Current Alzheimer Research, 2005, 2, 265-268 265 1567-2050/05 $50.00+.00 ©2005 Bentham Science Publishers Ltd. An Aβ Sequestration Approach Using Non-Antibody Aβ Binding Agents Yasuji Matsuoka 1,* , Li Shao 2 , Manik Debnath 2 , John LaFrancois 3 , Amanda Becker 1 , Audrey Gray 1 , Paul Aisen 1 , Chester Mathis 4 , William Klunk 2 and Karen Duff 3 1 Department of Neurology, Georgetown University Medical Center, Washington, DC, 2 Department of Psychiatry or 4 Department of Radiology, University of Pittsburgh, 3 Center for Dementia Research, Nathan Kline Institute and De- partment of Psychiatry, New York University Medical Center, New York, USA Abstract: Amyloid beta (Abeta) has been considered as a primary cause of Alzheimer’s disease (AD), and Abeta lower- ing approaches have been tested. Active immunization against Abeta is one of several promising Abeta-lowering ap- proaches. Two mechanisms have been proposed: enhancement of microglial phagocytosis and Abeta sequestration (also called “peripheral sink”). We hypothesized that Abeta sequestration without immune modulation is sufficient to reduce the brain Abeta load and have demonstrated effective sequestration with Abeta binding agents that do not stimulate an immune reaction. Recent reports from other groups showed two other non-immune related Abeta binding agents, which have no structural relation to compounds we previously tested, reduced brain Abeta after peripheral administration. Congo red is a chemically synthesized small molecule that has binding affinity to Abeta. In the present study, we tested three Congo red derivatives in Abeta plaque-forming mice at an early pathological stage. Unfortunately, peripheral administra- tion for three weeks did not substantially alter brain Abeta load. Optimized Abeta binding agents with high affinity to soluble Abeta are necessary for the sequestration approach. INTRODUCTION Alzheimer’s disease (AD) is a neurodegenerative afflic- tion associated with memory dysfunction. Amyloid beta (Abeta) is produced from the amyloid precursor protein (APP) by sequential proteolytic processing at the N and C termini of the Abeta domain by beta and gamma secretases, respectively. Abeta occurs principally in two forms consist- ing of 40 and 42 amino acids, Abeta1-40 and 1-42 [1,2]. Ac- cumulation of Abeta is a pathological hallmark of AD. Low- ering brain Abeta load is a promising therapeutic strategy in AD, and several approaches currently under evaluation are designed to reduce brain Abeta. One of these approaches is Abeta immunization. Immunologically provoked (or pas- sively administered) antibodies against Abeta have been shown to enhance microglial phagocytosis and reduce Abeta load in the brains of transgenic mice. Significantly, immuni- zation also reversed Abeta associated memory dysfunction. Concomitant with reduced brain Abeta is the independent observation by us [3] and others [4] that plasma Abeta levels are significantly elevated following immunization. As a re- sult of this observation, we have devised a new methodology to alter brain amyloid load, which has proved to be effective [5]. Evidence suggesting that sequestration is sufficient to reduce brain Abeta load has accumulated. An Fc receptor- independent pathway is supported by two lines of evidence: APP transgenic mice genetically lacking the Fc receptor (obtained by crossing APP overexpressing transgenic mice and Fc receptor knockout mice) showed reduction of brain *Address corresponding to this author at the Assistant Professor of Neurol- ogy, Georgetown University Medical Center, 4000 Reservoir Rd. NW, Bldg D, Room 202A, Washington, DC 20057, USA; Tel: 202-687-8117; Fax: 202-784-3504; E-mail: ym56@georgetown.edu Abeta load after immunization [6], and Fab fragments of anti-Abeta antibody (lacking the Fc region) reduced brain Abeta load [7,8]. Wilcock et al. [8] showed Fab fragment reduced brain Abeta load, though the effect was smaller than that of the intact antibody molecule. It should be noted that the Fab fragment is cleared much faster compare to intact antibody, which may be why Fab fragment is less efficient than intact antibody. Following our study using two proof-of-concept Abeta binding agents, gelsolin and GM1 [5], two other Abeta binding compounds, enoxaparin (low molecular weight heparin) [9] and transthyretin (Isaacs et al., 2004) reduced brain Abeta in Abeta-forming mice. [Note: unfractionated heparin consists of a mixture of polysaccharide chains which range in molecular weight from 3,000 to 30,000. Enoxaparin is a fractionated heparin with a molecular weight about 5,000. The molecular weight of enoxaparin is lower than standard heparin, but is not small enough to cross the blood- brain barrier to a great degree]. Soluble RAGE (sRAGE) is another Abeta binding agents showed Abeta lowering effects [10], but sRAGE inhibits the Abeta uptake transporter, RAGE; thus, the mode of action is uncertain. Overall, accumulating evidence suggests non-antibody Abeta binding agents may be sufficient to reduce brain Abeta load. However, these proof-of-concept compounds are ex- tracts from biological sources, and medicinal chemical modi- fication is very difficult; chemically synthesized Abeta binding agents are desired for the sequestration approach. Therefore, we explored the possibility of using Congo red derivatives, Abeta binding agents which have been exten- sively used in other studies, as sequestration compounds using a mouse model of AD.