Patent Application
20210093626
The present invention relates to compounds for use in the therapeutic treatment of a prion or prion-like disease and to pharmaceutical compositions comprising these compounds.
Over the last decades, the striking advancements in biomedical knowledge have led to a significant improvement of health conditions. This fact has ultimately led to the lengthening of life expectancy: by 2050, almost 400 million people will be 80 years old. As a consequence, the prevalence of neurodegenerative disorders is rapidly increasing. The fact of this augment is likely to represent a major social and economic issue in the near future, not only for high-income countries but also in low- and middle-income ones.
Even though great efforts have been dedicated to research for many years, the precise molecular mechanisms that lead to neurodegeneration in pathologies such as Alzheimer's, Parkinson's, Huntington's or Creutzfeldt-Jakob's diseases are far from being elucidated. In general, these disorders share a common mechanism of aberrant folding of distinct proteins that, upon misfolding, become more prone to aggregation, and, in turn, may become highly neurotoxic. This mechanism is referred to as “prion paradigm”.
The physiological cellular prion protein (PrPC) is a membrane-bound protein predominantly expressed in the nervous tissue, where it probably plays a role in neuronal development and function. When in an aberrant misfolded state, the cellular prion proteins associate with one another, leading to protein aggregation, and impose their anomalous structure on benign PrP molecules. Prions thus act as corruptive templates (seeds) that initiate a chain-reaction of PrP misfolding and aggregation. As prions grow, fragment and spread, they cause neuronal loss, thereby perturbing the function of the nervous system and ultimately causing the death of the affected individual.
Prion diseases or transmissible spongiform encephalopathies (TSEs) are a class of fatal infectious neurodegenerative disorders whose pathogenesis mechanisms are not fully understood. Prion diseases are characterized by neuronal vacuolation and cell loss within the brain, which lead to the characteristic spongiform changes, namely holes in the brain, which give these diseases their name. These diseases manifest as sporadic, genetic or acquired. So far, neither specific biomarkers for early diagnosis nor effective therapeutic targets have been identified.
The PrPC is encoded by the PRNP gene. Misfolding of this protein into the pathogenic PrPSc occurs in different prion diseases, and different types of human prion diseases are characterized by diverse PrPSc isoforms and by the polymorphisms present at PRNP codon 129. Mounting evidences suggest that in addition to gene coding for the PrP (PRNP) other genes may contribute to the genetic susceptibility of TSEs.
The misfolding and aggregation of specific proteins within nervous system occur also in neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and frontotemporal dementia (FTD), now referred as prion-like disorders. In these disorders, Tau, beta-amyloid, and alpha-synuclein are the most commonly misfolded proteins, which form highly ordered filamentous inclusions with a core region of cross-beta-conformation. These proteins have also been named ‘prionoids’ indicating that they exhibit prion-like properties.
Prion diseases affect also a wide range of animal species, most notably ruminants. Scrapie, a transmissible spongiform encephalopathy (TSE) in sheep, was first described in the eighteenth century and bovine spongiform encephalopathy (BSE), better known as mad cow disease, is among the many recently discovered zoonotic diseases. Most prion diseases in animals have basically occurred via the acquisition of infection from contaminated feed or via the exposure to contaminated environment. The realization that BSE is likely responsible for a new form of TSE in humans (variant Creutzfeldt-Jakob disease or vCJD), thereby indicating that prion diseases can cross species barriers from animals to humans, had posed a significant threat to human health. Therefore, the control of these disorders necessitates the development of efficacious therapeutics in order to achieve blocking of the cellular spread of infectivity or the propagation of prions.
Recent advances in the diagnosis of prion and prion-like diseases primarily rely on the identification and validation of disease-specific biomarkers. The scientific article Barbisin, M. et al. “Gene expression profiling of brains from bovine spongiform encephalopathy (BSE)-infected cynomolgus macaques” BMC Genomics 2014 15, 434, describes a first large-scale transcriptome gene expression analysis on BSE-infected cynomolgus macaques (Macaca fascicularis), which revealed a striking upregulation of the SERPINA3 protein in the frontal cortex of intracranially infected monkeys.
The researches described in Vanni S. et al “Differential overexpression of SERPINA3 in human prion diseases” Sci Rep. 2017 Nov. 15; 7(1):15637, on brain tissue samples of patients with different prion diseases revealed a strong increase in the expression of the serine protease inhibitor SERPINA3, both at the mRNA and protein level, in comparison with control subjects. This study further confirmed in various human prion disorders the SERPINA3 dysregulation pattern which had been previously highlighted in macaques. The authors of this publication suggest the use of SERPINA3 as a potential biomarker for human prion diseases, particularly as a tool for distinguishing different forms of these disorders.
