Inhibition of YAP function overcomes BRAF inhibitor resistance in melanoma cancer stem cells

Exploration of Antimicrobial Peptides in the Treatment of Gentamicin-Resistant Klebsiella pneumoniae Infection

Introduction

The emergence of multidrug-resistant Klebsiella pneumoniae (K. pneumoniae) and the decline of effective antibiotics lead to the urgent need for new antibacterial agents. The aim of this study is to investigate the therapeutic effect of antimicrobial peptides against gentamicin-resistant (RT) K. pneumoniae and to screen effective antimicrobial peptides.

Methods

In this study, the RT strains were induced by gradient gentamicin, and the RT strains were selected by detecting the expression levels of efflux pump genes, porin genes, and biofilm formation genes of the strains combined with their effects on the cells. Then the effects of four antimicrobial peptides on the efflux pump activity, biofilm formation level and cell condition after infection were detected to explore the effects of antimicrobial peptides on RT strains. Finally, the RT strain was used to induce a mouse model of pneumonia, and the four antimicrobial peptides were used to treat pneumonia mice for in vivo experiments. The pathological changes in lung tissues in each group were detected to explore the antimicrobial peptide with the most significant effect on the RT strain in vivo.

Results

The results showed that the minimal inhibitory concentrations of the RT strains (strain C and strain I) were significantly higher than those of the wild-type strain, and the expression of efflux pump, porin and biofilm formation genes was significantly increased. The antimicrobial peptides could effectively inhibit the biofilm formation and efflux pump protein function of the RT strains. In addition, the antimicrobial peptides showed promising antibacterial effects both in vitro and in vivo.

Discussion

Our study provided a theoretical basis for the treatment of gentamicin resistant K. pneumoniae infection with antimicrobial peptides, and found that KLA was significantly superior to LL37, Magainin I, KLA and Dermaseptin (10 μg/mL in cells, 50 μg in mice).

The role of yes activated protein (YAP) in melanoma metastasis

Hippo was first identified in a genetic screen as a protein that suppressed proliferation and cell growth. Subsequently, it was shown that hippo acted in a so-called canonical cascade to suppress Yorkie, the Drosophila equivalent of Yes-activated protein (YAP), a mechanosensitive transcriptional cofactor that enhances the activity of the TEAD family of transcription factors. YAP promotes fibrosis, activation of cancer-associated fibroblasts, angiogenesis and cancer cell invasion. YAP activates the expression of the matricellular proteins CCN1 (cyr61) and CCN2 (ctgf), themselves mediators of fibrogenesis and oncogenesis, and coordination of matrix deposition and angiogenesis. This review discusses how therapeutically targeting YAP through YAP inhibitors verteporfin and celastrol and its downstream mediators CCN1 and CCN2 might be useful in treating melanoma.

Targeting the Hippo Pathway in Cutaneous Melanoma

Melanoma is the most aggressive form of skin cancer. In the advanced stage of development, it is resistant to currently available therapeutic modalities. Increased invasiveness and metastatic potential depend on several proteins involved in various signal transduction pathways. Hippo signaling plays a vital role in malignant transformation. Dysfunctions of the Hippo pathway initiate the expression of tumor growth factors and are associated with tumor growth and metastasis formation. This review summarizes the recent achievements in studying the role of the Hippo pathway in melanoma pathogenesis and points to the potential specific targets for anti-melanoma therapy.

Prospects of focal adhesion kinase inhibitors as a cancer therapy in preclinical and early phase study

INTRODUCTION

FAK, a nonreceptor cytoplasmic tyrosine kinase, plays a crucial role in tumor metastasis, drug resistance, tumor stem cell maintenance, and regulation of the tumor microenvironment. FAK has emerged as a promising target for tumor therapy based on both preclinical and clinical data.

AREAS COVERED

This paper aims to summarize the molecular mechanisms underlying FAK's involvement in tumorigenesis and progression. Encouraging results have emerged from ongoing clinical trials of FAK inhibitors. Additionally, we present an overview of clinical trials for FAK inhibitors, examining their potential as promising treatments. The pertinent studies gathered from databases including PubMed, ClinicalTrials.gov.

EXPERT OPINION

Since the first finding in 1990s, targeting FAK has became the focus of interests in many pharmaceutical companies. Through 30 years' discovery, the industry and academy gradually realized the features of FAK target which may not be a driver gene but a solid defense system for the cancer initiation and development. Currently, the ongoing clinical regimens involving FAK inhibition are all the combination strategies in which FAK inhibitors can further strengthen the cancer cell killing effects of other testing agents. The emerging positive signal in clinical trials foresee targeting FAK as class will be an effective mean to fight against cancers.

Vascular mimicry as a facilitator of melanoma brain metastasis

Melanoma has the highest propensity among solid tumors to metastasize to the brain. Melanoma brain metastases (MBM) are a leading cause of death in melanoma and affect 40-60% of patients with late-stage disease. Therefore, uncovering the molecular mechanisms behind MBM is necessary to enhance therapeutic interventions. Vascular mimicry (VM) is a form of neovascularization linked to invasion, increased risk of metastasis, and poor prognosis in many tumor types, but its significance in MBM remains poorly understood. We found that VM density is elevated in MBM compared to paired extracranial specimens and is associated with tumor volume and CNS edema. In addition, our studies indicate a relevant role of YAP and TAZ, two transcriptional co-factors scarcely studied in melanoma, in tumor cell-vasculogenesis and in brain metastasis. We recently demonstrated activation of the Hippo tumor suppressor pathway and increased degradation of its downstream targets YAP and TAZ in a metastasis impaired cell line model. In the current study we establish the utility of anti-YAP/TAZ therapy in mouse models of metastatic melanoma whereby treatment effectively inhibits VM and prolongs survival of mice with MBM. The data presented herein suggest that VM may be an important and targetable mechanism in melanoma and that VM inhibition might be useful for treating MBM, an area of high unmet clinical need, thus having important implications for future treatment regimens for these patients.

Cancer-associated Fibroblast-specific Expression of the Matricellular Protein CCN1 Coordinates Neovascularization and Stroma Deposition in Melanoma Metastasis

Melanoma is the leading cause of skin cancer-related death. As prognosis of patients with melanoma remains problematic, identification of new therapeutic targets remains essential. Matricellular proteins are nonstructural extracellular matrix proteins. They are secreted into the tumor microenvironment to coordinate behavior among different cell types, yet their contribution to melanoma is underinvestigated. Examples of matricellular proteins include those comprising the CCN family. The CCN family member, CCN1, is highly proangiogenic. Herein, we show that, in human patients with melanoma, although found in several tumor cell types, CCN1 is highly expressed by a subset of cancer-associated fibroblasts (CAF) in patients with melanoma and this expression correlates positively with expression of proangiogenic genes and progressive disease/resistance to anti-PD1 checkpoint inhibitors. Consistent with these observations, in a syngeneic C57BL6 mouse model of melanoma, loss of CCN1 expression from Col1A2-Cre-, herein identified as "universal," fibroblasts, impaired metastasis of subcutaneously injected B16F10 tumor cells to lung, concomitant with disrupted neovascularization and collagen organization. Disruption of the extracellular matrix in the loss of CCN1 was validated using a novel artificial intelligence-based image analysis platform that revealed significantly decreased phenotypic fibrosis and composite morphometric collagen scores. As drug resistance is linked to matrix deposition and neoangiogenesis, these data suggest that CCN1, due to its multifaceted role, may represent a novel therapeutic target for drug-resistant melanoma. Our data further emphasize the essential role that cancer-associated, (universal) Col1A2-Cre-fibroblasts and extracellular matrix remodeling play in coordinating behavior among different cell types within the tumor microenvironment.

