Anticancer agent CHS-828 inhibits cellular synthesis of NAD

A role for novel adipose tissue-secreted factors in obesity-related carcinogenesis

Obesity, a pandemic disease, is caused by an excessive accumulation of fat that can have detrimental effects on health. Adipose tissue plays a very important endocrine role, secreting different molecules that affect body physiology. In obesity, this function is altered, leading to a dysfunctional production of several factors, known as adipocytokines. This process has been linked to various comorbidities associated with obesity, such as carcinogenesis. In fact, several classical adipocytokines with increased levels in obesity have been demonstrated to exert a pro-carcinogenic role, including leptin, TNF-α, IL-6 and resistin, whereas others like adiponectin, with decreased levels in obesity, might have an anti-carcinogenic function. In this expanding field, new proteomic techniques and approaches have allowed the identification of novel adipocytokines, a number of which exhibit an altered production in obesity and type 2 diabetes and thus are related to adiposity. Many of these novel adipocytokines have also been identified in various tumour types, such as that of the breast, liver or endometrium, thereby increasing the list of potential contributors to carcinogenesis. This review is focused on the regulation of these novel adipocytokines by obesity, including apelin, endotrophin, FABP4, lipocalin 2, omentin-1, visfatin, chemerin, ANGPTL2 or osteopontin, emphasizing its involvement in tumorigenesis.

Physiological and pathophysiological roles of NAMPT and NAD metabolism

Nicotinamide phosphoribosyltransferase (NAMPT) is a regulator of the intracellular nicotinamide adenine dinucleotide (NAD) pool. NAD is an essential coenzyme involved in cellular redox reactions and is a substrate for NAD-dependent enzymes. In various metabolic disorders and during ageing, levels of NAD are decreased. Through its NAD-biosynthetic activity, NAMPT influences the activity of NAD-dependent enzymes, thereby regulating cellular metabolism. In addition to its enzymatic function, extracellular NAMPT (eNAMPT) has cytokine-like activity. Abnormal levels of eNAMPT are associated with various metabolic disorders. NAMPT is able to modulate processes involved in the pathogenesis of obesity and related disorders such as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) by influencing the oxidative stress response, apoptosis, lipid and glucose metabolism, inflammation and insulin resistance. NAMPT also has a crucial role in cancer cell metabolism, is often overexpressed in tumour tissues and is an experimental target for antitumour therapies. In this Review, we discuss current understanding of the functions of NAMPT and highlight progress made in identifying the physiological role of NAMPT and its relevance in various human diseases and conditions, such as obesity, NAFLD, T2DM, cancer and ageing.

Combinative effects of β-Lapachone and APO866 on pancreatic cancer cell death through reactive oxygen species production and PARP-1 activation

Pancreatic cancer (PC) is one of the most lethal human malignancies and a major health problem. Patients diagnosed with PC and treated with conventional approaches have an overall 5-year survival rate of less than 5%. Novel strategies are needed to treat this disease. Herein, we propose a combinatorial strategy that targets two unrelated metabolic enzymes overexpressed in PC cells:

NAD(P)H

quinone oxidoreductase-1 (NQO1) and nicotinamide phosphoribosyl transferase (NAMPT) using β-lapachone (BL) and APO866, respectively. We show that BL tremendously enhances the antitumor activity of APO866 on various PC cell lines without affecting normal cells, in a PARP-1 dependent manner. The chemopotentiation of APO866 with BL was characterized by the following: (i) nicotinamide adenine dinucleotide (NAD) depletion; (ii) catalase (CAT) degradation; (iii) excessive H2O2 production; (iv) dramatic drop of mitochondrial membrane potential (MMP); and finally (v) autophagic-associated cell death. H2O2 production, loss of MMP and cell death (but not NAD depletion) were abrogated by exogenous supplementation with CAT or pharmacological or genetic inhibition of PARP-1. Our data demonstrates that the combination of a non-lethal dose of BL and low dose of APO866 optimizes significantly cell death on various PC lines over both compounds given separately and open new and promising combination in PC therapy.

New strategies to maximize therapeutic opportunities for NAMPT inhibitors in oncology

Nicotinamide phosphoribosyltransferase (NAMPT) is crucial for nicotinamide adenine dinucleotide (NAD(+)) biosynthesis in mammalian cells. NAMPT inhibitors represent multifunctional anticancer agents that act on NAD(+) metabolism to shut down glycolysis, nucleotide biosynthesis, and ATP generation and act indirectly as PARP and sirtuin inhibitors. The selectivity of NAMPT inhibitors preys on the increased metabolic requirements to replenish NAD(+) in cancer cells. Although initial clinical studies with NAMPT inhibitors did not achieve single-agent therapeutic levels before dose-limiting toxicities were reached, a new understanding of alternative rescue pathways and a biomarker that can be used to select patients provides new opportunities to widen the therapeutic window and achieve efficacious doses in the clinic. Recent work has also illustrated the potential for drug combination strategies to further enhance the therapeutic opportunities. This review summarizes recent discoveries in NAD(+)/NAMPT inhibitor biology in the context of exploiting this new knowledge to optimize the clinical outcomes for this promising new class of agents.

Inhibition of Nicotinamide Phosphoribosyltransferase (NAMPT), an Enzyme Essential for NAD+ Biosynthesis, Leads to Altered Carbohydrate Metabolism in Cancer Cells

Nicotinamide phosphoribosyltransferase (NAMPT) has been extensively studied due to its essential role in NAD(+) biosynthesis in cancer cells and the prospect of developing novel therapeutics. To understand how NAMPT regulates cellular metabolism, we have shown that the treatment with FK866, a specific NAMPT inhibitor, leads to attenuation of glycolysis by blocking the glyceraldehyde 3-phosphate dehydrogenase step (Tan, B., Young, D. A., Lu, Z. H., Wang, T., Meier, T. I., Shepard, R. L., Roth, K., Zhai, Y., Huss, K., Kuo, M. S., Gillig, J., Parthasarathy, S., Burkholder, T. P., Smith, M. C., Geeganage, S., and Zhao, G. (2013) Pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), an enzyme essential for NAD(+) biosynthesis, in human cancer cells: metabolic basis and potential clinical implications. J. Biol. Chem. 288, 3500-3511). Due to technical limitations, we failed to separate isotopomers of phosphorylated sugars. In this study, we developed an enabling LC-MS methodology. Using this, we confirmed the previous findings and also showed that NAMPT inhibition led to accumulation of fructose 1-phosphate and sedoheptulose 1-phosphate but not glucose 6-phosphate, fructose 6-phosphate, and sedoheptulose 7-phosphate as previously thought. To investigate the metabolic basis of the metabolite formation, we carried out biochemical and cellular studies and established the following. First, glucose-labeling studies indicated that fructose 1-phosphate was derived from dihydroxyacetone phosphate and glyceraldehyde, and sedoheptulose 1-phosphate was derived from dihydroxyacetone phosphate and erythrose via an aldolase reaction. Second, biochemical studies showed that aldolase indeed catalyzed these reactions. Third, glyceraldehyde- and erythrose-labeling studies showed increased incorporation of corresponding labels into fructose 1-phosphate and sedoheptulose 1-phosphate in FK866-treated cells. Fourth, NAMPT inhibition led to increased glyceraldehyde and erythrose levels in the cell. Finally, glucose-labeling studies showed accumulated fructose 1,6-bisphosphate in FK866-treated cells mainly derived from dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Taken together, this study shows that NAMPT inhibition leads to attenuation of glycolysis, resulting in further perturbation of carbohydrate metabolism in cancer cells. The potential clinical implications of these findings are also discussed.

