Non-peptide alpha(v)beta(3) antagonists. Part 4: potent and orally bioavailable chain-shortened RGD mimetics

Discovery and Development of Highly Potent and Orally Bioavailable Nonpeptidic αvβ6 Integrin Inhibitors

A series of 3-aryl((S)-3-fluoropyrrolidin-1-yl)butanoic acids were developed as potent orally bioavailable αvβ6 integrin inhibitors. Starting from a zwitterionic peptidomimetic series optimized for inhaled administration, the balancing of potency and passive permeability to achieve suitable oral agents through modification and exploration of aryl substituents and pKa of the central cyclic amine is described. (S)-4-((S)-3-Fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(3-(2-methoxyethoxy)phenyl)butanoic acid was found to have highly desirable oral pharmacokinetic profiles in rat, dog, and minipig, with low to moderate clearance (26%, 7%, and 18% liver blood flow, respectively), moderate volumes of distribution (3.6, 1.4, and 0.9 L/kg, respectively), high to complete oral bioavailabilities, high αvβ6 integrin potency of pIC50 of 8.0, and high solubility in physiological media (>2 mg/mL). Equating to the estimated human dose range of 10-75 mg b.i.d. to achieve 90% αvβ6 target engagement at Cmin, it was selected for further investigation as a potential therapeutic agent for the treatment of idiopathic pulmonary fibrosis.

Geometry encoded functional programming of tumor homing peptides for targeted drug delivery

Poly-peptide molecules have shown promising applications in drug delivery and tumor targeting. A series of tumor homing peptides were designed by exhaustively sampling low energy geometrical basins of amino acids at specific sites of a peptide molecule to induce a conformational lock. This peptide library was pruned to a limited set of eight molecules, employing electrostatic interactions, docking, and molecular dynamics simulations. These designed and optimized peptides were synthesized and tested on various cell lines, including breast cancer (MDA-MB-231), cervical cancer (HeLa), osteosarcoma (U2-OS), and non-cancerous mammary epithelial cells (MCF-10A) using confocal microscopy and flow cytometry. Peptides show differential uptake in cancerous MDA-MB-231, HeLa, U2-OS, and non-cancerous MCF-10A cells. Confocal imaging verified their ability to penetrate even in 3D tumorospheres of MDA-MB-231 cells. Further, experiments of mitochondrial membrane potential depolarization and Caspase-3 activation confirmed that their cytotoxic effects are by apoptosis. Homing ability of the designed peptides in in vivo system and fluorescence imaging with clinical samples of human origin have further confirmed that the in vitro studies are qualitatively identical and quantitatively comparable in their ability to selectively recognize tumor cells. Overall, we present a roadmap for the functional programming of peptide-based homing and penetrating molecules that can perform selective tumor targeting.

Discovery of ( S)-3-(3-(3,5-Dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic Acid, a Nonpeptidic αvβ6 Integrin Inhibitor for the Inhaled Treatment of Idiopathic Pulmonary Fibrosis

A series of 3-aryl(pyrrolidin-1-yl)butanoic acids were synthesized using a diastereoselective route, via a rhodium catalyzed asymmetric 1,4-addition of arylboronic acids in the presence of ( R)-BINAP to a crotonate ester to provide the ( S) absolute configuration for the major product. A variety of aryl substituents including morpholine, pyrazole, triazole, imidazole, and cyclic ether were screened in cell adhesion assays for affinity against α_vβ₁, α_vβ₃, α_vβ₅, α_vβ₆, and α_vβ₈ integrins. Numerous analogs with high affinity and selectivity for the α_vβ₆ integrin were identified. The analog ( S)-3-(3-(3,5-dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid hydrochloride salt was found to have very high affinity for α_vβ₆ integrin in a radioligand binding assay (p K_i = 11), a long dissociation half-life (7 h), very high solubility in saline at pH 7 (>71 mg/mL), and pharmacokinetic properties commensurate with inhaled dosing by nebulization. It was selected for further clinical investigation as a potential therapeutic agent for the treatment of idiopathic pulmonary fibrosis.

Passing on the medicinal chemistry baton: training undergraduates to be industry-ready through research projects between the University of Nottingham and GlaxoSmithKline

In this article we describe a radically different industry-academia collaboration between the School of Chemistry, University of Nottingham, and GlaxoSmithKline (GSK), aiming to train students in research and give them an insight into medicinal chemistry as practiced in industry. The project concerns the discovery of potent and selective αvβ6 integrin antagonists to treat idiopathic pulmonary fibrosis; the synthetic chemistry is performed by a group of ten final-year undergraduates and the biological and physicochemical screening data are generated by GSK. The project planning, organisation and operation are discussed, together with some of the challenges and rewards of working with undergraduates.

