Volume 2: Science
5. Diagnosis and therapy
Therapy

5.38 Before the emergence of BSE, work had been carried out at the NPU into the effect of various pharmacological and immunomodulatory compounds on the incubation period of experimental scrapie.

5.39 In an important paper in 1986, Dr Christine Farquhar of the NPU reported the effect of a polyanionic glycan, ¹ dextran sulphate, on scrapie infectivity. ² Polyanionic glycans were tested because they were known to be active against viruses. At that stage, it was thought that the scrapie agent might be an unconventional virus. A single dose of dextran sulphate reduced the susceptibility of mice to scrapie. It had to be given within one month of infection, and the prolongation of the incubation period was directly related to dose. Treatment close to infection doubled the average survival time, an effect equivalent to a 90 per cent reduction in scrapie titre.

5.40 Dr Richard Kimberlin, also of the NPU, confirmed these results in a separate investigation in 1986. ³ However, he added the proviso that for dextran sulphate to have any effect it must be administered before infection has established itself in the central nervous system.

5.41 Although the above results had been promising, and the emergence of BSE in cattle had suggested another use for polyanionic glycan therapy, advances in this area were slow. Certain independent scientists, notably Professor Lacey and Dr Dealler, recommended research into therapies early on in the epidemic. ⁴ However, even after the Medical Research Council (MRC) Coordinating Committee on Spongiform Encephalopathies recommended in 1991 that research into therapeutic intervention should be considered a priority, ⁵ very little progress was made. ⁶

5.42 In 1993 scientists at the National Institute for Allergy and Infectious Diseases in Montana (USA) also reported on the efficacy of polyanionic glycans for the inhibition of scrapie. ⁷ In addition, they investigated the mechanism behind the effects, using a scrapie-infected neural cell line. They found that these compounds prevented the formation of PrP^Sc, and that PrP^Sc accumulation remained depressed even after the removal of the compound.

5.43 Scientists at the Washington University School of Medicine supported these findings in 1995. They investigated the mechanism of action further and suggested polyanionic glycans prevented PrP^C from localising to the cell membrane, where it can be converted into PrP^Sc. This then prevented the accumulation of PrP^Sc. ⁸

5.44 In the early 1990s, other chemicals were identified that offered potential as treatment for TSEs. These included Congo red, a dye used to stain protein aggregates in diseases such as leprosy, tuberculosis and TSEs, ⁹ and amphotericin B (an antibiotic).

5.45 Until the identification of vCJD cases, in 1996, few people raised concerns over the lack of research into TSE treatment. However, as possible human health implications arose, committees such as the MRC Coordinating Committee on Spongiform Encephalopathies put more emphasis on research in this area. ¹⁰

5.46 Since 1996, several groups have studied these chemicals further, ¹¹ and identified new chemicals which may have a role in the treatment of TSEs. These treatments can be grouped under two main headings: those that inhibit PrP^Sc production, deposition and accumulation; and those that prevent the neurotoxic effects of PrP^Sc and the amyloid plaques.

5.47 Suggested methods of inhibiting PrP^Sc production, deposition and accumulation would be by:

1. Stabilising the structure of PrP^C, preventing its binding with PrP^Sc and thus preventing the transformation from PrP^C to PrP^Sc; or even using chemicals which transform PrP^Sc back to PrP^C. Examples of compounds which work in this way are dimethylsulphoxide, trimethylamine N-oxide and various polyols and sugars. ¹²
2. Using antibodies to prevent PrP^Sc from binding to PrP^C. Recently, one antibody has been produced, named 15B3, which is claimed to bind specifically to PrP^Sc. This would avoid any problems that might result from using antibodies directed against the normal PrP^C, as these antibodies might inhibit any important functions that this normal protein could have in humans. ¹³
3. Using nucleic acid molecules to prevent PrP^Sc from binding to PrP^C. ¹⁴
4. Inhibiting amyloid plaque formation with the use of non-steroidal anti-inflammatory agents ¹⁵ and other compounds such as anthracycline. ¹⁶
5. Inhibiting the formation of the abnormal form of PrP by treatment with certain cyclic tetrapyrroles, which have been shown to be effective in inhibiting TSE disease in experimental animals. ¹⁷
6. Inhibiting the activity of the protein that is the precursor to amyloid with compounds carrying many negative charges, eg, dextran sulphate. ¹⁸
7. Destroying PrP^Sc with branched polyamines. ¹⁹

A recent scientific paper proposes a rational approach to the discovery of drugs which inhibit PrP^Sc formation. Using this approach the authors identified two compounds (Cp-60 and Cp-62) which inhibited PrP^Sc formation in a dose-dependent manner and demonstrated low levels of toxicity. ²⁰

5.48 It has recently been shown that treatment of protease-resistant PrP^Sc with synthetic -sheet breaker peptides (iPrP13) can significantly reverse the protease resistance of the protein to a state similar to that of PrP^C. ²¹ The effect was shown by incubating scrapie-infected material with the -sheet breaker peptide for 48 hours and then testing the material by mouse bioassay. Incubation times were prolonged and the infectivity decreased by 90 to 95 per cent when compared with controls. This was confirmed by circular-dichroism analysis, which showed that the -sheet content of the PrP^Sc sample was decreased from 41 to 8 per cent. These studies are important in that they show for the first time that conformational changes of the PrP molecule can be reversed in vitro. They also confirm that the conformational change is an essential factor in the pathogenesis of TSEs. It remains to be seen whether -sheet breaker peptides have a place in the treatment of these diseases.

