A mutual prodrug ester of GABA and perphenazine exhibits antischizophrenic efficacy with diminished extrapyramidal effects

Factors affecting the GABAergic synapse function in Alzheimer's disease: Focus on microRNAs

Alzheimer's disease (AD) is a progressive neurological disease characterized by the loss of cognitive function, confusion, and memory deficit. Accumulation of abnormal proteins, amyloid beta (Aß), and phosphorylated Tau (p-tau) forms plaques and tangles that deteriorate synapse function, resulting in neurodegeneration and cognitive decline in AD. The human brain is composed of different types of neurons and/or synapses that are functionally defective in AD. The GABAergic synapse, the most abundant inhibitory neuron in the human brain was found to be dysfunctional in AD and contributes to disrupting neurological function. This study explored the types of GABA receptors associated with neurological dysfunction and various biological and environmental factors that cause GABAergic neuron dysfunction in AD, such as Aβ, p-tau, aging, sex, astrocytes, microglia, APOE, mental disorder, diet, physical activity, and sleep. Furthermore, we explored the role of microRNAs (miRNAs) in the regulation of GABAergic synapse function in neurological disorders and AD states. We also discuss the molecular mechanisms underlying GABAergic synapse dysfunction with a focus on miR-27b, miR-30a, miR-190a/b, miR-33, miR-51, miR-129-5p, miR-376-3p, miR-376c, miR-30b and miR-502-3p. The purpose of our article is to highlight the recent research on miRNAs affecting the regulation of GABAergic synapse function and factors that contribute to the progression of AD.

Hybrid molecules combining GABA-A and serotonin 5-HT6 receptors activity designed to tackle neuroinflammation associated with depression

There is clear evidence that the presence of inflammatory factors and impaired GABA-ergic neurotransmission in depressed patients is associated with poor clinical outcome. We designed hybrid molecules, bearing the GABA molecule assembled with chemical fragments that interact with the serotonin 5-HT₆ receptor. Such a combination aimed to curb neuroinflammation, remodel GABA-ergic signaling, and provide antidepressant-like activity. The most promising hybrid 3B exerted nanomolar affinity for 5-HT₆ receptors and exerted agonistic properties on GABA-A receptors. Developability studies conferred that 3B exerted favorable drug-like properties and optimal brain penetration. In in vivo studies, 3B exerted robust antidepressant-like activity and proved to be highly effective in reducing levels of oxidative stress markers and the pro-inflammatory cytokine IL-6. The inetersting pharmacological profile of 3B makes it a promising candidate for further development for depression associated with neuroinflammation.

Synthesis and preliminary biological evaluation of gabactyzine, a benactyzine-GABA mutual prodrug, as an organophosphate antidote

Organophosphates (OPs) are inhibitors of acetylcholinesterase and have deleterious effects on the central nervous system. Clinical manifestations of OP poisoning include convulsions, which represent an underlying toxic neuro-pathological process, leading to permanent neuronal damage. This neurotoxicity is mediated through the cholinergic, GABAergic and glutamatergic (NMDA) systems. Pharmacological interventions in OP poisoning are designed to mitigate these specific neuro-pathological pathways, using anticholinergic drugs and GABAergic agents. Benactyzine is a combined anticholinergic, anti-NMDA compound. Based on previous development of novel GABA derivatives (such as prodrugs based on perphenazine for the treatment of schizophrenia and nortriptyline against neuropathic pain), we describe the synthesis and preliminary testing of a mutual prodrug ester of benactyzine and GABA. It is assumed that once the ester crosses the blood-brain-barrier it will undergo hydrolysis, releasing benactyzine and GABA, which are expected to act synergistically. The combined release of both compounds in the brain offers several advantages over the current OP poisoning treatment protocol: improved efficacy and safety profile (where the inhibitory properties of GABA are expected to counteract the anticholinergic cognitive adverse effects of benactyzine) and enhanced chemical stability compared to benactyzine alone. We present here preliminary results of animal studies, showing promising results with early gabactyzine administration.

Cognitive Deficit in Schizophrenia: From Etiology to Novel Treatments

Schizophrenia is a major mental illness characterized by positive and negative symptoms, and by cognitive deficit. Although cognitive impairment is disabling for patients, it has been largely neglected in the treatment of schizophrenia. There are several reasons for this lack of treatments for cognitive deficit, but the complexity of its etiology-in which neuroanatomic, biochemical and genetic factors concur-has contributed to the lack of effective treatments. In the last few years, there have been several attempts to develop novel drugs for the treatment of cognitive impairment in schizophrenia. Despite these efforts, little progress has been made. The latest findings point to the importance of developing personalized treatments for schizophrenia which enhance neuroplasticity, and of combining pharmacological treatments with non-pharmacological measures.

