Cancer cell metabolic plasticity allows resistance to NAMPT inhibition but invariably induces dependence on LDHA

Mechanisms of resistance to NAMPT inhibitors in cancer

A common barrier to the development of effective anticancer agents is the development of drug resistance. This obstacle remains a challenge to successful clinical translation, particularly for targeted agents. Nicotinamide phosphoribosyltransferase (NAMPT) inhibitors represent a clinically applicable drug class that exploits the increased dependence of cancer cells on nicotinamide adenine dinucleotide (NAD+), a coenzyme essential to metabolism and other cellular functions. NAMPT catalyzes the rate-limiting step in the NAD+ salvage pathway of mammalian cells and is overexpressed in numerous types of cancers. Preclinical research has demonstrated that pharmacological targeting of NAMPT may be an effective strategy against certain cancers, and while several early-phase clinical trials testing NAMPT inhibitors in refractory cancers have been completed, drug resistance is a concern. Preclinical work in a variety of cancer models has demonstrated the emergence of resistance to multiple NAMPT inhibitors through several recurrent mechanisms. This review represents the first article summarizing the current state of knowledge regarding the mechanisms of acquired drug resistance to NAMPT inhibitors with a particular focus on upregulation of the compensatory NAD+ production enzymes nicotinate phosphoribosyltransferase (NAPRT) and quinolinate phosphoribosyltransferase (QPRT), acquired mutations in NAMPT, metabolic reprogramming, and altered expression of the ATP-binding cassette (ABC) efflux transporter ABCB1. An understanding of how these mechanisms interact with the biology of each given cancer cell type to predispose to the acquisition of NAMPT inhibitor resistance will be necessary to develop strategies to optimize the use of these agents moving forward.

NAD+ metabolism restriction boosts high-dose melphalan efficacy in patients with multiple myeloma

ABSTRACT

Elevated levels of the NAD+-generating enzyme nicotinamide phosphoribosyltransferase (NAMPT) are a common feature across numerous cancer types. Accordingly, we previously reported pervasive NAD+ dysregulation in multiple myeloma (MM) cells in association with upregulated NAMPT expression. Unfortunately, albeit being effective in preclinical models of cancer, NAMPT inhibition has proven ineffective in clinical trials because of the existence of alternative NAD+ production routes using NAD+ precursors other than nicotinamide. Here, by leveraging mathematical modeling approaches integrated with transcriptome data, we defined the specific NAD+ landscape of MM cells and established that the Preiss-Handler pathway for NAD+ biosynthesis, which uses nicotinic acid as a precursor, supports NAD+ synthesis in MM cells via its key enzyme nicotinate phosphoribosyltransferase (NAPRT). Accordingly, we found that NAPRT confers resistance to NAD+-depleting agents. Transcriptomic, metabolic, and bioenergetic profiling of NAPRT-knockout (KO) MM cells showed these to have weakened endogenous antioxidant defenses, increased propensity to oxidative stress, and enhanced genomic instability. Concomitant NAMPT inhibition further compounded the effects of NAPRT-KO, effectively sensitizing MM cells to the chemotherapeutic drug, melphalan; NAPRT added-back fully rescues these phenotypes. Overall, our results propose comprehensive NAD+ biosynthesis inhibition, through simultaneously targeting NAMPT and NAPRT, as a promising strategy to be tested in randomized clinical trials involving transplant-eligible patients with MM, especially those with more aggressive disease.

A review of the pathogenesis of mitochondria in breast cancer and progress of targeting mitochondria for breast cancer treatment

With breast cancer being the most common tumor among women in the world today, it is also the leading cause of cancer-related deaths. Standard treatments include chemotherapy, surgery, endocrine therapy, and targeted therapy. However, the heterogeneity, drug resistance, and poor prognosis of breast cancer highlight an urgent need for further exploration of its underlying mechanisms. Mitochondria, highly dynamic intracellular organelles, play a pivotal role in maintaining cellular energy metabolism. Altered mitochondrial function plays a critical role in various diseases, and recent studies have elucidated its pathophysiological mechanisms in breast carcinogenesis. This review explores the role of mitochondrial dysfunction in breast cancer pathogenesis and assesses potential mitochondria-targeted therapies.

Nuclear NAD+ synthase nicotinamide mononucleotide adenylyltransferase 1 contributes to nuclear atypia and promotes glioma growth

Background

Glioma is a malignant primary brain tumor with a poor prognosis and short survival. NAD+ is critical for cancer growth; however, clinical trials targeting NAD+ biosynthesis had limited success, indicating the need for mechanistic characterization. Nuclear atypia, aberrations in the size and shape of the nucleus, is widely observed in cancer and is often considered a distinctive feature in diagnosis; however, the molecular underpinnings are unclear.

Methods

We carried out high-resolution immunohistochemical analyses on glioma tissue samples from 19 patients to analyze the expression of NAD+ synthase nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), and its correlation with nuclear atypia in gliomas. Utilizing a Drosophila model of glial neoplasia, we investigated the genetic role of nuclear NMNAT in glioma growth in vivo, elucidating the cellular mechanisms of NMNAT1 in promoting nuclear atypia and glioma growth.

