Nicotinamide Phosphoribosyltransferase (NAMPT) as a Therapeutic Target in BRAF-Mutated Metastatic Melanoma

Targeting NAD + biosynthesis suppresses TGF-β1/Smads/RAB26 axis and potentiates cisplatin cytotoxicity in non-small cell lung cancer brain metastasis

Nicotinamide adenine dinucleotide (NAD+) plays an important role in tumor progression, but its role in non-small cell lung cancer with brain metastasis (NSCLC BM) remains unclear. Herein, we investigated NAD+ biosynthesis targeting as a new therapeutic strategy for NSCLC BM. Therapeutic activity of nicotinamide phosphoribosyl transferase (NAMPT) inhibitors was evaluated in mouse models of NSCLC BM and using various assays such as NAD+ quantitation, cell viability, and apoptosis assays. To explore impact on downstream signaling, RNA sequencing was used in NAMPT inhibitor-treated and control cells, followed by validation with genetic knockdown, western blot and qRT-PCR. Expression of NAMPT and downstream proteins in human NSCLC BM and its association with patient prognosis were examined. Finally, combination of NAMPT inhibitor and cisplatin was tested in vivo. Systemic treatment with NAMPT inhibitors demonstrated intracranial activity in an NSCLC BM model. NAMPT inhibitors decreased cellular NAD levels and suppressed proliferation and invasion, and induced apoptosis in NSCLC cells. Supplementation with NAD+ precursor NMN rescued these NAMPT inhibitor effects. Mechanistically, disruption of NAMPT-mediated NAD+ biosynthesis suppressed TGF-β1/Smads/RAB26 signaling, leading to inhibition of NSCLC cells. Expression of NAMPT/TGF-β1/Smads/RAB26 axis proteins was upregulated in NSCLC BM tissues and correlated with poor prognosis. Combining NAMPT inhibitors with cisplatin further extended the survival of NSCLC BM-bearing mice. Targeting NAD+ biosynthesis provides a new therapeutic strategy for NSCLC BM and can be effectively combined with cisplatin. Our studies identified the TGF-β1/Smads/RAB26 signaling downstream of NAMPT, which was targeted by NAMPT inhibition to mediate anti-cancer effects.

Differential Mitochondrial Redox Responses to the Inhibition of NAD+ Salvage Pathway of Triple Negative Breast Cancer Cells

Background/Objectives: Cancer cells rely on metabolic reprogramming that is supported by altered mitochondrial redox status and an increased demand for NAD+. Over expression of Nampt, the rate-limiting enzyme of the NAD+ biosynthesis salvage pathway, is common in breast cancer cells, and more so in triple negative breast cancer (TNBC) cells. Targeting the salvage pathway has been pursued for cancer therapy. However, TNBC cells have heterogeneous responses to Nampt inhibition, which contributes to the diverse outcomes. There is a lack of imaging biomarkers to differentiate among TNBC cells under metabolic stress and identify which are responsive. We aimed to characterize and differentiate among a panel of TNBC cell lines under NAD-deficient stress and identify which subtypes are more dependent on the NAD salvage pathway. Methods: Optical redox imaging (ORI), a label-free live cell imaging microscopy technique was utilized to acquire intrinsic fluorescence intensities of NADH and FAD-containing flavoproteins (Fp) thus the mitochondrial redox ratio Fp/(NADH + Fp) in a panel of TNBC cell lines. Various fluorescence probes were then added to the cultures to image the mitochondrial ROS, mitochondrial membrane potential, mitochondrial mass, and cell number. Results: Various TNBC subtypes are sensitive to Nampt inhibition in a dose- and time-dependent manner, they have differential mitochondrial redox responses; furthermore, the mitochondrial redox indices linearly correlated with mitochondrial ROS induced by various doses of a Nampt inhibitor. Moreover, the changes in the redox indices correlated with growth inhibition. Additionally, the redox state was found fully recovered after removing the Nampt inhibitor. Conclusions: This study supports the utility of ORI in rapid metabolic phenotyping of TNBC cells under NAD-deficient stress to identify responsive cells and biomarkers of treatment response, facilitating combination therapy strategies.

Role of mitochondria and potential of mitochondria-targeted therapy in BRAF mutant cancer: A review

The classical mitogen-activated protein kinase (MAPK) signaling pathway, the Ras/Raf/MEK (mitogen-activated protein kinase/ERK kinase)/ERK protein kinase cascade, is a conserved cascade that regulates cell growth, differentiation, and proliferation. The significance of BRAF in cancer was established with the discovery of cancer-activating mutations in BRAF in several human tumors in 2002. Currently, BRAF is recognized as a driver mutation that affects cancer phenotypes in different ways, making it an important therapeutic target for cancer. BRAF-selective inhibitors have shown promise in clinical trials involving patients with metastatic melanoma. However, resistance mechanisms to BRAF inhibitors therapy have resulted in short-lived therapeutic responses. Further in-depth research is imperative to explore resistance mechanisms that oppose the effectiveness of BRAF inhibitors. Metabolic reprogramming has emerging role in BRAF-mutant cancers. In particular, mitochondrial metabolism and its closely related signaling pathways mediated by mitochondria have become recognized as potential new targets for treating BRAF-mutant cancers. This review, examines the progress in understanding BRAF mutations in cancer, the clinicopathological correlation of BRAF inhibitors, and recent advances in mitochondrial metabolism, mitochondrial dynamics and mitochondrial mediated death in BRAF-mutant cancer. This review will inform future cancer research and lay the foundation for novel treatment combinations of BRAF-mutant cancers.

