Lead Optimization of Benzoxazolone Carboxamides as Orally Bioavailable and CNS Penetrant Acid Ceramidase Inhibitors

From pathological mechanisms in Krabbe disease to cutting-edge therapy: A comprehensive review

Since its initial documentation by Knud Krabbe in 1916, numerous studies have scrutinized the characteristics of Krabbe disease (KD) until the identification of the mutation in the GALC gene. In alignment with that, we investigated the natural history of KD spanning eight decades to gain a deeper understanding of the evolutionary trajectory of its mechanisms. Through our comprehensive analysis, we unearthed additional novel elements in molecular biology involving the micropathological mechanism of the disease. This review offers an updated perspective on the metabolic disorder that defines KD. Recently, extracellular vesicles (EVs), autophagy impairment, and α-synuclein have emerged as pivotal players in the neuropathological processes. EVs might serve as a cellular mechanism to avoid or alleviate the detrimental impacts of excessive toxic psychosine levels, and extracting EVs could contribute to synapse dysfunction. Autophagy impairment was found to be independent of psychosine and reliant on AKT and B-cell lymphoma 2. Additionally, α-synuclein has been recognized for inducing cellular death and dysfunction in common biological pathways. Our objective is to assess the effectiveness of advanced therapies in addressing this particular condition. While hematopoietic stem cells have been a primary treatment, its administration proves challenging, particularly in the presymptomatic phase. In this review, we have compiled information from over 10 therapy trials, comparing them based on their benefits and disadvantage.

High-throughput discovery of novel small-molecule inhibitors of acid Ceramidase

Ceramide has a key role in the regulation of cellular senescence and apoptosis. As Ceramide levels are lowered by the action of acid ceramidase (AC), abnormally expressed in various cancers, the identification of AC inhibitors has attracted increasing interest. However, this finding has been mainly hampered by the lack of formats suitable for the screening of large libraries. We have overcome this drawback by adapting a fluorogenic assay to a 384-well plate format. The performance of this optimised platform has been proven by the screening a library of 4100 compounds. Our results show that the miniaturised platform is well suited for screening purposes and it led to the identification of several hits, that belong to different chemical classes and display potency ranges of 2-25 µM. The inhibitors also show selectivity over neutral ceramidase and retain activity in cells and can therefore serve as a basis for further chemical optimisation.

Synthesis and biological profile of benzoxazolone derivatives

The benzoxazolone nucleus is an ideal scaffold for drug design, owing to its discrete physicochemical profile, bioisosteric preference over pharmacokinetically weaker moieties, weakly acidic behavior, presence of both lipophilic and hydrophilic fragments on a single framework, and a wider choice of chemical modification on the benzene and oxazolone rings. These properties apparently influence the interactions of benzoxazolone-based derivatives with their respective biological targets. Hence, the benzoxazolone ring is implicated in the synthesis and development of pharmaceuticals with a diverse biological profile ranging from anticancer, analgesics, insecticides, anti-inflammatory, and neuroprotective agents. This has further led to the commercialization of several benzoxazolone-based molecules and a few others under clinical trials. Nevertheless, the SAR exploration of benzoxazolone derivatives for the identification of potential "hits" followed by the screening of "leads" provides a plethora of opportunities for further exploration of the pharmacological profile of the benzoxazolone nucleus. In this review, we aim to present the biological profile of different derivatives based on the benzoxazolone framework.

Preclinical studies in Krabbe disease: A model for the investigation of novel combination therapies for lysosomal storage diseases

Krabbe disease (KD) is a lysosomal storage disease (LSD) caused by mutations in the galc gene. There are over 50 monogenetic LSDs, which largely impede the normal development of children and often lead to premature death. At present, there are no cures for LSDs and the available treatments are generally insufficient, short acting, and not without co-morbidities or long-term side effects. The last 30 years have seen significant advances in our understanding of LSD pathology as well as treatment options. Two gene therapy-based clinical trials, NCT04693598 and NCT04771416, for KD were recently started based on those advances. This review will discuss how our knowledge of KD got to where it is today, focusing on preclinical investigations, and how what was discovered may prove beneficial for the treatment of other LSDs.

Krabbe Disease: Prospects of Finding a Cure Using AAV Gene Therapy

Krabbe Disease (KD) is an autosomal metabolic disorder that affects both the central and peripheral nervous systems. It is caused by a functional deficiency of the lysosomal enzyme, galactocerebrosidase (GALC), resulting in an accumulation of the toxic metabolite, psychosine. Psychosine accumulation affects many different cellular pathways, leading to severe demyelination. Although there is currently no effective therapy for Krabbe disease, recent gene therapy-based approaches in animal models have indicated a promising outlook for clinical treatment. This review highlights recent findings in the pathogenesis of Krabbe disease, and evaluates AAV-based gene therapy as a promising strategy for treating this devastating pediatric disease.