Secretion of one adipokine Nampt/Visfatin suppresses the inflammatory stress-induced NF-κB activity and affects Nampt-dependent cell viability in Huh-7 cells

Nampt/visfatin acts in both intracellular and extracellular compartments to regulate multiple biological roles, including NAD metabolism, cancer, inflammation, and senescence. However, its function in chronic inflammation and carcinogenesis in hepatocellular carcinoma (HCC) has not been well-defined. Here we use Huh-7 hepatoma cells as a model to determine how Nampt/visfatin affects cellular survival under oxidative stress. We found that the transition of Nampt/visfatin from intracellular into extracellular form was induced by H₂O₂ treatment in 293T cells and confirmed that this phenomenon was not due to cell death but through the secretion of Nampt/visfatin. In addition, Nampt/visfatin suppressed cell viability in oxidative treatment in Huh-7 cells and acted on the inhibition of hepatoma cell growth. Oxidative stress also reduced the Nampt-mediated activation of NF-κB gene expression. In this study, we identify a novel feature of Nampt/visfatin which functions as an adipokine that can be secreted upon cellular stress. Our results provide an example to understand how adipokine interacts with chemotherapeutic treatment by oxidative stress in HCC.

Metabolomics analysis of metabolic effects of nicotinamide phosphoribosyltransferase (NAMPT) inhibition on human cancer cells

Nicotinamide phosphoribosyltransferase (NAMPT) plays an important role in cellular bioenergetics. It is responsible for converting nicotinamide to nicotinamide adenine dinucleotide, an essential molecule in cellular metabolism. NAMPT has been extensively studied over the past decade due to its role as a key regulator of nicotinamide adenine dinucleotide–consuming enzymes. NAMPT is also known as a potential target for therapeutic intervention due to its involvement in disease. In the current study, we used a global mass spectrometry–based metabolomic approach to investigate the effects of FK866, a small molecule inhibitor of NAMPT currently in clinical trials, on metabolic perturbations in human cancer cells. We treated A2780 (ovarian cancer) and HCT-116 (colorectal cancer) cell lines with FK866 in the presence and absence of nicotinic acid. Significant changes were observed in the amino acids metabolism and the purine and pyrimidine metabolism. We also observed metabolic alterations in glycolysis, the citric acid cycle (TCA), and the pentose phosphate pathway. To expand the range of the detected polar metabolites and improve data confidence, we applied a global metabolomics profiling platform by using both non-targeted and targeted hydrophilic (HILIC)-LC-MS and GC-MS analysis. We used Ingenuity Knowledge Base to facilitate the projection of metabolomics data onto metabolic pathways. Several metabolic pathways showed differential responses to FK866 based on several matches to the list of annotated metabolites. This study suggests that global metabolomics can be a useful tool in pharmacological studies of the mechanism of action of drugs at a cellular level.

Depletion of the central metabolite NAD leads to oncosis-mediated cell death

Depletion of the central metabolite NAD in cells results in broad metabolic defects leading to cell death and is a proposed novel therapeutic strategy in oncology. There is, however, a limited understanding of the underlying mechanisms that connect disruption of this central metabolite with cell death. Here we utilize GNE-617, a small molecule inhibitor of NAMPT, a rate-limiting enzyme required for NAD generation, to probe the pathways leading to cell death following NAD depletion. In all cell lines examined, NAD was rapidly depleted (average t½ of 8.1 h) following NAMPT inhibition. Concurrent with NAD depletion, there was a decrease in both cell proliferation and motility, which we attribute to reduced activity of NAD-dependent deacetylases because cells fail to deacetylate α-tubulin-K40 and histone H3-K9. Following depletion of NAD by >95%, cells lose the ability to regenerate ATP. Cell lines with a slower rate of ATP depletion (average t½ of 45 h) activate caspase-3 and show evidence of apoptosis and autophagy, whereas cell lines with rapid depletion ATP (average t½ of 32 h) do not activate caspase-3 or show signs of apoptosis or autophagy. However, the predominant form of cell death in all lines is oncosis, which is driven by the loss of plasma membrane homeostasis once ATP levels are depleted by >20-fold. Thus, our work illustrates the sequence of events that occurs in cells following depletion of a key metabolite and reveals that cell death caused by a loss of NAD is primarily driven by the inability of cells to regenerate ATP.

Nicotinamide phosphoribosyltransferase promotes epithelial-to-mesenchymal transition as a soluble factor independent of its enzymatic activity

Boosting NAD(+) biosynthesis with NAD(+) intermediates has been proposed as a strategy for preventing and treating age-associated diseases, including cancer. However, concerns in this area were raised by observations that nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme in mammalian NAD(+) biosynthesis, is frequently up-regulated in human malignancies, including breast cancer, suggesting possible protumorigenic effects for this protein. We addressed this issue by studying NAMPT expression and function in human breast cancer in vivo and in vitro. Our data indicate that high NAMPT levels are associated with aggressive pathological and molecular features, such as estrogen receptor negativity as well as HER2-enriched and basal-like PAM50 phenotypes. Consistent with these findings, we found that NAMPT overexpression in mammary epithelial cells induced epithelial-to-mesenchymal transition, a morphological and functional switch that confers cancer cells an increased metastatic potential. However, importantly, NAMPT-induced epithelial-to-mesenchymal transition was found to be independent of NAMPT enzymatic activity and of the NAMPT product nicotinamide mononucleotide. Instead, it was mediated by secreted NAMPT through its ability to activate the TGFβ signaling pathway via increased TGFβ1 production. These findings have implications for the design of therapeutic strategies exploiting NAD(+) biosynthesis via NAMPT in aging and cancer and also suggest the potential of anticancer agents designed to specifically neutralize extracellular NAMPT. Notably, because high levels of circulating NAMPT are found in obese and diabetic patients, our data could also explain the increased predisposition to cancer of these subjects.

NAMPT is the cellular target of STF-31-like small-molecule probes

The small-molecule probes STF-31 and its analogue compound 146 were discovered while searching for compounds that kill VHL-deficient renal cell carcinoma cell lines selectively and have been reported to act via direct inhibition of the glucose transporter GLUT1. We profiled the sensitivity of 679 cancer cell lines to STF-31 and found that the pattern of response is tightly correlated with sensitivity to three different inhibitors of nicotinamide phosphoribosyltransferase (NAMPT). We also performed whole-exome next-generation sequencing of compound 146-resistant HCT116 clones and identified a recurrent NAMPT-H191R mutation. Ectopic expression of NAMPT-H191R conferred resistance to both STF-31 and compound 146 in cell lines. We further demonstrated that both STF-31 and compound 146 inhibit the enzymatic activity of NAMPT in a biochemical assay in vitro. Together, our cancer-cell profiling and genomic approaches identify NAMPT inhibition as a critical mechanism by which STF-31-like compounds inhibit cancer cells.

A rise in NAD precursor nicotinamide mononucleotide (NMN) after injury promotes axon degeneration

NAD metabolism regulates diverse biological processes, including ageing, circadian rhythm and axon survival. Axons depend on the activity of the central enzyme in NAD biosynthesis, nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2), for their maintenance and degenerate rapidly when this activity is lost. However, whether axon survival is regulated by the supply of NAD or by another action of this enzyme remains unclear. Here we show that the nucleotide precursor of NAD, nicotinamide mononucleotide (NMN), accumulates after nerve injury and promotes axon degeneration. Inhibitors of NMN-synthesising enzyme NAMPT confer robust morphological and functional protection of injured axons and synapses despite lowering NAD. Exogenous NMN abolishes this protection, suggesting that NMN accumulation within axons after NMNAT2 degradation could promote degeneration. Ectopic expression of NMN deamidase, a bacterial NMN-scavenging enzyme, prolongs survival of injured axons, providing genetic evidence to support such a mechanism. NMN rises prior to degeneration and both the NAMPT inhibitor FK866 and the axon protective protein Wld^S prevent this rise. These data indicate that the mechanism by which NMNAT and the related Wld^S protein promote axon survival is by limiting NMN accumulation. They indicate a novel physiological function for NMN in mammals and reveal an unexpected link between new strategies for cancer chemotherapy and the treatment of axonopathies.

