Discovery of a Highly Selective NAMPT Inhibitor That Demonstrates Robust Efficacy and Improved Retinal Toxicity with Nicotinic Acid Coadministration.

NAMPT, an enzyme essential for NAD+ biosynthesis, has been extensively studied as an anticancer target for developing potential novel therapeutics. Several NAMPT inhibitors have been discovered, some of which have been subjected to clinical investigations. Yet, the on-target hematological and retinal toxicities have hampered their clinical development. In this study, we report the discovery of a unique NAMPT inhibitor, LSN3154567. This molecule is highly selective and has a potent and broad spectrum of anticancer activity. Its inhibitory activity can be rescued with nicotinic acid (NA) against the cell lines proficient, but not those deficient in NAPRT1, essential for converting NA to NAD+ LSN3154567 also exhibits robust efficacy in multiple tumor models deficient in NAPRT1. Importantly, this molecule when coadministered with NA does not cause observable retinal and hematological toxicities in the rodents, yet still retains robust efficacy. Thus, LSN3154567 has the potential to be further developed clinically into a novel cancer therapeutic. Mol Cancer Ther; 16(12); 2677-88. ©2017 AACR.

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.

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.

Derivatization of the tricarboxylic acid intermediates with O-benzylhydroxylamine for liquid chromatography-tandem mass spectrometry detection.

The tricarboxylic acid (TCA) cycle is an interface among glycolysis, lipid metabolism, and amino acid metabolism. Increasing interest in cancer metabolism has created a demand for rapid and sensitive methods for quantifying the TCA cycle intermediates and related organic acids. We have developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify the TCA cycle intermediates in a 96-well format after O-benzylhydroxylamine (O-BHA) derivatization under aqueous conditions. This method was validated for quantitation of all common TCA cycle intermediates with good sensitivity, including α-ketoglutarate, malate, fumarate, succinate, 2-hydroxyglutarate, citrate, oxaloacetate, pyruvate, isocitrate, and lactate using a 8-min run time in cancer cells and tissues. The method was used to detect and quantify changes in metabolite levels in cancer cells and tumor tissues treated with a pharmacological inhibitor of nicotinamide phosphoribosyl transferase (NAMPT). This method is rapid, sensitive, and reproducible, and it can be used to assess metabolic changes in cancer cells and tumor samples.

IRAK4 kinase activity is required for Th17 differentiation and Th17-mediated disease.

Both IL-23- and IL-1-mediated signaling pathways play important roles in Th17 cell differentiation, cytokine production, and autoimmune diseases. The IL-1R-associated kinase 4 (IRAK4) is critical for IL-1/TLR signaling. We show here that inactivation of IRAK4 kinase in mice (IRAK4 KI) results in significant resistance to experimental autoimmune encephalomyelitis due to a reduction in infiltrating inflammatory cells into the CNS and reduced Ag-specific CD4(+) T cell-mediated IL-17 production. Adoptive transfer of myelin oligodendrocyte glycoprotein 35-55-specific IRAK4 KI Th17 cells failed to induce experimental autoimmune encephalomyelitis in either wild-type or IRAK4 KI recipient mice, indicating the lack of autoantigen-specific Th17 cell activities in the absence of IRAK4 kinase activity. Furthermore, the absence of IRAK4 kinase activity blocked induction of IL-23R expression, STAT3 activation by IL-23, and Th17 cytokine expression in differentiated Th17 cells. Importantly, blockade of IL-1 signaling by IL-1RA inhibited Th17 differentiation and IL-23-induced cytokine expression in differentiated Th17 cells. The results of these studies demonstrate that IL-1-mediated IRAK4 kinase activity in T cells is essential for induction of IL-23R expression, Th17 differentiation, and autoimmune disease.

Embryonic synthesis of the inner limiting membrane and vitreous body.

PURPOSE: The inner limiting membrane (ILM) and the vitreous body (VB) are major parts of the extracellular matrix of the eye. The present study was undertaken to investigate the synthesis and turnover of the ILM and VB in chick and human embryonic and postembryonic eye development. METHODS: The abundance of ILM and VB proteins was determined by Western blot analysis using samples from chick and human VB of different ages. The mRNA expression of the ILM proteins in lens was determined by in situ hybridization and RT-PCR. RESULTS: Based on the abundance of mRNA expression, the prominent sources of ILM and VB proteins in chick eyes are the lens and ciliary body. In chick, ILM and VB matrix proteins were most abundant in embryonic VB, and their concentration declined precipitously after hatching. Most ILM and VB proteins were no longer detectable in the adult VB. In humans, a similar developmentally regulated expression of ILM and VB proteins in VB was detected: The highest concentrations of ILM and VB proteins were detected in fetal VB, the lowest in the adult VB. The decline in ILM and VB protein synthesis occurred within the first 2 years of life. CONCLUSIONS: The abundance of ILM and VB proteins in the embryonic VB, their sharp decline at postembryonic stages, and their very low abundance in the adult VB show that ILM and VB are assembled during embryogenesis and are maintained throughout life with minimum turnover.

Collagen XVIII/endostatin is essential for vision and retinal pigment epithelial function.

