Cellular models for discovering prion disease therapeutics: Progress and challenges

Abstract

Prion diseases, or transmissible spongiform encephalopathies (TSEs), are neurodegenerative disorders that affect both humans and animals. The first TSE observed historically was scrapie, which affects both ovine (sheep) and caprine (goat) species. Subsequently, prion diseases have been observed in cattle (bovine spongiform encephalopathy; BSE or "mad cow disease"); cervids such as deer, elk and moose (chronic wasting disease; CWD); minks (transmissible mink encephalopathy), felines (feline spongiform encephalopathy) and, most recently, dromedary camels (camel prion disease) (Babelhadj et al., AbstractPrions, which cause fatal neurodegenerative disorders such as Creutzfeldt-Jakob disease, are misfolded and infectious protein aggregates. Currently, there are no treatments available to halt or even delay the progression of prion disease in the brain.The infectious nature of prions has resulted in animal paradigms that accurately recapitulate all aspects of prion disease, and these have proven to be instrumental for testing the efficacy of candidate therapeutics. Nonetheless, infection of cultured cells with prions provides a much more powerful system for identifying molecules capable of interfering with prion propagation. Certain lines of cultured cells can be chronically infected with various types of mouse prions, and these models have been used to unearth candidate anti-prion drugs that are at least partially efficacious when administered to prion-infected rodents. However, these studies have also revealed that not all types of prions are equal, and that drugs active against mouse prions are not necessarily effective against prions from other species. Despite some recent progress, the number of cellular models available for studying non-mouse prions remains limited. In particular, human prions have proven to be particularly challenging to propagate in cultured cells, which has severely hindered the discovery of drugs for Creutzfeldt-Jakob disease. In this review, we summarize the cellular models that are presently available for discovering and testing drugs capable of blocking the propagation of prions and highlight challenges that remain on the path towards developing therapies for prion disease.

The aminoglycoside G418 hinders de novo prion infection in cultured cells

“…Several different lines of immortalized cells expressing murine PrP C have been identified that can become infected with mouse prions ( 13 , 14 , 15 , 16 , 17 , 18 , 19 ). Perhaps the most important use for these cellular models is the platform they provide for identifying small molecule inhibitors of prion replication ( 20 ). A high-throughput screen conducted in prion-infected N2a neuroblastoma cells yielded several 2-aminothiazole compounds, including IND24, which could reduce levels of proteinase K (PK)-resistant PrP (PrP res ) in cells and significantly increase the survival of prion-infected mice ( 21 , 22 ).…”

“…The availability of cellular paradigms for replicating nonmouse prions is comparatively limited. Very few PrP C -expressing cell lines from nonmouse species that can become infected with species-matched prions have been identified ( 20 , 26 , 27 , 28 ). A more fruitful approach has been to take a cell line that does not express detectable levels of PrP C and then engineer it to express PrP C from the desired species.…”

From Cell Culture to Organoids-Model Systems for Investigating Prion Strain Characteristics

“…Neurospheres are heterogenous balls of tissue containing both non-differentiated neuroprogenitor cells and differentiated neurons and astrocytes [95]. They also have the advantage of being self-renewing and can therefore be repeatedly passaged, overcoming the proliferation limitations of primary culture [19].…”

“…See Table 1 for an overview of the different species and strains of prion disease that are covered in this review. The efficiency or ability of strains to propagate depends on the culture system used, with cells of a particular type and species only able to propagate a subset of strains [19]. Moreover, different strains have been shown to have vastly different responses to drugs [20,21].…”

Volatile Anesthetic Sevoflurane Precursor 1,1,1,3,3,3-Hexafluoro-2-Propanol (HFIP) Exerts an Anti-Prion Activity in Prion-Infected Culture Cells

“…PrP Sc is thought to consist of many structures rather than of a uniform structure. As a therapeutic agent for prion diseases, attempts have also been made to identify compounds that inhibit the structural conversion of PrP C to PrP Sc , however many of these drugs have resulted in drug resistant prion strains [ 25 ]. On the other hand, HFIP has strong α-helix-inducing activity, should be able to unwind PrP Sc into PrP C , and PrP Sc structure itself will be normalized.…”