To date, despite numerous active efforts, there are no drugs available for the cure of the neurodegenerative diseases collectively referred as prion and prion-like disorders. Symptomatic treatment is the only available option, including the administration to patients of antipsychotics, such as quetiapine and clonazepam, to treat myoclonus, and of selective serotonin re-uptake inhibitors (SSRIs) to treat depression. Currently, drug discovery efforts aiming at the identification of compounds for the therapeutic treatment of prion diseases have been following the so-called ‘small molecule design’ approach, whose rationale relies in the ability of a given compound to interfere with PrPC conversion into PrPS, thereby blocking self-amplification of misfolded proteins and, consequently, halting the pathology spreading. However, despite the generation of a large number of compound libraries, all tested molecules have failed to prove effective when administered to humans.
It is therefore an object of the present invention to provide a medicament having activity against prion or prion-like diseases in a human or animal subject.
It is another object of the present invention to provide a medicament which is effective from an early stage of a prion or prion-like disease.
Further, an object of the present invention is to provide a medicament which is effective in preventing or delaying the onset of a prion or prion-like disease.
A yet further object of the present invention is to provide a medicament which is effective in inhibiting the progression of already established prion or prion-like disease-associated neurodegenerative processes.
The present invention provides a SERPINA3 inhibitor compound for use in the prevention and/or therapeutic treatment of a prion or prion-like disease in a subject in need thereof.
The SERPINA3 inhibitor compound for use according to the invention has the general formula (I)
wherein
R is a saturated or unsaturated 5- or 6-membered ring containing at least one heteroatom; and
R′ is a halogen atom or a C1-C4 alkyloxy group substituted with at least one halogen atom.
Preferably, the heteroatom is nitrogen.
A halogen atom is selected from the group consisting of fluorine (F), iodine (I), chlorine (Cl) and bromine (Br). More preferably, the halogen atom is fluorine.
A C1-C4 alkyloxy group is selected from the group consisting of methoxy, ethoxy, propyloxy, iso-propyloxy, n-butyloxy, iso-butyloxy, sec-butyloxy and terz-butyloxy.
In a particularly preferred embodiment, R in general formula (I) is a piperidine or pyrrole ring and/or R′ is a fluorine atom or a trifluoromethoxy group.
In a more preferred embodiment, the SERPINA3 inhibitor compound for use according to the invention has the formula (II):
In another more preferred embodiment, the SERPINA3 inhibitor compound for use according to the invention has the formula (III)
In one embodiment, the invention provides the use of the SERPINA3 inhibitor compound of general formula (I) as above defined for affecting the onset and/or progression of the prion or prion-like disease.
The invention also provides a pharmaceutical composition for use in the prevention and/or therapeutic treatment of a prion or prion-like disease in a subject in need thereof. The pharmaceutical composition contains the SERPINA3 inhibitor compound of general formula (I) as above defined in combination with a pharmaceutically acceptable vehicle, excipient and/or diluent.
Other features and advantages of the SERPINA3 inhibitor compound for use according to the invention are defined in the appended claims which form an integral part of the description.
It should be noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. As well, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, “characterized by” and “having” can be used interchangeably.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs.
As used herein, the term “subject” is meant to refer to an animal. The subject can be a vertebrate, more preferably a mammal. Mammals include, but are not limited to, primates, bovids, ovids, ungulates, felids, ceroids. A mammal can be, for example, a human being, a monkey, a cow, a sheep, a goat, a dog, a cat, a mink, a deer, an elk a pig, a mouse, a rat. In accordance to the present invention, the subject can be affected by a prion or prion-like disease, exhibiting symptoms which may vary from wild to severe. Alternatively, according to the present invention, the subject can be at risk of developing a prion or prion-like disease.
As used herein, unless otherwise specified, the term “treating” refers to the administration of the compound of the invention after the onset of symptoms of the prion or prion-like disease whereas “preventing” refers to the administration prior to the onset of the symptoms, particularly to subjects at risk of the disease.
As used herein, the term “affect” refers to either blocking or slow downing the pathological processes associated with prion or prion-like disorders.
As used herein, the term “therapeutically effective amount” refers to an amount of the compound for use according to the invention sufficient to exhibit a detectable therapeutic effect. The precise effective amount for a subject will depend upon the subject's size and health, the nature and severity of the condition to be treated.
