often of little useful purpose. Indeed, several recent reports have pointed out spectacular differences in terms of interaction patterns and inhibition values between hsTYR and abTYR, including for widely used standard tyrosinase inhibitors. In this review, we summarize the last developments regarding the potential role of hsTYR in human pathologies, the advances in recombinant expression systems and structural data retrieving, and the pioneer generation of true hsTYR inhibitors. Finally, we present suggestions for the design of future inhibitors of this highly attractive target in pharmacology and dermocosmetics.

CMT-308, a Nonantimicrobial Chemically-Modified Tetracycline, Exhibits Anti-Melanogenic Activity by Suppression of Melanosome Export

CMT-308 is a nonantimicrobial chemically-modified tetracycline (CMT), which we have previously shown exhibits antifungal activity and pleiotropic anti-inflammatory activities, including inhibition of the enzymatic activity of matrix metalloproteinases (MMPs). Based on its chemical structure, we hypothesized that CMT-308 could inhibit melanogenesis and might be a candidate for the treatment of skin hyperpigmentation disorders which occur due to unregulated melanin biosynthesis and/or transport. CMT-308 was first studied for any effects on activity of the enzyme tyrosinase in vitro using a purified preparation of mushroom tyrosinase; the mode of inhibition of the soluble fungal enzyme was evaluated by Lineweaver-Burk and Dixon plots as well as by non-linear least squares fitting. Next, the effects of CMT-308 were tested in mammalian cell cultures using B16F10 mouse melanoma cells and further validated in darkly-pigmented human melanocytes (HEMn-DP). Our results showed that micromolar concentrations of CMT-308 inhibited mushroom tyrosinase enzyme activity, using the first two substrates in the melanogenesis pathway (l-tyrosine and l-3,4-dihydroxyphenylalanine (l-DOPA)); CMT-308 inhibited mushroom tyrosinase primarily via a mixed mode of inhibition, with the major contribution from a competitive mode. In B16F10 cell cultures, CMT-308 (10 µM) significantly diminished total melanin levels with a selective reduction of extracellular melanin levels, under both basal and hormone-stimulated conditions without any cytotoxicity over a duration of 72 h. Studies of potential mechanisms of inhibition of melanogenesis in B16F10 cells showed that, in mammalian cells, CMT-308 did not inhibit intracellular tyrosinase activity or the activity of α-glucosidase, an enzyme that regulates maturation of tyrosinase. However, CMT-308 suppressed MITF protein expression in B16F10 cells and showed copper chelating activity and antioxidant activity in a cell-free system. The significantly lower extracellular melanin levels obtained at 10 µM indicate that CMT-308’s anti-melanogenic action may be attributed to a selective inhibition of melanosome export with the perinuclear aggregation of melanosomes, rather than a direct effect on the tyrosinase-catalyzed steps in melanin biosynthesis. These results were validated in HEMn-DP cells where CMT-308 suppressed dendricity in a fully reversible manner without affecting intracellular melanin synthesis. Furthermore, the capacity of CMT-308 to inhibit melanosome export was retained in cocultures of HEMn-DP and HaCaT. In summary, our results offer promise for therapeutic strategies to combat the effects of hyperpigmentation by use of CMT-308 at low micromolar concentrations.

Transcriptional characterization of conjunctival melanoma identifies the cellular tumor microenvironment and prognostic gene signatures

This study characterizes the transcriptome and the cellular tumor microenvironment (TME) of conjunctival melanoma (CM) and identifies prognostically relevant biomarkers. 12 formalin-fixed and paraffin-embedded CM were analyzed by MACE RNA sequencing, including six cases each with good or poor clinical outcome, the latter being defined by local recurrence and/or systemic metastases. Eight healthy conjunctival specimens served as controls. The TME of CM, as determined by bioinformatic cell type enrichment analysis, was characterized by the enrichment of melanocytes, pericytes and especially various immune cell types, such as plasmacytoid dendritic cells, natural killer T cells, B cells and mast cells. Differentially expressed genes between CM and control were mainly involved in inhibition of apoptosis, proteolysis and response to growth factors. POU3F3, BIRC5 and 7 were among the top expressed genes associated with inhibition of apoptosis. 20 genes, among them CENPK, INHA, USP33, CASP3, SNORA73B, AAR2, SNRNP48 and GPN1, were identified as prognostically relevant factors reaching high classification accuracy (area under the curve: 1.0). The present study provides new insights into the TME and the transcriptional profile of CM and additionally identifies new prognostic biomarkers. These results add new diagnostic tools and may lead to new options of targeted therapy for CM.

