Anti-prion Agents Research Articles

The biodistribution of maltotriose modified poly(propylene imine) (PPI) dendrimers conjugated with fluorescein—proofs of crossing blood–brain–barrier

Oligosaccharide-modified poly(propylene imine) dendrimers are promising candidates as drug carriers and as anti-prion agents. Here, we report the biodistribution of maltotriose-modified 4th generation poly(propylene imine) (PPI) dendrimers and their ability to cross the blood–brain–barrier that is important if these glycodendrimers are considered as potential therapeutic agents in the central nervous system (CNS).

Respiratory and cardiovascular toxicity studies of a novel antiprion compound, GN8, in rats and dogs

Prion diseases, also known as transmissible spongiform encephalopathies, are fatal neurodegenerative disorders for which no effective curative or prophylactic method has been established. Recently, we discovered a novel antiprion compound, GN8. Administration of GN8 was found to prolong the survival of prion-infected mice. The aim of this study was to characterize the toxicological and pharmacological features of GN8 in rats and dogs treated via a single intravenous injection. Minimum lethal doses of GN8 were estimated to be approximately 60 and 40 mg/kg in rats and dogs, respectively. In the respiratory toxicity experiments, GN8 was administered to rats at doses of 0, 15.6, and 46.9 mg/kg, and rats were observed for consciousness, behavior, autonomic nervous symptoms, and body weights. GN8 was found to have little adverse effect on the rat respiratory system at a dose of 46.9 mg/kg. In the cardiovascular toxicity experiments, GN8 was administered to dogs at doses of 0, 7.8, and 31.3 mg/kg, and dogs were observed similarly. Although GN8 was found to have a slight effect on the cardiovascular system at a dose of 31.3 mg/kg, we did not find severe adverse effects of GN8 at doses sufficient for antiprion activity. This study would serve as a stepping stone to a clinical application of GN8 as an antiprion agent.

Styryl-Based and Tricyclic Compounds as Potential Anti-Prion Agents

Prion diseases currently have no effective therapy. These illnesses affect both animal and human populations, and are characterized by the conformational change of a normal self protein PrPC (C for cellular) to a pathological and infectious conformer, PrPSc (Sc for scrapie). We used a well characterized tissue culture model of prion infection, where mouse neuroblastoma cells (N2a) were infected with 22L PrPSc, to screen compounds for anti-prion activity. In a prior study we designed a library of styryl based, potential imaging compounds which were selected for high affinity binding to Alzheimer's disease β-amyloid plaques and good blood-brain barrier permeability. In the current study we screened this library for activity in the N2a/22L tissue culture system. We also tested the anti-prion activity of two clinically used drugs, trimipramine and fluphenazine, in the N2a/22L system. These were selected based on their structural similarity to quinacrine, which was previously reported to have anti-prion activity. All the compounds were also screened for toxicity in tissue culture and their ability to disaggregate amyloid fibrils composed of PrP and β-amyloid synthetic peptides in vitro. Two of the imaging agents, 23I and 59, were found to be both effective at inhibiting prion infection in N2a/22L tissue culture and to be non-toxic. These two compounds, as well as trimipramine and fluphenazine were evaluated in vivo using wild-type CD-1 mice infected peripherally with 139A PrPSc. All four agents significantly prolonged the asymptomatic incubation period of prion infection (p<0.0001 log-rank test), as well as significantly reducing the degree of spongiform change, astrocytosis and PrPSc levels in the brains of treated mice. These four compounds can be considered, with further development, as candidates for prion therapy.

Discovery of 6-substituted indole-3-glyoxylamides as lead antiprion agents with enhanced cell line activity, improved microsomal stability and low toxicity

A series of highly potent indole-3-glyoxylamide based antiprion agents was previously characterized, focusing on optimization of structure–activity relationship (SAR) at positions 1–3 of the indole system. New libraries interrogating the SAR at indole C-4 to C-7 now demonstrate that introducing electron-withdrawing substituents at C-6 may improve biological activity by up to an order of magnitude, and additionally confer higher metabolic stability. For the present screening libraries, both the degree of potency and trends in SAR were consistent across two cell line models of prion disease, and the large majority of compounds showed no evidence of toxic effects in zebrafish. The foregoing observations thus make the indole-3-glyoxylamides an attractive lead series for continuing development as potential therapeutic agents against prion disease.

Characterizing the Interaction Between Phthalocyanine Tetrasulfonates and Mammalian Prion Protein

Phthalocyanine tetrasulfonates are known to interact with mammalian prion protein, having the ability to act as anti-prion agents and help prevent the conversion of native isoform PrPc to the scrapie isoform PrPsc. However, the interaction between phthalocyanines and PrP remains poorly characterized. We explore the phenomenology of this interaction in detail by examining the binding of phthalocyanines to monomeric native Syrian Hamster prion protein using multiple complementary assays: surface plasmon resonance, FCS, fluorescence quenching, calorimetry, and CD spectroscopy. We determine binding constants, kinetics, stoichiometry, structural and spectroscopic effects of binding, and the influence of buffer ionic strength.

