The staurosporine-like compound L-753,000 (NB-506) potentiates the neurotrophic effects of neurotrophin-3 by acting selectively at the TrkA receptor

Pharmacology of nerve growth factor and discovery of tanezumab, an anti-nerve growth factor antibody and pain therapeutic

The pharmacology of Nerve Growth Factor (NGF) and the discovery and development of tanezumab, a monoclonal anti-NGF antibody for the treatment of pain illustrate the complex and unpredictable nature of modern drug development. Initial efforts attempted to use NGF agonistically for Alzheimer's disease and neuropathies. Most unexpectedly, clinical studies unmasked hyperalgesic effects. These observations together with new data emerging from molecular and animal model studies stimulated the idea of using an NGF antagonist for chronic pain. These events also reflect the advances of neuropharmacology from classical small molecule efforts directed at neurotransmitter receptors to modern biotechnology with significant integration in molecular biology, biochemistry, and protein engineering.

Development of Precision Small-Molecule Proneurotrophic Therapies for Neurodegenerative Diseases

Age-related neurodegenerative diseases, such as Alzheimer's disease, will represent one of the largest future burdens on worldwide healthcare systems due to the increasing proportion of elderly in our society. As deficiencies in neurotrophins are implicated in the pathogenesis of many age-related neurodegenerative disorders, it is reasonable to consider that global neurotrophin resistance may also become a major healthcare threat. Central nervous system networks are effectively maintained through aging by neuroprotective and neuroplasticity signaling mechanisms which are predominantly controlled by neurotrophin receptor signaling. Neurotrophin receptors are single pass receptor tyrosine kinases that form dimeric structures upon ligand binding to initiate cellular signaling events that control many protective and plasticity-related pathways. Declining functionality of the neurotrophin ligand-receptor system is considered one of the hallmarks of neuropathological aging. Therefore, it is imperative to develop effective therapeutic strategies to contend with this significant issue. While the therapeutic applications of cognate ligands for neurotrophin receptors are limited, the development of nonpeptidergic, small-molecule ligands can overcome these limitations, and productively regulate this important receptor system with beneficial effects. Using our advanced knowledge of the high-dimensionality complexity of receptor systems, the future generation of precision medicines targeting these systems will be an attainable goal.

Activation of mitochondrial function and Hb expression in non-haematopoietic cells by an EPO inducer ameliorates ischaemic diseases in mice

BACKGROUND AND PURPOSE

Many organs suffer from ischaemic injuries that reduce their ability to generate sufficient energy, which is required for functional maintenance and repair. Erythropoietin (EPO) ameliorates ischaemic injuries by pleiotropic effects. The aim of this study was to investigate the effect and mechanism of a small molecule EH-201, and found it as a potent EPO inducer and its effect in non-haematopoietic cells for therapeutic potential in ischemic disorders.

EXPERIMENTAL APPROACH

Mice kidney slices, primary hepatocytes, primary cardiomyocytes and C2C12 myoblasts were treated with EH-201. The effects of this treatment on EPO, Hb expression and mitochondrial biogenesis were analysed. In vivo, doxorubicin-induced cardiomyopathic mice were treated with EH-201. The mice were subjected to an endurance test, electrocardiography and echocardiography, and a histological examination of the isolated hearts was performed. EH-201 was also administered to cisplatin-induced nephropathic mice.

KEY RESULTS

In non-haematopoietic cells, EH-201 was potent at inducing EPO. EH-201 also stimulated mitochondrial biogenesis and enhanced the expression of Hb by a mechanism dependent on EPO-mediated signalling. In mechanistic studies, using EPO and EPO receptor-neutralizing antibodies, we confirmed that EH-201 enhances EPO-EPOR autocrine activity. EH-201 robustly increased the endurance performance activity of healthy and cardiomyopathic mice during hypoxic stress, enhanced myocardial mitochondrial biogenesis and Hb expression, and also improved cardiac function. EH-201 ameliorated anaemia and renal dysfunction in nephropathic mice.

CONCLUSIONS AND IMPLICATIONS

The enhancement and recovery of cellular functions through the stimulation of mitochondrial activity and Hb production in non-haematopoietic cells by an inducer of endogenous EPO has potential as a therapeutic strategy for ischaemic diseases.

