The therapeutic efficacy of direct drug infusion into the brain, the target organ of transmissible spongiform encephalopathies, was assessed in transgenic mice intracerebrally infected with 263K scrapie agent. Pentosan polysulfate (PPS) gave the most dramatic prolongation of the incubation period, and amphotericin B had intermediate effects, but antimalarial drugs such as quinacrine gave no significant prolongation. Treatment with the highest dose of PPS at an early or late stage of the infection prolonged the incubation time by 2.4 or 1.7 times that of the control mice, respectively. PPS infusion decreased not only abnormal prion protein deposition but also neurodegenerative changes and infectivity. These alterations were observed within the brain hemisphere fitted with an intraventricular infusion cannula but not within the contralateral hemisphere, even at the terminal disease stage long after the infusion had ended. Therapeutic effects of PPS were also demonstrated in mice infected with either RML agent or Fukuoka-1 agent. However, at doses higher than that providing the maximal effects, intraventricular PPS infusion caused adverse effects such as hematoma formation in the experimental animals. These findings indicate that intraventricular PPS infusion might be useful for the treatment of transmissible spongiform encephalopathies in humans, providing that the therapeutic dosage is carefully evaluated.

We previously reported that quinacrine inhibited the formation of an abnormal prion protein (PrPres), a key molecule in the pathogenesis of transmissible spongiform encephalopathy, or prion disease, in scrapie-infected neuroblastoma cells. To elucidate the structural aspects of its inhibiting action, various chemicals with a quinoline ring were screened in the present study. Assays of the scrapie-infected neuroblastoma cells revealed that chemicals with a side chain containing a quinuclidine ring at the 4 position of a quinoline ring (represented by quinine) inhibited the PrPres formation at a 50% inhibitory dose ranging from 10 ؊1 to 10 1 M. On the other hand, chemicals with a side chain at the 2 position of a quinoline ring (represented by 2,2-biquinoline) more effectively inhibited the PrPres formation at a 50% inhibitory dose ranging from 10 ؊3 to 10 ؊1 M. A metabolic labeling study revealed that the action of quinine or biquinoline was not due to any alteration in the biosynthesis or turnover of normal prion protein, whereas surface plasmon resonance analysis showed a strong binding affinity of biquinoline with a recombinant prion protein. In vivo studies revealed that 4-week intraventricular infusion of quinine or biquinoline was effective in prolonging the incubation period in experimental mouse models of intracerebral infection. The findings suggest that quinoline derivatives with a nitrogen-containing side chain have the potential of both inhibiting PrPres formation in vitro and prolonging the incubation period of infected animals. These chemicals are new candidates for therapeutic drugs for use in the treatment of transmissible spongiform encephalopathies.Transmissible spongiform encephalopathies (TSEs), or prion diseases, are a group of fatal neurodegenerative disorders that include Creutzfeldt-Jakob disease and GerstmannSträussler-Scheinker disease (GSS) in humans and scrapie, bovine spongiform encephalopathy, and chronic wasting disease in animals. These disorders are characterized by the accumulation of an abnormal isoform of prion protein (PrPres), which is high in beta-sheet content and resistant to digestion with proteases (15). Recent outbreaks in younger people of acquired forms of human TSEs, such as variant CreutzfeldtJakob disease (19) and iatrogenic Creutzfeldt-Jakob disease with cadaveric growth hormone or dura graft (4), are prompting the development of therapeutic interventions as well as early diagnostics.One possible therapeutic strategy is to inhibit PrPres formation in the infected host. Doh-ura et al. first reported that cysteine protease inhibitors and lysomotropic agents inhibited PrPres formation in scrapie-infected neuroblastoma (ScNB) cells and that among them, quinacrine was one of the most potent inhibitors (8). Another research group has also reported that quinacrine and its related tricyclic compounds are effective in inhibiting PrPres formation (11). Quinacrine is a synthesized chemical which has a quinoline ring in its structure. It is used as a substitute for quinine in...

Diagnostic imaging probes have been developed to monitor cerebral amyloid lesions in patients with neurodegenerative disorders. A thioflavin derivative, 2-[49-(methylamino)phenyl] benzothiazole (BTA-1) and a Congo red derivative, (trans, trans),-1-bromo-2,5-bis-(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB) are representative chemicals of these probes. In this report, the two chemicals were studied in transmissible spongiform encephalopathies (TSE). Both BTA-1 and BSB selectively bound to compact plaques of prion protein (PrP), not only in the brain specimens of certain types of human TSE, but also in the brains of TSE-infected mice when the probes were injected intravenously. The chemicals bound to plaques in the brains were stable and could be detected for more than 42 h post-injection. In addition, the chemicals inhibited abnormal PrP formation in a cellular model of TSE with IC 50 values of 4 nM for BTA-1 and 1?4 mM for BSB. In an experimental mouse model, the intravenous injection of 1 mg BSB prolonged the incubation period by 14 %. This efficacy was only observed against the RML strain and not the other strains examined. These observations suggest that these chemicals bind directly to PrP aggregates and inhibit new formation of abnormal PrP in a strain-dependent manner. Both BTA-1 and BSB can be expected to be lead chemicals not only for imaging probes but also for therapeutic drugs for TSEs caused by certain strains.

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