Lipoate Derivatives Targeting Alzheimer's Amyloid

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DESCRIPTION (provided by applicant): The clinical benefits of current antioxidant/metal chelation therapies for Alzheimer's disease (AD), the most common form of senile dementia, are limited due to their poor disease target specificity. Moreover, the exact subserving mechanism(s) of antioxidant/metal chelation effects upon AD amyloid pathology are not clear. Our long-term objective is thus to design target-specific antioxidants/metal chelators and better understand their pharmacological mechanisms for AD and other human diseases, based on an emerging "pharmacophore conjugation" concept for drug development. The specific hypothesis for this proposal is that amyloid-targeting antioxidants/metal chelators assume targeted interdictions against cerebral A¿ amyloid pathology and associated oxidative stress. We have synthesized and characterized a novel bifunctional antioxidant- XH2 with chemically conjugated amyloid-binding (benzothiazole) and metal-chelating antioxidant (lipoate) moieties. We base the hypothesis on previous observations and current pilot data suggest that: (i) biometals such as Fe, Cu, Zn, which are strongly present in human amyloid plaques, promote A¿ amyloidosis and oligomerization that are mediated by reactive oxygen species (ROS) such as H2O2 and attenuated by catalase and metal chelators- DTPA and EDTA; (ii) XH2 molecule has only one NH group (<5 hydrogen-bond donors), two N and one O atoms (<10 hydrogen bond acceptors), MW=415 (<500), and the measured octanol/water partition coefficient = 2.1¿0.1 (<5). It agrees well with the general Lipinski's Rule of Five; (iii) XH2 interacts with A¿1-40 peptide computationally and has an affinity binding constant of KD=4.43 ¿M toward monomeric A¿1-40 peptide molecules in its freshly prepared solution; (iv) XH2 has no neurotoxicity at low micromolar concentrations, and it attenuates cerebral A¿ amyloid pathology in PS1/APP doubly transgenic mice without inducing apparent animal toxicity and behavior disturbances. We plan to test our current hypothesis and to achieve the objective of this application by pursuing the following three specific aims: 1. Determine the effects of XH2 upon A¿ neurotoxicity and APP translation in cell culture; 2. Determine XH2 binding constants for aggregated and mixed A¿1-40/42 peptides and blood-brain barrier (BBB) penetration of XH2; 3. Determine the effects of XH2 upon cerebral A¿ amyloid pathology, protein glutathionylation, and biometal profiles in amyloid plaques from PS1/APP transgenic mice. To achieve these specific aims, an array of experimental techniques such as surface plasmon resonance (SPR), LC/MS, SDS-PAGE, ELISA, semi-quantitative immunohistochemistry, laser capture microdissection (LCM) coupled with x-ray fluorescence microscopy (micro-XRM) techniques, and in vitro (human SH-SY5Y neuroblastoma and E17 primary rat cortical cells) and in vivo (PS1/APP doubly transgenic mouse) AD models, will be employed for the proposed studies. The overall rationale for the proposal is: our understanding about the molecular mechanism(s) and therapeutic values of amyloid-targeted antioxidants/chelators as potential AD-modifying agents need to be further clarified and validated.