Crosstalk in skin: melanocytes, keratinocytes, stem cells, and melanoma

Dangerous liaisons: Loss of keratinocyte control over melanocytes in melanomagenesis

Melanomas arise from transformed melanocytes, positioned at the dermal-epidermal junction in the basal layer of the epidermis. Melanocytes are completely surrounded by keratinocyte neighbors, with which they communicate through direct contact and paracrine signaling to maintain normal growth control and homeostasis. UV radiation from sunlight reshapes this communication network to drive a protective tanning response. However, repeated rounds of sun exposure result in accumulation of mutations in melanocytes that have been considered as primary drivers of melanoma initiation and progression. It is now clear that mutations in melanocytes are not sufficient to drive tumor formation-the tumor environment plays a critical role. This review focuses on changes in melanocyte-keratinocyte communication that contribute to melanoma initiation and progression, with a particular focus on recent mechanistic insights that lay a foundation for developing new ways to intercept melanoma development.

Contribution of Keratinocytes in Skin Cancer Initiation and Progression

Keratinocytes are major cellular components of the skin and are strongly involved in its homeostasis. Oncogenic events, starting mainly from excessive sun exposure, lead to the dysregulation of their proliferation and differentiation programs and promote the initiation and progression of non-melanoma skin cancers (NMSCs). Primary melanomas, which originate from melanocytes, initiate and develop in close interaction with keratinocytes, whose role in melanoma initiation, progression, and immune escape is currently being explored. Recent studies highlighted, in particular, unexpected modes of communication between melanocytic cells and keratinocytes, which may be of interest as sources of new biomarkers in melanomagenesis or potential therapeutic targets. This review aims at reporting the various contributions of keratinocytes in skin basal cell carcinoma (BCC), cutaneous squamous cell carcinoma (cSCC), and melanoma, with a greater focus on the latter in order to highlight some recent breakthrough findings. The readers are referred to recent reviews when contextual information is needed.

Tumor Microenvironment Modulation by Cancer-Derived Extracellular Vesicles

The tumor microenvironment (TME) plays an important role in the process of tumorigenesis, regulating the growth, metabolism, proliferation, and invasion of cancer cells, as well as contributing to tumor resistance to the conventional chemoradiotherapies. Several types of cells with relatively stable phenotypes have been identified within the TME, including cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), neutrophils, and natural killer (NK) cells, which have been shown to modulate cancer cell proliferation, metastasis, and interaction with the immune system, thus promoting tumor heterogeneity. Growing evidence suggests that tumor-cell-derived extracellular vesicles (EVs), via the transfer of various molecules (e.g., RNA, proteins, peptides, and lipids), play a pivotal role in the transformation of normal cells in the TME into their tumor-associated protumorigenic counterparts. This review article focuses on the functions of EVs in the modulation of the TME with a view to how exosomes contribute to the transformation of normal cells, as well as their importance for cancer diagnosis and therapy.

The Skin Molecular Ecosystem Holds the Key to Nevogenesis and Melanomagenesis

Early detection of melanoma is critical to good patient outcomes, but we still know little about the mechanisms of early melanoma development. Normal epidermis has many of the sequence variants and genetic architecture disruptions found in both benign nevi, melanomas, and other skin cancers, yet continues to behave more or less normally. One hypothesis is that many melanocytes in this context are "tumor competent" but are regulated by the microenvironment provided by the surrounding keratinocytes to inhibit progress to nevi or melanoma. There is evidence of accumulating disorder in several measures of the genomic and epigenomic landscape from normal skin through nevi to melanoma that may be key to promoting nevogenesis and melanomagenesis.

The Keratinocyte in the Picture Cutaneous Melanoma Microenvironment

Melanoma progression is a multistep evolution from a common melanocytic nevus through a radial superficial growth phase, the invasive vertical growth phase finally leading to metastatic dissemination into distant organs. Melanoma aggressiveness largely depends on the propensity to metastasize, which means the capacity to escape from the physiological microenvironment since tissue damage due to primary melanoma lesions is generally modest. Physiologically, epidermal melanocytes are attached to the basement membrane, and their adhesion/migration is under the control of surrounding keratinocytes. Thus, the epidermal compartment represents the first microenvironment responsible for melanoma spread. This complex process involves cell-cell contact and a broad range of secreted bioactive molecules. Invasion, or at the beginning of the microinvasion, implies the breakdown of the dermo-epidermal basement membrane followed by the migration of neoplastic melanocytic cells in the superficial papillary dermis. Correspondingly, several experimental evidences documented the structural and functional rearrangement of the entire tissue surrounding neoplasm that in some way reflects the atypia of tumor cells. Lastly, the microenvironment must support the proliferation and survival of melanocytes outside the normal epidermal-melanin units. This task presumably is mostly delegated to fibroblasts and ultimately to the self-autonomous capacity of melanoma cells. This review will discuss remodeling that occurs in the epidermis during melanoma formation as well as skin changes that occur independently of melanocytic hyperproliferation having possible pro-tumoral features.

Enhanced Cytotoxicity and Antimelanoma Activity of Novel Semisynthetic Derivatives of Betulinic Acid with Indole Conjugation

The prevalence and severity of skin cancer, specifically malignant melanoma, among Caucasians remains a significant concern. Natural compounds from plants have long been explored as potential anticancer agents. Betulinic acid (BI) has shown promise in its therapeutic properties, including its anticancer effects. However, its limited bioavailability has hindered its medicinal applications. To address this issue, two recently synthesized semisynthetic derivatives, N-(2,3-indolo-betulinoyl)diglycylglycine (BA1) and N-(2,3-indolo-betulinoyl)glycylglycine (BA2), were compared with previously reported compounds N-(2,3-indolo-betulinoyl)glycine (BA3), 2,3-indolo-betulinic acid (BA4), and BI. These compounds were evaluated for their effects on murine melanoma cells (B164A5) using various in vitro assays. The introduction of an indole framework at the C2 position of BI resulted in an increased cytotoxicity. Furthermore, the cytotoxicity of compound BA4 was enhanced by conjugating its carboxylic group with an amino acid residue. BA2 and BA3, with glycine and glycylglycine residues at C28, exhibited approximately 2.20-fold higher inhibitory activity compared to BA4. The safety assessment of the compounds on human keratinocytes (HaCaT) has revealed that concentrations up to 10 µM slightly reduced cell viability, while concentrations of 75 µM resulted in lower cell viability rates. LDH leakage assays confirmed cell membrane damage in B164A5 cells when exposed to the tested compounds. BA2 and BA3 exhibited the highest LDH release, indicating their strong cytotoxicity. The NR assay revealed dose-dependent lysosome disruption for BI and 2,3-indolo-betulinic acid derivatives, with BA1, BA2, and BA3 showing the most cytotoxic effects. Scratch assays demonstrated concentration-dependent inhibition of cell migration, with BA2 and BA3 being the most effective. Hoechst 3342 staining revealed that BA2 induced apoptosis, while BA3 induced necrosis at lower concentrations, confirming their anti-melanoma properties. In conclusion, the semisynthetic derivatives of BI, particularly BA2 and BA3, show promise as potential candidates for further research in developing effective anti-cancer therapies.

Layer-by-Layer Analysis of In Vitro Skin Models

In vitro human skin models are evolving into versatile platforms for the study of skin biology and disorders. These models have many potential applications in the fields of drug testing and safety assessment, as well as cosmetic and new treatment development. The development of in vitro skin models that accurately mimic native human skin can reduce reliance on animal models and also allow for more precise, clinically relevant testing. Recent advances in biofabrication techniques and biomaterials have led to the creation of increasingly complex, multilayered skin models that incorporate important functional components of skin, such as the skin barrier, mechanical properties, pigmentation, vasculature, hair follicles, glands, and subcutaneous layer. This improved ability to recapitulate the functional aspects of native skin enhances the ability to model the behavior and response of native human skin, as the complex interplay of cell-to-cell and cell-to-material interactions are incorporated. In this review, we summarize the recent developments in in vitro skin models, with a focus on their applications, limitations, and future directions.