The suppression of prion propagation using poly-l-lysine by targeting plasminogen that stimulates prion protein conversion

Poly-l-lysine (PLL), a homopolymer of amino acid l-lysine (LL), has been frequently used for drug delivery. Here, we report that PLL is an effective agent to inhibit propagation of prions that cause fatal and incurable neurologic disorders in humans and animals, termed prion diseases. In our recent investigation on prion propagation facilitated by conversion of the cellular prion protein (PrP) to the misfolded, disease-associated PrP (PrPSc), we demonstrated that plasminogen stimulates PrP conversion as a cellular cofactor. In the current study, we targeted plasminogen using PLL and assessed its anti-prion efficacy. The results showed that PLL strongly inhibited PrPSc propagation in the cell-free, cell culture, and mouse models of prion disease. These results confirm the role of plasminogen in PrPSc propagation, validates plasminogen as a therapeutic target to combat prion disease, and suggests PLL as a potential anti-prion agent. Therefore, our study represents a proof-of-concept that targeting plasminogen, a cofactor for PrP conversion, using PLL results in suppression of prion propagation, which represents a successful translation of our understanding on details of prion propagation into a potential therapeutic strategy for prion diseases.

Structure–Activity Relationship Refinement and Further Assessment of Indole‐3‐glyoxylamides as a Lead Series against Prion Disease

Structure-activity relationships within the indole-3-glyoxylamide series of antiprion agents have been explored further, resulting in discovery of several new compounds demonstrating excellent activity in a cell line model of prion disease (EC₅₀ <10 nM). After examining a range of substituents at the para-position of the N-phenylglyoxylamide moiety, five-membered heterocycles containing at least two heteroatoms were found to be optimal for the antiprion effect. A number of modifications were made to probe the importance of the glyoxylamide substructure, although none were well tolerated. The most potent compounds did, however, prove largely stable towards microsomal metabolism, and the most active library member cured scrapie-infected cells indefinitely on administration of a single treatment. The present results thereby confirm the indole-3-glyoxylamides as a promising lead series for continuing in vitro and in vivo evaluation against prion disease.

ChemInform Abstract: Biological Properties of Phosphorus Dendrimers

AbstractReview: 84 refs.

Inside Cover: Improved 2,4‐Diarylthiazole‐Based Antiprion Agents: Switching the Sense of the Amide Group at C5 Leads to an Increase in Potency (ChemMedChem 9/2010)

Inside Cover: Improved 2,4‐Diarylthiazole‐Based Antiprion Agents: Switching the Sense of the Amide Group at C5 Leads to an Increase in Potency (ChemMedChem 9/2010)

Peptide and glycopeptide dendrimers and analogous dendrimeric structures and their biomedical applications

The size of information that can be stored in nucleic acids, proteins, and carbohydrates was calculated. The number of hexamers for peptides is 64,000,000 (20(6)) and seems to be impressive in comparison with 4,096 (4(6)) hexanucleotides, but the number of isomers of hexasaccharides is 1.44 × 10(15). Carbohydrates are therefore the best high-density coding system. This language has been named glycocode resp. sugar code. In comparison with peptide dendrimers, the amount of information carried by glycopeptide dendrimers or glycodendrimers is therefore much higher. This is reflected by the variability of structures and functions (activities). This review is about the broad area of peptide and glycopeptide dendrimers. The dendrimeric state and physicochemical properties and general consequences are described, together with a cluster effect. The impact of cluster effect to biological, chemical, and physical properties is discussed. Synthesis of dendrimers by convergent and divergent approaches, "Lego" chemistry, ligation strategies, and click chemistry is given with many examples. Purification and characterization of dendrimers by chromatographic methods, electromigration methods, and mass spectrometry are briefly mentioned. Different types of dendrimers with cyclic core, i.e. RAFTs, TASPs and analogous cyclic structures, carbopeptides, carboproteins, octopus glycosides, inositol-based dendrimers, cyclodextrins, calix[4]arenes, resorcarenes, cavitands, and porphyrins are given. Dendrimers can be used for creation of libraries, catalysts, and solubilizing agents. Biocompatibility and toxicity of dendrimers is discussed, as well as their applications in nanoscience, nanotechnology, drug delivery, and gene delivery. Carbohydrate interactions of glycopeptide dendrimers (bacteria, viruses, and cancer) are described. Examples of dendrimers as anti-prion agents are given. Dendrimers represent a fast developing area which partly overlaps with nanoparticles and nanotechnologies.

