Acetyl-4'-phosphopantetheine is stable in serum and prevents phenotypes induced by pantothenate kinase deficiency

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

Drug Drop Test: How to Quickly Identify Potential Therapeutic Compounds for Mitochondrial Diseases Using Yeast Saccharomyces cerevisiae

Mitochondrial diseases (MDs) refer to a group of clinically and genetically heterogeneous pathologies characterized by defective mitochondrial function and energy production. Unfortunately, there is no effective treatment for most MDs, and current therapeutic management is limited to relieving symptoms. The yeast Saccharomyces cerevisiae has been efficiently used as a model organism to study mitochondria-related disorders thanks to its easy manipulation and well-known mitochondrial biogenesis and metabolism. It has been successfully exploited both to validate alleged pathogenic variants identified in patients and to discover potential beneficial molecules for their treatment. The so-called "drug drop test", a phenotype-based high-throughput screening, especially if coupled with a drug repurposing approach, allows the identification of molecules with high translational potential in a cost-effective and time-saving manner. In addition to drug identification, S. cerevisiae can be used to point out the drug's target or pathway. To date, drug drop tests have been successfully carried out for a variety of disease models, leading to very promising results. The most relevant aspect is that studies on more complex model organisms confirmed the effectiveness of the drugs, strengthening the results obtained in yeast and demonstrating the usefulness of this screening as a novel approach to revealing new therapeutic molecules for MDs.

Inherited Disorders of Coenzyme A Biosynthesis: Models, Mechanisms, and Treatments

Coenzyme A (CoA) is a vital and ubiquitous cofactor required in a vast number of enzymatic reactions and cellular processes. To date, four rare human inborn errors of CoA biosynthesis have been described. These disorders have distinct symptoms, although all stem from variants in genes that encode enzymes involved in the same metabolic process. The first and last enzymes catalyzing the CoA biosynthetic pathway are associated with two neurological conditions, namely pantothenate kinase-associated neurodegeneration (PKAN) and COASY protein-associated neurodegeneration (CoPAN), which belong to the heterogeneous group of neurodegenerations with brain iron accumulation (NBIA), while the second and third enzymes are linked to a rapidly fatal dilated cardiomyopathy. There is still limited information about the pathogenesis of these diseases, and the knowledge gaps need to be resolved in order to develop potential therapeutic approaches. This review aims to provide a summary of CoA metabolism and functions, and a comprehensive overview of what is currently known about disorders associated with its biosynthesis, including available preclinical models, proposed pathomechanisms, and potential therapeutic approaches.

PKAN pathogenesis and treatment

Studies aimed at supporting different treatment approaches for pantothenate kinase-associated neurodegeneration (PKAN) have revealed the complexity of coenzyme A (CoA) metabolism and the limits of our current knowledge about disease pathogenesis. Here we offer a foundation for critically evaluating the myriad approaches, argue for the importance of unbiased disease models, and highlight some of the outstanding questions that are central to our understanding and treating PKAN.

Thiophosphate Analogs of Coenzyme A and Its Precursors—Synthesis, Stability, and Biomimetic Potential

Coenzyme A (CoA) is ubiquitous and essential for key cellular processes in any living organism. Primary degradation of CoA occurs by enzyme-mediated pyrophosphate hydrolysis intracellularly and extracellularly to form adenosine 3’,5’-diphosphate and 4’-phosphopantetheine (PPanSH). The latter can be recycled for intracellular synthesis of CoA. Impairments in the CoA biosynthetic pathway are linked to a severe form of neurodegeneration with brain iron accumulation for which no disease-modifying therapy is available. Currently, exogenous administration of PPanSH is examined as a therapeutic intervention. Here, we describe biosynthetic access to thiophosphate analogs of PPanSH, 3′-dephospho-CoA, and CoA. The stabilizing effect of thiophosphate modifications toward degradation by extracellular and peroxisomal enzymes was studied in vitro. Experiments in a CoA-deficient cell model suggest a biomimetic potential of the PPanSH thiophosphate analog P_SPanSH (C1). According to our findings, the administration of P_SPanSH may provide an alternative approach to support intracellular CoA-dependent pathways.

