Structure-activity relationship study around guanabenz identifies two derivatives retaining antiprion activity but having lost α2-adrenergic receptor agonistic activity

New clinical insight in amyotrophic lateral sclerosis and innovative clinical development from the non-profit repurposing trial of the old drug guanabenz

Drug repurposing is considered a valid approach to accelerate therapeutic solutions for rare diseases. However, it is not as widely applied as it could be, due to several barriers that discourage both industry and academic institutions from pursuing this path. Herein we present the case of an academic multicentre study that considered the repurposing of the old drug guanabenz as a therapeutic strategy in amyotrophic lateral sclerosis. The difficulties encountered are discussed as an example of the barriers that academics involved in this type of study may face. Although further development of the drug for this target population was hampered for several reasons, the study was successful in many ways. Firstly, because the hypothesis tested was confirmed in a sub-population, leading to alternative innovative solutions that are now under clinical investigation. In addition, the study was informative and provided new insights into the disease, which are now giving new impetus to laboratory research. The message from this example is that even a repurposing study with an old product has the potential to generate innovation and interest from industry partners, provided it is based on a sound rationale, the study design is adequate to ensure meaningful results, and the investigators keep the full clinical development picture in mind.

Prion therapeutics: Lessons from the past

Prion diseases are a group of incurable zoonotic neurodegenerative diseases (NDDs) in humans and other animals caused by the prion proteins. The abnormal folding and aggregation of the soluble cellular prion proteins (PrPC) into scrapie isoform (PrPSc) in the Central nervous system (CNS) resulted in brain damage and other neurological symptoms. Different therapeutic approaches, including stalling PrPC to PrPSc conversion, increasing PrPSc removal, and PrPC stabilization, for which a spectrum of compounds, ranging from organic compounds to antibodies, have been explored. Additionally, a non-PrP targeted drug strategy using serpin inhibitors has been discussed. Despite numerous scaffolds being screened for anti-prion activity in vitro, only a few were effective in vivo and unfortunately, almost none of them proved effective in the clinical studies, most likely due to toxicity and lack of permeability. Recently, encouraging results from a prion-protein monoclonal antibody, PRN100, were presented in the first human trial on CJD patients, which gives a hope for better future for the discovery of other new molecules to treat prion diseases. In this comprehensive review, we have re-visited the history and discussed various classes of anti-prion agents, their structure, mode of action, and toxicity. Understanding pathogenesis would be vital for developing future treatments for prion diseases. Based on the outcomes of existing therapies, new anti-prion agents could be identified/synthesized/designed with reduced toxicity and increased bioavailability, which could probably be effective in treating prion diseases.

Therapeutic strategies for identifying small molecules against prion diseases

Prion diseases are fatal neurodegenerative disorders, for which there are no effective therapeutic and diagnostic agents. The main pathological hallmark has been identified as conformational changes of the cellular isoform prion protein (PrP^C) to a misfolded isoform of the prion protein (PrP^Sc). Targeting PrP^C and its conversion to PrP^Sc is still the central dogma in prion drug discovery, particularly in in silico and in vitro screening endeavors, leading to the identification of many small molecules with therapeutic potential. Nonetheless, multiple pathological targets are critically involved in the intricate pathogenesis of prion diseases. In this context, multi-target-directed ligands (MTDLs) emerge as valuable therapeutic approach for their potential to effectively counteract the complex etiopathogenesis by simultaneously modulating multiple targets. In addition, diagnosis occurs late in the disease process, and consequently a successful therapeutic intervention cannot be provided. In this respect, small molecule theranostics, which combine imaging and therapeutic properties, showed tremendous potential to cure and diagnose in vivo prion diseases. Herein, we review the major advances in prion drug discovery, from anti-prion small molecules identified by means of in silico and in vitro screening approaches to two rational strategies, namely MTDLs and theranostics, that have led to the identification of novel compounds with an expanded anti-prion profile.

