Therapeutic development of polymers for prion disease

Prion diseases, also known as transmissible spongiform encephalopathies, are caused by the accumulation of abnormal isoforms of the prion protein (scrapie isoform of the prion protein, PrPSc) in the central nervous system. Many compounds with anti-prion activities have been found using in silico screening, in vitro models, persistently prion-infected cell models, and prion-infected rodent models. Some of these compounds include several types of polymers. Although the inhibition or removal of PrPSc production is the main target of therapy, the unique features of prions, namely protein aggregation and assembly accompanied by steric structural transformation, may require different strategies for the development of anti-prion drugs than those for conventional therapeutics targeting enzyme inhibition, agonist ligands, or modulation of signaling. In this paper, we first overview the history of the application of polymers to prion disease research. Next, we describe the characteristics of each type of polymer with anti-prion activity. Finally, we discuss the common features of these polymers. Although drug delivery of these polymers to the brain is a challenge, they are useful not only as leads for therapeutic drugs but also as tools to explore the structure of PrPSc and are indispensable for prion disease research.

BMD42-2910, a Novel Benzoxazole Derivative, Shows a Potent Anti-prion Activity and Prolongs the Mean Survival in an Animal Model of Prion Disease

Prion diseases are a group of neurodegenerative and fatal central nervous system disorders. The pathogenic mechanism involves the conversion of cellular prion protein (PrP^C) to an altered scrapie isoform (PrP^Sc), which accumulates in amyloid deposits in the brain. However, no therapeutic drugs have demonstrated efficacy in clinical trials. We previously reported that BMD42-29, a synthetic compound discovered in silico, is a novel anti-prion compound that inhibits the conversion of PrP^C to protease K (PK)-resistant PrP^Sc fragments (PrP^res). In the present study, 14 derivatives of BMD42-29 were obtained from BMD42-29 by modifying in the side chain by in silico feedback, with the aim to determine whether they improve anti-prion activity. These derivatives were assessed in a PrP^Sc-infected cell model and some derivatives were further tested using real time-quaking induced conversion (RT-QuIC). Among them, BMD42-2910 showed high anti-prion activity at low concentrations in vitro and also no toxic effects in a mouse model. Interestingly, abundant PrP^res was reduced in brains of mice infected with prion strain when treated with BMD42-2910, and the mice survived longer than control mice and even that treated with BMD42-29. Finally, high binding affinity was predicted in the virtual binding sites (Asn159, Gln 160, Lys194, and Glu196) when PrP^C was combined with BMD-42-2910. Our findings showed that BMD42-2910 sufficiently reduces PrP^res generation in vitro and in vivo and may be a promising novel anti-prion compound.

Yeast-based screening of natural product extracts results in the identification of prion inhibitors from a marine sponge

One of the major medical challenges of the twenty-first century is the treatment of incurable and fatal neurodegenerative disorders caused by misfolded prion proteins. Since the discovery of these diseases a number of studies have been conducted to identify small molecules for their treatment, however to date no curative treatment is available. These studies can be highly expensive and time consuming, but more recent experimental approaches indicate a significant application for yeast prions in these studies. We therefore used yeast prions to optimize previous high-throughput methods for the cheaper, easier and more rapid screening of natural extracts. Through this approach we aimed to identify natural yeast-prion inhibitors that could be useful in the development of novel treatment strategies for neurodegenerative disorders. We screened 500 marine invertebrate extracts from temperate waters in Australia allowing the identification of yeast-prion inhibiting extracts. Through the bioassay-driven chemical investigation of an active Suberites sponge extract, a group of bromotyrosine derivatives were identified as potent yeast-prion inhibitors. This study outlines the importance of natural products and yeast prions as a first-stage screen for the identification of new chemically diverse and bioactive compounds.

Heparinase I-specific disaccharide unit of heparin is a key structure but insufficient for exerting anti-prion activity in prion-infected cells

Glycosaminoglycans reportedly play important roles in prion formation, but because of their structural complexity, the chemical structures affecting prion formation have not been fully evaluated. Here, we compared two types of low molecular weight heparins and found that heparinase I-sensitive structures influenced anti-prion activity in prion-infected cells. Surface plasmon resonance analyses showed significant binding of a representative heparinase I substrate disaccharide unit, GlcNS6S-IdoA2S, to recombinant prion protein (PrP) fragments, such as full-length PrP23-231 and N-terminal domain PrP23-89, but not to PrP89-230. This binding was competitively inhibited by heparin or pentosan polysulfate, but not by Cu(2+). These PrP binding profiles of the disaccharide unit are consistent with those previously reported for heparin. However, synthetic compounds comprising disaccharide unit alone or its multimers exhibited no anti-prion activity in prion-infected cells. Consequently, the findings suggest that the heparin disaccharide unit that binds to the N-terminal region of PrP is a key structure, but it is insufficient for exerting anti-prion activity.