Results

In low-grade glioma and glioblastoma, a higher transcription level of NMNAT1 is correlated with poorer disease-free survival. Samples of high-grade gliomas contained a higher percentage of glial cells enriched with NMNAT1 protein. We identified a specific correlation between nuclear NMNAT1 protein level with nuclear atypia. Mechanistic studies in human glioma cell lines and in vivo Drosophila model suggest that NMNAT1 disrupts the integrity of the nuclear lamina by altering the distribution of lamin A/C and promotes glioma growth.

Conclusions

Our study uncovers a novel functional connection between the NAD+ metabolic pathway and glioma growth, reveals the contribution of the NAD+ biosynthetic enzyme NMNAT1 to nuclear atypia, and underscores the role of nuclear NMNAT1 in exacerbating glioma pathology.

Glioblastoma Sensitization to Therapeutic Effects by Glutamine Deprivation Depends on Cellular Phenotype and Metabolism

Glutamine plays an important role in tumor metabolism. It is known that the core region of solid tumors is deprived of glutamine, which affects tumor growth and spread. Here we investigated the effect of glutamine deprivation on cellular metabolism and sensitivity of human glioblastoma cells U87MG and T98G to drugs of various origin: alkylating cytostatic agent temozolomide; cytokine TRAIL DR5-B - agonist of the DR5 receptor; and GMX1778 - a targeted inhibitor of the enzyme nicotinamide phosphoribosyltransferase (NAMPT), limiting NAD biosynthesis. Bioinformatics analysis of the cell transcriptomes showed that U87MG cells have a more differentiated phenotype than T98G, and also differ in the expression profile of the genes associated with glutamine metabolism. Upon glutamine deprivation, growth rate of the U87MG and T98G cells decreased. Analysis of cellular metabolism by FLIM microscopy of NADH as well as assessment of lactate content in the medium showed that glutamine deprivation shifted metabolic status of the U87MG cells towards glycolysis. This was accompanied by the increase in expression of the stemness marker CD133, which collectively could indicate de-differentiation of these cells. At the same time, we observed increase in both expression of the DR5 receptor and sensitivity of the U87MG cells to DR5-B. On the contrary, glutamine deprivation of T98G cells induced metabolic shift towards oxidative phosphorylation, decrease in the DR5 expression and resistance to DR5-B. The effects of NAMPT inhibition also differed between the two cell lines and were opposite to the effects of DR5-B: upon glutamine deprivation, U87MG cells acquired resistance, while T98G cells were sensitized to GMX1778. Thus, phenotypic and metabolic differences between the two human glioblastoma cell lines caused divergent metabolic changes and contrasting responses to different targeted drugs during glutamine deprivation. These data should be considered when developing treatment strategies for glioblastoma via drug-mediated deprivation of amino acids, as well as when exploring novel therapeutic targets.

Clustered ARPE-19 cells distinct in mitochondrial membrane potential may play a pivotal role in cell differentiation

Age-related macular degeneration (AMD) is associated with the dysfunction and degeneration of retinal pigment epithelium (RPE) cells. Here, we examined how the formation and expansions of cell clusters are regulated by the differentiation of the RPE　cells. In this study, ARPE-19 cells were cultivated in standard or differentiation media, i.e., without or with nicotinamide, to evaluate the spreading of cell clusters specified with differentiated cell phenotypes. Mitochondria membrane potential (MMP) and the distribution of the RPE cell clusters was also monitored with or without rotenone, a mitochondrial electron transport chain (ETC) complex I inhibitor. Cultured ARPE-19 cells generated scattered cell clusters composed mostly of smaller size cells expressing the differentiation markers mouse anti-cellular retinaldehyde-binding protein (CRALBP) and Bestrophin only in differentiation medium. After the increase of the number of clusters, the clusters appeared to paracellularly merge, resulting in expansion of the area occupied by the clusters. Of note, the cells within the clusters selectively had high MMP and were in accordance with the expression of RPE differentiation markers. Rotenone repressed the formation of the clusters and decreased intracellular MMP. The above results suggest that clustering of RPE cells with functional mitochondria plays a pivotal role in RPE cell differentiation process and the ETC complex I inhibition greatly influences the composition of RPE cells that are degenerated or differentiation disposed.

Inhibition of NAMPT by PAK4 Inhibitors

The serine/threonine kinase PAK4 plays a crucial role in regulating cell proliferation, survival, migration, and invasion. Overexpression of PAK4 correlates with poor prognosis in some cancers. KPT-9274, a PAK4 inhibitor, significantly reduces the growth of triple-negative breast cancer cells and mammary tumors in mouse models, and it also inhibits the growth of several other types of cancer cells. Interestingly, although it was first identified as a PAK4 inhibitor, KPT-9274 was also found to inhibit the enzyme NAMPT (nicotinamide phosphoribosyltransferase), which is crucial for NAD (nicotinamide adenine dinucleotide) synthesis and vital for cellular energy and growth. These results made us question whether growth inhibition in response to KPT-9274 was due to PAK4 inhibition, NAMPT inhibition, or both. To address this, we tested several other PAK4 inhibitors that also inhibit cell growth, to determine whether they also inhibit NAMPT activity. Our findings confirm that multiple PAK4 inhibitors also inhibit NAMPT activity. This was assessed both in cell-free assays and in a breast cancer cell line. Molecular docking studies were also used to help us better understand the mechanism by which PAK4 inhibitors block PAK4 and NAMPT activity, and we identified specific residues on the PAK4 inhibitors that interact with NAMPT and PAK4. Our results suggest that PAK4 inhibitors may have a more complex mechanism of action than previously understood, necessitating further exploration of how they influence cancer cell growth.

