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.

Drug repositioning strategy for the identification of novel telomere-damaging agents: A role for NAMPT inhibitors

Drug repositioning strategy represents a valid tool to accelerate the pharmacological development through the identification of new applications for already existing compounds. In this view, we aimed at discovering molecules able to trigger telomere-localized DNA damage and tumor cell death. By applying an automated high-content spinning-disk microscopy, we performed a screening aimed at identifying, on a library of 527 drugs, molecules able to negatively affect the expression of TRF2, a key protein in telomere maintenance. FK866, resulting from the screening as the best candidate hit, was then validated at biochemical and molecular levels and the mechanism underlying its activity in telomere deprotection was elucidated both in vitro and in vivo. The results of this study allow us to discover a novel role of FK866 in promoting, through the production of reactive oxygen species, telomere loss and deprotection, two events leading to an accumulation of DNA damage and tumor cell death. The ability of FK866 to induce telomere damage and apoptosis was also demonstrated in advanced preclinical models evidencing the antitumoral activity of FK866 in triple-negative breast cancer-a particularly aggressive breast cancer subtype still orphan of targeted therapies and characterized by high expression levels of both NAMPT and TRF2. Overall, our findings pave the way to the development of novel anticancer strategies to counteract triple-negative breast cancer, based on the use of telomere deprotecting agents, including NAMPT inhibitors, that would rapidly progress from bench to bedside.

Discovery of a novel NAMPT inhibitor that selectively targets NAPRT-deficient EMT-subtype cancer cells and alleviates chemotherapy-induced peripheral neuropathy

Background: Exploiting synthetic lethality (SL) relationships between protein pairs has emerged as an important avenue for the development of anti-cancer drugs. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme of the NAD+ salvage pathway, having an SL relationship with nicotinic acid phosphoribosyltransferase (NAPRT), the key enzyme in the NAD+ Preiss-Handler pathway. NAMPT inhibitor holds clinical potential not only as a promising cancer treatment but also as a means of protection against chemotherapy-induced-peripheral-neuropathy (CIPN). However, as NAD+ is essential for normal cells, the clinical use of NAMPT inhibitors is challenging. This study aimed to identify a novel NAMPT inhibitor with enhanced selective cytotoxicity against NAPRT-deficient cancer cells as well as prominent efficacy in alleviating CIPN. Methods: We began by conducting drug derivatives screening in a panel of lung cancer cell lines to select an agent with the broadest therapeutic window between the NAPRT-negative and-positive cancer cell lines. Both in vitro and In vivo comparative analyses were conducted between A4276 and other NAMPT inhibitors to evaluate the NAPRT-negative cancer cell selectivity and the underlying distinct NAMPT inhibition mechanism of A4276. Patient-derived tumor transcriptomic data and protein levels in various cancer cell lines were analyzed to confirm the correlation between NAPRT depletion and epithelial-to-mesenchymal transition (EMT)-like features in various cancer types. Finally, the efficacy of A4276 for axonal protection and CIPN remedy was examined in vitro and in vivo. Results: The biomarker-driven phenotypic screening led to a discovery of A4276 with prominent selectivity against NAPRT-negative cancer cells compared with NAPRT-positive cancer cells and normal cells. The cytotoxic effect of A4276 on NAPRT-negative cells is achieved through its direct binding to NAMPT, inhibiting its enzymatic function at an optimal and balanced level allowing NAPRT-positive cells to survive through NAPRT-dependent NAD+ synthesis. NAPRT deficiency serves as a biomarker for the response to A4276 as well as an indicator of EMT-subtype cancer in various tumor types. Notably, A4276 protects axons from Wallerian degeneration more effectively than other NAMPT inhibitors by decreasing NMN-to-NAD+ ratio. Conclusion: This study demonstrates that A4276 selectively targets NAPRT-deficient EMT-subtype cancer cells and prevents chemotherapy-induced peripheral neuropathy, highlighting its potential as a promising anti-cancer agent for use in cancer monotherapy or combination therapy with conventional chemotherapeutics.