Inherited variations in human pigmentation-related genes modulate cutaneous melanoma risk and clinicopathological features in Brazilian population

Ultraviolet light exposure and cutaneous pigmentation are important host risk factors for cutaneous melanoma (CM), and it is well known that inherited ability to produce melanin varies in humans. The study aimed to identify single-nucleotide variants (SNVs) on pigmentation-related genes with importance in risk and clinicopathological aspects of CM. The study was conducted in two stages. In stage 1, 103 CM patients and 103 controls were analyzed using Genome-Wide Human SNV Arrays in order to identify SNVs in pigmentation-related genes, and the most important SNVs were selected for data validation in stage 2 by real-time polymerase-chain reaction in 247 CM patients and 280 controls. ADCY3 c.675+9196T>G, CREB1 c.303+373G>A, and MITF c.938-325G>A were selected for data validation among 74 SNVs. Individuals with CREB1 GA or AA genotype and allele "A" were under 1.79 and 1.47-fold increased risks of CM than others, respectively. Excesses of CREB1 AA and MITF AA genotype were seen in patients with tumors at Clark levels III to V (27.8% versus 13.7%) and at III or IV stages (46.1% versus 24.9%) compared to others, respectively. When compared to others, patients with ADCY3 TT had 1.89 more chances of presenting CM progression, and those with MITF GA or AA had 2.20 more chances of evolving to death by CM. Our data provide, for the first time, preliminary evidence that inherited abnormalities in ADCY3, CREB1, and MITF pigmentation-related genes, not only can increase the risk to CM, but also influence CM patients' clinicopathological features.

Current Molecular Markers of Melanoma and Treatment Targets

Melanoma is a deadly skin cancer that becomes especially difficult to treat after it metastasizes. Timely identification of melanoma is critical for effective therapy, but histopathologic diagnosis can frequently pose a significant challenge to this goal. Therefore, auxiliary diagnostic tools are imperative to facilitating prompt recognition of malignant lesions. Melanoma develops as result of a number of genetic mutations, with UV radiation often acting as a mutagenic risk factor. Novel methods of genetic testing have improved detection of these molecular alterations, which subsequently revealed important information for diagnosis and prognosis. Rapid detection of genetic alterations is also significant for choosing appropriate treatment and developing targeted therapies for melanoma. This review will delve into the understanding of various mutations and the implications they may pose for clinical decision making.

Immunohistochemical detectability of cyclooxygenase-2 expression in cells of human melanocytic skin lesions: A methodological review

Increased cyclooxygenase-2 (COX-2) expression is thought to support tumorigenesis through various mechanisms and is analyzed as a potential cancer marker. In 18 studies, COX-2 expression in melanocytic lesions of human skin was examined immunohistochemically. However, results obtained by individual research groups differ in terms of detection frequency and level of this protein, as well as localization of stained cells within tumor. Possible reasons for the discrepancies are analyzed in this review: the application of different antibodies, the use of standard histopathological sections or tissue microarrays and the analyzes of staining results based on different algorithms. COX-2 level is significantly lower in nevi than in melanomas, increases gradually with progression of these malignant cancers and reaches the highest values in metastases. These gradual changes in COX-2 expression appear to be difficult to analyze based only on subjective assessment of staining intensity. The most convergent data were obtained using antibodies for N-terminal fragments of COX-2 protein and analyzing results based on calculation of percentage fraction of positive cells. The extent of stained area in specimen thus appears to be more important than the intensity of staining in terms of evaluation of COX-2 performance as a diagnostic and prognostic marker of cutaneous melanoma.

