Structural optimization of a CXCR2-directed antagonist that indirectly inhibits γ-secretase and reduces Aβ

Amyloid beta(A beta), a key molecule in the pathogenesis of Alzheimer's disease (AD), is derived from the amyloid precursor protein (APP) by sequential proteolysis via beta- and gamma-secretases. Because of their role in generation of A beta, these enzymes have emerged as important therapeutic targets for AD. In the case of gamma-secretase, progress has been made towards designing potent inhibitors with suitable pharmacological profiles. Direct gamma-secretase inhibitors are being evaluated in clinical trials and new strategies are being explored to block gamma-secretase activity indirectly as well. In this regard, we have previously reported an indirect regulation of gamma-secretase through antagonism of CXCR2, a G-protein coupled receptor (GPCR). We demonstrated that N-(2-hydroxy-4-nitrophenyl)-N'-(2-bromophenyl)urea (SB225002), a selective inhibitor of CXCR2 also plays a role in an indirect inhibition of gamma-secretase. Furthermore, we reported a similar to 5-fold difference in the selective inhibition of APP versus Notch processing via gamma-secretase following treatment with SB225002. Herein we describe the synthesis and optimization of SB225002. By determination of the structure-activity relationship (SAR), we derived small molecules that inhibit A beta 40 production with IC(50) values in the sub-micromolar range in a cell-based assay and also validated the potential of CXCR2 as a new target for therapeutic intervention in AD. (C) 2009 Elsevier Ltd. All rights reserved.