Oxygen-Dependent Interactions between the Ruthenium Cage and the Photoreleased Inhibitor in NAMPT-Targeted Photoactivated Chemotherapy

Photoactivated chemotherapy agents form a new branch of physically targeted anticancer agents with potentially lower systemic side effects for patients. On the other hand, limited information exists on the intracellular interactions between the photoreleased metal cage and the photoreleased anticancer inhibitor. In this work, we report a new biological study of the known photoactivated compound Ru-STF31 in the glioblastoma cancer cell line, U87MG. Ru-STF31 targets nicotinamide phosphoribosyltransferase (NAMPT), an enzyme overexpressed in U87MG. Ru-STF31 is activated by red light irradiation and releases two photoproducts: the ruthenium cage and the cytotoxic inhibitor STF31. This study shows that Ru-STF31 can significantly decrease intracellular NAD+ levels in both normoxic (21% O2) and hypoxic (1% O2) U87MG cells. Strikingly, NAD+ depletion by light activation of Ru-STF31 in hypoxic U87MG cells could not be rescued by the addition of extracellular NAD+. Our data suggest an oxygen-dependent active role of the ruthenium photocage released by light activation.

Inhibitors of NAD+ Production in Cancer Treatment: State of the Art and Perspectives

The addiction of tumors to elevated nicotinamide adenine dinucleotide (NAD+) levels is a hallmark of cancer metabolism. Obstructing NAD+ biosynthesis in tumors is a new and promising antineoplastic strategy. Inhibitors developed against nicotinamide phosphoribosyltransferase (NAMPT), the main enzyme in NAD+ production from nicotinamide, elicited robust anticancer activity in preclinical models but not in patients, implying that other NAD+-biosynthetic pathways are also active in tumors and provide sufficient NAD+ amounts despite NAMPT obstruction. Recent studies show that NAD+ biosynthesis through the so-called "Preiss-Handler (PH) pathway", which utilizes nicotinate as a precursor, actively operates in many tumors and accounts for tumor resistance to NAMPT inhibitors. The PH pathway consists of three sequential enzymatic steps that are catalyzed by nicotinate phosphoribosyltransferase (NAPRT), nicotinamide mononucleotide adenylyltransferases (NMNATs), and NAD+ synthetase (NADSYN1). Here, we focus on these enzymes as emerging targets in cancer drug discovery, summarizing their reported inhibitors and describing their current or potential exploitation as anticancer agents. Finally, we also focus on additional NAD+-producing enzymes acting in alternative NAD+-producing routes that could also be relevant in tumors and thus become viable targets for drug discovery.

The kynurenine pathway presents multi-faceted metabolic vulnerabilities in cancer

The kynurenine pathway (KP) and associated catabolites play key roles in promoting tumor progression and modulating the host anti-tumor immune response. To date, considerable focus has been on the role of indoleamine 2,3-dioxygenase 1 (IDO1) and its catabolite, kynurenine (Kyn). However, increasing evidence has demonstrated that downstream KP enzymes and their associated metabolite products can also elicit tumor-microenvironment immune suppression. These advancements in our understanding of the tumor promotive role of the KP have led to the conception of novel therapeutic strategies to target the KP pathway for anti-cancer effects and reversal of immune escape. This review aims to 1) highlight the known biological functions of key enzymes in the KP, and 2) provide a comprehensive overview of existing and emerging therapies aimed at targeting discrete enzymes in the KP for anti-cancer treatment.

Role of the ST6GAL1 sialyltransferase in regulating ovarian cancer cell metabolism

The ST6GAL1 sialyltransferase, which adds α2-6-linked sialic acids to N-glycosylated proteins, is upregulated in many malignancies including ovarian cancer. Through its activity in sialylating select surface receptors, ST6GAL1 modulates intracellular signaling to regulate tumor cell phenotype. ST6GAL1 has previously been shown to act as a survival factor that protects cancer cells from cytotoxic stressors such as hypoxia. In the present study, we investigated a role for ST6GAL1 in tumor cell metabolism. ST6GAL1 was overexpressed (OE) in OV4 ovarian cancer cells, which have low endogenous ST6GAL1, or knocked-down (KD) in ID8 ovarian cancer cells, which have high endogenous ST6GAL1. OV4 and ID8 cells with modulated ST6GAL1 expression were grown under normoxic or hypoxic conditions, and metabolism was assessed using Seahorse technology. Results showed that cells with high ST6GAL1 expression maintained a higher rate of oxidative metabolism than control cells following treatment with the hypoxia mimetic, desferrioxamine (DFO). This enrichment was not due to an increase in mitochondrial number. Glycolytic metabolism was also increased in OV4 and ID8 cells with high ST6GAL1 expression, and these cells displayed greater activity of the glycolytic enzymes, hexokinase and phosphofructokinase. Metabolism maps were generated from the combined Seahorse data, which suggested that ST6GAL1 functions to enhance the overall metabolism of tumor cells. Finally, we determined that OV4 and ID8 cells with high ST6GAL1 expression were more invasive under conditions of hypoxia. Collectively, these results highlight the importance of sialylation in regulating the metabolic phenotype of ovarian cancer cells.

