Identification of Riluzole derivatives as novel calmodulin inhibitors with neuroprotective activity by a joint synthesis, biosensor, and computational guided strategy.

The development of new molecules for the treatment of calmodulin related cardiovascular or neurodegenerative diseases is an interesting goal. In this work, we introduce a novel strategy with four main steps: (1) chemical synthesis of target molecules, (2) Förster Resonance Energy Transfer (FRET) biosensor development and in vitro biological assay of new derivatives, (3) Cheminformatics models development and in vivo activity prediction, and (4) Docking studies. This strategy is illustrated with a case study. Firstly, a series of 4-substituted Riluzole derivatives 1-3 were synthetized through a strategy that involves the construction of the 4-bromoriluzole framework and its further functionalization via palladium catalysis or organolithium chemistry. Next, a FRET biosensor for monitoring Ca2+-dependent CaM-ligands interactions has been developed and used for the in vitro assay of Riluzole derivatives. In particular, the best inhibition (80%) was observed for 4-methoxyphenylriluzole 2b. Besides, we trained and validated a new Networks Invariant, Information Fusion, Perturbation Theory, and Machine Learning (NIFPTML) model for predicting probability profiles of in vivo biological activity parameters in different regions of the brain. Next, we used this model to predict the in vivo activity of the compounds experimentally studied in vitro. Last, docking study conducted on Riluzole and its derivatives has provided valuable insights into their binding conformations with the target protein, involving calmodulin and the SK4 channel. This new combined strategy may be useful to reduce assay costs (animals, materials, time, and human resources) in the drug discovery process of calmodulin inhibitors.

Synthesis, characterization, in-silico, and pharmacological evaluation of new 2-amino-6­trifluoromethoxy benzothiazole derivatives.

Alzheimer's disease (AD), a relentless neurodegenerative disorder, is still waiting for safer profile drugs, risk factors affecting AD's pathogenesis include aß accumulation, tau protein hyperphosphorylation, and neuroinflammation. This research aimed to synthesize 2-amino-6­trifluoromethoxy benzothiazole schiff bases. Synthesis was straightforward, combining the riluzole skeleton with compounds containing the azomethine group. Schiff bases synthesized were characterized spectroscopically using proton NMR (1H NMR), and FTIR. In-vivo biological evaluation against scopolamine-induced neuronal damage revealed that these newly synthesized schiff bases were effective in protecting neurons against neuroinflammatory mediators. In-vitro results revealed that these compounds had remarkable potential in improving the anti-oxidant levels. It downregulated glutathione (GSH), glutathione S-transferase (GST), catalase levels, and upregulated lipid peroxidation (LPO) levels. Immunohistochemical studies revealed that groups treated with the newly synthesized schiff bases had reduced expression of inflammatory mediators such as cyclooxygenase 2 (COX-2), JNK, tumor necrosis factor (TNF-α), nuclear factor kappa B (NF-kB) in contrast to the disease group. Moreover, molecular docking studies on these compounds also showed that they possessed a better binding affinity for above mentioned inflammatory mediators. The results of these studies showed that 2-amino-6-trifluoromethoxy benzothiazole schiff bases are remarkably effective against oxidative stress-mediated neuroinflammation.

In silico studies reveal structural deviations of mutant profilin-1 and interaction with riluzole and edaravone in amyotrophic lateral sclerosis.

This study aimed to investigate four of the eight PFN-1 mutations that are located near the actin-binding domain and determine the structural changes due to each mutant and unravel how these mutations alter protein structural behavior. Swapaa's command in UCSF chimera for generating mutations, FTMAP were employed and the data was analyzed by RMSD, RMSF graphs, Rg, hydrogen bonding analysis, and RRdisMaps utilizing Autodock4 and GROMACS. The functional changes and virtual screening, structural dynamics, and chemical bonding behavior changes, molecular docking simulation with two current FDA-approved drugs for ALS were investigated. The highest reduction and increase in Rg were found to exist in the G117V and M113T mutants, respectively. The RMSF data consistently shows changes nearby to this site. The in silico data described indicate that each of the mutations is capable of altering the structure of PFN-1 in vivo. The potential effect of riluzole and edaravone two FDA approved drugs for ALS, impacting the structural deviations and stabilization of the mutant PFN-1 is evaluated using in silico tools. Overall, the analysis of data collected reveals structural changes of mutant PFN-1 protein that may explain the neurotoxicity and the reason(s) for possible loss and gain of function of PFN-1 in the neurotoxic model of ALS.

