Discovery of N-{N-[(3-Cyanophenyl)sulfonyl]-4(R)-cyclobutylamino-(l)-prolyl}-4-[(3′,5′-dichloroisonicotinoyl)amino]-(l)-phenylalanine (MK-0668), an Extremely Potent and Orally Active Antagonist of Very Late Antigen-4

Design, synthesis and binding properties of a fluorescent α₉β₁/α₄β₁ integrin antagonist and its application as an in vivo probe for bone marrow haemopoietic stem cells

The α9β1 and α4β1 integrin subtypes are expressed on bone marrow haemopoietic stem cells and have important roles in stem cell regulation and trafficking. Although the roles of α4β1 integrin have been thoroughly investigated with respect to HSC function, the role of α9β1 integrin remains poorly characterised. Small molecule fluorescent probes are useful tools for monitoring biological processes in vivo, to determine cell-associated protein localisation and activation, and to elucidate the mechanism of small molecule mediated protein interactions. Herein, we report the design, synthesis and integrin-dependent cell binding properties of a new fluorescent α9β1 integrin antagonist (R-BC154), which was based on a series of N-phenylsulfonyl proline dipeptides and assembled using the Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC) reaction. Using transfected human glioblastoma LN18 cells, we show that R-BC154 exhibits high nanomolar binding affinities to α9β1 integrin with potent cross-reactivity against α4β1 integrin under physiological mimicking conditions. On-rate and off-rate measurements revealed distinct differences in the binding kinetics between α9β1 and α4β1 integrins, which showed faster binding to α4β1 integrin relative to α9β1, but more prolonged binding to the latter. Finally, we show that R-BC154 was capable of binding rare populations of bone marrow haemopoietic stem and progenitor cells when administered to mice. Thus, R-BC154 represents a useful multi-purpose fluorescent integrin probe that can be used for (1) screening small molecule inhibitors of α9β1 and α4β1 integrins; (2) investigating the biochemical properties of α9β1 and α4β1 integrin binding and (3) investigating integrin expression and activation on defined cell phenotypes in vivo.

In vivo imaging of ligand receptor binding with Gaussia luciferase complementation

Studies of ligand-receptor binding and development of receptor antagonists would benefit greatly from imaging techniques that translate directly from cell-based assays to living animals. We used Gaussia luciferase protein fragment complementation to quantify binding of chemokine CXCL12 to receptors CXCR4 and CXCR7. Small molecule inhibitors of CXCR4 or CXCR7 specifically blocked CXCL12 binding in cell-based assays, and these studies revealed differences in kinetics for inhibiting chemokine binding to each receptor. Bioluminescence imaging showed CXCL12-CXCR7 binding in primary and metastatic tumors in a mouse model of breast cancer. We also used this imaging technique to quantify drug-mediated inhibition of CXCL12-CXCR4 binding in living mice. We expect this imaging technology to advance research in areas including ligand-receptor interactions and development of new therapeutic agents in cell-based assays and small animals.

Discovery of potential integrin VLA-4 antagonists using pharmacophore modeling, virtual screening and molecular docking studies

Very late antigen-4 (VLA-4) is an integrin protein, and its antagonists are useful as anti-inflammatory drugs. The aim of this study is to discover novel virtual lead compounds to use them in designing potent VLA-4 antagonists. A best pharmacophore model was generated with correlation coefficient of 0.935, large cost difference of 114.078, comprising two hydrogen bond acceptors and three hydrophobic features. It was further validated and used in database screening for potential VLA-4 antagonists. A homology model of VLA-4 was built and employed in molecular docking of screened hit compounds. Finally, two compounds were identified as potential virtual leads to be deployed in the designing of novel potent VLA-4 antagonists.

Discovery of trans-4-[1-[[2,5-Dichloro-4-(1-methyl-3-indolylcarboxamido)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid: an orally active, selective very late antigen-4 antagonist

We have focused on optimization of the inadequate pharmacokinetic profile of trans-4-substituted cyclohexanecarboxylic acid 5, which is commonly observed in many small molecule very late antigen-4 (VLA-4) antagonists. We modified the lipophilic moiety in 5 and found that reducing the polar surface area of this moiety results in improvement of the PK profile. Consequently, our efforts have led to the discovery of trans-4-[1-[[2,5-dichloro-4-(1-methyl-3-indolylcarboxamido)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid (14e) with potent activity (IC(50) = 5.4 nM) and significantly improved bioavailability in rats, dogs, and monkeys (100%, 91%, 68%), which demonstrated excellent oral efficacy in murine and guinea pig models of asthma. Based on its overall profile, compound 14e was progressed into clinical trails. In a single ascending-dose phase I clinical study, compound 14e exhibited favorable oral exposure as expected and had no serious adverse events.

Heterocycle-substituted proline dipeptides as potent VLA-4 antagonists

A variety of N-linked tertiary amines and heteroarylamines were examined at the 4-position of sulfonylated proline dipeptides in order to improve VLA-4 receptor off-rates and overcome the issue of CYP3A4 time-dependent inhibition of ester prodrugs. A tight-binding inhibitor 5j with a long off-rate provided sustained receptor occupancy despite poor oral pharmacokinetics.