Mutual Prodrugs of 5-Fluorouracil: From a Classic Chemotherapeutic Agent to Novel Potential Anticancer Drugs

The development of potent antitumor agents with a low toxicological profile against healthy cells is still one of the greatest challenges facing medicinal chemistry. In this context, the “mutual prodrug” approach has emerged as a potential tool to overcome undesirable physicochemical features and mitigate the side effects of approved drugs. Among broad‐spectrum chemotherapeutics available for clinical use today, 5‐fluorouracil (5‐FU) is one of the most representative, also included in the World Health Organization model list of essential medicines. Unfortunately, severe side effects and drug resistance phenomena are still the primary limits and drawbacks in its clinical use. This review describes the progress made over the last ten years in developing 5‐FU‐based mutual prodrugs to improve the therapeutic profile and achieve targeted delivery to cancer tissues.

Molecular mechanisms of metabotropic GABAB receptor function

Metabotropic γ-aminobutyric acid G protein-coupled receptors (GABA_B) represent one of the two main types of inhibitory neurotransmitter receptors in the brain. These receptors act both pre- and postsynaptically by modulating the transmission of neuronal signals and are involved in a range of neurological diseases, from alcohol addiction to epilepsy. A series of recent cryo-EM studies revealed critical details of the activation mechanism of GABA_B Structures are now available for the receptor bound to ligands with different modes of action, including antagonists, agonists, and positive allosteric modulators, and captured in different conformational states from the inactive apo to the fully active state bound to a G protein. These discoveries provide comprehensive insights into the activation of the GABA_B receptor, which not only broaden our understanding of its structure, pharmacology, and physiological effects but also will ultimately facilitate the discovery of new therapeutic drugs and neuromodulators.

GABAergic inhibitory neurons as therapeutic targets for cognitive impairment in schizophrenia

Schizophrenia is considered primarily as a cognitive disorder. However, functional outcomes in schizophrenia are limited by the lack of effective pharmacological and psychosocial interventions for cognitive impairment. GABA (gamma-aminobutyric acid) interneurons are the main inhibitory neurons in the central nervous system (CNS), and they play a critical role in a variety of pathophysiological processes including modulation of cortical and hippocampal neural circuitry and activity, cognitive function-related neural oscillations (eg, gamma oscillations) and information integration and processing. Dysfunctional GABA interneuron activity can disrupt the excitatory/inhibitory (E/I) balance in the cortex, which could represent a core pathophysiological mechanism underlying cognitive dysfunction in schizophrenia. Recent research suggests that selective modulation of the GABAergic system is a promising intervention for the treatment of schizophrenia-associated cognitive defects. In this review, we summarized evidence from postmortem and animal studies for abnormal GABAergic neurotransmission in schizophrenia, and how altered GABA interneurons could disrupt neuronal oscillations. Next, we systemically reviewed a variety of up-to-date subtype-selective agonists, antagonists, positive and negative allosteric modulators (including dual allosteric modulators) for α5/α3/α2 GABA_A and GABA_B receptors, and summarized their pro-cognitive effects in animal behavioral tests and clinical trials. Finally, we also discuss various representative histone deacetylases (HDAC) inhibitors that target GABA system through epigenetic modulations, GABA prodrug and presynaptic GABA transporter inhibitors. This review provides important information on current potential GABA-associated therapies and future insights for development of more effective treatments.

Investigational dopamine antagonists for the treatment of schizophrenia

INTRODUCTION

Schizophrenia is a debilitating illness with a chronic impact on social function and daily living. Although various antipsychotics are available, there are still many challenges and unmet needs. Thus, many compounds with diverse mechanisms have been investigated, but all approved antipsychotics still require interactions with dopamine D₂ receptors. Areas covered: We searched for investigational drugs using the key words 'dopamine' and 'schizophrenia' in American and European clinical trial registers (clinicaltrials.gov; clinicaltrialsregister.eu). Published articles were searched in PubMed, Embase, Medline, PsycINFO, Cumulative Index to Nursing and Allied Health Literature (CINAHL), the Web of Science and the Cochrane Central Register of Controlled Trials Library. Expert opinion: The prospect of developing a dopamine antagonist is hopeful. Brexpiprazole and cariprazine, which were agents listed as 'investigational dopamine antagonists,' just received FDA approval. Novel agents such as BL 1020, ITI-007, and JNJ-37822681 have solid published data available, and agents such as L-THP, Lu AF35700, S33138, and SB-773812 are under vigorous investigation. However, the expected benefits of the newly developed antagonists may not be great because they offer little enhanced efficacy for negative symptoms, cognition and functional outcomes.