From Riluzole to Dexpramipexole via Substituted-Benzothiazole Derivatives for Amyotrophic Lateral Sclerosis Disease Treatment: Case Studies.

The 1,3-benzothiazole (BTZ) ring may offer a valid option for scaffold-hopping from indole derivatives. Several BTZs have clinically relevant roles, mainly as CNS medicines and diagnostic agents, with riluzole being one of the most famous examples. Riluzole is currently the only approved drug to treat amyotrophic lateral sclerosis (ALS) but its efficacy is marginal. Several clinical studies have demonstrated only limited improvements in survival, without benefits to motor function in patients with ALS. Despite significant clinical trial efforts to understand the genetic, epigenetic, and molecular pathways linked to ALS pathophysiology, therapeutic translation has remained disappointingly slow, probably due to the complexity and the heterogeneity of this disease. Many other drugs to tackle ALS have been tested for 20 years without any success. Dexpramipexole is a BTZ structural analog of riluzole and was a great hope for the treatment of ALS. In this review, as an interesting case study in the development of a new medicine to treat ALS, we present the strategy of the development of dexpramipexole, which was one of the most promising drugs against ALS.

Repurposing Potential of Riluzole as an ITAF Inhibitor in mTOR Therapy Resistant Glioblastoma.

Internal ribosome entry site (IRES)-mediated protein synthesis has been demonstrated to play an important role in resistance to mechanistic target of rapamycin (mTOR) targeted therapies. Previously, we have demonstrated that the IRES trans-acting factor (ITAF), hnRNP A1 is required to promote IRES activity and small molecule inhibitors which bind specifically to this ITAF and curtail IRES activity, leading to mTOR inhibitor sensitivity. Here we report the identification of riluzole (Rilutek®), an FDA-approved drug for amyotrophic lateral sclerosis (ALS), via an in silico docking analysis of FDA-approved compounds, as an inhibitor of hnRNP A1. In a riluzole-bead coupled binding assay and in surface plasmon resonance imaging analyses, riluzole was found to directly bind to hnRNP A1 and inhibited IRES activity via effects on ITAF/RNA-binding. Riluzole also demonstrated synergistic anti-glioblastoma (GBM) affects with mTOR inhibitors in vitro and in GBM xenografts in mice. These data suggest that repurposing riluzole, used in conjunction with mTOR inhibitors, may serve as an effective therapeutic option in glioblastoma.

Osteosarcoma growth suppression by riluzole delivery via iron oxide nanocage in nude mice.

Osteosarcomas are the most commonly occurring malignant bone cancer in young individuals. The survival rate of patients with metastatic osteosarcoma is low and has been stagnant for over two decades. We previously demonstrated that the glutamate release inhibitor, riluzole inhibits osteosarcoma cell growth. Towards the development of more effective therapy, we investigated the delivery of riluzole in human metastatic osteosarcoma xenografts in mice. We compared the efficacy of riluzole delivery by intraperitoneally injecting either free riluzole or riluzole released via two different shapes of iron oxide nanoparticles (nanocage or nanosphere) of size 15±2.5 nm. We monitored tumor size using Vernier calipers and bioluminescence assay and found a significant reduction in tumor size in the riluzole­treated groups when injected, either in free form or via nanoparticles, compared to the control groups (PBS, nanosphere or nanocage). Importantly, nanocage­delivered riluzole was most effective in reducing tumor size in the xenograft nude mice. While riluzole delivery induced apoptosis in tumor tissues in all three groups of riluzole­treated animals, it was highest in tumors from the nanocage­delivered riluzole group. Therefore, we conclude that riluzole is an effective drug to reduce tumor size in osteosarcoma and the efficacy of riluzole as a apoptotic and tumor­reducing drug is enhanced when delivered via nanocage.