Inhibition of nicotinamide phosphoribosyltransferase (NAMPT) in cancer: a patent review

INTRODUCTION

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the biosynthesis of nicotinamide adenine dinucleotide (NAD) from nicotinamide. In addition to its role as essential redox cofactor, NAD also functions as a substrate for NAD-consuming enzymes, regulating multiple cellular processes such as DNA repair and gene expression, fundamental to sustain energetic needs for tumor growth. In this sense, NAMPT over-expression represents a common strategy that several tumor types adopt to sustain NAD production. In addition to its enzymatic role, NAMPT behaves as cytokine-like protein with pro-inflammatory function. Increasing evidence demonstrated that NAMPT inhibition represents a promising anti-cancer strategy to deplete NAD and impair cellular metabolism in cancer conditions.

AREAS COVERED

By using Espacenet, we collected the patents which identified new molecules, compounds, formulations and methods able to inhibit NAMPT from 2007 to date.

EXPERT OPINION

Most of the collected patents focused the attention on the ability of different compounds to inhibit the enzymatic activity of NAMPT, lacking other important aspects related to the extracellular role of NAMPT and the ability of alternative enzymes to counteract NAMPT-mediated NAD depletion. It is necessary to consider also these aspects to promote novel strategies and create novel inhibitors and molecules useful as anti-cancer compounds.

RICTOR/mTORC2 downregulation in BRAFV600E melanoma cells promotes resistance to BRAF/MEK inhibition

BACKGROUND

The main drawback of BRAF/MEK inhibitors (BRAF/MEKi)-based targeted therapy in the management of BRAF-mutated cutaneous metastatic melanoma (MM) is the development of therapeutic resistance. We aimed to assess in this context the role of mTORC2, a signaling complex defined by the presence of the essential RICTOR subunit, regarded as an oncogenic driver in several tumor types, including MM.

METHODS

After analyzing The Cancer Genome Atlas MM patients' database to explore both overall survival and molecular signatures as a function of intra-tumor RICTOR levels, we investigated the effects of RICTOR downregulation in BRAFV600E MM cell lines on their response to BRAF/MEKi. We performed proteomic screening to identify proteins modulated by changes in RICTOR expression, and Seahorse analysis to evaluate the effects of RICTOR depletion on mitochondrial respiration. The combination of BRAFi with drugs targeting proteins and processes emerged in the proteomic screening was carried out on RICTOR-deficient cells in vitro and in a xenograft setting in vivo.

RESULTS

Low RICTOR levels in BRAF-mutated MM correlate with a worse clinical outcome. Gene Set Enrichment Analysis of low-RICTOR tumors display gene signatures suggestive of activation of the mitochondrial Electron Transport Chain (ETC) energy production. RICTOR-deficient BRAFV600E cells are intrinsically tolerant to BRAF/MEKi and anticipate the onset of resistance to BRAFi upon prolonged drug exposure. Moreover, in drug-naïve cells we observed a decline in RICTOR expression shortly after BRAFi exposure. In RICTOR-depleted cells, both mitochondrial respiration and expression of nicotinamide phosphoribosyltransferase (NAMPT) are enhanced, and their pharmacological inhibition restores sensitivity to BRAFi.

CONCLUSIONS

Our work unveils an unforeseen tumor-suppressing role for mTORC2 in the early adaptation phase of BRAFV600E melanoma cells to targeted therapy and identifies the NAMPT-ETC axis as a potential therapeutic vulnerability of low RICTOR tumors. Importantly, our findings indicate that the evaluation of intra-tumor RICTOR levels has a prognostic value in metastatic melanoma and may help to guide therapeutic strategies in a personalized manner.

Targeting NAD+ metabolism: dual roles in cancer treatment

Nicotinamide adenine dinucleotide (NAD+) is indispensable for various oxidation-reduction reactions in mammalian cells, particularly during energy production. Malignant cells increase the expression levels of NAD+ biosynthesis enzymes for rapid proliferation and biomass production. Furthermore, mounting proof has indicated that NAD-degrading enzymes (NADases) play a role in creating the immunosuppressive tumor microenvironment (TME). Interestingly, both inhibiting NAD+ synthesis and targeting NADase have positive implications for cancer treatment. Here we summarize the detrimental outcomes of increased NAD+ production, the functions of NAD+ metabolic enzymes in creating an immunosuppressive TME, and discuss the progress and clinical translational potential of inhibitors for NAD+ synthesis and therapies targeting NADase.

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.

Review of various NAMPT inhibitors for the treatment of cancer

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in the NAD salvage pathway of mammalian cells and is overexpressed in numerous types of cancers. These include breast cancer, ovarian cancer, prostate cancer, gastric cancer, colorectal cancer, glioma, and b-cell lymphoma. NAMPT is also known to impact the NAD and NADPH pool. Research has demonstrated that NAMPT can be inhibited. NAMPT inhibitors are diverse anticancer medicines with significant anti-tumor efficacy in ex vivo tumor models. A few notable NAMPT specific inhibitors which have been produced include FK866, CHS828, and OT-82. Despite encouraging preclinical evidence of the potential utility of NAMPT inhibitors in cancer models, early clinical trials have yielded only modest results, necessitating the adaptation of additional tactics to boost efficacy. This paper examines a number of cancer treatment methods which target NAMPT, including the usage of individual inhibitors, pharmacological combinations, dual inhibitors, and ADCs, all of which have demonstrated promising experimental or clinical results. We intend to contribute further ideas regarding the usage and development of NAMPT inhibitors in clinical therapy to advance the field of research on this intriguing target.