The present inventors have found that, upon prion infection, the accumulation of misfolded prion protein PrPSc is significantly decreased in neural cells wherein the expression of SERPINA3 protein had been stably knock-out (
SERPINA3 is an alpha globulin glycoprotein, which is a member of the serine protease inhibitor family, able to inhibit several proteases, including mast cell chymase, pancreatic chymotrypsin, human glandular kallikrein 2, kallikrein 3 (prostate-specific antigen), and pancreatic cationic elastase. It is a typical acute-phase protein secreted into the circulation during acute and chronic inflammation. High levels of SERPINA3 have also been reported in several malignant melanomas and carcinomas where it might have a role in regulating apoptosis and invasiveness.
Based on these findings, the inventors have carried out experimental studies in order to exploit the role of the SERPINA3 protein as a potential target for drug design in therapeutic approaches aiming at contrasting the neurodegenerative processes which are the common hallmark of prion and prion-like disorders. As a first step, chemical compounds potentially acting as inhibitor of SERPINA3 activity have been selected by performing an in silico screening on several compound libraries for their ability to interact with the protein structure. Briefly, a drug target site has been identified on SERPINA3 by superimposing the protein structure with the known structures of other two molecules belonging to the Serpin family, which have been crystallized with their respective inhibitors. Following this screening, the effects of the compounds thus selected have been tested in in vitro cellular models of prion diseases. As shown in
To further improve drug efficacy, the chemical structure of compound G was used as a model to generate a library of structural analog compounds. The activity of these structural analogs have been assayed in vitro on neural cells infected with different prion strains, revealing that only one of them, hereinafter designated as compound number 5, was effective against the formation and accumulation of PrPSc across the range of prion strains tested, thereby leading to a significant reduction in prion load (
Surprisingly, the present inventors have found that the SERPINA3 inhibitor compounds whose therapeutic efficacy have been proven in vitro against misfolded proteins formation and accumulation, are illustrated by the general formula (I):
wherein
R is a saturated or unsaturated 5- or 6-membered ring containing at least one heteroatom; and
R′ is a halogen atom or a C1-C4alkyloxy group substituted with at least one halogen atom.
Therefore, an aspect of the present invention is a SERPINA3 inhibitor compound, for use in the therapeutic treatment of a prion or prion-like disease in a subject in need thereof, said compound having the above defined general formula (I).
Preferably, in the general formula (I) the heteroatom is nitrogen.
A halogen atom is selected from the group consisting of fluorine (F), iodine (I), chlorine (Cl) and bromine (Br). More preferably, the halogen atom is fluorine.
A C1-C4 alkyloxy group is selected from the group consisting of methoxy, ethoxy, propyloxy, iso-propyloxy, n-butyloxy, iso-butyloxy, sec-butyloxy and terz-butyloxy.
In a particularly preferred embodiment, R in general formula (I) is a piperidine or pyrrole ring and/or R′ is a fluorine atom or a trifluoromethoxy group.
In a more preferred embodiment, the SERPINA3 inhibitor compound for use according to the invention has the formula (II):
In another more preferred embodiment, the SERPINA3 inhibitor compound for use according to the invention has the formula (III)
According to the present invention, compound G is illustrated by the structural formula (II) and compound 5 is illustrated by the structural formula (III).
Accordingly, in the present description, the compound of formula (II) is also designated as compound G, and the compound of formula (III) is also designated as compound 5.
Advantageously, the therapeutic use of the SERPINA3 inhibitor compound against prion diseases enables to achieve a significant decrease in the conversion and/or accumulation of the misfolded prion protein without interfering with the activity of the cellular PrPC isoform. This protein is known to play an important physiological role in the central nervous system.
Moreover, since the compound for use according to the invention targets a protease inhibitor, which may be responsible for defective misfolded protein clearance, and acts independently from the particular structure of the misfolded protein, a therapeutic strategy based on the use of this compound is effective also in the treatment of prion-like neurodegenerative diseases which share the same protein misfolding mechanism.
Without wishing to be bound by any theory, the inventors believe that the SERPINA3 protein present in the brain tissues of diseased subjects may lead to the inhibition of the target protease(s) that, in physiological conditions, would degrade aberrant misfolded proteins such as PrPSc in the prion disease. By reducing the activity of the SERPINA3 protease inhibitor, the physiological intracellular function of the target protease(s) is restored, which, being active again, might effectively degrade misfolded proteins, thereby slowing down the progression of prion or prion-like diseases.