Melanoma cells repress Desmoglein 1 in keratinocytes to promote tumor cell migration

Melanoma is an aggressive cancer typically arising from transformation of melanocytes residing in the basal layer of the epidermis, where they are in direct contact with surrounding keratinocytes. The role of keratinocytes in shaping the melanoma tumor microenvironment remains understudied. We previously showed that temporary loss of the keratinocyte-specific cadherin, Desmoglein 1 (Dsg1), controls paracrine signaling between normal melanocytes and keratinocytes to stimulate the protective tanning response. Here, we provide evidence that melanoma cells hijack this intercellular communication by secreting factors that keep Dsg1 expression low in the surrounding keratinocytes, which in turn generate their own paracrine signals that enhance melanoma spread through CXCL1/CXCR2 signaling. Evidence suggests a model whereby paracrine signaling from melanoma cells increases levels of the transcriptional repressor Slug, and consequently decreases expression of the Dsg1 transcriptional activator Grhl1. Together, these data support the idea that paracrine crosstalk between melanoma cells and keratinocytes resulting in chronic keratinocyte Dsg1 reduction contributes to melanoma cell movement associated with tumor progression.

The impact of cellular elements of TME on melanoma biology and its sensitivity to EGFR and MET targeted therapy

Microenvironment of the melanoma consists of cellular elements like fibroblasts, adipocytes, and keratinocytes as well as extracellular matrix and physicochemical conditions. In our previous research, we have established that melanoma influences strongly above mentioned cells present in the tumor niche and recruits them to support cancer progression. In this work, we evaluated the impact of cancer-associated cells, namely fibroblasts (CAFs), adipocytes (CAAs), and keratinocytes (CAKs) on melanoma proliferation, signaling pathways activation, metabolism as well as the effectiveness of used anti-cancer therapy. Obtained results indicated elevated phosphorylation of STAT3, upregulated GLUT1 and GLUT3 as well as downregulated of MCT-1 expression level in melanoma cells under the influence of all examined cells present in the tumor niche. The proliferation of melanoma cells was increased after co-culture with CAFs and CAKs, while epithelial-mesenchymal transition markers' expression level was raised in the presence of CAFs and CAAs. The level of perilipin 2 and lipid content was elevated in melanoma cells under the influence of CAAs. Moreover, increased expression of CYP1A1, gene encoding drug metabolizing protein, in melanoma cells co-cultured with CAFs and CAKs prompted us to verify the effectiveness of the previously proposed by us anti-melanoma therapy based on combination of EGFR and MET inhibitors. Obtained results indicate that the designed therapy is still efficient, even if the fibroblasts, adipocytes, and keratinocytes, are present in the melanoma vicinity.

Skin Cancer Microenvironment: What We Can Learn from Skin Aging?

Aging is a natural intrinsic process associated with the loss of fibrous tissue, a slower cell turnover, and a reduction in immune system competence. In the skin, the continuous exposition of environmental factors superimposes extrinsic damage, mainly due to ultraviolet radiation causing photoaging. Although not usually considered a pathogenic event, photoaging affects cutaneous biology, increasing the risk of skin carcinogenesis. At the cellular level, aging is typified by the rise of senescence cells a condition characterized by reduced or absent capacity to proliferate and aberrant hyper-secretory activity. Senescence has a double-edged sword in cancer biology given that senescence prevents the uncontrolled proliferation of damaged cells and favors their clearance by paracrine secretion. Nevertheless, the cumulative insults and the poor clearance of injured cells in the elderly increase cancer incidence. However, there are not conclusive data proving that aged skin represents a permissive milieu for tumor onset. On the other hand, tumor cells are capable of activating resident fibroblasts onto a pro-tumorigenic phenotype resembling those of senescent fibroblasts suggesting that aged fibroblasts might facilitate cancer progression. This review discusses changes that occur during aging that can prime neoplasm or increase the aggressiveness of melanoma and non-melanoma skin cancer.

Melanocyte-keratinocyte cross-talk in vitiligo

Vitiligo is a common acquired pigmentary disorder that presents as progressive loss of melanocytes from the skin. Epidermal melanocytes and keratinocytes are in close proximity to each other, forming a functional and structural unit where keratinocytes play a pivotal role in supporting melanocyte homeostasis and melanogenesis. This intimate relationship suggests that keratinocytes might contribute to ongoing melanocyte loss and subsequent depigmentation. In fact, keratinocyte dysfunction is a documented phenomenon in vitiligo. Keratinocyte apoptosis can deprive melanocytes from growth factors including stem cell factor (SCF) and other melanogenic stimulating factors which are essential for melanocyte function. Additionally, keratinocytes control the mobility/stability phases of melanocytes via matrix metalloproteinases and basement membrane remodeling. Hence keratinocyte dysfunction may be implicated in detachment of melanocytes from the basement membrane and subsequent loss from the epidermis, also potentially interfering with repigmentation in patients with stable disease. Furthermore, keratinocytes contribute to the autoimmune insult in vitiligo. Keratinocytes express MHC II in perilesional skin and may present melanosomal antigens in the context of MHC class II after the pigmented organelles have been transferred from melanocytes. Moreover, keratinocytes secrete cytokines and chemokines including CXCL-9, CXCL-10, and IL-15 that amplify the inflammatory circuit within vitiligo skin and recruit melanocyte-specific, skin-resident memory T cells. In summary, keratinocytes can influence vitiligo development by a combination of failing to produce survival factors, limiting melanocyte adhesion in lesional skin, presenting melanocyte antigens and enhancing the recruitment of pathogenic T cells.

Unusual Canine Cutaneous Melanoma Presenting Parietal Bone Metastasis: A Case Report

Melanocytic tumour anatomic location is considered an important prognostic indicator. The cutaneous forms are generally considered benign and may show various biological behaviours. This work reports a rare case of canine cutaneous melanoma showing parietal bone metastasis. Bone invasion in melanocytic tumours is often described in oral or visceral melanomas, but not in cutaneous forms. The patient (dog, male, mixed breed, 12 years) was initially presented for the surgical removal of a cutaneous tumour located on the skin of the carpal region of the right forelimb. Four months after, the patient returned with enlarged lymph nodes and acute respiratory failure. The patient was euthanized due to a decline in physical condition. The necropsy showed metastases in the affected forelimb, regional lymph node, splanchnic organs, parietal bone and meninges. Histopathological examination of tumour tissue samples revealed a mixture of pigmented and non-pigmented spindle and epithelioid melanocytes, while according to immunohistochemistry, the tumours showed a strong immunopositivity for VEGF and MMP-10, and a moderate positivity for MMP-2 expression. This case shows that cutaneous melanocytic tumours may show an aggressive malignant form with positive immunohistochemical reactions for multiple invasiveness factors.

