Susan Molineaux

Characterization of cholyl-leu-val-phe-phe- ala-OH as an inhibitor of amyloid beta- peptide polymerization

Cholyl-LVFFA-OH (1, PPI-368) is an organic-modified peptide based on the sequence of amyloid beta-peptide (Aβ). It is a potent and selective inhibitor of A β polymerization that blocks the formation of neurotoxic species of Aβ. In a nucleation-dependent polymerization assay of 50μM Aβ1-40 equimolar concentrations of PPI-368 block polymerization based on turbidity and electron microscopy. Monomeric Aβ1-40 and Aβ1-42 are non-toxic when incubated with neuronal cell lines, but become toxic during polymerization. PPI-368 coordinately delays the onset of polymerization and the formation of neurotoxic Aβ species for both peptides. In a polymerization extension assay seeded with pre-formed Aβ polymer, similar inhibition and dose-dependency phenomena are observed with PPI-368. Radiolabeled PPI-368 is incorporated into fibrils during polymerization demonstrating binding to Aβ peptide within a fibrillar structure. Gel-filtration studies show progressive disappearance of Aβ monomer and concomitant appearance of soluble higher molecular weight oligomers. In the presence of submolar concentrations of PPI-368, monomeric Aβ is still present and oligomers are not observed. PPI-368 does not inhibit the polymerization of other amyloidogenic proteins such as transthyretin (TTR) or islet amyloid polypeptide(IAPP20-29).

Discovery and Characterization of Peptidoorganic Inhibitors of Amyloid β-Peptide Polymerization

Polymerization of amyloid β-peptide (Aβ) results in neuronal toxicity in vitro, and the formation in vivo of Aβ-peptide plaque is associated with the onset and progression of Alzheimer’s disease (AD) (Lorenzo and Yankner, 1994 and references therein). The precise mechanism by which AD-associated cellular toxicity and neurodegeneration occurs in humans is incompletely understood. Recent identification of the specific genetic defects that result in four classes of familial AD have the common feature of enhancing the production or deposition of Aβ (Scikoe, 1997). These data, in combination with additional observations regarding the progression of AD in Down syndrome patients or sporadic AD in older patients, the neurological and behavioral pathology of transgenic animal models of AD, and various biochemical properties of Aβ point to the production and subsequent polymerization of Aβ as an essential component of AD pathogenesis. This “Amyloid Hyposthesis” is reviewed in greater detail in the chapter by M. S. Shearman (see above). Thus, identification of compounds that slow, prevent, and possibly reverse the polymerization of Aβ has emerged as a goal in the development of therapeutic agents for AD.