Mitochondrial rewiring drives metabolic adaptation to NAD(H) shortage in triple negative breast cancer cells

Nicotinamide phosphoribosyltransferase (NAMPT) is a key metabolic enzyme in NAD⁺ synthesis pathways and is found upregulated in several tumors, depicting NAD(H) lowering agents, like the NAMPT inhibitor FK866, as an appealing approach for anticancer therapy. Like other small molecules, FK866 triggers chemoresistance, observed in several cancer cellular models, which can prevent its clinical application. The molecular mechanisms sustaining the acquired of resistance to FK866 were studied in a model of triple negative breast cancer (MDA-MB-231 parental - PAR), exposed to increasing concentrations of the small molecule (MDA-MB-231 resistant - RES). RES cells are not sensitive to verapamil or cyclosporin A, excluding a potential role of increased efflux pumps activity as a mechanism of resistance. Similarly, the silencing of the enzyme Nicotinamide Riboside Kinase 1 (NMRK1) in RES cells does not increase FK866 toxicity, excluding this pathway as a compensatory mechanism of NAD⁺ production. Instead, Seahorse metabolic analysis revealed an increased mitochondrial spare respiratory capacity in RES cells. These cells presented a higher mitochondrial mass compared to the FK866-sensitive counterparts, as well as an increased consumption of pyruvate and succinate for energy production. Interestingly, co-treatment of PAR cells with FK866 and the mitochondrial pyruvate carrier (MPC) inhibitors UK5099 or rosiglitazone, as well as with the transient silencing of MPC2 but not of MPC1, induces a FK866-resistant phenotype. Taken together, these results unravel novel mechanisms of cell plasticity to counteract FK866 toxicity, that, besides the previously described LDHA dependency, rely on mitochondrial rewiring at functional and energetic levels.

Targeting of Glucose Transport and the NAD Pathway in Neuroendocrine Tumor (NET) Cells Reveals New Treatment Options

(1) Background: the potency of drugs that interfere with glucose metabolism, i.e., glucose transporters (GLUT) and nicotinamide phosphoribosyltransferase (NAMPT) was analyzed in neuroendocrine tumor (NET, BON-1, and QPG-1 cells) and small cell lung cancer (SCLC, GLC-2, and GLC-36 cells) tumor cell lines. (2) Methods: the proliferation and survival rate of tumor cells was significantly affected by the GLUT-inhibitors fasentin and WZB1127, as well as by the NAMPT inhibitors GMX1778 and STF-31. (3) Results: none of the NET cell lines that were treated with NAMPT inhibitors could be rescued with nicotinic acid (usage of the Preiss-Handler salvage pathway), although NAPRT expression could be detected in two NET cell lines. We finally analyzed the specificity of GMX1778 and STF-31 in NET cells in glucose uptake experiments. As previously shown for STF-31 in a panel NET-excluding tumor cell lines, both drugs specifically inhibited glucose uptake at higher (50 μM), but not at lower (5 μM) concentrations. (4) Conclusions: our data suggest that GLUT and especially NAMPT inhibitors are potential candidates for the treatment of NET tumors.

CD38-Induced Metabolic Dysfunction Primes Multiple Myeloma Cells for NAD+-Lowering Agents

Cancer cells fuel growth and energy demands by increasing their NAD⁺ biosynthesis dependency, which therefore represents an exploitable vulnerability for anti-cancer strategies. CD38 is a NAD⁺-degrading enzyme that has become crucial for anti-MM therapies since anti-CD38 monoclonal antibodies represent the backbone for treatment of newly diagnosed and relapsed multiple myeloma patients. Nevertheless, further steps are needed to enable a full exploitation of these strategies, including deeper insights of the mechanisms by which CD38 promotes tumorigenesis and its metabolic additions that could be selectively targeted by therapeutic strategies. Here, we present evidence that CD38 upregulation produces a pervasive intracellular-NAD⁺ depletion, which impairs mitochondrial fitness and enhances oxidative stress; as result, genetic or pharmacologic approaches that aim to modify CD38 surface-level prime MM cells to NAD⁺-lowering agents. The molecular mechanism underlying this event is an alteration in mitochondrial dynamics, which decreases mitochondria efficiency and triggers energetic remodeling. Overall, we found that CD38 handling represents an innovative strategy to improve the outcomes of NAD⁺-lowering agents and provides the rationale for testing these very promising agents in clinical studies involving MM patients.

Dual Nicotinamide Phosphoribosyltransferase (NAMPT) and Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitors for the Treatment of Drug-Resistant Nonsmall-Cell Lung Cancer

Depleting NAD⁺ by blocking its biosynthesis has emerged as an attractive anticancer strategy. Simultaneous blockade of NAD⁺ production from the salvage and de novo synthesis pathways by targeting NAMPT and IDO1 could achieve more effective NAD⁺ reduction and, subsequently, more robust antitumor efficacy. Herein, we report the discovery of the first series of dual NAMPT and IDO1 inhibitors according to multitarget drug rationales. Compound 10e has good and balanced inhibitory potencies against NAMPT and IDO1, and significantly inhibits both proliferation and migration of a NSCLC cell line resistant to taxol and FK866 (A549/R cells). Compound 10e also displays potent antitumor efficacy in A549/R xenograft mouse models with no significant toxicity. Moreover, this compound enhances the susceptibility of A549/R cells to taxol in vitro and in vivo. This work provides an efficient approach to targeting NAD⁺ metabolism in the area of cancer therapy, especially in the context of drug resistance.

