The Complex Role of Autophagy in Melanoma Evolution: New Perspectives From Mouse Models

Exploring the Interplay of RUNX2 and CXCR4 in Melanoma Progression

Overexpression of the Runt-related transcription factor 2 (RUNX2) has been reported in several cancer types, and the C-X-C motif chemokine receptor 4 (CXCR4) has an important role in tumour progression. However, the interplay between CXCR4 and RUNX2 in melanoma cells remains poorly understood. In the present study, we used melanoma cells and a RUNX2 knockout (RUNX2-KO) in vitro model to assess the influence of RUNX2 on CXCR4 protein levels along with its effects on markers associated with cell invasion and autophagy. Osteotropism was assessed using a 3D microfluidic model. Moreover, we assessed the impact of CXCR4 on the cellular levels of key cellular signalling proteins involved in autophagy. We observed that melanoma cells express both RUNX2 and CXCR4. Restored RUNX2 expression in RUNX2 KO cells increased the expression levels of CXCR4 and proteins associated with the metastatic process. The protein markers of autophagy LC3 and beclin were upregulated in response to increased CXCR4 levels. The CXCR4 inhibitor WZ811 reduced osteotropism and activated the mTOR and p70-S6 cell signalling proteins. Our data indicate that the RUNX2 transcription factor promotes the expression of the CXCR4 chemokine receptor on melanoma cells, which in turn promotes autophagy, cell invasiveness, and osteotropism, through the inhibition of the mTOR signalling pathway. Our data suggest that RUNX2 promotes melanoma progression by upregulating CXCR4, and we identify the latter as a key player in melanoma-related osteotropism.

Assessment of Autophagy in Tumor Cells of Human Skin Melanoma of Different Stages

High levels of autophagy can increase the viability of tumor cells as well as their resistance to chemotherapy. Evaluation of the dynamics of autophagy processes at different stages of carcinogenesis can extend our understanding of melanoma pathogenesis to develop new therapeutic approaches. We performed a comparative study of tumor cell autophagy in stages II and III human skin melanoma. Tumor cells were characterized by high content of structures associated with autophagy (autophagosomes and autolysosomes). In stage III melanoma characterized by the presence of regional metastases in the lymph nodes, tumor cells showed higher expression of the autophagy marker protein LC3beta in comparison with stage II melanoma cells, which can indicate the involvement of autophagy processes in tumor progression and the formation of metastases in the lymph nodes.

Autophagy in BRAF-mutant cutaneous melanoma: recent advances and therapeutic perspective

Macroautophagy, hereafter referred to as autophagy, represents a highly conserved catabolic process that maintains cellular homeostasis. At present, the role of autophagy in cutaneous melanoma (CM) is still controversial, since it appears to be tumor-suppressive at early stages of malignant transformation and cancer-promoting during disease progression. Interestingly, autophagy has been found to be often increased in CM harboring BRAF mutation and to impair the response to targeted therapy. In addition to autophagy, numerous studies have recently conducted in cancer to elucidate the molecular mechanisms of mitophagy, a selective form of mitochondria autophagy, and secretory autophagy, a process that facilitates unconventional cellular secretion. Although several aspects of mitophagy and secretory autophagy have been investigated in depth, their involvement in BRAF-mutant CM biology has only recently emerged. In this review, we aim to overview autophagy dysregulation in BRAF-mutant CM, along with the therapeutic advantages that may arise from combining autophagy inhibitors with targeted therapy. In addition, the recent advances on mitophagy and secretory autophagy involvement in BRAF-mutant CM will be also discussed. Finally, since a number of autophagy-related non-coding RNAs (ncRNAs) have been identified so far, we will briefly discussed recent advances linking ncRNAs to autophagy regulation in BRAF-mutant CM.