AAK1 identified as an inhibitor of neuregulin-1/ErbB4-dependent neurotrophic factor signaling using integrative chemical genomics and proteomics

Target identification remains challenging for the field of chemical biology. We describe an integrative chemical genomic and proteomic approach combining the use of differentially active analogs of small molecule probes with stable isotope labeling by amino acids in cell culture-mediated affinity enrichment, followed by subsequent testing of candidate targets using RNA interference-mediated gene silencing. We applied this approach to characterizing the natural product K252a and its ability to potentiate neuregulin-1 (Nrg1)/ErbB4 (v-erb-a erythroblastic leukemia viral oncogene homolog 4)-dependent neurotrophic factor signaling and neuritogenesis. We show that AAK1 (adaptor-associated kinase 1) is a relevant target of K252a, and that the loss of AAK1 alters ErbB4 trafficking and expression levels, providing evidence for a previously unrecognized role for AAK1 in Nrg1-mediated neurotrophic factor signaling. Similar strategies should lead to the discovery of novel targets for therapeutic development.

Small molecule activators of the Trk receptors for neuroprotection

The neurotrophin signaling network is critical to the development and survival of many neuronal populations. Especially sensitive to imbalances in the neurotrophin system, cholinergic neurons in the basal forebrain are progressively lost in Alzheimer's disease. Therapeutic use of neurotrophins to prevent this loss is hampered, however, by a number of pharmacological challenges. These include a lack of transport across the blood-brain barrier, rapid degradation in the circulation, and difficulty in production. In this review we discuss the evidence supporting the neurotrophin system's role in preventing neurodegeneration and survey some of the pharmacological strategies being pursued to develop effective therapeutics targeting neurotrophin function.

A food-derived synergist of NGF signaling: identification of protein tyrosine phosphatase 1B as a key regulator of NGF receptor-initiated signal transduction

Neurotrophins, such as the nerve growth factor (NGF), play an essential role in the growth, development, survival and functional maintenance of neurons in the central and peripheral systems. They also prevent neuronal cell death under various stressful conditions, such as ischemia and neurodegenerative disorders. NGF induces cell differentiation and neurite outgrowth by binding with and activating the NGF receptor tyrosine kinase followed by activation of a variety of signaling cascades. We have investigated the NGF-dependent neuritogenesis enhancer potential of a food-derived small molecule contained in Brassica vegetables and identified the protein tyrosine phosphatase (PTP) 1B as a key regulator of the NGF receptor-initiated signal transduction. Based on an extensive screening of Brassica vegetable extracts for the neuritogenic-promoting activity in the rat pheochromocytoma cell line PC12, we found the Japanese horseradish, wasabi (Wasabia japonica, syn. Eutrema wasabi), as the richest source and identified 6-methylsulfinylhexyl isothiocyanate (6-HITC), an analogue of sulforaphane isolated from broccoli, as one of the major neuritogenic enhancers in the wasabi. 6-HITC strongly enhanced the neurite outgrowth and neurofilament expression elicited by a low-concentration of NGF that alone was insufficient to induce neuronal differentiation. 6-HITC also facilitated the sustained-phosphorylation of the extracellular signal-regulated kinase and the autophosphorylation of the NGF receptor TrkA. It was found that PTP1B act as a phosphatase capable of dephosphorylating Tyr-490 of TrkA and was inactivated by 6-HITC in a redox-dependent manner. The identification of PTP1B as a regulator of NGF signaling may provide new clues about the chemoprotective potential of food components, such as isothiocyanates.

The dark side of the NGF family: neurotrophins in neoplasias

Although neurotrophins of the nerve growth factor (NGF) family are best known for their neurite outgrowth-inducing and survival-promoting effects on neuronal cells, these are actually pleiotropic growth factors acting physiologically on many different cell types of our body. As for many other growth factors, dysregulation of neurotrophin signal transduction is found in a number of tumors where they can accompany or contribute to malignant transformation. Interestingly, tropomyosin-related kinase (Trk) receptor activation can either support or suppress tumor growth, depending on the tumor type. These same divergent responses have been observed with neurotrophins binding to the p75NTR neurotrophin receptor on tumor cells. This article summarizes the current knowledge on the role of neurotrophins and their receptors in malignancies, with special focus on tumors of neuropathological interest.