Structural basis for resistance to diverse classes of NAMPT inhibitors

Inhibiting NAD biosynthesis by blocking the function of nicotinamide phosphoribosyl transferase (NAMPT) is an attractive therapeutic strategy for targeting tumor metabolism. However, the development of drug resistance commonly limits the efficacy of cancer therapeutics. This study identifies mutations in NAMPT that confer resistance to a novel NAMPT inhibitor, GNE-618, in cell culture and in vivo, thus demonstrating that the cytotoxicity of GNE-618 is on target. We determine the crystal structures of six NAMPT mutants in the apo form and in complex with various inhibitors and use cellular, biochemical and structural data to elucidate two resistance mechanisms. One is the surprising finding of allosteric modulation by mutation of residue Ser165, resulting in unwinding of an α-helix that binds the NAMPT substrate 5-phosphoribosyl-1-pyrophosphate (PRPP). The other mechanism is orthosteric blocking of inhibitor binding by mutations of Gly217. Furthermore, by evaluating a panel of diverse small molecule inhibitors, we unravel inhibitor structure activity relationships on the mutant enzymes. These results provide valuable insights into the design of next generation NAMPT inhibitors that offer improved therapeutic potential by evading certain mechanisms of resistance.

Fragment-based identification of amides derived from trans-2-(pyridin-3-yl)cyclopropanecarboxylic acid as potent inhibitors of human nicotinamide phosphoribosyltransferase (NAMPT)

Potent, trans-2-(pyridin-3-yl)cyclopropanecarboxamide-containing inhibitors of the human nicotinamide phosphoribosyltransferase (NAMPT) enzyme were identified using fragment-based screening and structure-based design techniques. Multiple crystal structures were obtained of initial fragment leads, and this structural information was utilized to improve the biochemical and cell-based potency of the associated molecules. Many of the optimized compounds exhibited nanomolar antiproliferative activities against human tumor lines in in vitro cell culture experiments. In a key example, a fragment lead (13, KD = 51 μM) was elaborated into a potent NAMPT inhibitor (39, NAMPT IC50 = 0.0051 μM, A2780 cell culture IC50 = 0.000 49 μM) which demonstrated encouraging in vivo efficacy in an HT-1080 mouse xenograft tumor model.

NAD⁺ depletion by APO866 in combination with radiation in a prostate cancer model, results from an in vitro and in vivo study

BACKGROUND

APO866 is a highly specific inhibitor of nicotinamide phosphoribosyltransferase (NAMPT), inhibition of which reduces cellular NAD(+) levels. In this study we addressed the potential of NAD(+) depletion as an anti-cancer strategy and assessed the combination with radiation.

METHODS

The anticipated radiosensitizing property of APO866 was investigated in prostate cancer cell lines PC3 and LNCaP in vitro and in PC3 xenografts in vivo.

RESULTS

We show that APO866 treatment leads to NAD(+) depletion. Combination experiments with radiation lead to a substantial decrease in clonogenic cell survival in PC3 and LNCaP cells. In PC3 xenografts, treatment with APO866 resulted in reduced intratumoral NAD(+) levels and induced significant tumor growth delay. Combined treatment of APO866 and fractionated radiation was more effective than the single modalities. Compared with untreated tumors, APO866 and radiation alone resulted in tumor growth delays of 14 days and 33 days, respectively, whereas the combination showed a significantly increased tumor growth delay of 65 days.

CONCLUSIONS

Our studies show that APO866-induced NAD(+) depletion enhances radiation responses in tumor cell survival in prostate cancer. However, the in vitro data do not reveal a solid cellular mechanism to exploit further clinical development at this moment.

Nicotinamide phosphoribosyltransferase inhibitors, design, preparation, and structure-activity relationship

Existing pharmacological inhibitors for nicotinamide phosphoribosyltransferase (NAMPT) are promising therapeutics for treating cancer. By using medicinal and computational chemistry methods, the structure-activity relationship for novel classes of NAMPT inhibitors is described, and the compounds are optimized. Compounds are designed inspired by the NAMPT inhibitor APO866 and cyanoguanidine inhibitor scaffolds. In comparison with recently published derivatives, the new analogues exhibit an equally potent antiproliferative activity in vitro and comparable activity in vivo. The best performing compounds from these series showed subnanomolar antiproliferative activity toward a series of cancer cell lines (compound 15: IC50 0.025 and 0.33 nM, in A2780 (ovarian carcinoma) and MCF-7 (breast), respectively) and potent antitumor in vivo activity in well-tolerated doses in a xenograft model. In an A2780 xenograft mouse model with large tumors (500 mm(3)), compound 15 reduced the tumor volume to one-fifth of the starting volume at a dose of 3 mg/kg administered ip, bid, days 1-9. Thus, compounds found in this study compared favorably with compounds already in the clinic and warrant further investigation as promising lead molecules for the inhibition of NAMPT.

Next-generation NAMPT inhibitors identified by sequential high-throughput phenotypic chemical and functional genomic screens

Phenotypic high-throughput chemical screens allow for discovery of small molecules that modulate complex phenotypes and provide lead compounds for novel therapies; however, identification of the mechanistically relevant targets remains a major experimental challenge. We report the application of sequential unbiased high-throughput chemical and ultracomplex small hairpin RNA (shRNA) screens to identify a distinctive class of inhibitors that target nicotinamide phosphoribosyl transferase (NAMPT), a rate-limiting enzyme in the biosynthesis of nicotinamide adenine dinucleotide, a crucial cofactor in many biochemical processes. The lead compound STF-118804 is a highly specific NAMPT inhibitor, improves survival in an orthotopic xenotransplant model of high-risk acute lymphoblastic leukemia, and targets leukemia stem cells. Tandem high-throughput screening using chemical and ultracomplex shRNA libraries, therefore, provides a rapid chemical genetics approach for seamless progression from small-molecule lead identification to target discovery and validation.

Loss of NAPRT1 expression by tumor-specific promoter methylation provides a novel predictive biomarker for NAMPT inhibitors

PURPOSE

We sought to identify predictive biomarkers for a novel nicotinamide phosphoribosyltransferase (NAMPT) inhibitor.

EXPERIMENTAL DESIGN

We use a NAMPT inhibitor, GNE-617, to evaluate nicotinic acid rescue status in a panel of more than 400 cancer cell lines. Using correlative analysis and RNA interference (RNAi), we identify a specific biomarker for nicotinic acid rescue status. We next determine the mechanism of regulation of expression of the biomarker. Finally, we develop immunohistochemical (IHC) and DNA methylation assays and evaluate cancer tissue for prevalence of the biomarker across indications.

RESULTS

Nicotinate phosphoribosyltransferase (NAPRT1) is necessary for nicotinic acid rescue and its expression is the major determinant of rescue status. We demonstrate that NAPRT1 promoter methylation accounts for NAPRT1 deficiency in cancer cells, and NAPRT1 methylation is predictive of rescue status in cancer cell lines. Bisulfite next-generation sequencing mapping of the NAPRT1 promoter identified tumor-specific sites of NAPRT1 DNA methylation and enabled the development of a quantitative methylation-specific PCR (QMSP) assay suitable for use on archival formalin-fixed paraffin-embedded tumor tissue.

CONCLUSIONS

Tumor-specific promoter hypermethylation of NAPRT1 inactivates one of two NAD salvage pathways, resulting in synthetic lethality with the coadministration of a NAMPT inhibitor. NAPRT1 expression is lost due to promoter hypermethylation in most cancer types evaluated at frequencies ranging from 5% to 65%. NAPRT1-specific immunohistochemical or DNA methylation assays can be used on archival formalin paraffin-embedded cancer tissue to identify patients likely to benefit from coadministration of a Nampt inhibitor and nicotinic acid.

