Small molecule modulation of TrkB and TrkC neurotrophin receptors prevents cholinergic neuron atrophy in an Alzheimer's disease mouse model at an advanced pathological stage.

Degeneration of basal forebrain cholinergic neurons (BFCNs) in the nucleus basalis of Meynert (NBM) and vertical diagonal band (VDB) along with their connections is a key pathological event leading to memory impairment in Alzheimer's disease (AD). Aberrant neurotrophin signaling via Trks and the p75 neurotrophin receptor (p75NTR) contributes importantly to BFCN dystrophy. While NGF/TrkA signaling has received the most attention in this regard, TrkB and TrkC signaling also provide trophic support to BFCNs and these receptors may be well located to preserve BFCN connectivity. We previously identified a small molecule TrkB/TrkC ligand, LM22B-10, that promotes cell survival and neurite outgrowth in vitro and activates TrkB/TrkC signaling in the hippocampus of aged mice when given intranasally, but shows poor oral bioavailability. An LM22B-10 derivative, PTX-BD10-2, with improved oral bioavailability has been developed and this study examined its effects on BFCN atrophy in the hAPPLond/Swe (APPL/S) AD mouse model. Oral delivery of PTX-BD10-2 was started after appreciable amyloid and cholinergic pathology was present to parallel the clinical context, as most AD patients start treatment at advanced pathological stages. PTX-BD10-2 restored cholinergic neurite integrity in the NBM and VDB, and reduced NBM neuronal atrophy in symptomatic APPL/S mice. Dystrophy of cholinergic neurites in BF target regions, including the cortex, hippocampus, and amygdala, was also reduced with treatment. Finally, PTX-BD10-2 reduced NBM tau pathology and improved the survival of cholinergic neurons derived from human induced pluripotent stem cells (iPSCs) after amyloid-ß exposure. These data provide evidence that targeting TrkB and TrkC signaling with PTX-BD10-2 may be an effective disease-modifying strategy for combating cholinergic dysfunction in AD. The potential for clinical translation is further supported by the compound's reduction of AD-related degenerative processes that have progressed beyond early stages and its neuroprotective effects in human iPSC-derived cholinergic neurons.

A small molecule p75NTR ligand normalizes signalling and reduces Huntington's disease phenotypes in R6/2 and BACHD mice.

Decreases in the ratio of neurotrophic versus neurodegenerative signalling play a critical role in Huntington's disease (HD) pathogenesis and recent evidence suggests that the p75 neurotrophin receptor (NTR) contributes significantly to disease progression. p75NTR signalling intermediates substantially overlap with those promoting neuronal survival and synapse integrity and with those affected by the mutant huntingtin (muHtt) protein. MuHtt increases p75NTR-associated deleterious signalling and decreases survival signalling suggesting that p75NTR could be a valuable therapeutic target. This hypothesis was investigated by examining the effects of an orally bioavailable, small molecule p75NTR ligand, LM11A-31, on HD-related neuropathology in HD mouse models (R6/2, BACHD). LM11A-31 restored striatal AKT and other pro-survival signalling while inhibiting c-Jun kinase (JNK) and other degenerative signalling. Normalizing p75NTR signalling with LM11A-31 was accompanied by reduced Htt aggregates and striatal cholinergic interneuron degeneration as well as extended survival in R6/2 mice. The p75NTR ligand also decreased inflammation, increased striatal and hippocampal dendritic spine density, and improved motor performance and cognition in R6/2 and BACHD mice. These results support small molecule modulation of p75NTR as an effective HD therapeutic strategy. LM11A-31 has successfully completed Phase I safety and pharmacokinetic clinical trials and is therefore a viable candidate for clinical studies in HD.

The Neurotrophic Factor Receptor p75 in the Rat Dorsolateral Striatum Drives Excessive Alcohol Drinking.