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

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

Updated Functional Roles of NAMPT in Carcinogenesis and Therapeutic Niches

Simple Summary

The advantages and applications of using the non-invasive way to detect serum biomarkers for assessing cancer diagnosis and prognosis have been explored. Nicotinamide phosphoribosyltransferase (NAMPT), also designated as pre-B-cell colony-enhancing factor (PBEF) or visfatin, is a secreted adipokine known to modulate tumor malignancies. Its significance in predicting cancer patient’s survival outcome further renders the implementation of NAMPT in clinical practice. In this review, recent discoveries of NAMPT in cancer studies were focused and integrated. We aim to provide updates for researchers who are proposing relevant objectives.

Abstract

Nicotinamide phosphoribosyltransferase (NAMPT) is notable for its regulatory roles in tumor development and progression. Emerging evidence regarding NAMPT somatic mutations in cancer patients, NAMPT expressional signatures in normal tissues and cancers, and the prognostic significance of NAMPT in many cancer types has attracted attention, and NAMPT is considered a potential biomarker of cancer. Recent discoveries have demonstrated the indirect association and direct biological functions of NAMPT in modulating cancer metastasis, proliferation, angiogenesis, cancer stemness, and chemoresistance to anticancer drugs. These findings warrant further investigation of the underlying mechanisms to provide knowledge for developing novel cancer therapeutics. In this review article, we explore recent research developments involving the oncogenic activities of NAMPT by summarizing current knowledge regarding NAMPT somatic mutations, clinical trials, transcriptome data, and clinical information and discoveries related to the NAMPT-induced signaling pathway in modulating hallmarks of cancer. Furthermore, the comprehensive representation of NAMPT RNA expression in a pancancer panel as well as in specific normal cell types at single-cell level are demonstrated. The results suggest potential sites and cell types that could facilitate NAMPT-related tumorigenesis. With this review, we aim to shed light on the regulatory roles of NAMPT in tumor development and progression, and provide information to guide future research directions in this field.

NAMPT: A critical driver and therapeutic target for cancer

Nicotinamide phosphoribosyltransferase (NAMPT) possesses a vital role in mammalian cells due to its activity as a rate-limiting enzyme in the biosynthesis of nicotinamide adenine dinucleotide (NAD) from nicotinamide. NAD is an essential redox cofactor, but it also functions as a substrate for NAD-consuming enzymes, regulating multiple cellular processes such as DNA repair and gene expression, fundamental to sustain tumor growth and survival and energetic needs. A common strategy that several tumor types adopt to sustain NAD synthesis is to over-express NAMPT. However, beside its intracellular functions, this enzyme has a second life outside of cells exerting cytokine-like functions and mediating pro-inflammatory conditions activating signaling pathways. While the effects of NAMPT/NAD axis on energetic metabolism in tumors has been well-established, increasing evidence demonstrated the impact of NAMPT over-expression (intra-/extra-cellular) on several tumor cellular processes, including DNA repair, gene expression, signaling pathways, proliferation, invasion, stemness, phenotype plasticity, metastatization, angiogenesis, immune regulation, and drug resistance. For all these reasons, NAMPT targeting has emerged as promising anti-cancer strategy to deplete NAD and impair cellular metabolism, but also to counteract the other NAMPT-related functions. In this review, we summarize the key role of NAMPT in multiple biological processes implicated in cancer biology and the impact of NAMPT inhibition as therapeutic strategy for cancer treatment.

Tumors carrying BRAF-mutations over-express NAMPT that is genetically amplified and possesses oncogenic properties

Background

Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in nicotinamide adenine dinucleotide (NAD) biosynthesis, is up-regulated in several cancers, including metastatic melanoma (MM). The BRAF oncogene is mutated in different cancer types, among which MM and thyroid carcinoma (THCA) are prominent. Drugs targeting mutant BRAF are effective, especially in MM patients, even though resistance rapidly develops. Previous data have linked NAMPT over-expression to the acquisition of BRAF resistance, paving the way for therapeutic strategies targeting the two pathways.

Methods

Exploiting the TCGA database and a collection of MM and THCA tissue microarrays we studied the association between BRAF mutations and NAMPT expression. BRAF wild-type (wt) cell lines were genetically engineered to over-express the BRAF V600E construct to demonstrate a direct relationship between over-activation of the BRAF pathway and NAMPT expression. Responses of different cell line models to NAMPT (i)nhibitors were studied using dose–response proliferation assays. Analysis of NAMPT copy number variation was performed in the TCGA dataset. Lastly, growth and colony forming assays were used to study the tumorigenic functions of NAMPT itself.

Results

The first finding of this work is that tumor samples carrying BRAF-mutations over-express NAMPT, as demonstrated by analyzing the TCGA dataset, and MM and THC tissue microarrays. Importantly, BRAF wt MM and THCA cell lines modified to over-express the BRAF V600E construct up-regulated NAMPT, confirming a transcriptional regulation of NAMPT following BRAF oncogenic signaling activation. Treatment of BRAF-mutated cell lines with two different NAMPTi was followed by significant reduction of tumor growth, indicating NAMPT addiction in these cells. Lastly, we found that several tumors over-expressing the enzyme, display NAMPT gene amplification. Over-expression of NAMPT in BRAF wt MM cell line and in fibroblasts resulted in increased growth capacity, arguing in favor of oncogenic properties of NAMPT.