Interplay of adipokines and myokines in cancer pathophysiology: Emerging therapeutic implications

Excess body weight constitutes a worldwide health problem with epidemic proportions impacting on the risk and prognosis of several disease states including malignancies. It is believed that the metabolic changes associated with weight gain, particularly visceral obesity, and physical inactivity could lead to dysfunctional adipose and muscle tissues causing insulin resistance, low-grade chronic inflammation and abnormal secretion of adipokines and myokines. The complex paracrine and endocrine interconnection between adipokines and myokines reflects a yin-yang balance with important implications in processes such as lipolysis control, insulin sensitivity and prevention from obesity-driven chronic low-grade inflammation and cancer promotion through anti-inflammatory adipokines and myokines. Furthermore, the complex pathophysiology of cancer cachexia is based on the interplay between muscle and adipose tissue mediated by free fatty acids, various adipokines and myokines. The purpose of this editorial is to explore the role of the adipose and muscle tissue interplay in carcinogenesis, cancer progression and cachexia, and to examine the mechanisms underpinning their association with malignancy. Understanding of the mechanisms connecting the interplay of adipokines and myokines with cancer pathophysiology is expected to be of importance in the development of therapeutic strategies against cancer cachexia. Advances in the field of translational investigation may lead to tangible benefits to obese and inactive persons who are at increased risk of cancer as well as to cancer patients with cachexia.

Medicinal chemistry of nicotinamide phosphoribosyltransferase (NAMPT) inhibitors

Nicotinamide phoshophoribosyltransferase (NAMPT) plays a key role in the replenishment of the NAD pool in cells. This in turn makes this enzyme an important player in bioenergetics and in the regulation of NAD-using enzymes, such as PARPs and sirtuins. Furthermore, there is now ample evidence that NAMPT is secreted and has a role as a cytokine. An important role of either the intracellular or extracellular form of NAMPT has been shown in cancer, inflammation, and metabolic diseases. The first NAMPT inhibitors (FK866 and CHS828) have already entered clinical trials, and a surge in interest in the synthesis of novel molecules has occurred. The present review summarizes the recent progress in this field.

Biological activities of guanidine compounds, 2008 - 2012 update

INTRODUCTION

Compounds incorporating guanidine moiety have found many practical applications in diverse areas of chemistry, such as nucleophilic organocatalysis, anion recognition and coordination chemistry. Moreover, guanidine functional group is found in natural products, pharmaceuticals and cosmetic ingredients produced by synthetic methods. Thus, knowledge of their biological activities and therapeutic uses is of utmost importance for researchers involved in drug discovery processes.

AREAS COVERED

In this review the authors highlight the continued development and therapeutic applications of newly synthesized guanidine-containing compounds including small peptides and peptidomimetics incorporating arginine. The review presents patents and patent applications filed in the years 2008 - 2012 with emphasis placed on new mechanisms of pharmacological action of guanidine derivatives.

EXPERT OPINION

While guanidines are often thought of as strong organic bases and compounds hydrophilic in nature, over the last 4 years there has been an enormous increase in discovery of new promising lead structures with guanidine core, suitable for development of potential drugs acting at central nervous system, anti-inflammatory agents, anti-diabetic and chemotherapeutic agents as well as cosmetics.

Radionuclide therapy via SSTR: future aspects from experimental animal studies

There is need for better therapeutic options for neuroendocrine tumours. The aim of this review was to summarize results of experimental animal studies and raise ideas for future radionuclide therapy based on high expression of somatostatin (SS) receptors by many neuroendocrine tumours. In summary, one of the major options is individualized treatment for each patient, including choice of SS analogues, radionuclides and treatment schedules. Other options are methods to increase the treatment effect on tumour tissue (increasing tumour uptake and retention by upregulation of receptor expression and avoiding saturation of receptor binding), methods to increase the tumour tissue response (by choice of radionuclides, SS analogues or combined therapies), and methods to reduce side effects (diminished uptake and retention in critical organs and reduced normal tissue response). Furthermore, combination therapy with other radiopharmaceuticals, cytotoxic drugs or radiosensitizers can be considered to enhance the effects of radiolabelled SS analogues.

Pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), an enzyme essential for NAD+ biosynthesis, in human cancer cells: metabolic basis and potential clinical implications

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first rate-limiting step in converting nicotinamide to NAD(+), essential for cellular metabolism, energy production, and DNA repair. NAMPT has been extensively studied because of its critical role in these cellular processes and the prospect of developing therapeutics against the target, yet how it regulates cellular metabolism is not fully understood. In this study we utilized liquid chromatography-mass spectrometry to examine the effects of FK866, a small molecule inhibitor of NAMPT currently in clinical trials, on glycolysis, the pentose phosphate pathway, the tricarboxylic acid (TCA) cycle, and serine biosynthesis in cancer cells and tumor xenografts. We show for the first time that NAMPT inhibition leads to the attenuation of glycolysis at the glyceraldehyde 3-phosphate dehydrogenase step due to the reduced availability of NAD(+) for the enzyme. The attenuation of glycolysis results in the accumulation of glycolytic intermediates before and at the glyceraldehyde 3-phosphate dehydrogenase step, promoting carbon overflow into the pentose phosphate pathway as evidenced by the increased intermediate levels. The attenuation of glycolysis also causes decreased glycolytic intermediates after the glyceraldehyde 3-phosphate dehydrogenase step, thereby reducing carbon flow into serine biosynthesis and the TCA cycle. Labeling studies establish that the carbon overflow into the pentose phosphate pathway is mainly through its non-oxidative branch. Together, these studies establish the blockade of glycolysis at the glyceraldehyde 3-phosphate dehydrogenase step as the central metabolic basis of NAMPT inhibition responsible for ATP depletion, metabolic perturbation, and subsequent tumor growth inhibition. These studies also suggest that altered metabolite levels in tumors can be used as robust pharmacodynamic markers for evaluating NAMPT inhibitors in the clinic.

Regulation of cell survival and death by pyridine nucleotides

Pyridine nucleotides (PNs), such as NAD(H) and NADP(H), mediate electron transfer in many catabolic and anabolic processes. In general, NAD(+) and NADP(+) receive electrons to become NADH and NADPH by coupling with catabolic processes. These electrons are utilized for biologically essential reactions such as ATP production, anabolism and cellular oxidation-reduction (redox) regulation. Thus, in addition to ATP, NADH and NADPH could be defined as high-energy intermediates and "molecular units of currency" in energy transfer. We discuss the significance of PNs as energy/electron transporters and signal transducers, in regulating cell death and/or survival processes. In the first part of this review, we describe the role of NADH and NADPH as electron donors for NADPH oxidases (Noxs), glutathione (GSH), and thioredoxin (Trx) systems in cellular redox regulation. Noxs produce superoxide/hydrogen peroxide yielding oxidative environment, whereas GSH and Trx systems protect against oxidative stress. We then describe the role of NAD(+) and NADH as signal transducers through NAD(+)-dependent enzymes such as PARP-1 and Sirt1. PARP-1 is activated by damaged DNA in order to repair the DNA, which attenuates energy production through NAD(+) consumption; Sirt1 is activated by an increased NAD(+)/NADH ratio to facilitate signal transduction for metabolic adaption as well as stress responses. We conclude that PNs serve as an important interface for distinct cellular responses, including stress response, energy metabolism, and cell survival/death.