Chemoproteomic Profiling of Protein Substrates of a Major Lysine Acetyltransferase in the Native Cellular Context

The family of lysine acetyltransferases (KATs) regulates epigenetics and signaling pathways in eukaryotic cells. So far, knowledge of different KAT members contributing to the cellular acetylome is limited, which limits our understanding of biological functions of KATs in physiology and disease. Here, we found that a clickable acyl-CoA reporter, 3-azidopropanoyl CoA (3AZ-CoA), presented remarkable cell permeability and effectively acylated proteins in cells. We rationally engineered the major KAT member, histone acetyltransferase 1 (HAT1), to generate its mutant forms that displayed excellent bio-orthogonal activity for 3AZ-CoA in substrate labeling. We were able to apply the bio-orthogonal enzyme-cofactor pair combined with SILAC proteomics to achieve HAT1 substrate targeting, enrichment, and proteomic profiling in living cells. A total of 123 protein substrates of HAT1 were disclosed, underlining the multifactorial functions of this important enzyme than hitherto known. This study demonstrates the first example of utilizing bio-orthogonal reporters as a chemoproteomic strategy for substrate mapping of individual KAT isoforms in the native biological contexts.

Pantothenate biosynthesis is critical for chronic infection by the neurotropic parasite Toxoplasma gondii

Coenzyme A (CoA) is an essential molecule acting in metabolism, post-translational modification, and regulation of gene expression. While all organisms synthesize CoA, many, including humans, are unable to produce its precursor, pantothenate. Intriguingly, like most plants, fungi and bacteria, parasites of the coccidian subgroup of Apicomplexa, including the human pathogen Toxoplasma gondii, possess all the enzymes required for de novo synthesis of pantothenate. Here, the importance of CoA and pantothenate biosynthesis for the acute and chronic stages of T. gondii infection is dissected through genetic, biochemical and metabolomic approaches, revealing that CoA synthesis is essential for T. gondii tachyzoites, due to the parasite's inability to salvage CoA or intermediates of the pathway. In contrast, pantothenate synthesis is only partially active in T. gondii tachyzoites, making the parasite reliant on its uptake. However, pantothenate synthesis is crucial for the establishment of chronic infection, offering a promising target for intervention against the persistent stage of T. gondii.

Redesigning therapies for pantothenate kinase-associated neurodegeneration

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is an incurable rare genetic disorder of children and young adults caused by mutations in the PANK2 gene, which encodes an enzyme critical for the biosynthesis of Coenzyme A. Although PKAN affects only a small number of patients, it shares several hallmarks of more common neurodegenerative diseases of older adults such as Alzheimer's and Parkinson's. Advances in etiological understanding and treatment of PKAN could therefore have implications for our understanding of more common diseases and may shed new lights on the physiological importance of Coenzyme A, a cofactor critical for the operation of various cellular metabolic processes. The large body of knowledge which accumulated over the years around PKAN pathology, including but not limited to studies of various PKAN models and therapies, has contributed not only to progress in our understanding of the disease, but as importantly, to the crystallization of key questions that guide future investigations of the disease. In this Review, we will summarize this knowledge and demonstrate how it forms the backdrop to new avenues of research.

Towards Precision Therapies for Inherited Disorders of Neurodegeneration with Brain Iron Accumulation

Background:

Neurodegeneration with brain iron accumulation (NBIA) disorders comprise a group of rare but devastating inherited neurological diseases with unifying features of progressive cognitive and motor decline, and increased iron deposition in the basal ganglia. Although at present there are no proven disease-modifying treatments, the severe nature of these monogenic disorders lends to consideration of personalized medicine strategies, including targeted gene therapy. In this review we summarize the progress and future direction towards precision therapies for NBIA disorders.

Methods:

This review considered all relevant publications up to April 2021 using a systematic search strategy of PubMed and clinical trials databases.