Crosstalk in skin: Loss of desmoglein 1 in keratinocytes inhibits BRAFV600E-induced cellular senescence in human melanocytes

Melanoma arises from transformation of melanocytes in the basal layer of the epidermis where they are surrounded by keratinocytes, with which they interact through cell contact and paracrine communication. Considerable effort has been devoted to determining how the accumulation of oncogene and tumor suppressor gene mutations in melanocytes drive melanoma development. However, the extent to which alterations in keratinocytes that occur in the developing tumor niche serve as extrinsic drivers of melanoma initiation and progression is poorly understood. We recently identified the keratinocyte-specific cadherin, desmoglein 1 (Dsg1), as an important mediator of keratinocyte:melanoma cell crosstalk, demonstrating that its chronic loss, which can occur through melanoma cell-dependent paracrine signaling, promotes behaviors that mimic a malignant phenotype. Here we address the extent to which Dsg1 loss affects early steps in melanomagenesis. RNA-Seq analysis revealed that paracrine signals from Dsg1-deficient keratinocytes mediate a transcriptional switch from a differentiated to undifferentiated cell state in melanocytes expressing BRAFV600E, a driver mutation commonly present in both melanoma and benign nevi and reported to cause growth arrest and oncogene-induced senescence (OIS). Of ~220 differentially expressed genes in BRAFV600E cells treated with Dsg1-deficient conditioned media (CM), the laminin superfamily member NTN4/Netrin-4, which inhibits senescence in endothelial cells, stood out. Indeed, while BRAFV600E melanocytes treated with Dsg1-deficient CM showed signs of senescence bypass as assessed by increased senescence-associated β-galactosidase activity and decreased p16, knockdown of NTN4 reversed these effects. These results suggest that Dsg1 loss in keratinocytes provides an extrinsic signal to push melanocytes towards oncogenic transformation once an initial mutation has been introduced.

Oocyte aging in comparison to stem cells in mice

To maintain homeostasis, many tissues contain stem cells that can self-renew and differentiate. Based on these functions, stem cells can reconstitute the tissue even after injury. In reproductive organs, testes have spermatogonial stem cells that generate sperm in men throughout their lifetime. However, in the ovary, oocytes enter meiosis at the embryonic stage and maintain sustainable oogenesis in the absence of stem cells. After birth, oocytes are maintained in a dormant state in the primordial follicle, which is the most premature follicle in the ovary, and some are activated to form mature oocytes. Thus, regulation of dormancy and activation of primordial follicles is critical for a sustainable ovulatory cycle and is directly related to the female reproductive cycle. However, oocyte storage is insufficient to maintain a lifelong ovulation cycle. Therefore, the ovary is one of the earliest organs to be involved in aging. Although stem cells are capable of proliferation, they typically exhibit slow cycling or dormancy. Therefore, there are some supposed similarities with oocytes in primordial follicles, not only in their steady state but also during aging. This review aims to summarise the sustainability of oogenesis and aging phenotypes compared to tissue stem cells. Finally, it focuses on the recent breakthroughs in vitro culture and discusses future prospects.

Plants as Modulators of Melanogenesis: Role of Extracts, Pure Compounds and Patented Compositions in Therapy of Pigmentation Disorders

The kingdom of plants as a "green biofabric" of valuable bioactive molecules has long been used in many ailments. Currently, extracts and pure compounds of plant origin are used to aid in pigmentation skin problems by influencing the process of melanogenesis. Melanin is a very important pigment that protects human skin against ultraviolet radiation and oxidative stress. It is produced by a complex process called melanogenesis. However, disturbances in the melanogenesis mechanism may increase or decrease the level of melanin and generate essential skin problems, such as hyperpigmentation and hypopigmentation. Accordingly, inhibitors or activators of pigment formation are desirable for medical and cosmetic industry. Such properties may be exhibited by molecules of plant origin. Therefore, that literature review presents reports on plant extracts, pure compounds and compositions that may modulate melanin production in living organisms. The potential of plants in the therapy of pigmentation disorders has been highlighted.

Lentigo melanoma associated with Laser-Trel syndrome

Laser-Trela syndrome is characterized by the sudden appearance of a large amount of seborrheic keratosis . The syndrome is associated with the development of malignant tumors of internal organs. The article presents for the first time the observation of 82-year-old patient with lentigo maligna melanoma, who had multiple seborrheic keratosis in a short time. The observation is interesting for the atypical clinical picture of seborrheic keratosis, and the association with lentigo melanoma.

Association of Circular RNA and Long Non-Coding RNA Dysregulation with the Clinical Response to Immune Checkpoint Blockade in Cutaneous Metastatic Melanoma

Cutaneous melanoma (CM) is the most lethal form of skin cancer if it becomes metastatic, where treatment options and survival chances decrease dramatically. Immunotherapy treatments based on the immunologic checkpoint inhibitors programmed death cell protein 1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4) constituted a main breakthrough in the treatment of metastatic CM, particularly for the achievement of long-term benefits. Even though it is a very promising therapy, resistance to primary immune checkpoint blockade (ICB) arises in about 70% of CM patients treated with a CTLA-4 inhibitor, and 40–65% of CM patients administered with a PD-1-targeting treatment. Some long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) are implicated in triggering pro- and anti-tumorigenic responses to various cancer treatments. The relationship between lncRNAs, circRNAs and ICB immunotherapy has not been explored in cutaneous metastatic melanoma (CMM). The aim of this pilot study is to evaluate the potential role of circRNA and lncRNA expression as pre-treatment predictors of the clinical response to immunotherapy in CMM patients. RNA-seq from 12 formalin-fixed paraffin-embedded (FFPE) samples from the metastatic biopsies of CMM patients treated with nivolumab was used to identify response-associated transcripts. Our findings indicate that specific lncRNAs and circRNAs, probably acting as competitive endogenous RNAs (ceRNAs), are involved in the regulatory networks of the immune response against metastatic melanoma that these patients have under treatment with nivolumab. Moreover, we established a risk score that yields predictions of the overall survival (OS) and progression-free survival (PFS) of CMM patients with high accuracy. This proof-of-principle work provides a possible insight into the function of ceRNAs, contributing to efforts to decipher the complex molecular mechanisms of ICB cancer treatment response.

Melanoma stimulates the proteolytic activity of HaCaT keratinocytes

Background

Keratinocytes constitute a major part of the melanoma microenvironment, considering their protective role towards melanocytes in physiological conditions. However, their interactions with tumor cells following melanomagenesis are still unclear.

Methods

We used two in vitro models (melanoma-conditioned media and indirect co-culture of keratinocytes with melanoma cells on Transwell inserts) to activate immortalized keratinocytes towards cancer-associated ones. Western Blotting and qPCR were used to evaluate keratinocyte markers and mediators of cell invasiveness on protein and mRNA expression level respectively. The levels and activity of proteases and cytokines were analysed using gelatin-FITC staining, gelatin zymography, chemiluminescent enzymatic test, as well as protein arrays. Finally, to further study the functional changes influenced by melanoma we assessed the rate of proliferation of keratinocytes and their invasive abilities by employing wound healing assay and the Transwell filter invasion method.

Results

HaCaT keratinocytes activated through incubation with melanoma-conditioned medium or indirect co-culture exhibit properties of less differentiated cells (downregulation of cytokeratin 10), which also prefer to form connections with cancer cells rather than adjacent keratinocytes (decreased level of E-cadherin). While they express only a small number of cytokines, the variety of secreted proteases is quite prominent especially considering that several of them were never reported as a part of secretome of activated keratinocytes’ (e.g., matrix metalloproteinase 3 (MMP3), ADAM metallopeptidase with thrombospondin type 1 motif 1). Activated keratinocytes also seem to exhibit a high level of proteolytic activity mediated by MMP9 and MMP14, reduced expression of TIMPs (tissue inhibitor of metalloproteinases), upregulation of ERK activity and increased levels of MMP expression regulators-RUNX2 and galectin 3. Moreover, cancer-associated keratinocytes show slightly elevated migratory and invasive abilities, however only following co-culture with melanoma cells on Transwell inserts.

Conclusions

Our study offers a more in-depth view of keratinocytes residing in the melanoma niche, drawing attention to their unique secretome and mediators of invasive abilities, factors which could be used by cancer cells to support their invasion of surrounding tissues.

