May 8 th , BIOSE108 Therapeutic approaches in AD: -Beta and gamma secretase inhibitors

1. May 8th, BIOSE108 Therapeutic approaches in AD: -Beta and gamma secretase inhibitors -Abeta immunotherapy -Tau -Ongoing treatments in AD

2. b- and g-secretase : possible therapeutic targets in AD?

3. Could BACE be considered as a therapeutic target for AD? In favor: 1- BACE is the primary b-secretase aspartyl protease that cleaves APP generating b-amyloid species (secondary role of BACE2) 2-BACE KO mice DO NOT have amyloidogenic processing of APP Against: 1-BACE+/- heterozygous mice do not show altered production of b-amyloid and APP C-terminal fragments 2-BACE cleaves a number of other substrates, including *Amyloid Precursor Like Proteins APLP1 and APLP2 *Low-density lipoprotein receptor (LDLR)-related protein LRP Thus, targeting BACE for the treatment of AD would result in loss of BACE activity towards the other substrates, with possible consequent implications on their physiological function.

4. BACE KO mice show hypomyelination of hippocampal neurons… Hu et al.,

5. …and of the optic and sciatic nerves Optic Sciatic Hu et al.,

6. BACE KO- mediated hypomyelination is due to reduced activation of neuregulin Hu et al.,

7. BACE inhibition reduces or delays myelination in vitro BACE inhibitor ADAM inhibitor

8. BACE1KO primary hippocampal neurons have impaired axonal outgrowth

9. BACE KO mice have axon guidance defects in the hippocampus

10. BACE KO mice have the same phenotype as the neuronal cell adhesion molecule close homolog of L1 (CHL1) t2 KO mice L1 (CHL1) t2 a substrate for BACE?

11. CHL1 undergoes BACE1-dependent cleavage in hippocampus

12. CHL1 and BACE1 co-localize in growth cones of primary hippocampal neurons.

13. Thus reducing BACE levels (or activity) may lead to neurodegeneration as side effect

14. g-secretase cleaves different substrates Bart De Strooper What about targeting g-secretase for the treatment of AD? Some of these substrates have crucial activity in regulating cell fate decision. In this respect, targeting g-secretase for the treatment of AD is not an easy task, as blocking g-secretase activity would have consequences on the physiological functions of the other protein substrates.

15. Model for g-secretase complex and its interaction to the substrates The bars represent the transmembrane domains of the the proteins constituting the g-secretase complex

16. Gamma secretase inhibitors, peptide based inhibitors Aldehyde-type calpain and proteasome inhibitors. Weak potency and lack of selectivity: First studied Differential production of Abeta 40 to Abeta 42 Aldehydes are readily hydrated to a form that resembles the transition state of aspartyl protease catalysis. Transition state analogs: whether aldehyde or keto forms, they can be active toward serine and cisteine proteases. Conversion of one of these difluoroalcohol peptidomimetics into an affinity labeling reagent led to identification of PS1 NTF and CTF as the direct targets of this type of inhibitor. Hydroxyethylamines, more potent. Can isolate gamma-secretase in a detergent-solubilized state and demonstrate that immunoprecipitation of presenilin brought down gamma-secretase activity.

17. DAPT “showed good inhibitory potency orally active in vivo, capable of lowering brain Abeta levels in an APP transgenic mice. The target is the CTF.” Well known DAPT derivatives are the more potent Compound E and LY-411,575, the last one studied in vivo in humans. Compound E: “effective in reducing brain Abeta levels in APP transgenic mice upon oral dosing. However, this compound also illustrated the toxicity issues that might be expected by GSI over Notch (gastrointestinal bleeding and immunosuppression caused by peripheral inhibition of Notch). Despite this ominous result, non-selective GSIs of this type continued to be pursued on evidence from animal studies that careful dosing couldidentify a therapeutic window (e.g. Hyde et al. 2006)”.