Results:

We review what is currently known about the underlying pathophysiology of NBIA disorders, common NBIA disease pathways, and how this knowledge has influenced current management strategies and clinical trial design. The safety profile, efficacy and clinical outcome of clinical studies are reviewed. Furthermore, the potential for future therapeutic approaches is also discussed.

Discussion:

Therapeutic options in NBIAs remain very limited, with no proven disease-modifying treatments at present. However, a number of different approaches are currently under development with increasing focus on targeted precision therapies. Recent advances in the field give hope that novel strategies, such as gene therapy, gene editing and substrate replacement therapies are both scientifically and financially feasible for these conditions.

Highlights

This article provides an up-to-date review of the current literature about Neurodegeneration with Brain Iron Accumulation (NBIA), with a focus on disease pathophysiology, current and previously trialed therapies, and future treatments in development, including consideration of potential genetic therapy approaches.

The Coenzyme A Level Modulator Hopantenate (HoPan) Inhibits Phosphopantotenoylcysteine Synthetase Activity

The pantothenate analogue hopantenate (HoPan) is widely used as a modulator of coenzyme A (CoA) levels in cell biology and disease models─especially for pantothenate kinase associated neurodegeneration (PKAN), a genetic disease rooted in impaired CoA metabolism. This use of HoPan was based on reports that it inhibits pantothenate kinase (PanK), the first enzyme of CoA biosynthesis. Using a combination of in vitro enzyme kinetic studies, crystal structure analysis, and experiments in a typical PKAN cell biology model, we demonstrate that instead of inhibiting PanK, HoPan relies on it for metabolic activation. Once phosphorylated, HoPan inhibits the next enzyme in the CoA pathway─phosphopantothenoylcysteine synthetase (PPCS)─through formation of a nonproductive substrate complex. Moreover, the obtained structure of the human PPCS in complex with the inhibitor and activating nucleotide analogue provides new insights into the catalytic mechanism of PPCS enzymes─including the elusive binding mode for cysteine─and reveals the functional implications of mutations in the human PPCS that have been linked to severe dilated cardiomyopathy. Taken together, this study demonstrates that the molecular mechanism of action of HoPan is more complex than previously thought, suggesting that the results of studies in which it is used as a tool compound must be interpreted with care. Moreover, our findings provide a clear framework for evaluating the various factors that contribute to the potency of CoA-directed inhibitors, one that will prove useful in the future rational development of potential therapies of both human genetic and infectious diseases.

Coenzyme a Biochemistry: From Neurodevelopment to Neurodegeneration

Coenzyme A (CoA) is an essential cofactor in all living organisms. It is involved in a large number of biochemical processes functioning either as an activator of molecules with carbonyl groups or as a carrier of acyl moieties. Together with its thioester derivatives, it plays a central role in cell metabolism, post-translational modification, and gene expression. Furthermore, recent studies revealed a role for CoA in the redox regulation by the S-thiolation of cysteine residues in cellular proteins. The intracellular concentration and distribution in different cellular compartments of CoA and its derivatives are controlled by several extracellular stimuli such as nutrients, hormones, metabolites, and cellular stresses. Perturbations of the biosynthesis and homeostasis of CoA and/or acyl-CoA are connected with several pathological conditions, including cancer, myopathies, and cardiomyopathies. In the most recent years, defects in genes involved in CoA production and distribution have been found in patients affected by rare forms of neurodegenerative and neurodevelopmental disorders. In this review, we will summarize the most relevant aspects of CoA cellular metabolism, their role in the pathogenesis of selected neurodevelopmental and neurodegenerative disorders, and recent advancements in the search for therapeutic approaches for such diseases.

