Branched polyamines cure prion-infected neuroblastoma cells

Branched polyamines, including polyamidoamine and polypropyleneimine (PPI) dendrimers, are able to purge PrPSc, the disease-causing isoform of the pri on protein, from scrapie-infected neuroblastoma (ScN2a) cells in culture (S . Supattapone, H.-O. B. Nguyen, F. E. Cohen, S. B. Prusiner, and M. R. Scot t, Proc. Natl. Acad, Sci, USA 96:14529-14534, 1999), We now demonstrate tha t exposure of ScN2a cells to 3 mug of PPI generation 4.0/ml for 4 weeks not only reduced PrPSc to a level undetectable by Western blot but also eradic ated prion infectivity as determined by a bioassay in mice. Exposure of pur ified RML prions to branched polyamines in vitro disaggregated the prion ro ds, reduced the beta -sheet content of PrP 27-30, and rendered PrP 27-30 su sceptible to proteolysis. The susceptibility of PrPSc to proteolytic digest ion induced by branched polyamines in vitro was strain dependent. Notably, PrPSc from bovine spongiform encephalopathy-infected brain was susceptible to PPI-mediated denaturation in vitro, whereas PrPSc from natural sheep scr apie-infected brain was resistant. Fluorescein-labeled PPI accumulated spec ifically in lysosomes, suggesting that branched polyamines act within this acidic compartment to mediate PrPSc clearance. Branched polyamines are the first class of compounds shown to cure prion infection in living cells and may prove useful as therapeutic, disinfecting, and strain-typing reagents f or prion diseases.