Discovery of a Class of Diketopiperazines as Antiprion Compounds

Prion diseases are fatal neurodegenerative and infectious disorders for which effective pharmacological tools are not yet available. This unmet challenge and the recently proposed interplay between prion diseases and Alzheimer's have led to a more urgent demand for new antiprion agents. Herein, we report the identification of a novel bifunctional diketopiperazine (DKP) derivative 1 d, which exhibits activity in the low micromolar range against prion replication in ScGT1 cells, while showing low cytotoxicity. Supported by properly addressed molecular modeling studies, we hypothesized that a planar conformation is the major determinant for activity in this class of compounds. Moreover, studies aimed at assessing the mechanism-of-action at the molecular level showed that 1 d might interact directly with recombinant prion protein (recPrP) to prevent its conversion to the pathogenic misfolded prion protein (PrP(Sc))-like form. This investigation suggests that DKP based antiprion compounds can serve as a promising lead scaffold in developing new drugs to combat prion diseases.

Improved 2,4‐Diarylthiazole‐Based Antiprion Agents: Switching the Sense of the Amide Group at C5 Leads to an Increase in Potency

Amide derivatives of 2,4-diarylthiazole-5-carboxylic acids were synthesised and tested for efficacy in a cell line model of prion disease. A number of compounds demonstrating antiprion activity were thereby identified from the screening libraries, showing improved potency and reproducibility of results relative to amide derivatives of the related 2,4-diphenyl-5-aminothiazole, which have been documented previously. Thus, 'switching' the sense of the amide bond at thiazole C5 revealed a more promising lead series of potential prion disease therapeutics. Furthermore, 3,5-diaryl-1,2,4-thiadiazoles isolated as by-products during library synthesis provided a handful of additional examples possessing an antiprion effect, thereby augmenting the set of newly identified active compounds. Evaluation of binding to cellular prion protein (PrP(C)) showed only weak affinities at best, suggesting that the newly identified antiprion agents do not mediate their biological effect through direct interaction with PrP(C).

Biological properties of phosphorus dendrimers

This review will display the special role played by phosphorus-containing dendrimers when interacting with biological systems. After some synthetic aspects, the usefulness of these dendrimers for elaboration of highly sensitive bio-sensors and for in vitro drug delivery (for instance as transfection agents, or against HIV-1 and the scrapie form of prions) will be demonstrated. Then, emphasis will be put on the favourable influence of these dendrimers on cells growth, in particular for neuronal cells, and for human immune blood cells such as monocytes and Natural Killer cells, the latter playing a key-role for fighting against viral infections and cancers. This review will finally describe in vivo biological properties of these phosphorus dendrimers as anti-prion agents, for ocular drug delivery, and for imaging rat brain blood vessels. Some of these properties can be found also with other types of dendrimers, but others, in particular the interaction with the human immune blood cells, occur only and specifically with phosphorus dendrimers.

The inhibition of prions through blocking prion conversion by permanently charged branched polyamines of low cytotoxicity

Branched polyamines are effective in inhibiting prions in a cationic surface charge density dependent manner. However, toxicity associated with branched polyamines, in general, often hampers the successful application of the compounds to treat prion diseases. Here, we report that constitutively maintained cationic properties in branched polyamines reduced the intrinsic toxicity of the compounds while retaining the anti-prion activities. In prion-infected neuroblastoma cells, quaternization of amines in polyethyleneimine (PEI) and polyamidoamine (PAMAM) dendrimers markedly increased the nontoxic concentration ranges of the compounds and still supported, albeit reduced, an appreciable level of anti-prion activity in clearing prions from the infected cells. Furthermore, quaternized PEI was able to degrade prions at acidic pH conditions and inhibit the in vitro prion propagation facilitated by conversion of the normal prion protein isoform to its misfolded counterpart, although such activities were decreased by quaternization. Quaternized PAMAM was least effective in degrading prions but efficiently inhibited prion conversion with the same efficacy as unmodified PAMAM. Our results suggest that quaternization represents an effective strategy for developing nontoxic branched polyamines with potent anti-prion activity. This study highlights the importance of polyamine structural control for developing polyamine-based anti-prion agents and understanding of an action mechanism of quaternized branched polyamines.

Design, Synthesis, and Structure−Activity Relationship of Indole-3-glyoxylamide Libraries Possessing Highly Potent Activity in a Cell Line Model of Prion Disease

Transmissible spongiform encephalopathies (TSEs) are a family of invariably fatal neurodegenerative disorders for which no effective curative therapy currently exists. We report here the synthesis of a library of indole-3-glyoxylamides and their evaluation as potential antiprion agents. A number of compounds demonstrated submicromolar activity in a cell line model of prion disease together with a defined structure-activity relationship, permitting the design of more potent compounds that effected clearance of scrapie in the low nanomolar range. Thus, the indole-3-glyoxylamides described herein constitute ideal candidates to progress to further development as potential therapeutics for the family of human prion disorders.

