Acquired resistance to BRAF inhibitors mediated by a RAF kinase switch in melanoma can be overcome by cotargeting MEK and IGF-1R/PI3K

Silencing PEX26 as an unconventional mode to kill drug-resistant cancer cells and forestall drug resistance

Promoting the macroautophagy/autophagy-mediated degradation of specific proteins and organelles can potentially be utilized to induce apoptosis in cancer cells or sensitize tumor cells to therapy. To examine this concept, we enriched for autophagosomes from histone deacetylase inhibitor (HDACi)-sensitive U937 lymphoma cells and isogenic HDACi-resistant cells. Mass spectrometry on autophagosome-enriched fractions revealed that HDACi-resistant cells undergo elevated pexophagy, or autophagy of the peroxisome, an organelle that supports tumor growth. To disturb peroxisome homeostasis, we enhanced pexophagy in HDACi-resistant cells via genetic silencing of peroxisome exportomer complex components (PEX1, PEX6, or PEX26). This consequently sensitized resistant cells to HDACi-mediated apoptosis, which was rescued by inhibiting ATM/ataxia-telangiectasia mutated (ATM serine/threonine kinase), a mediator of pexophagy. We subsequently engineered melanoma cells to stably repress PEX26 using CRISPR interference (CRISPRi). Melanoma cells with repressed PEX26 expression showed evidence of both increased pexophagy and peroxisomal matrix protein import defects versus single guide scrambled (sgSCR) controls. In vivo studies showed that sgPEX26 melanoma xenografts recurred less compared to sgSCR xenografts, following the development of resistance to mitogen-activated protein kinase (MAPK)-targeted therapy. Finally, prognostic analysis of publicly available datasets showed that low expression levels of PEX26, PEX6 and MTOR, were significantly associated with prolonged patient survival in lymphoma, lung cancer and melanoma cohorts. Our work highlighted that drugs designed to disrupt peroxisome homeostasis may serve as unconventional therapies to combat therapy resistance in cancer.Abbreviations: ABCD3/PMP70: ATP binding cassette subfamily D member 3; ACOX1: acyl-CoA oxidase 1; AP: autophagosome; COX: cytochrome c oxidase; CQ: chloroquine; CRISPRi: clustered regularly interspaced short palindromic repeats interference; DLBCL: diffuse large B-cell lymphoma; GO: gene ontology; dCas9: Cas9 endonuclease dead, or dead Cas9; HDACi: histone deacetylase inhibitors; IHC: Immunohistochemistry; LAMP2: lysosomal associated membrane protein 2; LCFAs: long-chain fatty acids; LFQ-MS: label-free quantitation mass spectrometry; LPC: lysophoshatidylcholine; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PBD: peroxisome biogenesis disorders; PTS1: peroxisomal targeting signal 1; ROS: reactive oxygen species; sgRNA: single guide RNA; VLCFAs: very-long chain fatty acids; Vor: vorinostat; WO: wash-off.

Targeting the mercapturic acid pathway for the treatment of melanoma

The treatment of metastatic melanoma is greatly hampered by the simultaneous dysregulation of several major signaling pathways that suppress apoptosis and promote its growth and invasion. The global resistance of melanomas to therapeutics is also supported by a highly active mercapturic acid pathway (MAP), which is responsible for the metabolism and excretion of numerous chemotherapy agents. The relative importance of the MAP in melanoma survival was not recognized until demonstrated that B16 melanoma undergoes dramatic apoptosis and regression upon the depletion or inhibition of the MAP transporter protein RLIP. RLIP is a multi-functional protein that couples ATP hydrolysis with the movement of substances. As the rate-limiting step of the MAP, the primary function of RLIP in the plasma membrane is to catalyze the ATP-dependent efflux of unmetabolized drugs and toxins, including glutathione (GSH) conjugates of electrophilic toxins (GS-Es), which are the precursors of mercapturic acids. Clathrin-dependent endocytosis (CDE) is an essential mechanism for internalizing ligand-receptor complexes that promote tumor cell proliferation through autocrine stimulation (Wnt5a, PDGF, βFGF, TNFα) or paracrine stimulation by hormones produced by fibroblasts (IGF1, HGF) or inflammatory cells (IL8). Aberrant functioning of these pathways appears critical for melanoma cell invasion, metastasis, and evasion of apoptosis. This review focuses on the selective depletion or inhibition of RLIP as a highly effective targeted therapy for melanoma that could cause the simultaneous disruption of the MAP and critical peptide hormone signaling that relies on CDE.

Systematic screening reveals synergistic interactions that overcome MAPK inhibitor resistance in cancer cells

OBJECTIVE

Effective adjuvant therapeutic strategies are urgently needed to overcome MAPK inhibitor (MAPKi) resistance, which is one of the most common forms of resistance that has emerged in many types of cancers. Here, we aimed to systematically identify the genetic interactions underlying MAPKi resistance, and to further investigate the mechanisms that produce the genetic interactions that generate synergistic MAPKi resistance.

METHODS

We conducted a comprehensive pair-wise sgRNA-based high-throughput screening assay to identify synergistic interactions that sensitized cancer cells to MAPKi, and validated 3 genetic combinations through competitive growth, cell viability, and spheroid formation assays. We next conducted Kaplan-Meier survival analysis based on The Cancer Genome Atlas database and conducted immunohistochemistry to determine the clinical relevance of these synergistic combinations. We also investigated the MAPKi resistance mechanisms of these validated synergistic combinations by using co-immunoprecipitation, Western blot, qRT-PCR, and immunofluorescence assays.

RESULTS

We constructed a systematic interaction network of MAPKi resistance and identified 3 novel synergistic combinations that effectively targeted MAPKi resistance (ITGB3 + IGF1R, ITGB3 + JNK, and HDGF + LGR5). We next analyzed their clinical relevance and the mechanisms by which they sensitized cancer cells to MAPKi exposure. Specifically, we discovered a novel protein complex, HDGF-LGR5, that adaptively responded to MAPKi to enhance cancer cell stemness, which was up- or downregulated by the inhibitors of ITGB3 + JNK or ITGB3 + IGF1R.

CONCLUSIONS

Pair-wise sgRNA library screening provided systematic insights into elucidating MAPKi resistance in cancer cells. ITGB3- + IGF1R-targeting drugs (cilengitide + linsitinib) could be used as an effective therapy for suppressing the adaptive formation of the HDGF-LGR5 protein complex, which enhanced cancer stemness during MAPKi stress.

ARAF mutations confer resistance to the RAF inhibitor belvarafenib in melanoma

Although RAF monomer inhibitors (type I.5, BRAF(V600)) are clinically approved for the treatment of BRAF^V600-mutant melanoma, they are ineffective in non-BRAF^V600 mutant cells^1-3. Belvarafenib is a potent and selective RAF dimer (type II) inhibitor that exhibits clinical activity in patients with BRAF^V600E- and NRAS-mutant melanomas. Here we report the first-in-human phase I study investigating the maximum tolerated dose, and assessing the safety and preliminary efficacy of belvarafenib in BRAF^V600E- and RAS-mutated advanced solid tumours (NCT02405065, NCT03118817). By generating belvarafenib-resistant NRAS-mutant melanoma cells and analysing circulating tumour DNA from patients treated with belvarafenib, we identified new recurrent mutations in ARAF within the kinase domain. ARAF mutants conferred resistance to belvarafenib in both a dimer- and a kinase activity-dependent manner. Belvarafenib induced ARAF mutant dimers, and dimers containing mutant ARAF were active in the presence of inhibitor. ARAF mutations may serve as a general resistance mechanism for RAF dimer inhibitors as the mutants exhibit reduced sensitivity to a panel of type II RAF inhibitors. The combination of RAF plus MEK inhibition may be used to delay ARAF-driven resistance and suggests a rational combination for clinical use. Together, our findings reveal specific and compensatory functions for the ARAF isoform and implicate ARAF mutations as a driver of resistance to RAF dimer inhibitors.