Re-Sensitizing Cancer Stem Cells to Conventional Chemotherapy Agents

Cancer stem cells are found in many cancer types. They comprise a distinct subpopulation of cells within the tumor that exhibit properties of stem cells. They express a number of cell surface markers, such as CD133, CD44, ALDH, and EpCAM, as well as embryonic transcription factors Oct4, Nanog, and SOX2. CSCs are more resistant to conventional chemotherapy and can potentially drive tumor relapse. Therefore, it is essential to understand the molecular mechanisms that drive chemoresistance and to target them with specific therapy effectively. Highly conserved developmental signaling pathways such as Wnt, Hedgehog, and Notch are commonly reported to play a role in CSCs chemoresistance development. Studies show that particular pathway inhibitors combined with conventional therapy may re-establish sensitivity to the conventional therapy. Another significant contributor of chemoresistance is a specific tumor microenvironment. Surrounding stroma in the form of cancer-associated fibroblasts, macrophages, endothelial cells, and extracellular matrix components produce cytokines and other factors, thus creating a favorable environment and decreasing the cytotoxic effects of chemotherapy. Anti-stromal agents may potentially help to overcome these effects. Epigenetic changes and autophagy were also among the commonly reported mechanisms of chemoresistance. This review provides an overview of signaling pathway components involved in the development of chemoresistance of CSCs and gathers evidence from experimental studies in which CSCs can be re-sensitized to conventional chemotherapy agents across different cancer types.

Shining Light on Autophagy in Skin Pigmentation and Pigmentary Disorders

Autophagy is a vital process for cell survival and it preserves homeostasis by recycling or disassembling unnecessary or dysfunctional cellular constituents. Autophagy ameliorates skin integrity, regulating epidermal differentiation and constitutive pigmentation. It induces melanogenesis and contributes to skin color through melanosome turnover. Autophagy activity is involved in skin phenotypic plasticity and cell function maintenance and, if altered, it concurs to the onset and/or progression of hypopigmentary and hyperpigmentary disorders. Overexpression of autophagy exerts a protective role against the intrinsic metabolic stress occurring in vitiligo skin, while its dysfunction has been linked to the tuberous sclerosis complex hypopigmentation. Again, autophagy impairment reduces melanosome degradation by concurring to pigment accumulation characterizing senile lentigo and melasma. Here we provide an updated review that describes recent findings on the crucial role of autophagy in skin pigmentation, thus revealing the complex interplay among melanocyte biology, skin environment and autophagy. Hence, targeting this process may also represent a promising strategy for treating pigmentary disorders.

NAD/NAMPT and mTOR Pathways in Melanoma: Drivers of Drug Resistance and Prospective Therapeutic Targets

Malignant melanoma represents the most fatal skin cancer due to its aggressive behavior and high metastatic potential. The introduction of BRAF/MEK inhibitors and immune-checkpoint inhibitors (ICIs) in the clinic has dramatically improved patient survival over the last decade. However, many patients either display primary (i.e., innate) or develop secondary (i.e., acquired) resistance to systemic treatments. Therapeutic resistance relies on the rewiring of multiple processes, including cancer metabolism, epigenetics, gene expression, and interactions with the tumor microenvironment that are only partially understood. Therefore, reliable biomarkers of resistance or response, capable of facilitating the choice of the best treatment option for each patient, are currently missing. Recently, activation of nicotinamide adenine dinucleotide (NAD) metabolism and, in particular, of its rate-limiting enzyme nicotinamide phosphoribosyltransferase (NAMPT) have been identified as key drivers of targeted therapy resistance and melanoma progression. Another major player in this context is the mammalian target of rapamycin (mTOR) pathway, which plays key roles in the regulation of melanoma cell anabolic functions and energy metabolism at the switch between sensitivity and resistance to targeted therapy. In this review, we summarize known resistance mechanisms to ICIs and targeted therapy, focusing on metabolic adaptation as one main mechanism of drug resistance. In particular, we highlight the roles of NAD/NAMPT and mTOR signaling axes in this context and overview data in support of their inhibition as a promising strategy to overcome treatment resistance.

Autophagy: Guardian of Skin Barrier

Autophagy is a major degradation pathway that removes harmful intracellular substances to maintain homeostasis. Various stressors, such as starvation and oxidative stress, upregulate autophagy, and the dysregulation of autophagy is associated with various human diseases, including cancer and skin diseases. The skin is the first defense barrier against external environmental hazards such as invading pathogens, ultraviolet rays, chemical toxins, and heat. Although the skin is exposed to various stressors that can activate autophagy, the roles of autophagy in the skin have not yet been fully elucidated. Accumulating evidence suggests that autophagy is closely associated with pathogenesis and the treatment of immune-related skin diseases. In this study, we review how autophagy interacts with skin cells, including keratinocytes and immune cells, enabling them to successfully perform their protective functions by eliminating pathogens and maintaining skin homeostasis. Furthermore, we discuss the implications of autophagy in immune-related skin diseases, such as alopecia areata, psoriasis, and atopic dermatitis, and suggest that a combination of autophagy modulators with conventional therapies may be a better strategy for the treatment of these diseases.