As further illustrated in the Experimental Section below, the present inventors have found that the appearance and accumulation of misfolded protein strongly correlate with the rapid increase in the expression levels of the protein SERPINA3 in neural cells from very early passages after prion infection. These findings highlight the role of SERPINA3 as a therapeutic target for early intervention in prion and prion-like disorders and indicate that the administration of the compound of the invention at an early disease stage is effective to achieve a delay in the disease onset, or to prevent the disease itself.
A preferred embodiment of the present invention relates to a therapeutic method aiming at affecting the onset and/or progression of the prion or prion-like disease in a subject.
Human prion or prion-like diseases, associated with abnormal protein misfolding, that can be treated with the SERPINA3 inhibitor compound for use according to the invention include, but are not limited to, Creutzfeldt-Jacob disease (CJD), fatal familial insomnia (FFI), Gerstmann-Straussler-Scheinker syndrome (GSS), Alzheimer's disease, Parkinson's disease, Huntington's Chorea, Amyotrophic lateral sclerosis (ALS) and Frontotemporal Dementia (FTD).
Exemplary animal prion or prion-like diseases include, but are not limited to, feline spongiform encephalopathy of zoological and domestic cats (FSE) and transmissible spongiform encephalopathy (TSE) of zoological ruminants and non-human primates, as well as chronic wasting disease of deer and elk (CWD) and transmissible mink encephalopathy of farmed mink (TME).
The exact dose of the SERPINA3 inhibitor compound for use according to the invention may vary depending on the targeted disease as well as on the subject's characteristics (e.g. sex, age, weight, etc.). The effective amount for a given situation can be determined by routine experimentation.
The SERPINA3 inhibitor compound for use according to the invention may also be effectively administered in the form of a pharmaceutical composition.
Accordingly, a second aspect of the present invention is a pharmaceutical composition for use in the therapeutic treatment of a prion or prion-like disease, comprising a therapeutically effective amount of a SERPINA3 inhibitor compound and pharmaceutically acceptable vehicles, excipients and/or diluents, wherein said SERPINA3 inhibitor compound has the formula (I):
wherein
R is a saturated or unsaturated 5- or 6-membered ring containing at least one heteroatom; and
R′ is a halogen atom or a C1-C4 alkyloxy group substituted with at least one halogen atom.
Preferably, the heteroatom is nitrogen.
A halogen atom is selected from the group consisting of fluorine (F), iodine (I), chlorine (Cl) and bromine (Br). More preferably, the halogen atom is fluorine.
A C1-C4 alkyloxy group is selected from the group consisting of methoxy, ethoxy, propyloxy, iso-propyloxy, n-butyloxy, iso-butyloxy, sec-butyloxy and terz-butyloxy.
In a particularly preferred embodiment, R in general formula (I) is a piperidine or pyrrole ring and/or R′ is a fluorine atom or a trifluoromethoxy group.
In a more preferred embodiment, the SERPINA3 inhibitor compound in the pharmaceutical composition for use according to the invention has the formula (II):
In another more preferred embodiment, the SERPINA3 inhibitor compound for use according to the invention has the formula (III)
In a pharmaceutical composition, the amount of the administered active ingredient can vary widely according to considerations such as the particular compound and dosage unit employed, the mode and time of administration, the period of treatment, the age, sex, and general condition of the subject treated, the nature and extent of the condition treated, the rate of drug metabolism and excretion, the potential drug combinations and drug-drug interactions.
The pharmaceutical composition for use according to the invention is suitable to be administered as therapy against a prion or prion-like disease to any vertebrate, including human beings. Modifications of pharmaceutical compositions suitable for administration to humans in order to render the compositions suitable for administration to various animals are well known, and the person of ordinary skill in the art can design and perform such modifications by using his/her normal knowledge.
The term “pharmaceutically acceptable” refers to compounds and compositions which may be administered to mammals without undue toxicity at concentrations consistent with effective activity of the active ingredient. Pharmaceutically acceptable carriers (excipients) can for example be fillers, disintegrants, glidants and lubricants. Disintegrants are compounds which enhance the ability of the dosage form, such as tablet, to break into smaller fragments when in contact with a liquid, preferably water. Glidants can be used to improve the drug flowability. Suitable glidants are for example colloidal silicon dioxide, talcum or mixtures thereof. Lubricants generally can be regarded as substances which are suitable to reduce friction, such as static friction, sliding friction and rolling friction. Exemplary pharmaceutically acceptable salts include mineral acid salts such as hydrochlorides, hydrobromides, phosphates and sulfates; and the salts of organic acids such as acetates, propionates, malonates or benzoates.
