Bumetanide for Core Symptoms of Autism Spectrum Disorder (BAMBI): A Single Center, Double-Blinded, Participant-Randomized, Placebo-Controlled, Phase-2 Superiority Trial

CNS pharmacology of NKCC1 inhibitors

The Na-K-2Cl cotransporter NKCC1 and the neuron-specific K-Cl cotransporter KCC2 are considered attractive CNS drug targets because altered neuronal chloride regulation and consequent effects on GABAergic signaling have been implicated in numerous CNS disorders. While KCC2 modulators are not yet clinically available, the loop diuretic bumetanide has been used off-label in attempts to treat brain disorders and as a tool for NKCC1 inhibition in preclinical models. Bumetanide is known to have anticonvulsant and neuroprotective effects under some pathophysiological conditions. However, as shown in several species from neonates to adults (mice, rats, dogs, and by extrapolation in humans), at the low clinical doses of bumetanide approved for diuresis, this drug has negligible access into the CNS, reaching levels that are much lower than what is needed to inhibit NKCC1 in cells within the brain parenchyma. Several drug discovery strategies have been initiated over the last ∼15 years to develop brain-permeant compounds that, ideally, should be selective for NKCC1 to eliminate the diuresis mediated by inhibition of renal NKCC2. The strategies employed to improve the pharmacokinetic and pharmacodynamic properties of NKCC1 blockers include evaluation of other clinically approved loop diuretics; development of lipophilic prodrugs of bumetanide; development of side-chain derivatives of bumetanide; and unbiased high-throughput screening approaches of drug discovery based on large chemical compound libraries. The main outcomes are that (1), non-acidic loop diuretics such as azosemide and torasemide may have advantages as NKCC1 inhibitors vs. bumetanide; (2), bumetanide prodrugs lead to significantly higher brain levels than the parent drug and have lower diuretic activity; (3), the novel bumetanide side-chain derivatives do not exhibit any functionally relevant improvement of CNS accessibility or NKCC1 selectivity vs. bumetanide; (4) novel compounds discovered by high-throughput screening may resolve some of the inherent problems of bumetanide, but as yet this has not been achieved. Thus, further research is needed to optimize the design of brain-permeant NKCC1 inhibitors. In parallel, a major challenge is to identify the mechanisms whereby various NKCC1-expressing cellular targets of these drugs within (e.g., neurons, oligodendrocytes or astrocytes) and outside the brain parenchyma (e.g., the blood-brain barrier, the choroid plexus, and the endocrine system), as well as molecular off-target effects, might contribute to their reported therapeutic and adverse effects.

The sensory-reactivity PROM set: identification of a parent reported outcome measure set for autism spectrum disorder

Background

Most children with autism spectrum disorder (ASD) suffer from aberrant responses to sensory stimuli that significantly impact the quality of life. To develop sensory interventions, individually tailored outcome measures are crucially needed for the domain of sensory reactivity problems. Here, we describe the identification of relevant sensory themes according to caregivers of children with ASD according to the guidelines for developing a (parent proxy) patient-reported outcome measure set. Subsequently, we identify parallels between these themes and a well-validated and supported PROMIS® portal to facilitate implementation. Interviews with clinicians and focus groups and interviews with parents of children with ASD were used in the initial phase for concept elicitation. Codes and themes were generated by qualitative thematic data analysis on the transcripts and cognitive interviews with different parents were used for revisions. The resulting themes were compared to existing generic PROMIS-item banks and other existing questionnaires.

Results

A total of 11 parent-reported outcomes were identified that could be either classified as directly or indirectly related to sensory reactivity. Directly related themes comprised of: (1) sensory stimulation tolerance and (2) sensitivity to sensory stimuli. Indirectly related themes were: (3) irritable behavior (4) anxiety problems (5) mood problems (6) sleep problems (7) fatigue (8) physical complaints (9) daily functioning and participation (10) routines, structure and dealing with change and (11) problems in social interaction and communication. Seven out of 11 themes could be measured with generic PROMIS item banks. The four remaining outcomes (sensory stimulation tolerance; irritable behaviour; routines, structure and dealing with change; and sensitivity to sensory stimuli) were found suitable to be inventoried by existing PROMs.

Conclusion

The majority of parent-reported problems seemed related to indirect consequences of sensory reactivity, which are suitable to be measured with generic item banks. In sum, we identified a sensory-reactivity PROM (parent-proxy) set consisting of PROMIS® item banks and additional domains that together form a comprehensive and readily available outcome set for sensory reactivity problems in children with ASD.