Nerve growth factor in treatment and pathogenesis of Alzheimer's disease

The etiology of Alzheimer's disease (AD) is still unknown. In addition, this terrible neurodegenerative disease will increase exponentially over the next two decades due to longer lifespan and an aging "baby-boomer" generation. All treatments currently approved for AD have moderate efficacy in slowing the rate of cognitive decline in patients, and no efficacy in halting progression of the disease. Hence, there is an urgent need for new drug targets and delivery methods to slow or reverse the progression of AD. One molecule that has received much attention in its potential therapeutic role in AD is nerve growth factor (NGF). This review will demonstrate data from humans and animals which promote NGF as a potential therapeutic target by (1) outlining the hypothesis behind using NGF for the treatment of AD, (2) reviewing both the normal and AD altered signaling pathways and effects of NGF in the central nervous system (CNS), and (3) examining the results of NGF treatment obtained from animal models of AD and AD patients.

Neuroprotection by the inhibition of apoptosis

Accumulating evidence strongly suggests that apoptosis contributes to neuronal cell death in a variety of neurodegenerative contexts. Activation of the cysteine protease caspase-3 appears to be a key event in the execution of apoptosis in the central nervous system (CNS). As a result, mice null for caspase-3 display considerable neuronal expansion usually resulting in death by the second week of life. At present, 14 caspase family members have been identified and subdivided into three subgroups on the basis of preference for specific tetrapeptide motifs using a positional scanning combinatorial substrate library. Caspase-3 is a group II member (2, 3, 7) categorized by an absolute substrate requirement for aspartic acid in the P4 position of the scissile bond. The preferred cleavage motif (DExD) for group II caspases is found in many structural, metabolic and repair proteins essential for cellular homeostasis. Consistent with the proposal that apoptosis plays a central in role human neurodegenerative disease, caspase-3 activation has recently been observed in stroke, spinal cord trauma, head injury and Alzheimer's disease. Indeed, peptide-based caspase inhibitors prevent neuronal loss in animal models of head injury and stroke suggesting that these compounds may be the forerunners of non-peptide small molecules that halt apoptosis processes implicated in these neurodegenerative disorders. A clear link between an hereditary neurodegenerative disorder and failed caspase inhibition has recently been proposed for spinal muscular atrophy (SMA). In severe SMA, the neuronal specific inhibitor of apoptosis (IAP) family member known as NAIP is often dysfunctional due to missense and truncation mutations. IAPs such as NAIP potently block the enzymatic activity of group II caspases (3 and 7) suggesting that NAIP mutations may permit unopposed developmental apoptosis to occur in sensory and motor systems resulting in lethal muscular atrophy. Conversely, adenovirally-mediated overexpression of NAIP or the X-linked IAP called XIAP reduces the loss of CA1 hippocampal neurons following transient forebrain ischemia. Taken together, these findings suggest that anti-apoptotic strategies may some day have utility in the treatment of neurodegenerative disease. The present review will summarize some of the recent evidence suggesting that apoptosis inhibitors may become a practical therapeutic approach for both acute and chronic neurodegenerative conditions.

Keynote review: Allosterism in membrane receptors

Allosteric modulation of membrane receptors has been intensively studied in the past three decades and is now considered to be an important indirect mechanism for the control of receptor function. The allosteric site on the GABA(A) receptor is the target for the most widely prescribed sleep medicines, the benzodiazepines. Cinacalcet, an allosteric enhancer of the calcium-sensing receptor, is used to treat secondary hyperparathyroidism. Allosteric ligands might be especially valuable to control receptors for which the design of selective orthosteric agonists or antagonists has been elusive, such as muscarinic acetylcholine receptors.