Degradable and Injectable Hydrogel for Drug Delivery in Soft Tissues.

Injectable hydrogels are promising platforms for tissue engineering and local drug delivery as they allow minimal invasiveness. We have here developed an injectable and biodegradable hydrogel based on an amphiphilic PNIPAAm- b-PLA- b-PEG- b-PLA- b-PNIPAAm pentablock copolymer synthesized by ring-opening polymerization/nitroxide-mediated polymerization (ROP/NMP) combination. The hydrogel formation at around 30 °C was demonstrated to be mediated by intermicellar bridging through the PEG central block. Such a result was particularly highlighted by the inability of a PEG- b-PLA- b-PNIPAAm triblock analog of the same composition to gelify. The hydrogels degraded through hydrolysis of the PLA esters until complete mass loss due to the diffusion of the recovered PEG and PNIPAAm/micelle based residues in the solution. Interestingly, hydrophobic molecules such as riluzole (neuroprotective drug) or cyanine 5.5 (imaging probe) could be easily loaded in the hydrogels' micelle cores by mixing them with the copolymer solution at room temperature. Drug release was correlated to polymer mass loss. The hydrogel was shown to be cytocompatible (neuronal cells, in vitro) and injectable through a small-gauge needle (in vivo in rats). Thus, this hydrogel platform displays highly attractive features for use in brain/soft tissue engineering as well as in drug delivery.

Electromembrane extraction of verapamil and riluzole from urine and wastewater samples using a mixture of organic solvents as a supported liquid membrane: Study on electric current variations.

In this study, the application of a mixture of organic solvents as a supported liquid membrane for improving the efficiency of the electromembrane extraction procedure was investigated. The extraction process was followed by high-performance liquid chromatography analysis of two model drugs (verapamil and riluzole). In this research, four organic solvents, including 1-heptanol, 1-octanol, 2-nitrophenyl octyl ether, and 2-ethyl hexanol, were selected as model solvents and different binary mixtures (v/v 2:1, 1:1 and 1:2) were used as the supported liquid membrane. The mixture of 2-ethyl hexanol and 1-otanol (v/v, 2:1) improved the extraction efficiency of model drugs by 1.5 to 12 times. It was found that extraction efficiency is greatly influenced by the level of electric current. In this study, for various mixtures of organic solvents, the electric current fluctuated between 50 and 2500 µA, and the highest extraction efficiencies were obtained with low and stable electric currents. Finally, the optimized extraction condition was validated and applied for the determination of model drugs in urine and wastewater samples.

Targeting Protein Kinase CK1δ with Riluzole: Could It Be One of the Possible Missing Bricks to Interpret Its Effect in the Treatment of ALS from a Molecular Point of View?

Riluzole, approved by the US Food and Drug Administration (FDA) in 1995, is the most widespread oral treatment for the fatal neurodegenerative disorder amyotrophic lateral sclerosis (ALS). The drug, whose mechanism of action is still obscure, mitigates progression of the illness, but unfortunately with only limited improvements. Herein we report the first demonstration, using a combination of computational and in vitro studies, that riluzole is an ATP-competitive inhibitor of the protein kinase CK1 isoform δ, with an IC50 value of 16.1 µm. This allows us to rewrite its possible molecular mechanism of action in the treatment of ALS. The inhibition of CK1δ catalytic activity indeed links the two main pathological hallmarks of ALS: transactive response DNA-binding protein of 43 kDa (TDP-43) proteinopathy and glutamate excitotoxicity, exacerbated by the loss of expression of glial excitatory amino acid transporter-2 (EAAT2).

Rational design and development of a stable liquid formulation of riluzole and its pharmacokinetic evaluation after oral and IV administrations in rats.