UNLABELLED: Brain-derived neurotrophic factor (BDNF) signaling in the dorsolateral striatum (DLS) keeps alcohol intake in moderation. For example, activation of the BDNF receptor tropomyosin receptor kinase B (TrkB) in the DLS reduces intake in rats that consume moderate amounts of alcohol. Here, we tested whether long-term excessive consumption of alcohol produces neuroadaptations in BDNF signaling in the rat DLS. We found that BDNF was no longer able to gate alcohol self-administration after a history of repeated cycles of binge alcohol drinking and withdrawal. We then elucidated the possible neuroadaptations that could block the ability of BDNF to keep consumption of alcohol in moderation. We report that intermittent access to 20% alcohol in a two-bottle choice paradigm that models excessive alcohol drinking produces a mobilization of DLS p75 neurotrophin receptor (p75NTR), whose activities oppose those of the Trk receptors, including TrkB. These neuroadaptations were not observed in the DLS of rats exposed to continuous access to 10% alcohol or in rats consuming sucrose. Furthermore, short hairpin RNA (shRNA)-mediated knockdown of the p75NTR gene in the DLS, as well as intra-DLS infusion or systemic administration of the p75NTR modulator, LM11A-31, significantly reduced binge drinking of alcohol. Together, our results suggest that excessive alcohol consumption produces a change in BDNF signaling in the DLS, which is mediated by the recruitment of p75NTR. Our data also imply that modulators of p75NTR signaling could be developed as medications for alcohol abuse disorders. SIGNIFICANCE STATEMENT: Neuroadaptations gate or drive excessive, compulsive alcohol drinking. We previously showed that brain-derived neurotrophic factor and its receptor, TrkB, in the dorsolateral striatum (DLS), are part of an endogenous system that keeps alcohol drinking in moderation. Here, we show that a history of excessive alcohol intake produces neuroadaptations in the DLS that preclude BDNF's ability to gate alcohol self-administration in rats by the recruitment of the low-affinity neurotrophin receptor, p75NTR, whose activities opposes those of the Trk receptors. Finally, we show that the administration of the p75NTR modulator, LM11A-31, significantly reduces excessive alcohol intake suggesting that the drug may be developed as a new treatment for alcohol abuse disorders.

A small molecule TrkB ligand reduces motor impairment and neuropathology in R6/2 and BACHD mouse models of Huntington's disease.

Loss of neurotrophic support in the striatum caused by reduced brain-derived neurotrophic factor (BDNF) levels plays a critical role in Huntington's disease (HD) pathogenesis. BDNF acts via TrkB and p75 neurotrophin receptors (NTR), and restoring its signaling is a prime target for HD therapeutics. Here we sought to determine whether a small molecule ligand, LM22A-4, specific for TrkB and without effects on p75(NTR), could alleviate HD-related pathology in R6/2 and BACHD mouse models of HD. LM22A-4 was administered to R6/2 mice once daily (5-6 d/week) from 4 to 11 weeks of age via intraperitoneal and intranasal routes simultaneously to maximize brain levels. The ligand reached levels in the R6/2 forebrain greater than the maximal neuroprotective dose in vitro and corrected deficits in activation of striatal TrkB and its key signaling intermediates AKT, PLCγ, and CREB. Ligand-induced TrkB activation was associated with a reduction in HD pathologies in the striatum including decreased DARPP-32 levels, neurite degeneration of parvalbumin-containing interneurons, inflammation, and intranuclear huntingtin aggregates. Aggregates were also reduced in the cortex. Notably, LM22A-4 prevented deficits in dendritic spine density of medium spiny neurons. Moreover, R6/2 mice given LM22A-4 demonstrated improved downward climbing and grip strength compared with those given vehicle, though these groups had comparable rotarod performances and survival times. In BACHD mice, long-term LM22A-4 treatment (6 months) produced similar ameliorative effects. These results support the hypothesis that targeted activation of TrkB inhibits HD-related degenerative mechanisms, including spine loss, and may provide a disease mechanism-directed therapy for HD and other neurodegenerative conditions.

Oral administration of a small molecule targeted to block proNGF binding to p75 promotes myelin sparing and functional recovery after spinal cord injury.

The lack of effective therapies for spinal cord injury points to the need for identifying novel targets for therapeutic intervention. Here we report that a small molecule, LM11A-31, developed to block proNGF-p75 interaction and p75-mediated cell death crosses the blood-brain barrier efficiently when delivered orally. Administered starting 4 h postinjury, LM11A-31 promotes functional recovery without causing any toxicity or increased pain in a mouse model of spinal contusion injury. In both weight-bearing open-field tests and nonweight-bearing swim tests, LM11A-31 was effective in improving motor function and coordination. Such functional improvement correlated with a >50% increase in the number of surviving oligodendrocytes and myelinated axons. We also demonstrate that LM11A-31 indeed inhibits proNGF-p75 interaction in vivo, thereby curtailing the JNK3-mediated apoptotic cascade. These results thus highlight p75 as a novel therapeutic target for an orally delivered treatment for spinal cord injury.