Conclusions

Overall, the association between BRAF mutations and NAMPT expression identifies a subset of tumors more sensitive to NAMPT inhibition opening the way for novel combination therapies including NAMPTi with BRAFi/MEKi, to postpone and/or overcome drug resistance. Lastly, the over-expression of NAMPT in several tumors could be a key and broad event in tumorigenesis, substantiated by the finding of NAMPT gene amplification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03315-9.

The Extracellular NADome Modulates Immune Responses

The term NADome refers to the intricate network of intracellular and extracellular enzymes that regulate the synthesis or degradation of nicotinamide adenine dinucleotide (NAD) and to the receptors that engage it. Traditionally, NAD was linked to intracellular energy production through shuffling electrons between oxidized and reduced forms. However, recent data indicate that NAD, along with its biosynthetic and degrading enzymes, has a life outside of cells, possibly linked to immuno-modulating non-enzymatic activities. Extracellular NAD can engage puriginergic receptors triggering an inflammatory response, similar - to a certain extent - to what described for adenosine triphosphate (ATP). Likewise, NAD biosynthetic and degrading enzymes have been amply reported in the extracellular space, where they possess both enzymatic and non-enzymatic functions. Modulation of these enzymes has been described in several acute and chronic conditions, including obesity, cancer, inflammatory bowel diseases and sepsis. In this review, the role of the extracellular NADome will be discussed, focusing on its proposed role in immunomodulation, together with the different strategies for its targeting and their potential therapeutic impact.

Inhibition of nicotinamide phosphoribosyltransferase, the rate-limiting enzyme of the nicotinamide adenine dinucleotide salvage pathway, to target glioma heterogeneity through mitochondrial oxidative stress

BACKGROUND

Tumor-specific metabolic processes essential for cell survival are promising targets to potentially circumvent intratumoral heterogeneity, a major resistance factor in gliomas. Tumor cells preferentially using nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the salvage pathway for synthesis of NAD, a critical cofactor for diverse biological processes including cellular redox reactions, energy metabolism and biosynthesis. NAMPT is overexpressed in most malignancies, including gliomas, and can serve as a tumor-specific target.

METHODS

Effects of pharmacological inhibition of NAMPT on cellular oxygen consumption rate, extracellular acidification, mitochondrial respiration, cell proliferation, invasion and survival were assessed through in vitro and ex vivo studies on genetically heterogeneous glioma cell lines, glioma stem-like cells (GSCs) and mouse and human ex vivo organotypic glioma slice culture models.

RESULTS

Pharmacological inhibition of the NAD salvage biosynthesis pathway using a highly specific inhibitor, KPT-9274, resulted in reduction of NAD levels and related downstream metabolites, inhibited proliferation, and induced apoptosis in vitro in cell lines and ex vivo in human glioma tissue. These effects were mediated by mitochondrial dysfunction, DNA damage and increased oxidative stress leading to apoptosis in GSCs independent of genotype, IDH status or MGMT promoter methylation status. Conversely, NAMPT inhibition had minimal in vitro effects on normal human astrocytes (NHA) and no apparent in vivo toxicity in non-tumor-bearing mice.

CONCLUSIONS

Pharmacological NAMPT inhibition by KPT9274 potently targeted genetically heterogeneous gliomas by activating mitochondrial dysfunction. Our preclinical results provide a rationale for targeting the NAMPT-dependent alternative NAD biosynthesis pathway as a novel clinical strategy against gliomas.

The heme synthesis-export system regulates the tricarboxylic acid cycle flux and oxidative phosphorylation

Heme is an iron-containing porphyrin of vital importance for cell energetic metabolism. High rates of heme synthesis are commonly observed in proliferating cells. Moreover, the cell-surface heme exporter feline leukemia virus subgroup C receptor 1a (FLVCR1a) is overexpressed in several tumor types. However, the reasons why heme synthesis and export are enhanced in highly proliferating cells remain unknown. Here, we illustrate a functional axis between heme synthesis and heme export: heme efflux through the plasma membrane sustains heme synthesis, and implementation of the two processes down-modulates the tricarboxylic acid (TCA) cycle flux and oxidative phosphorylation. Conversely, inhibition of heme export reduces heme synthesis and promotes the TCA cycle fueling and flux as well as oxidative phosphorylation. These data indicate that the heme synthesis-export system modulates the TCA cycle and oxidative metabolism and provide a mechanistic basis for the observation that both processes are enhanced in cells with high-energy demand.

Metabolic Interplay between the Immune System and Melanoma Cells: Therapeutic Implications

Malignant melanoma represents the most fatal skin cancer due to its aggressive biological behavior and high metastatic potential. Treatment strategies for advanced disease have dramatically changed over the last years due to the introduction of BRAF/MEK inhibitors and immunotherapy. However, many patients either display primary (i.e., innate) or eventually develop secondary (i.e., acquired) resistance to systemic treatments. Treatment resistance depends on multiple mechanisms driven by a set of rewiring processes, which involve cancer metabolism, epigenetic, gene expression, and interactions within the tumor microenvironment. Prognostic and predictive biomarkers are needed to guide patients’ selection and treatment decisions. Indeed, there are no recognized clinical or biological characteristics that identify which patients will benefit more from available treatments, but several biomarkers have been studied with promising preliminary results. In this review, we will summarize novel tumor metabolic pathways and tumor-host metabolic crosstalk mechanisms leading to melanoma progression and drug resistance, with an overview on their translational potential as novel therapeutic targets.