SIGNIFICANCE

In human patients, the expression of proangiogenic matricellular protein CCN1 in CAFs correlates positively with expression of stroma and angiogenic markers and progressive disease/resistance to checkpoint inhibitor therapy. In an animal model, loss of CCN1 from CAFs impaired metastasis of melanoma cells, neovascularization, and collagen deposition, emphasizing that CAFs coordinate cellular behavior in a tumor microenvironment and that CCN1 may be a novel target.

Identification of a Gene Signature That Predicts Dependence upon YAP/TAZ-TEAD

Targeted therapies are effective cancer treatments when accompanied by accurate diagnostic tests that can help identify patients that will respond to those therapies. The YAP/TAZ-TEAD axis is activated and plays a causal role in several cancer types, and TEAD inhibitors are currently in early-phase clinical trials in cancer patients. However, a lack of a reliable way to identify tumors with YAP/TAZ-TEAD activation for most cancer types makes it difficult to determine which tumors will be susceptible to TEAD inhibitors. Here, we used a combination of RNA-seq and bioinformatic analysis of metastatic melanoma cells to develop a YAP/TAZ gene signature. We found that the genes in this signature are TEAD-dependent in several melanoma cell lines, and that their expression strongly correlates with YAP/TAZ activation in human melanomas. Using DepMap dependency data, we found that this YAP/TAZ signature was predictive of melanoma cell dependence upon YAP/TAZ or TEADs. Importantly, this was not limited to melanoma because this signature was also predictive when tested on a panel of over 1000 cancer cell lines representing numerous distinct cancer types. Our results suggest that YAP/TAZ gene signatures like ours may be effective tools to predict tumor cell dependence upon YAP/TAZ-TEAD, and thus potentially provide a means to identify patients likely to benefit from TEAD inhibitors.

Mechanisms of Melanoma Progression and Treatment Resistance: Role of Cancer Stem-like Cells

Melanoma is the third most common type of skin cancer, characterized by its heterogeneity and propensity to metastasize to distant organs. Melanoma is a heterogeneous tumor, composed of genetically divergent subpopulations, including a small fraction of melanoma-initiating cancer stem-like cells (CSCs) and many non-cancer stem cells (non-CSCs). CSCs are characterized by their unique surface proteins associated with aberrant signaling pathways with a causal or consequential relationship with tumor progression, drug resistance, and recurrence. Melanomas also harbor significant alterations in functional genes (BRAF, CDKN2A, NRAS, TP53, and NF1). Of these, the most common are the BRAF and NRAS oncogenes, with 50% of melanomas demonstrating the BRAF mutation (BRAFV600E). While the successful targeting of BRAFV600E does improve overall survival, the long-term efficacy of available therapeutic options is limited due to adverse side effects and reduced clinical efficacy. Additionally, drug resistance develops rapidly via mechanisms involving fast feedback re-activation of MAPK signaling pathways. This article updates information relevant to the mechanisms of melanoma progression and resistance and particularly the mechanistic role of CSCs in melanoma progression, drug resistance, and recurrence.

Tumor Cell Resistance to the Inhibition of BRAF and MEK1/2

BRAF is one of the most frequently mutated oncogenes, with an overall frequency of about 50%. Targeting BRAF and its effector mitogen-activated protein kinase kinase 1/2 (MEK1/2) is now a key therapeutic strategy for BRAF-mutant tumors, and therapies based on dual BRAF/MEK inhibition showed significant efficacy in a broad spectrum of BRAF tumors. Nonetheless, BRAF/MEK inhibition therapy is not always effective for BRAF tumor suppression, and significant challenges remain to improve its clinical outcomes. First, certain BRAF tumors have an intrinsic ability to rapidly adapt to the presence of BRAF and MEK1/2 inhibitors by bypassing drug effects via rewired signaling, metabolic, and regulatory networks. Second, almost all tumors initially responsive to BRAF and MEK1/2 inhibitors eventually acquire therapy resistance via an additional genetic or epigenetic alteration(s). Overcoming these challenges requires identifying the molecular mechanism underlying tumor cell resistance to BRAF and MEK inhibitors and analyzing their specificity in different BRAF tumors. This review aims to update this information.

Multi-Functional Regulation by YAP/TAZ Signaling Networks in Tumor Progression and Metastasis

The Hippo pathway transcriptional co-activators, YES-associated protein (YAP) and Transcriptional Co-Activator with PDZ Binding Motif (TAZ), have both been linked to tumor progression and metastasis. These two proteins possess overlapping and distinct functions, and their activities lead to the expression of genes involved in multiple cellular processes, including cell proliferation, survival, and migration. The dysregulation of YAP/TAZ-dependent cellular processes can result in altered tumor growth and metastasis. In addition to their well-documented roles in the regulation of cancer cell growth, survival, migration, and invasion, the YAP/TAZ-dependent signaling pathways have been more recently implicated in cellular processes that promote metastasis and therapy resistance in several solid tumor types. This review highlights the role of YAP/TAZ signaling networks in the regulation of tumor cell plasticity mediated by hybrid and reversible epithelial-mesenchymal transition (EMT) states, and the promotion of cancer stem cell/progenitor phenotypes. Mechanistically, YAP and TAZ regulate these cellular processes by targeting transcriptional networks. In this review, we detail recently uncovered mechanisms whereby YAP and TAZ mediate tumor growth, metastasis, and therapy resistance, and discuss new therapeutic strategies to target YAP/TAZ function in various solid tumor types. Understanding the distinct and overlapping roles of YAP and TAZ in multiple cellular processes that promote tumor progression to metastasis is expected to enable the identification of effective therapies to treat solid tumors through the hyper-activation of YAP and TAZ.

BRAF Mutations in Melanoma: Biological Aspects, Therapeutic Implications, and Circulating Biomarkers

Melanoma is an aggressive form of skin cancer resulting from the malignant transformation of melanocytes. Recent therapeutic approaches, including targeted therapy and immunotherapy, have improved the prognosis and outcome of melanoma patients. BRAF is one of the most frequently mutated oncogenes recognised in melanoma. The most frequent oncogenic BRAF mutations consist of a single point mutation at codon 600 (mostly V600E) that leads to constitutive activation of the BRAF/MEK/ERK (MAPK) signalling pathway. Therefore, mutated BRAF has become a useful target for molecular therapy and the use of BRAF kinase inhibitors has shown promising results. However, several resistance mechanisms invariably develop leading to therapeutic failure. The aim of this manuscript is to review the role of BRAF mutational status in the pathogenesis of melanoma and its impact on differentiation and inflammation. Moreover, this review focuses on the mechanisms responsible for resistance to targeted therapies in BRAF-mutated melanoma and provides an overview of circulating biomarkers including circulating tumour cells, circulating tumour DNA, and non-coding RNAs.

YAP at the Crossroads of Biomechanics and Drug Resistance in Human Cancer

Biomechanical forces are of fundamental importance in biology, diseases, and medicine. Mechanobiology is an emerging interdisciplinary field that studies how biological mechanisms are regulated by biomechanical forces and how physical principles can be leveraged to innovate new therapeutic strategies. This article reviews state-of-the-art mechanobiology knowledge about the yes-associated protein (YAP), a key mechanosensitive protein, and its roles in the development of drug resistance in human cancer. Specifically, the article discusses three topics: how YAP is mechanically regulated in living cells; the molecular mechanobiology mechanisms by which YAP, along with other functional pathways, influences drug resistance of cancer cells (particularly lung cancer cells); and finally, how the mechanical regulation of YAP can influence drug resistance and vice versa. By integrating these topics, we present a unified framework that has the potential to bring theoretical insights into the design of novel mechanomedicines and advance next-generation cancer therapies to suppress tumor progression and metastasis.