A small molecule p75(NTR) ligand protects neurogenesis after traumatic brain injury.

The p75 neurotrophin receptor (p75(NTR)) influences the proliferation, survival, and differentiation of neuronal precursors and its expression is induced in injured brain, where it regulates cell survival. Here, we test the hypotheses that pharmacologic modulation of p75(NTR) signaling will promote neural progenitor survival and proliferation, and improve outcomes of traumatic brain injury (TBI). LM11A-31, an orally available, blood-brain barrier-permeant small-molecule p75(NTR) signaling modulator, significantly increased proliferation and survival, and decreased JNK phosphorylation, in hippocampal neural stem/progenitor cells in culture expressing wild-type p75(NTR), but had no effect on cells expressing a mutant neurotrophin-unresponsive form of the receptor. The compound also enhanced the production of mature neurons from adult hippocampal neural progenitors in vitro. In vivo, intranasal administration of LM11A-31 decreased postinjury hippocampal and cortical neuronal death, neural progenitor cell death, gliogenesis, and microglial activation, and enhanced long-term hippocampal neurogenesis and reversed spatial memory impairments. LM11A-31 diminished the postinjury increase of SOX2-expressing early progenitor cells, but protected and increased the proliferation of endogenous polysialylated-neural cell adhesion molecule positive intermediate progenitors, and restored the long-term production of mature granule neurons. These findings suggest that modulation of p75(NTR) actions using small molecules such as LM11A-31 may constitute a potent therapeutic strategy for TBI.

p75 neurotrophin receptor modulation in mild to moderate Alzheimer disease: a randomized, placebo-controlled phase 2a trial.

p75 neurotrophin receptor (p75NTR) signaling pathways substantially overlap with degenerative networks active in Alzheimer disease (AD). Modulation of p75NTR with the first-in-class small molecule LM11A-31 mitigates amyloid-induced and pathological tau-induced synaptic loss in preclinical models. Here we conducted a 26-week randomized, placebo-controlled, double-blinded phase 2a safety and exploratory endpoint trial of LM11A-31 in 242 participants with mild to moderate AD with three arms: placebo, 200 mg LM11A-31 and 400 mg LM11A-31, administered twice daily by oral capsules. This trial met its primary endpoint of safety and tolerability. Within the prespecified secondary and exploratory outcome domains (structural magnetic resonance imaging, fluorodeoxyglucose positron-emission tomography and cerebrospinal fluid biomarkers), significant drug-placebo differences were found, consistent with the hypothesis that LM11A-31 slows progression of pathophysiological features of AD; no significant effect of active treatment was observed on cognitive tests. Together, these results suggest that targeting p75NTR with LM11A-31 warrants further investigation in larger-scale clinical trials of longer duration. EU Clinical Trials registration: 2015-005263-16 ; ClinicalTrials.gov registration: NCT03069014 .

A TrkB small molecule partial agonist rescues TrkB phosphorylation deficits and improves respiratory function in a mouse model of Rett syndrome.

Rett syndrome (RTT) results from loss-of-function mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2) and is characterized by abnormal motor, respiratory and autonomic control, cognitive impairment, autistic-like behaviors and increased risk of seizures. RTT patients and Mecp2-null mice exhibit reduced expression of brain-derived neurotrophic factor (BDNF), which has been linked in mice to increased respiratory frequency, a hallmark of RTT. The present study was undertaken to test the hypotheses that BDNF deficits in Mecp2 mutants are associated with reduced activation of the BDNF receptor, TrkB, and that pharmacologic activation of TrkB would improve respiratory function. We characterized BDNF protein expression, TrkB activation and respiration in heterozygous female Mecp2 mutant mice (Het), a model that recapitulates the somatic mosaicism for mutant MECP2 found in typical RTT patients, and evaluated the ability of a small molecule TrkB agonist, LM22A-4, to ameliorate biochemical and functional abnormalities in these animals. We found that Het mice exhibit (1) reduced BDNF expression and TrkB activation in the medulla and pons and (2) breathing dysfunction, characterized by increased frequency due to periods of tachypnea, and increased apneas, as in RTT patients. Treatment of Het mice with LM22A-4 for 4 weeks rescued wild-type levels of TrkB phosphorylation in the medulla and pons and restored wild-type breathing frequency. These data provide new insight into the role of BDNF signaling deficits in the pathophysiology of RTT and highlight TrkB as a possible therapeutic target in this disease.

