Emapunil

Emapunil(AC-5216;XBD-173) is a translocator protein [TSPO (18 kDa)] ligand. IC50 value: Target: TSPO ligand XBD173 enhanced gamma-aminobutyric acid-mediated neurotransmission and counteracted induced panic attacks in rodents in the absence of sedation and tolerance development. XBD173 also exerted antipanic activity in humans and, in contrast to benzodiazepines, did not cause sedation or withdrawal symptoms [1]. The selective TSPO ligand, XBD173 (AC-5216, Emapunil), exerts anxiolytic effects not only in animal models, but also in human volunteers [2].

References:
[1]. Costa B, et al. Translocator protein as a promising target for novel anxiolytics. Curr Top Med Chem. 2012;12(4):270-85. [2]. Rupprecht R, et al. Translocator protein (18 kD) as target for anxiolytics without benzodiazepine-like side effects. Science. 2009 Jul 24;325(5939):490-3. [3]. Qiu ZK, et al. The antidepressant-like activity of AC-5216, a ligand for 18KDa translocator protein (TSPO), in an animal model of diabetes mellitus. Sci Rep. 2016 Nov 25;6:37345.

Translocator protein ligand protects against neurodegeneration in the MPTP mouse model of Parkinsonism.[Pubmed:30796158]

J Neurosci. 2019 Feb 22. pii: JNEUROSCI.2070-18.2019.

Parkinson's disease (PD) is the second most common neurodegenerative disease, after Alzheimer's disease. PD is a movement disorder with characteristic motor features that arise due to the loss of dopaminergic neurons from the substantia nigra. Although symptomatic treatment by the dopamine precursor levodopa and dopamine agonists can improve motor symptoms, no disease-modifying therapy exists yet. Here, we show that Emapunil (AC-5216, XBD-173), a synthetic ligand of the translocator protein 18 (TSPO), ameliorates degeneration of dopaminergic neurons, preserves striatal dopamine metabolism and prevents motor dysfunction in female mice treated with the 1-methyl-4-phenyl-1,-2,-3,-6-tetrahydropyridine (MPTP), as a model of parkinsonism. We found that Emapunil modulates the inositol requiring kinase 1 alpha (IRE alpha)/-X-box binding protein 1 (XBP1) unfolded protein response pathway and induces a shift from pro- towards anti-inflammatory microglia activation. Previously, Emapunil was shown to cross the blood brain barrier and to be safe and well-tolerated in a phase II clinical trial. Therefore, our data suggest that Emapunil may be a promising approach in the treatment of Parkinson's disease.Significance statementOur study reveals a beneficial effect of Emapunil on dopaminergic neuron survival, dopamine metabolism and motor phenotype in the MPTP mouse model of parkinsonism. In addition, our work uncovers molecular networks which mediate neuroprotective effects of Emapunil, including microglial activation state and unfolded protein response pathways. These findings not only contribute to our understanding of biological mechanisms of TSPO function but also indicate that TSPO may be a promising therapeutic target. We thus propose to further validate Emapunil in other Parkinson's disease mouse models and subsequently in clinical trials to treat Parkinson's disease.

The translocator protein ligand XBD173 improves clinical symptoms and neuropathological markers in the SJL/J mouse model of multiple sclerosis.[Pubmed:28899788]

Biochim Biophys Acta Mol Basis Dis. 2017 Dec;1863(12):3016-3027.

Multiple sclerosis (MS) is a severe autoimmune disease characterized by inflammatory, demyelinating and neurodegenerative components causing motor, sensory, visual and/or cognitive symptoms. The relapsing-remitting MS affecting 85% of patients is reliably mimicked by the proteolipid-protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE) SJL/J-mouse model. Significant progress was made for MS treatment but the development of effective therapies devoid of severe side-effects remains a great challenge. Here, we combine clinical, behavioral, histopathological, biochemical and molecular approaches to demonstrate that low and well tolerated doses (10-20mg/kg) of TSPO ligand XBD173 (Emapunil) efficiently ameliorate clinical signs and neuropathology of PLP-EAE mice. In addition to the conventional clinical scoring of symptoms, we applied the robust behavioral Catwalk-method to confirm that XBD173 (10mg/kg) increases the maximum contact area parameter at EAE-disease peak, indicating an improvement/recovery of motor functions. Consistently, histopathological studies coupled with microscope-cellSens quantification and RT-qPCR analyzes showed that XBD173 prevented demyelination by restoring normal protein and mRNA levels of myelin basic protein that was significantly repressed in PLP-EAE mice spinal cord and brain. Interestingly, ELISA-based measurement revealed that XBD173 increased allopregnanolone concentrations in PLP-EAE mice spinal and brain tissues. Furthermore, flow cytometry assessment demonstrated that XBD173 therapy decreased serum level of pro-inflammatory cytokines, including interleukin-17A, Interleukin-6 and tumor-necrosis-factor alpha in PLP-EAE mice. As the optimal XBD173 dosing exerting the maximal beneficial action in EAE mice is the lower 10mg/kg dose, the paper opens interesting perspectives for the development of efficient and safe therapies against MS with slight or no side-effects.