Anti-melanoma potential of two benzoquinone homologues embelin and rapanone - a comparative in vitro study

Rapanone and embelin are simple alkyl benzoquinone derivatives, mainly distributed in the Primulaceae. They have an interesting scope of biological activities including cytotoxicity. As melanoma is one of the most common types of cancer, in many cases resistant to current treatment regimens, the aim of this study was to assess and compare anti-melanoma activity of the two benzoquinones. Cytotoxicity of both compounds towards different melanoma cell lines (A375, HTB140, WM793) and selectivity with respect to normal keratinocytes (HaCaT) were investigated. Furthermore, interactions with a reference chemotherapeutic, doxorubicine, were assessed. Finally, analysis of anti-inflammatory, antioxidant and anti-tyrosinase activities of both benzoquinones was conducted as well. Rapanone showed selective and higher than doxorubicine cytotoxic potential against primary melanoma cell line, WM793. Although embelin was also highly cytotoxic, its selectivity was much poorer. Interestingly, in case of HTB140 and HaCaT cell lines a combination of each benzoquinone with doxorubicine potentiated the cytotoxic potential in a synergistic manner. Embelin revealed higher albumin anti-denaturation potential than rapanone but lower than diclofenac sodium. Anti-hyaluronidase effect of both benzoquinones was higher than quercetin. Both compounds showed antioxidant potential although significantly lower as compared to vitamin C. Finally, neither embelin nor rapanone had any inhibitory effect on tyrosinase.

Combination of Gas Plasma and Radiotherapy Has Immunostimulatory Potential and Additive Toxicity in Murine Melanoma Cells in Vitro

Despite continuous advances in therapy, malignant melanoma is still among the deadliest types of cancer. At the same time, owing to its high plasticity and immunogenicity, melanoma is regarded as a model tumor entity when testing new treatment approaches. Cold physical plasma is a novel anticancer tool that utilizes a plethora of reactive oxygen species (ROS) being deposited on the target cells and tissues. To test whether plasma treatment would enhance the toxicity of an established antitumor therapy, ionizing radiation, we combined both physical treatment modalities targeting B16F10 murine melanoma cell in vitro. Repeated rather than single radiotherapy, in combination with gas plasma-introduced ROS, induced apoptosis and cell cycle arrest in an additive fashion. In tendency, gas plasma treatment sensitized the cells to subsequent radiotherapy rather than the other way around. This was concomitant with increased levels of TNFα, IL6, and GM-CSF in supernatants. Murine JAWS dendritic cells cultured in these supernatants showed an increased expression of cell surface activation markers, such as MHCII and CD83. For PD-L1 and PD-L2, increased expression was observed. Our results are the first to suggest an additive therapeutic effect of gas plasma and radiotherapy, and translational tumor models are needed to develop this concept further.

Melatonin exerts oncostatic capacity and decreases melanogenesis in human MNT-1 melanoma cells

Melanogenesis is a key parameter of differentiation in melanocytes and melanoma cells; therefore, search for factors regulating this pathway are strongly desired. Herein, we investigated the effects of melatonin, a ubiquitous physiological mediator that is found throughout animals and plants. In mammals, the pineal gland secretes this indoleamine into the blood circulation to exert an extensive repertoire of biological activities. Our in vitro assessment indicates an oncostatic capacity of melatonin in time-dependent manner (24, 48, 72 hours) in highly pigmented MNT-1 melanoma cells. The similar pattern of regulation regarding cell viability was observed in amelanotic Sk-Mel-28 cells. Subsequently, MNT-1 cells were tested for the first time for evaluation of melanin/melatonin interaction. Thus primary, electron paramagnetic resonance (EPR) spectroscopy demonstrated that melatonin reduced melanin content. Artificially induced disturbances of melanogenesis by selected inhibitors (N-phenylthiourea or kojic acid) were slightly antagonized by melatonin. Additionally, analysis using transmission electron microscopy has shown that melatonin, particularly at higher dose of 10-3  mol/L, triggered the appearance of premelanosomes (stage I-II of melanosome) and MNT-1 cells synthesize de novo endogenous melatonin shown by LC-MS. In conclusion, these studies show a melanogenic-like function of melatonin suggesting it as an advantageous agent for treatment of pigmentary disorders.

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.