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.

Melanoma Progression under Obesity: Focus on Adipokines

Simple Summary

Obesity is a rapidly growing public health problem and the reason for numerous diseases in the human body, including cancer. This article reviews the current knowledge of the effect of molecules secreted by adipose tissue-adipokines on melanoma progression. We also discuss the role of these factors as markers of incidence, metastasis, and melanoma patient survival. Understanding the functions of adipokines will lead to knowledge of whether and how obesity promotes melanoma growth.

Abstract

Obesity is a growing problem in the world and is one of the risk factors of various cancers. Among these cancers is melanoma, which accounts for the majority of skin tumor deaths. Current studies are looking for a correlation between obesity and melanoma. They suspect that a potential cause of its development is connected to the biology of adipokines, active molecules secreted by adipose tissue. Under physiological conditions, adipokines control many processes, including lipid and glucose homeostasis, insulin sensitivity, angiogenesis, and inflammations. However, when there is an increased amount of fat in the body, their secretion is dysregulated. This article reviews the current knowledge of the effect of adipokines on melanoma growth. This work focuses on the molecular pathways by which adipose tissue secreted molecules modify the angiogenesis, migration, invasion, proliferation, and death of melanoma cells. We also discuss the role of these factors as markers of incidence, metastasis, and melanoma patient survival. Understanding the functions of adipokines will lead to knowledge of whether and how obesity promotes melanoma growth. Further studies may contribute to the innovations of therapies and the use of adipokines as predictive and/or prognostic biomarkers.

Melanoma models for the next generation of therapies

There is a lack of appropriate melanoma models that can be used to evaluate the efficacy of novel therapeutic modalities. Here, we discuss the current state of the art of melanoma models including genetically engineered mouse, patient-derived xenograft, zebrafish, and ex vivo and in vitro models. We also identify five major challenges that can be addressed using such models, including metastasis and tumor dormancy, drug resistance, the melanoma immune response, and the impact of aging and environmental exposures on melanoma progression and drug resistance. Additionally, we discuss the opportunity for building models for rare subtypes of melanomas, which represent an unmet critical need. Finally, we identify key recommendations for melanoma models that may improve accuracy of preclinical testing and predict efficacy in clinical trials, to help usher in the next generation of melanoma therapies.

Visfatin facilitates gastric cancer malignancy by targeting snai1 via the NF-κB signaling

BACKGROUND

Visfatin acts as an oncogenic factor in numerous tumors through a variety of cellular processes. Visfatin has been revealed to promote cell migration and invasion in gastric cancer (GC). Snai1 is a well-known regulator of EMT process in cancers. However, the relationship between visfatin and snai1 in GC remains unclear. The current study aimed to explore the role of visfatin in GC.

METHODS

The RT-qPCR and western blot analysis were used to measure RNA and protein levels, respectively. The cell migration and invasion were tested by Trans-well assays and western blot analysis.

RESULTS

Visfatin showed upregulation in GC cells. Additionally, Visfatin with increasing concentration facilitated epithelial-mesenchymal transition (EMT) process by increasing E-cadherin and reducing N-cadherin and Vimentin protein levels in GC cells. Moreover, endogenous overexpression and knockdown of visfatin promoted and inhibited migratory and invasive abilities of GC cells, respectively. Then, we found that snai1 protein level was positively regulated by visfatin in GC cells. In addition, visfatin activated the NF-κB signaling to modulate snai1 protein expression. Furthermore, the silencing of snai1 counteracted the promotive impact of visfatin on cell migration, invasion and EMT process in GC.

CONCLUSION

Visfatin facilitates cell migration, invasion and EMT process by targeting snai1 via the NF-κB signaling, which provides a potential insight for the treatment of GC.

Oral nicotinamide: The role in skin cancer chemoprevention

The incidence of skin cancer has gradually increased in the last years and exposition to ultraviolet radiation remains the main risk factor. We performed a comprehensive review on the role of nicotinamide (NAM) in the chemoprevention of skin cancers. NAM, a water-soluble form of vitamin B3, interferes with skin carcinogenesis as it regulates immunosuppressor genes such as p53 and sirtuins and restores intracellular level of NAD+, a co-enzyme essential for energy production. Efficacy and safety of NAM was evaluated in a Phase III double-blinded control-placebo study (ONTRAC), thus demonstrating that the incidence of actinic keratoses and non-melanoma skin cancers was lower in the nicotinamide group than in placebo group. Further studies showed the efficacy of NAM also in transplanted patients and among inhabitants living in arsenic contamination areas. Despite the quick response to NAM supplementation, its intake need to be carried on chronically as the efficacy seems to vanish rapidly.

NAD+ Metabolism Maintains Inducible PD-L1 Expression to Drive Tumor Immune Evasion

NAD⁺ metabolism is implicated in aging and cancer. However, its role in immune checkpoint regulation and immune evasion remains unclear. Here, we find nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD⁺ biogenesis, drives interferon γ (IFNγ)-induced PD-L1 expression in multiple types of tumors and governs tumor immune evasion in a CD8⁺ T cell-dependent manner. Mechanistically, NAD⁺ metabolism maintains activity and expression of methylcytosine dioxygenase Tet1 via α-ketoglutarate (α-KG). IFNγ-activated Stat1 facilitates Tet1 binding to Irf1 to regulate Irf1 demethylation, leading to downstream PD-L1 expression on tumors. Importantly, high NAMPT-expressing tumors are more sensitive to anti-PD-L1 treatment and NAD⁺ augmentation enhances the efficacy of anti-PD-L1 antibody in immunotherapy-resistant tumors. Collectively, these data delineate an NAD⁺ metabolism-dependent epigenetic mechanism contributing to tumor immune evasion, and NAD⁺ replenishment combined with PD-(L)1 antibody provides a promising therapeutic strategy for immunotherapy-resistant tumors.

