SR 57746A: An Orally Active Non-Peptide Compound with Neurotrophic and Neuroprotective Effects

SR 57746A/xaliproden, a non-peptide neurotrophic compound: prospects and constraints for the treatment of nervous system diseases

Neurodegenerative disorders such as Alzheimer's disease or amyotrophic lateral sclerosis as well as peripheral neuropathies are difficult to treat due to a limited range of effective drugs. Neurotrophic growth factors promote neuronal survival and differentiation and could hence be interesting tools to treat these diseases. Their therapeutic use is limited due their short half-life, their inability to cross the BBB and potential side effects including tumor promotion. SR 57746A is a non-peptide, orally active compound that exhibits neuroprotective effects in various model systems in vitro and in vivo. SR 57746A shows--amongst other activities--agonistic activity on 5-HT(1A) receptors. Several clinical trials examined SR 57746A in patients with Alzheimer's disease, amyotrophic lateral sclerosis or chemotherapy-induced peripheral sensory neuropathy. This article reviews the preclinical and clinical data on SR 57746A and points out potential future applications of this compound. However, due to disapointing results in phase III trials, Sanofi-Aventis recently decided to discontinue the development of this drug.

Bivalent peptidomimetic ligands of TrkC are biased agonists and selectively induce neuritogenesis or potentiate neurotrophin-3 trophic signals

This study was initiated to find small molecule ligands that would induce a functional response when docked with neurotrophin Trk receptors. "Minimalist" mimics of beta-turns were designed for this purpose. These mimics are (i) rigid, yet easily folded into turn-like conformations, and (ii) readily accessible from amino acids bearing most of the natural side chains. Gram quantities of 16 of these turn mimics were prepared and then assembled into 152 fluorescein-labeled bivalent peptidomimetics via a solution-phase combinatorial method. Fluorescence-based screening of these molecules using cells transfected with the Trk receptors identified 10 potential ligands of TrkC, the receptor for neurotrophin-3. Analogues of these bivalent peptidomimetics with biotin replacing the fluorescein label were then prepared and tested to confirm that binding was not due to the fluorescein. Several assays were conducted to find the mode of action of these biotinylated compounds. Thus, direct binding, survival and neuritogenic, and biochemical signal transduction assays showed 8 of the original 10 hits were agonistic ligands binding to the ectodomain of TrkC. Remarkably, some peptidomimetics afford discrete signals leading to either cell survival or neuritogenic differentiation. The significance of this work is three-fold. First, we succeeded in finding small, selective, proteolytically stable ligands for the TrkC receptor; there are very few of these in the literature. Second, we show that it is possible to activate distinct and biased signaling pathways with ligands binding at the ectodomain of wild-type receptors. Third, the discovery that some peptidomimetics initiate different modes of cell signaling increases their potential as pharmacological probes and therapeutic leads.

Xaliproden in amyotrophic lateral sclerosis: early clinical trials

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motor neurons. We report the safety and functional efficacy results of a double-blind, placebo-controlled phase II study of xaliproden, a non-peptidic compound with growth factor activities, in 54 ALS patients treated for up to 32 weeks. In order to overcome the interference of mortality with functional assessment in exploratory studies, we identified from our ALS database prognostic factors to establish a staging process for selection pf patients: age, disease duration, slopes of deterioration of the functional scores calculated during the two months prior to the inclusion, and the value at entry of the forced vital capacity (FVC). The six months intent-to-treat analysis showed no statistically significant effect but a trend in favour of 2 mg xaliproden compared to placebo for reduction in the rate of deterioration of FVC, limbs functional score, and manual muscle testing score (MMT). The results in the completer analysis showed a significant 43% slower rate of deterioration in FVC (P=0.046) in xaliproden-treated patients but not in functional and MMT scores. These results support the use of a staging process to select suitable patients for phase II studies, and suggest that xaliproden may have potential effects in ALS and deserve further study.

