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.

The FDA-approved compound, pramipexole and the clinical-stage investigational drug, dexpramipexole, reverse chronic allodynia from sciatic nerve damage in mice, and alter IL-1ß and IL-10 expression from immune cell culture.

During the onset of neuropathic pain from a variety of etiologies, nociceptors become hypersensitized, releasing neurotransmitters and other factors from centrally-projecting nerve terminals within the dorsal spinal cord. Consequently, glial cells (astrocytes and microglia) in the spinal cord are activated and mediate the release of proinflammatory cytokines that act to enhance pain transmission and sensitize mechanical non-nociceptive fibers which ultimately results in light touch hypersensitivity, clinically observed as allodynia. Pramipexole, a D2/D3 preferring agonist, is FDA-approved for the treatment of Parkinson's disease and demonstrates efficacy in animal models of inflammatory pain. The clinical-stage investigational drug, R(+) enantiomer of pramipexole, dexpramipexole, is virtually devoid of D2/D3 agonist actions and is efficacious in animal models of inflammatory and neuropathic pain. The current experiments focus on the application of a mouse model of sciatic nerve neuropathy, chronic constriction injury (CCI), that leads to allodynia and is previously characterized to generate spinal glial activation with consequent release IL-1ß. We hypothesized that both pramipexole and dexpramipexole reverse CCI-induced chronic neuropathy in mice, and in human monocyte cell culture studies (THP-1 cells), pramipexole prevents IL-1ß production. Additionally, we hypothesized that in rat primary splenocyte culture, dexpramixole increases mRNA for the anti-inflammatory and pleiotropic cytokine, interleukin-10 (IL-10). Results show that following intravenous pramipexole or dexpramipexole, a profound decrease in allodynia was observed by 1 hr, with allodynia returning 24 hr post-injection. Pramipexole significantly blunted IL-1ß protein production from stimulated human monocytes and dexpramipexole induced elevated IL-10 mRNA expression from rat splenocytes. The data support that clinically-approved compounds like pramipexole and dexpramipexole support their application as anti-inflammatory agents to mitigate chronic neuropathy, and provide a blueprint for future, multifaceted approaches for opioid-independent neuropathic pain treatment.

Dexpramipexole attenuates myocardial ischemia/reperfusion injury through upregulation of mitophagy.

Reperfusion causes undesirable damage to the ischemic myocardium while restoring the blood flow. In this study, we evaluated the effects of dexpramipexole (DPX) on myocardial injury induced by ischemia/reperfusion (I/R) in-vivo and the hypoxia/reoxygenation (HR) in-vitro and examined the functional mechanisms of DPX. DPX protected cells against H/R-induced mitochondrial dysfunction and prevented H/R damage. Both myocardial infarct size and tissue damage due to I/R was reduced upon DPX treatment. We discovered that DPX enhanced mitophagy in-vivo and in-vitro, which was accompanied by enhanced expression of PINK1 and Parkin. Knock-down of PINK1 and Parkin by specific siRNAs reversed DPX-induced inhibition of myocardial I/R injury. These findings suggest that DPX might protect against myocardial injury via PINK1 and Parkin.

Advances in disease-modifying pharmacotherapies for the treatment of amyotrophic lateral sclerosis.

INTRODUCTION: To date, riluzole and edaravone are the only two drugs that have successfully passed clinical trials for the treatment of Amyotrophic Lateral Sclerosis (ALS). Unfortunately, both drugs exhibit very modest effects. Most other drugs have failed at phase III to show significant effects in phase III when tested in larger cohorts. This pattern necessitates improvements in the approach to ALS pharmacotherapy. AREAS COVERED: The authors discuss the two approved drugs, as well as several examples of drug candidates whose clinical trials did not demonstrate efficacy in phase III. Post-hoc analyses reveal that future clinical trials should include disease-staging procedures, longer-term trials to correctly assess survival, genetic studies of participants to aid in stratification, and more similarity between the protocols on preclinical models and clinical trials. Finally, they discuss the trials in process that demonstrate some of these suggestions and improvements. EXPERT OPINION: The approval of riluzole and edaravone was essentially a desperate attempt to provide urgent pharmacotherapy to the ALS community. To evolve toward more efficient therapies, we must conduct clinical trials with optimal stratification based on rapid/slow progressors and cognitive decline. Pharmaco-metabolomics should allow for the identification of biomarkers that are adapted for a given drug.

Dexpramipexole depletes blood and tissue eosinophils in nasal polyps with no change in polyp size.