Treatment Effect of Bumetanide in Children With Autism Spectrum Disorder: A Systematic Review and Meta-Analysis

Background: The therapeutic effect of bumetanide on autism spectrum disorder (ASD) seems to be controversial. To obtain better evidence on the efficacy of bumetanide, a systematic review and meta-analysis were performed. Methods: Randomized, placebo-controlled trials (RCTs) of bumetanide treatment in children with ASD were identified through systematic review from database inception to January 17, 2021. Subsequently, a meta-analysis was carried out to examine the effect of bumetanide on the severity of symptoms of ASD as assessed by the Childhood Autism Rating Scale (CARS) and Social Responsive Scale (SRS); core symptoms according to criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM)-5 of the American Psychiatric Association [social affect (SA), restricted, repetitive patterns of behavior, interests, or activities (RRB) and sensory symptoms]; and the therapeutic effect as assessed by Clinical Global Impressions-Efficacy (CGI-E). Results: In total, six RCTs involving 496 participants with ASD were identified in our study. The results showed that bumetanide could significantly improve the severity of the ASD symptoms measured by CARS and SRS. There was also evidence that bumetanide had positive effect on the core symptoms of ASD such as the SA and RRB, but there was no statistically significant effect on sensory symptoms. A significant positive effect on CGI-E scores in ASD patients was also observed. Conclusion: Our meta-analysis provided some support that bumetanide could improve the symptoms of children with ASD. However, additional large-scale longitudinal studies that provide clearer information and better control for confounding factors are needed to confirm our findings.

Recent Updates in Psychopharmacology for the Core and Associated Symptoms of Autism Spectrum Disorder

PURPOSE OF REVIEW

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by core deficits in social communication and restricted, repetitive patterns of behavior. This article aims to review the recent literature pertaining to psychopharmacology for the core and associated symptoms of ASD including social impairment, repetitive behaviors, irritability, and language impairment.

RECENT FINDINGS

Recent medication trials targeting social impairment in ASD have focused on neuropeptides (oxytocin and vasopressin) and memantine. None of these three medications has demonstrated consistent benefit for social impairment in ASD; however, additional studies are underway. Two double-blind, placebo-controlled studies on selective serotonin reuptake inhibitors (SSRIs) provide evidence against the use of SSRIs for repetitive behaviors in youth with ASD. Preliminary studies have investigated cannabidiol (CBD) for irritability in ASD but further studies are needed to demonstrate safety and efficacy. Finally, three double-blind, placebo-controlled studies provide preliminary evidence for folinic acid for the treatment of verbal language deficits in children with ASD. The identification of safe and effective pharmacological treatments to ameliorate the core and associated symptoms of ASD has proven difficult.

Pharmacological tools to target NKCC1 in brain disorders

The chloride importer NKCC1 and the chloride exporter KCC2 are key regulators of neuronal chloride concentration. A defective NKCC1/KCC2 expression ratio is associated with several brain disorders. Preclinical/clinical studies have shown that NKCC1 inhibition by the United States FDA-approved diuretic bumetanide is a potential therapeutic strategy in preclinical/clinical studies of multiple neurological conditions. However, bumetanide has poor brain penetration and causes unwanted diuresis by inhibiting NKCC2 in the kidney. To overcome these issues, a growing number of studies have reported more brain-penetrating and/or selective bumetanide prodrugs, analogs, and new molecular entities. Here, we review the evidence for NKCC1 pharmacological inhibition as an effective strategy to manage neurological disorders. We also discuss the advantages and limitations of bumetanide repurposing and the benefits and risks of new NKCC1 inhibitors as therapeutic agents for brain disorders.

Decades of Progress in the Psychopharmacology of Autism Spectrum Disorder

Recent decades have been marked by a wave drug treatment research in autism spectrum disorder (ASD). This work has resulted in improved ability to treat commonly occurring behavioral challenges associated with ASD including most prominently irritability marked by aggression, self-injurious behavior, and severe tantrums. While treatment of interfering behavior has progressed in our field, there remain several areas of unmet medical need including most prominently a lack of any approved drug therapies for the core, defining symptoms of autism. We outline the progress to date in the field of autism drug treatment while taking a future look forward into how decades of work can inform better future steps in this field.

Bumetanide Oral Liquid Formulation for the Treatment of Children and Adolescents with Autism Spectrum Disorder: Design of Two Phase III Studies (SIGN Trials)

There are currently no approved pharmacological treatments to improve social reciprocity and limit repetitive and rigid behaviors in autism spectrum disorder (ASD). We describe the design of two Phase III studies evaluating the efficacy/safety of bumetanide oral liquid formulation in ASD. These are international, multicenter, randomized, double-blind, placebo-controlled studies in children and adolescents with ASD aged 7 to 17 years (n = 200; study 1), or younger children with ASD aged 2 to 6 years (n = 200; study 2). The primary endpoint of each is change in Childhood Autism Rating Scale 2 total raw score after 6 months. These studies could contribute to the first pharmacological treatment to improve social reciprocity and limit repetitive and rigid behaviors in children and adolescents with ASD.

