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Dexpramipexole, also known as R-(+)-Pramipexole, is a neuroprotective agent and weak non-ergoline dopamine agonist. Dexpramipexole has been found to have neuroprotective effects and is being investigated for treatment of amyotrophic lateral sclerosis (ALS). Dexpramipexole reduces mitochondrial reactive oxygen species (ROS) production, inhibits the activation of apoptotic pathways, and increase cell survival in response to a variety of neurotoxins and β-amyloid neurotoxicity. Compared to the S-(-) isomer, Dexpramipexole has much lower dopamine agonist activity.
1 . Cheah BC, Kiernan MC. Dexpramipexole, the R(+) enantiomer of pramipexole, for the potential treatment of amyotrophic lateral sclerosis. IDrugs. 2010 Dec;13(12):911-20. Abstract Dexpramipexole (KNS-760704), the R(+) enantiomer of pramipexole, is under development by Knopp Neurosciences and Biogen Idec as a potential neuroprotective therapy for amyotrophic lateral sclerosis (ALS), a universally fatal neurodegenerative disease. Pramipexole, exclusively the S(-) enantiomer, is a non-ergot dopaminergic autoreceptor agonist that is currently marketed for use in the treatment of Parkinson/'s disease and restless legs syndrome. Pramipexole has been proposed to exert a broad spectrum of neuroprotective properties, primarily through antioxidant effects, inhibiting apoptotic enzymes and preserving mitochondrial structure and activity. More recent work has suggested that pramipexole possesses anti-excitotoxic properties, raising the possibility of beneficial effects in patients with ALS. However, pramipexole has high intrinsic dopaminergic receptor activity and, consequently, dose-limiting side effects, including orthostatic hypotension and hallucination, are frequent. Dexpramipexole exhibits significantly lower affinity for dopaminergic receptors, thereby making it unlikely to be associated with dopaminergic side effects. In clinical trials to date, dexpramipexole has been safe and well tolerated at doses up to 67-fold higher than the maximum recommended daily dose of pramipexole in patients with Parkinson/'s disease, and has demonstrated signs of neuroprotective benefit. This report summarizes the chemical and pharmacological properties of dexpramipexole and describes the potential utility of the drug in the pharmaceutical development pipeline. 2 . Bozik ME, Mather JL, Kramer WG, et al. Safety, tolerability, and pharmacokinetics of KNS-760704 (dexpramipexole) in healthy adult subjects. J Clin Pharmacol. 2011 Aug;51(8):1177-85. Abstract Dexpramipexole (KNS-760704; [6R]-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine) is a novel synthetic amino-benzothiazole in development for the treatment of amyotrophic lateral sclerosis (ALS). Preclinical studies have shown that dexpramipexole is neuroprotective in vitro and in vivo, is highly orally bioavailable and water soluble, and rapidly achieves and maintains high central nervous system concentrations relative to plasma. Two phase 1 clinical studies were conducted to assess the safety, tolerability, and pharmacokinetics (PK) of single and multiple doses of dexpramipexole in 54 healthy male and female adults. The effect of food on the single-dose PK of dexpramipexole was also evaluated. Single doses (50 mg, 150 mg, or 300 mg) and multiple doses (50 mg twice daily, 100 mg twice daily, or 150 mg twice daily) of dexpramipexole over 4.5 days were safe and well tolerated. Dexpramipexole was rapidly absorbed, with time to maximum plasma concentration ranging from 1.8 to 2.6 hours and half-life ranging from 6.4 to 8.1 hours under fasted conditions, and was mostly eliminated in urine as unchanged parent drug (84%-90% of dose). Food had no effect on the single-dose PK of dexpramipexole. These findings support the ongoing development of dexpramipexole for the treatment of ALS and further evaluation of the compound/'s therapeutic potential in other neurodegenerative diseases. 