SCA® Slows the Decline of Functional Parameters Associated with Senescence in Skin Cells

The identification of compounds and natural ingredients that can counteract tissue stress and dysfunction induced by aging in skin cells is warranted. Here, we investigated the activity of the secretion from the snail Cryptomphalus aspersa (SCA^®), an active compound with well-established beneficial effects on skin integrity and aging. To determinate its senescence-regulation mechanisms, we used a model where damage was induced by hydrogen peroxide (H₂O₂). The results showed that SCA^® positively modulated factors involved in cell senescence such as β-galactosidase and cell morphology, secretory efficiency markers (SIRT1/6 and carboxymethyl-lysine), and metabolic and redox homeostasis (mTOR and ROS). This study demonstrated a novel compound that is activity-modulating, reduces cell senescence, and increases longevity to maintain skin homeostasis and functionality.

Enhanced BRAF engagement by NRAS mutants capable of promoting melanoma initiation

A distinct profile of NRAS mutants is observed in each tumor type. It is unclear whether these profiles are determined by mutagenic events or functional differences between NRAS oncoproteins. Here, we establish functional hallmarks of NRAS mutants enriched in human melanoma. We generate eight conditional, knock-in mouse models and show that rare melanoma mutants (NRAS G12D, G13D, G13R, Q61H, and Q61P) are poor drivers of spontaneous melanoma formation, whereas common melanoma mutants (NRAS Q61R, Q61K, or Q61L) induce rapid tumor onset with high penetrance. Molecular dynamics simulations, combined with cell-based protein-protein interaction studies, reveal that melanomagenic NRAS mutants form intramolecular contacts that enhance BRAF binding affinity, BRAF-CRAF heterodimer formation, and MAPK > ERK signaling. Along with the allelic series of conditional mouse models we describe, these results establish a mechanistic basis for the enrichment of specific NRAS mutants in human melanoma.

Progressing Vulvar Melanoma Caused by Instability in cKIT Juxtamembrane Domain: A Case Report and Review of Literature

In order to identify the molecular pathways governing melanoma and track its progression, the next-generation sequencing (NGS) approach and targeted sequencing of cancer genes were employed. The primary tumor, as well as metastatic tissue, of an 84-year-old patient diagnosed with vulvar melanoma (VM), were investigated. The primary tumor specimen showed multiple somatic mutations in TP53 gene, suggesting its major contribution to melanoma origin. The metastatic sample showed additional alterations, including other melanoma-related genes. Clinical relevancy is postulated to juxtamembrane region instability of KIT gene (c-KIT). We did not identify BRAF or NRAS alterations, which are typical for the most common melanoma pathway–MAPK cascade. However, it should be noted that this is the first report evidencing PDGFRA in melanoma, although its role in triggering VM needs to be further elucidated.

Targeting Sphingolipid Metabolism as a Therapeutic Strategy in Cancer Treatment

Sphingolipids are bioactive molecules that have key roles in regulating tumor cell death and survival through, in part, the functional roles of ceramide accumulation and sphingosine-1-phosphate (S1P) production, respectively. Mechanistic studies using cell lines, mouse models, or human tumors have revealed crucial roles of sphingolipid metabolic signaling in regulating tumor progression in response to anticancer therapy. Specifically, studies to understand ceramide and S1P production pathways with their downstream targets have provided novel therapeutic strategies for cancer treatment. In this review, we present recent evidence of the critical roles of sphingolipids and their metabolic enzymes in regulating tumor progression via mechanisms involving cell death or survival. The roles of S1P in enabling tumor growth/metastasis and conferring cancer resistance to existing therapeutics are also highlighted. Additionally, using the publicly available transcriptomic database, we assess the prognostic values of key sphingolipid enzymes on the overall survival of patients with different malignancies and present studies that highlight their clinical implications for anticancer treatment.

Melanin concentration maps by label-free super-resolution photo-thermal imaging on melanoma biopsies

Surgical excision followed by histopathological examination is the gold standard for melanoma screening. However, the color-based inspection of hematoxylin-and-eosin-stained biopsies does not provide a space-resolved quantification of the melanin content in melanocytic lesions. We propose a non-destructive photo-thermal imaging method capable of characterizing the microscopic distribution and absolute concentration of melanin pigments in excised melanoma biopsies. By exploiting the photo-thermal effect primed by melanin absorption of visible laser light we obtain label-free super-resolution far-infrared thermal images of tissue sections where melanin is spatially mapped at sub-diffraction 40-μm resolution. Based on the finite-element simulation of the full 3D heat transfer model, we are able to convert temperature maps into quantitative images of the melanin molar concentration on B16 murine melanoma biopsies, with 4·10^-4 M concentration sensitivity. Being readily applicable to human melanoma biopsies in combination with hematoxylin-and-eosin staining, the proposed approach could complement traditional histopathology in the characterization of pigmented lesions ex-vivo.

Crosstalk with keratinocytes causes GNAQ oncogene specificity in melanoma

Different melanoma subtypes exhibit specific and non-overlapping sets of oncogene and tumor suppressor mutations, despite a common cell of origin in melanocytes. For example, activation of the Gα_q/11 signaling pathway is a characteristic initiating event in primary melanomas that arise in the dermis, uveal tract, or central nervous system. It is rare in melanomas arising in the epidermis. The mechanism for this specificity is unknown. Here, we present evidence that in the mouse, crosstalk with the epidermal microenvironment actively impairs the survival of melanocytes expressing the GNAQ^Q209L oncogene. We found that GNAQ^Q209L, in combination with signaling from the interfollicular epidermis (IFE), stimulates dendrite extension, leads to actin cytoskeleton disorganization, inhibits proliferation, and promotes apoptosis in melanocytes. The effect was reversible and paracrine. In contrast, the epidermal environment increased the survival of wildtype and Braf^V600E expressing melanocytes. Hence, our studies reveal the flip side of Gα_q/11 signaling, which was hitherto unsuspected. In the future, the identification of the epidermal signals that restrain the GNAQ^Q209L oncogene could suggest novel therapies for GNAQ and GNA11 mutant melanomas.

Flavonoid Glycosides from Ziziphus jujuba var. inermis (Bunge) Rehder Seeds Inhibit α-Melanocyte-Stimulating Hormone-Mediated Melanogenesis

Ziziphus jujuba extracts possess a broad spectrum of biological activities, such as antioxidant and anticancer activities in melanoma cancers. Nevertheless, the compounds contain high antioxidant capacities and anticancer activities in melanoma cells, shown to be effective in hyperpigmentation disorders, but whether flavonoid glycosides from Z. jujuba regulate anti-melanogenesis remains unclear. In this study, we evaluated the anti-melanogenic activity of five flavonoid glycosides from Z. jujuba var. inermis (Bunge) Rehder seeds, including jujuboside A (JUA), jujuboside B (JUB), epiceanothic acid (EPA), betulin (BTL), and 6’’’-feruloylspinosin (FRS), in B16F10 melanoma cells and zebrafish larvae. According to our results, JUB, EPA, and FRS potently inhibited α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis and prevented hyperpigmentation in zebrafish larvae. In particular, under α-MSH-stimulated conditions, FRS most significantly inhibited α-MSH-induced intracellular and extracellular melanin content in B16F10 melanoma cells. Additionally, JUB, EPS, and FRS remarkably downregulated melanogenesis in α-MSH-treated zebrafish larvae, with no significant change in heart rate. Neither JUA nor BTA were effective in downregulating melanogenesis in B16F10 melanoma cells and zebrafish larvae. Furthermore, JUB, EPA, and FRS directly inhibited in vitro mushroom tyrosinase enzyme activity. JUB, EPA, and FRS also downregulated cyclic adenosine monophosphate (cAMP) levels and the phosphorylation of cAMP-response element-binding protein (CREB), and subsequent microphthalmia transcription factor (MITF) and tyrosinase expression. In conclusion, this study demonstrated that JUB, EPA, and FRS isolated from Z. jujuba var. inermis (Bunge) Rehder seeds exhibit potent anti-melanogenic properties by inhibition of the cAMP-CERB-MITF axis and consequent tyrosinase activity.