Relationship between metabolic reprogramming and drug resistance in breast cancer

Breast cancer is the leading cause of cancer death in women. At present, chemotherapy is the main method to treat breast cancer in addition to surgery and radiotherapy, but the process of chemotherapy is often accompanied by the development of drug resistance, which leads to a reduction in drug efficacy. Furthermore, mounting evidence indicates that drug resistance is caused by dysregulated cellular metabolism, and metabolic reprogramming, including enhanced glucose metabolism, fatty acid synthesis and glutamine metabolic rates, is one of the hallmarks of cancer. Changes in metabolism have been considered one of the most important causes of resistance to treatment, and knowledge of the mechanisms involved will help in identifying potential treatment deficiencies. To improve women's survival outcomes, it is vital to elucidate the relationship between metabolic reprogramming and drug resistance in breast cancer. This review analyzes and investigates the reprogramming of metabolism and resistance to breast cancer therapy, and the results offer promise for novel targeted and cell-based therapies.

The Kynurenine Pathway and Cancer: Why Keep It Simple When You Can Make It Complicated

Simple Summary

The kynurenine pathway has two main physiological roles: (i) it protects specific organs such as the eyes and placenta from strong immune reactions and (ii) it additionally generate in the liver and kidney a metabolite essential to all cells of human body. Abnormal activation of this pathway is recurrently observed in numerous cancer types. Its two functions are hijacked to promote tumor growth and cancer cell dissemination through multiple mechanisms. Clinical assays including administration of inhibitors of this pathway have not yet been successful. The complex regulation of this pathway is likely the reason behind this failure. In this review, we try to give an overview of the current knowledge about this pathway, to point out the next challenges, and to propose alternative therapeutic routes.

Abstract

The kynurenine pathway has been highlighted as a gatekeeper of immune-privileged sites through its ability to generate from tryptophan a set of immunosuppressive metabolic intermediates. It additionally constitutes an important source of cellular NAD⁺ for the organism. Hijacking of its immunosuppressive functions, as recurrently observed in multiple cancers, facilitates immune evasion and promotes tumor development. Based on these observations, researchers have focused on characterizing indoleamine 2,3-dioxygenase (IDO1), the main enzyme catalyzing the first and limiting step of the pathway, and on developing therapies targeting it. Unfortunately, clinical trials studying IDO1 inhibitors have thus far not met expectations, highlighting the need to unravel this complex signaling pathway further. Recent advances demonstrate that these metabolites additionally promote tumor growth, metastatic dissemination and chemoresistance by a combination of paracrine and autocrine effects. Production of NAD⁺ also contributes to cancer progression by providing cancer cells with enhanced plasticity, invasive properties and chemoresistance. A comprehensive survey of this complexity is challenging but necessary to achieve medical success.

NAD+ depletion enhances reovirus-induced oncolysis in multiple myeloma

Cancer cell energy metabolism plays an important role in dictating the efficacy of oncolysis by oncolytic viruses. To understand the role of multiple myeloma metabolism in reovirus oncolysis, we performed semi-targeted mass spectrometry-based metabolomics on 12 multiple myeloma cell lines and revealed a negative correlation between NAD+ levels and susceptibility to oncolysis. Likewise, a negative correlation was observed between the activity of the rate-limiting NAD+ synthesis enzyme NAMPT and oncolysis. Indeed, depletion of NAD+ levels by pharmacological inhibition of NAMPT using FK866 sensitized several myeloma cell lines to reovirus-induced killing. The myelomas that were most sensitive to this combination therapy expressed a functional p53 and had a metabolic and transcriptomic profile favoring mitochondrial metabolism over glycolysis, with the highest synergistic effect in KMS12 cells. Mechanistically, U-¹³C-labeled glucose flux, extracellular flux analysis, multiplex proteomics, and cell death assays revealed that the reovirus + FK866 combination caused mitochondrial dysfunction and energy depletion, leading to enhanced autophagic cell death in KMS12 cells. Finally, the combination of reovirus and NAD+ depletion achieved greater antitumor effects in KMS12 tumors in vivo and patient-derived CD138+ multiple myeloma cells. These findings identify NAD+ depletion as a potential combinatorial strategy to enhance the efficacy of oncolytic virus-based therapies in multiple myeloma.

Enhanced Intracellular Reactive Oxygen Species by Photodynamic Therapy Effectively Promotes Chemoresistant Cell Death

Anti-cancer chemo-drugs can cause a rapid elevation of intracellular reactive oxygen species (ROS) levels. An imbalance in ROS production and elimination systems leads to cancer cell resistance to chemotherapy. This study aimed to evaluate the mechanism and effect of ROS on multidrug resistance in various human chemoresistant cancer cells by detecting the changes in the amount of ROS, the expression of ROS-related and glycolysis-related genes, and cell death. We found that ROS was decreased while oxidative phosphorylation was increased in chemoresistant cells. We verified that the chemoresistance of cancer cells was achieved in two ways. First, chemoresistant cells preferred oxidative phosphorylation instead of anaerobic glycolysis for energy generation, which increased ATPase activity and produced much more ATP to provide energy. Second, ROS-scavenging systems were enhanced in chemoresistant cancer cells, which in turn decreased ROS amount and thus inhibited chemo-induced cell death. Our in vitro and in vivo photodynamic therapy further demonstrated that elevated ROS production efficiently inhibited chemo-drug resistance and promoted chemoresistant cell death. Taken together, targeting ROS systems has a great potential to treat cancer patients with chemoresistance.