Age-related macular degeneration (ARMD) with abnormal deposit formation under the retinal pigment epithelium (RPE) is the major cause of blindness in the Western world. basal laminar deposits are found in early ARMD and are composed of excess basement membrane material produced by the RPE. Here, we demonstrate that mice lacking the basement membrane component collagen XVIII/endostatin have massive accumulation of sub-RPE deposits with striking similarities to basal laminar deposits, abnormal RPE, and age-dependent loss of vision. The progressive attenuation of visual function results from decreased retinal rhodopsin content as a consequence of abnormal vitamin A metabolism in the RPE. In addition, aged mutant mice show photoreceptor abnormalities and increased expression of glial fibrillary acidic protein in the neural retina. Our data demonstrate that collagen XVIII/endostatin is essential for RPE function, and suggest an important role of this collagen in Bruch's membrane. Consistent with such a role, the ultrastructural organization of collagen XVIII/endostatin in basement membranes, including Bruch's membrane, shows that it is part of basement membrane molecular networks.

Expression of collagen XVIII and localization of its glycosaminoglycan attachment sites.

Collagen XVIII is the only currently known collagen that carries heparan sulfate glycosaminoglycan side chains. The number and location of the glycosaminoglycan attachment sites in the core protein were determined by eukaryotic expression of full-length chick collagen XVIII and site-directed mutagenesis. Three Ser-Gly consensus sequences carrying glycosaminoglycan side chains were detected in the middle and N-terminal part of the core protein. One of the Ser-Gly consensus sequences carried a heparan sulfate side chain, and the remaining two had mixed chondroitin and heparan sulfate side chains; thus, recombinant collagen XVIII was a hybrid of heparan sulfate and chondroitin proteoglycan. In contrast, collagen XVIII from all chick tissues so far assayed have exclusively heparan sulfate side chains, indicating that the posttranslational modification of proteins expressed in vitro is not entirely identical to the processing that occurs in a living embryo. Incubating the various mutated collagen XVIIIs with retinal basement membranes showed that the heparan sulfate glycosaminoglycan side chains mediate the binding of collagen XVIII to basement membranes.

A critical function of the pial basement membrane in cortical histogenesis.

Mice with a targeted deletion of the nidogen-binding site of laminin gamma1 were used to study the function of the pial basement membrane in cortical histogenesis. The pial basement membrane in the mutant embryos assembled but was unstable and disintegrated at random segments. In segments with a disrupted basement membrane, radial glia cells were retracted from the pial surface, and radially migrating neurons, including Cajal-Retzius cells and cortical plate neurons, passed the meninges or terminated their migration prematurely. By correlating the disruptions in the pial basal lamina with changes in the morphology of radial glia cells, the aberrant migration of Cajal-Retzius cells, and subsequent dysplasia of cortical plate neurons, the present data establish a causal relationship of proper cortical histogenesis with the presence of an intact pial basement membrane.

Expression of basal lamina protein mRNAs in the early embryonic chick eye.

Laminin, collagen IV, collagen XVIII, agrin, and nidogen are major protein constituents of the chick retinal basal lamina. To determine their sites of synthesis during de novo basal lamina assembly in vivo, we localized their mRNA expression in the eye during maximum expansion of the retina between embryonic day (E) 2.5 and E6. Our in situ hybridization studies showed that the expression pattern of every basal lamina protein mRNA in the developing eye is unique. Collagen IV and perlecan originate predominantly from the lens epithelium, whereas collagen XVIII, nidogen, and the laminin gamma 1 and beta1 chains are synthesized mainly by the ciliary body. Agrin, collagen XVIII, collagen IV, and laminin gamma 1 also originate from cells of the optic disc. The only basal lamina protein that is synthesized by the neural retina throughout development is agrin with ganglion cells as its main source. Some of the mRNAs have short, transient expressions in the retina, most notably that of collagen IV and laminin gamma 1, both of which appear in the ventral retina between E4 and E5. That most retinal basal lamina proteins originate from extraretinal tissues infers that the basal lamina proteins have to be shed from the lens, optic disc, and ciliary body into the vitreous body. The assembly of the retinal basal lamina then occurs by the binding of these proteins by cellular receptor proteins on the vitreal endfeet of the retinal neuroepithelial cells.

The critical role of basement membrane-independent laminin gamma 1 chain during axon regeneration in the CNS.

We have addressed the question of whether a family of axon growth-promoting molecules known as the laminins may play a role during axon regeneration in the CNS. A narrow sickle-shaped region containing a basal lamina-independent form of laminin exists in and around the cell bodies and proximal portion of the apical dendrites of CA3 pyramidal neurons of the postnatal hippocampus. To understand the possible function of laminin in axon regeneration within this pathway, we have manipulated laminin synthesis at the mRNA level in a slice culture model of the lesioned mossy system. In this model early postnatal mossy fibers severed near the hilus can regenerate across the lesion and elongate rapidly within strata lucidum and pyramidale. In slice cultures of the postnatal day 4 hippocampus, 2 d before lesion and then continuing for 1-5 d after lesion, translation of the gamma1 chain product of laminin was reduced by using antisense oligodeoxyribonucleotides and DNA enzymes. In the setting of the lesioned organotypic hippocampal slice, astroglial repair of the lesion and overall glial patterning were unperturbed by the antisense or DNA enzyme treatments. However, unlike controls, in the treated, lesioned slices the vast majority of regenerating mossy fibers could not cross the lesion site; those that did were very much shorter than usual, and they took a meandering course. In a recovery experiment in which the DNA enzyme or antisense oligos were washed away, laminin immunoreactivity returned and mossy fiber regeneration resumed. These results demonstrate the critical role of laminin(s) in an axon regeneration model of the CNS.