Nrf2 as a Therapeutic Target in the Resistance to Targeted Therapies in Melanoma

The use of specific inhibitors towards mutant BRAF (BRAFi) and MEK (MEKi) in BRAF-mutated patients has significantly improved progression-free and overall survival of metastatic melanoma patients. Nevertheless, half of the patients still develop resistance within the first year of therapy. Therefore, understanding the mechanisms of BRAFi/MEKi-acquired resistance has become a priority for researchers. Among others, oxidative stress-related mechanisms have emerged as a major force. The aim of this study was to evaluate the contribution of Nrf2, the master regulator of the cytoprotective and antioxidant response, in the BRAFi/MEKi acquired resistance of melanoma. Moreover, we investigated the mechanisms of its activity regulation and the possible cooperation with the oncogene YAP, which is also involved in chemoresistance. Taking advantage of established in vitro melanoma models resistant to BRAFi, MEKi, or dual resistance to BRAFi/MEKi, we demonstrated that Nrf2 was upregulated in melanoma cells resistant to targeted therapy at the post-translational level and that the deubiquitinase DUB3 participated in the control of the Nrf2 protein stability. Furthermore, we found that Nrf2 controlled the expression of YAP. Importantly, the inhibition of Nrf2, directly or through inhibition of DUB3, reverted the resistance to targeted therapies.

Mesothelioma cancer cells are glutamine addicted and glutamine restriction reduces YAP1 signaling to attenuate tumor formation

Glutamine addiction is an important phenotype displayed in some types of cancer. In these cells, glutamine depletion results in a marked reduction in the aggressive cancer phenotype. Mesothelioma is an extremely aggressive disease that lacks effective therapy. In this study, we show that mesothelioma tumors are glutamine addicted suggesting that glutamine depletion may be a potential therapeutic strategy. We show that glutamine restriction, by removing glutamine from the medium or treatment with inhibitors that attenuate glutamine uptake (V-9302) or conversion to glutamate (CB-839), markedly reduces mesothelioma cell proliferation, spheroid formation, invasion, and migration. Inhibition of the SLC1A5 glutamine importer, by knockout or treatment with V-9302, an SLC1A5 inhibitor, also markedly reduces mesothelioma cell tumor growth. A relationship between glutamine utilization and YAP1/TEAD signaling has been demonstrated in other tumor types, and the YAP1/TEAD signaling cascade is active in mesothelioma cells and drives cell survival and proliferation. We therefore assessed the impact of glutamine depletion on YAP1/TEAD signaling. We show that glutamine restriction, SLC1A5 knockdown/knockout, or treatment with V-9302 or CB-839, reduces YAP1 level, YAP1/TEAD-dependent transcription, and YAP1/TEAD target protein (e.g., CTGF, cyclin D1, COL1A2, COL3A1, etc.) levels. These changes are observed in both cells and tumors. These findings indicate that mesothelioma is a glutamine addicted cancer, show that glutamine depletion attenuates YAP1/TEAD signaling and tumor growth, and suggest that glutamine restriction may be useful as a mesothelioma treatment strategy.

The crosstalk between classic cell signaling pathways, non-coding RNAs and ferroptosis in drug resistance of tumors

Ferroptosis is an iron-dependent oxidative cell death characterized by the lethal accumulation of lipid-based reactive oxygen species (ROS), which is distinct from apoptosis, necrosis, and autophagy. Extensive studies suggest that ferroptosis be critical in regulating the growth and drug resistance of tumors, thus providing potential targets for cancer therapy. The development of resistance to cancer therapy remains a major challenge. Ferroptosis is associated with cancer drug resistance and inducing ferroptosis has been demonstrated to reverse drug resistance. This review focuses on a detailed account of the interplay between ferroptosis and related signaling pathways, including the Hippo signaling pathway, Keap1-Nrf2-ARE signaling pathway, Autophagy, and non-coding RNAs, which will shed light on developing the therapeutic role of regulating ferroptosis in reversing the resistance of cancer.

Targeting Transcription Factors in Cancer: From "Undruggable" to "Druggable"

Deregulation of transcription factors is critical to hallmarks of cancer. Genetic mutations, gene fusions, amplifications or deletions, epigenetic alternations, and aberrant post-transcriptional modification of transcription factors are involved in the regulation of various stages of carcinogenesis, including cancer initiation, progression, and metastasis. Thus, targeting the dysfunctional transcription factors may lead to new cancer therapeutic strategies. However, transcription factors are conventionally considered as "undruggable." Here, we summarize the recent progresses in understanding the regulation of transcription factors in cancers and strategies to target transcription factors and co-factors for preclinical and clinical drug development, particularly focusing on c-Myc, YAP/TAZ, and β-catenin due to their significance and interplays in cancer.

Inactivation of the Hippo tumor suppressor pathway promotes melanoma

Melanoma is commonly driven by activating mutations in the MAP kinase BRAF; however, oncogenic BRAF alone is insufficient to promote melanomagenesis. Instead, its expression induces a transient proliferative burst that ultimately ceases with the development of benign nevi comprised of growth-arrested melanocytes. The tumor suppressive mechanisms that restrain nevus melanocyte proliferation remain poorly understood. Here we utilize cell and murine models to demonstrate that oncogenic BRAF leads to activation of the Hippo tumor suppressor pathway, both in melanocytes in vitro and nevus melanocytes in vivo. Mechanistically, we show that oncogenic BRAF promotes both ERK-dependent alterations in the actin cytoskeleton and whole-genome doubling events, which independently reduce RhoA activity to promote Hippo activation. We also demonstrate that functional impairment of the Hippo pathway enables oncogenic BRAF-expressing melanocytes to bypass nevus formation and rapidly form melanomas. Our data reveal that the Hippo pathway enforces the stable arrest of nevus melanocytes and represents a critical barrier to melanoma development.

Activating mutations of BRAF alone are inadequate to drive melanoma formation. Here the authors show that activation of Hippo signalling by oncogenic BRAF represents an additional safeguard to limit BRAF-dependent human melanocyte growth and melanoma formation.

Functions of Yes-association protein (YAP) in cancer progression and anticancer therapy resistance

The Hippo pathway, a highly conserved kinase cascade, regulates cell proliferation, apoptosis, organ size, and tissue homeostasis. Dysregulation of this pathway reportedly plays an important role in the progression of various human cancers. Yes-association protein (YAP), the Hippo pathway’s core effector, is considered a marker for cancer therapy and patient prognosis. In addition, studies have indicated that YAP is involved in promoting anticancer drug resistance. This review summarizes current knowledge on YAP’s role in cancer progression, anticancer drug resistance, and advances in the development of YAP-targeting drugs. A thorough understanding of the complex interactions among molecular, cellular, and environmental factors concerning YAP function in cancer progression may provide new insight into the underlying mechanism of anticancer drug resistance. It might lead to improved prognosis through novel combined therapies.

Matrix stiffening and acquired resistance to chemotherapy: concepts and clinical significance

Extracellular matrix (ECM) refers to the non-cellular components of the tumour microenvironment, fundamentally providing a supportive scaffold for cellular anchorage and transducing signaling cues that orchestrate cellular behaviour and function. The ECM integrity is abrogated in several cases of cancer, ending in aberrant activation of a number of mechanotransduction pathways and induction of multiple tumorigenic events such as extended proliferation, cell death resistance, epithelial-mesenchymal transition and most importantly the development of chemoresistance. In this regard, the present study mainly aims to elucidate how the ECM-stiffening process may contribute to the development of chemoresistance during cancer progression and what pharmacological approaches are required for tackling this issue. Hence, the first section of this review explains the process of ECM stiffening and the ways it may affect biochemical pathways to induce chemoresistance in a clinic. In addition, the second part focuses on describing some of the most important pharmacological agents capable of targeting ECM components and underlying pathways for overcoming ECM-induced chemoresistance. Finally, the third part discusses the obtained results from the application of these agents in the clinic for overcoming chemoresistance.