Structure Activity Relationships of αv Integrin Antagonists for Pulmonary Fibrosis by Variation in Aryl Substituents

Antagonism of αvβ6 is emerging as a potential treatment of idiopathic pulmonary fibrosis based on strong target validation. Starting from an αvβ3 antagonist lead and through simple variation in the nature and position of the aryl substituent, the discovery of compounds with improved αvβ6 activity is described. The compounds also have physicochemical properties commensurate with oral bioavailability and are high quality starting points for a drug discovery program. Compounds 33S and 43E1 are pan αv antagonists having ca. 100 nM potency against αvβ3, αvβ5, αvβ6, and αvβ8 in cell adhesion assays. Detailed structure activity relationships with these integrins are described which also reveal substituents providing partial selectivity (defined as at least a 0.7 log difference in pIC50 values between the integrins in question) for αvβ3 and αvβ5.

Breaking the dogma of the metal-coordinating carboxylate group in integrin ligands: introducing hydroxamic acids to the MIDAS to tune potency and selectivity

A suitable substitute: All integrin receptors bind their ligands, which contain an aspartate residue, in the metal-ion- dependent adhesion site (MIDAS). So far all attempts to replace the carboxyl group of aspartate with other, pharmacologically favorable isosteric groups have failed. Now it has been shown that a hydroxamic acid group can replace the carboxyl group; the resulting ligand retains its high binding activity. The picture shows one such ligand in the binding site of alphavbeta3.

Design and Chemical Synthesis of Integrin Ligands

The design and synthesis of peptidic and nonpeptidic integrin ligands derived from the most abundant natural tripeptide sequence, RGD, are described in this article. Special emphasis is placed on the activity and selectivity of the ligands to integrin subtypes. Two approaches are described-ligand- and structure-oriented design. When no structure of the complex or the target is known, one may derive suitable starting points from natural peptide sequences, which often require conformational restriction for a further optimization. A "spatial screening" procedure was used to identify highly active and selective ligands for the integrin subtypes alphavbeta3 and alphaIIbbeta3. Structure-based methods require knowledge of the binding domain of the target. Hence, the first structure of the alphavbeta3 integrin with bound cilengitide was a landmark for the structure-based approach. Meanwhile, a design using homology models of other integrin subtypes has also been successfully applied. To improve the ADME profile, nonpeptidic ligands have been developed using the information of the spatial distances and orientations of the most important pharmacophoric groups (especially the carboxyl group and the basic moiety at the other end of the molecule). Applications of the alphavbeta3 ligands as drugs in antiangiogenic tumor therapy for molecular imaging of metastases and for improvement of biocompatibility of grafts are briefly described.

Tricyclic pharmacophore-based molecules as novel integrin alpha(v)beta3 antagonists. Part 2: synthesis of potent alpha(v)beta3/alpha(IIb)beta3 dual antagonists

We synthesized 4-aminopiperidine derivatives of our prototype integrin alpha(v)beta3 antagonist 1 in an attempt to increase the activity and water solubility. Introduction of one or two hydrophilic moieties into the central aromatic ring and/or the benzene ring at the C-terminus of 1 increased water solubility and enhanced inhibition of cell adhesion. The results of a structure-activity relationships (SAR) study indicated that the torsion angle between the central aromatic ring and the piperidine ring, and the acidity at the sulfonamide moiety, might be important for alpha(v)beta3 receptor binding activity. Some of these compounds are novel and potent alpha(v)beta3/alpha(IIb)beta3 dual antagonists with acceptable water solubility and a satisfactory early absorption, distribution, metabolism, excretion, and toxicity (ADMET) profile.

Tricyclic pharmacophore-based molecules as novel integrin alpha(v)beta3 antagonists. Part III: synthesis of potent antagonists with alpha(v)beta3/alpha(IIb)beta3 dual activity and improved water solubility

In order to optimize our novel integrin alpha(v)beta3/alpha(IIb)beta3 dual antagonists, spatial screening at the N-terminus was performed. The alpha(v)beta3 antagonistic activity varied depending on the space that was occupied by the N-terminus, but high potency against alpha(IIb)beta3 was well maintained. The (3S)-aminopiperidine analogue had the strongest activity against alpha(v)beta3, and the S isomer at piperidine was more potent than the R isomer. Compounds selected on the basis of SAR analysis of a novel lead compound showed acceptable early absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles and sufficient water solubility for use as infusion drugs. Docking studies with the alpha(v)beta3 receptor were performed to confirm the SAR findings.