Targeting the p300/NONO axis sensitizes melanoma cells to BRAF inhibitors

BRAF inhibitors (BRAFi) that target BRAF V600E kinase, a driver mutation found in 50% of melanomas, show a significant antitumor response, but the common emergence of acquired resistance remains a challenge. Abnormal expression of RAF isoforms CRAF and ARAF reactivates pERK1/2, which plays crucial roles in the acquisition of resistance of melanoma cells. However, the mechanisms of dysregulation of RAF isoforms in resistant melanoma cells remain unknown. Here, we identified NONO interacted with and stabilized both CRAF and ARAF in melanoma cells, and that NONO was acetylated at 198K by p300 acetyltransferase, which stabilized NONO via antagonizing its ubiquitination/degradation mediated by RNF8. The upregulation of both p300 and NONO promoted the rebound of pERK1/2 and the subsequent resistance of melanoma cells to BRAFi, and the activation of ERK1/2 in turn induced p300 to form a positive feedback loop in resistant melanoma cells. There was a positive correlation between p300 and NONO in resistant melanoma cells and clinical samples, and p300 inhibitor C646 overcame the resistance of resistant melanoma cells to BRAF inhibitors in vitro and in vivo. Our findings reveal that targeting the positive feedback loop of p300-NONO-CRAF/ARAF-pERK1/2 may be excellent strategies to overcome the resistance of BRAF inhibitors for melanoma patients.

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.

HDAC8 Activates AKT through Upregulating PLCB1 and Suppressing DESC1 Expression in MEK1/2 Inhibition-Resistant Cells

Inhibition of the RAF-MEK1/2-ERK signaling pathway is an ideal strategy for treating cancers with NRAS or BRAF mutations. However, the development of resistance due to incomplete inhibition of the pathway and activation of compensatory cell proliferation pathways is a major impediment of the targeted therapy. The anthrax lethal toxin (LT), which cleaves and inactivates MEKs, is a modifiable biomolecule that can be delivered selectively to tumor cells and potently kills various tumor cells. However, resistance to LT and the mechanism involved are yet to be explored. Here, we show that LT, through inhibiting MEK1/2-ERK activation, inhibits the proliferation of cancer cells with NRAS/BRAF mutations. Among them, the human colorectal tumor HT-29 and murine melanoma B16-BL6 cells developed resistance to LT in 2 to 3 days of treatment. These resistant cells activated AKT through a histone deacetylase (HDAC) 8-dependent pathway. Using an Affymetrix microarray, followed by qPCR validation, we identified that the differential expression of the phospholipase C-β1 (PLCB1) and squamous cell carcinoma-1 (DESC1) played an important role in HDAC8-mediated AKT activation and resistance to MEK1/2-ERK inhibition. By using inhibitors, small interference RNAs and/or expression vectors, we found that the inhibition of HDAC8 suppressed PLCB1 expression and induced DESC1 expression in the resistant cells, which led to the inhibition of AKT and re-sensitization to LT and MEK1/2 inhibition. These results suggest that targeting PLCB1 and DESC1 is a novel strategy for inhibiting the resistance to MEK1/2 inhibition.

Developments in therapy for brain metastases in melanoma patients

Introduction: Cutaneous melanoma brain metastases (MBM) are a major cause of morbidity and mortality. While cytotoxic agents, interferon, or interleukin-2, have been used with some success in extracranial disease, limited efficacy is demonstrated in MBM. The rare patient with long-term survival presented with limited intracranial disease amenable to surgery or radiation therapy. However, the development of targeted therapy and immunotherapy over the last decade has significantly improved overall survival in this formerly devastating presentation of metastatic melanoma.Areas covered: This article reviews the mechanism of brain metastasis, challenges with treating the central nervous system, historical treatment of MBM, and outcomes in clinical trials with targeted therapy and immunotherapy.Expert opinion: The MBM patient population now, more than ever, requires a multidisciplinary approach with surgery, radiation therapy, and the use of newer systemic therapies such as immunotherapy agents and targeted therapy agents. MBM has traditionally been excluded from clinical trials for systemic therapy due to poor survival. However, recent data show overall survival rates have significantly improved, supporting the need for inclusion of MBM patients in systemic therapy clinical trials. Understanding the mechanisms of therapeutic activity in the brain, resistance  mechanisms, and the appropriate multi-modality treatment approach requires further investigation. Nevertheless, these therapies continue to give some hope to patients with historically poor survival.

Costunolide suppresses melanoma growth via the AKT/mTOR pathway in vitro and in vivo

Melanoma is the most common type of skin cancer and its incidence is rapidly increasing. AKT, and its related signaling pathways, are highly activated in many cancers including lung, colon, and esophageal cancers. Costunolide (CTD) is a sesquiterpene lactone that has been reported to possess neuroprotective, anti-inflammatory, and anti-cancer properties. However, the target and mechanism underlying its efficacy in melanoma have not been identified. In this study, we elucidated the mechanism behind the anti-cancer effect of CTD in melanoma in vitro and in vivo by identifying CTD as an AKT inhibitor. We first verified that p-AKT and AKT are highly expressed in melanoma patient tissues and cell lines. CTD significantly inhibited the proliferation, migration, and invasion of melanoma cells including SK-MEL-5, SK-MEL-28, and A375 that are overexpressed p-AKT and AKT proteins. We investigated the mechanism of CTD using a computational docking modeling, pull-down, and site directed mutagenesis assay. CTD directly bound to AKT thereby arresting cell cycle at the G1 phase, and inducing the apoptosis of melanoma cells. In addition, CTD regulated the G1 phase and apoptosis biomarkers, and inhibited the expression of AKT/mTOR/GSK3b/p70S6K/4EBP cascade proteins. After reducing AKT expression in melanoma cells, cell growth was significantly decreased and CTD did not showed further inhibitory effects. Furthermore, CTD administration suppressed tumor growth and weight in cell-derived xenograft mice models in vivo without body weight loss and inhibited the expression of Ki-67, p-AKT, and p70S6K in tumor tissues. In summary, our study implied that CTD inhibited melanoma progression in vitro and in vivo. In this study, we reported that CTD could affect melanoma growth by targeting AKT. Therefore, CTD has considerable potential as a drug for melanoma therapy.

Novel and Potent Small Molecules against Melanoma Harboring BRAF Class I/II/III Mutants for Overcoming Drug Resistance

Melanoma accounts for the majority of skin cancer deaths. About 50% of all melanomas are associated with BRAF mutations. BRAF mutations are classified into three classes with regard to dependency on RAF dimerization and RAS signaling. The most frequently occurring class I BRAF V600 mutations are sensitive to vemurafenib whereas class II and class III mutants, non-V600 BRAF mutants are resistant to vemurafenib. Herein we report six pyrimido[4,5-d]pyrimidin-2-one derivatives possessing highly potent anti-proliferative activities on melanoma cells harboring BRAF class I/II/III mutants. Novel and most potent derivative, SIJ1777, possesses not only two-digit nanomolar potency but also 2 to 14-fold enhanced anti-proliferative activities compared with reference compound, GNF-7 against melanoma cells (SK-MEL-2, SK-MEL-28, A375, WM3670, WM3629). Moreover, SIJ1777 substantially inhibits the activation of MEK, ERK, and AKT and remarkably induces apoptosis and significantly blocks migration, invasion, and anchorage-independent growth of melanoma cells harboring BRAF class I/II/II mutations while both vemurafenib and PLX8394 have little to no effects on melanoma cells expressing BRAF class II/III mutations. Taken together, our six GNF-7 derivatives exhibit highly potent activities against melanoma cells harboring class I/II/III BRAF mutations compared with vemurafenib as well as PLX8394.

Targeted drug delivery strategies for precision medicines

Progress in the field of precision medicine has changed the landscape of cancer therapy. Precision medicine is propelled by technologies that enable molecular profiling, genomic analysis, and optimized drug design to tailor treatments for individual patients. Although precision medicines have resulted in some clinical successes, the use of many potential therapeutics has been hindered by pharmacological issues, including toxicities and drug resistance. Drug delivery materials and approaches have now advanced to a point where they can enable the modulation of a drug's pharmacological parameters without compromising the desired effect on molecular targets. Specifically, they can modulate a drug's pharmacokinetics, stability, absorption, and exposure to tumours and healthy tissues, and facilitate the administration of synergistic drug combinations. This Review highlights recent progress in precision therapeutics and drug delivery, and identifies opportunities for strategies to improve the therapeutic index of cancer drugs, and consequently, clinical outcomes.