The immunomodulatory role of IDO1-Kynurenine-NAD+ pathway in switching cold tumor microenvironment in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is the most common exocrine tumor of the pancreas characterized by late diagnosis, adverse overall 5-year survival, a higher propensity for metastatic disease, and lack of efficacy of systemic therapy options. These adverse outcomes can be partly attributed to complex tumor microenvironment (TME). Over the past decade, immunotherapy has revolutionized the management of certain cancers; thus far, the immunologically 'non-inflamed' tumor microenvironment in PDACs has proven to be challenging. Indolamine 2,3-dioxygenase 1 (IDO1) is the rate-limiting enzyme in the catabolic pathway of L-Tryptophan, an essential amino acid, that gives rise to the immunosuppressive metabolite Kynurenine. IDO1, Indolamine 2,3-dioxygenase 2 (IDO2), and Tryptophan 2,3-dioxygenase (TDO) are the key enzymes in the tryptophan catabolic pathway but we focus on the role of the predominant enzyme form IDO1 in this review. Nicotinamide phosphoribosyl transferase (iNAMPT) regulates the intracellular concentration of NAD and is upregulated in the tumor. In light of the potential role of IDO1 as a driver of hostile TME in PDAC and NAD⁺ as a key coenzyme in anti-tumor immune response, this review urges focus on extensive research and initiation of clinical trials using IDO1 and NAMPT inhibitors in pancreatic cancer in the future.

Anticancer Activities of Novel Nicotinamide Phosphoribosyltransferase Inhibitors in Hematological Malignancies

Targeting cancer cells that are highly dependent on the nicotinamide adenine dinucleotide (NAD+) metabolite is a promising therapeutic strategy. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme catalyzing NAD⁺ production. Despite the high efficacy of several developed NAMPT inhibitors (i.e., FK866 (APO866)) in preclinical studies, their clinical activity was proven to be limited. Here, we report the synthesis of new NAMPT Inhibitors, JJ08, FEI191 and FEI199, which exhibit a broad anticancer activity in vitro. Results show that these compounds are potent NAMPT inhibitors that deplete NAD⁺ and NADP(H) after 24 h of drug treatment, followed by an increase in reactive oxygen species (ROS) accumulation. The latter event leads to ATP loss and mitochondrial depolarization with induction of apoptosis and necrosis. Supplementation with exogenous NAD⁺ precursors or catalase (ROS scavenger) abrogates the cell death induced by the new compounds. Finally, in vivo administration of the new NAMPT inhibitors in a mouse xenograft model of human Burkitt lymphoma delays tumor growth and significantly prolongs mouse survival. The most promising results are collected with JJ08, which completely eradicates tumor growth. Collectively, our findings demonstrate the efficient anticancer activity of the new NAMPT inhibitor JJ08 and highlight a strong interest for further evaluation of this compound in hematological malignancies.

Nicotinaldehyde, a Novel Precursor of NAD Biosynthesis, Abrogates the Anti-Cancer Activity of an NAD-Lowering Agent in Leukemia

Targeting NAD depletion in cancer cells has emerged as an attractive therapeutic strategy for cancer treatment, based on the higher reliance of malignant vs. healthy cells on NAD to sustain their aberrant proliferation and altered metabolism. NAD depletion is exquisitely observed when NAMPT, a key enzyme for the biosynthesis of NAD, is inhibited. Growing evidence suggests that alternative NAD sources present in a tumor environment can bypass NAMPT and render its inhibition ineffective. Here, we report the identification of nicotinaldehyde as a novel precursor that can be used for NAD biosynthesis by human leukemia cells. Nicotinaldehyde supplementation replenishes the intracellular NAD level in leukemia cells treated with NAMPT inhibitor APO866 and prevents APO866-induced oxidative stress, mitochondrial dysfunction and ATP depletion. We show here that NAD biosynthesis from nicotinaldehyde depends on NAPRT and occurs via the Preiss-Handler pathway. The availability of nicotinaldehyde in a tumor environment fully blunts the antitumor activity of APO866 in vitro and in vivo. This is the first study to report the role of nicotinaldehyde in the NAD-targeted anti-cancer treatment, highlighting the importance of the tumor metabolic environment in modulating the efficacy of NAD-lowering cancer therapy.

Synthesis and Evaluation of Reactive Oxygen Species Sensitive Prodrugs of a NAMPT Inhibitor FK866

NAMPT is an attractive target in cancer therapy and numerous NAMPT inhibitors have been developed. However, the clinical activities of NAMPT inhibitors have displayed disappointing results in clinical trials for their dose-limiting toxicities. In this study, reactive oxygen species (ROS)-responsive prodrugs of a NAMPT inhibitor FK866 were designed and synthesized. A short synthesis method was developed to shield the activity of FK866 through a quaternary ammonium connection. Two prodrugs, with boronic acid as a responsive group to ROS, were prepared and one of the prodrugs 122-066 also contained a fluorescence carrier. Both of the prodrugs released the active compound by the treatment of H₂O_2,, and the biological evaluation showed that they exhibited a higher potency in cells with high levels of ROS. Moreover, prodrug 122-066 had the ability to release FK866 and simultaneously induce the fluorescence activation under the stimulation of H₂O₂. This method has the potential to improve the therapeutic window of NAMPT inhibitors.