BRAF Inhibitor Resistance in Melanoma: Mechanisms and Alternative Therapeutic Strategies

OPINION STATEMENT

Melanoma is caused by a variety of somatic mutations, and among these mutations, BRAF mutation occurs most frequently and has routinely been evaluated as a critical diagnostic biomarker in clinical practice. The introduction of targeted agents for BRAF-mutant melanoma has significantly improved overall survival in a large proportion of patients. However, there is BRAF inhibitor resistance in most patients, and its mechanisms are complicated and need further clarification. Additionally, treatment approaches to overcome resistance have evolved rapidly, shifting from monotherapy to multimodality treatment, which has dramatically improved patient outcomes in clinical trials and practice. This review highlights the mechanisms of BRAF inhibitor resistance in melanoma and discusses the current state of its therapeutic approaches that can be further explored in clinical practice.

YAP facilitates melanoma migration through regulation of actin-related protein 2/3 complex subunit 5 (ARPC5)

Yes-associated protein 1 (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional coactivators that have been implicated in driving metastasis and progression in many cancers, mainly through their transcriptional regulation of downstream targets. Although YAP and TAZ have shown redundancy in many contexts, it is still unknown whether or not this is true in melanoma. Here, we show that while both YAP and TAZ are expressed in a panel of melanoma cell lines, depletion of YAP results in decreased cell numbers, focal adhesions, and the ability to invade matrigel. Using non-biased RNA-sequencing analysis, we find that melanoma cells depleted of YAP, TAZ, or YAP/TAZ exhibit drastically different transcriptomes. We further uncover the ARP2/3 subunit ARPC5 as a specific target of YAP but not TAZ and that ARPC5 is essential for YAP-dependent maintenance of melanoma cell focal adhesion numbers. Our findings suggest that in melanoma, YAP drives melanoma progression, survival, and invasion.

Ibrutinib Blocks YAP1 Activation and Reverses BRAF Inhibitor Resistance in Melanoma Cells

Most B-Raf proto-oncogene (BRAF)-mutant melanoma tumors respond initially to BRAF inhibitor (BRAFi)/mitogen-activated protein kinase kinase 1 inhibitor (MEKi) therapy, although few patients have durable long-term responses to these agents. The goal of this study was to use an unbiased computational approach to identify inhibitors that reverse an experimentally derived BRAFi resistance gene expression signature. Using this approach, we found that ibrutinib effectively reverses this signature, and we demonstrate experimentally that ibrutinib resensitizes a subset of BRAFi-resistant melanoma cells to vemurafenib. Ibrutinib is used clinically as an inhibitor of the Src family kinase Bruton tyrosine kinase (BTK); however, neither BTK deletion nor treatment with acalabrutinib, another BTK inhibitor with reduced off-target activity, resensitized cells to vemurafenib. These data suggest that ibrutinib acts through a BTK-independent mechanism in vemurafenib resensitization. To better understand this mechanism, we analyzed the transcriptional profile of ibrutinib-treated BRAFi-resistant melanoma cells and found that the transcriptional profile of ibrutinib was highly similar to that of multiple Src proto-oncogene kinase inhibitors. Since ibrutinib, but not acalabrutinib, has appreciable off-target activity against multiple Src family kinases, it suggests that ibrutinib may be acting through this mechanism. Furthermore, genes that are differentially expressed in ibrutinib-treated cells are enriched in Yes1-associated transcriptional regulator (YAP1) target genes, and we showed that ibrutinib, but not acalabrutinib, reduces YAP1 activity in BRAFi-resistant melanoma cells. Taken together, these data suggest that ibrutinib, or other Src family kinase inhibitors, may be useful for treating some BRAFi/MEKi-refractory melanoma tumors. SIGNIFICANCE STATEMENT: MAPK-targeted therapies provide dramatic initial responses, but resistance develops rapidly; a subset of these tumors may be rendered sensitive again by treatment with an approved Src family kinase inhibitor-ibrutinub-potentially providing improved clinical outcomes.

Genomic and Transcriptomic Underpinnings of Melanoma Genesis, Progression, and Metastasis

Melanoma is a deadly skin cancer with rapidly increasing incidence worldwide. The discovery of the genetic drivers of melanomagenesis in the last decade has led the World Health Organization to reclassify melanoma subtypes by their molecular pathways rather than traditional clinical and histopathologic features. Despite this significant advance, the genomic and transcriptomic drivers of metastatic progression are less well characterized. This review describes the known molecular pathways of cutaneous and uveal melanoma progression, highlights recently identified pathways and mediators of metastasis, and touches on the influence of the tumor microenvironment on metastatic progression and treatment resistance. While targeted therapies and immune checkpoint blockade have significantly aided in the treatment of advanced disease, acquired drug resistance remains an unfortunately common problem, and there is still a great need to identify potential prognostic markers and novel therapeutic targets to aid in such cases.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

Mitochondrial Metabolism in Melanoma

Melanoma and its associated alterations in cellular pathways have been growing areas of interest in research, especially as specific biological pathways are being elucidated. Some of these alterations include changes in the mitochondrial metabolism in melanoma. Many mitochondrial metabolic changes lead to differences in the survivability of cancer cells and confer resistance to targeted therapies. While extensive work has gone into characterizing mechanisms of resistance, the role of mitochondrial adaptation as a mode of resistance is not completely understood. In this review, we wish to explore mitochondrial metabolism in melanoma and how it impacts modes of resistance. There are several genes that play a major role in melanoma mitochondrial metabolism which require a full understanding to optimally target melanoma. These include BRAF, CRAF, SOX2, MCL1, TRAP1, RHOA, SRF, SIRT3, PTEN, and AKT1. We will be discussing the role of these genes in melanoma in greater detail. An enhanced understanding of mitochondrial metabolism and these modes of resistance may result in novel combinatorial and sequential therapies that may lead to greater therapeutic benefit.

Neural Crest-Like Stem Cell Transcriptome Analysis Identifies LPAR1 in Melanoma Progression and Therapy Resistance

Metastatic melanoma is challenging to clinically address. Although standard-of-care targeted therapy has high response rates in patients with BRAF-mutant melanoma, therapy relapse occurs in most cases. Intrinsically resistant melanoma cells drive therapy resistance and display molecular and biologic properties akin to neural crest-like stem cells (NCLSC) including high invasiveness, plasticity, and self-renewal capacity. The shared transcriptional programs and vulnerabilities between NCLSCs and cancer cells remains poorly understood. Here, we identify a developmental LPAR1-axis critical for NCLSC viability and melanoma cell survival. LPAR1 activity increased during progression and following acquisition of therapeutic resistance. Notably, genetic inhibition of LPAR1 potentiated BRAFi ± MEKi efficacy and ablated melanoma migration and invasion. Our data define LPAR1 as a new therapeutic target in melanoma and highlights the promise of dissecting stem cell-like pathways hijacked by tumor cells. SIGNIFICANCE: This study identifies an LPAR1-axis critical for melanoma invasion and intrinsic/acquired therapy resistance.