M-CSF as a therapeutic target in BRAFV600E melanoma resistant to BRAF inhibitors

BACKGROUND

Disseminated BRAF^V600E melanoma responds to BRAF inhibitors (BRAFi) but easily develops resistance with poor prognosis. Secretome plays a pivotal role during tumour progression causing profound effects on therapeutic efficacy. Secreted M-CSF is involved in both cytotoxicity suppression and tumour progression in melanoma. We aimed to analyse the M-CSF contribution in resistant metastatic melanoma to BRAF-targeted therapies.

METHODS

Conditioned media from melanoma cells were analysed by citoarray. Viability and migration/invasion assays were performed with paired melanoma cells and tumour growth in xenografted SCID mice. We evaluated the impact of M-CSF plasma levels with clinical prognosis from 35 metastatic BRAF^V600E-mutant melanoma patients.

RESULTS

BRAFi-resistant melanoma cells secretome is rich in pro-tumour cytokines. M-CSF secretion is essential to induce a Vemurafenib-resistant phenotype in melanoma cells. Further, we demonstrated that M-CSF mAb in combination with Vemurafenib and autophagy blockers synergistically induce apoptosis, impair migration and reduce tumour growth in BRAFi-resistant melanoma cells. Interestingly, lower M-CSF plasma levels are associated with better prognosis in metastatic melanoma patients.

CONCLUSIONS

Secreted M-CSF induces a BRAFi-resistant phenotype and means worse prognosis in BRAF^V600E metastatic melanoma patients. These results identify secreted M-CSF as a promising therapeutic target toward BRAFi-resistant melanomas.

Secretory Autophagy Forges a Therapy Resistant Microenvironment in Melanoma

Melanoma is the most aggressive skin cancer characterized by high mutational burden and large heterogeneity. Cancer cells are surrounded by a complex environment, critical to tumor establishment and progression. Thus, tumor-associated stromal components can sustain tumor demands or impair cancer cell progression. One way to manage such processes is through the regulation of autophagy, both in stromal and tumor cells. Autophagy is a catabolic mechanism that provides nutrients and energy, and it eliminates damaged organelles by degradation and recycling of cellular elements. Besides this primary function, autophagy plays multiple roles in the tumor microenvironment capable of affecting cell fate. Evidence demonstrates the existence of novel branches in the autophagy system related to cytoplasmic constituent's secretion. Hence, autophagy-dependent secretion assembles a tangled network of signaling that potentially contributes to metabolism reprogramming, immune regulation, and tumor progression. Here, we summarize the current awareness regarding secretory autophagy and the intersection with exosome biogenesis and release in melanoma and their role in tumor resistance. In addition, we present and discuss data from public databases concerning autophagy and exosome-related genes as important mediators of melanoma behavior. Finally, we will present the main challenges in the field and strategies to translate most of the pre-clinical findings to clinical practice.

Establishment and validation of an autophagy-related prognostic signature for survival predicting in cutaneous melanoma

Existing staging system for prognosis evaluating for Skin Cutaneous Melanoma (SKCM) patients had defects of subjective, inaccuracy and inconsistently, therefore, to identify specific and applicable prognostic markers and promote personalized therapeutic interventions is urgently required. This study aims to build a robust autophagy-related genes (ARGs) signature for prognosis monitoring of SKCM patients. We determined 26 ARGs as differentially expressed autophagy-related genes (DEARGs) from 103 SKCM and 23 normal skin samples in GSE15605 and GSE3189 datasets. Optimal prognostic DEARGs composed the risk model were screened and verified in 458 SKCM patients in TCGA cohort as the training cohort and 209 patients in GSE65904 as the test cohort. Finally, 4 optimal independent prognostic DEARGs (CAPNS1, DAPK2, PARP1 and PTK6) were filtered out in the training cohort to establish the risk model. A prognostic nomogram was established for quantitative survival prediction. The risk model grouped high-risk SKCM cancer patients exhibited significantly shorter survival times in both training and test cohorts. The area under the ROC curve for risk score model was 0.788 and 0.627 in the training and test cohorts indicated the risk model was relatively accurate for prognosis monitoring. Clinical correlation analysis exhibited that risk score was an independent predictor for prognosis significantly associated with T/N classification. The prognostic value of the 4 risk genes formed the risk model was also validated respectively. We identified a novel autophagy-related signature for prognosis monitoring. It has the potential to be an independent prognostic indicator and can benefit targeted therapy.