A Nicotinamide Phosphoribosyltransferase Inhibitor, FK866, Suppresses the Growth of Anaplastic Meningiomas and Inhibits Immune Checkpoint Expression by Regulating STAT1

Anaplastic meningioma is classified as a World Health Organization (WHO) grade III tumor and shows a strong tendency to recur. Although the incidence of anaplastic meningioma is low, the high rate of recurrence and death still makes treatment a challenge. A proteomics analysis was performed to investigate the differentially expressed proteins between anaplastic meningiomas and fibrous meningiomas by micro-LC-MS/MS. The key metabolic enzyme nicotinamide phosphoribosyltransferase (NAMPT) showed upregulated expression in anaplastic meningiomas. However, targeting NAMPT to treat anaplastic meningiomas has not been reported. In vitro, NAMPT inhibitor -FK866 reduced the viability of anaplastic meningiomas by inducing cell cycle arrest at the G2/M phase. Intriguingly, the NAMPT inhibitor -FK866 decreased the protein expression of immune checkpoints PD-L1 and B7-H3 by down-regulating the STAT1 and p-STAT1 expression in vitro. Furthermore, FK866 suppressed the growth of anaplastic meningiomas in an in vivo xenograft model. The expression of Ki-67 and immune checkpoint proteins (PD-L1 and B7-H3) showed significant differences between the group treated with FK866 and the control group treated with DMSO. In conclusion, the expression of NAMPT, which plays a crucial role in energy metabolism, was upregulated in anaplastic meningiomas. The NAMPT inhibitor -FK866 significantly suppressed the growth of anaplastic meningiomas in vitro and in vivo. More strikingly, FK866 potently inhibited immune checkpoint protein (PD-L1 and B7-H3) expression by regulating STAT1 in vitro and in vivo. Our results demonstrated that NAMPT inhibitors could potentially be an effective treatment method for patients suffering from anaplastic meningiomas.

Quantitative Analysis of Daporinad (FK866) and Its In Vitro and In Vivo Metabolite Identification Using Liquid Chromatography-Quadrupole-Time-of-Flight Mass Spectrometry

Daporinad (FK866) is one of the highly specific inhibitors of nicotinamide phosphoribosyl transferase (NAMPT) and known to have its unique mechanism of action that induces the tumor cell apoptosis. In this study, a simple and sensitive liquid chromatography–quadrupole-time-of-flight–mass spectrometric (LC-qTOF-MS) assay has been developed for the evaluation of drug metabolism and pharmacokinetics (DMPK) properties of Daporinad in mice. A simple protein precipitation method using acetonitrile (ACN) was used for the sample preparation and the pre-treated samples were separated by a C18 column. The calibration curve was evaluated in the range of 1.02~2220 ng/mL and the quadratic regression (weighted 1/concentration²) was used for the best fit of the curve with a correlation coefficient ≥ 0.99. The qualification run met the acceptance criteria of ±25% accuracy and precision values for QC samples. The dilution integrity was verified for 5, 10 and 30-fold dilution and the accuracy and precision of the dilution QC samples were also satisfactory within ±25% of the nominal values. The stability results indicated that Daporinad was stable for the following conditions: short-term (4 h), long-term (2 weeks), freeze/thaw (three cycles). This qualified method was successfully applied to intravenous (IV) pharmacokinetic (PK) studies of Daporinad in mice at doses of 5, 10 and 30 mg/kg. As a result, it showed a linear PK tendency in the dose range from 5 to 10 mg/kg, but a non-linear PK tendency in the dose of 30 mg/kg. In addition, in vitro and in vivo metabolite identification (Met ID) studies were conducted to understand the PK properties of Daporinad and the results showed that a total of 25 metabolites were identified as ten different types of metabolism in our experimental conditions. In conclusion, the LC-qTOF-MS assay was successfully developed for the quantification of Daporinad in mouse plasma as well as for its in vitro and in vivo metabolite identification.