NAMPT Over-Expression Recapitulates the BRAF Inhibitor Resistant Phenotype Plasticity in Melanoma

Simple Summary

Malignant melanoma (MM) is the most fatal skin cancer due to its high metastatic potential. Treatment strategies are dramatically changing due to the introduction of BRAF/MEK inhibitors (i) and immunotherapy; however, multiple resistant mechanisms rapidly occur including metabolic rewiring. This study aimed to establish the driver role of the nicotinamide adenine dinucleotide (NAD)-biosynthetic enzyme nicotinamide phosphoribosyltransferase (NAMPT) in BRAFi resistance development. We defined that NAMPT over-expressing MM cells were strikingly similar to cells that acquired resistance to BRAFi in terms of growth, invasion, and phenotype plasticity. These findings confirmed NAMPT as a key factor in melanoma progression and in the onset of BRAFi resistance in melanoma patients, opening new therapeutic possibilities for this subset of patients.

Abstract

Serine–threonine protein kinase B-RAF (BRAF)-mutated metastatic melanoma (MM) is a highly aggressive type of skin cancer. Treatment of MM patients using BRAF/MEK inhibitors (BRAFi/MEKi) eventually leads to drug resistance, limiting any clinical benefit. Herein, we demonstrated that the nicotinamide adenine dinucleotide (NAD)-biosynthetic enzyme nicotinamide phosphoribosyltransferase (NAMPT) is a driving factor in BRAFi resistance development. Using stable and inducible NAMPT over-expression systems, we showed that forced NAMPT expression in MM BRAF-mutated cell lines led to increased energy production, MAPK activation, colony-formation capacity, and enhance tumorigenicity in vivo. Moreover, NAMPT over-expressing cells switched toward an invasive/mesenchymal phenotype, up-regulating expression of ZEB1 and TWIST, two transcription factors driving the epithelial to mesenchymal transition (EMT) process. Consistently, within the NAMPT-overexpressing cell line variants, we observed an increased percentage of a rare, drug-effluxing stem cell-like side population (SP) of cells, paralleled by up-regulation of ABCC1/MRP1 expression and CD133-positive cells. The direct correlation between NAMPT expression and gene set enrichments involving metastasis, invasiveness and mesenchymal/stemness properties were verified also in melanoma patients by analyzing The Cancer Genome Atlas (TCGA) datasets. On the other hand, CRISPR/Cas9 full knock-out NAMPT BRAFi-resistant MM cells are not viable, while inducible partial silencing drastically reduces tumor growth and aggressiveness. Overall, this work revealed that NAMPT over-expression is both necessary and sufficient to recapitulate the BRAFi-resistant phenotype plasticity.

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.

Risk stratification of cutaneous melanoma reveals carcinogen metabolism enrichment and immune inhibition in high-risk patients

Cutaneous melanoma (CM) is the most lethal form of skin cancer. Risk assessment should facilitate stratified surveillance and guide treatment selection. Here, based on the mRNA-seq data from 419 CM patients in the Cancer Genome Atlas (TCGA), we developed a prognostic 21-gene signature to distinguish the outcomes of high- and low-risk patients, which was further validated in two external cohorts. The signature achieved a higher C-index as compared with other known biomarkers and clinical characteristics in both the TCGA and validation cohorts. Notably, in high-risk patients the expression levels of three driver genes, BRAF, NRAS, and NF1 in the MAPK pathway, were lower but exhibited a stronger positive correlation as compared with low-risk patients. Moreover, the genes involved in nicotinamide adenine dinucleotide metabolism were negatively correlated with the expression of BRAF in the high-risk group. Function analysis revealed that the upregulated genes in the high-risk group were enriched in the cytochrome P450-mediated metabolism of chemical carcinogens. Furthermore, the low-risk group had high levels of gamma delta T cells infiltration, while regulatory T cells were accumulated in the high-risk group. The present study offers a promising new prognostic signature for CM, and provides insight into the mechanisms of melanoma progression.

Metabolic Plasticity of Melanoma Cells and Their Crosstalk With Tumor Microenvironment

Cutaneous melanoma (CM) is a highly aggressive and drug resistant solid tumor, showing an impressive metabolic plasticity modulated by oncogenic activation. In particular, melanoma cells can generate adenosine triphosphate (ATP) during cancer progression by both cytosolic and mitochondrial compartments, although CM energetic request mostly relies on glycolysis. The upregulation of glycolysis is associated with constitutive activation of BRAF/MAPK signaling sustained by BRAFV600E kinase mutant. In this scenario, the growth and progression of CM are strongly affected by melanoma metabolic changes and interplay with tumor microenvironment (TME) that sustain tumor development and immune escape. Furthermore, CM metabolic plasticity can induce a metabolic adaptive response to BRAF/MEK inhibitors (BRAFi/MEKi), associated with the shift from glycolysis toward oxidative phosphorylation (OXPHOS). Therefore, in this review article we survey the metabolic alterations and plasticity of CM, its crosstalk with TME that regulates melanoma progression, drug resistance and immunosurveillance. Finally, we describe hallmarks of melanoma therapeutic strategies targeting the shift from glycolysis toward OXPHOS.