Turnover rate of coenzyme A in mouse brain and liver

Coenzyme A (CoA) is a fundamental cofactor involved in a number of important biochemical reactions in the cell. Altered CoA metabolism results in severe conditions such as pantothenate kinase-associated neurodegeneration (PKAN) in which a reduction of the activity of pantothenate kinase isoform 2 (PANK2) present in CoA biosynthesis in the brain consequently lowers the level of CoA in this organ. In order to develop a new drug aimed at restoring the sufficient amount of CoA in the brain of PKAN patients, we looked at its turnover. We report here the results of two experiments that enabled us to measure the half-life of pantothenic acid, free CoA (CoASH) and acetylCoA in the brains and livers of male and female C57BL/6N mice, and total CoA in the brains of male mice. We administered (intrastriatally or orally) a single dose of a [13C3-15N-18O]-labelled coenzyme A precursor (fosmetpantotenate or [13C3-15N]-pantothenic acid) to the mice and measured, by liquid chromatography-mass spectrometry, unlabelled- and labelled-coenzyme A species appearance and disappearance over time. We found that the turnover of all metabolites was faster in the liver than in the brain in both genders with no evident gender difference observed. In the oral study, the CoASH half-life was: 69 ± 5 h (male) and 82 ± 6 h (female) in the liver; 136 ± 14 h (male) and 144 ± 12 h (female) in the brain. AcetylCoA half-life was 74 ± 9 h (male) and 71 ± 7 h (female) in the liver; 117 ± 13 h (male) and 158 ± 23 (female) in the brain. These results were in accordance with the corresponding values obtained after intrastriatal infusion of labelled-fosmetpantotenate (CoASH 124 ± 13 h, acetylCoA 117 ± 11 and total CoA 144 ± 17 in male brain).

Rational Design of Novel Therapies for Pantothenate Kinase-Associated Neurodegeneration

BACKGROUND

This review highlights the recent scientific advances that have enabled rational design of novel clinical trials for pantothenate kinase-associated neurodegeneration (PKAN), a rare autosomal recessive neurogenetic disorder associated with progressive neurodegenerative changes and functional impairment. PKAN is caused by genetic variants in the PANK2 gene that result in dysfunction in pantothenate kinase 2 (PANK2) enzyme activity, with consequent disruption of coenzyme A (CoA) synthesis, and subsequent accumulation of brain iron. The clinical phenotype is varied and may include dystonia, rigidity, bradykinesia, postural instability, spasticity, loss of ambulation and ability to communicate, feeding difficulties, psychiatric issues, and cognitive and visual impairment. There are several symptom-targeted treatments, but these do not provide sustained benefit as the disorder progresses.

OBJECTIVES

A detailed understanding of the molecular and biochemical pathogenesis of PKAN has opened the door for the design of novel rationally designed therapeutics that target the underlying mechanisms.

METHODS

Two large double-blind phase 3 clinical trials have been completed for deferiprone (an iron chelation treatment) and fosmetpantotenate (precursor replacement therapy). A pilot open-label trial of pantethine as a potential precursor replacement strategy has also been completed, and a trial of 4-phosphopantetheine has begun enrollment. Several other compounds have been evaluated in pre-clinical studies, and additional clinical trials may be anticipated.

CONCLUSIONS

Experience with these trials has encouraged a critical evaluation of optimal trial designs, as well as the development of PKAN-specific measures to monitor outcomes. PKAN provides a valuable example for understanding targeted drug development and clinical trial design for rare disorders. © 2021 International Parkinson and Movement Disorder Society.

Emerging Disease-Modifying Therapies in Neurodegeneration With Brain Iron Accumulation (NBIA) Disorders

