BACKGROUND AND PURPOSEThe) is an antagonist at the CXC chemokine receptor CXCR4, which plays a role in human immunodeficiency virus infection, cancer and stem cell recruitment. Binding modes for FC131 in CXCR4 have previously been suggested based on molecular docking guided by structure-activity relationship (SAR) data; however, none of these have been verified by in vitro experiments.
EXPERIMENTAL APPROACHHeterologous 125 I-12G5-competition binding and functional assays (inhibition of CXCL12-mediated activation) of FC131 and three analogues were performed on wild-type CXCR4 and 25 receptor mutants. Computational modelling was used to rationalize the experimental data.
KEY RESULTS
CONCLUSIONS AND IMPLICATIONSLigand modification, receptor mutagenesis and computational modelling approaches were used to identify the binding mode of FC131 in CXCR4, which was in agreement with binding modes suggested from previous SAR studies. Furthermore, insights into the mechanism for CXCR4 activation by CXCL12 were gained. The combined findings will facilitate future design of novel CXCR4 antagonists.
Abbreviations2-Nal, 3-(2-naphthyl)alanine; 7TM, 7 transmembrane helix; Aib, 2-aminoisobutyric acid; Cit, citrulline; ECL, extracellular loop; HIV, human immunodeficiency virus; IP, inositol phosphate; SAR, structure-activity relationship; WT, wild type BJP British Journal of Pharmacology
In the absence of an experimentally determined binding mode for the cyclopentapeptide CXCR4 antagonists, we have rationally designed conformationally constrained analogues to further probe the small peptide binding pocket of CXCR4. Two different rigidification strategies were employed, both resulting in highly potent ligands (9 and 13). The information provided by this cyclopentapeptide ligand series will be very valuable in the development of novel peptidomimetic CXCR4 antagonists.
The cyclopentapeptide CXCR4 antagonist FC131 (cyclo(-Arg 1 -Arg 2 -2-Nal 3 -Gly 4 -D-Tyr 5 -), 2; 2-Nal = 3-(2-naphthyl)alanine) represents an excellent starting point for development of novel drug-like ligands with therapeutic potential in HIV, cancer, stem-cell mobilization, inflammation, and autoimmune diseases. While the structure-activity relationships for Arg 1 , Arg 2 , and Gly 4 are well established, less is 10 understood about the roles of the aromatic residues 2-Nal 3 and D-Tyr 5 . Here we report further structureactivity relationship studies of these two positions, which showed that (i) the distal aromatic ring of the 2-Nal 3 side chain is required in order to maintain high potency, and (ii) replacement of D-Tyr 5 with conformationally constrained analogues results in significantly reduced activity. However, a simplified analogue that contained Gly instead of D-Tyr 5 was only 13-fold less potent than 2, which means that the 15 D-Tyr 5 side chain is dispensable. These findings were rationalized based on molecular docking, and the collective structure-activity data for the cyclopentapeptides suggest that appropriately designed Arg 2 -2-Nal 3 dipeptidomimetics have potential as CXCR4 antagonists.
Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were developed based on comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA), on a series of 43 hydroxyethylamine derivatives, acting as potent inhibitors of beta-site amyloid precursor protein (APP) cleavage enzyme (BACE-1). The crystal structure of the BACE-1 enzyme (PDB ID: 2HM1) with one of the most active compound 28 was available, and we assumed it to be the bioactive conformation of the studied series, for 3D-QSAR analysis. Statistically significant 3D-QSAR model was established on a training set of 34 compounds, which were validated by a test set of 9 compounds. For the best CoMFA model, the statistics are, r2 = 0.998, r2 cv =0.810, n = 34 for the training set and r2 pred = 0.934, n = 9 for the test set. For the best CoMSIA model (combined steric, electrostatic, hydrophobic, and hydrogen bond donor fields), the statistics are r2 = 0.978, r2 cv = 0.754, n = 34 for the training set and r2 pred = 0.750, n = 9 for the test set. The resulting contour maps, produced by the best CoMFA and CoMSIA models, were used to identify the structural features relevant to the biological activity in this series of analogs. The data generated from the present study will further help to design novel, potent, and selective BACE-1 inhibitors.
A quantitative structure-activity relationship (QSAR) analysis was performed on a data set of 104 molecules showing N-type calcium channel blocking activity. Several types of descriptors, including electrotopological, structural, thermodynamics and ADMET, were used to derive a quantitative relationship between N-type calcium channel blocking activity and structural properties. The genetic algorithm-based genetic function approximation (GFA) method of variable selection was used to generate the 2D-QSAR model. The model was established on a training set of 83 molecules, and validated by a test set of 21 molecules. The model was developed using five information-rich descriptors--Atype_C_24, Atype_N_68, Rotlbonds, S_sssN, and ADME_Solubility--playing an important role in determining N-type calcium channel blocking activity. For the best QSAR model (model 4), the statistics were r (2) = 0.798; q (2) = 0.769; n = 83 for the training set. This model was further validated using the leave-one-out (LOO) cross-validation approach, Fischer statistics (F), Y-randomisation test, and predictions based on the test data set. The resulting descriptors produced by QSAR model 4 were used to identify physico-chemical features relevant to N-type calcium channel blocking activity.
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