Iodine Catalyzed Oxidative Coupling of Diaminoazines and Amines for the Synthesis of 3,5-Disubstituted-1,2,4-Triazoles

A simple, convenient, transition metal-free one pot synthesis of 3,5-disubstituted-1,2,4-triazoles has been established. The innovation in this reaction is the use of easily available 1,1-diaminoazines as substrates. This method provides the products with wider substrate scope, at an expedited rate, and with relatively better yields in comparison to the reported methods. The reaction mechanism involves an initial intermolecular nucleophilic addition (facilitated by I₂) followed by intramolecular nucleophilic cyclization.

Anti-prion Drugs Targeting the Protein Folding Activity of the Ribosome Reduce PABPN1 Aggregation

Prion diseases are caused by the propagation of PrPSc, the pathological conformation of the PrPC prion protein. The molecular mechanisms underlying PrPSc propagation are still unsolved and no therapeutic solution is currently available. We thus sought to identify new anti-prion molecules and found that flunarizine inhibited PrPSc propagation in cell culture and significantly prolonged survival of prion-infected mice. Using an in silico therapeutic repositioning approach based on similarities with flunarizine chemical structure, we tested azelastine, duloxetine, ebastine, loperamide and metixene and showed that they all have an anti-prion activity. Like flunarizine, these marketed drugs reduced PrPSc propagation in cell culture and in mouse cerebellum organotypic slice culture, and inhibited the protein folding activity of the ribosome (PFAR). Strikingly, some of these drugs were also able to alleviate phenotypes due to PABPN1 nuclear aggregation in cell and Drosophila models of oculopharyngeal muscular dystrophy (OPMD). These data emphasize the therapeutic potential of anti-PFAR drugs for neurodegenerative and neuromuscular proteinopathies.

Diastereoselective Synthesis of Nonplanar 3-Amino-1,2,4-oxadiazine Scaffold: Structure Revision of Alchornedine

Herein, we report the diastereoselective synthesis of a 3-amino-1,2,4-oxadiazine (AOXD) scaffold. The presence of a N-O bond in the ring prevents the planar geometry of the aromatic system and induces a strong decrease in the basicity of the guanidine moiety. While DIBAL-H appeared to be the most efficient reducing agent because it exhibited high diastereoselectivity, we observed various behaviors of the Mitsunobu reaction on the resulting β-aminoalcohol, leading to either inversion or retention of the configuration depending on the steric hindrance in the vicinity of the hydroxy group. The physicochemical properties (pK_a and log D) and hepatic stability of several AOXD derivatives were experimentally determined and found that the AOXD scaffold possesses promising properties for drug development. Moreover, we synthesized alchornedine, the only natural product with the AOXD scaffold. Based on a comparison of the analytical data, we found that the reported structure of alchornedine was incorrect and hypothesized a new one.

Ribosomal RNA Modulates Aggregation of the Podospora Prion Protein HET-s

The role of the nucleic acids in prion aggregation/disaggregation is becoming more and more evident. Here, using HET-s prion from fungi Podospora anserina (P. anserina) as a model system, we studied the role of RNA, particularly of different domains of the ribosomal RNA (rRNA), in its aggregation process. Our results using Rayleigh light scattering, Thioflavin T (ThT) binding, transmission electron microscopy (TEM) and cross-seeding assay show that rRNA, in particular the domain V of the major rRNA from the large subunit of the ribosome, substantially prevents insoluble amyloid and amorphous aggregation of the HET-s prion in a concentration-dependent manner. Instead, it facilitates the formation of the soluble oligomeric “seeds”, which are capable of promoting de novo HET-s aggregation. The sites of interactions of the HET-s prion protein on domain V rRNA were identified by primer extension analysis followed by UV-crosslinking, which overlap with the sites previously identified for the protein-folding activity of the ribosome (PFAR). This study clarifies a missing link between the rRNA-based PFAR and the mode of propagation of the fungal prions.