Acylation or phosphorylation of hydroxyurea unexpectedly takes place on N rather than on O, leading to the formation of amides instead of the expected esters

Attempted acylation of the anticancer agent hydroxyurea (HU) with acyl chlorides or anhydrides led to acylation on the NH group rather than on the OH.

Emerging drugs for schizophrenia

INTRODUCTION

Since the development of clozapine, scores of antipsychotics have been introduced. These are, with one exception (aripiprazole), based on the pharmacological principle of 5-HT(2)/dopamine antagonism. Research on other treatment targets, which, in part, influence dopaminergic pathways directly or indirectly, is mounting. Managing psychotic symptoms is only one facet of successful treatment of schizophrenia. Effective remedies against negative symptoms and cognitive deficits are still an unmet clinical need.

AREAS COVERED

With the focus on the topics mentioned above, the authors briefly review the latest clinical research organized on the basis of receptor systems and other drug targets, which are discussed to be involved in the pathophysiology of schizophrenia.

EXPERT OPINION

In conclusion, although clinicians will have to have considerable patience before truly novel anti-schizophrenia treatments become obtainable, a number of interesting leads with considerable theoretical potential are being explored. As yet, it is difficult to predict which of these mechanisms will effectively augment the currently available treatments.

An open-label tolerability study of BL-1020 antipsychotic: a novel gamma aminobutyric acid ester of perphenazine

BACKGROUND

BL-1020, a novel gamma aminobutyric acid (GABA) ester of perphenazine, is a new oral antipsychotic with a strong affinity for dopamine and serotonin receptors. Unlike first- and second-generation antipsychotics, it has agonist activity at GABA(A).

OBJECTIVE

This is the first study to examine tolerability and safety of BL-1020 in schizophrenia.

METHODS

This was a phase-II, open-label, multicenter, 6-week study treating patients (n = 36) with chronic schizophrenia. Dosing started at 20 mg/d and increased over 7 days to 40 mg/d. Weekly assessments were conducted.

RESULTS

All but 1 patient was titrated to 30 mg/d at day 4; on day 7, 30 were titrated to 40 mg/d. Four patients discontinued the study prematurely. There was no clinically relevant increase in vital signs, sedation, dizziness, or other central nervous system effects or electrocardiogram or laboratory abnormalities and a small increase in weight. Ten patients experienced extrapyramidal symptoms (EPS) requiring treatment with an anticholinergic; 4 patients were unable to reach maximum dose because of EPS. Extrapyramidal Symptom Rating Scale did not indicate clinically significant changes in EPS. The most common adverse event was insomnia (6 patients); other frequent adverse effects (all n = 3) were extrapyramidal disorder, headache, parkinsonism, tremor, and hyperprolactinemia. There was improvement on Positive and Negative Syndrome Scale and Clinical Global Impression of Change with 22 patients showing at least 20% decrease by end point on Positive and Negative Syndrome Scale and 31 patients showing at least minimal improvement on Clinical Global Impression of Change.

CONCLUSIONS

These data suggest that 20 to 40 mg/d of BL-1020 is associated with clinically relevant improvement of psychosis with no worsening of EPS and support further testing in randomized controlled trials.

Selected Gamma Aminobutyric Acid (GABA) Esters may Provide Analgesia for Some Central Pain Conditions

Central pain is an enigmatic, intractable condition, related to destruction of thalamic areas, resulting in likely loss of inhibitory synaptic transmission mediated by GABA. It is proposed that treatment of central pain, a localized process, may be treated by GABA supplementation, like Parkinson’s disease and depression. At physiologic pH, GABA exists as a zwitterion that is poorly permeable to the blood brain barrier (BBB). Because the pH of the cerebral spinal fluid (CSF) is acidic relative to the plasma, ion trapping may allow a GABA ester prodrug to accumulate and be hydrolyzed within the CSF. Previous investigations with ester local anesthetics may be applicable to some GABA esters since they are weak bases, hydrolyzed by esterases and cross the BBB. Potential non-toxic GABA esters are discussed. Many GABA esters were investigated in the 1980s and it is hoped that this paper may spark renewed interest in their development.