3 . Cudkowicz M, Bozik ME, Ingersoll EW, et al. The effects of dexpramipexole (KNS-760704) in individuals with amyotrophic lateral sclerosis. Nat Med. 2011 Nov 20;17(12):1652-6. Abstract Amyotrophic lateral sclerosis (ALS) is characterized by upper and lower motor neuron dysfunction and loss, rapidly progressive muscle weakness, wasting and death. Many factors, including mitochondrial dysfunction, may contribute to ALS pathogenesis. Riluzole, which has shown only modest benefits in a measure of survival time without demonstrated effects on muscle strength or function, is the only approved treatment for ALS. We tested the putative mitochondrial modulator dexpramipexole (KNS-760704; (6R)-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine) in subjects with ALS in a two-part, double-blind safety and tolerability study, with a preliminary assessment of its effects on functional decline and mortality. In part 1, the effects of dexpramipexole (50, 150 or 300 mg d(-1)) versus placebo were assessed over 12 weeks. In part 2, after a 4-week, single-blind placebo washout, continuing subjects were re-randomized to dexpramipexole at 50 mg d(-1) or 300 mg d(-1) as double-blind active treatment for 24 weeks. Dexpramipexole was safe and well tolerated. Trends showing a dose-dependent attenuation of the slope of decline of the ALS Functional Rating Scale-Revised (ALSFRS-R) in part 1 and a statistically significant (P = 0.046) difference between groups in a joint rank test of change from baseline in ALSFRS-R and mortality in part 2 strongly support further testing of dexpramipexole in ALS. 4 . Alavian KN, Dworetzky SI, Bonanni L, et al. Effects of dexpramipexole on brain mitochondrial conductances and cellular bioenergetic efficiency. Brain Res. 2012 Mar 29;1446:1-11. Abstract Cellular stress or injury can result in mitochondrial dysfunction, which has been linked to many chronic neurological disorders including amyotrophic lateral sclerosis (ALS) and Parkinson/'s disease (PD). Stressed and dysfunctional mitochondria exhibit an increase in large conductance mitochondrial membrane currents and a decrease in bioenergetic efficiency. Inefficient energy production puts cells, and particularly neurons, at risk of death when energy demands exceed cellular energy production. Here we show that the candidate ALS drug dexpramipexole (DEX; KNS-760704; ((6R)-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine) and cyclosporine A (CSA) inhibited increases in ion conductance in whole rat brain-derived mitochondria induced by calcium or treatment with a proteasome inhibitor, although only CSA inhibited calcium-induced permeability transition in liver-derived mitochondria. In several cell lines, including cortical neurons in culture, DEX significantly decreased oxygen consumption while maintaining or increasing production of adenosine triphosphate (ATP). DEX also normalized the metabolic profile of injured cells and was protective against the cytotoxic effects of proteasome inhibition. These data indicate that DEX increases the efficiency of oxidative phosphorylation, possibly by inhibition of a CSA-sensitive mitochondrial conductance. 5 . Rudnicki SA, Berry JD, Ingersoll E, et al. Dexpramipexole effects on functional decline and survival in subjects with amyotrophic lateral sclerosis in a Phase II study: subgroup analysis of demographic and clinical characteristics. Amyotroph Lateral Scler Frontotemporal Degener. 2013 Jan;14(1):44-51. Abstract Our objective was to explore treatment effects in patient subgroups using post hoc analyses of data from part 2 of the dexpramipexole Phase II study. Subjects with amyotrophic lateral sclerosis (ALS) received dexpramipexole 300 mg/day or 50 mg/day for 24 weeks. Treatment effects on the slope of the revised ALS Functional Rating Score (ALSFRS-R) and Combined Assessment of Function and Survival (CAFS) were evaluated in dichotomized subgroups: riluzole use, gender, site of symptom onset. Other subgroups were dichotomized using median baseline values for age, ALSFRS-R, slow vital capacity, symptom duration, diagnostic delay, and progression rate. Results showed that there was a 21% reduction in ALSFRS-R decline favoring the 300-mg vs. 50-mg arm (p = 0.177); mean CAFS ranking was significantly higher in the 300-mg vs. 50-mg arm (52.4 vs. 41.1; p = 0.046). Trends were recapitulated in virtually all subgroups. Generally, ALSFRS-R decline was reduced and CAFS rankings were higher in the 300-mg vs. 50-mg arm across subgroups. CAFS rankings were significantly higher in the 300-mg vs. 50-mg arm among subjects with ALSFRS-R scores ≤35, symptom duration <18.7 months, or progression rate ≥ 0.7 points/month (p < 0.03). In conclusion, the observed benefit of 300- vs. 50-mg dexpramipexole on functional decline and survival was generally consistent among subjects regardless of baseline characteristics.