Neurodegeneration with Brain Iron Accumulation (NBIA) is a heterogeneous group of progressive neurodegenerative diseases characterized by iron deposition in the globus pallidus and the substantia nigra. As of today, 15 distinct monogenetic disease entities have been identified. The four most common forms are pantothenate kinase-associated neurodegeneration (PKAN), phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN), beta-propeller protein-associated neurodegeneration (BPAN) and mitochondrial membrane protein-associated neurodegeneration (MPAN). Neurodegeneration with Brain Iron Accumulation disorders present with a wide spectrum of clinical symptoms such as movement disorder signs (dystonia, parkinsonism, chorea), pyramidal involvement (e.g., spasticity), speech disorders, cognitive decline, psychomotor retardation, and ocular abnormalities. Treatment remains largely symptomatic but new drugs are in the pipeline. In this review, we discuss the rationale of new compounds, summarize results from clinical trials, provide an overview of important results in cell lines and animal models and discuss the future development of disease-modifying therapies for NBIA disorders. A general mechanistic approach for treatment of NBIA disorders is with iron chelators which bind and remove iron. Few studies investigated the effect of deferiprone in PKAN, including a recent placebo-controlled double-blind multicenter trial, demonstrating radiological improvement with reduction of iron load in the basal ganglia and a trend to slowing of disease progression. Disease-modifying strategies address the specific metabolic pathways of the affected enzyme. Such tailor-made approaches include provision of an alternative substrate (e.g., fosmetpantotenate or 4′-phosphopantetheine for PKAN) in order to bypass the defective enzyme. A recent randomized controlled trial of fosmetpantotenate, however, did not show any significant benefit of the drug as compared to placebo, leading to early termination of the trials' extension phase. 4′-phosphopantetheine showed promising results in animal models and a clinical study in patients is currently underway. Another approach is the activation of other enzyme isoforms using small molecules (e.g., PZ-2891 in PKAN). There are also compounds which counteract downstream cellular effects. For example, deuterated polyunsaturated fatty acids (D-PUFA) may reduce mitochondrial lipid peroxidation in PLAN. In infantile neuroaxonal dystrophy (a subtype of PLAN), desipramine may be repurposed as it blocks ceramide accumulation. Gene replacement therapy is still in a preclinical stage.

FIT2 is an acyl-coenzyme A diphosphatase crucial for endoplasmic reticulum homeostasis

The endoplasmic reticulum is a cellular hub of lipid metabolism, coordinating lipid synthesis with continuous changes in metabolic flux. Maintaining ER lipid homeostasis despite these fluctuations is crucial to cell function and viability. Here, we identify a novel mechanism that is crucial for normal ER lipid metabolism and protects the ER from dysfunction. We identify the molecular function of the evolutionarily conserved ER protein FIT2 as a fatty acyl–coenzyme A (CoA) diphosphatase that hydrolyzes fatty acyl–CoA to yield acyl 4′-phosphopantetheine. This activity of FIT2, which is predicted to be active in the ER lumen, is required in yeast and mammalian cells for maintaining ER structure, protecting against ER stress, and enabling normal lipid storage in lipid droplets. Our findings thus solve the long-standing mystery of the molecular function of FIT2 and highlight the maintenance of optimal fatty acyl–CoA levels as key to ER homeostasis.

Coenzyme A levels influence protein acetylation, CoAlation and 4'-phosphopantetheinylation: Expanding the impact of a metabolic nexus molecule

Coenzyme A (CoA) is a key molecule in cellular metabolism including the tricarboxylic acid cycle, fatty acid synthesis, amino acid synthesis and lipid metabolism. Moreover, CoA is required for biological processes like protein post-translational modifications (PTMs) including acylation. CoA levels affect the amount of histone acetylation and thereby modulate gene expression. A direct influence of CoA levels on other PTMs, like CoAlation and 4'-phosphopantetheinylation has been relatively less addressed and will be discussed here. Increased CoA levels are associated with increased CoAlation, whereas decreased 4'-phosphopantetheinylation is observed under circumstances of decreased CoA levels. We discuss how these two PTMs can positively or negatively influence target proteins depending on CoA levels. This review highlights the impact of CoA levels on post-translational modifications, their counteractive interplay and the far-reaching consequences thereof.

Exploring Yeast as a Study Model of Pantothenate Kinase-Associated Neurodegeneration and for the Identification of Therapeutic Compounds