Disease-modifying therapies in Alzheimer's disease

Alzheimer's disease (AD) is a chronic, progressive, neurodegenerative disorder that places a substantial burden on patients, their families, and society. The disease affects approximately 5 million individuals in the United States, with an annual cost of care greater than $100 billion. During the past dozen years, several agents have been approved that enhance cognition and global function of AD patients, and recent advances in understanding AD pathogenesis has led to the development of numerous compounds that might modify the disease process. A wide array of antiamyloid and neuroprotective therapeutic approaches are under investigation on the basis of the hypothesis that amyloid beta (A beta) protein plays a pivotal role in disease onset and progression and that secondary consequences of A beta generation and deposition, including tau hyperphosphorylation and neurofibrillary tangle formation, oxidation, inflammation, and excitotoxicity, contribute to the disease process. Interventions in these processes with agents that reduce amyloid production, limit aggregation, or increase removal might block the cascade of events comprising AD pathogenesis. Reducing tau hyperphosphorylation, limiting oxidation and excitotoxicity, and controlling inflammation might be beneficial disease-modifying strategies. Potentially neuroprotective and restorative treatments such as neurotrophins, neurotrophic factor enhancers, and stem cell-related approaches are also under investigation.

MAPK activation via 5-hydroxytryptamine 1A receptor is involved in the neuroprotective effects of xaliproden

Motoneurons require neurotrophic factors for their survival and their differentiation. Xaliproden (SR57746A) is a synthetic compound that exhibits in vivo and in vitro neurotrophic effects in several experimental studies. Here we demonstrate that neuroprotective effects of Xaliproden on motoneuron cultures are mediated by the activation of the mitogen activated protein kinase pathway. It is inhibited by PD98059, a selective and irreversible inhibitor of MEK1. The activation of this pathway seems to involve two different proteins, the protein kinase C and the Ras. Indeed, we show that Xaliproden is able to activate the MAP kinases ERK1/2 and PKC in motoneurons. In addition, the use of a 5-hydroxytryptamine 1A receptor antagonist, Pindobind and pertussis toxin, inhibits the effect of Xaliproden on motoneuron survival, suggesting the involvement of this G-protein coupled receptor. Morever, 8-OH-DPAT, an agonist of 5-hydroxytryptamine 1A receptor, increases the survival of mouse motoneurons but not by the same extent as BDNF or xaliproden. Since 8-OH-DPAT does not act synergistically with Xaliproden, it is likely that their neuroprotective properties involve a similar pathway. Taken together, these results indicate that neuroprotective effects of Xaliproden on mouse motoneurons are dependent on the mitogen-activated protein kinase activation via 5-hydroxytryptamine 1A receptor.

Quantification of neurotrophin mRNA expression in PMN mouse: modulation by xaliproden

Compounds possessing neurotrophic properties may represent a possible treatment for neurodegenerative disorders such as amyotrophic lateral sclerosis. Xaliproden (SR57746A), an orally-active non-peptide compound, which has been found to exhibit neurotrophic effects in vitro and in vivo, increased the lifespan and delayed the progression of the motor neuron degeneration in PMN mice. We have used a quantitative reverse transcription/polymerase chain reaction amplification technique to study the regulation of neurotrophin mRNA and trk mRNA expression in PMN mice. NGF and NT-3 mRNA are downregulated in PMN mice. These deficiencies can be overcome by a treatment with xaliproden. Such an effect could contribute to neurotrophic effects of xaliproden in vivo and in vitro.

Effect of the nonpeptide neurotrophic compound SR 57746A on the phenotypic survival of purified mouse motoneurons