Microfluidic model with air-walls reveals fibroblasts and keratinocytes modulate melanoma cell phenotype, migration, and metabolism

Melanoma evolution is a complex process. The role epidermal keratinocytes and dermal fibroblasts play in this process and the mechanisms involved in tumor-stroma interactions remain poorly understood. Here, we used a microfluidic platform to evaluate the cross-talk between human primary melanoma cells, keratinocytes and dermal fibroblasts. The microfluidic device included multiple circular chambers separated by a series of narrow connection channels. The microdevice design allowed us to develop a new cell patterning method based on air-walls, removing the need for hydrogel barriers, porous membranes, or external equipment. Using this method, we co-cultured melanoma cells in the presence of keratinocytes and/or dermal fibroblasts. The results demonstrated that the presence of dermal fibroblasts and keratinocytes led to changes in melanoma cell morphology and growth pattern. Molecular analysis revealed changes in the chemokine secretion pattern, identifying multiple secreted factors involved in tumor progression. Finally, optical metabolic imaging showed that melanoma cells, fibroblasts, and keratinocytes exhibited different metabolic features. Additionally, the presence of stromal cells led to a metabolic shift in melanoma cells, highlighting the role the skin microenvironment on melanoma evolution.

Adherence to Primary Prevention and Skin Self-Examination Practices by Spanish Melanoma Patients

BACKGROUND

The incidence of cutaneous melanoma, an important global public health problem, has been increasing over the last several decades.

OBJECTIVES

In order to decrease melanoma-related mortality, ways to communicate and implement the correct methods for conducting primary and secondary prevention measures (such as early detection via self-examination) should be investigated.

MATERIALS AND METHODS

An observational, cross-sectional, retrospective study consisting of 409 patients diagnosed with cutaneous melanoma was conducted. An online questionnaire was created to evaluate knowledge levels, attitudes, and adherence to primary preventive measures and to skin self-examination practices.

RESULTS

The results revealed that even when 43% of the patients perform cutaneous self-examinations, only half of them fully followed the recommendations. Patients aged <45 years, female, with a I-II phototype, with an intermediate/high level of education, and with a history of NMSC were more likely to have an adequate degree of knowledge. Moreover, patients aged <45 years and with an adequate degree of knowledge more frequently showed an adequate adherence to the primary prevention measures. Finally, patients aged 45-60 years and with an adequate degree of knowledge presented a good adherence to the self-skin examination measures.

LIMITATIONS

Possible limitations of this study were memory bias through the influence of age within the study population, and bias due to a greater proportion of subjects with a high education level.

CONCLUSION

Within the population of patients with melanoma, a high percentage of patients do not rigorously follow the recommended prevention measures. Our study highlights the need to implement awareness in this population to improve the prevention of cutaneous cancer.

Stromal Cells Present in the Melanoma Niche Affect Tumor Invasiveness and Its Resistance to Therapy

Malignant melanoma is a highly metastatic type of cancer, which arises frequently from transformed pigment cells and melanocytes as a result of long-term UV radiation exposure. In recent years, the incidence of newly diagnosed melanoma patients reached 5% of all cancer cases. Despite the development of novel targeted therapies directed against melanoma-specific markers, patients' response to treatment is often weak or short-term due to a rapid acquisition of drug resistance. Among the factors affecting therapy effectiveness, elements of the tumor microenvironment play a major role. Melanoma niche encompasses adjacent cells, such as keratinocytes, cancer-associated fibroblasts (CAFs), adipocytes, and immune cells, as well as components of the extracellular matrix and tumor-specific physicochemical properties. In this review, we summarize the current knowledge concerning the influence of cancer-associated cells (keratinocytes, CAFs, adipocytes) on the process of melanomagenesis, tumor progression, invasiveness, and the emergence of drug resistance in melanoma. We also address how melanoma can alter the differentiation and activation status of cells present in the tumor microenvironment. Understanding these complex interactions between malignant and cancer-associated cells could improve the development of effective antitumor therapeutic strategies.

LRIG1 is a conserved EGFR regulator involved in melanoma development, survival and treatment resistance

Leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) is a pan-negative regulator of receptor tyrosine kinase (RTK) signaling and a tumor suppressor in several cancers, but its involvement in melanoma is largely unexplored. Here, we aim to determine the role of LRIG1 in melanoma tumorigenesis, RTK signaling, and BRAF inhibitor resistance. We find that LRIG1 is downregulated during early tumorigenesis and that LRIG1 affects activation of the epidermal growth factor receptor (EGFR) in melanoma cells. LRIG1-dependent regulation of EGFR signaling is evolutionary conserved to the roundworm C. elegans, where negative regulation of the EGFR-Ras-Raf pathway by sma-10/LRIG completely depends on presence of the receptor let-23/EGFR. In a cohort of metastatic melanoma patients, we observe an association between LRIG1 and survival in the triple wild-type subtype and in tumors with high EGFR expression. During in vitro development of BRAF inhibitor resistance, LRIG1 expression decreases; and mimics LRIG1 knockout cells for increased EGFR expression. Treating resistant cells with recombinant LRIG1 suppresses AKT activation and proliferation. Together, our results show that sma-10/LRIG is a conserved regulator of RTK signaling, add to our understanding of LRIG1 in melanoma and identifies recombinant LRIG1 as a potential therapeutic against BRAF inhibitor-resistant melanoma.

A Framework of Major Tumor-Promoting Signal Transduction Pathways Implicated in Melanoma-Fibroblast Dialogue

Simple Summary

Melanoma cells reside in a complex stromal microenvironment, which is a critical component of disease onset and progression. Mesenchymal or fibroblastic cell type are the most abundant cellular element of tumor stroma. Factors secreted by melanoma cells can activate non-malignant associated fibroblasts to become melanoma associate fibroblasts (MAFs). MAFs promote tumorigenic features by remodeling the extracellular matrix, supporting tumor cells proliferation, neo-angiogenesis and drug resistance. Additionally, environmental factors may contribute to the acquisition of pro-tumorigenic phenotype of fibroblasts. Overall, in melanoma, perturbed tissue homeostasis contributes to modulation of major oncogenic intracellular signaling pathways not only in tumor cells but also in neighboring cells. Thus, targeted molecular therapies need to be considered from the reciprocal point of view of melanoma and stromal cells.

Abstract

The development of a modified stromal microenvironment in response to neoplastic onset is a common feature of many tumors including cutaneous melanoma. At all stages, melanoma cells are embedded in a complex tissue composed by extracellular matrix components and several different cell populations. Thus, melanomagenesis is not only driven by malignant melanocytes, but also by the altered communication between melanocytes and non-malignant cell populations, including fibroblasts, endothelial and immune cells. In particular, cancer-associated fibroblasts (CAFs), also referred as melanoma-associated fibroblasts (MAFs) in the case of melanoma, are the most abundant stromal cells and play a significant contextual role in melanoma initiation, progression and metastasis. As a result of dynamic intercellular molecular dialogue between tumor and the stroma, non-neoplastic cells gain specific phenotypes and functions that are pro-tumorigenic. Targeting MAFs is thus considered a promising avenue to improve melanoma therapy. Growing evidence demonstrates that aberrant regulation of oncogenic signaling is not restricted to transformed cells but also occurs in MAFs. However, in some cases, signaling pathways present opposite regulation in melanoma and surrounding area, suggesting that therapeutic strategies need to carefully consider the tumor–stroma equilibrium. In this novel review, we analyze four major signaling pathways implicated in melanomagenesis, TGF-β, MAPK, Wnt/β-catenin and Hyppo signaling, from the complementary point of view of tumor cells and the microenvironment.