Pharmacological modulation of the ER stress response ameliorates oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare late onset genetic disease leading to ptosis, dysphagia and proximal limb muscles at later stages. A short abnormal (GCN) triplet expansion in the polyA-binding protein nuclear 1 (PABPN1) gene leads to PABPN1-containing aggregates in the muscles of OPMD patients. Here we demonstrate that treating mice with guanabenz acetate (GA), an FDA-approved antihypertensive drug, reduces the size and number of nuclear aggregates, improves muscle force, protects myofibers from the pathology-derived turnover and decreases fibrosis. GA targets various cell processes, including the unfolded protein response (UPR), which acts to attenuate endoplasmic reticulum (ER) stress. We demonstrate that GA increases both the phosphorylation of the eukaryotic translation initiation factor 2α subunit and the splicing of Xbp1, key components of the UPR. Altogether these data show that modulation of protein folding regulation is beneficial for OPMD and promote the further development of GA or its derivatives for treatment of OPMD in humans. Furthermore, they support the recent evidences that treating ER stress could be therapeutically relevant in other more common proteinopathies.

Anti-prion drug screening system in Saccharomyces cerevisiae based on an artificial [LEU2+] prion

Proteinaceous infectious particles causing mammalian transmissible spongiform encephalopathies or prions are being extensively studied. However due to their hazardous nature, the initial screening of potential anti-prion drugs is often made in a yeast-based screening system utilizing a well-characterized [PSI⁺] prion (amyloid formed by the translation termination factor Sup35p). In the [PSI⁺] prion screening system (white/red colony assay), the prion phenotype yields white colonies while addition of an anti-prion drug will yield red colonies. However, this system has some limitations. It is difficult to quantify the effectiveness of the anti-prion compound, the diffusion of the studied compound may affect the result, and the deficiency of glutathione in cells may prevent the formation of red pigment in cured cells. Therefore, alternative yeast prion screening systems are still needed. This article aims to present an alternative yeast-based system to evaluate anti-prion activity of chemical compounds. The method that was used is based on an artificial [LEU2⁺] prion created by fusing Leu2p with the prion-forming domain of Sup35p in Saccharomyces cerevisiae. Phenotypic analysis and semi-denaturating detergent agarose gel electrophoresis (SDD-AGE) confirmed the presence of the artificial [LEU2⁺] prion in yeast cells. This screening system verified the anti-prion activity of 3 drugs that were found to have been active in the white/red colony assay, while one compound (6-chlorotacrine) that was active in the white/red colony assay was found to be inactive in the [LEU2⁺] system. This new system also appears to be more sensitive than the white/red colony assay.

PromISR-6, a Guanabenz Analogue, Improves Cellular Survival in an Experimental Model of Huntington's Disease

Guanabenz (GBZ), an α₂-adrenergic agonist, demonstrated off-target effects that restored protein homeostasis and ameliorated pathobiology in experimental models of neurodegenerative disease. However, GBZ did not directly activate the integrated stress response (ISR), and its proposed mode of action remains controversial. Utilizing an iterative in silico screen of over 10,000 GBZ analogues, we analyzed 432 representative compounds for cytotoxicity in Wild-type, PPP1R15A-/-, and PPP1R15B-/- mouse embryonic fibroblasts. Nine compounds clustering into three functional groups were studied in detail using cell biological and biochemical assays. Our studies demonstrated that PromISR-6 is a potent GBZ analogue that selectively activated ISR, eliciting sustained eIF2α phosphorylation. ISRIB, an ISR inhibitor, counteracted PromISR-6-mediated translational inhibition and reduction in intracellular mutant Huntingtin aggregates. Reduced protein synthesis combined with PromISR-6-stimulated autophagic clearance made PromISR-6 the most efficacious GBZ analogue to reduce Huntingtin aggregates and promote survival in a cellular model of Huntington's disease.