PPP6C negatively regulates oncogenic ERK signaling through dephosphorylation of MEK

Flux through the RAF-MEK-ERK protein kinase cascade is shaped by phosphatases acting on the core components of the pathway. Despite being an established drug target and a hub for crosstalk regulation, little is known about dephosphorylation of MEK, the central kinase within the cascade. Here, we identify PPP6C, a phosphatase frequently mutated or downregulated in melanoma, as a major MEK phosphatase in cells exhibiting oncogenic ERK pathway activation. Recruitment of MEK to PPP6C occurs through an interaction with its associated regulatory subunits. Loss of PPP6C causes hyperphosphorylation of MEK at activating and crosstalk phosphorylation sites, promoting signaling through the ERK pathway and decreasing sensitivity to MEK inhibitors. Recurrent melanoma-associated PPP6C mutations cause MEK hyperphosphorylation, suggesting that they promote disease at least in part by activating the core oncogenic pathway driving melanoma. Collectively, our studies identify a key negative regulator of ERK signaling that may influence susceptibility to targeted cancer therapies.

Through an shRNA screen, Cho et al. identify PPP6C as a phosphatase that inactivates the kinase MEK, sensitizing tumor cells to clinical MEK inhibitors. This study suggests that cancer-associated loss-of-function PPP6C mutations prevalent in melanoma serve to activate the core oncogenic RAF-MEK-ERK pathway that drives the disease.

Chromatin assembly factor 1 suppresses epigenetic reprogramming toward adaptive drug resistance

The long-term effectiveness of targeted cancer therapies is limited by the development of resistance. Although epigenetic reprogramming has been implicated in resistance, the mechanisms remain elusive. Herein, we demonstrate that increased chromatin accessibility is involved in adaptive BRAF inhibitor (BRAFi)-resistance in melanoma cells. We observed loss of chromatin assembly factor 1 (CAF-1) and its related histone H3 lysine 9 trimethylation (H3K9me3) with adaptive BRAFi resistance. We further showed that depletion of CAF-1 provides chromatin plasticity for effective reprogramming by AP1 components to promote BRAFi resistance. Our data suggest that therapeutic approaches to restore H3K9me3 levels may compensate for the loss of CAF-1 and, in turn, suppress resistance to BRAF inhibitors.

Inhibition of BRAF and ERK1/2 has synergistic effects on thyroid cancer growth in vitro and in vivo

Mutations in the BRAF gene are highly prevalent in thyroid cancer. However, the response rate of thyroid tumors to BRAF-directed therapies has been mixed. Increasingly, combination therapies inhibiting the MAPK pathway at multiple nodes have shown promise. Recently developed ERK1/2 inhibitors are of interest for use in combination therapies as they have the advantage of inhibiting the most downstream node of the MAPK pathway, therefore preventing pathway reactivation. Here, we examined the effect of combined BRAF inhibition (dabrafenib) and ERK1/2 inhibition (SCH772984) on the growth and survival of a panel of BRAF-mutant thyroid cancer cell lines using in vitro and in vivo approaches. We found that resistance due to MAPK pathway reactivation occurs quickly with single-agent BRAF inhibition, but can be prevented with combined BRAF and ERK1/2 inhibition. Combined inhibition also results in synergistic growth inhibition, decreased clonogenic survival, and enhanced induction of apoptosis in a subset of BRAF-mutant thyroid cancer cells. Finally, combined inhibition of BRAF and ERK1/2 results in enhanced inhibition of tumor growth in an anaplastic thyroid cancer in vivo model. These results provide key rationale to pursue combined BRAF and ERK1/2 inhibition as an alternative therapeutic strategy for BRAF-mutant advanced thyroid cancer patients.

Exquisitely Specific anti-KRAS Biodegraders Inform on the Cellular Prevalence of Nucleotide-Loaded States

Mutations to RAS proteins (H-, N-, and K-RAS) are among the most common oncogenic drivers, and tumors harboring these lesions are some of the most difficult to treat. Although covalent small molecules against KRAS^G12C have shown promising efficacy against lung cancers, traditional barriers remain for drugging the more prevalent KRAS^G12D and KRAS^G12V mutants. Targeted degradation has emerged as an attractive alternative approach, but for KRAS, identification of the required high-affinity ligands continues to be a challenge. Another significant hurdle is the discovery of a hybrid molecule that appends an E3 ligase-recruiting moiety in a manner that satisfies the precise geometries required for productive polyubiquitin transfer while maintaining favorable druglike properties. To gain insights into the advantages and feasibility of KRAS targeted degradation, we applied a protein-based degrader (biodegrader) approach. This workflow centers on the intracellular expression of a chimeric protein consisting of a high-affinity target-binding domain fused to an engineered E3 ligase adapter. A series of anti-RAS biodegraders spanning different RAS isoform/nucleotide-state specificities and leveraging different E3 ligases provided definitive evidence for RAS degradability. Further, these established that the functional consequences of KRAS degradation are context dependent. Of broader significance, using the exquisite degradation specificity that biodegraders can possess, we demonstrated how this technology can be applied to answer questions that other approaches cannot. Specifically, application of the GDP-state specific degrader uncovered the relative prevalence of the "off-state" of WT and various KRAS mutants in the cellular context. Finally, if delivery challenges can be addressed, anti-RAS biodegraders will be exciting candidates for clinical development.

Effect of stress-induced polyploidy on melanoma reprogramming and therapy resistance

Melanomas and their precursors, the melanocytes, are frequently exposed to UV due to their anatomic location, leading to DNA damage and reactive oxygen stress related harm. Such damage can result in multinucleation or polyploidy, in particularly in presence of mitotic or cell division failure. As a consequence, the cell encounters either of two fates: mitotic catastrophe, resulting in cell death, or survival and recovery, the latter occurring less frequently. However, when cells manage to recover in an polyploid state, they have often acquired new features, which allow them to tolerate and adapt to oncogene- or therapy induced stress. This review focuses on polyploidy inducers in melanoma and their effects on transcriptional reprogramming and phenotypic adaptation as well as the relevance of polyploid melanoma cells for therapy resistance.

Harnessing the polyamine transport system to treat BRAF inhibitor-resistant melanoma

BRAF mutations are present in over half of all melanoma tumors. Although BRAF inhibitors significantly improve survival of patients with metastatic melanoma, recurrences occur within several months. We previously reported that BRAF mutant melanoma cells are more sensitive to a novel arylmethyl-polyamine (AP) compound that exploits their increased polyamine uptake compared to that of BRAF wildtype cells. Using an animal model of BRAF inhibitor-resistant melanoma, we show that co-treatment with the BRAF inhibitor, PLX4720, and AP significantly delays the recurrence of PLX4720-resistant melanoma tumors and decreases tumor-promoting macrophages. Development of BRAF inhibitor-resistance enriches for metastatic cancer stem cells (CSC) and increases tumor-promoting macrophages. In vitro studies demonstrated that CD304⁺, CXCR4⁺ spheroid cultures of BRAF mutant melanoma cells are resistant to PLX4720 but are more sensitive to AP compared to monolayer cultures of the same cells. AP significantly inhibited YUMM1.7 melanoma cell invasiveness across a Matrigel-coated filter using the CXCR4 ligand, SDF-1α, as the chemoattractant. AP also blocked the chemotactic effect of SDF-1α on CXCR4⁺ macrophages and inhibited M2 polarization of macrophages. In melanoma-macrophage co-cultures, AP prevented the PLX4720-induced release of pro-tumorigenic growth factors, such as VEGF, from macrophages and prevented the macrophage rescue of BRAF mutant melanoma cells treated with PLX4720. Our study offers a novel therapy (AP) to treat chemo-resistant melanoma. AP is unique because it targets the polyamine transport system in BRAF inhibitor-resistant CSCs and also blocks CXCR4 signaling in invasive melanoma cells and pro-tumorigenic macrophages.

Simultaneous blocking of the pan-RAF and S100B pathways as a synergistic therapeutic strategy against malignant melanoma

Melanoma is a very aggressive form of skin cancer. Although BRAF inhibitors have been utilized for melanoma therapy, advanced melanoma patients still face a low five-year survival rate. Recent studies have shown that CRAF can compensate for BRAF depletion via regulating DNA synthesis to remain melanoma proliferation. Hence, targeting CRAF either alone or in combination with other protein pathways is a potential avenue for melanoma therapy. Based on our previously reported CRAF-selective inhibitor for renal cancer therapy, we have herein discovered an analogue (complex 1) from the reported CRAF library suppresses melanoma cell proliferation and melanoma tumour growth in murine models of melanoma via blocking the S100B and RAF pathways. Intriguingly, we discovered that inhibiting BRAF together with S100B exerts a novel synergistic effect to significantly restore p53 transcription activity and inhibit melanoma cell proliferation, whereas blocking BRAF together with CRAF only had an additive effect. We envision that blocking the pan-RAF and S100B/p53 pathways might be a novel synergistic strategy for melanoma therapy and that complex 1 is a potential inhibitor against melanoma via blocking the pan-RAF and S100B pathways.