Somatic mutational landscapes of adherens junctions and their functional consequences in cutaneous melanoma development

Cell-cell interaction in skin homeostasis is tightly controlled by adherens junctions (AJs). Alterations in such regulation lead to melanoma development. However, mutations in AJs and their functional consequences are still largely unknown.

Methods: Cadherin mutations in skin cutaneous melanoma were identified using sequencing data from TCGA dataset, followed by cross-validation with data from non-TCGA cohorts. Mutations with significant occurrence were subjected to structural prediction using MODELLER and functional protein simulation using GROMACS software. Neo-antigen prediction was carried out using NetMHCpan tool. Cell-based fluorescence reporter assay was used to validate β-catenin activity in the presence of cadherin mutations. Clinical significance was analyzed using datasets from TCGA and other non-TCGA cohorts. Targeted gene exon sequencing and immunofluorescence staining on melanoma tissues were performed to confirm the in silico findings.

Results: Highly frequent mutations in type-II classical cadherins were found in melanoma with one unique recurrent mutation (S524L) in the fifth domain of CDH6, which potentially destabilizes Ca²⁺-binding and cell-cell contacts. Mutational co-occurrence and physical dynamics analyses placed CDH6 at the center of the top-four mutated cadherins (core CDHs; all type-II), suggesting altered heterophilic interactions in melanoma development. Mutations in the intracellular domains significantly disturbed CDH6/β-catenin complex formation, resulting in β-catenin translocation into cytosol or nucleus and dysregulation of canonical Wnt/β-catenin signaling. Although mutations in core CDH genes correlated with advanced cancer stages and lymph node invasion, the overall and disease-free survival times in those patients were longer in patients with wild-type. Peptide/MHC-I binding affinity predictions confirmed overall increased neo-antigen potentials of mutated cadherins, which associated with T-lymphocyte infiltration and better clinical outcomes after immunotherapy.

Conclusion: Changes in cell-cell communications by somatic mutations in AJ cadherins function as one of mechanisms to trigger melanoma development. Certain mutations in AJs may serve as potential neo-antigens which conversely benefit patients for longer survival times.

WNT11-FZD7-DAAM1 signalling supports tumour initiating abilities and melanoma amoeboid invasion

Melanoma is a highly aggressive tumour that can metastasize very early in disease progression. Notably, melanoma can disseminate using amoeboid invasive strategies. We show here that high Myosin II activity, high levels of ki-67 and high tumour-initiating abilities are characteristic of invasive amoeboid melanoma cells. Mechanistically, we find that WNT11-FZD7-DAAM1 activates Rho-ROCK1/2-Myosin II and plays a crucial role in regulating tumour-initiating potential, local invasion and distant metastasis formation. Importantly, amoeboid melanoma cells express both proliferative and invasive gene signatures. As such, invasive fronts of human and mouse melanomas are enriched in amoeboid cells that are also ki-67 positive. This pattern is further enhanced in metastatic lesions. We propose eradication of amoeboid melanoma cells after surgical removal as a therapeutic strategy.

Role of the p53‑TRPM1/miR‑211‑MMP9 axis in UVB‑induced human melanocyte migration and its potential in repigmentation

Clinical studies have proven that ultraviolet B (UVB) based phototherapy can induce perifollicular and marginal repigmentation patterns in the skin of vitiligo patients. It is, however, difficult to conceive how melanocytes can easily exit from their tightly interconnected epidermal microenvironment to re‑enter a different location in the skin to establish a new network with neighboring keratinocytes. While it is known that matrix metalloprotease 9 (MMP9) is involved in the degradation of the extracellular matrix in physiological or pathological processes, little is known about whether MMP9 affects melanocyte migration in vitiligo repigmentation. To investigate the effects of the p53‑ transient receptor potential cation channel subfamily M member 1 (TRPM1)/microRNA (miR/miRNA)‑211‑MMP9 axis to regulate melanocyte migration following exposure to UVB, the expression profile of MMP9 in cultured human melanocytes transfected with or without the miR‑211‑mimic and p53‑GFP lentiviral vector, respectively were determined. Quantitative polymerase chain reaction and western blotting were used to examine p53, TRPM1 and MMP9 mRNA and protein levels in UVB‑exposed and unexposed cells. The capacity of melanocytes to migrate on collagen IV substrate was estimated using a Transwell migration assay. Interestingly, the upregulation of p53 and MMP9 at the mRNA and protein levels was evident in melanocytes treated with single or repeat exposures to UVB, whereas levels of TRPM1 and miR‑211 were significantly suppressed in UVB‑exposed melanocytes compared with the UVB‑unexposed control cells. These results indicate that the p53‑TRPM1/miR‑211‑MMP9 axis is significantly activated in melanocytes exposed to UVB. Notably, the ability of melanocyte migration was altered by the overexpression of p53 using a lentiviral vector and by the upregulation of miR‑211 using an miRNA mimic. That altered migration could be neutralized by co‑treatment with GM6001 (a broad‑spectrum MMP inhibitor). Overall, these results show that the MMP9‑mediated migration of melanocytes is regulated by a novel mechanism driven by the p53‑TRPM1/miR‑211‑MMP9 axis. Activation of the p53‑TRPM1/miR‑211‑MMP9 axis potentially represents an attractive therapeutic target to improve repigmentation outcomes in vitiligo patients.

Melanoma in the Eyes of Mechanobiology

Skin is the largest organ of the human body with several important functions that can be impaired by injury, genetic or chronic diseases. Among all skin diseases, melanoma is one of the most severe, which can lead to death, due to metastization. Mechanotransduction has a crucial role for motility, invasion, adhesion and metastization processes, since it deals with the response of cells to physical forces. Signaling pathways are important to understand how physical cues produced or mediated by the Extracellular Matrix (ECM), affect healthy and tumor cells. During these processes, several molecules in the nucleus and cytoplasm are activated. Melanocytes, keratinocytes, fibroblasts and the ECM, play a crucial role in melanoma formation. This manuscript will address the synergy among melanocytes, keratinocytes, fibroblasts cells and the ECM considering their mechanical contribution and relevance in this disease. Mechanical properties of melanoma cells can also be influenced by pigmentation, which can be associated with changes in stiffness. Mechanical changes can be related with the adhesion, migration, or invasiveness potential of melanoma cells promoting a high metastization capacity of this cancer. Mechanosensing, mechanotransduction, and mechanoresponse will be highlighted with respect to the motility, invasion, adhesion and metastization in melanoma cancer.