Recent Advances in Phenolic Metabolites and Skin Cancer

Skin cancer represents any tumor development from the cutaneous structures within the epidermis, dermis or subcutaneous tissue, and is considered to be the most prevalent type of cancer. Compared to other types of cancer, skin cancer is proven to have a positive growth rate of prevalence and mortality. There are available various treatments, including chemotherapy, immunotherapy, radiotherapy and targeted therapy, but because of the multidrug resistance development, a low success has been registered. By this, the importance of studying naturally occurring compounds that are both safe and effective in the chemoprevention of skin cancer is emphasized. This review focuses on melanoma because it is the deadliest form of skin cancer, with a significantly increasing incidence in the last decades. As chemopreventive agents, we present polyphenols and their antioxidant activity, anti-inflammatory effect, their ability to balance the cell cycle and to induce apoptosis and their various other effects on skin melanoma. Besides chemoprevention, studies suggest that polyphenols can have treating abilities in some conditions. The limitations of using polyphenols are also pointed out, which are related to their poor bioavailability and stability, but as the technology is well developed, it is possible to augment the efficacy of polyphenols in the case of melanoma.

Preclinical autophagy modulatory nanomedicines: big challenges, slow advances

INTRODUCTION

Autophagy is a critical housekeeping pathway to remove toxic protein aggregates, damaged organelles, providing cells with bioenergetic substrates needed to survive under adverse conditions. Since altered autophagy is associated with diverse diseases, its pharmacological modulation is considered of therapeutic interest. Nanomedicines may reduce the toxicity and improve the activity of toxic autophagy modulatory drugs (amd).

AREAS COVERED

The status of the most relevant anti-tumor, anti-inflammatory, and anti-infectious treatments mediated by autophagy modulatory nanomedicines (amN) published in the last 5 years is discussed.

EXPERT OPINION

Antitumor and anti-inflammatory treatments may be improved by administering amN for selective, massive, and targeted delivery of amd to diseased tissues. The use of amN as antimicrobial agent remains almost underexploited. Assessing the effect of amN on the complex autophagy machinery operating under different basal diseases, however, is not a trivial task. Besides structural reproducibility, nanomedicines must grant higher efficiency, and lower adverse effects than conventional medication. Simplicity of design, carefully chosen (scalable) preparation techniques, and rigorous monitoring of preclinical efficacy and nanotoxicity will improve the chances of clinical success. Currently, available data are not sufficient to envisage a fast-succeeding translation. Application of quality by design criteria would help to reach such milestones.

BNIP3 promotes HIF-1α-driven melanoma growth by curbing intracellular iron homeostasis

BNIP3 is a mitophagy receptor with context-dependent roles in cancer, but whether and how it modulates melanoma growth in vivo remains unknown. Here, we found that elevated BNIP3 levels correlated with poorer melanoma patient's survival and depletion of BNIP3 in B16-F10 melanoma cells compromised tumor growth in vivo. BNIP3 depletion halted mitophagy and enforced a PHD2-mediated downregulation of HIF-1α and its glycolytic program both in vitro and in vivo. Mechanistically, we found that BNIP3-deprived melanoma cells displayed increased intracellular iron levels caused by heightened NCOA4-mediated ferritinophagy, which fostered PHD2-mediated HIF-1α destabilization. These effects were not phenocopied by ATG5 or NIX silencing. Restoring HIF-1α levels in BNIP3-depleted melanoma cells rescued their metabolic phenotype and tumor growth in vivo, but did not affect NCOA4 turnover, underscoring that these BNIP3 effects are not secondary to HIF-1α. These results unravel an unexpected role of BNIP3 as upstream regulator of the pro-tumorigenic HIF-1α glycolytic program in melanoma cells.

Loss of Ambra1 promotes melanoma growth and invasion

Melanoma is the deadliest skin cancer. Despite improvements in the understanding of the molecular mechanisms underlying melanoma biology and in defining new curative strategies, the therapeutic needs for this disease have not yet been fulfilled. Herein, we provide evidence that the Activating Molecule in Beclin-1-Regulated Autophagy (Ambra1) contributes to melanoma development. Indeed, we show that Ambra1 deficiency confers accelerated tumor growth and decreased overall survival in Braf/Pten-mutated mouse models of melanoma. Also, we demonstrate that Ambra1 deletion promotes melanoma aggressiveness and metastasis by increasing cell motility/invasion and activating an EMT-like process. Moreover, we show that Ambra1 deficiency in melanoma impacts extracellular matrix remodeling and induces hyperactivation of the focal adhesion kinase 1 (FAK1) signaling, whose inhibition is able to reduce cell invasion and melanoma growth. Overall, our findings identify a function for AMBRA1 as tumor suppressor in melanoma, proposing FAK1 inhibition as a therapeutic strategy for AMBRA1 low-expressing melanoma.