18. LY-411,575

20. Structure of the inhibitors LY-411,575 and LY-D

21. LY-411-575 reduces Abeta levels in the plasma and in the brain of TgCRND8 mice

22. Chronic administration of LY-411,575 causes atrophy of the thymus in TgCNDR8 mice (15 days) One lobule Two lobules One lobule

23. Decreased Lymphocytes B generation in chronically treated TgCNRD8 mice with LY-411,575: Immunosuppression

24. Chronic administration of LY-411,575 causes deterioration of the intestinal epithelium

25. Higher doses of Semagacestat

27. Inactivation of Notch1 causes the formation of skin tumors Notch1KO

28. Other more selective gamma-secretase inhibitors Abeta42 lowering GSM Notch sparing GSM PS1-selective g-secretase inhibitor

29. PS2 is part of the gamma-secretase too, and can actively cleave both APP and Notch What could happen if GSIs were designed to target only PS1 and not PS2?

30. PS2-sparing GSI (MRK-560) reduces Ab40 and Ab42 levels in plasma and brain plasma brain

31. Lack of PS2 expression in PS2 KO mice, but not lack of endogenous PS2 expression, exacerbates guts histopathology

32. PS2 is present, although at moderate levels, in brain, spleen and thymus

33. Under conditions of PS1-specific inhibition, PS2 can compensate for PS1, although not up-regulated.

34. PS1 is not an easy therapeutic target for the treatment of AD Could Nicastrin be a good target?

35. Mechanism by which Nicastrin participates in the “Regulated Intracellular Proteolysis” RIP BACE b-secretase Steps: 1-The substrates gets in close proximity with the g-secretase complex (i.e. after internalization from the plasma membrane). 2-Nicastrin specifically recognizes the substrate, and binds to it. 3-Presenilin (PS1) cuts the substrate within the exposed sequence (in the case of APP will be the Ab sequence). Shah et al.,

36. Chemical blocking of the N-terminal portion of the substrates will regulate nicastrin capability to recognize and to bind to it. Implications for the treatment for AD Will NOT bind to Nicastrin Shah et al., Will bind to Nicastrin

37. How to target Ab oligomers? Using molecules that interfere with the structure of the oligomer and break it up to single Ab monomers. Advantages of this therapeutic approach would be: 1-decreased accumulation of Ab oligomers, thus reduced formation of b-amyloid plaques 2-the single Ab monomers have higher chances to be removed by the action of clearing enzymes like neprilysin or Insulin Degrading Enzyme IDE 3-both intracellular and extracellular formed Ab oligomers would be targeted and disrupted.

38. New approaches for future therapeutic intervention in AD 1-molecules that disrupt the structure of the Ab oligomers 2-use of selected b- or g-secretase inhibitors. 3-used of vaccines, to remove Ab deposits and plaques

39. Events leading to AD and roles of Ab immune-therapy

40. Active and Passive immunization in AD immuno-therapy APC: antigen Presenting Cells

41. Abeta immuno-therapy reduces the plaque load in AD animal model

42. Before immunization, AD patients show plaques with dystrophic neurites (a) and tau staining (b) Nicoll et al.,

43. Areas devoid of Ab plaques (c) do show NFTs but not dystrophic neurites (d) Nicoll et al.,

44. Macrophages infiltrates the cerebral white matter in patients treated with Ab42 vaccine Meningoencephalites in AD patients treated with AN1792 Infiltration of cerebral white matter by macrophages Vacuolation and refraction in myelinated fibers in the white matter Nicoll et al.,

46. Ongoing clinical trials for passive Abeta immuno-therapy

47. Ongoing clinical trials for active Abeta immuno-therapy

48. The protein tau and tau pathology in AD

49. Deposition of fibrillar proteinacious material in Alzheimer’s disease Alzheimer’s disease: characterized by extracellular depositions, the b-amyloid plaque, and intracellular depositions, the Neurofibrillary Tangles(NFT) comprised of Paired Helical Filaments (PHF), aggregates of hyperphosphorylated protein tau. Bossy-Wetzel E, et al., Nat Med. 2004 Jul;10 Suppl:S2-9. Review.

50. The human tau gene and the 6 tau isoforms