Anti-Prion Drug mPPIg5 Inhibits PrPC Conversion to PrPSc

Abstract

Prion diseases, also known as transmissible spongiform encephalopathies, are a group of fatal neurodegenerative diseases that include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in humans. The ‘protein only hypothesis’ advocates that PrPSc, an abnormal isoform of the cellular protein PrPC, is the main and possibly sole component of prion infectious agents. Currently, no effective therapy exists for these diseases at the symptomatic phase for either humans or animals, though a number of compounds have demonstrated the ability to eliminate PrPSc in cell culture models. Of particular interest are synthetic polymers known as dendrimers which possess the unique ability to eliminate PrPSc in both an intracellular and in vitro setting. The efficacy and mode of action of the novel anti-prion dendrimer mPPIg5 was investigated through the creation of a number of innovative bio-assays based upon the scrapie cell assay. These assays were used to demonstrate that mPPIg5 is a highly effective anti-prion drug which acts, at least in part, through the inhibition of PrPC to PrPSc conversion. Understanding how a drug works is a vital component in maximising its performance. By establishing the efficacy and method of action of mPPIg5, this study will help determine which drugs are most likely to enhance this effect and also aid the design of dendrimers with anti-prion capabilities for the future.

Interaction study between maltose-modified PPI dendrimers and lipidic model membranes

“…For the successful use of sugar-decorated poly(propylene imine) (PPI) dendrimers as a DDS [10][11][12] and a biological [13][14][15] and stabilizing [16] agent in (bio-)medical applications, one has to not only search for those potential application fields but also understand the cellular uptake and cellular trafficking in various cells. Moreover, a fundamental understanding of their molecular interaction properties against a biological cell membrane and model lipid membranes is mostly unknown.…”

Nanomedicine for prion disease treatment

“…As immunoblotting is a laborious technique and at best semi-quantitative, we developed a high throughput and highly quantitative assay known as the modified scrapie cell assay (mSCA), to measure the efficacy of anti-prion drugs in a cell culture setting. 10 The mSCA is based upon the standard scrapie cell assay (sSCA), an Elispot based assay for determining the level of infectious prions in a sample. 11 In the sSCA, susceptible cells are exposed to prion-containing samples, grown to confluence and passaged three times.…”

“…Thus it can be seen that maltose dendrimers are a highly promising class of therapeutics, which specifically target misfolded PrP and prevent the conversion of PrP C to PrP Sc . 10 There are a number of possible explanations for how mPPIg5 achieves this. 16 However, in our opinion the most likely explanation is that mPPIg5 alters the structure of PrP Sc to such an extent that it is no longer capable of initiating the misfolding of PrP C .…”

“…7,13 Most pertinently, a small number of dendrimers, including mPPIg5, have been shown to be effective in an intracellular environment but not always in an in vitro one, even when tested against the same prion strain. 10,14 If dendrimers do indeed act directly against protease resistant PrP Sc to render it sensitive to protease degradation, how can one explain a dendrimer working intracellularly on PrP Sc but not in vitro? Was it possible that dendrimers act through a different mechanism intracellularly?…”

“…Additionally, this model allows dendrimers to eliminate prions intracellularly by increasing their degradation as the original experiments in this area suggest 1,4,5 and/or eliminate prions by inhibiting the conversion of PrP C to PrP Sc as some of the more recent studies in this area, including our own, suggest. 10,14 Dendrimers altering the conformation of misfolded PrP may also explain in vitro studies which have shown that numerous dendrimers (including mPPI) inhibit the fibrilization of PrP peptides in vitro. 2,[17][18][19] Dendrimers increasing the fibril breakage rate and dendrimers blocking the ends of growing fibrils are two of the explanations offered for this phenomena.…”