Tracking of Glycans Structure and Metallomics Profiles in BRAF Mutated Melanoma Cells Treated with Vemurafenib

Nearly half of patients with advanced and metastatic melanomas harbor a BRAF mutation. Vemurafenib (VEM), a BRAF inhibitor, is used to treat such patients, however, responses to VEM are very short-lived due to intrinsic, adaptive and/or acquired resistance. In this context, we present the action of the B-Raf serine-threonine protein kinase inhibitor (vemurafenib) on the glycans structure and metallomics profiles in melanoma cells without (MeWo) and with (G-361) BRAF mutations. The studies were performed using α1-acid glycoprotein (AGP), a well-known acute-phase protein, and concanavalin A (Con A), which served as the model receptor. The detection of changes in the structure of glycans can be successfully carried out based on the frequency shifts and the charge transfer resistance after interaction of AGP with Con A in different VEM treatments using QCM-D and EIS measurements. These changes were also proved based on the cell ultrastructure examined by TEM and SEM. The LA-ICP-MS studies provided details on the metallomics profile in melanoma cells treated with and without VEM. The studies evidence that vemurafenib modifies the glycans structures and metallomics profile in melanoma cells harboring BRAF mutation that can be further implied in the resistance phenomenon. Therefore, our data opens a new avenue for further studies in the short-term addressing novel targets that hopefully can be used to improve the therapeutic regiment in advanced melanoma patients. The innovating potential of this study is fully credible and has a real impact on the global patient society suffering from advanced and metastatic melanomas.

Mefloquine Inhibits Esophageal Squamous Cell Carcinoma Tumor Growth by Inducing Mitochondrial Autophagy

Esophageal squamous cell carcinoma (ESCC) has a worldwide impact on human health, due to its high incidence and mortality. Therefore, identifying compounds to increase patients' survival rate is urgently needed. Mefloquine (MQ) is an FDA-approved anti-malarial drug, which has been reported to inhibit cellular proliferation in several cancers. However, the anti-tumor activities of the drug have not yet been completely defined. In this study, mass spectrometry was employed to profile proteome changes in ESCC cells after MQ treatment. Sub-cellular localization and gene ontology term enrichment analysis suggested that MQ treatment mainly affect mitochondria. The KEGG pathway enrichment map of down-regulated pathways and Venn diagram indicated that all of the top five down regulated signaling pathways contain four key mitochondrial proteins (succinate dehydrogenase complex subunit C (SDHC), succinate dehydrogenase complex subunit D, mitochondrially encoded cytochrome c oxidase III and NADH: ubiquinone oxidoreductase subunit V3). Meanwhile, mitochondrial autophagy was observed in MQ-treated KYSE150 cells. More importantly, patient-derived xenograft mouse models of ESCC with SDHC high expression were more sensitive to MQ treatment than low SDHC-expressing xenografts. Taken together, mefloquine inhibits ESCC tumor growth by inducing mitochondrial autophagy and SDHC plays a vital role in MQ-induced anti-tumor effect on ESCC.

Non-Apoptotic Cell Death Signaling Pathways in Melanoma

Resisting cell death is a hallmark of cancer. Disturbances in the execution of cell death programs promote carcinogenesis and survival of cancer cells under unfavorable conditions, including exposition to anti-cancer therapies. Specific modalities of regulated cell death (RCD) have been classified based on different criteria, including morphological features, biochemical alterations and immunological consequences. Although melanoma cells are broadly equipped with the anti-apoptotic machinery and recurrent genetic alterations in the components of the RAS/RAF/MEK/ERK signaling markedly contribute to the pro-survival phenotype of melanoma, the roles of autophagy-dependent cell death, necroptosis, ferroptosis, pyroptosis, and parthanatos have recently gained great interest. These signaling cascades are involved in melanoma cell response and resistance to the therapeutics used in the clinic, including inhibitors of BRAFmut and MEK1/2, and immunotherapy. In addition, the relationships between sensitivity to non-apoptotic cell death routes and specific cell phenotypes have been demonstrated, suggesting that plasticity of melanoma cells can be exploited to modulate response of these cells to different cell death stimuli. In this review, the current knowledge on the non-apoptotic cell death signaling pathways in melanoma cell biology and response to anti-cancer drugs has been discussed.