Growth Hormone Upregulates Melanocyte-Inducing Transcription Factor Expression and Activity via JAK2-STAT5 and SRC Signaling in GH Receptor-Positive Human Melanoma

Growth hormone (GH) facilitates therapy resistance in the cancers of breast, colon, endometrium, and melanoma. The GH-stimulated pathways responsible for this resistance were identified as suppression of apoptosis, induction of epithelial-to-mesenchymal transition (EMT), and upregulated drug efflux by increased expression of ATP-binding cassette containing multidrug efflux pumps (ABC-transporters). In extremely drug-resistant melanoma, ABC-transporters have also been reported to mediate drug sequestration in intracellular melanosomes, thereby reducing drug efficacy. Melanocyte-inducing transcription factor (MITF) is the master regulator of melanocyte and melanoma cell fate as well as the melanosomal machinery. MITF targets such as the oncogene MET, as well as MITF-mediated processes such as resistance to radiation therapy, are both known to be upregulated by GH. Therefore, we chose to query the direct effects of GH on MITF expression and activity towards conferring chemoresistance in melanoma. Here, we demonstrate that GH significantly upregulates MITF as well as the MITF target genes following treatment with multiple anticancer drug treatments such as chemotherapy, BRAF-inhibitors, as well as tyrosine-kinase inhibitors. GH action also upregulated MITF-regulated processes such as melanogenesis and tyrosinase activity. Significant elevation in MITF and MITF target gene expression was also observed in mouse B16F10 melanoma cells and xenografts in bovine GH transgenic (bGH) mice compared to wild-type littermates. Through pathway inhibitor analysis we identified that both the JAK2-STAT5 and SRC activities were critical for the observed effects. Additionally, a retrospective analysis of gene expression data from GTEx, NCI60, CCLE, and TCGA databases corroborated our observed correlation of MITF function and GH action. Therefore, we present in vitro, in vivo, and in silico evidence which strongly implicates the GH-GHR axis in inducing chemoresistance in human melanoma by driving MITF-regulated and ABC-transporter-mediated drug clearance pathways.

Coriolus versicolor-derived protein-bound polysaccharides trigger the caspase-independent cell death pathway in amelanotic but not melanotic melanoma cells

We have investigated the potential cell death mechanism promoted by Coriolus versicolor fungus-derived protein-bound polysaccharides (PBPs) in melanoma cells. Knowing that melanogenesis has the potential to affect the tumor behavior and melanoma therapy outcome, the cytotoxic effects of PBPs were evaluated in human SKMel-188 melanoma cell line, whose phenotype, amelanotic versus pigmented, depends on the concentration of melanin precursors in the culture medium. Our results showed that inhibitory effect of PBPs (100 and 200 μg/ml) towards melanoma cells is inversely associated with the pigmentation level. This cytotoxicity induced in nonpigmented melanoma cells by PBPs was caspase-independent; however, it was accompanied by an increased intracellular reactive oxygen species (ROS) generation. The ROS production was controlled by c-Jun N-terminal kinase (JNK) because SP600125, a JNK inhibitor, significantly reduced ROS generation and protected cells against PBPs-induced death. We also found that PBPs-induced lactate dehydrogenase release in amelanotic melanoma cells was abolished by co-treatment with receptor-interacting serine/threonine-protein kinase 1 inhibitor, implying engagement of this kinase in PBPs-induced death pathway. The results suggest that PBPs induce an alternative programmed cell death, regulated by receptor-interacting protein-1 and ROS and that this process is modified by melanin content in melanoma cells. These findings are remarkable when considering the use of commercially available Coriolus versicolor by patients who suffer from melanoma cancer.

On the relationship between VDR, RORα and RORγ receptors expression and HIF1-α levels in human melanomas

We analysed the correlation between the expression of HIF-1α (hypoxia-inducible factor 1 alpha), the nuclear receptors: VDR (vitamin D receptor), RORα (retinoic acid receptor-related orphan receptor alpha), and RORγ and CYP24A1 (cytochrome P450 family 24 subfamily A member 1) and CYP27B1 (cytochrome P450 family 27 subfamily B member 1), enzymes involved in vitamin D metabolism. In primary and metastatic melanomas, VDR negatively correlated with nuclear HIF-1α expression (r = -.2273, P = .0302; r = -.5081, P = .0011). Furthermore, the highest HIF-1α expression was observed in pT3-pT4 VDR-negative melanomas. A comparative analysis of immunostained HIF-1α and CYP27B1 and CYP24A1 showed lack of correlation between these parameters both in primary tumors and melanoma metastases. In contrast, RORα expression correlated positively with nuclear HIF-1α expression in primary and metastatic lesions (r = .2438, P = .0175; r = .3662, P = .0166). Comparable levels of HIF-1α expression pattern was observed in localized and advanced melanomas. RORγ in primary melanomas correlated also positively with nuclear HIF-1α expression (r = .2743, P = .0129). HIF-1α expression was the lowest in localized RORγ-negative melanomas. In addition, HIF-1α expression correlated with RORγ-positive lymphocytes in melanoma metastases. We further found that in metastatic lymph nodes FoxP3 immunostaining correlated positively with HIF-1α and RORγ expression in melanoma cells (r = .3667; P = .0327; r = .4208, P = .0129). In summary, our study indicates that the expression of VDR, RORα and RORγ in melanomas is related to hypoxia and/or HIF1-α activity, which also affects FoxP3 expression in metastatic melanoma. Therefore, the hypoxia can affect tumor biology by changing nuclear receptors expression and molecular pathways regulated by nuclear receptors and immune responses.