The antibiotic robenidine exhibits guanabenz-like cytoprotective properties by a mechanism independent of protein phosphatase PP1:PPP1R15A

The aminoguanidine compound robenidine is widely used as an antibiotic for the control of coccidiosis, a protozoal infection in poultry and rabbits. Interestingly, robenidine is structurally similar to guanabenz (analogs), which are currently undergoing clinical trials as cytoprotective agents for the management of neurodegenerative diseases. Here we show that robenidine and guanabenz protect cells from a tunicamycin-induced unfolded protein response to a similar degree. Both compounds also reduced the tumor necrosis factor α-induced activation of NF-κB. The cytoprotective effects of guanabenz (analogs) have been explained previously by their ability to maintain eIF2α phosphorylation by allosterically inhibiting protein phosphatase PP1:PPP1R15A. However, using a novel split-luciferase-based protein-protein interaction assay, we demonstrate here that neither robenidine nor guanabenz disrupt the interaction between PPP1R15A and either PP1 or eIF2α in intact cells. Moreover, both drugs also inhibited the unfolded protein response in cells that expressed a nonphosphorylatable mutant (S51A) of eIF2α. Our results identify robenidine as a PP1:PPP1R15A-independent cytoprotective compound that holds potential for the management of protein misfolding-associated diseases.

Azines: synthesis, structure, electronic structure and their applications

Azines (2,3-diaza-1,3-butadienes): structure, electronic structure, tautomerism, and their applications in organic synthesis, medicinal chemistry and materials chemistry.

Aminoguanidine Hydrazone Derivatives as Nonpeptide NPFF1 Receptor Antagonists Reverse Opioid Induced Hyperalgesia

Neuropeptide FF receptors (NPFF1R and NPFF2R) and their endogenous ligand neuropeptide FF have been shown previously to display antiopioid properties and to play a critical role in the adverse effects associated with chronic administrations of opiates including the development of opioid-induced hyperalgesia and analgesic tolerance. In this work, we sought to identify novel NPFF receptors ligands by focusing our interest in a series of heterocycles as rigidified nonpeptide NPFF receptor ligands, starting from already described aminoguanidine hydrazones (AGHs). Binding experiments and functional assays highlighted AGH 1n and its rigidified analogue 2-amino-dihydropyrimidine 22e for in vivo experiments. As shown earlier with the prototypical dipeptide antagonist RF9, both 1n and 22e reduced significantly the long lasting fentanyl-induced hyperalgesia in rodents. Altogether these data indicate that AGH rigidification maintains nanomolar affinities for both NPFF receptors, while improving antagonist character toward NPFF1R.

Guanabenz promotes neuronal survival via enhancement of ATF4 and parkin expression in models of Parkinson disease

Reduced function of parkin appears to be a central pathogenic event in Parkinson disease (PD). Increasing parkin levels enhances survival in models of PD-related neuronal death and is a promising therapeutic objective. Previously, we demonstrated that the transcription factor ATF4 promotes survival in response to PD-mimetic stressors by maintaining parkin levels. ATF4 translation is up-regulated by phosphorylation of the translation initiation factor eIF2α. The small molecule guanabenz enhances eIF2α phosphorylation by blocking the function of GADD34, a regulatory protein that promotes eIF2α dephosphorylation. We tested the hypothesis that guanabenz, by inhibiting GADD34 and consequently increasing eIF2α phosphorylation and elevating ATF4, would improve survival in models of PD by up-regulating parkin. We found that GADD34 is strongly induced by 6-OHDA, and that GADD34 localization is dramatically altered in dopaminergic substantia nigra neurons in PD cases. We further demonstrated that guanabenz attenuates 6-hydroxydopamine (6-OHDA) induced cell death of differentiated PC12 cells and primary ventral midbrain dopaminergic neurons in culture, and of dopaminergic neurons in the substantia nigra of mice. In culture models, guanabenz also increases eIF2α phosphorylation and ATF4 and parkin levels in response to 6-OHDA. Furthermore, if either ATF4 or parkin is silenced, then the protective effect of guanabenz is lost. We also found similar results in a distinct model of neuronal death: primary cultures of cortical neurons treated with the topoisomerase I inhibitor camptothecin, in which guanabenz limited camptothecin-induced neuronal death in an ATF4- and parkin-dependent manner. In summary, our data suggest that guanabenz and other GADD34 inhibitors could be used as therapeutic agents to boost parkin levels and thereby slow neurodegeneration in PD and other neurodegenerative conditions.