Advanced Melanoma: Resistance Mechanisms to Current Therapies

Novel therapeutic agents introduced over the past decade, including immune checkpoint inhibitors and targeted therapies, have revolutionized the management of metastatic melanoma and significantly improved patient outcomes. Although robust and durable responses have been noted in some cases, treatment is often limited by innate or acquired resistance to these agents. This article provides an overview of known and suspected mechanisms involved with acquired resistance to BRAF/MEK inhibitors as well as developing insights into innate and acquired resistance to checkpoint inhibitors in patients with melanoma.

EIF3H knockdown inhibits malignant melanoma through regulating cell proliferation, apoptosis and cell cycle

Malignant melanoma (MM) causes 80% of skin cancer-related deaths and becomes the most lethal type of skin cancer. The molecular mechanism of MM is still not clear. This study aimed to reveal the relationship between MM and EIF3H. Clinical specimens were collected to preliminarily explore the role of EIF3H in MM. MM cell lines with EIF3H knockdown were constructed for investigating the effects of EIF3H on cell proliferation, apoptosis, cell cycle and cell motility. Mice xenograft model was constructed for verification in vivo. We found that EIF3H was obviously upregulated in MM tissues compared with normal skin tissues, which was correlated with tumor stage and risk of lymphatic metastasis. The in vitro results indicated that silencing EIF3H in MM cells could significantly suppress cell proliferation, promote cell apoptosis and induce cell cycle arrest. Moreover, EIF3H knockdown significantly restrained cell motility through regulating EMT-related proteins. The effects of EIF3H knockdown were also verified in mice xenograft model, which were represented by slower growth rate, smaller volume and lighter weight of tumors. Therefore, EIF3H was identified as a critical factor in the development and progression of MM which may be used as a novel therapeutic target in the treatment of MM.

NECTIN4: A Novel Therapeutic Target for Melanoma

Malignant melanoma is the most common lethal skin cancer and causes death in a short time when metastasized. Although BRAF inhibitors (BRAFi) have greatly improved the prognosis of BRAF-mutated melanoma, drug resistance is a major concern even when they are combined with MEK inhibitors. Alternative treatments for BRAFi-resistant melanoma are highly anticipated. Nectin cell adhesion molecule 4 (NECTIN4) is highly expressed and associated with progression in tumors. We aimed to investigate the role of NECTIN4 in melanoma and its potency as a therapeutic target using 126 melanoma samples and BRAFi-resistant cells. Immunohistochemically, most of the clinical samples expressed NECTIN4, at least in part. NECTIN4 was highly expressed in BRAF-mutated melanoma and its high expression was associated with disease-free survival. In BRAFi-resistant melanoma cells, NECTIN4 and the PI3K/Akt pathway were upregulated, along with the acquisition of BRAFi resistance. Monomethyl auristatin E, a cytotoxic part of NECTIN4-targeted antibody-drug conjugate, was effective for BRAF-mutated or BRAFi-resistant melanoma cells. NECTIN4 inhibition increased the sensitivity of BRAFi-resistant cells to BRAFi and induced apoptosis. In conclusion, we revealed the expression and roles of NECTIN4 in melanoma. Targeted therapies against NECTIN4 can be a novel treatment strategy for melanoma, even after the acquisition of BRAFi resistance.

Downregulation of lncRNA TSLNC8 promotes melanoma resistance to BRAF inhibitor PLX4720 through binding with PP1α to re-activate MAPK signaling

PURPOSE

Approximately 60% of patients with melanoma harbor BRAF mutation and targeting BRAF offers enormous advance in the treatment of those patients. Unfortunately, the efficacy of the BRAF inhibitors is usually restricted by the onset of drug resistance. Therefore, better understanding of the adaptive drug resistance mechanisms is essential for the development of alternative therapeutic strategies, and offers more promising measures to promote the short duration of response to BRAF inhibitors.

METHODS

The levels of tumor suppressive long noncoding RNA on chromosome 8p12 (TSLNC8) were evaluated by qPCR. The MTT assay, colony formation assay, apoptosis assay, and in vivo xenograft tumor model were performed to assess the functions of TSLNC8 on drug resistance. Western blotting, RNA pull-down, and RNA immunoprecipitation (RIP) assays were applied to investigate the mechanisms of TSLNC8 in melanoma.

RESULTS

Herein, our findings demonstrate that TSLNC8 is significantly downregulated in BRAF inhibitor-resistant melanoma tissues and cells. Moreover, downregulation of TSLNC8 in BRAF inhibitor sensitive cells reduces the toxicity response to BRAF inhibitor PLX4720, and inhibits apoptosis of melanoma cells-treated with PLX4720. Further assay elucidates that TSLNC8 can bind with the catalytic subunit of protein phosphatase 1α (PP1α) to regulate its distribution, and Downregulation of TSLNC8 results in PP1α cytoplasmic accumulation, thus re-activating the MAPK signaling. Eventually, the overexpression of TSLNC8 in BRAF inhibitor PLX4720-resistant melanoma cells restores the sensitive to BRAF inhibitor.

CONCLUSION

Collectively, our research provides a compelling rationale for resistance to BRAF inhibitor in melanoma, and the patient might benefit from the combinatorial therapy of BRAF inhibitors and lncRNA TSLNC8.

Emerging strategies to treat rare and intractable subtypes of melanoma

Melanoma is the deadliest form of skin cancer, possessing a diverse landscape of subtypes with distinct molecular signatures and levels of aggressiveness. Although immense progress has been achieved therapeutically for patients with the most common forms of this disease, little is known of how to effectively treat patients with rarer subtypes of melanoma. These subtypes include acral lentiginous (the rarest form of cutaneous melanoma; AL), uveal, and mucosal melanomas, which display variations in distribution across (a) the world, (b) patient age-groups, and (c) anatomic sites. Unfortunately, patients with these relatively rare subtypes of melanoma typically respond worse to therapies approved for the more common, non-AL cutaneous melanoma and do not have effective alternatives, and thus consequently have worse overall survival rates. Achieving durable therapeutic responses in these high-risk melanoma subtypes represents one of the greatest challenges of the field. This review aims to collate and highlight effective preclinical and/or clinical strategies against these rare forms of melanoma.

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

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

Preclinical and Clinical Advances of Targeted Protein Degradation as a Novel Cancer Therapeutic Strategy: An Oncologist Perspective

PROteolysis Targeting Chimeras (PROTACs) are a family of heterobifunctional small molecules that specifically target cellular proteins for degradation. Given that their mode of action is distinct from that of small-molecule inhibitors widely used in clinical practice, PROTACs have the potential to improve current cancer therapies. Multiple studies have suggested that PROTACs exhibit enhanced pharmacodynamics and reduced toxicity both in vitro and in vivo compared to clinically relevant small-molecule kinase inhibitors. In addition, PROTACs have been reported to be less prone to mutation-mediated drug resistance in specific disease settings. Since its development in 2001, the field of targeted protein degradation, in which PROTACs are used, has expanded rapidly. However, earlier studies focused on the advancement of the technology itself, while preclinical and clinical data on the disease-modifying effect of PROTACs have only recently been reported. As preclinical and clinical evidence accumulates, the efficacy of PROTACs as targeted therapeutics-distinct from that of small-molecule kinase inhibitors-suggests potential translational benefit in the clinical setting. In this short review, we aim to describe translational potentials of PROTACs. We offer our perspectives as practicing oncologists on the preclinical and clinical data on PROTACs as novel therapeutics for both solid and hematological malignancies.

Multidimensional indicators of scholarly impact in the skin oncology literature: is there a correlation between bibliometric and altmetric profiles?

Introduction: Bibliometric and altmetric analyses are used to identify landmark publications in their respective research field. We hypothesised that highly cited skin oncology articles correlate positively with the Oxford Evidence Based Medicine scoring level, altmetric score (AS) and rank within the top 100 manuscripts.Methods: Thomson Reuter's Web of Science citation indexing database was searched to identify all English-language skin oncology full-text articles in the last 75 years. The top 100 articles with the highest citation count were analysed by subject matter, publishing journal, author, year, institution, individual and five-year impact factor, AS and Oxford EBM level. Results: 180,132 articles were identified. The most cited article (Hodi et al.) demonstrated improved survival with ipilimumab in patients with metastatic melanoma (7894 citations). The article with the highest AS was Esteva et al. (AS = 576.7, 'dermatologist-level classification of skin cancer with deep neural networks'). No difference was found between evidence level and citation count (r = -0.1239, p = 0.2291), but a significant difference was seen for AS (r = -0.3024, p = 0.0028). AS scores increased over time, whereas bibliometrics did not. Conclusion: This work highlights the most influential work in the skin oncology field in the last 75 years. We have identified a differential relationship between commonly used metrics and evidence level in the field of skin oncology. As the digitalisation of research output and consumption increases, both bibliometric and altmetric analyses need to be considered when an article's impact is being assessed.