OBJECTIVE: Chronic rhinosinusitis with nasal polyps (CRSwNP) and eosinophilia is a disease of the upper respiratory tract for which few therapies are available. Because the oral investigational drug dexpramipexole serendipitously decreased blood eosinophils in amyotrophic lateral sclerosis studies, we assessed its safety, eosinophil-lowering activity, and preliminary clinical efficacy in patients with CRSwNP and eosinophilia. METHODS: Sixteen subjects with CRSwNP, absolute eosinophil count (AEC) ≥ 0.300 × 109 /L, and polyp tissue eosinophils were evaluable for efficacy in a 6-month open-label, multi-center study of dexpramipexole 150 mg twice daily. The coprimary endpoints were change in AEC and change in total polyp score (TPS) from baseline to month 6, with additional clinical and histologic endpoints assessed. RESULTS: Thirteen of 16 subjects completed 6 months of dexpramipexole treatment. Geometric mean baseline AEC was 0.525 ± 0.465 eosinophils × 109 /L and decreased to 0.031 ± 0.019 after 6 months of dexpramipexole treatment, a 94% reduction (P < 0.001). Ten of 16 subjects had eosinophil counts reduced to ≤ 0.020 × 109 /L at month 6. In 12 subjects with nasal polyp biopsies at baseline and month 6, tissue eosinophils were reduced from a mean of 168 ± 134 to 5 ± 2 per high-power field (HPF) (P = 0.001), a 97% reduction from baseline. There was no significant reduction in TPS or improvement in other clinical endpoints. Dexpramipexole was well tolerated, with no drug-related serious adverse events. CONCLUSION: Dexpramipexole treatment produced profound eosinophil-lowering in peripheral blood and nasal polyp tissue. Despite the near-elimination of polyp eosinophils, decreased TPS and nasal symptom improvement were not observed. LEVEL OF EVIDENCE: 2 Laryngoscope, 129:E61-E66, 2019.

Repurposing of dexpramipexole to treatment of neonatal hypoxic/ischemic encephalopathy.

Dexpramipexole (DEX) is a drug with a good safety profile in humans, known for its ability to increase mitochondrial ATP production and prompt neuroprotection in adult rodents subjected to cerebral ischemia. In the present study we evaluated the effect of DEX in rat pups subjected to common carotid artery occlusion plus hypoxia (CCAoH, the classic Rice-Vannucci model). Because of the wide range of infarct size distribution in the CCAoH model, a priori subanalysis based on the effect of DEX on mild/moderate or severe brain injuries was conducted. The subanalysis showed that the drug (3 mg/kg bid i.p, after the hypoxic insult) decreased the infarction size in pups with mild/moderate injuries. Next, we developed a distal middle cerebral artery occlusion plus hypoxia (dMCAoH) model, characterized by an intra-experimental infarct size variability lower than that of the CCAoH model. Post-ischemic treatment with DEX (3 mg/kg bid i.p, after the hypoxic insult) reduced brain infarcts in pups exposed to dMCAoH. For the first time, we show that DEX reduces brain injury in different models of neonatal HIE. In light of the favorable safety profile of DEX in humans, the drug might have a realistic translational potential to treatment of perinatal cerebrovascular disorders.

Diagnosis and Novel Approaches to the Treatment of Hypereosinophilic Syndromes.

PURPOSE OF REVIEW: Hypereosinophilic syndrome (HES) is characterized by persistent hypereosinophilia associated with end-organ damage. As our understanding of the pathogenesis of various forms of HES broadens, so does our ability to tailor steroid-sparing therapies for each subtype. The purpose of this review is to summarize recent literature related to the etiology, diagnosis, and management of HES. RECENT FINDINGS: Mutations involved in subsets of HES can guide the choice of tyrosine kinase inhibitors beyond just imatinib. Several biologics that target interleukin-5 or its receptor have shown beneficial and selective eosinophil-reducing effects in clinical trials for asthma and other disorders including HES. Early clinical data with emerging therapies such as dexpramipexole and anti-Siglec-8 antibody show promise, but need to be confirmed in randomized trials. Several new biologics and tyrosine kinase inhibitors have been shown to lower eosinophil numbers, but more randomized trials are needed to confirm efficacy in HES.

Development and validation of a highly sensitive gradient chiral separation of pramipexole in human plasma by LC-MS/MS.