Enterally administered riluzole is currently being investigated in a Phase II/III clinical trial for the treatment of acute spinal cord injury (SCI). Many SCI patients suffer from severe motor dysfunction and exhibit swallowing difficulties and cannot swallow riluzole tablets. The purpose of the present study was to develop a liquid solution formulation of riluzole, which can be administered more easily to this patient population with the capability to adjust the dose if needed. Riluzole was solubilized using water miscible organic solvents, namely, polyethylene glycol 400, propylene glycol and glycerin. A Central Composite Design (CCD) approach was used to develop an optimum co-solvent composition that can solubilize the entire 50 mg dose of riluzole in 5 ml. A three-factor five-level design was employed to investigate the effects of composition of co-solvents on riluzole solubility. The selected optimum formulation consists of 15% v/v PEG 400, 20% v/v propylene glycol and 10% v/v glycerin, with riluzole concentration of 10 mg/ml. The optimum composition was assessed for stability at different temperatures. Satisfactory stability was obtained at room temperature and 4 °C (t90 of 17 and 35 months, respectively). The optimum formulation of riluzole was suitable for both oral and intravenous administrations. Single dose pharmacokinetic studies of the optimum formulation by oral and IV routes were evaluated in rats, using commercially available Rilutek® tablets as a reference. The co-solvent formulation was well tolerated both orally and intravenously. In comparison to the commercial tablet, the co-solvent formulation had a faster rate of absorption and more sustained plasma levels with a significantly longer elimination half-life. Higher concentrations of riluzole in brain and spinal cord were achieved from co-solvent formulation as compared to tablet. The riluzole solution formulation is stable and offers advantages of ease of administration, consistent dosing, rapid onset and longer duration of action, better availability at site of action which can be extremely beneficial for the therapy in SCI patients.

Riluzole Inhibits Proliferation, Migration and Cell Cycle Progression and Induces Apoptosis in Tumor Cells of Various Origins.

BACKGROUND: Regardless of contemporary improvements in cancer treatment, the results of drug treatment are not always efficacious. Thus, the development of novel approaches that affect cancer cell-specific metabolic pathways is needed. Since much evidence has shown that tumor cell proliferation and motility are stimulated by glutamate via activation of its receptors, use of antagonists to these receptors may be the key to control cancer cell progression. Riluzole noncompetitive metabotropic glutamate receptor 1 (mGluR1) antagonist, commonly used to treat patients with amyotrophic lateral sclerosis (ALS), has shown some antineoplastic properties against melanoma, breast and prostate cancer. Yet little is known about its molecular mode of action. AIMS: The current study aims at evaluating the abilities of Riluzole to inhibit proliferation of several cancer cell lines, as well as resolve the mechanism of its action. METHOD: We demonstrated antiproliferative and antimigrative properties of Riluzole in rhabdomyosarcomamedulloblastoma, neuroblastoma, astrocytoma, glioma, colon cancer, lung cancer, thyroid carcinoma, leukemia, erythroleukemia and multiple myeloma. Our studies revealed apoptosis induction and G2-M cell cycle arrest in Riluzole treated A549, C6 and HT-29 cells. RESULT: At the molecular level, we found that these cells treated with Riluzole had a decrease of Cyclin B and an increase of p21 Waf1/Cip1 and p53 expression. We also observed an enhancement of CDK1 and Chk2 phosphorylation. Reported changes may suggest the involvement of these proteins in G2-M arrest, observed in flow cytometry analysis. These data indicated the potential use of Riluzole in the treatment of different types of cancers.

An Intracellular Allosteric Modulator Binding Pocket in SK2 Ion Channels Is Shared by Multiple Chemotypes.

Small conductance potassium (SK) ion channels define neuronal firing rates by conducting the after-hyperpolarization current. They are key targets in developing therapies where neuronal firing rates are dysfunctional, such as in epilepsy, Parkinson's, and amyotrophic lateral sclerosis (ALS). Here, we characterize a binding pocket situated at the intracellular interface of SK2 and calmodulin, which we show to be shared by multiple small-molecule chemotypes. Crystallization of this complex revealed that riluzole (approved for ALS) and an analog of the anti-ataxic agent (4-chloro-phenyl)-[2-(3,5-dimethyl-pyrazol-1-yl)-pyrimidin-4-yl]-amine (CyPPA) bind to and allosterically modulate via this site. Solution-state nuclear magnetic resonance demonstrates that riluzole, NS309, and CyPPA analogs bind at this bipartite pocket. We demonstrate, by patch-clamp electrophysiology, that both classes of ligand interact with overlapping but distinct residues within this pocket. These data define a clinically important site, laying the foundations for further studies of the mechanism of action of riluzole and related molecules.