Multifaceted effect of chlorpromazine in cancer: implications for cancer treatment

Since its discovery in 1951, chlorpromazine (CPZ) has been one of the most widely used antipsychotic medications for treating schizophrenia and other psychiatric disorders. In addition to its antipsychotic effect, many studies in the last several decades have found that CPZ has a potent antitumorigenic effect. These studies have shown that CPZ affects a number of molecular oncogenic targets through multiple pathways, including the regulation of cell cycle, cancer growth and metastasis, chemo-resistance and stemness of cancer cells. Here we review studies on molecular mechanisms of CPZ’s action on key proteins involved in cancer, including p53, YAP, Ras protein, ion channels, and MAPKs. We discuss common and overlapping signaling pathways of CPZ’s action, its cancer-type specificity, antitumorigenic effects of CPZ reported in animal models and population studies on the rate of cancer in psychiatric patients. We also discuss the potential benefits and limitations of repurposing CPZ for cancer treatment.

Resistance to Targeted Therapy and RASSF1A Loss in Melanoma: What Are We Missing?

Melanoma is one of the most aggressive forms of skin cancer and is therapeutically challenging, considering its high mutation rate. Following the development of therapies to target BRAF, the most frequently found mutation in melanoma, promising therapeutic responses were observed. While mono- and combination therapies to target the MAPK cascade did induce a therapeutic response in BRAF-mutated melanomas, the development of resistance to MAPK-targeted therapies remains a challenge for a high proportion of patients. Resistance mechanisms are varied and can be categorised as intrinsic, acquired, and adaptive. RASSF1A is a tumour suppressor that plays an integral role in the maintenance of cellular homeostasis as a central signalling hub. RASSF1A tumour suppressor activity is commonly lost in melanoma, mainly by aberrant promoter hypermethylation. RASSF1A loss could be associated with several mechanisms of resistance to MAPK inhibition considering that most of the signalling pathways that RASSF1A controls are found to be altered targeted therapy resistant melanomas. Herein, we discuss resistance mechanisms in detail and the potential role for RASSF1A reactivation to re-sensitise BRAF mutant melanomas to therapy.

Ultrasound-Mediated Microbubble Destruction Inhibits Skin Melanoma Growth by Affecting YAP1 Translation Using Ribosome Imprinting Sequencing

Cutaneous melanoma (CMM) is a skin tumor with a high degree of malignancy. BRAF resistance imposes great difficulty to the treatment of CMM, and partially contributes to the poor prognosis of CMM. YAP is involved in the growth and drug resistance of a variety of tumors, and mechanical signals may affect the activation of YAP1. As a novel ultrasound treatment technology, ultrasound-mediated microbubble destruction (UMMD) has been reported to have a killing effect on isolated CMM cells. In this study, the tumor tissue samples were collected from 64 CMM patients. We found that YAP1 mRNA expression was irrelevant to the clinicopathological characteristics and prognostic survival of the CMM patients. The drug-resistant cell line was constructed and subcutaneously implanted into nude mice, which were further separately treated with UMMD, ultrasound (US), and microbubbles (MB). The result showed that UMMD significantly inhibited the growth of tumor tissues. Ribosome imprinting sequencing (Ribo-seq) is a genetic technology for studying protein translation at genetic level. Ribo-seq, RNA-seq, and RT-qPCR were applied to detect YAP1 expression in CMM mouse tumor tissues. Ribo-seq data revealed that UMMD greatly up-regulated the expression of YAP1, interestingly, the up-regulated YAP1 was found to be negatively correlated with the weight of tumor tissues, while no significant change in YAP1 expression was detected by RNA-seq or RT-qPCR assay. These results indicated that UMMD could inhibit the tumor growth of drug-resistant CMM by affecting the translation efficiency of YAP1, providing a strong basis for the clinical treatment of UMMD in CMM.

Targeting the YAP/TAZ Pathway in Uveal and Conjunctival Melanoma With Verteporfin

Purpose

The purpose of this study was to determine whether YAP/TAZ activation in uveal melanoma (UM) and the susceptibility of melanoma cell lines to YAP/TAZ inhibition by verteporfin (VP) is related to the tumor's genetic background.

Methods

Characteristics of 144 patients with enucleated UM were analyzed together with mRNA expression levels of YAP/TAZ-related genes (80 patients from the The Cancer Genome Atlas [TCGA] project and 64 patients from Leiden, The Netherlands). VP was administered to cell lines 92.1, OMM1, Mel270, XMP46, and MM28 (UM), CRMM1 and CRMM2 (conjunctival melanoma), and OCM3 (cutaneous melanoma). Viability, growth speed, and expression of YAP1-related proteins were assessed.

Results

In TCGA data, high expression of YAP1 and WWTR1 correlated with the presence of monosomy 3 (P = 0.009 and P < 0.001, respectively) and BAP1-loss (P = 0.003 and P = 0.001, respectively) in the primary UM; metastasis development correlated with higher expression of YAP1 (P = 0.05) and WWTR1 (P = 0.003). In Leiden data, downstream transcription factor TEAD4 was increased in cases with M3/BAP1-loss (P = 0.002 and P = 0.006) and related to metastasis (P = 0.004). UM cell lines 92.1, OMM1, and Mel270 (GNAQ/11-mutation, BAP1-positive) and the fast-growing cell line OCM3 (BRAF-mutation) showed decreased proliferation after exposure to VP. Two slow-growing UM cell lines XMP46 and MM28 (GNAQ/11-mutation, BAP1-negative) were not sensitive to VP, and neither were the two conjunctival melanoma cell lines (BRAF/NRAS-mutation).

Conclusions

High risk UM showed an increased expression of YAP/TAZ-related genes. Although most UM cell lines responded in vitro to VP, BAP1-negative and conjunctival melanoma cell lines did not. Not only the mutational background, but also cell growth rate is an important predictor of response to YAP/TAZ inhibition by VP.

USP22 promotes melanoma and BRAF inhibitor resistance via YAP stabilization

Yes-associated protein (YAP) is a conserved transcriptional coactivator that plays key roles in controlling organ size, tumorigenesis and drug resistance. Emerging evidence shows that YAP is overexpressed and associated with resistance to BRAF inhibitor treatment in melanoma. However, the mechanism accounting for YAP-overexpression in melanoma is largely unknown. The present study characterized ubiquitin-specific peptidase 22 (USP22) as a deubiquitinase controlling YAP abundance and biological functions in melanoma. Using western blotting and immunohistochemical staining, it was found that the expression of USP22 and YAP was associated in melanoma cell lines and patient samples. Moreover, USP22 interacted with and deubiquitinated YAP to prevent YAP turnover. Depletion of USP22 decreased YAP expression, which in turn suppressed cell proliferation and tumorigenesis. Furthermore, overexpression of USP22 conferred vemurafenib resistance in a YAP-dependent manner. Overall, the present study revealed the important role of the USP22/YAP axis in melanoma and BRAF inhibitor resistance, and provides a rationale to target USP22/YAP for melanoma treatment.

Role of the HIPPO pathway as potential key player in the cross talk between oncology and cardiology

The HIPPO pathway (HP) is a highly conserved kinase cascade that affects organ size by regulating proliferation, cell survival and differentiation. Discovered in Drosophila melanogaster to early 2000, it immediately opened wide frontiers in the field of research. Over the last years the field of knowledge on HP is quickly expanding and it is thought will offer many answers on complex pathologies. Here, we summarized the results of several studies that have investigated HP signaling both in oncology than in cardiology field, with an overview on future perspectives in cardiology research.