1. Neurotrophic factors have been used for the treatment of several neurodegenerative diseases. However, their use is limited by their inability to cross the blood-brain barrier, their short half life and their side effects. SR 57746A is a new orally active compound that exhibits in vivo and in vitro neurotrophic effects in several experimental models. 2. We show here that SR 57746A (1 microM) increases the phenotypic survival of embryonic purified mouse motoneurons in vitro to the same extent as brain-derived neurotrophic factor (100 ng ml-1), and increases the outgrowth and number of their neurites. It acts in a dose-dependent manner up to 1 microM which is the optimal concentration. Above this concentration, its neurotrophic effect decreases. 3. Genistein (10 microM), a protein tyrosine kinase inhibitor, also increases the phenotypic survival and differentiation of mouse motoneurons. It does not act in a synergistic or additive manner with SR 57746A. However, at concentrations equal or superior to 25 microM, it decreases the survival of motoneurons. This suggests that the neurotrophic effect of genistein is due to a favourable alteration of equilibrium between phosphorylated and dephosphorylated states of proteins involved in survival and differentiation of motoneurons. 4. Like genistein, SR 57746A should be used at a critical concentration (1 microM) to exert its optimal effects. Since SR 57746A does not act synergistically with genistein, it is likely that its mechanism of action involves a pathway similar to that affected by this tyrosine kinase inhibitor. 5. At the present time, SR 57746A is the only orally active compound and the only synthetic compound shown to be active on motoneurons in vitro. It should thus be considered as a good candidate for the treatment of motoneuron diseases.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood-brain barrier disruption: implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood-brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor alpha and IFN-gamma mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.

Effect of the neuroprotective compound SR57746A on nerve growth factor synthesis in cultured astrocytes from neonatal rat cortex

The neurotrophic factor promoting activity of the neuroprotective compound SR57746A was evaluated in primary cultures of neonatal rat cortical astrocytes by studying the synthesis of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). A concentration- and time-dependent increase of nerve growth factor mRNA was induced by SR57746A (10 nM-1 microM). In these astrocytes, BDNF mRNA contents were increased to a significant but smaller extent, and beta-actin mRNA showed no variation. SR57746A (1 microM) induced increases of both de novo protein translation after 6 h of incubation and NGF release into the extracellular medium after 6-24 h. These effects were preceded by a transient augmentation of junB, c-fos and c-jun mRNA contents. These increases of AP-1 family mRNA were associated with increased nuclear AP-1 binding activity. The results show that SR57746A can increase the synthesis and release of NGF in rat cortical astrocytes. Such effects may contribute to the drug's previously described neuroprotective effects.

The effect of the nonpeptide neurotrophic compound SR 57746A on the progression of the disease state of the pmn mouse

1. The progressive motor neuronopathy (pmn) mouse is an autosomal recessive mutant, in which the homozygotes suffer caudio-cranial degeneration of motor axons and die several weeks after birth. This strain provides the opportunity of testing potential therapeutic strategies for the treatment of motor neurone diseases such as amyotrophic lateral sclerosis. We have performed a study of the effects on the pmn mouse of SR 57746A, an orally-active, non-peptide compound which has been found to exhibit neurotrophic effects in vitro and in vivo. In order to treat the affected mice from birth, the mothers were administered 2.5 mg kg(-1). p.o., SR 57746A every two days until the weaning of the offspring (at day 20); then the offspring were given every two days a dose of 30 microg kg(-1), p.o., until their death. 2. Affected mice treated with SR 57746A had a lifespan 50% longer than that of the vehicle-treated mice (P=0.01). Compared to vehicle-treated pmn mice, SR 57746A improved the performance of the pmn mice in three different behavioural tasks. SR 57746A also maintained the amplitude of the motor evoked response of the gastrocnemius muscle, reduced the distal motor latency, and delayed the occurrence of the spontaneous denervation activity in this muscle. Histological studies indicated that at 20 days of age the mean surface areas of the fibres of the sciatic nerve were higher in SR 57746A-treated than in vehicle-treated mice. 3. At present, SR 57746A is the only orally active, nonpeptide compound known to be capable of delaying the progression of the motor neurone degeneration in pmn mice.

Inhibition of lysophosphatidic acid-induced neurite retraction and cell rounding by SR 57746A

Rapid neurite retraction and transient rounding of serum-starved NG108-15 and PC12 cells by lysophosphatidic acid (LPA) is retarded and reduced by pre-incubation of the cells with the small non-peptidic molecule, SR 57746A, which exhibits neurotrophic properties. The compound also antagonizes the redistribution of filamentous actin by LPA in both cell types. We hypothesize that the SR 57746A attenuation of LPA-induced effects may account for at least some of the neuroprotective properties of this molecule.