Preferably, the SERPINA3 inhibitor compound for use according to the invention is dissolved in a liquid vehicle selected from aqueous solution, saline solution, Phosphate-buffered saline (PBS) solution or Dimethyl sulfoxide (DMSO) solution.
The selection of vehicles, excipients and/or diluents suitable for the pharmaceutical composition of the invention can be determined by a person of ordinary skill in the art by using his/her normal knowledge.
The pharmaceutical composition for use according to the invention is suitable for administration via any of the known administration routes, e.g. topical, oral, enteral, parenteral, intrathecal, epidural and intranasal.
As used herein, parenteral administration includes, but is not limited to, administration of a pharmaceutical composition by subcutaneous and intramuscular injection, implantation of sustained release depots, intravenous injection administration.
Intrathecal administration is generally characterized by the direct injection of the drug into the cerebrospinal fluid (CSF) within the intrathecal space of the spinal column.
Injectables can be prepared as liquid solutions or suspensions, solid forms that can be reconstituted into solutions or suspensions prior to injection, or as emulsions. The pharmaceutical composition for use according to the invention may be in the form of a sterile injectable suspension. This suspension may be formulated according to known methods using suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation may also be a sterile injectable solution or suspension in a non-toxic parenterally-acceptable diluent or solvent. Sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed including synthetic mono- or diglycerides, fatty acids (including oleic acid), naturally occurring vegetable oils like sesame oil, coconut oil, peanut oil, cottonseed oil, etc., or synthetic fatty vehicles like ethyl oleate or the like. Buffers, preservatives, antioxidants, and the like can be incorporated as required.
The pharmaceutical composition for use according to the invention may be administered by topical application in a solution, ointment, gel, cream or any local application. The pharmaceutical composition for use according to the invention may also be administered transdermally by means of a drug eluting device, such as gauze, a patch, pad, or a sponge.
Examples of enteral routes include, but is not limited to, oral, mucosal, buccal, rectal and intragastric route.
The pharmaceutical composition for use according to the invention may be in a form suitable for oral use in any acceptable form, such as a tablet, liquid, capsule, powered, syrup, and the like. The pharmaceutical composition intended for oral use may contain one or more agents selected from the group consisting of a sweetening agent such as sucrose, lactose, or saccharin, flavoring agents such as peppermint, oil of wintergreen or cherry, coloring agents and preserving agents in order to provide pharmaceutically elegant and palatable preparations. Tablets contain the compound for use according to the invention in admixture with non-toxic pharmaceutically acceptable excipients. The excipients used may be, for example, (1) inert diluents such as calcium carbonate, lactose, calcium phosphate or sodium phosphate; (2) granulating and disintegrating agents such as corn starch, potato starch or alginic acid; (3) binding agents such as gum tragacanth, corn starch, gelatin or acacia, and (4) lubricating agents such as magnesium stearate, stearic acid or talc. The tablets may be uncoated or they may be coated by known techniques to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. For example, a time delay material such as glyceryl monostearate or glyceryl distearate may be employed.
The pharmaceutical composition according to the invention may also be administered in the form of suppositories for rectal administration of the SERPINA3 inhibitor compound. These compositions may be prepared by mixing the invention compounds with a suitable non-irritating excipient, such as cocoa butter, synthetic glyceride esters of polyethylene glycols, which are solid at ordinary temperatures, but liquefy and/or dissolve in the rectal cavity to release the drug.
For solid dosage forms, non-toxic solid excipients for admixture with compounds for use according to the invention include, but are not limited to, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharin, polyalkylene glycols, talcum, cellulose, glucose, sucrose, and magnesium carbonate. The solid dosage forms may be coated by a material such as glyceryl monostearate or glyceryl distearate, which is utilized in known techniques to delay disintegration and absorption in the gastrointestinal tract for the purpose of providing a sustained action over a longer period.
Pharmaceutically administrable liquid dosage forms can, for example, comprise a solution or suspension of a compound for use according to the invention and optional pharmaceutical adjutants in a carrier, such as water, saline, aqueous dextrose, glycerol, ethanol and the like. The liquid dosage forms may also contain nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like. Examples of such auxiliary agents include sodium acetate, sorbitan monolaurate, triethanolamine, sodium acetate, triethanolamine oleate, etc. Methods for preparing such dosage forms are well-known to persons skilled in the art.