Use of Botulinum Toxin for Limb Immobilization for Rehabilitation in Rats with Experimental Stroke.

Motor rehabilitation strategies after unilateral stroke suggest that the immobilization of the healthy, unimpaired limb can promote the functional recovery of a paretic limb. In rodents, this has been modeled using casts, harnesses, and other means of restricting the use of the non-paretic forelimb in models of experimental stroke. Here, we evaluated an alternative approach, using botulinum toxin injections to limit the function of the non-paretic forelimb. Adult male rats were subjected to permanent ligation of the left distal middle cerebral artery, resulting in right forelimb paresis. The rats were then subjected to: (1) no treatment; (2) botulinum toxin injections 1 day post stroke; or (3) cast placement 5 days post stroke. Casts were removed after 5 weeks, while the botulinum toxin injection effectively immobilized subjects for approximately the same duration. Rats with bilateral forelimb impairment due to the stroke plus casting or botulinum injections were still able to feed and groom normally. Both immobilization groups showed modest recovery following the stroke compared to those that did not receive immobilization, but the casting approach led to unacceptable levels of animal stress. The botulinum toxin approach to limb immobilization had both advantages and disadvantages over traditional physical limb immobilization. The major advantage was that it was far less stress-inducing to the subject animals and appeared to be well tolerated. A disadvantage was that the paresis took roughly 10 weeks to fully resolve, and any degree of residual paresis could confound the interpretation of the behavioral assessments.

Delayed administration of a small molecule tropomyosin-related kinase B ligand promotes recovery after hypoxic-ischemic stroke.

BACKGROUND AND PURPOSE: Stroke is the leading cause of long-term disability in the United States, yet no drugs are available that are proven to improve recovery. Brain-derived neurotrophic factor stimulates neurogenesis and plasticity, processes that are implicated in stroke recovery. It binds to both the tropomyosin-related kinase B and p75 neurotrophin receptors. However, brain-derived neurotrophic factor is not a feasible therapeutic agent, and no small molecule exists that can reproduce its binding to both receptors. We tested the hypothesis that a small molecule (LM22A-4) that selectively targets tropomyosin-related kinase B would promote neurogenesis and functional recovery after stroke. METHODS: Four-month-old mice were trained on motor tasks before stroke. After stroke, functional test results were used to randomize mice into 2 equally, and severely, impaired groups. Beginning 3 days after stroke, mice received LM22A-4 or saline vehicle daily for 10 weeks. RESULTS: LM22A-4 treatment significantly improved limb swing speed and accelerated the return to normal gait accuracy after stroke. LM22A-4 treatment also doubled both the number of new mature neurons and immature neurons adjacent to the stroke. Drug-induced differences were not observed in angiogenesis, dendritic arborization, axonal sprouting, glial scar formation, or neuroinflammation. CONCLUSIONS: A small molecule agonist of tropomyosin-related kinase B improves functional recovery from stroke and increases neurogenesis when administered beginning 3 days after stroke. These findings provide proof-of-concept that targeting of tropomyosin-related kinase B alone is capable of promoting one or more mechanisms relevant to stroke recovery. LM22A-4 or its derivatives might therefore serve as "pro-recovery" therapeutic agents for stroke.

Microglial activation induced by brain trauma is suppressed by post-injury treatment with a PARP inhibitor.