NAD- and NADPH-Contributing Enzymes as Therapeutic Targets in Cancer: An Overview

Actively proliferating cancer cells require sufficient amount of NADH and NADPH for biogenesis and to protect cells from the detrimental effect of reactive oxygen species. As both normal and cancer cells share the same NAD biosynthetic and metabolic pathways, selectively lowering levels of NAD(H) and NADPH would be a promising strategy for cancer treatment. Targeting nicotinamide phosphoribosyltransferase (NAMPT), a rate limiting enzyme of the NAD salvage pathway, affects the NAD and NADPH pool. Similarly, lowering NADPH by mutant isocitrate dehydrogenase 1/2 (IDH1/2) which produces D-2-hydroxyglutarate (D-2HG), an oncometabolite that downregulates nicotinate phosphoribosyltransferase (NAPRT) via hypermethylation on the promoter region, results in epigenetic regulation. NADPH is used to generate D-2HG, and is also needed to protect dihydrofolate reductase, the target for methotrexate, from degradation. NAD and NADPH pools in various cancer types are regulated by several metabolic enzymes, including methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, and aldehyde dehydrogenase. Thus, targeting NAD and NADPH synthesis under special circumstances is a novel approach to treat some cancers. This article provides the rationale for targeting the key enzymes that maintain the NAD/NADPH pool, and reviews preclinical studies of targeting these enzymes in cancers.

Association of ABC Transporter With Resistance to FK866, a NAMPT Inhibitor, in Human Colorectal Cancer Cells

BACKGROUND/AIM

Nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme in the NAD⁺ biosynthetic pathway, is a drug target of potent anticancer candidates, including FK866 and other reported NAMPT inhibitors. However, it is known that NAMPT point-mutations render resistance to specific NAMPT inhibitors in several cancer cells. We investigated the resistance mechanisms of NAMPT inhibitor FK866 in human colorectal cancer (CRC) cells.

MATERIALS AND METHODS

We used CRC human cell line HCT116 to determine the expression profiles of FK866-sensitive parental HCT116 cells and FK866-resistant HCT116 (HCT116R^FK866) cells by DNA microarray analysis. The levels of multidrug resistance protein 1 (MDR1) were assessed via western blot. In addition, we analyzed the sensitivity of FK866 in parental HCT116 cells and HCT116R^FK866 cells by co-treatment with MDR1 inhibitor verapamil.

RESULTS

Our results revealed an association between ATP-binding cassette (ABC) transporter gene ABCB1 and resistance to NAMPT inhibitor FK866 in both HCT116R^FK866 cells and parental HCT116 cells. The expression of ABCB1, which encodes MDR1, was lower in HCT116R^FK866 cells than in parental HCT116 cells. Furthermore, the protein level of MDR1/ATP-binding cassette sub-family B member 1 (ABCB1) was 0.5-fold lower in HCT116R^FK866 cells than in parental HCT116 cells. Additionally, HCT116R^FK866 cells showed improved sensitivity to FK866 when co-treated with verapamil, an ABCB1 inhibitor. Interestingly, the efficacy of FK866 in parental HCT116 cells was the same for the treatment with FK866 alone or in combination with verapamil.

CONCLUSION

The change in expression of ABCB1 plays a key role in CRC drug resistance to NAMPT inhibitor FK866. This suggests that the MDR1/ABCB1 mechanism may regulate the resistance of anticancer NAMPT inhibitor FK866.

Genomic and tumor biological aspects of the anticancer nicotinamide phosphoribosyltransferase inhibitor FK866 in resistant human colorectal cancer cells

Cancer cells' resistance to drugs remains an important problem affecting cancer treatment strategies. We previously studied the nicotinamide phosphoribosyltransferase (NAMPT) inhibitor FK866's resistance mechanisms in the human colorectal cancer HCT116 cells. We established an acquired FK866-resistant cell line, HCT116R^FK866. In this study, we investigated gene mutations in parental HCT116 and HCT116R^FK866 cells using exome sequencing technology. The results indicated cluster genes related to NAD⁺ biosynthesis (including NAMPT), DNA repair, and ATP-binding cassette transporters were differentially altered in these cells. Interestingly, HCT116R^FK866 cells, which are resistant to other class NAMPT inhibitors, were more sensitive to the anticancer 5-fluorouracil and cisplatin and γ-ray irradiation compared to parental HCT116 cells. This higher sensitivity appears to cause a genetic change in the identified gene clusters by resistance to the NAMPT inhibitor FK866. Collectively, these novel findings provide a better understanding of anticancer candidate NAMPT inhibitors with regard to resistance mechanisms and cancer chemotherapy strategies.