Treating Autism With Bumetanide: Are Large Multicentric and Monocentric Trials on Selected Populations Complementary?

In their article in the Journal, Sprengers et al.¹ conclude that bumetanide does not attenuate autism spectrum disorder (ASD) despite a nominally significant treatment effect in repetitive behaviors, which is a core symptom of ASD but was defined as a secondary measure in this trial. Four earlier studies performed by 3 independent institutes, including 2 studies^2,3 not mentioned by Sprengers et al., testing a total of 169 children (versus 122 placebo) showed a significant amelioration of ASD symptoms. Bumetanide also significantly attenuated behavioral features of patients with tuberous sclerosis according to another study by Sprengers' same group.⁴.

Dr. Sprengers et al. Reply

Before we elaborate on the postulated discrepancies between our trial and previous bumetanide in autism spectrum disorder (ASD) trials, we would like to acknowledge the crucial pioneering work on the γ-aminobutyric acid (GABA) developmental sequence by Dr. Ben-Ari and colleagues. Chloride dysregulation and altered GABA polarity have been implicated in neurological and neurodevelopmental disorders, including some forms of ASD. Etiologies underlying ASD are profoundly heterogeneous, and an important challenge is to link the optimal treatment to individual patients. Indeed, ASD animal models indicate reversed GABA polarity as a treatment target in some,^1,2 but not all, studies.³ The aim of the Bumetanide in Autism Medication and Biomarker (BAMBI) trial was to replicate previous trial findings and to develop stratification biomarkers that may help to understand expected variability in treatment response.

Editorial: Targeting the Core Symptoms of Autism Spectrum Disorder With Mechanism-Based Medications

Medications can help manage behavioral problems associated with autism spectrum disorder (ASD), but no pharmacological treatment has proved effective for the core symptoms of the disorder. The article by Sprengers et al.¹ in this issue of the Journal reports the primary results of the randomized clinical trial Bumetanide in Autism Medication and Biomarker (BAMBI), which tested the efficacy of bumetanide, a loop diuretic acting as a selective antagonist of the chloride importer NKCC1, for the core symptoms of ASD in 92 children 7-15 years of age.¹ The study by Sprengers and colleagues was carefully designed and powered to detect a medium treatment effect size. Great attention was paid to protecting the blindness of the experiment in light of the adverse effects of the medication. After the 3-month treatment, bumetanide was not better than placebo at decreasing social communication deficits, as measured with the Social Responsiveness Scale-2 (the primary outcome), although a decrease in repetitive behaviors (a secondary outcome) was found. This study attests to the progress from clinical serendipity to pathogenesis-driven treatment research in ASD and is remarkable in a number of ways.

Novel treatments for autism spectrum disorder based on genomics and systems biology

BACKGROUND

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder with a complex underlying genetic architecture. There are currently no known pharmacologic treatments for the core ASD symptoms of social deficits and restricted/ repetitive behavior. However, there are dozens of clinical trials currently underway that are testing the impact of novel and existing agents on core and associated symptoms in ASD.

METHODS

We present a narrative synthesis of the historical and contemporary challenges to drug discovery in ASD. We then provide an overview of novel treatments currently under investigation from a genomics and systems biology perspective.

RESULTS

Data driven network and cluster analyses suggest alterations in transcriptional regulation, chromatin remodelling, synaptic transmission, neuropeptide signalling, and/or immunological mechanisms may contribute to or underlie the development of ASD. Agents and upcoming trials targeting each of the above listed systems are reviewed.

CONCLUSION

Identifying effective pharmacologic treatments for the core and associated symptom domains in ASD will require further collaboration and innovation in the areas of outcome measurement, biomarker research, and genomics, as well as systematic efforts to identify and treat subgroups of individuals with ASD who may be differentially responsive to specific treatments.

Design, Synthesis, In Vitro and In Vivo Characterization of Selective NKCC1 Inhibitors for the Treatment of Core Symptoms in Down Syndrome

Intracellular chloride concentration [Cl^-]_i is defective in several neurological disorders. In neurons, [Cl^-]_i is mainly regulated by the action of the Na⁺-K⁺-Cl^- importer NKCC1 and the K⁺-Cl^- exporter KCC2. Recently, we have reported the discovery of ARN23746 as the lead candidate of a novel class of selective inhibitors of NKCC1. Importantly, ARN23746 is able to rescue core symptoms of Down syndrome (DS) and autism in mouse models. Here, we describe the discovery and extensive characterization of this chemical class of selective NKCC1 inhibitors, with focus on ARN23746 and other promising derivatives. In particular, we present compound 40 (ARN24092) as a backup/follow-up lead with in vivo efficacy in a mouse model of DS. These results further strengthen the potential of this new class of compounds for the treatment of core symptoms of brain disorders characterized by the defective NKCC1/KCC2 expression ratio.