Identification and characterization of compounds that potentiate NT-3-mediated Trk receptor activity

Neurotrophins are a family of secreted proteins that play an important role in the development, differentiation, and survival of neurons. Studies also suggest that aberrant neurotrophin signaling may play a role in processes underlying disease states such as schizophrenia, Alzheimer's disease, and depression. Whereas the development of agents that selectively stimulate neurotrophin signaling has proven to be difficult, compounds have been identified that potentiate neurotrophin 3 (NT-3)-mediated activation of trk A. In the present studies, we extend those initial observations to identify compounds that also potentiate NT-3-mediated activation of trk B. Compound potentiation of NT-3 was observed using several readouts of transfected and endogenous trk receptor activity, including trk receptor phosphorylation, mitogen-activated protein kinase phosphorylation, reporter assay activity (beta-lactamase and luciferase), cell survival and neurite extension assays. Studies using chimeric trk receptors demonstrated that the extracellular domain is essential for compound potentiation and rule out interaction with intracellular signaling molecules as a mechanism of compound activity. Thus, the present studies demonstrate that trk B receptor activity can be potentiated by small-molecule compounds via the extracellular domain of the receptor and provide reagents for further evaluating the role of NT-3-mediated trk A and trk B activity in vivo.

Edotecarin: a novel topoisomerase I inhibitor

Edotecarin (PHA-782615; formerly J-107088) is a derivative of NB-506, an indolocarbazole antitumor agent. It is a novel inhibitor of topoisomerase I that induces single-strand DNA cleavage more effectively than NB-506 or camptothecin (CPT) and at different DNA sequences. The DNA-topoisomerase I complexes induced by edotecarin are more stable than those occurring after exposure to CPT or NB-506. The antitumor activity of edotecarin is less cell cycle dependent than other topoisomerase I inhibitors. Being an indolocarbazole, it is structurally related to staurosporine but does not possess protein kinase inhibitory properties. In addition, edotecarin does not form active metabolites and is not a substrate for in vitro P450-mediated metabolism. The antitumor activity of edotecarin has been tested in vitro and in vivo, and inhibition of tumor growth has been observed in breast, cervix, pharynx, lung, prostate, colon, gastric, and hepatic cancer models. Edotecarin is effective on cells that have acquired resistance related to P-glycoprotein. In vitro synergy has been demonstrated when edotecarin was tested in combination with cisplatin, 5-fluorouracil, etoposide, paclitaxel, doxorubicin, vincristine, CPT, and gemcitabine. Three phase I and 5 phase II studies have been carried out to date. Combination studies of edotecarin with other chemotherapeutic agents are in current clinical trials. The primary dose-limiting toxicities were grade 3/4 neutropenia and febrile neutropenia. Dose-limiting diarrhea was observed only with a twice-weekly administration schedule. Recent progress in preclinical and clinical studies of edotecarin is reviewed.

Blocked MAP kinase activity selectively enhances neurotrophic growth responses

Bone morphogenetic proteins (BMPs) 4 and 6 as well as MEK inhibitors PD98059 and U0126 potentiate neurotrophin 3 (NT3)- and neurturin (NTN)-induced neurite outgrowth and survival of peripheral neurons from the E9 chicken embryo. Preexposure to BMP4 or PD98059 was sufficient to prime the potentiation of subsequently added NT3. Phosphorylation of Erk2, induced by NT3, was reduced by MEK inhibition but unaffected by BMP signaling. Real-time PCR showed that neither BMP stimulation nor MEK inhibition increased Trk receptor expression and that the BMP-induced genes Smad6 and Id1 were not upregulated by PD98059. In contrast, both MEK inhibition and BMP signaling suppressed transcription of the serum-response element (SRE)-driven Egr1 gene. A reporter assay using NGF-stimulated PC12 cells demonstrated that MEK/Erk/Elk-driven transcriptional activity was inhibited by Smad1/5 and by PD98059. Thus, suppression of SRE-controlled transcription represents a likely convergence point for pathways regulating neurotrophic responses.

Topoisomerase I and II Inhibitors Control Caspase-2 Pre-Messenger RNA Splicing in Human Cells

