N-isonicotinoyl-(L)-4-aminophenylalanine derivatives as tight binding VLA-4 antagonists

Exploring N-Arylsulfonyl-l-proline Scaffold as a Platform for Potent and Selective αvβ1 Integrin Inhibitors

One small molecule inhibitor of αvβ1 integrin, c8, shows antifibrotic effects in multiple in vivo mouse models. Here we synthesized c8 analogues and systematically investigate their structure-activity relationships (SAR) in αvβ1 integrin inhibition. N-Phenylsulfonyl-l-homoproline analogues of c8 maintained excellent potency against αvβ1 integrin while retaining good selectivity over other RGD integrins. In addition, 2-aminopyridine or cyclic guanidine analogues were shown to be equally potent to c8. A rigid phenyl linker increased the potency compared to c8, but the selectivity over other RGD integrins diminished. These results can provide further insights on design of αvβ1 integrin inhibitors as antifibrotics.

Modeling the molecular basis for α4β1 integrin antagonism

We report a 3D QSAR study of almost 300 structurally diverse small molecule antagonists of the integrin α4β1 whose biological activity spans six orders of magnitude. The alignment of the molecules was based on the conformation of a structurally related ligand bound to the αIIBβ3 and αvβ3 integrins in X-ray crystallographic studies. The molecular field method, CoMSIA, was used to generate the 3D QSAR models. The resulting models showed that the lipophilic properties were the most important, with hydrogen bond donor and steric properties less relevant. The models were highly significant (r(2)=0.89, q2(LOO)=0.67, r(2) (test set)=0.76), and could make robust predictions of the data (SEE=0.46, SEP=0.78, SEP (test set)=0.66). We predicted the antagonist activities of a further ten compounds with useful accuracy. The model appears capable of predicting α4β1 integrin antagonist activity to within a factor of five for compounds within its domain of applicability. The implications for design of improved integrin antagonists will be discussed.

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.

Characterization of alpha(4)beta(1) (CD49d/CD29) on equine leukocytes: potential utility of a potent alpha(4)beta(1) (CD49d/CD29) receptor antagonist in the treatment of equine heaves (recurrent airway obstruction)

The purpose of this study was to characterize the alpha(4)beta(1) receptor (CD49d/CD29, very late antigen-4, VLA-4) on circulating equine leukocytes and to evaluate the intrinsic potency of an alpha(4)beta(1) receptor antagonist (Compound B) in the horse. Ultimately, these studies would allow us to determine the suitability of treating recurrent airway obstruction (RAO; heaves) affected horses by blocking the cellular recruitment of lymphocytes and neutrophils into the lung. The data demonstrates the alpha(4)beta(1) integrin is present on horse lymphocytes and neutrophils (fluorescence-assisted cell sorter, FACS) and can bind low molecular weight alpha(4)beta(1) antagonists (Compounds A and B) with high affinity. K(D) values for the binding of Compound A to non-activated alpha(4)beta(1) on isolated horse PBMCs (peripheral blood mononuclear cells) and activated neutrophils were 17 pM and 27 pM, respectively. Compound B was identified as a suitable antagonist for performing a series of in vivo experiments. Compound B was found to possess excellent potency in horse whole blood, possessing IC(50) and IC(90) values of 39 pM and 172 pM, respectively. This represents a 3.9-fold molar excess of drug over the alpha(4)beta(1) concentration in blood. Following oral administration of Compound B (5 mg/kg) to beagle dogs and rhesus monkeys, rapid and sustained alpha(4)beta(1) receptor occupancy (>80%) was achieved and maintained for a period of 24 h. When Compound B was administered intravenously to the horse, by either a slow or rapid infusion at a dose of 0.3 mg/kg, receptor blockade of >80% was observed out to 24 h with a concomitant leukocytosis. We believe that Compound B possesses suitable intrinsic and pharmacological properties to be evaluated clinically in horses affected by RAO.

Stereoselective Synthesis of Quaternary Proline Analogues

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of alpha-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton.

Targeting integrin structure and function in disease

Initially linked to the pathogenesis of inflammatory and hematologic diseases, integrins have become validated drug targets with the approval of five drugs. Moreover, there are several promising drug candidates in preclinical and clinical stages of development for multiple clinical indications. Integrins are attractive drug targets as their antagonism can block several steps in disease progression or maintenance. Integrin inhibitors can block the proliferation, migration, or tissue localization of inflammatory, angiogenic, and tumor cells, as well as signaling and gene expression contributing to disease. There has been a rapid increase in the elucidation of integrin structure, their allosteric mechanisms of bidirectional signaling, and the structure of complexes with drugs. This information brings greater focus to how integrins support various cellular functions and how they have been and may be targeted to develop novel drugs. Here we review conformational switches, including an internal ligand, which allosterically regulate the transition from low- to high-affinity ligand binding. We address some of the successes, disappointments, and challenges in targeting competitive or allosteric sites to develop therapeutics. We also discuss new opportunities, including a structure-based approach to discover novel drugs to treat inflammatory and other diseases. This approach targets structural relatives of the von Willebrand factor A-domain present in integrins and many functionally diverse proteins.

Aza-bicyclic amino acid carboxamides as α4β1/α4β7 integrin receptor antagonists

A series of N-carboxy, N-alkyl, and N-carboxamido azabicyclo[2.2.2]octane carboxamides were prepared and assayed for inhibition of alpha4beta1-VCAM-1 and alpha4beta7-MAdCAM-1 interactions. Potency and alpha4beta1/alpha4beta7 selectivity were sensitive to the substituent R1-R3 in the structures 6, 7, and 8. Several compounds demonstrated low nanomolar balanced alpha4beta1/alpha4beta7 in vitro activity. Two compounds were selected for in vivo leukocytosis studies and demonstrated increases in circulating lymphocytes up to 250% over control.

Aza-bicyclic amino acid sulfonamides as alpha(4)beta(1)/alpha(4)beta(7) integrin antagonists

The design, synthesis, and biological activity of novel alpha(4)beta(1) and alpha(4)beta(7) integrin antagonists, containing a bridged azabicyclic nucleus, are reported. Conformational analysis of targets containing an azabicyclo[2.2.2]octane carboxylic acid and known integrin antagonists indicated that this azabicycle would be a suitable molecular scaffold. Variation of substituents on the pendant arylsulfonamide and phenylalanine groups resulted in potent alpha(4)beta(1)-selective and dual alpha(4)beta(1)/alpha(4)beta(7) antagonists. Potent compounds 11i, 11h, and 14 were effective in the antigen-sensitized sheep model of asthma.

Bioisosteric replacement of anilide with benzoxazole: potent and orally bioavailable antagonists of VLA-4

We have designed and synthesized a series of heterocyclic bioisosteres for an anilide based on molecular modeling. Excellent potency was retained in the benzoxazole and the benzimidazole derivatives, where a hydrogen bond acceptor is appropriately positioned to mimic the amide bond oxygen. The deletion of the hydrogen bond donor (N-H) led to improved lipophilicity and bioavailability. In the process, 9a was identified as a potent, specific, and bioavailable VLA-4 antagonist, while 9c was found to be a potent and bioavailable dual antagonist of VLA-4 and alpha(4)beta(7).