Identification of novel, immune-mediating extracellular vesicles in human lymphatic effluent draining primary cutaneous melanoma

Epithelial tumors including melanoma often first metastasize to regional, sentinel lymph nodes (SLN). Thus, the presence of SLN metastases is a critical prognostic factor of survival. Prior to metastasis, accumulating evidence suggests the SLN is immunologically compromised; however, the process by which pre-metastatic niche formation occurs remains unknown. In this prospective study, freshly dissected, afferent lymphatic fluid was obtained during SLN biopsy in three patients with primary cutaneous melanoma. Lymphatic extracellular vesicles (L-EV) were visualized by transmission electron microscopy and proteomic cargo profiled by mass spectrometry. Flow cytometry assessed L-EV effects on autologous dendritic cell maturation in vitro. Immunogold electron microscopy and immunohistochemistry visualized expression of EV cargo within the primary tumor and SLN. Lymphatic extracellular vesicles from each afferent lymphatic channel demonstrated inhibition of autologous dendritic cell maturation. Proteomic profiling identified 81 peptides shared among the L-EV preparations including a signature of 18 immune-modulating proteins including previously established inhibitor of dendritic cell maturation, S100A9. Immunohistochemistry and immunogold electron microscopy confirmed S100A9 tracking along the lymphatic path, from keratinocytes in the primary tumor to sub-capsular macrophages in the SLN. Our findings suggest L-EV cargo may serve as early mediators of tumor-induced immune subversion in regional lymph nodes, by preceding malignant cells and trafficking within the lymphatic vasculature to harbor the first pre-metastatic niche.

Photodynamic therapy of melanoma by blue-light photoactivation of flavin mononucleotide

Melanoma is one of the most aggressive and lethal form of cancer. Photodynamic therapy (PDT) is a clinically approved technique for cancer treatment, including non-melanoma skin cancer. However, the most of conventional photosensitizers are of low efficacy against melanoma due to the possible dark toxicity at high drug concentrations, melanin pigmentation, and induction of anti-oxidant defense mechanisms. In the current research we propose non-toxic flavin mononucleotide (FMN), which is a water-soluble form of riboflavin (vitamin B2) as a promising agent for photodynamic therapy of melanoma. We demonstrated selective accumulation of FMN in melanoma cells in vivo and in vitro in comparison with keratinocytes and fibroblasts. Blue light irradiation with dose 5 J/cm² of melanoma cells pre-incubated with FMN led to cell death through apoptosis. Thus, the IC₅₀ values of human melanoma A375, Mel IL, and Mel Z cells were in a range of FMN concentration 10–30 µM that can be achieved in tumor tissue under systemic administration. The efficiency of reactive oxygen species (ROS) generation under FMN blue light irradiation was measured in single melanoma cells by a label-free technique using an electrochemical nanoprobe in a real-time control manner. Melanoma xenograft regression in mice was observed as a result of intravenous injection of FMN followed by blue-light irradiation of tumor site. The inhibition of tumor growth was 85–90% within 50 days after PDT treatment.

CADM1 is a TWIST1-regulated suppressor of invasion and survival

Metastatic cancer remains a clinical challenge; however, patients diagnosed prior to metastatic dissemination have a good prognosis. The transcription factor, TWIST1 has been implicated in enhancing the migration and invasion steps within the metastatic cascade, but the range of TWIST1-regulated targets is poorly described. In this study, we performed expression profiling to identify the TWIST1-regulated transcriptome of melanoma cells. Gene ontology pathway analysis revealed that TWIST1 and epithelial to mesenchymal transition (EMT) were inversely correlated with levels of cell adhesion molecule 1 (CADM1). Chromatin immunoprecipitation (ChIP) studies and promoter assays demonstrated that TWIST1 physically interacts with the CADM1 promoter, suggesting TWIST1 directly represses CADM1 levels. Increased expression of CADM1 resulted in significant inhibition of motility and invasiveness of melanoma cells. In addition, elevated CADM1 elicited caspase-independent cell death in non-adherent conditions. Expression array analysis suggests that CADM1 directed non-adherent cell death is associated with loss of mitochondrial membrane potential and subsequent failure of oxidative phosphorylation pathways. Importantly, tissue microarray analysis and clinical data from TCGA indicate that CADM1 expression is inversely associated with melanoma progression and positively correlated with better overall survival in patients. Together, these data suggest that CADM1 exerts tumor suppressive functions in melanoma by reducing invasive potential and may be considered a biomarker for favorable prognosis.

Advances in Carbon Nanotubes for Malignant Melanoma: A Chance for Treatment

Malignant melanoma is an aggressive skin cancer with limited therapeutic options. Cancer is the second largest cause of death in society and one of the most difficult diseases to treat. Advances in biotechnology have enabled the current use of nanotechnology via the application of nanomaterials, especially as drug delivery systems for the transportation of very small particles. In this context, carbon nanotubes, with a potential role in the diagnosis and treatment of melanoma, are still an emerging research field. Their properties have been extensively studied for the use of antineoplastics drugs, as well as for DNA and RNA interference for the treatment of cancer. However, the most important challenge in nanomedicine is to decrease the toxicity and increase the biocompatibility of the nanomaterials used to transport therapeutic molecules. In this sense, this article addresses the recent advances in the use of carbon nanotubes in melanoma therapy and highlights the opportunities and challenges in this area. The advances and challenges involving these topics are essential to the success of nanoconjugate systems, and studies improving the comprehension of these nanosystems contribute to the development of specific antitumor therapies.

Betulin silver nanoparticles qualify as efficient antimelanoma agents in in vitro and in vivo studies

The current study was purported to assess the: (i) in vitro toxicity of betulin silver nanoparticles (AgNPs-B), bare and capped with polyethylene glycol (PEG), on two murine melanoma cell lines (B164A5 and B16Ova) and on healthy cell lines (keratinocytes and melanocytes), and (ii) in vivo antitumor efficacy of PEGylated AgNPs-B in an experimental melanoma model. Bare and PEG-capped AgNPs-B were synthesized by a chemical reduction method resulting in stable and non-aggregated spherical AgNPs-B and PEG-AgNPs-B, of narrow size distributions and mean hydrodynamic diameters of 25 nm and 75 nm, respectively. In vitro assessments were achieved by MTT and Annexin V-FITC assays and in vivo evaluation involved non-invasive techniques for the surveillance of the physiological skin parameters changes and histopathological examination of the harvested organs. The in vitro results revealed selective cytotoxicity against melanoma cells, at low doses that are nontoxic to normal cells; higher doses were associated with the loss of selectivity and toxicity for healthy cells. PEGylated formulation of betulin exerted a dose-dependent pro-apoptotic effect, more obvious in the case of B164A5 cells. Histopathological analysis suggested that PEGylated AgNPs-B developed relevant in vivo effects as antimelanoma agents by decreasing the tumor volume and inhibiting the development of secondary tumors.

Breslow Density Is a Novel Prognostic Feature That Adds Value to Melanoma Staging

Histomorphologic prognostic biomarkers that can be measured using only an hematoxylin and eosin stain are very attractive because they are simple and cheap. We conceived an entirely novel biomarker of this type, the Breslow density (BD), which measures invasive melanoma cell density at the site where Breslow thickness (BT) is measured. This study assessed BD's prognostic value. In this study, BD was measured in 1329 melanoma patients. Measurement accuracy and precision was assessed using intraclass correlation coefficient (ICC). Survival was assessed with a primary end-point of melanoma-specific survival (MSS) and also overall survival and metastasis-free survival. We found that BD measurement was accurate compared with gold standard image analysis (ICC, 0.84). Precision was excellent for 3 observers with different experience (ICC, 0.93) and for an observer using only written instructions (ICC, 0.93). BD was a highly significant predictor in multivariable analysis for overall survival, MSS, and metastasis-free survival (each, P<0.001) and it explained MSS better than BT, but BT and BD together had best explanatory capability. A BD cut point of ≥65% was trained in 970 melanomas and validated in 359. This cut point showed promise as a novel way to upstage melanoma from T stage "a" to "b." BD was combined with BT to create a targeted burden score. This was a validated as an adjunct to American Joint Committee on Cancer stage. In summary, BD can be measured accurately and precisely. It demonstrated independent prognostic value and explained MSS better than BT alone. Notably, we demonstrated ways that BD could be used with American Joint Committee on Cancer version 8 staging.