Rho GTPase effectors and NAD metabolism in cancer immune suppression

INTRODUCTION

Sustained proliferative signaling and de-regulated cellular bioenergetics are two of the chief hallmarks of cancer. Alterations in the Ras pathway and its downstream effectors are among the major drivers for uncontrolled cell growth in many cancers. The GTPases are one of the signaling molecules that activate crucial signal transducing pathways downstream of Ras through several effector proteins. The GTPases (GTP bound) interact with several effectors and modulate a number of different biological pathways including those that regulate cytoskeleton, cellular motility, cytokinesis, proliferation, apoptosis, transcription and nuclear signaling. Similarly, the altered glycolytic pathway, the so-called 'Warburg effect', rewires tumor cell metabolism to support the biosynthetic requirements of uncontrolled proliferation. There exists strong evidence for the critical role of the glycolytic pathway's rate limiting enzymes in promoting immunosuppression. Areas covered: We review the emerging roles of GTPase effector proteins particularly the p21 activated kinase 4 (PAK4) and nicotinamide biosynthetic pathway enzyme nicotinamide phosphoribosyltransferase (NAMPT) as signaling molecules in immune surveillance and the immune response. Expert opinion: In this expert opinion article we highlight the recent information on the role of GTPases and the metabolic enzymes on the immune microenvironment and propose some unique immune therapeutic opportunities.

Novel NAPRT specific antibody identifies small cell lung cancer and neuronal cancers as promising clinical indications for a NAMPT inhibitor/niacin co-administration strategy

Tumor cells are particularly dependent on NAD⁺ due to higher rates of metabolism, DNA synthesis and repair. Nicotinamide phosphoribosyltransferase inhibitors (NAMPTis) inhibit NAD⁺ biosynthesis and represent promising new anti-cancer agents. However, clinical efficacy has been limited by toxicities demonstrating the need for drug combinations to broaden the therapeutic index. One potential combination involves niacin/NAMPTi co-administration. Niacin can rescue NAD⁺ biosynthesis through a parallel pathway that depends on nicotinic acid phosphoribosyltransferase (NAPRT) expression. Most normal tissues express NAPRT while a significant proportion of malignant cells do not, providing a possible selection marker for patients to achieve NAMPTi efficacy while minimizing toxicities.

Here we identify and validate a novel highly NAPRT-specific monoclonal antibody (3C6D2) that detects functional NAPRT in paraffin embedded tissue sections by immunohistochemistry (IHC). NAPRT detection by 3C6D2 coincides with the ability of niacin to rescue cells from NAMPTi induced cytotoxicity in cell lines and animal xenograft models. 3C6D2 binds to an epitope that is unique to NAPRT among phosphoribosyltransferases. In a series of primary tumor samples from lung and brain cancer patients, we demonstrate that >70 % of human small cell lung carcinomas, glioblastomas and oligodendrogliomas lack NAPRT identifying them as potentially suitable indications for the NAMPT/niacin combination.

NAMPT Inhibitor GMX1778 Enhances the Efficacy of 177Lu-DOTATATE Treatment of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) can be treated by peptide receptor radionuclide therapy using radiolabeled somatostatin analogs. However, the efficacy of such treatment is low and needs to be optimized. Our study evaluated the potential radiosensitizing effects of inhibition of nicotineamide phosphoribosyltransferase on ¹⁷⁷Lu-DOTATATE treatment in a NET model.

METHODS

Nude mice xenografted with the human NET cell line GOT1 were treated with semiefficient doses of ¹⁷⁷Lu-DOTATATE (7.5 MBq, intravenously) or the nicotineamide phosphoribosyltransferase inhibitor GMX1778 (100 mg/kg/wk, orally).

RESULTS

Median time to tumor progression (tumor volume larger than at day 0) was 3 d for controls, 7 d for single-dose GMX1778, 28 d for single-dose ¹⁷⁷Lu-DOTATATE, 35 d for 3 weekly doses of GMX1778, and 98 d for combined treatment with ¹⁷⁷Lu-DOTATATE and GMX1778 × 1. After ¹⁷⁷Lu-DOTATATE and 3 weekly doses of GMX1778, none of the tumors progressed within 120 d.

CONCLUSION

GMX1778 enhances the efficacy of ¹⁷⁷Lu-DOTATATE treatment and induces a prolonged antitumor response.