Nicotinamide phosphoribosyl-transferase/visfatin: a missing link between overweight/obesity and postmenopausal breast cancer? Potential preventive and therapeutic perspectives and challenges

Worldwide breast cancer (BC) constitutes a significant public health concern. Excess body weight is associated with postmenopausal BC (PBC) risk. Recent studies have shown that the constellation of obesity, insulin resistance and serum adipokine levels are associated with the risk and prognosis of PBC. Nicotinamide phosphoribosyl-transferase (Nampt), also known as visfatin and pre-B-cell-colony-enhancing factor, found in the visceral fat, represents a novel pleiotropic adipokine acting as a cytokine, a growth factor and an enzyme. It plays an important role in a variety of metabolic and stress responses as well as in the cellular energy metabolism, particularly NAD biosynthesis. Nampt exhibits proliferative, anti-apoptotic, pro-inflammatory and pro-angiogenic properties. Nampt's insulin-mimetic function remains a controversial issue. Circulating Nampt levels are increased in obese women. Also, Nampt levels are significantly elevated in women suffering from PBC than in healthy controls independently from known risk factors of BC, anthropometric and metabolic parameters as well as serum concentrations of well known adipokines. High expression of Nampt in BC tissues was reported to be associated with more malignant cancer behavior as well as adverse prognosis. Taking into account the mitogenicity of Nampt as well as its proliferative, anti-apoptotic and pro-angiogenic properties, a novel hypothesis is proposed whereas Nampt may be involved in the etiopathogenesis of PBC and may represent a missing link between overweight/obesity and PBC. Nampt could exert its effects on the normal and neoplastic mammary tissue by endocrine and paracrine mechanisms; Nampt could also be secreted by tumor epithelial cells in an autocrine manner. It could stimulate mammary epithelial cell proliferation, invasion, metastasis, and angiogenesis, which is essential for BC development and progression. Serum Nampt might be a novel risk factor as well as a potential diagnostic and prognostic biomarker in PBC. In addition, pharmacologic agents that neutralize biochemically Nampt or medications that decrease Nampt levels or downregulate signaling pathways downstream of Nampt may prove to be useful anti-cancer agents. The potential harmful effect on PBC risk due to vitamin B3 (nicotinic acid, a natural NAD precursor in the biosynthetic route leading to NAD) intake is speculated for the first time. In this hypothesis, the role of Nampt in BC carcinogenesis and progression is explored as well as the pathophysiological mechanisms that underlie the association between Nampt and PBC in the context of a dysfunctional adipose tissue in obesity. Understanding of these mechanisms may be important for the development of preventive and therapeutic strategies against PBC.

Nicotinamide phosphoribosyl transferase (Nampt) is required for de novo lipogenesis in tumor cells

Tumor cells have increased metabolic requirements to maintain rapid growth. In particular, a highly lipogenic phenotype is a hallmark of many tumor types, including prostate. Cancer cells also have increased turnover of nicotinamide adenine dinucleotide (NAD⁺), a coenzyme involved in multiple metabolic pathways. However, a specific role for NAD⁺ in tumor cell lipogenesis has yet to be described. Our studies demonstrate a novel role for the NAD⁺-biosynthetic enzyme Nicotinamide phosphoribosyltransferase (Nampt) in maintaining de novo lipogenesis in prostate cancer (PCa) cells. Inhibition of Nampt reduces fatty acid and phospholipid synthesis. In particular, short chain saturated fatty acids and the phosphatidylcholine (PC) lipids into which these fatty acids are incorporated were specifically reduced by Nampt inhibition. Nampt blockade resulted in reduced ATP levels and concomitant activation of AMP-activated protein kinase (AMPK) and phosphorylation of acetyl-CoA carboxylase (ACC). In spite of this, pharmacological inhibition of AMPK was not sufficient to fully restore fatty acid synthesis. Rather, Nampt blockade also induced protein hyperacetylation in PC-3, DU145, and LNCaP cells, which correlated with the observed decreases in lipid synthesis. Moreover, the sirtuin inhibitor Sirtinol, and the simultaneous knockdown of SIRT1 and SIRT3, phenocopied the effects of Nampt inhibition on fatty acid synthesis. Altogether, these data reveal a novel role for Nampt in the regulation of de novo lipogenesis through the modulation of sirtuin activity in PCa cells.

Elevated serum visfatin/nicotinamide phosphoribosyl-transferase levels are associated with risk of postmenopausal breast cancer independently from adiponectin, leptin, and anthropometric and metabolic parameters

OBJECTIVE

Obesity has been implicated in the etiology of postmenopausal breast cancer (PBC). We hypothesized that altered secretion of visfatin may underlie this association. We thus investigated the association of serum visfatin with PBC risk, taking into account known risk factors including adipokines and anthropometric and metabolic parameters.

METHODS

In a case-control study, we studied 102 postmenopausal women with pathologically confirmed, incident invasive breast cancer and 102 control women matched on age and time of diagnosis between 2003 and 2010 at Army Share Fund Hospital, Veterans' Hospital (NIMTS). Levels of serum visfatin, adiponectin, leptin, metabolic parameters, carcinoembryonic antigen, and CA 15-3 were determined.

RESULTS

The mean serum visfatin level was significantly higher in case than in control participants (P < 0.001). Women in the highest quartile of visfatin concentration presented significantly higher odds for PBC, adjusting for age, date of diagnosis, education, body mass index, waist circumference, years with menstruation, parity/age at first full-term pregnancy, breast-feeding, family history of cancer, use of exogenous hormones, alcohol consumption, smoking status, homeostasis model assessment score, and serum leptin and adiponectin concentrations (odds ratio, 7.93; 95% CI, 2.52-24.9). In case participants, the visfatin level correlated significantly with the tumor marker CA 15-3 (P = 0.03) but not with metabolic and anthropometric variables (P > 0.05).

CONCLUSIONS

Further prospective studies are needed to determine whether an elevated serum visfatin level is implicated in the etiopathogenesis of PBC or reflects changes during PBC progression and could therefore be used as a biomarker for PBC.

Could serum visfatin be a potential biomarker for postmenopausal breast cancer?

OBJECTIVE

Previous studies have shown that visfatin is significantly elevated in patients with gastric carcinoma and postmenopausal breast cancer (PBC). We thus explored whether serum visfatin could be used as a potential diagnostic and prognostic tool for PBC, taking into account clinicopathological features, serum tumor markers, anthropometric and metabolic parameters.

METHODS

Serum visfatin, tumor marker CA 15-3, carcinoembryonic antigen, metabolic and anthropometric parameters were determined in 103 postmenopausal women with pathologically confirmed, incident invasive breast cancer, 103 controls matched on age and time of diagnosis, and 51 patients with benign breast lesions (BBL).

RESULTS

Mean serum visfatin was significantly higher in cases than in controls and patients with BBL (p<0.001). In cases, visfatin was significantly associated with CA 15-3 (p=0.03), hormone-receptor status (p<0.001), lymph node invasion (p=0.06) but not with metabolic and anthropometric variables (p>0.05). Multivariable regression analysis revealed that absence of estrogen and progesterone receptors (ER-PR-) was the strongest significant determinant of serum visfatin (p<0.001) in cases adjusting for demographic, metabolic and clinicopathological features. Based upon receiver operator characteristic analysis, serum visfatin outperformed CA 15-3 only in discriminating between PBC cases with early cancer stage than those with late stage, and in differentiating particularly patients with ER-PR- breast tumors.

CONCLUSION

Further prospective and longitudinal studies are needed to determine whether serum visfatin could be used as a prognostic tool in the armamentarium of PBC monitoring and management in conjunction with other biomarkers.