Protein misfolding, amyotrophic lateral sclerosis and guanabenz: protocol for a phase II RCT with futility design (ProMISe trial)

INTRODUCTION

Recent studies suggest that endoplasmic reticulum stress may play a critical role in the pathogenesis of amyotrophic lateral sclerosis (ALS) through an altered regulation of the proteostasis, the cellular pathway-balancing protein synthesis and degradation. A key mechanism is thought to be the dephosphorylation of eIF2α, a factor involved in the initiation of protein translation. Guanabenz is an alpha-2-adrenergic receptor agonist safely used in past to treat mild hypertension and is now an orphan drug. A pharmacological action recently discovered is its ability to modulate the synthesis of proteins by the activation of translational factors preventing misfolded protein accumulation and endoplasmic reticulum overload. Guanabenz proved to rescue motoneurons from misfolding protein stress both in in vitro and in vivo ALS models, making it a potential disease-modifying drug in patients. It is conceivable investigating whether its neuroprotective effects based on the inhibition of eIF2α dephosphorylation can change the progression of ALS.

METHODS AND ANALYSES

Protocolised Management In Sepsis is a multicentre, randomised, double-blind, placebo-controlled phase II clinical trial with futility design. We will investigate clinical outcomes, safety, tolerability and biomarkers of neurodegeneration in patients with ALS treated with guanabenz or riluzole alone for 6 months. The primary aim is to test if guanabenz can reduce the proportion of patients progressed to a higher stage of disease at 6 months compared with their baseline stage as measured by the ALS Milano-Torino Staging (ALS-MITOS) system and to the placebo group. Secondary aims are safety, tolerability and change in at least one biomarker of neurodegeneration in the guanabenz arm compared with the placebo group. Findings will provide reliable data on the likelihood that guanabenz can slow the course of ALS in a phase III trial.

ETHICS AND DISSEMINATION

The study protocol was approved by the Ethics Committee of IRCCS 'Carlo Besta Foundation' of Milan (Eudract no. 2014-005367-32 Pre-results) based on the Helsinki declaration.

Opioid adjuvant strategy: improving opioid effectiveness

Opioid analgesics continue to be the mainstay of pharmacologic treatment of moderate to severe pain. Many patients, particularly those suffering from chronic pain, require chronic high-dose analgesic therapy. Achieving clinical efficacy and tolerability of such treatment regimens is hampered by the appearance of opioid-induced side effects such as tolerance, hyperalgesia and withdrawal syndrome. Among the therapeutic options to improve the opioid effectiveness, this current review focuses on strategies combining opioids to other drugs that can modulate opioid-mediated effects. We will discuss about experimental evidences reported for several potential opioid adjuvants, including N-methyl-d-aspartate receptor antagonists, 5-HT7 agonists, sigma-1 antagonists, I2-R ligands, cholecystokinin antagonists, neuropeptide FF-R antagonists and toll-like receptor 4 antagonists.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Harnessing the integrated stress response for the treatment of multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating autoimmune disease of the central nervous system (CNS) with no known cure. Though a dozen immunomodulatory therapies exist, their impact on progression of disease appears limited. The field has hence focused on alternate strategies for treatment such as enhancing remyelination and CNS repair. Recent progress has been made on a third complimentary treatment approach that involves protecting oligodendrocytes, and the myelin they generate and maintain, from inflammatory-mediated death via enhancement of the integrated stress response (ISR). Studies in cells and mouse models of MS have demonstrated that the ISR, an innate protective pathway that maintains proteostasis, may be effectively harnessed to aid in the protection of oligodendrocytes and myelin during inflammation. With one ISR-modifying drug already in clinical trial and a number of potential future therapies under investigation, this approach may offer an important component in halting the progression of multiple sclerosis.