A validated UHPLC-MS/MS method for the measurement of riluzole in plasma and myocardial tissue samples.

Through blocking the cardiac persistent sodium current, riluzole has the potential to prevent myocardial damage post cardiac bypass surgery. A sensitive UHPLC-MS/MS method was developed and validated for quantitation of riluzole and 5-methoxypsoralen in human plasma and myocardial tissue homogenate using a liquid-liquid extraction with dichloromethane. The chromatographic separation was achieved using Shimadzu Shim-pack XR-ODS III, 2.0 × 50 mm, 1.6 µm column with a gradient mobile phase comprising methanol and ammonium acetate buffer pH 3.6 in purified water. The analyte and internal standard were separated within 3.5 min. Riluzole quantitation was achieved using the mass transitions of 235-138 for riluzole and 217-156 for 5-methoxypsoralen. The method was linear for riluzole plasma concentrations from 0.2 to 500 ng/mL and myocardial tissue homogenate concentrations from 0.2 to 100 ng/mL. The method developed was successfully applied to a clinical study for patients receiving riluzole while undergoing cardiac bypass surgery.

Enhancement in the Neuroprotective Power of Riluzole Against Cerebral Ischemia Using a Brain Targeted Drug Delivery Vehicle.

Riluzole is the only available drug for motor neuron diseases quite well-known for its neuroprotective activity. But its poor aqueous solubility, short half-life with some side-effects at higher concentration poses a limitation to its use as a therapeutic agent. The present study was performed to investigate the therapeutic potential of nanoriluzole (NR), i.e., riluzole encapsulated in nanoparticles against cerebral ischemia (stroke) at three different concentrations [10 (NRL), 20 (NRM), and 40 (NRH) µg/kg body weight intraperitoneally (i.p.)]. Chitosan conjugated NIPAAM (N-isopropylacrylamide) nanoparticles coated with tween80 were synthesized through free radical polymerization. The particles were characterized with Transmission Electron Microscopy, Dynamic Light Scattering, and Fourier Transform Infrared spectroscopy and were found to have size of ∼50 nm. Cerebral ischemia was induced by Middle Cerebral Artery Occlusion (MCAO) model for 1 h and NR was given intraperitoneally after 1 h of MCAO. Animals were dissected after a reperfusion period of 24 h for evaluation of various parameters. Triphenyl tetrazolium chloride staining shows substantial reduction in infarct size in all three treated groups. It was also supported by histopathological results, biochemical parameters, and behavioral studies. Immunological parameters like NOS-2, NF-kB, and COX-2 also show profound reduction in expression in NR treated groups. Thus, the present work clearly demonstrated that the nanoparticle was good enough to carry large amount of drug across the Blood Brain Barrier which results in significant neuroprotection even at a very low concentration. It also substantially lowered the required concentration by overcoming the poor aqueous solubility; hence hardly leaving any scope for side-effects.

The influence of hydroxypropyl-ß-cyclodextrin on the solubility, dissolution, cytotoxicity, and binding of riluzole with human serum albumin.

Cyclodextrin-related host-guest encapsulation is fundamental to modulate the solubility of riluzole (RLZ), promoting its potential pharmaceutical applications. The supramolecular interaction of RLZ and hydroxypropyl-ß-cyclodextrin (HP-ß-CD) was examined through FT-IR spectroscopy, DSC-TGA, PXRD, (1)HNMR, 2D ROESY, ssNMR, and SEM. The HP-ß-CD/RLZ inclusion complex was formed at a molar ratio of 1:1. The stability constant (K=2327 M(-1)) and the corresponding thermodynamic parameters were ascertained through phase solubility studies. The water solubility and dissolution rate of RLZ notably increased in the presence of HP-ß-CD, whereas the inclusion complex did not increase the RLZ toxicity toward the LO2 cell line. The influence of HP-ß-CD on RLZ-human serum albumin (HSA) binding was investigated via fluorescence spectroscopy. Fluorescence quenching of HSA by RLZ in the presence and absence of HP-ß-CD were both static quenching. Data analysis showed that the addition of HP-ß-CD weakened the quenching and binding of RLZ with HSA but did not affect the binding site and binding force between RLZ and HSA. Furthermore, molecular models were generated to determine the binding site between HSA and RLZ, and these models were consistent with the experimental data.