BACKGROUND: Traumatic brain injury (TBI) induces activation of microglia. Activated microglia can in turn increase secondary injury and impair recovery. This innate immune response requires hours to days to become fully manifest, thus providing a clinically relevant window of opportunity for therapeutic intervention. Microglial activation is regulated in part by poly(ADP-ribose) polymerase-1 (PARP-1). Inhibition of PARP-1 activity suppresses NF-kB-dependent gene transcription and thereby blocks several aspects of microglial activation. Here we evaluated the efficacy of a PARP inhibitor, INO-1001, in suppressing microglial activation after cortical impact in the rat. METHODS: Rats were subjected to controlled cortical impact and subsequently treated with 10 mg/kg of INO-1001 (or vehicle alone) beginning 20 - 24 hours after the TBI. Brains were harvested at several time points for histological evaluation of inflammation and neuronal survival, using markers for microglial activation (morphology and CD11b expression), astrocyte activation (GFAP), and neuronal survival (NeuN). Rats were also evaluated at 8 weeks after TBI using measures of forelimb dexterity: the sticky tape test, cylinder test, and vermicelli test. RESULTS: Peak microglial and astrocyte activation was observed 5 to 7 days after this injury. INO-1001 significantly reduced microglial activation in the peri-lesion cortex and ipsilateral hippocampus. No rebound inflammation was observed in rats that were treated with INO-1001 or vehicle for 12 days followed by 4 days without drug. The reduced inflammation was associated with increased neuronal survival in the peri-lesion cortex and improved performance on tests of forelimb dexterity conducted 8 weeks after TBI. CONCLUSIONS: Treatment with a PARP inhibitor for 12 days after TBI, with the first dose given as long as 20 hours after injury, can reduce inflammation and improve histological and functional outcomes.

The p75 neurotrophin receptor promotes amyloid-beta(1-42)-induced neuritic dystrophy in vitro and in vivo.

Oligomeric forms of amyloid-beta (Abeta) are thought to play a causal role in Alzheimer's disease (AD), and the p75 neurotrophin receptor (p75(NTR)) has been implicated in Abeta-induced neurodegeneration. To further define the functions of p75(NTR) in AD, we examined the interaction of oligomeric Abeta(1-42) with p75(NTR), and the effects of that interaction on neurite integrity in neuron cultures and in a chronic AD mouse model. Atomic force microscopy was used to ascertain the aggregated state of Abeta, and fluorescence resonance energy transfer analysis revealed that Abeta oligomers interact with the extracellular domain of p75(NTR). In vitro studies of Abeta-induced death in neuron cultures isolated from wild-type and p75(NTR-/-) mice, in which the p75(NTR) extracellular domain is deleted, showed reduced sensitivity of mutant cells to Abeta-induced cell death. Interestingly, Abeta-induced neuritic dystrophy and activation of c-Jun, a known mediator of Abeta-induced deleterious signaling, were completely prevented in p75(NTR-/-) neuron cultures. Thy1-hAPP(Lond/Swe) x p75(NTR-/-) mice exhibited significantly diminished hippocampal neuritic dystrophy and complete reversal of basal forebrain cholinergic neurite degeneration relative to those expressing wild-type p75(NTR). Abeta levels were not affected, suggesting that removal of p75(NTR) extracellular domain reduced the ability of excess Abeta to promote neuritic degeneration. These findings indicate that although p75(NTR) likely does not mediate all Abeta effects, it does play a significant role in enabling Abeta-induced neurodegeneration in vitro and in vivo, establishing p75(NTR) as an important therapeutic target for AD.

Small molecule modulation of the p75 neurotrophin receptor inhibits multiple amyloid beta-induced tau pathologies.

Longitudinal preclinical and clinical studies suggest that Aß drives neurite and synapse degeneration through an array of tau-dependent and independent mechanisms. The intracellular signaling networks regulated by the p75 neurotrophin receptor (p75NTR) substantially overlap with those linked to Aß and to tau. Here we examine the hypothesis that modulation of p75NTR will suppress the generation of multiple potentially pathogenic tau species and related signaling to protect dendritic spines and processes from Aß-induced injury. In neurons exposed to oligomeric Aß in vitro and APP mutant mouse models, modulation of p75NTR signaling using the small-molecule LM11A-31 was found to inhibit Aß-associated degeneration of neurites and spines; and tau phosphorylation, cleavage, oligomerization and missorting. In line with these effects on tau, LM11A-31 inhibited excess activation of Fyn kinase and its targets, tau and NMDA-NR2B, and decreased Rho kinase signaling changes and downstream aberrant cofilin phosphorylation. In vitro studies with pseudohyperphosphorylated tau and constitutively active RhoA revealed that LM11A-31 likely acts principally upstream of tau phosphorylation, and has effects preventing spine loss both up and downstream of RhoA activation. These findings support the hypothesis that modulation of p75NTR signaling inhibits a broad spectrum of Aß-triggered, tau-related molecular pathology thereby contributing to synaptic resilience.