The pharmaceutical composition for use according to the invention should be administered as frequently as necessary and for as long of a time as necessary in order to achieve the desired effect, i.e. affecting the onset and/or progression of the prion or prion-like disease.
Additionally, the mode of administration of the pharmaceutical composition for use according to the invention may be designed to delay release of the active compound over a given period of time, or to carefully control the amount of drug released at a given time during the course of therapy.
One of ordinary skill in the art can readily determine a suitable course of treatment utilizing the pharmaceutical compositions for use according to the invention.
The following experimental section is provided purely by way of illustration and is not intended to limit the scope of the invention as defined in the appended claims.
1. Material and Methods
1.1 Maintenance of Cell Culture
The mouse hypothalamic cell line GT1 and GT1 cells infected with RML prion strain (ScGT1) were cultured in Dulbecco's modified Eagle's medium (DMEM), supplemented with 10% of FBS and 1% penicillin-streptomycin. The mouse neuroblastoma cell line N2a and N2a cells infected with RML prion strain (ScN2a) were cultured in Minimal Essential Medium (MEM) complemented with 10% fetal bovine serum (FBS), 1% non-essential amino acids (NEAA), 1% L-glutamax and 1% penicillin/streptomycin. All cell lines were maintained in a 5% CO2 atmosphere.
1.2 MTT Assay for Cell Viability
Cells were maintained in culture and grown to confluence. The cells were detached and the medium was refreshed. Cell density was adjusted to 2×104 cell/ml with MEM (N2a, ScN2a) or 3×104 with DMEM (GT1, ScGT1) by using Scepter™ 2.0 Cell Counter (Millipore). Cells were seeded in a 96-well plate and allowed to settle for 24 hours prior to the addition of the compounds. Each compound—dissolved in DMSO—was diluted in the cell medium to a final concentration of 0.1, 1 and 10 μM. The day after, cell culture medium was refreshed together with the addition of the compound. The plate was incubated for 4 days. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide powder (MTT) (SIGMA) was diluted in phosphate buffer solution (PBS) to a working dilution of 5 mg/mL and added to the medium. Cells were incubated with the MTT solution for 3 hours at 37° C. After incubation, a solution of DMSO/2-Propanol (1:1) was added to each well and the plate was kept at room temperature (RT) for 30 minutes before reading. The emission intensity was quantified using a Spectramax Gemini EM (SoftMax Pro) plate reader, excitation/emission ratio equal to 570/690 nm. MTT assays were performed in triplicate.
1.3 in Silico Screening
Several libraries of compounds have been virtually screened using the Glide program for their potential interaction with the SERPINA3 protein target. A protein site has been identified through superimposition of a SerpinaA3 structural model (obtained by homology modeling) built in house with other two proteins of the same family which have been crystallized with respective inhibitors: human plasminogen activator inhibitor PAI-1 complexed with CDE-096 (PDB ID: 4G80) and alpha-1-antitrypsin SERPINA1 complexed with citrate (PDB ID: 3CWM) (
1.4 Drug Treatment
All the tested compounds were dissolved in 100% dimethyl sulfoxide (DMSO) to a concentration of 10 mM. This solution was further diluted into a final stock solution of 200 μM with PBS. Confluent GT1 and ScGT1 cells were split 1:10 and the day after the drug (20 μM) was added to the medium and incubated for 4 days. Confluent N2a and ScN2a cells were split 1:20 and the day after the drug (20 μM) was added to the medium and incubated for 4 days. Control cells were treated with the vehicle (0.001% DMSO). All the experiments were repeated at least three times.
1.5 Western Blot analysis Cell lysis. After medium removal, cells were rinsed twice with cold PBS and 300 μl of lysis buffer (10 mM Tris-HCl pH 8.0, 150 mM NaCl, 0.5% nonidet P-40, 0.5% deoxycholic acid sodium salt) was added directly to the cell plate. Cell lysates were centrifuged at 2000 rpm for 10 minutes at 4° C. in a bench microfuge (Eppendorf) and pellet was discarded. Total protein concentration was assessed with BCA assay (bicinchoninic acid method, Euroclone).