BL-1020, a novel antipsychotic candidate with GABA-enhancing effects: D2 receptor occupancy study in humans

BL-1020 is a potentially novel antipsychotic, which comprises the typical antipsychotic perphenazine linked by an ester bound to gamma-aminobutyric acid (GABA), intending a simultaneous dopamine-2 (D(2)) receptor blockade and GABA facilitation in the brain. This positron emission tomography (PET) study, using [(11)C]raclopride, assessed the extent and duration of D(2) receptor occupancy (D(2) RO) and safety for single doses of BL-1020 in healthy male subjects. Overall, this study did not raise any safety concern. Single doses of 16-32 mg BL-1020 caused a dose dependent striatal D(2) RO. The 32 mg dose of BL-1020 resulted in an average D(2) RO of 44% at 4-6 h post dosing (pd), which declined to 33% at 24 h pd. Equimolar doses of BL-1020 and perphenazine resulted in similar D(2) RO at 24 h pd. Pharmacokinetic-pharmacodynamic analysis predicted that oral once daily administration of 32 mg BL-1020 would result in D(2) ROs ranging from 52 to 66% at a steady state.

Of mice and men: bridging the translational disconnect in CNS drug discovery

The tremendous advances in transgene animal technology, especially in the area of Alzheimer's disease, have not resulted in a significantly better success rate for drugs entering clinical development. Despite substantial increases in research and development budgets, the number of approved drugs in general has not increased, leading to the so-called innovation gap. While animal models have been very useful in documenting the possible pathological mechanisms in many CNS diseases, they are not very predictive in the area of drug development. This paper reports on a number of under-appreciated fundamental differences between animal models and human patients in the context of drug discovery with special emphasis on Alzheimer's disease and schizophrenia, such as different affinities of the same drug for human versus rodent target subtypes and the absence of many functional genotypes in animal models. I also offer a number of possible solutions to bridge the translational disconnect and improve the predictability of preclinical models, such as more emphasis on good-quality translational studies, more pre-competitive information sharing and the embracing of multi-target pharmacology strategies. Re-engineering the process for drug discovery and development, in a similar way to other more successful industries, is another possible but disrupting solution to the growing innovation gap. This includes the development of hybrid computational models, based upon documented preclinical physiology and pharmacology, but populated and validated with clinical data from actual patients.

Gamma-aminobutyric acid amides of nortriptyline and fluoxetine display improved pain suppressing activity

The GABA amides of the antidepressants nortriptyline and fluoxetine, 1 and 2, were compared to their respective parent compounds in rodent models of pain. The amides significantly reduced early nociceptive and late inflammatory responses compared to nortriptyline or fluoxetine, where 1 exhibited overall better efficacy than 2. Amide 1 was most efficacious in lowering cytokine secretion, edema and hyperalgesia induced by formalin and lambda-carrageenan, respectively. Thus, 1 is a promising candidate for the treatment of pain.

BL-1020: a novel antipsychotic drug with GABAergic activity and low catalepsy, is efficacious in a rat model of schizophrenia

Reduced brain gamma-amino-butyric acid (GABA) participates in the pathogenesis of schizophrenia. GABA scarcely penetrates the brain. We evaluated the pharmacological properties of BL-1020, a novel GABA ester of perphenazine. Oral BL-1020 or perphenazine were assessed in acute and subchronic schizophrenia rat models. Catalepsy, serum prolactin, receptor binding profile and cortical (PFC), hippocampal (Hip) and dopamine (DA) levels were determined. Radioactive [14C] labeled BL-1020 was used for pharmacokinetics (PK). Acute and subchronic treatment with BL-1020 antagonized amphetamine-induced hyperactivity, with significantly lower catalepsy and sedation compared to equimolar perphenazine. At the same time, BL-1020 increased DA release in the PFC and Hip. BL-1020 and perphenazine stimulated prolactin secretion equally. BL-1020 displayed strong DA and serotonin (5HT) receptor inhibition (D(2L)K(iz)=0.066 nM, D(2S)K(i)=0.062 nM, 5-HT(2A)K(i)=0.21 nM). PK data revealed that BL-1020 penetrated the brain.

CONCLUSIONS

The advantages of BL-1020 for treatment of schizophrenia stem from its being a DA/5HT antagonist and a GABAergic agonist that releases cortical DA and antagonizes amphetamine-induced hyperactivity with reduced catalepsy and sedation.