Small-molecule modulation of the p75 neurotrophin receptor inhibits a wide range of tau molecular pathologies and their sequelae in P301S tauopathy mice.

In tauopathies, phosphorylation, acetylation, cleavage and other modifications of tau drive intracellular generation of diverse forms of toxic tau aggregates and associated seeding activity, which have been implicated in subsequent synaptic failure and neurodegeneration. Suppression of this wide range of pathogenic species, seeding and toxicity mechanisms, while preserving the physiological roles of tau, presents a key therapeutic goal. Identification and targeting of signaling networks that influence a broad spectrum of tau pathogenic mechanisms might prevent or reverse synaptic degeneration and modify disease outcomes. The p75 neurotrophin receptor (p75NTR) modulates such networks, including activation of multiple tau kinases, calpain and rhoA-cofilin activity. The orally bioavailable small-molecule p75NTR modulator, LM11A-31, was administered to tauP301S mice for 3 months starting at 6 months of age, when tau pathology was well established. LM11A-31 was found to reduce: excess activation of hippocampal cdk5 and JNK kinases and calpain; excess cofilin phosphorylation, tau phosphorylation, acetylation and cleavage; accumulation of multiple forms of insoluble tau aggregates and filaments; and, microglial activation. Hippocampal extracts from treated mice had substantially reduced tau seeding activity. LM11A-31 treatment also led to a reversal of pyramidal neuron dendritic spine loss, decreased loss of dendritic complexity and improvement in performance of hippocampal behaviors. These studies identify a therapeutically tractable upstream signaling module regulating a wide spectrum of basic mechanisms underlying tauopathies.

Signaling through Rho GTPase pathway as viable drug target.

Signaling through the Rho family of small GTPases has been increasingly investigated for their involvement in a wide variety of diseases such as cardiovascular, pulmonary, and neurological disorders as well as cancer. Rho GTPases are a subfamily of the Ras superfamily proteins which play essential roles in a number of biological processes, especially in the regulation of cell shape change, cytokinesis, cell adhesion, and cell migration. Many of these processes demonstrate a common theme: the rapid and dynamic reorganization of actin cytoskeleton of which Rho signaling has now emerged as a major switch control. The involvement of dynamic changes of Rho GTPases in disease states underscores the need to produce effective inhibitors for their therapeutic applications. Fasudil and Y-27632, with many newer additions, are two classes of widely used chemical compounds that inhibit Rho kinase (ROCK), an important downstream effector of RhoA subfamily GTPases. These inhibitors have been successful in many preclinical studies, indicating the potential benefit of clinical Rho pathway inhibition. On the other hand, except for Rac1 inhibitor NSC23766, there are few effective inhibitors directly targeting Rho GTPases, likely due to the lack of optimal structural information on individual Rho-RhoGEF, Rho-RhoGAP, or Rho-RhoGDI interaction to achieve specificity. Recently, LM11A-31 and other derivatives of peptide mimetic ligands for p75 neurotrophin receptor (p75(NTR)) show promising effects upstream of Rho GTPase signaling in neuronal regeneration. CCG-1423, a chemical compound showing profiles of inhibiting downstream of RhoA, is a further attempt for the development of novel pharmacological tools to disrupt Rho signaling pathway in cancer. Because of a rapidly growing number of studies deciphering the role of the Rho proteins in many diseases, specific and potent pharmaceutical modulators of various steps of Rho GTPase signaling pathway are critically needed to target for therapeutic intervention in cardiovascular disease, neurological disorders, and cancer progression.

Modulation of the p75 neurotrophin receptor suppresses age-related basal forebrain cholinergic neuron degeneration.

Age-related degeneration of basal forebrain cholinergic neurons (BFCNs) is linked to cognitive impairment. The p75 neurotrophin receptor (p75NTR) has been proposed to mediate neuronal degeneration in aging. Therefore, we tested the hypothesis that modifying p75NTR function would prevent or reverse aging-related neuronal degeneration using LM11A-31, a small molecule p75NTR modulator that downregulates degenerative and upregulates trophic receptor-associated signaling. Morphological analysis in mice showed loss of BFCN area detectable by 18 months of age. Oral administration of LM11A-31 from age 15 to 18 months resulted in a dose-related preservation of BFCN area and one month of treatment from 17 to 18 months also preserved cell area. To evaluate reversal of established neuronal atrophy, animals were treated from 21 to 25 months of age. Treatment was associated with an increase of cell size to a mean area larger than that observed at 18 months, accompanied by increases in mean MS/VDB neurite length, as well as increased cholinergic fiber density and synaptophysin pre-synaptic marker levels in the hippocampus. These findings support the idea that modulation of p75NTR activity can prevent and potentially reverse age-associated BFCN degeneration. Moreover, this may be achieved therapeutically with orally bioavailable agents such as LM11A-31.