LDHA is enriched in human islet alpha cells and upregulated in type 2 diabetes

The lactate dehydrogenase isoform A (LDHA) is a key metabolic enzyme that preferentially catalyzes the conversion of pyruvate to lactate. Whereas LDHA is highly expressed in many tissues, its expression is turned off in the differentiated adult β-cell within the pancreatic islets. The repression of LDHA under normal physiological condition and its inappropriate upregulation under a diabetogenic environment is well-documented in rodent islets/β-cells but little is known about LDHA expression in human islet cells and whether its abundance is altered under diabetic conditions. Analysis of public single-cell RNA-seq (sc-RNA seq) data as well as cell type-specific immunolabeling of human pancreatic islets showed that LDHA was mainly localized in human α-cells while it is expressed at a very low level in β-cells. Furthermore, LDHA, both at mRNA and protein, as well as lactate production is upregulated in human pancreatic islets exposed to chronic high glucose treatment. Microscopic analysis of stressed human islets and autopsy pancreases from individuals with type 2 diabetes (T2D) showed LDHA upregulation mainly in human α-cells. Pharmacological inhibition of LDHA in isolated human islets enhanced insulin secretion under physiological conditions but did not significantly correct the deregulated secretion of insulin or glucagon under diabetic conditions.

Advances in NAD-Lowering Agents for Cancer Treatment

Nicotinamide adenine dinucleotide (NAD) is an essential redox cofactor, but it also acts as a substrate for NAD-consuming enzymes, regulating cellular events such as DNA repair and gene expression. Since such processes are fundamental to support cancer cell survival and proliferation, sustained NAD production is a hallmark of many types of neoplasms. Depleting intratumor NAD levels, mainly through interference with the NAD-biosynthetic machinery, has emerged as a promising anti-cancer strategy. NAD can be generated from tryptophan or nicotinic acid. In addition, the "salvage pathway" of NAD production, which uses nicotinamide, a byproduct of NAD degradation, as a substrate, is also widely active in mammalian cells and appears to be highly exploited by a subset of human cancers. In fact, research has mainly focused on inhibiting the key enzyme of the latter NAD production route, nicotinamide phosphoribosyltransferase (NAMPT), leading to the identification of numerous inhibitors, including FK866 and CHS-828. Unfortunately, the clinical activity of these agents proved limited, suggesting that the approaches for targeting NAD production in tumors need to be refined. In this contribution, we highlight the recent advancements in this field, including an overview of the NAD-lowering compounds that have been reported so far and the related in vitro and in vivo studies. We also describe the key NAD-producing pathways and their regulation in cancer cells. Finally, we summarize the approaches that have been explored to optimize the therapeutic response to NAMPT inhibitors in cancer.

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.

Mono(ADP-ribosyl)ation Enzymes and NAD+ Metabolism: A Focus on Diseases and Therapeutic Perspectives

Mono(ADP-ribose) transferases and mono(ADP-ribosyl)ating sirtuins use NAD+ to perform the mono(ADP-ribosyl)ation, a simple form of post-translational modification of proteins and, in some cases, of nucleic acids. The availability of NAD+ is a limiting step and an essential requisite for NAD+ consuming enzymes. The synthesis and degradation of NAD+, as well as the transport of its key intermediates among cell compartments, play a vital role in the maintenance of optimal NAD+ levels, which are essential for the regulation of NAD+-utilizing enzymes. In this review, we provide an overview of the current knowledge of NAD+ metabolism, highlighting the functional liaison with mono(ADP-ribosyl)ating enzymes, such as the well-known ARTD10 (also named PARP10), SIRT6, and SIRT7. To this aim, we discuss the link of these enzymes with NAD+ metabolism and chronic diseases, such as cancer, degenerative disorders and aging.

NAD+ metabolism, stemness, the immune response, and cancer

NAD⁺ was discovered during yeast fermentation, and since its discovery, its important roles in redox metabolism, aging, and longevity, the immune system and DNA repair have been highlighted. A deregulation of the NAD⁺ levels has been associated with metabolic diseases and aging-related diseases, including neurodegeneration, defective immune responses, and cancer. NAD⁺ acts as a cofactor through its interplay with NADH, playing an essential role in many enzymatic reactions of energy metabolism, such as glycolysis, oxidative phosphorylation, fatty acid oxidation, and the TCA cycle. NAD⁺ also plays a role in deacetylation by sirtuins and ADP ribosylation during DNA damage/repair by PARP proteins. Finally, different NAD hydrolase proteins also consume NAD⁺ while converting it into ADP-ribose or its cyclic counterpart. Some of these proteins, such as CD38, seem to be extensively involved in the immune response. Since NAD cannot be taken directly from food, NAD metabolism is essential, and NAMPT is the key enzyme recovering NAD from nicotinamide and generating most of the NAD cellular pools. Because of the complex network of pathways in which NAD⁺ is essential, the important role of NAD⁺ and its key generating enzyme, NAMPT, in cancer is understandable. In the present work, we review the role of NAD⁺ and NAMPT in the ways that they may influence cancer metabolism, the immune system, stemness, aging, and cancer. Finally, we review some ongoing research on therapeutic approaches.