Mutations in the pantothenate kinase 2 gene (PANK2) are the cause of pantothenate kinase-associated neurodegeneration (PKAN), the most common form of neurodegeneration with brain iron accumulation. Although different disease models have been created to investigate the pathogenic mechanism of PKAN, the cascade of molecular events resulting from CoA synthesis impairment is not completely understood. Moreover, for PKAN disease, only symptomatic treatments are available. Despite the lack of a neural system, Saccharomyces cerevisiae has been successfully used to decipher molecular mechanisms of many human disorders including neurodegenerative diseases as well as iron-related disorders. To gain insights into the molecular basis of PKAN, a yeast model of this disease was developed: a yeast strain with the unique gene encoding pantothenate kinase CAB1 deleted, and expressing a pathological variant of this enzyme. A detailed functional characterization demonstrated that this model recapitulates the main phenotypes associated with human disease: mitochondrial dysfunction, altered lipid metabolism, iron overload, and oxidative damage suggesting that the yeast model could represent a tool to provide information on pathophysiology of PKAN. Taking advantage of the impaired oxidative growth of this mutant strain, a screening for molecules able to rescue this phenotype was performed. Two molecules in particular were able to restore the multiple defects associated with PKAN deficiency and the rescue was not allele-specific. Furthermore, the construction and characterization of a set of mutant alleles, allowing a quick evaluation of the biochemical consequences of pantothenate kinase (PANK) protein variants could be a tool to predict genotype/phenotype correlation.

4'-Phosphopantetheine corrects CoA, iron, and dopamine metabolic defects in mammalian models of PKAN

Pantothenate kinase-associated neurodegeneration (PKAN) is an inborn error of CoA metabolism causing dystonia, parkinsonism, and brain iron accumulation. Lack of a good mammalian model has impeded studies of pathogenesis and development of rational therapeutics. We took a new approach to investigating an existing mouse mutant of Pank2 and found that isolating the disease-vulnerable brain revealed regional perturbations in CoA metabolism, iron homeostasis, and dopamine metabolism and functional defects in complex I and pyruvate dehydrogenase. Feeding mice a CoA pathway intermediate, 4'-phosphopantetheine, normalized levels of the CoA-, iron-, and dopamine-related biomarkers as well as activities of mitochondrial enzymes. Human cell changes also were recovered by 4'-phosphopantetheine. We can mechanistically link a defect in CoA metabolism to these secondary effects via the activation of mitochondrial acyl carrier protein, which is essential to oxidative phosphorylation, iron-sulfur cluster biogenesis, and mitochondrial fatty acid synthesis. We demonstrate the fidelity of our model in recapitulating features of the human disease. Moreover, we identify pharmacodynamic biomarkers, provide insights into disease pathogenesis, and offer evidence for 4'-phosphopantetheine as a candidate therapeutic for PKAN.

Inborn errors of mitochondrial acyl-coenzyme a metabolism: acyl-CoA biology meets the clinic

The last decade saw major advances in understanding the metabolism of Coenzyme A (CoA) thioesters (acyl-CoAs) and related inborn errors (CoA metabolic diseases, CAMDs). For diagnosis, acylcarnitines and organic acids, both derived from acyl-CoAs, are excellent markers of most CAMDs. Clinically, each CAMD is unique but strikingly, three main patterns emerge: first, systemic decompensations with combinations of acidosis, ketosis, hypoglycemia, hyperammonemia and fatty liver; second, neurological episodes, particularly acute "stroke-like" episodes, often involving the basal ganglia but sometimes cerebral cortex, brainstem or optic nerves and third, especially in CAMDs of long chain fatty acyl-CoA metabolism, lipid myopathy, cardiomyopathy and arrhythmia. Some patients develop signs from more than one category. The pathophysiology of CAMDs is not precisely understood. Available data suggest that signs may result from CoA sequestration, toxicity and redistribution (CASTOR) in the mitochondrial matrix has been suggested to play a role. This predicts that most CAMDs cause deficiency of CoA, limiting mitochondrial energy production, and that toxic effects from the abnormal accumulation of acyl-CoAs and from extramitochondrial functions of acetyl-CoA may also contribute. Recent progress includes the following. (1) Direct measurements of tissue acyl-CoAs in mammalian models of CAMDs have been related to clinical features. (2) Inborn errors of CoA biosynthesis were shown to cause clinical changes similar to those of inborn errors of acyl-CoA degradation. (3) CoA levels in cells can be influenced pharmacologically. (4) Roles for acetyl-CoA are increasingly identified in all cell compartments. (5) Nonenzymatic acyl-CoA-mediated acylation of intracellular proteins occurs in mammalian tissues and is increased in CAMDs.