MEK inhibitor resistance mechanisms and recent developments in combination trials

The mitogen-activated protein kinase (MAPK) pathway plays a vital role in cellular processes such as gene expression, cell proliferation, cell survival, and apoptosis. Also known as the RAS-RAF-MEK-ERK pathway, the MAPK pathway has been implicated in approximately one-third of all cancers. Mutations in RAS or RAF genes such as KRAS and BRAF are common, and these mutations typically promote malignancies by over-activating MEK and ERK downstream, which drives sustained cell proliferation and uninhibited cell growth. Development of drugs targeting this pathway has been a research area of great interest, especially drugs targeting the inhibition of MEK. In vitro and clinical studies have shown promise for certain MEK inhibitors (MEKi) , and MEKi have become the first treatment option for certain cancers. Despite promising results, not all patients have a response to MEKi, and mechanisms of resistance typically arise in patients who do have a positive initial response. This paper summarizes recent developments regarding MEKi, the mechanisms of adaptive resistance to MEKi, and the potential solutions to the issue of adaptive MEKi resistance.

Computational evaluation of potent 2-(1H-imidazol-2-yl) pyridine derivatives as potential V600E-BRAF inhibitors

Background

V600E-BRAF is a major protein target involved in various types of human cancers. However, the acquired resistance of the V600E-BRAF kinase to the vemurafenib and the side effects of other identified drugs initiate the search for efficient inhibitors. In the current paper, virtual docking screening combined with drug likeness and ADMET properties predictions were jointly applied to evaluate potent 2-(1H-imidazol-2-yl) pyridines as V600E-BRAF kinase inhibitors.

Results

Most of the studied compounds showed better docking scores and favorable interactions with theiV600E-BRAF target. Among the screened compounds, the two most potent (14 and 30) with good rerank scores (−124.079 and − 122.290) emerged as the most effective, and potent V600E-BRAF kinase inhibitors which performed better than vemurafenib (−116.174), an approved V600E-BRAF kinase inhibitor. Thus, the docking studies exhibited that these compounds have shown competing inhibition of V600E-BRAF kinase with vemurafenib at the active site and revealed better pharmacological properties based on Lipinski’s and Veber’s drug-likeness rules for oral bioavailability and ADMET properties.

Conclusion

The docking result, drug-likeness rules, and ADMET parameters identified compounds (14 and 30) as the best hits against V600E-BRAF kinase with better pharmacological properties. This suggests that these compounds may be developed as potent V600E-BRAF inhibitors.

Isoform- and Paralog-Switching in IR-Signaling: When Diabetes Opens the Gates to Cancer

Insulin receptor (IR) and IR-related signaling defects have been shown to trigger insulin-resistance in insulin-dependent cells and ultimately to give rise to type 2 diabetes in mammalian organisms. IR expression is ubiquitous in mammalian tissues, and its over-expression is also a common finding in cancerous cells. This latter finding has been shown to associate with both a relative and absolute increase in IR isoform-A (IR-A) expression, missing 12 aa in its EC subunit corresponding to exon 11. Since IR-A is a high-affinity transducer of Insulin-like Growth Factor-II (IGF-II) signals, a growth factor is often secreted by cancer cells; such event offers a direct molecular link between IR-A/IR-B increased ratio in insulin resistance states (obesity and type 2 diabetes) and the malignant advantage provided by IGF-II to solid tumors. Nonetheless, recent findings on the biological role of isoforms for cellular signaling components suggest that the preferential expression of IR isoform-A may be part of a wider contextual isoform-expression switch in downstream regulatory factors, potentially enhancing IR-dependent oncogenic effects. The present review focuses on the role of isoform- and paralog-dependent variability in the IR and downstream cellular components playing a potential role in the modulation of the IR-A signaling related to the changes induced by insulin-resistance-linked conditions as well as to their relationship with the benign versus malignant transition in underlying solid tumors.

Targeting Extracellular Matrix Remodeling Restores BRAF Inhibitor Sensitivity in BRAFi-resistant Melanoma

PURPOSE

The extracellular matrix (ECM) is an intriguing, yet understudied component of therapy resistance. Here, we investigated the role of ECM remodeling by the collagenase, MT1-MMP, in conferring resistance of v-Raf murine sarcoma viral oncogene homolog B1 (BRAF)-mutant melanoma to BRAF inhibitor (BRAFi) therapy.

EXPERIMENTAL DESIGN

Publicly available RNA-sequencing data and reverse phase protein array were used to determine the relevance of MT1-MMP upregulation in BRAFi-resistant melanoma in patients, patient-derived xenografts, and cell line-derived tumors. Short hairpin RNA (shRNA)-mediated knockdown of MT1-MMP, inhibition via the selective MT1-MMP/MMP2 inhibitor, ND322, or overexpression of MT1-MMP was used to assess the role of MT1-MMP in mediating resistance to BRAFi.

RESULTS

MT1-MMP was consistently upregulated in posttreatment tumor samples derived from patients upon disease progression and in melanoma xenografts and cell lines that acquired resistance to BRAFi. shRNA- or ND322-mediated inhibition of MT1-MMP synergized with BRAFi leading to resensitization of resistant cells and tumors to BRAFi. The resistant phenotype depends on the ability of cells to cleave the ECM. Resistant cells seeded in MT1-MMP uncleavable matrixes were resensitized to BRAFi similarly to MT1-MMP inhibition. This is due to the inability of cells to activate integrinβ1 (ITGB1)/FAK signaling, as restoration of ITGB1 activity is sufficient to maintain resistance to BRAFi in the context of MT1-MMP inhibition. Finally, the increase in MT1-MMP in BRAFi-resistant cells is TGFβ dependent, as inhibition of TGFβ receptors I/II dampens MT1-MMP overexpression and restores sensitivity to BRAF inhibition.

CONCLUSIONS

BRAF inhibition results in a selective pressure toward higher expression of MT1-MMP. MT1-MMP is pivotal to an ECM-based signaling pathway that confers resistance to BRAFi therapy.

Integrin-Src-YAP1 signaling mediates the melanoma acquired resistance to MAPK and PI3K/mTOR dual targeted therapy

Activation of PI3K/AKT pathway is one of the most recurrent resistant mechanisms for BRAF-targeted therapy, and the combination of MAPK and PI3K/AKT inhibitors becomes one of the most promising regimens for BRAF-targeted relapsed melanoma patients. Although the potent drug efficacy was observed in preclinical experiments and early clinical trials, the dual-drug resistance is inevitable observed. In this study, we systematically explored the mechanisms of dual-drug resistance to MAPKi and PI3K/mTORi in melanoma. With transcriptomic dissection of dual-drug resistant models, we identified that the drug tolerance was mediated by ECM-integrins α3β1 and α11β1 signaling. Upon binding ECM, the integrins activated downstream kinase Src rather than FAK, WNT, or TGFβ. Knockdown of integrins α3, α11, and β1 significantly inhibited the proliferation of dual-drug resistant sublines while with trivial effects on parental cells. Although Src inhibition suppressed the phosphorylation of AKT, c-JUN, and p38, none of inhibitors targeting these kinases reversed the dual-drug resistance in model cells. Notably, Src inhibitor promoted the phosphorylations of LATS1 and YAP1, subsequently, re-localized YAP1 from nucleus to cytosol facilitating further degradation. Both small molecule inhibitors and shRNAs targeting YAP1 or Src overcame the MAPKi and PI3K/mTORi dual-drug resistance. In conclusion, our data not only illuminated an integrin-Src-YAP1 pathway mediated MAPKi and PI3K/mTORi dual-drug resistant mechanism but also provided a potential combinatorial regimen for the drug-relapsed melanoma patients.