Nanoemulsions for Intranasal Delivery of Riluzole to Improve Brain Bioavailability: Formulation Development and Pharmacokinetic Studies.

BACKGROUND: Amyotrophic Lateral Sclerosis (ALS), a motor neuron disease (MND), is a progressive neurodegenerative disorder characterized by the deterioration of both upper and lower motor neurons. Only one drug (riluzole) has been approved for the treatment of ALS. Riluzole is a BCS class II drug having 60% absolute bioavailability. It is a substrate of P-glycoprotein and BBB restricts its entry in brain. OBJECTIVE: This investigation was aimed to develop O/W nanoemulsion system of riluzole to improve its brain bioavailability. METHODS: Riluzole loaded nanoemulsion was prepared by phase titration method. It was consisting of 3% w/w Sefsol 218, 28.3% w/w Tween 80:Carbitol (1:1) and 68.7% w/w water. It was characterized for drop size, drop size distribution, transmittance, viscosity, pH, zeta potential, conductivity and nasal ciliotoxicity study. Thermodynamic stability and room temperature stability of prepared nanoemulsion formulation were evaluated. Pharmacokinetic and brain uptake study was carried out using albino rats (wistar) post intranasal and oral administration. RESULTS: Riluzole loaded nanoemulsion was having a drop size of 23.92±0.52 nm. It was free from nasal ciliotoxicity and stable for three months. Brain uptake of riluzole post intranasal administration of riluzole loaded nanoemulsion was significantly (P <4.10 × 10-6) higher when it was compared with oral administration of riluzole loaded nanoemulsion. CONCLUSION: This study indicates that nanoemulsion of riluzole for intranasal administration could be a promising approach for the treatment of ALS to minimize the dose of riluzole in order to avoid dose related adverse events.

Characterization and evaluation of synthetic riluzole with ß-cyclodextrin and 2,6-di-O-methyl-ß-cyclodextrin inclusion complexes.

ß-Cyclodextrin (ß-CD) and 2,6-di-O-methyl-ß-cyclodextrin (DM-ß-CD) inclusion complexes with riluzole (RLZ) were prepared to improve water solubility and broaden potential pharmaceutical applications. CDs/RLZ inclusion complexes were confirmed via phase solubility studies, FT-IR spectroscopy, PXRD, DSC, (1)H NMR, and SEM. Phase solubility studies indicated that ß-CD and DM-ß-CD can form 1:1 inclusion complexes with RLZ, and the stability constants were 663.17 and 1609.07M(-1), respectively. Water solubility and dissolution rate of RLZ were significantly improved in complex forms, implying that the inclusion complexes may develop pharmaceutical applications. Preliminary in vitro cytotoxicity assay also showed that RLZ hepatotoxicity was not increased in the inclusion complexes.

Physically cross-linked hydrogels of ß -cyclodextrin polymer and poly(ethylene glycol)-cholesterol as delivery systems for macromolecules and small drug molecules.

An injectable hydrogel based on the inclusion complexation of polymerized ß-cyclodextrin (pß-CD) and cholesterol terminated poly(ethylene glycol) (PEG-chol) was developed and used as a delivery system for both macromolecules and small drugs. The hydrogel was characterized by different analyses including X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The effects of pß-CD/PEG-chol ratio and PEG-chol architecture on the hydrogel properties were also investigated. Cytotoxicity of the hydrogel was evaluated in NIH 3T3 fibroblasts using MTS assay. The hydrogel had an elastic behavior even at high temperature since the gelation temperature was observed at 68 °C. The highest hydrogel strength and stability were observed for the 8-armed PEG-chol at a pß-CD/PEG-chol ratio of 1:1, w/w. Hydrogel degradation in phosphate buffered saline occurred by gradual erosion over the course of two months. IgG, a model hydrophilic macromolecule and riluzole, a model hydrophobic small drug were incorporated into the hydrogel and quantitatively released in a sustained fashion. The released IgG maintained its bioactivity confirming the absence of deleterious effects on protein structure during loading and release. The hydrogels showed no toxicity on NIH 3T3 fibroblasts confirming their biocompatibility. These results confirm the potential of pß-CD/PEG-chol hydrogel as a versatile delivery system for drugs of different molecular weights and nature.