Proposed Therapies for Pantothenate-Kinase-Associated Neurodegeneration

Multiple approaches to therapy have been proposed for the rare inherited neurodegenerative disease associated with mutations in the PANK2 gene, called pantothenate-kinase-associated neurodegeneration (PKAN). Penetration of the blood-brain barrier for treatment of a central nervous system (CNS) disorder is a major challenge in drug discovery. Evaluation of the biochemistry and medicinal chemistry of the proposed therapies reveals potential liabilities among several compounds under consideration for clinical development.

Inborn errors of coenzyme A metabolism and neurodegeneration

Two inborn errors of coenzyme A (CoA) metabolism are responsible for distinct forms of neurodegeneration with brain iron accumulation (NBIA), a heterogeneous group of neurodegenerative diseases having as a common denominator iron accumulation mainly in the inner portion of globus pallidus. Pantothenate kinase-associated neurodegeneration (PKAN), an autosomal recessive disorder with progressive impairment of movement, vision and cognition, is the most common form of NBIA and is caused by mutations in the pantothenate kinase 2 gene (PANK2), coding for a mitochondrial enzyme, which phosphorylates vitamin B5 in the first reaction of the CoA biosynthetic pathway. Another very rare but similar disorder, denominated CoPAN, is caused by mutations in coenzyme A synthase gene (COASY) coding for a bi-functional mitochondrial enzyme, which catalyzes the final steps of CoA biosynthesis. It still remains a mystery why dysfunctions in CoA synthesis lead to neurodegeneration and iron accumulation in specific brain regions, but it is now evident that CoA metabolism plays a crucial role in the normal functioning and metabolism of the nervous system.

A therapeutic approach to pantothenate kinase associated neurodegeneration

Pantothenate kinase (PANK) is a metabolic enzyme that regulates cellular coenzyme A (CoA) levels. There are three human PANK genes, and inactivating mutations in PANK2 lead to pantothenate kinase associated neurodegeneration (PKAN). Here we performed a library screen followed by chemical optimization to produce PZ-2891, an allosteric PANK activator that crosses the blood brain barrier. PZ-2891 occupies the pantothenate pocket and engages the dimer interface to form a PANK•ATP•Mg2+•PZ-2891 complex. The binding of PZ-2891 to one protomer locks the opposite protomer in a catalytically active conformation that is refractory to acetyl-CoA inhibition. Oral administration of PZ-2891 increases CoA levels in mouse liver and brain. A knockout mouse model of brain CoA deficiency exhibited weight loss, severe locomotor impairment and early death. Knockout mice on PZ-2891 therapy gain weight, and have improved locomotor activity and life span establishing pantazines as novel therapeutics for the treatment of PKAN.

Silencing of pantothenate kinase 2 reduces endothelial cell angiogenesis

Coenzyme A (CoA) is an essential cofactor of cellular metabolism that is involved in ~4% of cellular reactions. Its de novo production relies on five subsequent enzymatic steps, starting with the phosphorylation of vitamin B5. Pantothenate kinase 2 (PANK2) and coenzyme A synthase (COASY) catalyze the first and last steps of this pathway. Mutations in these genes lead to severe and progressive movement disorders, with neurodegeneration and iron accumulation in the basal ganglia, known as PANK2‑ and COASY protein‑associated neurodegeneration, respectively. Given the ubiquitous role of CoA in cellular metabolism, it is still not clear why patients carrying PANK2 and COASY mutations develop almost exclusively neurological symptoms. Important clues are the energetic profile of neural cells as well as the high levels of PANK2 expression in the brain; however, other features may contribute to this selective tissue vulnerability. Notably, when pank2 or coasy expression was suppressed in zebrafish evident perturbation of neuronal development was observed, as well as severe defects in vasculature formation. Supplementation of CoA to fish water prevented the appearance of the phenotype, thereby confirming the specific connection with the availability of the metabolic cofactor. The present study investigated the associations between PANK2 defects and angiogenesis in a mammalian setting, and revealed that PANK2 expression was required for normal angiogenetic properties of human umbilical vein endothelial cells.