We have recently shown that the topoisomerase II inhibitor, etoposide (VP16), could trigger caspase-2 pre-mRNA splicing in human leukemic cell lines. This leads to increased inclusion of exon 9, which is specifically inserted into the short caspase-2S isoform mRNA and absent from the long caspase-2L isoform mRNA. One of the consequences of this alternative splicing is a decrease in the total amount of the mature form of caspase-2L mRNA and protein. In this study, we analyzed the effects of several representative molecules of various classes of cytotoxic agents on caspase-2 pre-mRNA splicing in both U937 leukemic cells and in HeLa cervix carcinoma cells. Very strikingly, both topoisomerase I (camptothecin and homocamptothecin derivatives) and II (VP16, amsacrine, doxorubicin, mitoxantrone) inhibitors induced exon 9 inclusion. DNA intercalating glycosyl indolocarbazole derivatives as well as DNA alkylating agents, such as cisplatin and melphalan, antimetabolites like 5-fluorouracil, and mitotic spindle poisons like vinblastine had no effect. Therefore, both classes of DNA topoisomerases can control pre-mRNA splicing of the caspase-2 transcript. In addition, the splicing reaction brought about by camptothecin was hampered in human CEM/C2 and in murine P388-45R leukemic deficient in topoisomerase I activity. Conversely, VP16 did not trigger caspase-2 alternative splicing in human HL60/MX2 leukemic cells harboring a mutant topoisomerase II. Minigene transfection analysis revealed that topoisomerase inhibitors did not change the splicing profile when cis-acting elements in intron-9, reported to control exon 9 inclusion independently of drug treatment, were removed. Rather, our experiments suggest that exon 9 inclusion induced by topoisomerase inhibitors reflects the activity exerted by topoisomerase I or II on proteins that control splicing reactions, or their direct involvement in pre-mRNA splicing.

(−)-3,5-Dicaffeoyl-muco-quinic acid isolated from Aster scaber contributes to the differentiation of PC12 cells: through tyrosine kinase cascade signaling

Aster scaber T. (Asteraceae) has been used in traditional Korean and Chinese medicine to treat bruises, snakebites, headaches, and dizziness. (-)-3,5-Dicaffeoyl-muco-quinic acid (DQ) isolated from A. scaber induced neurite outgrowth in PC12 cells. It has been reported that the activation of the extracellular signal regulated kinase 1/2 (Erk 1/2) and phosphoinositide 3 (PI3) kinase plays a crucial role in the NGF-induced differentiation of PC12 cells. This study showed that the effect of DQ on neurite outgrowth is mediated via the Erk 1/2 and PI3 kinase-dependent pathways like NGF. Furthermore, DQ stimulated the phosphorylation of Trk A. Overall, DQ elicited the differentiation of PC12 cells through Trk A phosphorylation followed by Erk 1/2 and PI3 kinase activation.

Automated screening of neurite outgrowth

Outgrowth of neurites in culture is used for assessing neurotrophic activity. Neurite measurements have been performed very slowly using manual methods or more efficiently with interactive image analysis systems. In contrast, medium-throughput and noninteractive image analysis of neurite screens has not been well described. The authors report the performance of an automated image acquisition and analysis system (IN Cell Analyzer 1000) in the neurite assay. Neuro-2a (N2a) cells were plated in 96-well plates and were exposed to 6 conditions of retinoic acid. Immunofluorescence labeling of the cytoskeleton was used to detect neurites and cell bodies. Acquisition of the images was automatic. The image set was then analyzed by both manual tracing and automated algorithms. On 5 relevant parameters (number of neurites, neurite length, total cell area, number of cells, neurite length per cell), the authors did not observe a difference between the automated analysis and the manual analysis done by tracing. These data suggest that the automated system addresses the same biology as human scorers and with the same measurement precision for treatment effects. However, throughput of the automated system is orders of magnitude higher than with manual methods.

Sequential interactions of fibroblast growth factor-2, brain-derived neurotrophic factor, neurotrophin-3, and their receptors define critical periods in the development of cochlear ganglion cells

We studied the interactions of neurotrophin-3 (NT3) with brain-derived neurotrophic factor (BDNF), fibroblast growth factor-2 (FGF-2), and their effects on tyrosine kinase C (TrkC) expression during cochlear ganglion development. Otocysts were explanted from white leghorn chicken embryos at stages when the neuronal precursors normally start to migrate. Cultures were fed with various combinations of NT3, BDNF, and FGF-2. NT3 appeared to have a greater effect on neurite outgrowth than on migration and was enhanced by BDNF. The results from in situ hybridization and immunostaining for TrkC receptor revealed up-regulation of the mRNA and protein by combining NT-3 and BDNF. NT-3 combined with FGF-2 produced down-regulation of receptor. Neutralizing antibody to NT3 had an inhibitory effect on neuronal development, suggesting that endogenous NT3 is normally active during the period examined. The findings suggest an interactive role of NT3 in early neuronal development. The trophic synergism of NT3 and BDNF may result from up-regulation of TrkC. This hypothesis is consistent with immunostaining in the embryonic basilar papilla, which localized TrkC to the initial axonal invasion sites. While the growth factors each produce particular trophic effects, the interactions of these factors define a critical sequence of developmental events based on modulation of receptor expression.