Targeting complex, adaptive responses in melanoma therapy

Our understanding of the complex, adaptive mechanisms of response to targeted therapies in metastatic melanoma is now leading to more effective combination treatments. These include the simultaneous inhibition of signalling pathways and metabolic programmes, as well as epigenetic mechanisms or immunological checkpoints. We review the latest pre-clinical and clinical results of strategies to delay tumor progression through combination approaches, and also highlight some of the problems ahead, including patient stratification, the complexity of targeting adaptive responses, and the management of more severe toxicities that result from double and triple-drug treatments.

Targeting the NAD+ salvage pathway suppresses APC mutation-driven colorectal cancer growth and Wnt/β-catenin signaling via increasing Axin level

Background

The role and mechanism of the nicotinamide adenine dinucleotide (NAD⁺) salvage pathway in cancer cell proliferation is poorly understood. Nicotinamide phosphoribosyltransferase (NAMPT), which converts nicotinamide into NAD⁺, is the rate-limiting enzyme in the NAD⁺ salvage pathway. Here, we assessed the role of NAMPT in the proliferation of colorectal cancer.

Methods

Real-time PCR, immunohistochemistry, western blotting, and analyses of datasets from Oncomine and Gene Expression Omnibus were conducted to assess the expression of NAMPT at the mRNA and protein levels in colorectal cancer. The Kaplan Meier plotter online tool was used to evaluate the prognostic role of NAMPT. Knockdown of NAMPT was performed to assess the role of NAMPT in colorectal cancer cell proliferation and tumorigenesis both in vitro and in vivo. Overexpression of NAMPT was used to evaluate impact of NAMPT on colorectal cancer cell proliferation in vitro. NAD⁺ quantitation, immunofluorescence, dual luciferase assay and western blot were used to explore the mechanism of colorectal cancer proliferation. Transwell migration and invasion assays were conducted to assess the role of NAMPT in cell migration and invasion abilities of colorectal cancer cells.

Results

Our study indicated that the inhibition of NAMPT decreased proliferation capacity of colorectal cancer cells both in vitro and in vivo. Conversely, overexpression of NAMPT could promote cell proliferation in vitro. NAMPT inhibition induced β-catenin degradation by increasing Axin expression levels; this resulted in the inhibition of Wnt/β-catenin signaling and cell proliferation in colorectal cancer. The addition of nicotinamide mononucleotide, the enzymatic product of NAMPT, effectively reversed β-catenin protein degradation and inhibited growth. Similarly, the knockdown of Axin also decreased the cell death induced by the inhibition of NAMPT. In addition, we showed that colorectal cancer tissues harbored significantly higher levels of NAMPT than the levels harbored by paired normal tissues, especially in colorectal cancer stages I and II. And the overexpression of NAMPT was associated with unfavorable survival results.

Conclusions

Our findings reveal that NAMPT plays an important role in colorectal cancer proliferation via Wnt/β-catenin pathway, which could have vital implications for the diagnosis, prognosis and treatment of colorectal cancer.

Beyond Energy Metabolism: Exploiting the Additional Roles of NAMPT for Cancer Therapy

Tumor cells have increased requirements for NAD⁺. Thus, many cancers exhibit an increased reliance on NAD⁺ production pathways. This dependence may be exploited therapeutically through pharmacological targeting of NAMPT, the rate-limiting enzyme in the NAD⁺ salvage pathway. Despite promising preclinical data using NAMPT inhibitors in cancer models, early NAMPT inhibitors showed limited efficacy in several early phase clinical trials, necessitating the identification of strategies, such as drug combinations, to enhance their efficacy. While the effect of NAMPT inhibitors on impairment of energy metabolism in cancer cells has been well-described, more recent insights have uncovered a number of additional targetable cellular processes that are impacted by inhibition of NAMPT. These include sirtuin function, DNA repair machinery, redox homeostasis, molecular signaling, cellular stemness, and immune processes. This review highlights the recent findings describing the effects of NAMPT inhibitors on the non-metabolic functions of malignant cells, with a focus on how this information can be leveraged clinically. Combining NAMPT inhibitors with other therapies that target NAD⁺-dependent processes or selecting tumors with specific vulnerabilities that can be co-targeted with NAMPT inhibitors may represent opportunities to exploit the multiple functions of this enzyme for greater therapeutic benefit.

Quinolinate Phosphoribosyltransferase Promotes Invasiveness of Breast Cancer Through Myosin Light Chain Phosphorylation

Perturbed Nicotinamide adenine dinucleotide (NAD⁺) homeostasis is involved in cancer progression and metastasis. Quinolinate phosphoribosyltransferase (QPRT) is the rate-limiting enzyme in the kynurenine pathway participating in NAD⁺ generation. In this study, we demonstrated that QPRT expression was upregulated in invasive breast cancer and spontaneous mammary tumors from MMTV-PyVT transgenic mice. Knockdown of QPRT expression inhibited breast cancer cell migration and invasion. Consistently, ectopic expression of QPRT promoted cell migration and invasion in breast cancer cells. Treatment with QPRT inhibitor (phthalic acid) or P2Y₁₁ antagonist (NF340) could reverse the QPRT-induced invasiveness and phosphorylation of myosin light chain. Similar reversibility could be observed following treatment with Rho inhibitor (Y16), ROCK inhibitor (Y27632), PLC inhibitor (U73122), or MLCK inhibitor (ML7). Altogether, these results indicate that QPRT enhanced breast cancer invasiveness probably through purinergic signaling and might be a potential prognostic indicator and therapeutic target in breast cancer.