YAP activation in melanoma contributes to anoikis resistance and metastasis

Melanoma is inherently heterogeneous, providing resistance to apoptosis. Anoikis resistance is a hallmark feature of metastatic melanoma to escape apoptosis when cells lose contact with adjacent cells or extracellular matrix. The yes-associated protein transcription co-activator is the effector of Hippo pathway. Herein, we investigated the function of yes-associated protein in anoikis resistance of melanoma cells. When melanoma cells were grown under anchorage-independent condition, anoikis-resistant cells displayed higher levels of yes-associated protein activation than the cells that were attached to the basement membrane, as evidenced by downregulated phosphorylated yes-associated protein at Ser127 and higher expression of downstream genes BCL2 and MCL-1. Yes-associated protein overexpression directly enhanced the anoikis resistance and metastatic potential of melanoma cells. Conversely, yes-associated protein inhibitor CA3 exhibited Dose-dependent induction of anoikis in resistant melanoma cells and exerted great inhibition on cell migration. Knockdown of yes-associated protein expression by shRNA also rendered melanoma cells susceptible to anoikis and interrupted cell invasiveness. Yes-associated protein inhibition in anoikis-resistant cells also reduced the number of metastatic nodules in the lung sections of SCID mice. Clinically, higher yes-associated protein level in the lung metastasis tissues correlated with higher BCL2 and MCL1 expressions compared with the non-metastasis tissues. Overall, our finding suggests that the aberrant activation of yes-associated protein exerts important role on anoikis resistance and metastatic capability of melanoma cells.

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.

Mechanisms of Acquired BRAF Inhibitor Resistance in Melanoma: A Systematic Review

This systematic review investigated the literature on acquired v-raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor resistance in patients with melanoma. We searched MEDLINE for articles on BRAF inhibitor resistance in patients with melanoma published since January 2010 in the following areas: (1) genetic basis of resistance; (2) epigenetic and transcriptomic mechanisms; (3) influence of the immune system on resistance development; and (4) combination therapy to overcome resistance. Common resistance mutations in melanoma are BRAF splice variants, BRAF amplification, neuroblastoma RAS viral oncogene homolog (NRAS) mutations and mitogen-activated protein kinase kinase 1/2 (MEK1/2) mutations. Genetic and epigenetic changes reactivate previously blocked mitogen-activated protein kinase (MAPK) pathways, activate alternative signaling pathways, and cause epithelial-to-mesenchymal transition. Once BRAF inhibitor resistance develops, the tumor microenvironment reverts to a low immunogenic state secondary to the induction of programmed cell death ligand-1. Combining a BRAF inhibitor with a MEK inhibitor delays resistance development and increases duration of response. Multiple other combinations based on known mechanisms of resistance are being investigated. BRAF inhibitor-resistant cells develop a range of 'escape routes', so multiple different treatment targets will probably be required to overcome resistance. In the future, it may be possible to personalize combination therapy towards the specific resistance pathway in individual patients.

Mechanisms of resistance and predictive biomarkers of response to targeted therapies and immunotherapies in metastatic melanoma

PURPOSE OF REVIEW

Thanks to mitogen-activated protein kinase inhibitors (MAPKi) and immune checkpoint inhibitors (ICI), major progress has been made in the field of melanoma treatment. However, long-term success is still scarce because of the development of resistance. Understanding these mechanisms of resistance and identifying predictive genomic biomarkers are now key points in the therapeutic management of melanoma patients.

RECENT FINDINGS

Multiple and complex mechanisms of resistance to MAPKi or ICI have been uncovered in the past few years. The lack of response can be driven by mutations and nonmutational events in tumor cells, as well as by changes in the tumor microenvironment. Melanoma cells are also capable of rapidly switching their molecular and cellular phenotype, leading to an initial drug-tolerant favorizing melanoma resistance. Tumor molecular profiling and circulating tumor cell analyses are of high interest as predictive biomarkers as well as studying immunogenic changes and microbiome in ICI-treated patients.

SUMMARY

Resistance to MAPKi and ICI is a key point in therapeutic management of metastatic melanoma patients. Validated biomarkers predicting response to therapy are urgently needed to move toward personalized medicine. Combinatory treatments guided by the understanding of resistance mechanisms will be of major importance in the future of melanoma therapy.

Hippo signaling-a central player in cystic kidney disease?

Cystic transformation of kidney tissue is a key feature of various disorders including autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and disorders of the nephronophthisis spectrum (NPH). While ARPKD and NPH typically affect children and adolescents, pediatric onset of ADPKD is less frequently found. While both ADPKD and ARPKD are characterized by formation of hundreds of cysts accompanied by hyperproliferation of tubular epithelia with massive renal enlargement, NPH patients usually show kidneys of normal or reduced size with cysts limited to the corticomedullary border. Recent results suggest the hippo pathway to be a central regulator at the crossroads of the renal phenotype in both diseases. Hippo signaling regulates organ size and proliferation by keeping the oncogenic transcriptional co-activators Yes associated protein 1 (YAP) and WW domain containing transcription regulator 1 (TAZ) in check. Once this inhibition is released, nuclear YAP/TAZ interacts with TEAD family transcription factors and the consecutive transcriptional activation of TEA domain family members (TEAD) target genes mediates an increase in proliferation. Here, we review the current knowledge on the impact of NPHP and ADPKD mutations on Hippo signaling networks. Furthermore, we provide an outlook towards potential future therapeutic strategies targeting Hippo signaling to alleviate cystic kidney disease.

An alternative pathway for cellular protection in BRAF inhibitor resistance in aggressive melanoma type skin cancer

Oncogenic alterations in the BRAF gene are identified in an estimate of 50% of melanomas and cause melanoma development. BRAF kinase inhibitors (BRAFi), including vemurafenib and dabrafenib, were discovered and used in the clinical treatment of BRAF-mutant metastatic melanoma. Though, BRAFi's therapeutic advantages are short term and short-lived associated with drug resistance. Although a few pathways of developed BRAFi resistance have also been established, in approximately 40% of melanomas, the cause for inherited resistance remains unclear. Recognizing a new process of developed BRAFi resistance might provide new possibilities to successfully treat BRAF mutant melanoma. In this study, we are exploring the compensatory alternative pathway followed by BRAFi/MEKi treated resistant cell for maintaining the long-term integrity and survival.

A Review of the Molecular Pathways Involved in Resistance to BRAF Inhibitors in Patients with Advanced-Stage Melanoma

Melanoma is an aggressive malignancy of melanocytes and most commonly arises in the skin. In 2002, BRAF gene mutations were identified in melanoma, and this finding resulted in the development of several small-molecule molecular inhibitors that specifically targeted the BRAF V600E mutation. The development of targeted therapies for advanced-stage melanoma, including tyrosine kinase inhibitors (TKIs) of the BRAF (V600E) kinase, vemurafenib and dabrafenib, have been approved for the treatment of advanced melanoma leading to improved clinical outcomes. However, the development of BRAF inhibitor (BRAFi) resistance has significantly reduced the therapeutic efficacy after prolonged treatment. Recent studies have identified the molecular mechanisms for BRAFi resistance. This review aims to describe the impact of BRAFi resistance on the pathogenesis of melanoma, the current status of molecular pathways involved in BRAFi resistance, including intrinsic resistance, adaptive resistance, and acquired resistance. This review will discuss how an understanding of the mechanisms associated with BRAFi resistance may aid the identification of useful strategies for overcoming the resistance to BRAF-targeted therapy in patients with advanced-stage melanoma.