Drug-selected population in melanoma A2058 cells as melanoma stem-like cells retained angiogenic features - the potential roles of heparan-sulfate binding ANGPTL4 protein

Malignant cancer may contain highly heterogeneous populations of cells, including stem-like cells which were resistant to chemotherapy agents, radiation, mechanical stress, and immune surveillance. The characterization of these specific subpopulations might be critical to develop novel strategy to remove malignant tumors. We selected and enriched small population of human melanoma A2058 cells by repetitive selection cycles (selection, restoration, and amplification). These subpopulation of melanoma cells persisted the characteristics of slower cell proliferation, enhanced drug-resistance, elevated percentage of side population as analyzed by Hoechst33342 exclusion, in vitro sphere formation, and in vivo xenograft tumor formation by small amount of tumor cells. The selected populations would be melanoma stem-like cells with high expression of stem cell markers and altered kinase activation. Microarray and bioinformatics analysis highlighted the high expression of angiopoietin-like 4 protein in drug-selected melanoma stem-like cells. Further validation by specific shRNA demonstrated the role of angiopoietin-like 4 protein in drug-selected subpopulation associated with enhanced drug-resistance, sphere formation, reduced kinase activation, in vitro tube-forming ability correlated with heparan-sulfate proteoglycans. Our finding would be applicable to explore the mechanism of melanoma stemness and use angiopoietin-like 4 as potential biomarkers to identify melanoma stem-like cells.

Loss of ACK1 Upregulates EGFR and Mediates Resistance to BRAF Inhibition

Targeted BRAF(V600E) suppression by selective BRAF inhibitors (BRAFis; e.g., vemurafenib and dabrafenib) has led to a sea change in the treatment of metastatic melanoma. Despite frequent upfront responses, acquired resistance has compromised long-term applicability. Among the various mechanisms of resistance, activation of multiple receptor tyrosine kinases is a known critical factor that contributes to vemurafenib resistance⁠. EGFR activation has been recurrently identified in a set of vemurafenib-resistant melanomas, but little is known about how EGFR, or possibly other receptor tyrosine kinases, becomes activated. Here, we report that ACK1, a protein kinase that modulates EGFR turnover, is downregulated in vemurafenib-resistant melanoma cells. We also found that ACK1 depletion with short hairpin RNA decreased EGFR degradation when activated by epidermal growth factor, increased EGFR protein expression, and conferred resistance to BRAFis both in vitro and in vivo. Vemurafenib resistance mediated by ACK1 inhibition can be reversed by the EGFR inhibitor gefitinib. Our data indicate that ACK1 loss may be a post-transcriptional mechanism that increases EGFR signaling and contributes to drug resistance.

Evolution of Molecular Targets in Melanoma Treatment

Melanoma is the deadliest type of skin cancers, accounting for more than 80% of skin cancer mortality. Although melanoma was known very early in the history of medicine, treatment for this disease had remained largely the same until very recently. Previous treatment options, including removal surgery and systemic chemotherapy, offered little benefit in extending the survival of melanoma patients. However, the last decade has seen breakthroughs in melanoma treatment, which all emerged following new insight into the oncogenic signaling of melanoma. This paper reviewed the evolution of drug targets for melanoma treatment based on the emergence of novel findings in the molecular signaling of melanoma. One of the findings that are most influential in melanoma treatment is that more than 50% of melanoma tumors contain BRAF mutations. This is fundamental for the development of BRAF inhibitors, which is the first group of drugs that significantly improves the overall survival of melanoma patients compared to the traditional chemotherapeutic dacarbazine. More recently, findings of the role of immune checkpoint molecules such as CTLA-4 and PD1/PD-L1 in melanoma biology have led to the development of a new therapeutic category: immune checkpoint inhibitors, which, for the first time in the history of cancer treatment, produced a durable response in a subset of melanoma patients. However, as this paper discussed next, there is still an unmet need for melanoma treatment. A significant population of patients did not respond to either BRAF inhibitors or immune checkpoint inhibitors. Of those patients who gained an initial response from those therapies, a remarkable percentage would develop drug resistance even when MEK inhibitors were added to the treatment. Finally, this paper discusses some possible targets for melanoma treatment.

miR-524-5p reduces the progression of the BRAF inhibitor-resistant melanoma

BRAF inhibitors were approved for the treatment of BRAF-mutant melanoma. However, most patients acquire the resistance to BRAF inhibitors after several months of treatment. miR-524-5p is considered as a tumor suppressor in many cancers, including melanoma. In this study, we investigated the biological functions of miR-524-5p in melanoma with acquired resistance to BRAF inhibitor and evaluated the endogenous miR-524-5p expression as a biomarker for melanoma. The results showed that the expression of miR-524-5p was 0.481-fold lower in melanoma tissues (n = 117) than in nevus tissues (n = 40). Overexpression of miR-524-5p significantly reduced proliferative, anchorage-independent growth, migratory and invasive abilities of BRAF inhibitor-resistant melanoma cells. Moreover, the introduction of miR-524-5p led to a reduced development of BRAF inhibitor-resistant melanoma in vivo. Remarkably, the MAPK/ERK signaling pathway was decreased after treatment with miR-524-5p. Furthermore, next-generation sequencing analysis implied that the complement system, leukocyte extravasation, liver X receptor/retinoid-X-receptor activation, and cAMP-mediated signaling may be related to miR-524-5p-induced pathways in the resistant cells. The miR-524-5p level was higher on average in complete response and long-term partial response patients than in progressive disease and short-term partial response patients treated with BRAF inhibitors. Our results proposed that miR-524-5p could be considered as a target for treatment BRAF inhibitor-resistant melanoma and a prognostic marker in the response of patients to BRAF inhibitors for melanoma.

Combating acquired resistance to MAPK inhibitors in melanoma by targeting Abl1/2-mediated reactivation of MEK/ERK/MYC signaling

Metastatic melanoma remains an incurable disease for many patients due to the limited success of targeted and immunotherapies. BRAF and MEK inhibitors reduce metastatic burden for patients with melanomas harboring BRAF mutations; however, most eventually relapse due to acquired resistance. Here, we demonstrate that ABL1/2 kinase activities and/or expression are potentiated in cell lines and patient samples following resistance, and ABL1/2 drive BRAF and BRAF/MEK inhibitor resistance by inducing reactivation of MEK/ERK/MYC signaling. Silencing/inhibiting ABL1/2 blocks pathway reactivation, and resensitizes resistant cells to BRAF/MEK inhibitors, whereas expression of constitutively active ABL1/2 is sufficient to promote resistance. Significantly, nilotinib (2^nd generation ABL1/2 inhibitor) reverses resistance, in vivo, causing prolonged regression of resistant tumors, and also, prevents BRAFi/MEKi resistance from developing in the first place. These data indicate that repurposing the FDA-approved leukemia drug, nilotinib, may be effective for prolonging survival for patients harboring BRAF-mutant melanomas.

Spatial dynamics of the Girolando breed in Brazil: analysis of genetic integration and environmental factors

Brazil is one of the world's largest milk producers. Several scientific studies have been developed related to landscape analyses that combine genetic with landscape structure data. In the present study, we aimed to analyze the relationship between genetic, environmental, and socioeconomic aspects of production in Girolando cattle in Brazil, as well as verify the spatial patterns of its genetic diversity. Genetic values and accuracy of 46,289 animals were used as well as information from DNA of 310 Girolando animals. Canonic, discriminant, and cluster analyses were conducted in SAS® and K-means method in ArcGIS 10.3 software. The relationship between genetic and geographic distance was analyzed using different methods in software Alleles in Space®. Clusters with animals with higher genetic values for milk production are located in municipalities with lower gross domestic product, fewer family-based establishments, and lower human development index. These clusters are associated with regions with higher area planted with crops, lower percentage of pastures that were less degraded, higher humidity, lower temperature range, and lower normalized difference vegetation index (NDVI) values. The greater the geographical distance between groups of animals, the greater the genetic distance between them with a significant distinction over 504 km. There is high genetic heterogeneity among animals. From these results, it will be possible to develop methodologies for better evaluation of the animals within the production systems.

In Cellulo Evaluation of the Therapeutic Potential of NHC Platinum Compounds in Metastatic Cutaneous Melanoma

We describe here the evaluation of the cytotoxic efficacy of two platinum (II) complexes bearing an N-heterocyclic carbene (NHC) ligand, a pyridine ligand and bromide or iodide ligands on a panel of human metastatic cutaneous melanoma cell lines representing different genetic subsets including BRAF-inhibitor-resistant cell lines, namely A375, SK-MEL-28, MeWo, HMCB, A375-R, SK-MEL-5-R and 501MEL-R. Cisplatin and dacarbazine were also studied for comparison purposes. Remarkably, the iodine-labelled Pt-NHC complex strongly inhibited proliferation of all tested melanoma cells after 1-h exposure, likely due to its rapid uptake by melanoma cells. The mechanism of this inhibitory activity involves the formation of DNA double-strand breaks and apoptosis. Considering the intrinsic chemoresistance of metastatic melanoma cells of current systemic treatments, these findings are promising and could give research opportunities in the future to improve the prognosis of patients suffering from unresectable metastatic melanoma that are not eligible or that do not respond to the most effective drugs available to date, namely BRAF inhibitors and the anti-PD-1 monoclonal antibody (mAb).