AIM: Development of a high-sensitivity chiral LC-MS/MS method was required to evaluate a combination of pramipexole (S-PPX) and its enantiomer dexpramipexole (R-PPX) in a proposed clinical trial. The previously available methods suffered from low sensitivity for the (S)-enantiomer in the presence of the more abundant (R)-enantiomer. Based on the projected dosing regimen in the clinical trial, a 5000-fold improvement in sensitivity was required for the (S)-enantiomer. METHODOLOGY: Spiked human plasma samples were extracted by liquid-liquid extraction using ethyl acetate and injected onto a CHIRALPAK ID column under pH gradient conditions. CONCLUSION: An improved analytical method was developed and validated with a final LLQ for (S)-PPX of 0.1 ng/ml in the presence of 2000 ng/ml of (R)-PPX.

Pharmacokinetics of renally excreted drug dexpramipexole in subjects with impaired renal function.

This phase I, open-label, single-dose study evaluated the pharmacokinetics, safety, and tolerability of renally excreted drug dexpramipexole in subjects with normal and impaired renal function, i.e. mild, moderate, severe renal impairment, or end-stage renal disease (ESRD) requiring hemodialysis when matched by age and sex. Dexpramipexole area under the curves (AUCs), but not Cmax , were significantly increased with the severity of renal impairment after a single dose administration. The geometric mean ratio of dose-normalized AUC(0-72) was 1.4, 1.7, 2.7, and 4.5, respectively, in mild, moderate, severe renal impairment, and ESRD subjects when compared to healthy subjects. There was a strong association between renal function (eGFR) and dexpramipexole CLr. The slope (90% confidence interval(CI)) of eGFR and renal clearance (CLr) in the regression model was 3.1 (2.4, 3.7). Dexpramipexole elimination in ESRD subjects during both dialysis and non-dialysis (i.e., interval between dialysis) was insignificant. Single 75 mg and 150 mg doses of dexpramipexole were well tolerated, and the safety profile was comparable across renal function groups. Extensive drug accumulation may occur with repeated dosing in patients with significant renal impairment. It is recommended that dexpramipexole not to be given to patients with severe renal impairment or in those with ESRD.

Chiral liquid chromatography-tandem mass spectrometry assay to determine that dexpramipexole is not converted to pramipexole in vivo after administered in humans.

Dexpramipexole (DEX) was being investigated in clinical studies for the treatment of amyotrophic lateral sclerosis (ALS). To monitor the potential chiral interconversion of dexpramipexole to pramipexole (PPX) in vivo, a highly sensitive and selective chiral LC-MS/MS assay was developed and qualified for the detection of pramipexole in the presence of dexpramipexole in human plasma. In this assay, plasma samples were extracted by protein precipitation coupled with solid phase extraction (SPE). The analyte PPX was separated from its enantiomer DEX using a chiral HPLC method. The assay was qualified with a dynamic range of 0.150-1.00ng/mL. The lower limit of quantitation (LLOQ) for PPX was 0.150ng/mL in the presence of up to 1000ng/mL of DEX. The qualified method was used to analyze plasma samples from a DEX clinical study. No PPX was detected in humans at pharmacologically significant levels after administration of dexpramipexole at single doses up to 600mg per day.

Amyotrophic lateral sclerosis and the clinical potential of dexpramipexole.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that leads to progressive weakness from loss of motor neurons and death on average in less than 3 years after symptom onset. No clear causes have been found and just one medication, riluzole, extends survival. Researchers have identified some of the cellular processes that occur after disease onset, including mitochondrial dysfunction, protein aggregation, oxidative stress, excitotoxicity, inflammation, and apoptosis. Mitochondrial disease may be a primary event in neurodegeneration or occur secondary to other cellular processes, and may itself contribute to oxidative stress, excitotoxicity, and apoptosis. Clinical trials currently aim to slow disease progression by testing drugs that impact one or more of these pathways. While every agent tested in the 18 years after the approval of riluzole has been ineffective, basic and clinical research methods in ALS have become dramatically more sophisticated. Dexpramipexole (RPPX), the R(+) enantiomer of pramiprexole, which is approved for symptomatic treatment of Parkinson disease, carries perhaps the currently largest body of pre-and early clinical data that support testing in ALS. The neuroprotective properties of RPPX in various models of neurodegeneration, including the ALS murine model, may be produced through protective actions on mitochondria. Early phase trials in human ALS suggest that the drug can be taken safely by patients in doses that provide neuroprotection in preclinical models. A Phase III trial to test the efficacy of RPPX in ALS is underway.