The YAP1 Signaling Inhibitors, Verteporfin and CA3, Suppress the Mesothelioma Cancer Stem Cell Phenotype

Mesothelioma is an aggressive cancer that has a poor prognosis. Tumors develop in the mesothelial lining of the pleural and peritoneal cavities in response to asbestos exposure. Surgical debulking followed by chemotherapy is initially effective, but this treatment ultimately selects for resistant cells that form aggressive and therapy-resistant recurrent tumors. Mesothelioma cancer stem cells (MCS) are a highly aggressive subpopulation present in these tumors that are responsible for tumor maintenance and drug resistance. In this article, we examine the impact of targeting YAP1/TAZ/TEAD signaling in MCS cells. YAP1, TAZ, and TEADs are transcriptional mediators of the Hippo signaling cascade that activate gene expression to drive tumor formation. We show that two YAP1 signaling inhibitors, verteporfin and CA3, attenuate the MCS cell phenotype. Verteporfin or CA3 treatment reduces YAP1/TEAD level/activity to suppress MCS cell spheroid formation, Matrigel invasion, migration, and tumor formation. These agents also increase MCS cell apoptosis. Moreover, constitutively active YAP1 expression antagonizes inhibitor action, suggesting that loss of YAP1/TAZ/TEAD signaling is required for response to verteporfin and CA3. These agents are active against mesothelioma cells derived from peritoneal (epithelioid) and patient-derived pleural (sarcomatoid) mesothelioma, suggesting that targeting YAP1/TEAD signaling may be a useful treatment strategy. IMPLICATIONS: These studies suggest that inhibition of YAP1 signaling may be a viable approach to treating mesothelioma.

Rho-mediated signaling promotes BRAF inhibitor resistance in de-differentiated melanoma cells

Over half of cutaneous melanoma tumors have BRAFV600E/K mutations. Acquired resistance to BRAF inhibitors (BRAFi) remains a major hurdle in attaining durable therapeutic responses. In this study we demonstrate that ~50-60% of melanoma cell lines with vemurafenib resistance acquired in vitro show activation of RhoA family GTPases. In BRAFi-resistant melanoma cell lines and tumors, activation of RhoA is correlated with decreased expression of melanocyte lineage genes. Using a machine learning approach, we built gene expression-based models to predict drug sensitivity for 265 common anticancer compounds. We then projected these signatures onto the collection of TCGA cutaneous melanoma and found that poorly differentiated tumors were predicted to have increased sensitivity to multiple Rho kinase (ROCK) inhibitors. Two transcriptional effectors downstream of Rho, MRTF and YAP1, are activated in the RhoHigh BRAFi-resistant cell lines, and resistant cells are more sensitive to inhibition of these transcriptional mechanisms. Taken together, these results support the concept of targeting Rho-regulated gene transcription pathways as a promising therapeutic approach to restore sensitivity to BRAFi-resistant tumors or as a combination therapy to prevent the onset of drug resistance.

NUAK2 localization in normal skin and its expression in a variety of skin tumors with YAP

BACKGROUND

NUAK2 is a critical gene that participates in the carcinogenesis of various types of cancers including melanomas. However, the expression patterns of NUAK2 in normal skin and in various types of skin tumors have not been fully elucidated to date.

OBJECTIVES

To elucidate the distribution and localization of NUAK2 expression in normal skin, and characterize the expression patterns of NUAK2 and YAP in various types of skin tumors.

METHODS

In this study, we characterized the expression of NUAK2 in tissues by developing a novel NUAK2-specific monoclonal antibody and using that to determine NUAK2 expression patterns in normal skin and in 155 cases of various types of skin tumors, including extramammary Paget's disease (EMPD), squamous cell carcinoma (SCC), Bowen's disease (BD), actinic keratosis (AK), basal cell carcinoma (BCC) and angiosarcoma (AS). Further, we analyzed the expression patterns of YAP and p-Akt in those tumors.

RESULTS

Our analyses revealed that NUAK2 is expressed at high frequencies in EMPD, SCC, BD, AK, BCC and AS. The expression of p-Akt was positively correlated with tumor size in EMPD (P = 0.001). Importantly, the expression of NUAK2 was significantly correlated with YAP in SCC (P = 0.012) and in BD (P = 0.009).

CONCLUSIONS

Our results suggest that the YAP-NUAK2 axis has critical importance in the tumorigenesis of SCC and BD, and that therapeutic modalities targeting the YAP-NUAK2 axis may be an effective approach against skin tumors including SCC and BD.

Multiple roles and context-specific mechanisms underlying YAP and TAZ-mediated resistance to anti-cancer therapy

Understanding the molecular mechanisms driving resistance to anti-cancer drugs is both a crucial step to define markers of response to therapy and a clinical need in many cancer settings. YAP and TAZ transcriptional cofactors behave as oncogenes in different cancer types. Deregulation of YAP/TAZ expression or alterations in components of the multiple signaling pathways converging on these factors are important mechanisms of resistance to chemotherapy, target therapy and hormone therapy. Moreover, response to immunotherapy may also be affected by YAP/TAZ activities in both tumor and microenvironment cells. For these reasons, various compounds inhibiting YAP/TAZ function by different direct and indirect mechanisms have been proposed as a mean to counter-act drug resistance in cancer. A particularly promising approach may be to simultaneously target both YAP/TAZ expression and their transcriptional activity through BET inhibitors.

The Hippo Tumor Suppressor Pathway (YAP/TAZ/TEAD/MST/LATS) and EGFR-RAS-RAF-MEK in cancer metastasis

Hippo Tumor Suppressor Pathway is the main pathway for cell growth that regulates tissue enlargement and organ size by limiting cell growth. This pathway is activated in response to cell cycle arrest signals (cell polarity, transduction, and DNA damage) and limited by growth factors or mitogens associated with EGF and LPA. The major pathway consists of the central kinase of Ste20 MAPK (Saccharomyces cerevisiae), Hpo (Drosophila melanogaster) or MST kinases (mammalian) that activates the mammalian AGC kinase dmWts or LATS effector (MST and LATS). YAP in the nucleus work as a cofactor for a wide range of transcription factors involved in proliferation (TEA domain family, TEAD1-4), stem cells (Oct4 mononuclear factor and SMAD-related TGFβ effector), differentiation (RUNX1), and Cell cycle/apoptosis control (p53, p63, and p73 family members). This is due to the diverse roles of YAP and may limit tumor progression and establishment. TEAD also coordinates various signal transduction pathways such as Hippo, WNT, TGFβ and EGFR, and effects on lack of regulation of TEAD cancerous genes, such as KRAS, BRAF, LKB1, NF2 and MYC, which play essential roles in tumor progression, metastasis, cancer metabolism, immunity, and drug resistance. However, RAS signaling is a pivotal factor in the inactivation of Hippo, which controls EGFR-RAS-RAF-MEK-ERK-mediated interaction of Hippo signaling. Thus, the loss of the Hippo pathway may have significant consequences on the targets of RAS-RAF mutations in cancer.

Angiotropism, pericytic mimicry and extravascular migratory metastasis: an embryogenesis-derived program of tumor spread

Intravascular dissemination of tumor cells is the accepted mechanism of cancer metastasis. However, the phenomenon of angiotropism, pericyte mimicry (PM), and extravascular migratory metastasis (EVMM) has questioned the concept that tumor cells metastasize exclusively via circulation within vascular channels. This new paradigm of cancer spread and metastasis suggests that metastatic cells employ embryonic mechanisms for attachment to the abluminal surfaces of blood vessels (angiotropism) and spread via continuous migration, competing with and replacing pericytes, i.e., pericyte mimicry (PM). This is an entirely extravascular phenomenon (i.e., extravascular migratory metastasis or EVMM) without entry (intravasation) into vascular channels. PM and EVMM have mainly been studied in melanoma but also occur in other cancer types. PM and EVMM appear to be a reversion to an embryogenesis-derived program. There are many analogies between embryogenesis and cancer progression, including the important role of laminins, epithelial-mesenchymal transition, and the re-activation of embryonic signals by cancer cells. Furthermore, there is no circulation of blood during the first trimester of embryogenesis, despite the fact that there is extensive migration of cells to distant sites and formation of organs and tissues during this period. Embryonic migration therefore is a continuous extravascular migration as are PM and EVMM, supporting the concept that these embryonic migratory events appear to recur abnormally during the metastatic process. Finally, the perivascular location of tumor cells intrinsically links PM to vascular co-option. Taken together, these two new paradigms may greatly influence the development of new effective therapeutics for metastasis. In particular, targeting embryonic factors linked to migration that are detected during cancer metastasis may be particularly relevant to PM/EVMM.