Redox modification of cell signaling in the cardiovascular system

Oxidative stress is presumed to be involved in the pathogenesis of many diseases, including cardiovascular disease. However, oxidants are also generated in healthy cells, and increasing evidence suggests that they can act as signaling molecules. The intracellular reduction-oxidation (redox) status is tightly regulated by oxidant and antioxidant systems. Imbalance between them causes oxidative or reductive stress which triggers cellular damage or aberrant signaling, leading to dysregulation. In this review, we will briefly summarize the aspects of ROS generation and neutralization mechanisms in the cardiovascular system. ROS can regulate cell signaling through oxidation and reduction of specific amino acids within proteins. Structural changes during post-translational modification allow modification of protein activity which can result in altered cellular function. We will focus on the molecular basis of redox protein modification and how this regulatory mechanism affects signal transduction in the cardiovascular system. Finally, we will discuss some techniques applied to monitoring redox status and identifying redox-sensitive proteins in the heart. This article is part of a Special Section entitled "Post-translational Modification."

Reciprocal potentiation of the antitumoral activities of FK866, an inhibitor of nicotinamide phosphoribosyltransferase, and etoposide or cisplatin in neuroblastoma cells

NAD is an essential coenzyme involved in numerous metabolic pathways. Its principal role is in redox reactions, and as such it is not heavily "consumed" by cells. Yet a number of signaling pathways that bring about its consumption have recently emerged. This has brought about the hypothesis that the enzymes that lead to its biosynthesis may be targets for anticancer therapy. In particular, inhibition of the enzyme nicotinamide phosphoribosyl transferase has been shown to be an effective treatment in a number of preclinical studies, and two lead molecules [N-[4-(1-benzoyl-4-piperidinyl)butyl]-3-(3-pyridinyl)-2E-propenamide (FK866) and (E)-1-[6-(4-chlorophenoxy)hexyl]-2-cyano-3-(pyridin-4-yl)guanidine (CHS 828)] have now entered preclinical trials. Yet, the full potential of these drugs is still unclear. In the present study we have investigated the role of FK866 in neuroblastoma cell lines. We now confirm that FK866 alone in neuroblastoma cells induces autophagy, and its effects are potentiated by chloroquine and antagonized by 3-methyladenine or by down-regulating autophagy-related protein 7. Autophagy, in this model, seems to be crucial for FK866-induced cell death. On the other hand, a striking potentiation of the effects of cisplatin and etoposide is given by cotreatment of cells with ineffective concentrations of FK866 (1 nM). The effect of etoposide on DNA damage is potentiated by FK866 treatment, whereas the effect of FK866 on cytosolic NAD depletion is potentiated by etoposide. Even more strikingly, cotreatment with etoposide/cisplatin and FK866 unmasks an effect on mitochondrial NAD depletion.

Target enzyme mutations are the molecular basis for resistance towards pharmacological inhibition of nicotinamide phosphoribosyltransferase

Background

Inhibitors of nicotinamide phosphoribosyltransferase (NAMPT) are promising cancer drugs currently in clinical trials in oncology, including APO866, CHS-828 and the CHS-828 prodrug EB1627/GMX1777, but cancer cell resistance to these drugs has not been studied in detail.

Methods

Here, we introduce an analogue of CHS-828 called TP201565 with increased potency in cellular assays. Further, we describe and characterize a panel of cell lines with acquired stable resistance towards several NAMPT inhibitors of 18 to 20,000 fold compared to their parental cell lines.

Results

We find that 4 out of 5 of the resistant sublines display mutations of NAMPT located in the vicinity of the active site or in the dimer interface of NAMPT. Furthermore, we show that these mutations are responsible for the resistance observed. All the resistant cell lines formed xenograft tumours in vivo. Also, we confirm CHS-828 and TP201565 as competitive inhibitors of NAMPT through docking studies and by NAMPT precipitation from cellular lysate by an analogue of TP201565 linked to sepharose. The NAMPT precipitation could be inhibited by addition of APO866.

Conclusion

We found that CHS-828 and TP201565 are competitive inhibitors of NAMPT and that acquired resistance towards NAMPT inhibitors can be expected primarily to be caused by mutations in NAMPT.

A preclinical study on the rescue of normal tissue by nicotinic acid in high-dose treatment with APO866, a specific nicotinamide phosphoribosyltransferase inhibitor

Inhibitor of nicotinamide phosphoribosyltransferase APO866 is a promising cancer drug currently in phase II clinical trials in oncology. Here, we present a strategy for increasing the therapeutic potential of APO866 through the rescue of normal tissues by coadministration of nicotinic acid (Vitamin B(3)). We examined the toxicity profile of APO866 in B6D2F1 mice and the effect of oral administration of nicotinic acid on tissue toxicity. Nicotinic acid (50 mg/kg) protects mice from death and severe toxicity from an APO866 dose (60 mg/kg) four times the monotherapy maximum tolerated dose (15 mg/kg). In a panel of six cancer cell lines, we find that three (including ML-2 cells) are protected by nicotinic acid in vitro, whereas the cytotoxicity of APO866 remains unaffected in the remaining three (including A2780 cells). A selective biomarker for the protection by nicotinic acid was subsequently identified by quantitative RT-PCR. The expression of nicotinic acid phosphoribosyltransferase is low in the cell lines not rescued from APO866 by nicotinic acid compared with protected cell lines. The findings in cell lines translated into xenograft models in which the combination of 50 mg/kg nicotinic acid and 50 mg/kg APO866 in mouse xenografts of A2780 cells increased life span by >3-fold compared with standard treatment of 15 mg/kg, and the effect of APO866 was clearly decreased when using the same treatment paradigm in ML-2 xenografts. In conclusion, the combination of high doses of APO866 with rescue by nicotinic acid may significantly increase the therapeutic potential in a subset of cancers with low expression of nicotinic acid phosphoribosyltransferase.

Metronomic administration of the drug GMX1777, a cellular NAD synthesis inhibitor, results in neuroblastoma regression and vessel maturation without inducing drug resistance

High-risk neuroblastoma is a rapidly growing tumor with a survival rate below 50%. A new treatment strategy is to administer chemotherapeutic drugs metronomically, i.e., at lower doses and frequent intervals. The aim of the study was to investigate the effects of GMX1777, a chemotherapeutic drug affecting cellular energy metabolism, in a mouse model for high-risk neuroblastoma. Female SCID mice were injected s.c. with MYCN-amplified human neuroblastoma cells and randomized to either treatment with GMX1777 or vehicle. In some animals, treatment was discontinued allowing tumor relapse. Treatment response was evaluated using the pediatric preclinical testing program (PPTP). Immunohistochemistry and qRT-PCR was performed on tumor cryosections to investigate the microscopic and molecular changes in tumors in response to GMX1777. Despite an increase in vessel density, tumor regression and a high group response score according to PPTP criteria was induced by GMX1777 without inducing drug resistance. Treatment resulted in inhibition of tumor cell proliferation, vessel maturation, reduced hypoxia, increased infiltration of MHC class II negative macrophages and expansion of the nonvascular stromal compartment. Decreased stromal VEGF-A and PDGF-B mRNA in response to treatment together with the structural data suggest a "deactivation" or "silencing" of the tumor stroma as a paracrine entity. In conclusion, GMX1777 was highly efficient against high-risk neuroblastoma xenografts through modulation of both the tumor cell and stromal compartment.

Vitamin B3, the nicotinamide adenine dinucleotides and aging

Organism aging is a process of time and maturation culminating in senescence and death. The molecular details that define and determine aging have been intensely investigated. It has become appreciated that the process is partly an accumulation of random yet inevitable changes, but it can be strongly affected by genes that alter lifespan. In this review, we consider how NAD(+) metabolism plays important roles in the random patterns of aging, and also in the more programmatic aspects. The derivatives of NAD(+), such as reduced and oxidized forms of NAD(P)(+), play important roles in maintaining and regulating cellular redox state, Ca(2+) stores, DNA damage and repair, stress responses, cell cycle timing and lipid and energy metabolism. NAD(+) is also a substrate for signaling enzymes like the sirtuins and poly-ADP-ribosylpolymerases, members of a broad family of protein deacetylases and ADP-ribosyltransferases that regulate fundamental cellular processes such as transcription, recombination, cell division, proliferation, genome maintenance, apoptosis, stress resistance and senescence. NAD(+)-dependent enzymes are increasingly appreciated to regulate the timing of changes that lead to aging phenotypes. We consider how metabolism, specifically connected with Vitamin B3 and the nicotinamide adenine dinucleotides and their derivatives, occupies a central place in the aging processes of mammals.