Krabbe disease: New hope for an old disease

Krabbe disease (globoid cell leukodystrophy) is a lysosomal storage disease (LSD) characterized by progressive and profound demyelination. Infantile, juvenile and adult-onset forms of Krabbe disease have been described, with infantile being the most common. Children with an infantile-onset generally appear normal at birth but begin to miss developmental milestones by six months of age and die by two to four years of age. Krabbe disease is caused by a deficiency of the acid hydrolase galactosylceramidase (GALC) which is responsible for the degradation of galactosylceramides and sphingolipids, which are abundant in myelin membranes. The absence of GALC leads to the toxic accumulation of galactosylsphingosine (psychosine), a lysoderivative of galactosylceramides, in oligodendrocytes and Schwann cells resulting in demyelination of the central and peripheral nervous systems, respectively. Treatment strategies such as enzyme replacement, substrate reduction, enzyme chaperones, and gene therapy have shown promise in LSDs. Unfortunately, Krabbe disease has been relatively refractory to most single-therapy interventions. Although hematopoietic stem cell transplantation can alter the course of Krabbe disease and is the current standard-of-care, it simply slows the progression, even when initiated in pre-symptomatic children. However, the recent success of combinatorial therapeutic approaches in small animal models of Krabbe disease and the identification of new pathogenic mechanisms provide hope for the development of effective treatments for this devastating disease. This review provides a brief history of Krabbe disease and the evolution of single and combination therapeutic approaches and discusses new pathogenic mechanisms and how they might impact the development of more effective treatment strategies.

Substrate Reduction Therapy for Krabbe Disease: Exploring the Repurposing of the Antibiotic D-Cycloserine

Krabbe disease is a lysosomal storage disease that is caused by a deficiency in galactosylceramidase. Infantile onset disease is the most common presentation, which includes progressive neurological deterioration with corresponding demyelination, development of globoid cells, astrocyte gliosis, etc. Hemopoietic stem cell transplantation (HSCT) is a disease modifying therapy, but this intervention is insufficient with many patients still experiencing developmental delays and progressive deterioration. Preclinical studies have used animal models, e.g., twitcher mice, to test different experimental therapies resulting in developments that have led to progressive improvements in the therapeutic impact. Some recent advances have been in the areas of gene therapy and substrate reduction therapy (SRT), as well as using these in combination with HSCT. Unfortunately, new experimental approaches have encountered obstacles which have impeded the translation of novel therapies to human patients. In an effort to identify a safe adjunct therapy, D-cycloserine was tested in preliminary studies in twitcher mice. When administered as a standalone therapy, D-cycloserine was shown to lengthen the lifespan of twitcher mice in a small but significant manner. D-Cycloserine is an FDA approved antibiotic used for drug resistant tuberculosis. It also acts as a partial agonist of the NMDA receptor, which has led to numerous human studies for a range of neuropsychiatric and neurological conditions. In addition, D-cycloserine may inhibit serine palmitoyltransferase (SPT), which catalyzes the rate-limiting step in sphingolipid production. The enantiomer, L-cycloserine, is a much more potent inhibitor of SPT than D-cycloserine. Previously, L-cycloserine was found to act as an effective SRT agent in twitcher mice as both a standalone therapy and as part of combination therapies. L-Cycloserine is not approved for human use, and its potent inhibitory properties may limit its ability to maintain a level of partial inactivation of SPT that is also safe. In theory, D-cycloserine would encompass a much broader dosage range to achieve a safe degree of partial inhibition of SPT, which increases the likelihood it could advance to human studies in patients with Krabbe disease. Furthermore, additional properties of D-cycloserine raise the possibility of other therapeutic mechanisms that could be exploited for the treatment of this disease.

Design, Synthesis, and Biological Evaluation of a Series of Oxazolone Carboxamides as a Novel Class of Acid Ceramidase Inhibitors

Acid ceramidase (AC) is a cysteine hydrolase that plays a crucial role in the metabolism of lysosomal ceramides, important members of the sphingolipid family, a diversified class of bioactive molecules that mediate many biological processes ranging from cell structural integrity, signaling, and cell proliferation to cell death. In the effort to expand the structural diversity of the existing collection of AC inhibitors, a novel class of substituted oxazol-2-one-3-carboxamides were designed and synthesized. Herein, we present the chemical optimization of our initial hits, 2-oxo-4-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 8a and 2-oxo-5-phenyl-N-(4-phenylbutyl)oxazole-3-carboxamide 12a, which resulted in the identification of 5-[4-fluoro-2-(1-methyl-4-piperidyl)phenyl]-2-oxo-N-pentyl-oxazole-3-carboxamide 32b as a potent AC inhibitor with optimal physicochemical and metabolic properties, showing target engagement in human neuroblastoma SH-SY5Y cells and a desirable pharmacokinetic profile in mice, following intravenous and oral administration. 32b enriches the arsenal of promising lead compounds that may therefore act as useful pharmacological tools for investigating the potential therapeutic effects of AC inhibition in relevant sphingolipid-mediated disorders.

Simultaneous Formation and Functionalization of Aryliminophosphoranes Using 1,3-Dihydro-1H-benzimidazol-2-ones as Precursors

An atom- and step-economic synthesis of aryliminophosphoranes bearing ortho urea was achieved via unprecedented Ph₃P-I₂ mediated ring-opening of 1,3-dihydro-1H-benzimidazol-2-ones with secondary amines. Tandem aza-Wittig/heterocyclization of the functionalized aryliminophosphoranes upon treatment with isothiocyanates enables a facile access to a single regioisomer of N¹-substituted 2-aminobenzimidazoles as well as fused tetracyclic quinazolinone derivatives in one-pot. ³¹P{¹H} NMR studies suggested that the urea C-N bond of benzimidazolone is weakened by N-phosphorylation, leading to aminolysis rather than the expected deoxygenative amination.