Nonpeptide αvβ3 antagonists: identification of potent, chain-shortened 7-oxo RGD mimetics

Potent, novel 7-oxo alpha(v)beta3 antagonists have been prepared. These antagonists offer decreased plasma protein binding and excellent pharmacokinetic profiles.

1,2,3,4-Tetrahydroquinoline-containing αVβ3 integrin antagonists with enhanced oral bioavailability

Reduction of the quinoline ring in an alpha(v)beta(3) antagonist yielded a 1,2,3,4-tetrahydro derivative as two diastereomers, the four isomers of which were separated by sequential chiral HPLC. Two isomers had significant alpha(V)beta(3) antagonist activity with improved oral bioavailability, relative to the corresponding quinoline derivative.

Nonpeptide αvβ3 antagonists. Part 9: Improved pharmacokinetic profile through the use of an aliphatic, des-amide backbone

A series of alphaVbeta3 receptor antagonists lacking the amide bond of previously-reported 'chain-shortened' compounds is described. Replacement of the lone amide bond with two methylene groups in this series yields more lipophilic compounds that have longer half-lives, lower clearance, and greater oral bioavailability when administered to dogs.

Design, synthesis, and biochemical evaluation of novel αvβ3 integrin ligands

Studies on integrin alphaVbeta3 have implicated this receptor in a number of pathologies. In this article we describe some of our initial efforts to design small molecules alphaVbeta3 ligands incorporating an indole core template and an oxyguanidine as basic ending. Synthesis, biochemical activity and pharmacological properties are analyzed.

Solid-phase synthesis of a small library of 3-phenylthio-3-nicotinyl propionic acid derivatives acting as antagonists of the integrin αVβ3

We describe the synthesis of a series of low molecular weight inhibitors of the alphavbeta3 integrin obtained by modifying a high-throughput screening hit with micromolar activity. A solid phase synthesis to prepare 3-phenylthio-3-nicotinyl propionic acid derivatives, exemplified by 13c, was set up. Compounds with nanomolar activity in the biochemical assay and able to efficiently inhibit cell adhesion mediated by vitronectin have been obtained.

Non-peptide α v β 3 antagonists. Part 7: 3-Substituted tetrahydro- [1,8] naphthyridine derivatives

A series of 3-substituted tetrahydro-[1,8]naphthyridine containing alpha(v)beta(3) antagonists was prepared. A comparison of their in vitro IC(50) values to the electron properties of the 3-substituents revealed a good linear Hammett correlation (rho=-1.96, R(2)=0.959). Electron-withdrawing groups at the 3-position of the tetrahydro-[1,8]naphthyridine decreased potency while electron-donating groups enhanced potency.

Non-peptide α v β 3 antagonists: Identification of potent, chain-shortened RGD mimetics that incorporate a central pyrrolidinone constraint

Antagonists of the integrin receptor alpha(v)beta(3) are expected to have utility in the treatment of osteoporosis through inhibition of bone resorption. A series of potent, chain-shortened, pyrrolidinone-containing alpha(v)beta(3) receptor antagonists is described. Two sets of diasteromeric pairs of high-affinity antagonists demonstrated marked differences in log P values, which translated into differing dog pharmacokinetic properties. One member of this set was demonstrated to be effective in reducing bone resorption in rats.

Non-peptide alphavbeta3 antagonists. Part 6: design and synthesis of alphavbeta3 antagonists containing a pyridone or pyrazinone central scaffold

Two novel series of small-molecule RGD mimetics containing either a substituted pyridone or pyrazinone central constraint were prepared. Modification of the beta-alanine 3-substituent produced compounds that are potent and selective alpha(v)beta(3) antagonists and exhibit a range of physicochemical properties.

Non-peptide alpha(v)beta(3) antagonists. Part 5: identification of potent RGD mimetics incorporating 2-aryl beta-amino acids as aspartic acid replacements

A series of novel, highly potent alpha(v)beta(3) receptor antagonists with favorable pharmacokinetic profiles has been identified. In this series of antagonists, 2-aryl beta-amino acids function as potent aspartic acid replacements.