Effect of Starvation in Reversing Cancer Chemoresistance Based on Drug-Resistance Detection by Dextran Nanoparticles

INTRODUCTION

Chemoresistance leads to chemotherapy failure in patients with cancer. Multidrug resistance (MDR) in cancer is mainly caused by the high expression of P-glycoprotein encoded by the MDR1 gene, which is an ATP-dependent protease. Keeping the stronger invasion and migration abilities of chemoresistant cells in cancer also requires more ATP consumption. Herein, we aimed to reverse resistance by reducing the glucose supply in the cellular environment.

METHODS

A starvation approach in reversing chemoresistance was applied, which was implemented through preparing fluorescent dextran-based nanoparticles to detect the proportion of chemoresistant cells in the chemoresistant/chemosensitive cell mixture after cells cultured in a low-glucose condition.

RESULTS

Chemoresistant cells had higher glucose consumption with higher ATPase expression and stronger glucose dependence compared to chemosensitive cells. Moreover, cancer cells cultured in a low-glucose condition reduced the proportion of chemoresistant cells.

CONCLUSION

Starvation therapy can be used as a new method to reverse drug resistance in cancer.

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

Nicotinamide adenine dinucleotide (NAD+) and its metabolites function as critical regulators to maintain physiologic processes, enabling the plastic cells to adapt to environmental changes including nutrient perturbation, genotoxic factors, circadian disorder, infection, inflammation and xenobiotics. These effects are mainly achieved by the driving effect of NAD+ on metabolic pathways as enzyme cofactors transferring hydrogen in oxidation-reduction reactions. Besides, multiple NAD+-dependent enzymes are involved in physiology either by post-synthesis chemical modification of DNA, RNA and proteins, or releasing second messenger cyclic ADP-ribose (cADPR) and NAADP+. Prolonged disequilibrium of NAD+ metabolism disturbs the physiological functions, resulting in diseases including metabolic diseases, cancer, aging and neurodegeneration disorder. In this review, we summarize recent advances in our understanding of the molecular mechanisms of NAD+-regulated physiological responses to stresses, the contribution of NAD+ deficiency to various diseases via manipulating cellular communication networks and the potential new avenues for therapeutic intervention.

Recent Advances in NAMPT Inhibitors: A Novel Immunotherapic Strategy

Nicotinamide adenine dinucleotide (NAD) is a cofactor of many enzymatic reactions as well as being a substrate for a number of NAD-consuming enzymes (e.g., PARPS, sirtuins, etc). NAD can be synthesized de novo starting from tryptophan, nicotinamide, nicotinic acid, or nicotinamide riboside from the diet. On the other hand, the nicotinamide that is liberated by NAD-consuming enzymes can be salvaged to re-form NAD. In this former instance, nicotinamide phosphoribosyltransferase (NAMPT) is the bottleneck enzyme. In the many cells in which the salvage pathway is predominant, NAMPT, therefore, represents an important controller of intracellular NAD concentrations, and as a consequence of energy metabolism. It is, therefore, not surprising that NAMPT is over expressed by tumoral cells, which take advantage from this to sustain growth rate and tumor progression. This has led to the initiation of numerous medicinal chemistry programs to develop NAMPT inhibitors in the context of oncology. More recently, however, it has been shown that NAMPT inhibitors do not solely target the tumor but also have an effect on the immune system. To add complexity, this enzyme can also be secreted by cells, and in the extracellular space it acts as a cytokine mainly through the activation of Toll like Receptor 4 (TLR4), although it has not been clarified yet if this is the only receptor responsible for its actions. While specific small molecules have been developed only against the intracellular form of NAMPT, growing evidences sustain the possibility to target the extracellular form. In this contribution, the most recent evidences on the medicinal chemistry of NAMPT will be reviewed, together with the key elements that sustain the hypothesis of NAMPT targeting and the drawbacks so far encountered.

Extracellular NAD+ enhances PARP-dependent DNA repair capacity independently of CD73 activity

Changes in nicotinamide adenine dinucleotide (NAD⁺) levels that compromise mitochondrial function trigger release of DNA damaging reactive oxygen species. NAD⁺ levels also affect DNA repair capacity as NAD⁺ is a substrate for PARP-enzymes (mono/poly-ADP-ribosylation) and sirtuins (deacetylation). The ecto-5′-nucleotidase CD73, an ectoenzyme highly expressed in cancer, is suggested to regulate intracellular NAD⁺ levels by processing NAD⁺ and its bio-precursor, nicotinamide mononucleotide (NMN), from tumor microenvironments, thereby enhancing tumor DNA repair capacity and chemotherapy resistance. We therefore investigated whether expression of CD73 impacts intracellular NAD⁺ content and NAD⁺-dependent DNA repair capacity. Reduced intracellular NAD⁺ levels suppressed recruitment of the DNA repair protein XRCC1 to sites of genomic DNA damage and impacted the amount of accumulated DNA damage. Further, decreased NAD⁺ reduced the capacity to repair DNA damage induced by DNA alkylating agents. Overall, reversal of these outcomes through NAD⁺ or NMN supplementation was independent of CD73. In opposition to its proposed role in extracellular NAD⁺ bioprocessing, we found that recombinant human CD73 only poorly processes NMN but not NAD⁺. A positive correlation between CD73 expression and intracellular NAD⁺ content could not be made as CD73 knockout human cells were efficient in generating intracellular NAD⁺ when supplemented with NAD⁺ or NMN.