A novel potent nicotinamide phosphoribosyltransferase inhibitor synthesized via click chemistry

The inhibition of NAD synthesis or salvage pathways has been proposed as a novel target for antitumoral drugs. Two molecules with this mechanism of action are at present undergoing clinical trials. In searching for similar novel molecules, we exploited copper-catalyzed [3 + 2] cycloaddition between azides and alkynes (click chemistry) to synthesize 185 novel analogues. The most promising compound displays an IC(50) for cytotoxicity in vitro of 3.8 +/- 0.3 nM and an IC(50) for NAD depletion of 3.0 +/- 0.4 nM. Herein, we strengthen previous data suggesting that this class of compounds induces autophagic cell death. In addition to characterizing this compound and providing a rationale via molecular docking, we reinforce the excellent potential of click chemistry for rapidly generating structure-activity relationships and for drug screening.

Efficacy of combining GMX1777 with radiation therapy for human head and neck carcinoma

PURPOSE

Rapidly metabolizing tumor cells have elevated levels of nicotinamide phosphoribosyltransferase, an enzyme involved in NAD(+) biosynthesis, which serves as an important substrate for proteins involved in DNA repair. GMX1777, which inhibits nicotinamide phosphoribosyltransferase, was evaluated in two human head and neck cancer models in combination with radiotherapy.

EXPERIMENTAL DESIGN

Effects of GMX1777-mediated radiosensitization were examined via metabolic and cytotoxicity assays in vitro; mechanism of action, in vivo antitumor efficacy, and radiosensitization were also investigated.

RESULTS

IC(50) values of GMX1777 for FaDu and C666-1 cells were 10 and 5 nmol/L, respectively, which interacted synergistically with radiotherapy. GMX1777 induced a rapid decline in intracellular NAD(+) followed by ATP reduction associated with significant cytotoxicity. These metabolic changes were slightly increased with the addition of radiotherapy, although poly(ADP-ribose) polymerase activity was significantly reduced when GMX1777 was combined with radiotherapy, thereby accounting for the synergistic cytotoxicity of these two modalities. Systemic GMX1777 administration with local tumor radiotherapy caused complete disappearance of FaDu and C666-1 tumors for 50 and 20 days, respectively. There was also significant reduction in tumor vascularity, particularly for the more sensitive FaDu model. [(18)F]FDG-positron emission tomography/computed tomography images showed reduction in [(18)F]FDG uptake after GMX1777 administration, showing decreased glucose metabolism in vivo.

CONCLUSIONS

Our data represent the first report showing that GMX1777 plus radiotherapy is an effective therapeutic strategy for head and neck cancer, mediated via pleiotropic effects of inhibition of DNA repair and tumor angiogenesis, while sparing normal tissues. Therefore, GMX1777 combined with radiotherapy definitely warrants clinical evaluation in human head and neck cancer patients.

Safety and efficacy of NAD depleting cancer drugs: results of a phase I clinical trial of CHS 828 and overview of published data

PURPOSE

Depletion of cellular nicotinamide adenine dinucleotide (NAD) by inhibition of its synthesis is a new pharmacological principle for cancer treatment currently in early phases of clinical development. We present new and previously published data on the safety and efficacy of these drugs based on early clinical trials.

METHODS

A phase I clinical trial of CHS 828 in patients with advanced solid tumours was performed. Published clinical trials on NAD depleting drugs for cancer treatment were summarised for safety and efficacy.

RESULTS

Seven patients with previously treated solid tumours received oral administration of CHS 828 in the dose range 20-80 mg once weekly for 3 weeks in 4 weeks cycles. Toxicity was dominated by gastrointestinal symptoms including nausea, vomiting, diarrhoea, constipation, subileus and gastric ulcer. One patient had thrombocytopenia grade 2. There were two cases each of grade 3-4 hyperuricemia and hypokalemia. Safety and efficacy of the NAD depleting drugs CHS 828 and FK866 have been reported from four phase I clinical trials, including a total of 97 patients with previously treated solid tumours. Outstanding toxicity reported was thrombocytopenia and various gastrointestinal symptoms. No objective tumour remission has been observed in the total of 104 patients treated in the above early trials.

CONCLUSIONS

Critical toxicity from NAD depleting cancer drugs to consider in future trials seems to be thrombocytopenia and various gastrointestinal symptoms. Efficacy of NAD depleting drugs when used alone is expected to be low.

The small molecule GMX1778 is a potent inhibitor of NAD+ biosynthesis: strategy for enhanced therapy in nicotinic acid phosphoribosyltransferase 1-deficient tumors

GMX1777 is a prodrug of the small molecule GMX1778, currently in phase I clinical trials for the treatment of cancer. We describe findings indicating that GMX1778 is a potent and specific inhibitor of the NAD(+) biosynthesis enzyme nicotinamide phosphoribosyltransferase (NAMPT). Cancer cells have a very high rate of NAD(+) turnover, which makes NAD(+) modulation an attractive target for anticancer therapy. Selective inhibition by GMX1778 of NAMPT blocks the production of NAD(+) and results in tumor cell death. Furthermore, GMX1778 is phosphoribosylated by NAMPT, which increases its cellular retention. The cytotoxicity of GMX1778 can be bypassed with exogenous nicotinic acid (NA), which permits NAD(+) repletion via NA phosphoribosyltransferase 1 (NAPRT1). The cytotoxicity of GMX1778 in cells with NAPRT1 deficiency, however, cannot be rescued by NA. Analyses of NAPRT1 mRNA and protein levels in cell lines and primary tumor tissue indicate that high frequencies of glioblastomas, neuroblastomas, and sarcomas are deficient in NAPRT1 and not susceptible to rescue with NA. As a result, the therapeutic index of GMX1777 can be widended in the treatment animals bearing NAPRT1-deficient tumors by coadministration with NA. This provides the rationale for a novel therapeutic approach for the use of GMX1777 in the treatment of human cancers.

Preclinical development of the nicotinamide phosphoribosyl transferase inhibitor prodrug GMX1777

GMX1778 was recently shown to function as a potent inhibitor of nicotinamide phosphoribosyl transferase. To translate the discovery of GMX1778 mechanism of action into optimal clinical use of its intravenously administered prodrug, GMX1777, the efficacy of GMX1777 was evaluated in xenograft models and the pharmacokinetic profile of GMX1778 and its effect on nicotinamide adenine dinucleotide cellular levels was measured by liquid chromatography/mass spectrometry. Consistent with the requirement for a prolonged exposure for cytotoxicity in vitro, a dose of 75 mg/kg of GMX1777 administered as two bolus intravenous injections in 1 day were not effective at reducing the growth of multiple myeloma (IM-9) tumors, whereas the same dose of GMX1777 administered over a 24 h intravenous infusion caused tumor regression in the IM-9 model, a small-cell lung cancer (SHP-77) model, and a colon carcinoma (HCT-116) model. A 72 h continuous intravenous infusion of GMX1777 was also effective in the IM-9 model, but was associated with a smaller therapeutic index. GMX1777 at a dose of 75 mg/kg administered over a 24 h intravenous infusion produced GMX1778 steady-state plasma levels of approximately 1 microg/ml and caused nicotinamide adenine dinucleotide levels to decrease significantly in tumors. Consistent with the GMX1778 mechanism of action, nicotinic acid protected mice treated with a lethal dose of GMX1777. These data support the design of an open-label, dose-escalation trial, in which patients with refractory solid tumors and lymphomas receive 24 h infusions of GMX1777 as a single agent in 3-week cycles. Furthermore, these results indicate that nicotinic acid is a potent antidote to treat GMX1777 overdose.