PK digestion. 250 μl of 1 mg/ml cell lysates were digested with 25 μg/ml of PK for 1 hour at 37° C. The reaction was stopped with 2 mM of phenylmethylsulphonylfluoride (PMSF) and the PK-digested cell lysates were centrifuged at 55000 rpm for 75 minutes at 4° C. in an ultracentrifuge (Beckman Coulter). The pellets were re-suspended in 2× sample loading buffer (125 mM Tris HCl, pH 6.8, 10% 2-mercapethanol, 4% SDS, 0.2% bromophenol blue, 20% glycerol). For the non-PK digested sample, 25 μg of cell lysates were used and 2× loading buffer was added. All the samples were boiled for 10 minutes at 100° C.
SDS page and immunoblotting. Samples were loaded onto 12% Tris-Glycine SDS-PAGE gel and proteins were transferred onto a PVDF membrane (Millipore). The membrane was then blocked with 5% non-fat milk for 1 hour at RT in continuous shaking and then incubated with 1 μg/ml monoclonal anti-PrP W226 at 4° C. overnight. After 3 washings with TBS-T (Tris 200 mM, NaCl 1.5 mM, 1% Tween-20) the membrane was incubated with goat anti-mouse IgG F(Ab)2 conjugated with horseradish peroxidase (HRP) for 1 hour at RT, continuous shaking. Actin beta was detected using monoclonal anti-β-actin-peroxidase antibody (1:10,000 Sigma), SerpinA3n detection was performed using Mouse Serpin A3N Antibody (1:500 R&D Systems) and a rabbit anti-goat HRP secondary antibody. Blots were developed with enhanced chemiluminescent system (ECL, Amersham Biosciences) and visualized on Uvitec Alliance (Cambridge).
1.6 De Novo Prion Infection
ScGT1 cells chronically infected with mouse-adapted RML were grown to confluence and 20×106 cells were resuspended in fresh medium and sonicated three times for 15 seconds at 70% amplitude. This solution was incubated with 5×105 GT1 cells seeded on 10 cm petri dish the day before. GT1 cells were grown for 7 days without changing medium. After a week, GT1 cells were split 1:5 with fresh medium for the first passage and for each subsequent passage 1:10. Similarly, chronically RML-infected ScN2a cells were used to infect normal N2a cells. In this case, for the first passage cells were split 1:15 after 4 days and the conditioned medium was added to the cells for additional 4 days. Then, starting from the second passage, cells were split 1:30 with fresh medium. For each passage, the remaining cells were lysed and an aliquot of the cell lysate was subjected to PK-digestion and immunoblot analysis to check the presence of PrPSc.
1.7 Stable Transfection with Plasmid Lipofectamine 2000 was used for all plasmid transfection experiments according to the manufacturer's protocol. Briefly, cells were plated in 96-wells plates for each experiment at a density of 1000 cells. Lipofectamine and Optimem medium were mixed and incubated for 5 min, then added to a plasmid and Optimem medium mixture and kept for 15 minutes at room temperature (RT). This solution was added stepwise to cells and gently mixed. Cells were incubated at 37° C. overnight, afterwards the medium was replaced by fresh complete medium. Passage cells at a 1:50 into selective medium in the following day. Plasmid for overexpression was pcDNA-SERPINA3N and plasmids for knock-out experiments were pSPCas9n-SERPINA3N-A, pSPCas9n-SERPINA3N-B.