Nerve Growth Factor Pathobiology During the Progression of Alzheimer's Disease.

The current review summarizes the pathobiology of nerve growth factor (NGF) and its cognate receptors during the progression of Alzheimer's disease (AD). Both transcript and protein data indicate that cholinotrophic neuronal dysfunction is related to an imbalance between TrkA-mediated survival signaling and the NGF precursor (proNGF)/p75NTR-mediated pro-apoptotic signaling, which may be related to alteration in the metabolism of NGF. Data indicate a spatiotemporal pattern of degeneration related to the evolution of tau pathology within cholinotrophic neuronal subgroups located within the nucleus basalis of Meynert (nbM). Despite these degenerative events the cholinotrophic system is capable of cellular resilience and/or plasticity during the prodromal and later stages of the disease. In addition to neurotrophin dysfunction, studies indicate alterations in epigenetically regulated proteins occur within cholinotrophic nbM neurons during the progression of AD, suggesting a mechanism that may underlie changes in transcript expression. Findings that increased cerebrospinal fluid levels of proNGF mark the onset of MCI and the transition to AD suggests that this proneurotrophin is a potential disease biomarker. Novel therapeutics to treat NGF dysfunction include NGF gene therapy and the development of small molecule agonists for the cognate prosurvival NGF receptor TrkA and antagonists against the pan-neurotrophin p75NTR death receptor for the treatment of AD.

Anti-cancer drug induced neurotoxicity and identification of Rho pathway signaling modulators as potential neuroprotectants.

Many chemotherapy drugs are known to cause significant clinical neurotoxicity, which can result in the early cessation of treatment. To identify and develop more effective means of neuroprotection it is important to understand the toxicity of these drugs at the molecular and cellular levels. In the present study, we examine the effects of paclitaxel (taxol), cisplatin, and methotrexate on primary rat neurons including hippocampal, cortical, and dorsal horn/dorsal root ganglion neuronal cultures. We found that all of these anti-cancer drugs induce substantial neurotoxicity evidenced by neurite degeneration. The neurons are capable of recovering after treatment withdrawal, but taxol exerts a biphasic effect that results in the collapse of processes days after treatment is withdrawn. After cisplatin and methotrexate treatment, we observed the degeneration of neuronal processes including the reduction of dendritic branching, length, and altered growth cone formation, indicating an abnormal arrangement of the actin cytoskeleton consistent with the involvement of Rho family small GTPases. Inhibiting RhoA downstream effector p160 ROCK/Rho kinase using Y-27632, or activating p75 neurotrophin receptor (p75 NTR) using non-peptide mimetic LM11A-31, were able to reverse the degeneration caused by cisplatin and methotrexate. Therefore, the neurotoxicity resulting from exposure to the anti-cancer drugs cisplatin and methotrexate can be alleviated by inhibiting Rho signaling pathway.

Small, nonpeptide p75NTR ligands induce survival signaling and inhibit proNGF-induced death.

Studies showing that neurotrophin binding to p75NTR can promote cell survival in the absence of Trk (tropomyosin-related kinase) receptors, together with recent structural data indicating that NGF may bind to p75NTR in a monovalent manner, raise the possibility that small molecule p75NTR ligands that positively regulate survival might be found. A pharmacophore designed to capture selected structural and physical chemical features of a neurotrophin domain known to interact with p75NTR was applied to in silico screening of small molecule libraries. Small, nonpeptide, monomeric compounds were identified that interact with p75NTR. In cells showing trophic responses to neurotrophins, the compounds promoted survival signaling through p75NTR-dependent mechanisms. In cells susceptible to proneurotrophin-induced death, compounds did not induce apoptosis but inhibited proneurotrophin-mediated death. These studies identify a unique range of p75NTR behaviors that can result from isolated receptor liganding and establish several novel therapeutic leads.