Structure-activity relationship analysis of cytotoxic cyanoguanidines: selection of CHS 828 as candidate drug

Background

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N''-4-pyridyl guanidine) (CHS 828) is the first candidate drug from a novel group of anti-tumour agents – the pyridyl cyanoguanidines, shown to be potent compounds interfering with cellular metabolism (inhibition of nicotinamide phosphoribosyl transferase) and NF-κB signalling. Substituted cyanoguanidines are also found in anti-hypertensive agents such as the potassium channel opener pinacidil (N-cyano-N'-(4-pyridyl)-N''-(1,2,2-trimethylpropyl)guanidine) and histamine-II receptor antagonists (e.g. cimetidine, N-cyano-N'-methyl-N''-[2-[[(5-methylimidazol-4-yl]methyl]thio]ethyl)guanidine). In animal studies, CHS 828 has shown very promising activity, and phase I and II studies resulted in further development of a with a water soluble prodrug.

Findings

To study the structural requirements for cyanoguanidine cytotoxicity a set of 19 analogues were synthesized. The cytotoxic effects were then studied in ten cell lines selected for different origins and mechanisms of resistance, using the fluorometric microculture cytotoxicity assay (FMCA). The compounds showed varying cytotoxic activity even though the dose-response curves for some analogues were very shallow. Pinacidil and cimetidine were found to be non-toxic in all ten cell lines. Starting with cyanoguanidine as the crucial core it was shown that 4-pyridyl substitution was more efficient than was 3-pyridyl substitution. The 4-pyridyl cyanoguanidine moiety should be linked by an alkyl chain, optimally a hexyl, heptyl or octyl chain, to a bulky end group. The exact composition of this end group did not seem to be of crucial importance; when the end group was a mono-substituted phenyl ring it was shown that the preferred position was 4-substitution, followed by 3- and, finally, 2-substitution as the least active. Whether the substituent was a chloro, nitro or methoxy substituent seemed to be of minor importance. Finally, the activity patterns in the ten cell lines were compared. Substances with similar structures correlated well, whilst substances with large differences in molecular structure demonstrated lower correlation coefficients.

Conclusion

According to this structure-activity relationship (SAR) study, CHS 828 meets the requirements for optimal cytotoxic activity for this class of compounds.

Circadian control of the NAD+ salvage pathway by CLOCK-SIRT1

Many metabolic and physiological processes display circadian oscillations. We have shown that the core circadian regulator, CLOCK, is a histone acetyltransferase whose activity is counterbalanced by the nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase SIRT1. Here we show that intracellular NAD+ levels cycle with a 24-hour rhythm, an oscillation driven by the circadian clock. CLOCK:BMAL1 regulates the circadian expression of NAMPT (nicotinamide phosphoribosyltransferase), an enzyme that provides a rate-limiting step in the NAD+ salvage pathway. SIRT1 is recruited to the Nampt promoter and contributes to the circadian synthesis of its own coenzyme. Using the specific inhibitor FK866, we demonstrated that NAMPT is required to modulate circadian gene expression. Our findings in mouse embryo fibroblasts reveal an interlocked transcriptional-enzymatic feedback loop that governs the molecular interplay between cellular metabolism and circadian rhythms.

Nampt: linking NAD biology, metabolism and cancer

Nicotinamide phosphoribosyltransferase (Nampt) converts nicotinamide to nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD) intermediate. Previously identified as a cytokine pre-B-cell colony-enhancing factor and controversially claimed as an insulin-mimetic hormone visfatin, Nampt has recently drawn much attention in several fields, including NAD biology, metabolism and inflammation. As a NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins and influences a variety of metabolic and stress responses. Nampt also plays an important part in regulating insulin secretion in pancreatic beta-cells. Nampt seems to have another function as an immunomodulatory cytokine and, therefore, has a role in inflammation. This review summarizes these various functional aspects of Nampt and discusses its potential roles in diseases, including type 2 diabetes and cancer.

Regression of orthotopic neuroblastoma in mice by targeting the endothelial and tumor cell compartments

BACKGROUND

High-risk neuroblastoma has an overall five-year survival of less than 40%, indicating a need for new treatment strategies such as angiogenesis inhibition. Recent studies have shown that chemotherapeutic drugs can inhibit angiogenesis if administered in a continuous schedule. The aim of this study was primarily to characterize tumor spread in an orthotopic, metastatic model for aggressive, MYCN-amplified neuroblastoma and secondarily to study the effects of daily administration of the chemotherapeutic agent CHS 828 on tumor angiogenesis, tumor growth, and spread.

METHODS

MYCN-amplified human neuroblastoma cells (IMR-32, 2 x 10(6)) were injected into the left adrenal gland in SCID mice through a flank incision. Nine weeks later, a new laparotomy was performed to confirm tumor establishment and to estimate tumor volume. Animals were randomized to either treatment with CHS 828 (20 mg/kg/day; p.o.) or vehicle control. Differences between groups in tumor volume were analyzed by Mann-Whitney U test and in metastatic spread using Fisher's exact test. Differences with p < 0.05 were considered statistically significant.

RESULTS

The orthotopic model resembled clinical neuroblastoma in respect to tumor site, growth and spread. Treatment with CHS 828 resulted in tumor regression (p < 0.001) and reduction in viable tumor fraction (p < 0.001) and metastatic spread (p < 0.05) in correlation with reduced plasma levels of the putative tumor marker chromogranin A (p < 0.001). These effects were due to increased tumor cell death and reduced angiogenesis. No treatment-related toxicities were observed.

CONCLUSION

The metastatic animal model in this study resembled clinical neuroblastoma and is therefore clinically relevant for examining new treatment strategies for this malignancy. Our results indicate that daily scheduling of CHS 828 may be beneficial in treating patients with high-risk neuroblastoma.

Extracellular Nampt promotes macrophage survival via a nonenzymatic interleukin-6/STAT3 signaling mechanism

Macrophages play key roles in obesity-associated pathophysiology, including inflammation, atherosclerosis, and cancer, and processes that affect the survival-death balance of macrophages may have an important impact on obesity-related diseases. Adipocytes and other cells secrete a protein called extracellular nicotinamide phosphoribosyltransferase (eNampt; also known as pre-B cell colony enhancing factor or visfatin), and plasma levels of eNampt increase in obesity. Herein we tested the hypothesis that eNampt could promote cell survival in macrophages subjected to endoplasmic reticulum (ER) stress, a process associated with obesity and obesity-associated diseases. We show that eNampt potently blocks macrophage apoptosis induced by a number of ER stressors. The mechanism involves a two-step sequential process: rapid induction of interleukin 6 (IL-6) secretion, followed by IL-6-mediated autocrine/paracrine activation of the prosurvival signal transducer STAT3. The ability of eNampt to trigger this IL-6/STAT3 cell survival pathway did not depend on the presence of the Nampt enzymatic substrate nicotinamide in the medium, could not be mimicked by the Nampt enzymatic product nicotinamide mononucleotide (NMN), was not blocked by the Nampt enzyme inhibitor FK866, and showed no correlation with enzyme activity in a series of site-directed mutant Nampt proteins. Thus, eNampt protects macrophages from ER stress-induced apoptosis by activating an IL-6/STAT3 signaling pathway via a nonenzymatic mechanism. These data suggest a novel action and mechanism of eNampt that could affect the balance of macrophage survival and death in the setting of obesity, which in turn could play important roles in obesity-associated diseases.