Immune System Evasion as Hallmark of Melanoma Progression: The Role of Dendritic Cells

Melanoma is an immunogenic tumor whose relationship with immune cells resident in the microenvironment significantly influences cancer cell proliferation, progression, and metastasis. During melanomagenesis, both immune and melanoma cells undergo the immunoediting process that includes interconnected phases as elimination, equilibrium, and escape or immune evasion. In this context, dendritic cells (DCs) are active players that indirectly counteract the proliferation of melanoma cells. Moreover, DC maturation, migration, and cross-priming as well as their functional interplay with cytotoxic T-cells through ligands of immune checkpoint receptors result impaired. A number of signals propagated by highly proliferating melanoma cells and accessory cells as T-cells, natural killer cells (NKs), tumor-associated macrophages (TAMs), T-regulatory cells (T-regs), myeloid-derived suppressor cells (MDSCs), and endothelial cells participate to create an immunosuppressive milieu that results engulfed of tolerogenic factors and interleukins (IL) as IL-6 and IL-10. To underline the role of the immune infiltrate in blocking the melanoma progression, it has been described that the composition, density, and distribution of cytotoxic T-cells in the surrounding stroma is predictive of responsiveness to immunotherapy. Here, we review the major mechanisms implicated in melanoma progression, focusing on the role of DCs.

Extracellular nicotinate phosphoribosyltransferase binds Toll like receptor 4 and mediates inflammation

Damage-associated molecular patterns (DAMPs) are molecules that can be actively or passively released by injured tissues and that activate the immune system. Here we show that nicotinate phosphoribosyltransferase (NAPRT), detected by antibody-mediated assays and mass spectrometry, is an extracellular ligand for Toll-like receptor 4 (TLR4) and a critical mediator of inflammation, acting as a DAMP. Exposure of human and mouse macrophages to NAPRT activates the inflammasome and NF-κB for secretion of inflammatory cytokines. Furthermore, NAPRT enhances monocyte differentiation into macrophages by inducing macrophage colony-stimulating factor. These NAPRT-induced effects are independent of NAD-biosynthetic activity, but rely on NAPRT binding to TLR4. In line with our finding that NAPRT mediates endotoxin tolerance in vitro and in vivo, sera from patients with sepsis contain the highest levels of NAPRT, compared to patients with other chronic inflammatory conditions. Together, these data identify NAPRT as a endogenous ligand for TLR4 and a mediator of inflammation.

The enzyme nicotinate phosphoribosyltransferase (NAPRT) mediates the rate-limiting step in NAD salvage pathway starting from nicotinic acid. Here the authors show that NAPRT can be detected extracellularly, binds to Toll like receptor 4, and activates NF-kB signaling and cytokine production in macrophage via NAD synthesis-independent pathways.

Targeting metabolic reprogramming in metastatic melanoma: The key role of nicotinamide phosphoribosyltransferase (NAMPT)

Cancer cells rewire their metabolism to support proliferation, growth and survival. In metastatic melanoma the BRAF oncogenic pathway is a master regulator of this process, highlighting the importance of metabolic reprogramming in the pathogenesis of this tumor and offering potential therapeutic approaches. Metabolic adaptation of melanoma cells generally requires increased amounts of NAD⁺, an essential redox cofactor in cellular metabolism and a signaling molecule. Nicotinamide phosphoribosyltransferase (NAMPT) is the most important NAD⁺ biosynthetic enzyme in mammalian cells and a direct target of the BRAF oncogenic signaling pathway. These findings suggest that NAMPT is an attractive new therapeutic target, particularly in combination strategies with BRAF or MEK inhibitors. Here we review current knowledge on how oncogenic signaling reprograms metabolism in BRAF-mutated melanoma, and discuss how NAMPT/NAD⁺ axis contributes to these processes. Lastly, we present evidence supporting a role of NAMPT as a novel therapeutic target in metastatic melanoma.

Extracellular nicotinamide phosphoribosyltransferase (eNAMPT) is a novel marker for patients with BRAF-mutated metastatic melanoma

Metastatic melanoma carrying BRAF mutations represent a still unmet medical need as success of BRAF inhibitors is limited by development of resistance. Nicotinamide phosphoribosyltransferase (NAMPT) is a key enzyme in NAD biosynthesis. An extracellular form (eNAMPT) possesses cytokine-like functions and is up-regulated in inflammatory disorders, including cancer. Here we show that eNAMPT is actively released in culture supernatants of melanoma cell lines. Furthermore, cells that become resistant to BRAF inhibitors (BiR) show a significant increase of eNAMPT levels. Plasma from mice xenografted with BiR cell lines contain higher eNAMPT levels compared to tumor-free animals. Consistently, eNAMPT levels are elevated in 113 patients with BRAF-mutated metastatic melanoma compared to 50 with localized disease or to 38 healthy donors, showing a direct correlation with markers of tumor burden, such as LDH, or aggressive disease (such as PD-L1). eNAMPT concentrations decrease in response to therapy with BRAF/MEK inhibitors, but increase again at progression, as inferred from the serial analysis of 50 patients. Lastly, high eNAMPT levels correlate with a significantly shorter overall survival.

Our findings suggest that eNAMPT is a novel marker of tumor burden and response to therapy in patients with metastatic melanoma carrying BRAF mutations.