Guanabenz (Wytensin™) selectively enhances uptake and efficacy of hydrophobically modified siRNAs

One of the major obstacles to the pharmaceutical success of oligonucleotide therapeutics (ONTs) is efficient delivery from the point of injection to the intracellular setting where functional gene silencing occurs. In particular, a significant fraction of internalized ONTs are nonproductively sequestered in endo-lysosomal compartments. Here, we describe a two-step, robust assay for high-throughput de novo detection of small bioactive molecules that enhance cellular uptake, endosomal escape, and efficacy of ONTs. Using this assay, we screened the LOPAC (Sigma–Aldrich) Library of Pharmacologically Active Compounds and discovered that Guanabenz acetate (Wytensin™), an FDA-approved drug formerly used as an antihypertensive agent, is capable of markedly increasing the cellular internalization and target mRNA silencing of hydrophobically modified siRNAs (hsiRNAs), yielding a ∼100-fold decrease in hsiRNA IC₅₀ (from 132 nM to 2.4 nM). This is one of the first descriptions of a high-throughput small-molecule screen to identify novel chemistries that specifically enhance siRNA intracellular efficacy, and can be applied toward expansion of the chemical diversity of ONTs.

Approaches for discovering anti-prion compounds: lessons learned and challenges ahead

INTRODUCTION

Recent years have witnessed major advances in our understanding of the molecular bases of prion diseases. These studies not only highlight the protein misfolding as a potential initiator of a neurodegenerative process, they also provide a foundation for considering whether such a process can be common to many neurodegenerative diseases, including Alzheimer's disease. This makes prion diseases a sort of prototype of neurodegenerative disease, endowed with some intrinsic positive features in terms of drug development. Thanks to the fact that disappearance of the scrapie protein can serve as a clear readout of drug efficiency, phenotypic approaches have high potential for prion disease drug discovery.

AREAS COVERED

In this review, the authors discuss phenotypic screening and how it lends itself to drug repositioning. Furthermore, they discuss the advantages of working with a molecule with proven safety, tolerability and drug-like properties in combination with a reliable phenotypic screening and how it could improve the success rate for prion drug development. They also provide examples of several interesting candidates that have been identified using this approach, including quinacrine, astemizole, guanabenz and doxycycline.

EXPERT OPINION

The availability of persistently scrapie-infected murine neuroblastoma cells has greatly helped to identify compounds that inhibit prion formation. However, a human neuronal model infected with the human isoform would ultimately serve as the ideal disease model toward the discovery of effective drugs.

Elements toward novel therapeutic targeting of the adrenergic system

Adrenergic receptors belong to the family of the G protein coupled receptors that represent important targets in the modern pharmacotherapies. Studies on different physiological and pathophysiological properties of the adrenergic system have led to novel evidences and theories that suggest novel possible targeting of such system in a variety of pathologies and disorders, even beyond the classical known therapeutic possibilities. Herein, those advances have been illustrated with selected concepts and different examples. Furthermore, we illustrated the applications and the therapeutic implications that such findings and advances might have in the contexts of experimental pharmacology, therapeutics and clinic. We hope that the content of this work will guide researches devoted to the adrenergic aspects that combine neurosciences with pharmacology.

[Chemobiology at happy hour: yeast as a model for pharmacological screening]

Since its discovery and description by Louis Pasteur, the budding yeast Saccharomyces cerevisiae, which was used for thousands of years for alcoholic fermentation and as a leavening agent, has become a popular model system in biology. One of the reasons for this popularity is the strong conservation from yeast to human of most of the pathways controlling cell growth and fate. In addition, at least 30 % of human genes involved in diseases have a functional homolog in yeast. Hence, yeast is now widely used for modelling and deciphering physiopathological mechanisms as well as for developing pharmacological approaches like phenotype-based drug screening. Three examples of such yeast-based chemobiological studies are presented.