CRISPR Loss-of-Function Screen Identifies the Hippo Signaling Pathway as the Mediator of Regorafenib Efficacy in Hepatocellular Carcinoma

Regorafenib is used for hepatocellular carcinoma (HCC), but its response does not last long, partly due to chemoresistance acquisition. We performed a clustered regularly interspaced short palindromic repeats (CRISPR)-based loss-of-function genetic screen and aimed to discover molecules involved in regorafenib resistance in HCC. Xenograft tumors established from Cas9-expressing HCC cells with pooled CRISPR kinome libraries were treated with regorafenib or a vehicle. Sequencing analysis identified 31 genes, with the abundance of multiple guide RNAs increased in regorafenib-treated tumors compared to that in vehicle-treated tumors, including 2 paralogues, LATS2 and LATS1, core components of the Hippo signaling pathway. Notably, all eight designed guide RNAs targeting LATS2 increased in regorafenib-treated tumors, suggesting that LATS2 deletion confers regorafenib resistance in HCC cells. LATS2 knockdown significantly mitigated the cytotoxic and proapoptotic effects of regorafenib on HCC cells. LATS2 inhibition stabilized the Hippo signaling mediator YAP, leading to the upregulation of antiapoptotic Bcl-xL and the multidrug resistance transporter ABCB1. Among 12 hepatoma cell lines, the half maximal inhibitory concentration (IC50) values of regorafenib were positively correlated with any of YAP, Bcl-xL and ABCB1 levels. The inhibition of YAP or Bcl-xL in regorafenib-insensitive HCC cells restored their susceptibility to regorafenib. In conclusion, our screen identified the Hippo signaling pathway as the mediator of regorafenib efficacy in HCC.

Targeting Oncogenic BRAF: Past, Present, and Future

Identifying recurrent somatic genetic alterations of, and dependency on, the kinase BRAF has enabled a "precision medicine" paradigm to diagnose and treat BRAF-driven tumors. Although targeted kinase inhibitors against BRAF are effective in a subset of mutant BRAF tumors, resistance to the therapy inevitably emerges. In this review, we discuss BRAF biology, both in wild-type and mutant settings. We discuss the predominant BRAF mutations and we outline therapeutic strategies to block mutant BRAF and cancer growth. We highlight common mechanistic themes that underpin different classes of resistance mechanisms against BRAF-targeted therapies and discuss tumor heterogeneity and co-occurring molecular alterations as a potential source of therapy resistance. We outline promising therapy approaches to overcome these barriers to the long-term control of BRAF-driven tumors and emphasize how an extensive understanding of these themes can offer more pre-emptive, improved therapeutic strategies.

miR-126-3p down-regulation contributes to dabrafenib acquired resistance in melanoma by up-regulating ADAM9 and VEGF-A

Background

Development of resistance to inhibitors of BRAF (BRAFi) and MEK (MEKi) remains a great challenge for targeted therapy in patients with BRAF-mutant melanoma. Here, we explored the role of miRNAs in melanoma acquired resistance to BRAFi.

Methods

miRNA expression in two BRAF-mutant melanoma cell lines and their dabrafenib-resistant sublines was determined using Affymetrix GeneChip® miRNA 3.1 microarrays and/or qRT-PCR. The effects of miR-126-3p re-expression on proliferation, apoptosis, cell cycle, ERK1/2 and AKT phosphorylation, dabrafenib sensitivity, invasiveness and VEGF-A secretion were evaluated in the dabrafenib-resistant sublines using MTT assays, flow cytometry, immunoblotting, invasion assays in Boyden chambers and ELISA. ADAM9, PIK3R2, MMP7 and CXCR4 expression in the sensitive and dabrafenib-resistant cells was determined by immunoblotting. Small RNA interference was performed to investigate the consequence of VEGFA or ADAM9 silencing on proliferation, invasiveness or dabrafenib sensitivity of the resistant sublines. Long-term proliferation assays were carried out in dabrafenib-sensitive cells to assess the effects of enforced miR-126-3p expression or ADAM9 silencing on resistance development. VEGF-A serum levels in melanoma patients treated with BRAFi or BRAFi+MEKi were evaluated at baseline (T0), after two months of treatment (T2) and at progression (TP) by ELISA.

Results

miR-126-3p was significantly down-regulated in the dabrafenib-resistant sublines as compared with their parental counterparts. miR-126-3p replacement in the drug-resistant cells inhibited proliferation, cell cycle progression, phosphorylation of ERK1/2 and/or AKT, invasiveness, VEGF-A and ADAM9 expression, and increased dabrafenib sensitivity. VEGFA or ADAM9 silencing impaired proliferation and invasiveness of the drug-resistant sublines. ADAM9 knock-down in the resistant cells increased dabrafenib sensitivity, whereas miR-126-3p enforced expression or ADAM9 silencing in the drug-sensitive cells delayed the development of resistance. At T0 and T2, statistically significant differences were observed in VEGF-A serum levels between patients who responded to therapy and patients who did not. In responder patients, a significant increase of VEGF-A levels was observed at TP versus T2.

Conclusions

Strategies restoring miR-126-3p expression or targeting VEGF-A or ADAM9 could restrain growth and metastasis of dabrafenib-resistant melanomas and increase their drug sensitivity. Circulating VEGF-A is a promising biomarker for predicting patients’ response to BRAFi or BRAFi+MEKi and for monitoring the onset of resistance.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1238-4) contains supplementary material, which is available to authorized users.

Regulation of TEAD Transcription Factors in Cancer Biology

Transcriptional enhanced associate domain (TEAD) transcription factors play important roles during development, cell proliferation, regeneration, and tissue homeostasis. TEAD integrates with and coordinates various signal transduction pathways including Hippo, Wnt, transforming growth factor beta (TGFβ), and epidermal growth factor receptor (EGFR) pathways. TEAD deregulation affects well-established cancer genes such as KRAS, BRAF, LKB1, NF2, and MYC, and its transcriptional output plays an important role in tumor progression, metastasis, cancer metabolism, immunity, and drug resistance. To date, TEADs have been recognized to be key transcription factors of the Hippo pathway. Therefore, most studies are focused on the Hippo kinases and YAP/TAZ, whereas the Hippo-dependent and Hippo-independent regulators and regulations governing TEAD only emerged recently. Deregulation of the TEAD transcriptional output plays important roles in tumor progression and serves as a prognostic biomarker due to high correlation with clinicopathological parameters in human malignancies. In addition, discovering the molecular mechanisms of TEAD, such as post-translational modifications and nucleocytoplasmic shuttling, represents an important means of modulating TEAD transcriptional activity. Collectively, this review highlights the role of TEAD in multistep-tumorigenesis by interacting with upstream oncogenic signaling pathways and controlling downstream target genes, which provides unprecedented insight and rationale into developing TEAD-targeted anticancer therapeutics.

The Roles of YAP/TAZ and the Hippo Pathway in Healthy and Diseased Skin

Skin is the largest organ of the human body. Its architecture and physiological functions depend on diverse populations of epidermal cells and dermal fibroblasts. Reciprocal communication between the epidermis and dermis plays a key role in skin development, homeostasis and repair. While several stem cell populations have been identified in the epidermis with distinct locations and functions, there is additional heterogeneity within the mesenchymal cells of the dermis. Here, we discuss the current knowledge of how the Hippo pathway and its downstream effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) contribute to the maintenance, activation and coordination of the epidermal and dermal cell populations during development, homeostasis, wound healing and cancer.