The glutamate hypothesis in ALS: pathophysiology and drug development.

Amyotrophic lateral sclerosis (ALS) is an age-related neurodegenerative disorder that is believed to have complex genetic and environmental influences in the pathogenesis, but etiologies are unidentified for most patients. Until the major causes are better defined, drug development is directed at downstream pathophysiological mechanisms, themselves incompletely understood. For nearly 30 years, glutamate-induced excitotoxicity has lain at the core of theories behind the spiraling events, including mitochondrial dysfunction, oxidative stress, and protein aggregation, that lead to neurodegenerative cell death. One drug, riluzole, which possesses anti-glutamatergic properties, is approved as neuroprotective for ALS. Following the achievement of the riluzole trials, numerous other agents with similar mechanisms have been tested without success. This article provides an overview of excitotoxicity in ALS, focusing on the events that contribute to excess glutamate, how the excess might damage nerve cells, and how this information is being harnessed in the development of potential new neuroprotective agents. The work highlights clinical trials of drugs that have targeted the glutamate system, comments on the potential role of glutamate as a biomarker and concludes with a section on future directions for the field. As research uncovers elusive etiologies and brings clarity to pathophysiological mechanisms, the success of new interventions will increasingly depend on the design of agents that target particular mechanisms for specific individuals. The heady future of personalized drug regimens for ALS rests with medicinal chemists, the scientists whose ideas and work produce these designer drugs.

Riluzole: validation of stability-indicating HPLC, D1 and DD1 spectrophotometric assays.

A stability-indicating reversed-phase high-performance liquid chromatographic assay procedure has been developed and validated for riluzole in the presence of alkaline and oxidative degradation products. The liquid chromatographic separation was achieved and compared isocratically on C18 Zorbax ODS and Poroshell 120 EC-C18 columns by using a mobile phase containing methanol-water, pH = 3.10 (70:30, v/v), at a flow rate of 1 mL/min and ultraviolet detection at 264 nm. The method was linear over the concentration ranges of 20-200 µg/mL (r = 0.9997) and 10-200 µg/mL (r = 0.9995). The limit of detection and quantitation for the two columns were 2 and 6 µg/mL and 1 and 3 µg/mL, respectively. Moreover, spectrophotometric methods were applied for the determination of riluzole in the presence of its oxidative degradation products by using first derivative spectrophotometry at 252.5 and 275.0 nm. The method was linear over the concentration range of 1-20 µg/mL (r = 0.9995 and 0.9996) at the studied wavelengths, with limits of detection and quantitation of 0.1 and 0.3 µg/mL. In addition, the first derivative ratio spectrophotometry (DD1) method was applied for the determination of riluzole in the presence of its alkaline degradation product at 252.0, 278.5 and 306.3 nm by using 100 µg/mL of alkaline degraded riluzole as a divisor; riluzole was additionally determined in the presence of its hydrogen peroxide oxidative degradation products at 252.5, 275.0 and 305.0 nm by using 200 µg/mL of oxidative degraded riluzole as a divisor. The DD1 method was linear over the concentration range of 1-20 µg/mL (r = 0.9996, 0.9995 and 0.9996 for the alkaline degradation product at the three studied wavelengths, respectively; and r = 0.9995, 0.9996 and 0.9995 for the oxidative degradation product at the three studied wavelengths, respectively), with limits of detection and quantitation of 0.1 and 0.3 µg/mL for both alkaline and oxidative degradation products. The two studied chromatographic and spectrophotometric methods were comparable and display the required accuracy, selectivity, sensitivity and precision to assay riluzole in bulk and pharmaceutical dosage forms. Degradation products resulting from the stress studies did not interfere with the detection of riluzole, which indicates that these are stability-indicating assays.