Continuous versus intermittent BRAF and MEK inhibition in patients with BRAF-mutated melanoma: a randomized phase 2 trial

Preclinical modeling suggests that intermittent BRAF inhibitor therapy may delay acquired resistance when blocking oncogenic BRAF^V600 in melanoma^1,2. We conducted S1320, a randomized, open-label, phase 2 clinical trial (NCT02196181) evaluating whether intermittent dosing of the BRAF inhibitor dabrafenib and the MEK inhibitor trametinib improves progression-free survival in patients with metastatic and unresectable BRAF^V600 melanoma. Patients were enrolled at 68 academic and community sites nationally. All patients received continuous dabrafenib and trametinib during an 8-week lead-in period, after which patients with non-progressing tumors were randomized to either continuous or intermittent dosing of both drugs on a 3-week-off, 5-week-on schedule. The trial has completed accrual and 206 patients with similar baseline characteristics were randomized 1:1 to the two study arms (105 to continuous dosing, 101 to intermittent dosing). Continuous dosing yielded a statistically significant improvement in post-randomization progression-free survival compared with intermittent dosing (median 9.0 months versus 5.5 months, P = 0.064, pre-specified two-sided α = 0.2). Therefore, contrary to the initial hypothesis, intermittent dosing did not improve progression-free survival in patients. There were no differences in the secondary outcomes, including overall survival and the overall incidence of treatment-associated toxicity, between the two groups.

CEN-tools: an integrative platform to identify the contexts of essential genes

An emerging theme from large-scale genetic screens that identify genes essential for cell fitness is that essentiality of a given gene is highly context-specific. Identification of such contexts could be the key to defining gene function and also to develop novel therapeutic interventions. Here, we present Context-specific Essentiality Network-tools (CEN-tools), a website and python package, in which users can interrogate the essentiality of a gene from large-scale genome-scale CRISPR screens in a number of biological contexts including tissue of origin, mutation profiles, expression levels and drug responses. We show that CEN-tools is suitable for the systematic identification of genetic dependencies and for more targeted queries. The associations between genes and a given context are represented as dependency networks (CENs), and we demonstrate the utility of these networks in elucidating novel gene functions. In addition, we integrate the dependency networks with existing protein-protein interaction networks to reveal context-dependent essential cellular pathways in cancer cells. Together, we demonstrate the applicability of CEN-tools in aiding the current efforts to define the human cellular dependency map.

In silico evaluation of some 4-(quinolin-2-yl)pyrimidin-2-amine derivatives as potent V600E-BRAF inhibitors with pharmacokinetics ADMET and drug-likeness predictions

Background

The resistance of V600E-BRAF to the vemurafenib and the side effects of the identified inhibitors trigger the research for a novel and more potent anti-melanoma agents. In this study, virtual docking screening along with pharmacokinetics ADMET and drug-likeness predictions were combined to evaluate some 4-(quinolin-2-yl)pyrimidin-2-amine derivatives as potent V600E-BRAF inhibitors.

Results

Some of the selected compounds exhibited better binding scores and favorable interaction with the V600E-BRAF enzyme. Out of the screened compounds, two most potent (5 and 9) having good Rerank scores (− 128.011 and − 126.258) emerged as effective and potent V600E-BRAF inhibitors that outperformed the FDA-approved V600E-BRAF inhibitor (vemurafenib, − 118.607). Thus, the molecular docking studies revealed that the studied compounds showed competing for inhibition of V600E-BRAF with vemurafenib at the binding site and possessed better pharmacological parameters based on the drug-likeness rules filters for the oral bioavailability, and ADMET risk parameters.

Conclusion

The docking analysis, drug-likeness rules filters, and ADMET study identified compounds (5 and 9) as the best hits against V600E-BRAF kinase with enhanced pharmacological properties. This recommends that these compounds may be developed as potent anti-melanoma agents.

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.

Synthetic Lethal Interaction of SHOC2 Depletion with MEK Inhibition in RAS-Driven Cancers

The mitogen-activated protein kinase (MAPK) pathway is a critical effector of oncogenic RAS signaling, and MAPK pathway inhibition may be an effective combination treatment strategy. We performed genome-scale loss-of-function CRISPR-Cas9 screens in the presence of a MEK1/2 inhibitor (MEKi) in KRAS-mutant pancreatic and lung cancer cell lines and identified genes that cooperate with MEK inhibition. While we observed heterogeneity in genetic modifiers of MEKi sensitivity across cell lines, several recurrent classes of synthetic lethal vulnerabilities emerged at the pathway level. Multiple members of receptor tyrosine kinase (RTK)-RAS-MAPK pathways scored as sensitizers to MEKi. In particular, we demonstrate that knockout, suppression, or degradation of SHOC2, a positive regulator of MAPK signaling, specifically cooperated with MEK inhibition to impair proliferation in RAS-driven cancer cells. The depletion of SHOC2 disrupted survival pathways triggered by feedback RTK signaling in response to MEK inhibition. Thus, these findings nominate SHOC2 as a potential target for combination therapy.

Acquired Secondary RAS Mutation in BRAFV600E-Mutated Thyroid Cancer Patients Treated with BRAF Inhibitors

Background: The BRAF^V600E mutation is the most common driver mutation in papillary thyroid cancer (PTC) and anaplastic thyroid cancer (ATC). This mutation is considered actionable and, for BRAF^V600E-mutated ATC, a BRAF inhibitor (dabrafenib) in combination with an MEK inhibitor (trametinib) is FDA approved. BRAF inhibitors have also shown efficacy in BRAF^V600E-mutated PTC. However, as with all targeted therapies, resistance to these drugs eventually develops. It is essential that we understand the mechanisms of resistance to the BRAF inhibitors in thyroid cancer to develop future strategies to effectively treat these patients and improve survival. Patients: Herein, we describe four patients with thyroid cancer treated with selective BRAF inhibitors, who developed a RAS mutation in addition to the BRAF^V600E mutation at progression. Results: Patients 1 and 3 acquired a KRAS^G12V mutation in the progressive tumor, patient 2 acquired a NRAS^Q61K mutation in a progressive lymph node, and patient 4 acquired NRAS^G13D mutation on liquid biopsy performed at the time of radiographic disease progression. Conclusion: Similar to the melanoma experience, the emergence of RAS mutations appears to act as a mechanism of resistance to BRAF inhibitors in thyroid cancers.

Inhibitors of BRAF dimers using an allosteric site

BRAF kinase, a critical effector of the ERK signaling pathway, is hyperactivated in many cancers. Oncogenic BRAF^V600E signals as an active monomer in the absence of active RAS, however, in many tumors BRAF dimers mediate ERK signaling. FDA-approved RAF inhibitors poorly inhibit BRAF dimers, which leads to tumor resistance. We found that Ponatinib, an FDA-approved drug, is an effective inhibitor of BRAF monomers and dimers. Ponatinib binds the BRAF dimer and stabilizes a distinct αC-helix conformation through interaction with a previously unrevealed allosteric site. Using these structural insights, we developed PHI1, a BRAF inhibitor that fully uncovers the allosteric site. PHI1 exhibits discrete cellular selectivity for BRAF dimers, with enhanced inhibition of the second protomer when the first protomer is occupied, comprising a novel class of dimer selective inhibitors. This work shows that Ponatinib and BRAF dimer selective inhibitors will be useful in treating BRAF-dependent tumors.

FDA-approved RAF inhibitors poorly inhibit BRAF dimers, which limits their clinical efficacy in tumors expressing BRAFV600E mutant monomers. Here the authors identify FDA-approved Ponatinib as an effective inhibitor of BRAF monomers and dimers and designed PHI1, an inhibitor with a unique mode of action and selectivity for oncogenic BRAF dimers.