Fibroblasts potentiate melanoma cells in vitro invasiveness induced by UV-irradiated keratinocytes

Melanoma represents a malignant disease with steadily increasing incidence. UV-irradiation is a recognized key factor in melanoma initiation. Therefore, the efficient prevention of UV tissue damage bears a critical potential for melanoma prevention. In this study, we tested the effect of UV irradiation of normal keratinocytes and their consequent interaction with normal and cancer-associated fibroblasts isolated from melanoma, respectively. Using this model of UV influenced microenvironment, we measured melanoma cell migration in 3-D collagen gels. These interactions were studied using DNA microarray technology, immunofluorescence staining, single cell electrophoresis assay, viability (dead/life) cell detection methods, and migration analysis. We observed that three 10 mJ/cm² fractions at equal intervals over 72 h applied on keratinocytes lead to a 50% increase (p < 0.05) in in vitro invasion of melanoma cells. The introduction cancer-associated fibroblasts to such model further significantly stimulated melanoma cells in vitro invasiveness to a higher extent than normal fibroblasts. A panel of candidate gene products responsible for facilitation of melanoma cells invasion was defined with emphasis on IL-6, IL-8, and CXCL-1. In conclusion, this study demonstrates a synergistic effect between cancer microenvironment and UV irradiation in melanoma invasiveness under in vitro condition.

Targeting invasive properties of melanoma cells

Melanoma is a skin cancer notorious for its metastatic potential. As an initial step of the metastatic cascade, melanoma cells part from the primary tumour and invade the surrounding tissue, which is crucial for their dissemination and the formation of distant secondary tumours. Over the last two decades, our understanding of both, general and melanoma specific mechanisms of invasion has significantly improved, but to date no efficient therapeutic strategy tackling the invasive properties of melanoma cells has reached the clinic. In this review, we assess the major contributions towards the understanding of the molecular biology of melanoma cell invasion with a focus on melanoma specific traits. These traits are based on the neural crest origin of melanoma cells and explain their intrinsic invasive nature. A particular emphasis is given not only to lineage specific signalling mediated by TGFβ, and noncanonical and canonical WNT signalling, but also to the role of PDE5A and RHO-GTPases in modulating modes of melanoma cell invasion. We discuss existing caveats in the current understanding of the metastatic properties of melanoma cells, as well as the relevance of the 'phenotype switch' model and 'co-operativity' between different phenotypes in heterogeneous tumours. At the centre of these phenotypes is the lineage commitment factor microphthalmia-associated transcription factor, one of the most crucial regulators of the balance between de-differentiation (neural crest specific gene expression) and differentiation (melanocyte specific gene expression) that defines invasive and noninvasive melanoma cell phenotypes. Finally, we provide insight into the current evidence linking resistance to targeted therapies to invasive properties of melanoma cells.

Next generation human skin constructs as advanced tools for drug development

Many diseases, as well as side effects of drugs, manifest themselves through skin symptoms. Skin is a complex tissue that hosts various specialized cell types and performs many roles including physical barrier, immune and sensory functions. Therefore, modeling skin in vitro presents technical challenges for tissue engineering. Since the first attempts at engineering human epidermis in 1970s, there has been a growing interest in generating full-thickness skin constructs mimicking physiological functions by incorporating various skin components, such as vasculature and melanocytes for pigmentation. Development of biomimetic in vitro human skin models with these physiological functions provides a new tool for drug discovery, disease modeling, regenerative medicine and basic research for skin biology. This goal, however, has long been delayed by the limited availability of different cell types, the challenges in establishing co-culture conditions, and the ability to recapitulate the 3D anatomy of the skin. Recent breakthroughs in induced pluripotent stem cell (iPSC) technology and microfabrication techniques such as 3D-printing have allowed for building more reliable and complex in vitro skin models for pharmaceutical screening. In this review, we focus on the current developments and prevailing challenges in generating skin constructs with vasculature, skin appendages such as hair follicles, pigmentation, immune response, innervation, and hypodermis. Furthermore, we discuss the promising advances that iPSC technology offers in order to generate in vitro models of genetic skin diseases, such as epidermolysis bullosa and psoriasis. We also discuss how future integration of the next generation human skin constructs onto microfluidic platforms along with other tissues could revolutionize the early stages of drug development by creating reliable evaluation of patient-specific effects of pharmaceutical agents. Impact statement Skin is a complex tissue that hosts various specialized cell types and performs many roles including barrier, immune, and sensory functions. For human-relevant drug testing, there has been a growing interest in building more physiological skin constructs by incorporating different skin components, such as vasculature, appendages, pigment, innervation, and adipose tissue. This paper provides an overview of the strategies to build complex human skin constructs that can faithfully recapitulate human skin and thus can be used in drug development targeting skin diseases. In particular, we discuss recent developments and remaining challenges in incorporating various skin components, availability of iPSC-derived skin cell types and in vitro skin disease models. In addition, we provide insights on the future integration of these complex skin models with other organs on microfluidic platforms as well as potential readout technologies for high-throughput drug screening.

Mouse models of UV-induced melanoma: genetics, pathology, and clinical relevance

Melanocytes, a neural crest cell derivative, produce pigment to protect keratinocytes from ultraviolet radiation (UVR). Although melanocytic lesions such as nevi and cutaneous malignant melanomas are known to be associated with sun exposure, the role of UVR in oncogenesis is complex and has yet to be clearly elucidated. UVR appears to have a direct mutational role in inducing or promoting melanoma formation as well as an indirect role through microenvironmental changes. Recent advances in the modeling of human melanoma in animals have built platforms upon which prospective studies can begin to investigate these questions. This review will focus exclusively on genetically engineered mouse models of UVR-induced melanoma. The role that UVR has in mouse models depends on multiple factors, including the waveband, timing, and dose of UVR, as well as the nature of the oncogenic agent(s) driving melanomagenesis in the model. Work in the field has examined the role of neonatal and adult UVR, interactions between UVR and common melanoma oncogenes, the role of sunscreen in preventing melanoma, and the effect of UVR on immune function within the skin. Here we describe relevant mouse models and discuss how these models can best be translated to the study of human skin and cutaneous melanoma.

The Presence of Alpha-Synuclein in Skin from Melanoma and Patients with Parkinson's Disease

Background

The misfolding and prion-like propagation of the protein α-synuclein (α-syn) is the leading molecular signature in Parkinson's disease (PD). There is a significant coincidence of PD and melanoma that may suggest a shared pathophysiology. This study compared the presence of α-syn in neural crest-derived tissues, such as nevi, melanoma, skin tags, and skin biopsies from patients with PD and healthy controls.

Methods

Biopsies from participants with PD were obtained from patients from a tertiary referral center for dermatology and neurology in Mexico and a private dermatopathology center in Florida between January 2015 and March 2016. Biopsies from 7 patients with melanoma, 15 with nevi, 9 with skin tags, 8 with PD, and 9 skin biopsies from healthy volunteers were analyzed for immunohistochemical determination of α-syn and tyrosinase. All analyses were performed by pathologists who were blinded with respect to the clinical diagnosis.

Results

In healthy controls, positive α-syn status was restricted to scattered cells in the basal layer of the epidermis and accounted for 1 ± 0.8% of the analyzed area. In patients with PD, there was increased staining for α-syn PD (3.3 ± 2.3%), with a higher percentage of positive cells in nevi (7.7 ± 5.5%) and melanoma (13.6 ± 3.5%). There was no increased staining in skin tags compared with healthy controls.

Conclusion

Patients with PD and melanoma have increased staining for α-syn in their skin. The authors propose that neurons and melanocytes, both derived from neuroectodermal cells, may share protein synthesis and regulation pathways that become dysfunctional in PD and melanoma.