Metabolomic profiles of induced pluripotent stem cells derived from patients with rheumatoid arthritis and osteoarthritis

Background

Metabolomics is the systemic study of the unique fingerprints of metabolites involved in cellular processes and biochemical reactions. The metabolomic approach is useful in diagnosing and predicting the development of rheumatoid arthritis (RA) and osteoarthritis (OA) and is emerging as a useful tool for identifying disease biomarkers. The aim of this study was to compare the metabolic blueprint of fibroblast-like synoviocyte (FLS) cells and induced pluripotent stem cells (iPSCs) derived from RA and OA patients.

Methods

Somatic cells of RA patients (n = 3) and OA patients (n = 3) were isolated, transduced with a lentiviral plasmid, and reprogrammed into iPSCs displaying pluripotency. Metabolic profiling of RA and OA patient–derived FLS cells and iPSCs was performed using liquid chromatography/mass spectrometry and statistical analysis. After normalization by the sum of the peak intensities through LC/MS, 37 metabolites were detected across RA and OA patients.

Results

The metabolites of RA and OA were distinguishable according to the PLS-DA analysis. LysoPC (20:4), 4-methoxychalcone, phosphorylcholine, and nicotinamide (NAM) were significantly higher in RA iPSCs than in OA iPSCs (p < 0.05). The NMNAT-3 enzyme, which catalyzes an important step in the biosynthesis of NAD⁺ from adenosine triphosphate, was also upregulated in RA iPSCs. Interestingly, the proliferation of RA iPSCs was significantly greater than OA iPSC proliferation (p < 0.05). NAM played a critical role in the proliferation of RA iPSCs but not in OA iPSCs. When iPSCs were treated with 100 nM of the NAM inhibitor tannic acid (TA), the proliferation of RA iPSCs was significantly reduced (p < 0.001).

Conclusions

The metabolites of RA and OA FLS cells and RA and OA iPSCs were all clearly distinguishable from each other. NAM played a critical role in the proliferation of RA iPSCs but not in OA iPSCs. TA effectively inhibited the expression of NAM in RA iPSCs and is a possible effective treatment for RA patients.

Subcellular compartmentalization of NAD+ and its role in cancer: A sereNADe of metabolic melodies

Nicotinamide adenine dinucleotide (NAD+) is an essential biomolecule involved in many critical processes. Its role as both a driver of energy production and a signaling molecule underscores its importance in health and disease. NAD+ signaling impacts multiple processes that are dysregulated in cancer, including DNA repair, cell proliferation, differentiation, redox regulation, and oxidative stress. Distribution of NAD+ is highly compartmentalized, with each subcellular NAD+ pool differentially regulated and preferentially involved in distinct NAD+-dependent signaling or metabolic events. Emerging evidence suggests that targeting NAD+ metabolism is likely to repress many specific mechanisms underlying tumor development and progression, including proliferation, survival, metabolic adaptations, invasive capabilities, heterotypic interactions with the tumor microenvironment, and stress response including notably DNA maintenance and repair. Here we provide a comprehensive overview of how compartmentalized NAD+ metabolism in mitochondria, nucleus, cytosol, and extracellular space impacts cancer formation and progression, along with a discussion of the therapeutic potential of NAD+-targeting drugs in cancer.

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.

Polydatin Attenuates Atherosclerosis in ApoE -∕- Mice through PBEF Mediated Reduction of Cholesterol Deposition

Cholesterol metabolism becomes imbalanced during the formation of macrophage-derived foam cells. Pre-B-cell colony-enhancing factor (PBEF) has recently been found to affect lipid deposition and inflammation in atherosclerosis. Here, we aimed to study the effects and molecular mechanism of Polydatin on atherosclerosis in ApoE-knockout (ApoE -∕- ) mice. Thirty ApoE -∕- mice were fed a high-fat diet (HFD) for 12 weeks, and then treated with Polydatin for another 12 weeks. Whole aortas and cryosections were stained with oil red O. Blood lipid, PBEF and cytokine levels were measured by ELISA. The mRNAs of cholesterol metabolism-related genes were determined by qRT-PCR and protein levels by Western blotting. Cell cholesterol content and viability were determined in macrophages and RAW 264.7 cells. PBEF siRNA was used to study the effect of Polydatin on cholesterol metabolism in macrophages incubated with ox-LDL. Polydatin lowered blood lipids and decreased atherosclerotic lesions in ApoE -∕- mice. The expression of cytokines and the mRNA of cholesterol metabolism-related genes were markedly regulated by Polydatin. Meanwhile, PBEF mRNA and protein were both greatly down-regulated by Polydatin. In vitro, Polydatin protected RAW 264.7 cells treated by ox-LDL and inhibited cholesterol uptake by macrophages. The PBEF siRNA result indicates that Polydatin can modulate cholesterol metabolism in macrophages, partly through down-regulation of PBEF. In conclusion, Polydatin relieves atherosclerosis injury in ApoE -∕- mice, mainly through down-regulation of PBEF and inhibition of PBEF-inducing cholesterol deposits in macrophages.