ABSTRACT
Detection of cerebral ß-amyloid (Aß) by targeted contrast agents is of great interest for in vivo diagnosis of Alzheimer's disease (AD). Partly because of their planar structure several bis-styrylbenzenes have been previously reported as potential Aß imaging agents. However, these compounds are relatively hydrophobic, which likely limits their in vivo potential. Based on their structures, we hypothesized that less hydrophobic bis-pyridylethenylbenzenes may also label amyloid. We synthesized several bis-pyridylethenylbenzenes and tested whether these compounds indeed display improved solubility and lower LogP values, and studied their fluorescent properties and Aß binding characteristics. Bis-pyridylethenylbenzenes showed a clear affinity for Aß plaques on both human and murine AD brain sections. Competitive binding experiments suggested a different binding site than Chrysamine G, a well-known stain for amyloid. With a LogP value between 3 and 5, most bis-pyridylethenylbenzenes were able to enter the brain and label murine amyloid in vivo with the bis(4-pyridylethenyl)benzenes showing the most favorable characteristics. In conclusion, the presented results suggest that bis-pyridylethenylbenzene may serve as a novel backbone for amyloid imaging agents.
Subject(s)
Amyloid beta-Peptides/chemistry , Contrast Media/chemistry , Fluorescent Dyes/chemistry , Plaque, Amyloid/diagnostic imaging , Pyridines/chemistry , Styrenes/chemistry , Animals , Brain/diagnostic imaging , Brain/pathology , Contrast Media/chemical synthesis , Fluorescent Dyes/chemical synthesis , Humans , Hydrophobic and Hydrophilic Interactions , Male , Mice, Transgenic , Microscopy, Fluorescence , Molecular Imaging , Protein Binding , Pyridines/chemical synthesis , Solubility , Stilbenes/chemistry , Styrenes/chemical synthesisABSTRACT
The chemokine receptor CCR2 is a G protein-coupled receptor that is activated primarily by the endogenous CC chemokine ligand 2 (CCL2). Many different small-molecule antagonists have been developed to inhibit this receptor, as it is involved in a variety of diseases characterized by chronic inflammation. Unfortunately, all these antagonists lack clinical efficacy, and therefore a better understanding of their mechanism of action is warranted. In this study, we examined the pharmacological properties of small-molecule CCR2 antagonists in radioligand binding and functional assays. Six structurally different antagonists were selected for this study, all of which displaced the endogenous agonist (125)I-CCL2 from CCR2 with nanomolar affinity. Two of these antagonists, INCB3344 [N-(2-(((3S,4S)-1-((1r,4S)-4-(benzo[d][1,3]dioxol-5-yl)-4-hydroxycyclohexyl)-4-ethoxypyrrolidin-3-yl)amino)-2-oxoethyl)-3-(trifluoromethyl)benzamide] and CCR2-RA, were radiolabeled to study the binding site in greater detail. We discovered that [(3)H]INCB3344 and [(3)H]CCR2-RA bind to distinct binding sites at CCR2, the latter being the first allosteric radioligand for CCR2. Besides the binding properties of the antagonists, we examined CCR2 inhibition in multiple functional assays, including a novel label-free whole-cell assay. INCB3344 competitively inhibited CCL2-induced G protein activation, whereas CCR2-RA showed a noncompetitive or allosteric mode of inhibition. These findings demonstrated that the CCR2 antagonists examined in this study can be classified into two groups with different binding sites and thereby different modes of inhibition. We have provided further insights in CCR2 antagonism, and these insights are important for the development of novel CCR2 inhibitors.