Factors controlling axonal and dendritic arbors

The sculpting and maintenance of axonal and dendritic arbors is largely under the control of molecules external to the cell. These factors include both substratum-associated and soluble factors that can enhance or inhibit the outgrowth of axons and dendrites. A large number of factors that modulate axonal outgrowth have been identified, and the first stages of the intracellular signaling pathways by which they modify process outgrowth have been characterized. Relatively fewer factors and pathways that affect dendritic outgrowth have been described. The factors that affect axonal arbors form an incompletely overlapping set with those that affect dendritic arbors, allowing selective control of the development and maintenance of these critical aspects of neuronal morphology.

The non-peptidyl fungal metabolite L-783,281 activates TRK neurotrophin receptors

Neurotrophin binding to the extracellular surface of the Trk family of tyrosine kinase receptors leads to the activation of multiple signalling cascades, culminating in neuroregenerative effects, including neuronal survival and neurite outgrowth. Since neurotrophins themselves are not ideal drug candidates due to their poor pharmacokinetic behaviour and bioavailability, small molecule neurotrophin mimetics may be beneficial in treating a number of neurodegenerative disorders. The present study demonstrates that L-783,281, a non-peptidyl fungal metabolite, is capable of stimulating TrkA, B and C phosphorylation to various extents in CHO cells stably expressing human Trk receptors. L-783,281 also stimulated Trk phosphorylation in a number of rat and human primary neuronal cultures, whereas the highly similar compound, L-767,827, was without effect. Mechanistic studies utilizing transiently transfected PDGF/TrkA and TrkA/PDGF chimeras, demonstrated that L-783,281 is likely to interact with the intracellular domain of the TrkA receptor. Further investigations suggested that L-783,281 was nevertheless able to instigate receptor dimerization by binding in a non-covalent manner. Although the cytotoxicity of the compound was shown to preclude its effects in neuronal survival and neurite outgrowth assays, it is a prototype for a small molecule neurotrophin mimetic that activates Trk by interacting at a site different from the neurotrophin-binding site.

Development of pharmacological agents for targeting neurotrophins and their receptors

Neurotrophins comprise a family of protein growth factors that control the survival, growth, and/or differentiation of neurons and several other cell populations derived from the neuroectoderm. Neurotrophins and their receptors are important targets for the therapy of human disease, with potential applications ranging from the treatment of chronic or acute neurodegeneration to pain and cancer. Neurotrophins have been used clinically but are poor pharmacological agents. Consequently, approaches to develop pharmacological agents that target neurotrophins, their receptors or neurotrophin signaling pathways have been attempted.

A rapid method for semi-quantitative analysis of neurite outgrowth from chick DRG explants using image analysis

Neurite outgrowth from dorsal root ganglion (DRG) explants is a method of evaluating neurotrophic activity of growth factors and neurotrophin mimetics. The drawbacks to this approach are the difficulties in quantifying the response. Neurite counts are time consuming and labour intensive, and the accuracy is often questionable due to branching and fasciculation of the neurites. We report here a method of semi-quantitative analysis of neurite outgrowth from chick DRG explants, using image analysis to quantify the area occupied by neurites emanating from the ganglion. This method is rapid, takes into account both the length and number of neurites, and is unaffected by neurite fasciculation or branching. Primary explants of chick DRGs were treated with the neurotrophins nerve growth factor (NGF) or neurotrophin-3 (NT-3) and with the compound K252a. K252b was tested for potentiation of the response to NT-3. The results show a dose dependent outgrowth of neurites from explants treated with NGF, NT-3 and K252a, and potentiation of the NT-3 response by K252b. These responses were quantified by neurite area quantification using image analysis. We conclude that neurite area measurement using image analysis provides a robust means of evaluating neurotrophic activity of growth factors and neurotrophin mimetics in vitro.