ST1859 reduces prion infectivity and increase survival in experimental scrapie

On the basis of the structural homologies between ST1859 (1[(2-hydroxy-1-naphtyl)methyl]-2-naphthol) and the anti-prion agents and its anti-amyloidogenic activity, we tested whether this molecule altered the biochemical properties of aggregates formed in vitro by synthetic prion peptides and affected prion infectivity in experimental scrapie. Co-incubation of ST1859 with the peptides PrP 106-126 and PrP 82-146 reduced their fibrillogenic capacity and their resistance to digestion with protease K. Hamsters inoculated with the ST1859-treated homogenate showed a significant delay in the onset of clinical signs of disease and longer survival. Survival was also significantly longer in infected hamsters treated peripherally with ST1859 for the whole post-inoculation period until the onset of clinical symptoms. Similar results were found with the analogue ST1745. Our data indicate that ST1859 reduces prion infectivity and can exert a therapeutic effect in experimental scrapie.

Heparin-induced circular dichroism of chloroquine

Circular dichroism (CD) and UV/Visible absorption (UV/Vis) spectroscopy techniques were used to investigate the interaction between heparin and chloroquine, an antimalarial drug that has shown potential as an anti-prion agent. CD spectra of rac-chloroquine upon addition of heparin provide evidence of glycosaminoglycan (GAG) binding, support recent findings suggesting that interactions between heparin and antimalarial drugs are largely due to electrostatic interactions, and represent the first reported GAG-induced CD signal of a bicyclic, aromatic compound. The association constant (∼10 3 M −1) between chloroquine and heparin was calculated from a UV titration curve and provided additional insight into the nature of the association between these two compounds.

The Influence of Densely Organized Maltose Shells on the Biological Properties of Poly(propylene imine) Dendrimers: New Effects Dependent on Hydrogen Bonding

Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized.

The Efficacy of Tetracyclines in Peripheral and Intracerebral Prion Infection

We have previously shown that tetracyclines interact with and reverse the protease resistance of pathological prion protein extracted from scrapie-infected animals and patients with all forms of Creutzfeldt-Jakob disease, lowering the prion titre and prolonging survival of cerebrally infected animals. To investigate the effectiveness of these drugs as anti-prion agents Syrian hamsters were inoculated intramuscularly or subcutaneously with 263K scrapie strain at a 10−4 dilution. Tetracyclines were injected intramuscularly or intraperitoneally at the dose of 10 mg/kg. A single intramuscular dose of doxycycline one hour after infection in the same site of inoculation prolonged median survival by 64%. Intraperitoneal doses of tetracyclines every two days for 40 or 44 days increased survival time by 25% (doxycycline), 32% (tetracycline); and 81% (minocycline) after intramuscular infection, and 35% (doxycycline) after subcutaneous infection. To extend the therapeutic potential of tetracyclines, we investigated the efficacy of direct infusion of tetracyclines in advanced infection. Since intracerebroventricular infusion of tetracycline solutions can cause overt acute toxicity in animals, we entrapped the drugs in liposomes. Animals were inoculated intracerebrally with a 10−4 dilution of the 263K scrapie strain. A single intracerebroventricular infusion of 25 µg/ 20 µl of doxycycline or minocycline entrapped in liposomes was administered 60 days after inoculation, when 50% of animals showed initial symptoms of the disease. Median survival increased of 8.1% with doxycycline and 10% with minocycline. These data suggest that tetracyclines might have therapeutic potential for humans.

Binding of anti-prion agents to glycosaminoglycans: Evidence from electronic absorption and circular dichroism spectroscopy

The polyanionic glycosaminoglycans (GAGs) are intimately involved in the pathogenesis of protein conformational disorders such as amyloidosis and prion diseases. Several cationic agents are known to exhibit anti-prion activity but their mechanism of action is poorly understood. In this study, UV absorption and circular dichroism (CD) spectroscopic techniques were used to investigate the interaction between heparin and chondroitin-6-sulfate and anti-prion drugs including acridine, quinoline, and phenothiazine derivatives. UV band hypochromism of (±)-quinacrine, (±)-primaquine, tacrine, quinidine, chlorpromazine, and induced CD spectra of (±)-quinacrine upon addition of GAGs provided evidence for the GAG binding of these compounds. The association constants (∼10 6–10 7 M −1) estimated from the UV titration curves show high-affinity drug-heparin interactions. Ionic strength-dependence of the absorption spectra suggested that the interaction between GAGs and the cationic drugs is principally electrostatic in nature. Drug binding differences of heparin and chondroitin-6-sulfate were attributed to their different negative charge density. These results call the attention to the alteration of GAG-prion/GAG-amyloid interactions by which these compounds might exert their anti-prion/anti-amyloidogenic activities.