5.49 Treatments based on preventing the neurotoxic effects of PrP^Sc and the amyloid plaques start with the assumption that PrP^Sc is intrinsically toxic and thus directly responsible for pathogenesis. Suggested methods of treatments are:

1. Using compounds that protect cells from destruction, eg, 1,4-benzoquinone derivatives and 1,2-hydroquinone derivatives. ²²
2. Using compounds, eg, antioxidants, that protect the cells from oxidative stress, ²³ which has an important role in the neurodegenerative changes associated with CJD.

5.50 However, the treatments mentioned above are based mainly on theory, in vitro experiments and limited data from animal experiments, with no definitive evidence of efficacy or safety in human disease. This lack of progress is partly a result of many bodies, including the pharmaceutical industry, not being prepared to conduct substantial research and development programmes in relation to therapies because human TSEs are still so rare and progress so rapidly following the appearance of clinical symptoms, allowing little time for intervention. ²⁴ However, research into other human neurodegenerative diseases might produce results relevant to TSEs.

¹ A polyanionic glycan is a negatively charged compound

² Farquhar, C. and Dickinson, A. (1986). Prolongation of Scrapie Incubation Period by an Injection of Dextran Sulphate 500 within the Month Before or After Infection, Journal of General Virology, 67, 463-73

³ Kimberlin, R. and Walker, C. (1986). Suppression of Scrapie Infection in Mice by Heteropolyanion 23, Dextran Sulfate, and Some Other Polyanions, Antimicrobial Agents and Chemotherapy, 30, 409-13

⁴ IBD1 tab 7 p. 23

⁵ S53 Radda para. 49

⁶ S74 Dickinson para. 47; T31 (Dickinson) p. 56

⁷ Caughey, B. and Raymond, G. (1993) Sulfated Polyanion Inhibition of Scrapie-Associated PrP Accumulation in Cultured Cells, Journal of Virology, 67, 643-50

⁸ Shyny, S.L., Lehmann, S., Moulder, K.L. and Harris, D.A. (1995) Sulfated Glycans Stimulate Endocytosis of the Cellular Isoform of the Prion Protein, PrP^C, in Cultured Cells, Journal of Biological Chemistry, 270, 30221-9

⁹ Caughey, B., Ernst, D. and Race, R.E. (1993) Congo Red Inhibition of Scrapie Agent Replication, Journal of Virology, 67, 6270-2

¹⁰ S053 Radda para. 78

¹¹ Dr I. Gilbert, Welsh School of Pharmacy, from 1997 to 2000, G9630430, Design and Synthesis of Potential Chemotherapeutic Agents for the Treatment of Transmissible Spongiform Encephalopathies; Farquhar, C., Dickinson, A. and Bruce, M. (1999) Prophylactic Potential of Pentosan Polysulphate in Transmissible Spongiform Encephalopathies, The Lancet, 353, 117

¹² Knight, R. (2000) Therapeutic Possibilities in CJD: Patents 1996-9, Expert Opinion on Therapeutic Patents, 10, 49-57

¹³ Ibid.

¹⁴ Ibid.

¹⁵ Ibid.

¹⁶ Tagliavini, F., McArthur, R.A., Canciani, B., Giaccone, G., Porro, M., Bugiani, M., Lievens, P.M., Bugiani, O., Peri, E., Dall'Ara, P., Rocchi, M., Poli, G., Forloni, G., Bandiera, T., Varasi, M., Suarato, A., Cassutti, P., Cervini, M.A., Lansen, J., Salmona, M., Post, C. (1997) Effectiveness of Anthracycline Against Experimental Prion Disease in Syrian Hamsters, Science, 276, 1119-22

¹⁷ Priola, S.A., Raines, A. and Caughey, W.S. (2000) Porphyrin and phthalocyanine antiscrapie compounds, Science, 287(5457), 1503-6

¹⁸ Knight, R. (2000) Therapeutic Possibilities in CJD: Patents 1996-9, Expert Opinion on Therapeutic Patents, 10, 49-57

¹⁹ Supattapone, S., Nguyen, H.O., Cohen, F.E., Prusiner, S.B. and Scott, M.R. (1999) Elimination of Prions by Branched Polyamines and Implication for Therapeutics, Proceedings of the National Academy of Sciences of the USA, 96, 14529-34

²⁰ Perrier, V., Wallace, A.C., Kaneko, K., Safar, J., Prusiner, S.B. and Cohen, F.E. (2000) Mimicking dominant negative inhibition of prion replication through structure-based drug design, Proceedings of the National Academy of Science (USA), 97(11), 6073-8

²¹ Soto, C., Kascsak, R.J., Saborío, G.P., Aucouturier, P., Wisniewski, T., Prelli, F., Kascsak, R., Mendez, E., Harris, D.A., Ironside, J., Tagliavini F., Carp R.I. and Frangione, B. (2000) Reversion of Prion Protein Conformation Changes by Synthetic -sheet Breaker Peptides, The Lancet, 355, 192-7

²² Knight, R. (2000) Therapeutic Possibilities in CJD: Patents 1996-9, Expert Opinion on Therapeutic Patents, 10, 49-57

²³ An oxidative stress is a highly oxidised environment within cells

²⁴ YB97/6.3/1.3