Translocator protein as a promising target for novel anxiolytics.[Pubmed:22204481]

Curr Top Med Chem. 2012;12(4):270-85.

Neurosteroids are able to rapidly control the excitability of the central nervous system, acting as regulators of type A receptors for GABA. Over the last two decades, many authors have confirmed that neurosteroid level alterations occur in psychiatric disorders, including anxiety disorders. More recently, investigators have manipulated neurosteroidogenesis in an effort to correct neuronal excitation and inhibition imbalances, which may lie at the root of neuropsychiatric conditions. In line with this strategy, emerging data have demonstrated that a promising target for therapy of anxiety disorders is the Translocator Protein (TSPO). TSPO is a five transmembrane domain protein (18 kDa) that is expressed predominantly in steroid-synthesizing tissues. At the subcellular level, TSPO is localized at contact sites between the outer and inner mitochondrial membranes and mediates the rate-limiting step of neurosteroidogenesis. Brain concentrations of neurosteroids can be affected by selective TSPO activation. Indeed, TSPO drug ligands are able to stimulate the primary neurosteroid formations that enhance GABAA receptor activity, pregnenolone and allopregnenalone, both in in vitro steroidogenic cells and in vivo animal models. A spectrum of TSPO ligands has been shown to exert anxiolytic actions when administered in rodents. Some TSPO drug ligands could potentially reach clinical development. For example, recent evidence has shown that the selective TSPO ligand, XBD173 (AC-5216, Emapunil), exerts anxiolytic effects not only in animal models, but also in human volunteers. Herein, we review the current literature regarding the central nervous system biology of TSPO, a promising molecular target, in combination with its available ligands.

Repeated administration of AC-5216, a ligand for the 18 kDa translocator protein, improves behavioral deficits in a mouse model of post-traumatic stress disorder.[Pubmed:23624119]

Prog Neuropsychopharmacol Biol Psychiatry. 2013 Aug 1;45:40-6.

Post-traumatic stress disorder (PTSD) is a severely disabling anxiety disorder that may occur following exposure to a serious traumatic event. It is a psychiatric condition that can afflict anyone who has experienced a life-threatening or violent event. Previous studies have shown that changes in 18 kDa translocator protein (TSPO) expression (or function), a promising target for treating neurological disorders without benzodiazepine-like side effects, may correlate with PTSD. However, few studies have investigated the anti-PTSD effects of TSPO ligands. AC-5216, a ligand for TSPO, induces anxiolytic- and anti-depressant-like effects in animal models. The present study aimed to determine whether AC-5216 ameliorates PTSD behavior in mice. Following the training session consisting of exposure to inescapable electric foot shocks, animals were administered AC-5216 daily during the behavioral assessments, i.e., situational reminders (SRs), the open field (OF) test, the elevated plus-maze (EPM) test, and the staircase test (ST). The results indicated that exposure to foot shocks induced long-term behavioral deficiencies in the mice, including freezing and anxiety-like behavior, which were significantly ameliorated by repeated treatment with AC-5216 but without any effect on spontaneous locomotor activity or body weight. In summary, this study demonstrated the anti-PTSD effects of AC-5216 treatment, suggesting that TSPO may represent a therapeutic target for anti-PTSD drug discovery and that TSPO ligands may be a promising new class of drugs for the future treatment of PTSD.

Antianxiety and antidepressant-like effects of AC-5216, a novel mitochondrial benzodiazepine receptor ligand.[Pubmed:15249420]

Br J Pharmacol. 2004 Aug;142(7):1059-72.

We investigated the ability of N-benzyl-N-ethyl-2-(7,8-dihydro-7-methyl-8-oxo-2-phenyl-9H-purin-9-yl)acetamide (AC-5216), a novel mitochondrial benzodiazepine receptor (MBR) ligand, to produce anti-anxiety and antidepressant-like effects in various animal models. AC-5216 showed high affinity for MBRs prepared from rat whole brain (Ki 0.297 nm), rat glioma cells (IC50 3.04 nm) and human glioma cells (IC50 2.73 nm), but only negligible affinity for the other main receptors including central benzodiazepine receptors. AC-5216 produced anti-anxiety effects in the Vogel-type conflict test in rats, and in the light/dark box and social interaction tests in mice at 0.1-3, 0.003-0.01 and 0.01-0.3 mg kg(-1), p.o., respectively. These effects of AC-5216 were antagonized by PK11195, an MBR antagonist. In the forced swimming test in rats, AC-5216 (3-30 mg kg(-1), p.o.) reduced the immobility time, and this effect was blocked by PK11195. AC-5216 had no myorelaxant effects, did not affect the memory or prolong hexobarbitone-induced sleep in mice, even at doses as high as 1000 mg kg(-1), p.o. Although it did slightly prolong the ethanol-induced sleep time at 1000 mg kg(-1), AC-5216 (1-100 mg kg(-1), p.o.) produced no distinct change in the rat electroencephalogram. These results indicate that AC-5216 produces anti-anxiety and antidepressant-like effects that are mediated by MBR, but does not cause the side effects normally associated with conventional benzodiazepines. Hence, AC-5216 shows potential for the treatment of stress-related disorders including anxiety and depression.