2. Results
2.1. SerpinA3n Expression in GT1, N2a, ScGT1 and ScN2a Cell Lines
The present inventors investigated the expression of Serpina3n, which is the murine homologue of human SERPINA3, in GT1 and N2a cell lines chronically infected with RML prion strain, designated as ScGT1 and ScN2a, respectively, using non-infected cells as controls. As shown in
2.2 De Novo Prion Infection of GT1 Cell Line
To further investigate the correlation between Serpina3n levels and PrPSc proteins accumulation, the inventors performed de novo prion infection of GT1 cells, monitoring each passage for both protein levels. As shown in
2.3 De Novo Prion Infection of N2a Cell Lines Overexpressing Serpina3n
As a further assessment of the functional correlation between Serpina3n levels and PrPSc, the present inventors carried out de novo infection experiments also on N2a cells which stably overexpress Serpina3n. N2a clone 2 cell line—which overexpresses Serpina3n about 7000-fold in comparison to parental N2a cells (
2.4 De Novo Prion Infection of Serpina3n Knock-Out GT1 Cell Line
De novo infection experiments were carried out by the present inventors on GT1 cell line wherein Serpina3n had been stably knock-out. Following infection, Serpina3n knock-out GT1 clone 2 cell line displayed much lower levels (on average 60% less) of PrPSc in each single passage in comparison to the same passage of parental GT1 cell line (
2.4 Serpina3n Knock-Out ScN2a Cell Line
Based on the above-illustrated experimental results, the present inventor generated chronically prion-infected N2a (ScN2a) cell lines knock-out for Serpina3n (
2.5 Treatment of ScGT1 Cell Line with Serpina3n Inhibitor Compounds
In order to exploit the role of Serpina3n as potential drug target in prion or prion-like diseases, RML ScGT1 cells were treated with the Serpina3 inhibitor compounds which had been selected in silico as above detailed at paragraph 1.3. Among the 19 molecules selected from the first library screening (named A-U), two were discarded because of high citotoxicity. The remaining 17 compounds were tested in in vitro cellular models. Compound G of formula (II) showed the highest efficacy in reducing PrPSc accumulation of about 50% (
2.6 Treatment of ScN2a Cell Line with Serpina3n Inhibitor Compounds
Following the results of in vitro test on ScGT1 cells, compound 5 of formula (III) was also administered to RML-infected ScN2a cell line. As shown in
3. Discussion and Conclusion
The expression of the serine protease inhibitor Serpina3n is strongly increased in prion-infected cells, both at the mRNA and protein level. Notably, the present inventors found that the increase in Serpina3n levels is evident since the pre-clinical stage in mice as well as in de novo prion-infected cell lines, indicating that SERPINA3 plays a central role not only in supporting the progression of prion or prion-like diseases but also in the onset of these disorders. More importantly, the present inventors observed that ablation of the Serpina3n protein—or inhibition of its activity—leads to a significant decrease in the accumulation of PrPSc.
Without wishing to be bound by any theory, the inventors believe that the SERPINA3 inhibitor compounds for use according to the invention may act by blocking the first step in the serpin-protease interaction that leads to the non-covalent binding of the serpin with the target protease. Indeed, based on the general mechanism which has been described for serpins and proteases, the reaction comprises the following subsequent steps: (i) formation of non-covalent Michaelis-Menten complex between serpin and target protease, (ii) catalytic binding of the protease to the serpin, (iii) formation of the covalent complex, (iv) insertion of the cleaved RCL site in the beta-sheet A, (v) translocation of the protease to the opposite pole of the serpin, (vi) dissociation of the protease.
For other similar complexes, such as the complex formed between human plasminogen activator inhibitor PAI-1 and the inhibitor molecule CDE-096, it has been demonstrated that the inhibitor compound binds the sB/sC pocket between beta sheets B and C, thereby blocking the Michaelis-Menten complex formation between the serpin and the protease. In this way, the RCL region of the serpin cannot longer interact with the active site of the protease, and therefore the serpin protein is sequestered in a conformation in which the RCL region cannot interact with the beta-sheet A. On the other hand, studies carried out on the complex formed between alpha-1-antitrypsin SERPINA1 and citrate have demonstrated that citrate is capable to prevent the aggregation of serpin by blocking the sB/sC pocket and the conformation rearrangements needed for the polymerization.
Finally, the specificity of the SERPINA3 inhibitor compounds for use according to the invention is discussed. Despite the high structural homology among all the serpin proteins, the sB/sC pocket is considered a protein site that can be exploited for modulating the activity of different serpins. Such protein site corresponds to the serpin region which interacts with the respective ligand. Indeed, even if citrate and CDE-096 bind in a similar manner to SERPINA1 and human plasminogen activator inhibitor PAI-1, respectively, they exert different effects—inhibition of aggregation for the citrate, inhibition of protease binding for CDE-096. Moreover, the alignment of the amino acid sequences of human PAI-1, SERPINA1 and SERPINA3 reveals that the sB/sC pocket, i.e, the ligand binding site, is actually one of the least conserved amino acid portions.
So far, no inhibitors against SERPINA3 or the mouse orthologue Serpina3n have been developed for neurodegenerative disorders. Some studies exist describing the use of Serpina3n itself as inhibitor of other enzymes. For instance, Serpina3n has been used to inhibit the activity of granzyme-B in a mouse model of Multiple Sclerosis, showing reduced axonal and neuronal injury.
In conclusion, the present inventors found a new class of small molecules acting as SERPINA3 inhibitors, which are able to reduce PrPSc accumulation in prion-infected cell lines, thereby representing a new therapeutic treatment against prion and prion-like diseases.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18170092.3 | Apr 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/061014 | 4/30/2019 | WO | 00 |