Methylwogonin exerts anticancer effects in A375 human malignant melanoma cells through apoptosis induction, DNA damage, cell invasion inhibition and downregulation of the mTOR/PI3K/Akt signalling pathway

INTRODUCTION

The main purpose of the present research was to study the anticancer effects of methylwogonin in A375 human malignant melanoma cells by evaluating its effects on apoptosis, DNA fragmentation, cancer cell invasion and the mTOR/PI3K/AKT signalling pathway.

MATERIAL AND METHODS

Effects on cell cytotoxicity were evaluated by MTT assay while a clonogenic assay determined the effects of methylwogonin on colony formation. Fluorescence microscopy evaluated apoptotic effects of methylwogonin in these cells using acridine orange/propidium iodide and Hoechst 33342 staining dyes. Gel electrophoresis evaluated the effects of methylwogonin on DNA fragmentation while the Matrigel invasion assay evaluated the effects of the drug on cancer cell invasion. Effects of methylwogonin on the mTOR/PI3K/AKT signalling pathway were evaluated by western blot assay.

RESULTS

Methylwogonin induces concentration-dependent as well as time-dependent growth inhibitory effects inducing significant cytotoxicity in these cancer cells. Methylwogonin led to dose-dependent inhibition of colony formation in A375 human malignant melanoma cells. The number of cell colonies decreased significantly as the methylwogonin dose increased from 0, 50, 150, to 300 μM. Methylwogonin treatment of cells at lower doses led to yellow fluorescence (early apoptosis), which changed to red/orange fluorescence, indicating late apoptosis at higher doses. Similar results were obtained using Hoechst 33342 staining, revealing that 50, 150 and 300 μM doses of methylwogonin led to significant morphological changes including chromatin condensation, fragmented nuclei and cellular shrinkage. DNA ladder formation was also observed, and this effect increased with increasing doses of methylwogonin. Methylwogonin also inhibited cancer cell invasion in a dose-dependent manner.

CONCLUSIONS

Different doses of methylwogonin led to concentration-dependent downregulation of phosphorylated PI3K, AKT and mTOR.

Utilizing 808 nm laser for sensitizing of melanoma tumors to megavoltage radiation therapy

Melanotic melanoma has high content of melanin and laser can destroy melanin-containing cells through thermal effect. In this study, the therapeutic effect of 808 nm laser therapy was investigated on B16-F10 melanoma tumor growth and tumor-bearing mice survival time. In addition, as laser can destroy melanin as the main cause of melanoma radioresistance, the effect of laser administration to enhance radiation therapy efficacy at B16-F10 cancer cells was evaluated in vitro and in vivo. Laser therapy (1 W/cm² × 4 min) could cause significant (P < 0.05) inhibition of melanoma tumors' growth (~ 61%) and about three times increase of the tumor-bearing mice survival time in comparison with no-treatment group. In addition, the mice which were treated with 1 W/cm² × 4 min laser administration plus 6 Gy megavoltage radiation therapy exhibited ~ 68% lesser tumors' volume and 27 days increase of survival time in comparison with 6 Gy irradiated tumor-bearing mice. Also, significantly higher (P < 0.05) tumor necrosis percentage was observed at the histopathological slides of 1 W/cm² × 4 min laser + RT treated mice tumors (57 ± 12%) in comparison with radiation therapy group (31 ± 10%). Therefore, not only laser therapy can inhibit melanoma tumors' growth per se but also its combination with radiation therapy can cause a significant enhancement of radiation therapy efficacy. The laser administration can be used as a radiosensitizing method for melanotic melanoma radiation therapy.