Circulating Tumor DNA Genomics Reveal Potential Mechanisms of Resistance to BRAF-Targeted Therapies in Patients with BRAF-Mutant Metastatic Non-Small Cell Lung Cancer

PURPOSE

The limited knowledge on the molecular profile of patients with BRAF-mutant non-small cell lung cancer (NSCLC) who progress under BRAF-targeted therapies (BRAF-TT) has hampered the development of subsequent therapeutic strategies for these patients. Here, we evaluated the clinical utility of circulating tumor DNA (ctDNA)-targeted sequencing to identify canonical BRAF mutations and genomic alterations potentially related to resistance to BRAF-TT, in a large cohort of patients with BRAF-mutant NSCLC.

EXPERIMENTAL DESIGN

This was a prospective study of 78 patients with advanced BRAF-mutant NSCLC, enrolled in 27 centers across France. Blood samples (n = 208) were collected from BRAF-TT-naïve patients (n = 47), patients nonprogressive under treatment (n = 115), or patients at disease progression (PD) to BRAF-TT (24/46 on BRAF monotherapy and 22/46 on BRAF/MEK combination therapy). ctDNA sequencing was performed using InVisionFirst-Lung. In silico structural modeling was used to predict the potential functional effect of the alterations found in ctDNA.

RESULTS

BRAF^V600E ctDNA was detected in 74% of BRAF-TT-naïve patients, where alterations in genes related with the MAPK and PI3K pathways, signal transducers, and protein kinases were identified in 29% of the samples. ctDNA positivity at the first radiographic evaluation under treatment, as well as BRAF-mutant ctDNA positivity at PD were associated with poor survival. Potential drivers of resistance to either BRAF-TT monotherapy or BRAF/MEK combination were identified in 46% of patients and these included activating mutations in effectors of the MAPK and PI3K pathways, as well as alterations in U2AF1, IDH1, and CTNNB1.

CONCLUSIONS

ctDNA sequencing is clinically relevant for the detection of BRAF-activating mutations and the identification of alterations potentially related to resistance to BRAF-TT in BRAF-mutant NSCLC.

Baicalein and Baicalin Promote Melanoma Apoptosis and Senescence via Metabolic Inhibition

Malignant melanoma is one of the most common and dangerous skin cancers with a high rate of death every year. Furthermore, N-RAS and B-RAF mutations in melanoma cells increase the difficulties for clinical treatment in patients. Therefore, development of effective and universal drugs against melanoma is urgently needed. Here we demonstrate that baicalein and baicalin, the active components of the Chinese traditional medicinal plant Scutellaria baicalensis Georgi, can significantly inhibit melanoma cell growth and proliferation, suppress tumor cell colony formation and migration, as well as induce apoptosis and senescence in melanoma cells. The anti-tumor effects mediated by baicalein and baicalin are independent of N-RAS and B-RAF mutation statuses in melanoma cells. Mechanistically, we identify that the suppression of baicalein and baicalin on melanoma cells is due to inhibition of tumor cell glucose uptake and metabolism by affecting the mTOR-HIF-1α signaling pathway. In addition, we demonstrated that baicalein and baicalin can suppress tumorigenesis and tumor growth in vivo in the melanoma model. These studies clearly indicate that baicalein and baicalin can control tumor growth and development metabolically and have great potential as novel and universal drugs for melanoma therapy.

Modulation of Cancer-Associated Fibrotic Stroma by An Integrin αvβ3 Targeting Protein for Pancreatic Cancer Treatment

BACKGROUND & AIMS

Pancreatic ductal adenocarcinoma (PDAC) is resistant to most therapeutics owing to dense fibrotic stroma orchestrated by cancer-associated pancreatic stellate cells (CAPaSC). CAPaSC also support cancer cell growth, metastasis, and resistance to apoptosis. Currently, there is no effective therapy for PDAC that specifically targets CAPaSC. We previously reported a rationally designed protein, ProAgio, that targets integrin αvβ3 at a novel site and induces apoptosis in integrin αvβ3-expressing cells. Because both CAPaSC and angiogenic endothelial cells express high levels of integrin αvβ3, we aimed to analyze the effects of ProAgio in PDAC tumor.

METHODS

Expression of integrin αvβ3 was examined in both patient tissue and cultured cells. The effects of ProAgio on CAPaSC were analyzed using an apoptosis assay kit. The effects of ProAgio in PDAC tumor were studied in 3 murine tumor models: subcutaneous xenograft, genetic engineered (KrasG12D; p53R172H; Pdx1-Cre, GEM-KPC) mice, and an orthotopic KrasG12D; p53R172H; Pdx1-Cre (KPC) model.

RESULTS

ProAgio induces apoptosis in CAPaSC. ProAgio treatment significantly prolonged survival of a genetically engineered mouse-KPC and orthotopic KPC mice alone or in combination with gemcitabine (Gem). ProAgio specifically induced apoptosis in CAPaSC, resorbed collagen, and opened collapsed tumor vessels without an increase in angiogenesis in PDAC tumor, enabling drug delivery into the tumor. ProAgio decreased intratumoral insulin-like growth factor 1 levels as a result of depletion of CAPaSC and consequently decreased cytidine deaminase, a Gem metabolism enzyme in cancer cells, and thereby reduced resistance to Gem-induced apoptosis.

CONCLUSIONS

Our study suggests that ProAgio is an effective PDAC treatment agent because it specifically depletes CAPaSC and eliminates tumor angiogenesis, thereby enhancing drug delivery and Gem efficacy in PDAC tumors.

Insulin Reduces the Efficacy of Vemurafenib and Trametinib in Melanoma Cells

BACKGROUND

Despite the progress made in the clinical management of metastatic melanoma, a patient's response to treatment cannot be fully predicted, and intrinsic or acquired resistance that is developed in most melanoma patients warrants further research efforts. In addition to genetic factors, microenvironmental input should be considered to explain the diversity of response to treatment among melanoma patients. In this study, we evaluated the impact of insulin on patient-derived BRAFV600E melanoma cells, either untreated or treated with vemurafenib or trametinib, inhibitors of BRAFV600 and MEK1/2, respectively.

METHODS

Cells were cultured in serum-free conditions, either with or without insulin. The activity of the MAPK/ERK and PI3K/AKT pathways was assessed by Western blotting, cell viability, and percentages of Ki-67- and NGFR-positive cells by flow cytometry. Transcript levels were analyzed using qRT-PCR, and γ-H2AX levels by immunoblotting and confocal microscopy. A luminescence-based assay was used to measure glutathione content.

RESULTS

While insulin did not influence the MAPK/ERK pathway activity, it had a strong influence on melanoma cells, in which this pathway was suppressed by either vemurafenib or trametinib. In the presence of insulin, both drugs were much less efficient in 1) inhibiting proliferation and reducing the percentage of Ki-67-positive cells, and 2) inducing apoptosis and phosphorylation of histone H2AX in melanoma cells. Changes induced by vemurafenib and trametinib in glutathione homeostasis and DNA repair gene expression were also attenuated by insulin. Moreover, insulin impaired the combined effects of targeted drugs and doxorubicin in melanoma cells. In addition to insulin-induced PI3K/AKT activity, which was either transient or sustainable depending on the cell line, an insulin-triggered increase in the percentage of cells expressing NGFR, a marker of neural crest stem-like cells, may contribute to the reduced drug efficacy.

CONCLUSION

Our results demonstrate the role of insulin in reducing the efficacy of vemurafenib and trametinib. This needs clinical assessment.

The MAP kinase signal transduction pathway: promising therapeutic targets used in the treatment of melanoma

INTRODUCTION

Mitogen-activated protein kinase (MAPK) signal transduction pathway inhibition through the use of agents binding to signal cascade kinases BRAF and MEK has become a key treatment strategy of patients with BRAF-mutant, unresectable melanoma.

AREAS COVERED

Detailed analysis is undertaken of the current data, presenting the efficacy and safety of recently developed therapies targeting BRAF and MEK inhibition in the setting of unresectable melanoma. MAPK signal transduction, translational findings, current phase I, II and III clinical trials, and ongoing studies are explored, including use of MAPK pathway inhibition in the neoadjuvant and adjuvant settings as well as in combination with immunotherapy and other therapies.

EXPERT OPINION

Inhibition of the MAPK pathway significantly improves response, progression-free survival, disease specific survival, and overall survival for patients with BRAF-mutant, unresectable melanoma. The concurrent administration of BRAF and MEK inhibiting agents improves response rate and outcomes and reduces serious adverse effects, including development of new cutaneous malignancies. Triplet therapy with BRAK/MEK combination and immunotherapy has shown in early results to increase duration of response and may be best used sequentially as opposed to concurrently to avoid treatment limiting toxicities. Current clinical trials will further define these therapies and their impact on treatment of melanoma.