Richard M. Keenan

Identification and in vivo efficacy of small-molecule antagonists of integrin αvβ3 (the vitronectin receptor)

Abstract The integrin αvβ3 is thought to play a key role in the initiation and/or progression of several human diseases, including osteoporosis, restenosis following percutaneous transluminal coronary angioplasty (PTCA), rheumatoid arthritis, cancer and ocular diseases. Antagonism of integrin αvβ3 is therefore expected to provide an approach for the treatment and/or prevention of these diseases. A variety of potent, small-molecule αvβ3 antagonists have been identified, several of which are active in disease models, thereby demonstrating the therapeutic potential of αvβ3 antagonism. This review will focus on recent advances in the identification of small-molecule αvβ3 antagonists, with an emphasis on those studies where small-molecule αvβ3 antagonists have been used in proof-of-concept studies in vivo.

Identification of 4-(2-(4-amino-1,2,5-oxadiazol-3-yl)-1-ethyl-7-{[(3S)-3-piperidinylmethyl]oxy}-1H-imidazo[4,5-c]pyridin-4-yl)-2-methyl-3-butyn-2-ol (GSK690693), a novel inhibitor of AKT kinase.

Overexpression of AKT has an antiapoptotic effect in many cell types, and expression of dominant negative AKT blocks the ability of a variety of growth factors to promote survival. Therefore, inhibitors of AKT kinase activity might be useful as monotherapy for the treatment of tumors with activated AKT. Herein, we describe our lead optimization studies culminating in the discovery of compound 3g (GSK690693). Compound 3g is a novel ATP competitive, pan-AKT kinase inhibitor with IC 50 values of 2, 13, and 9 nM against AKT1, 2, and 3, respectively. An X-ray cocrystal structure was solved with 3g and the kinase domain of AKT2, confirming that 3g bound in the ATP binding pocket. Compound 3g potently inhibits intracellular AKT activity as measured by the inhibition of the phosphorylation levels of GSK3beta. Intraperitoneal administration of 3g in immunocompromised mice results in the inhibition of GSK3beta phosphorylation and tumor growth in human breast carcinoma (BT474) xenografts.

Nonpeptidic urotensin-II receptor antagonists I: in vitro pharmacological characterization of SB-706375

1 SB‐706375 potently inhibited [125I]hU‐II binding to both mammalian recombinant and ‘native’ UT receptors (Ki 4.7±1.5 to 20.7±3.6 nM at rodent, feline and primate recombinant UT receptors and Ki 5.4±0.4 nM at the endogenous UT receptor in SJRH30 cells). 2 Prior exposure to SB‐706375 (1 μM, 30 min) did not alter [125I]hU‐II binding affinity or density in recombinant cells (KD 3.1±0.4 vs 5.8±0.9 nM and Bmax 3.1±1.0 vs 2.8±0.8 pmol mg−1) consistent with a reversible mode of action. 3 The novel, nonpeptidic radioligand [3H]SB‐657510, a close analogue of SB‐706375, bound to the monkey UT receptor (KD 2.6±0.4 nM, Bmax 0.86±0.12 pmol mg−1) in a manner that was inhibited by both U‐II isopeptides and SB‐706375 (Ki 4.6±1.4 to 17.6±5.4 nM) consistent with the sulphonamides and native U‐II ligands sharing a common UT receptor binding domain. 4 SB‐706375 was a potent, competitive hU‐II antagonist across species with pKb 7.29–8.00 in HEK293‐UT receptor cells (inhibition of [Ca2+]i‐mobilization) and pKb 7.47 in rat isolated aorta (inhibition of contraction). SB‐706375 also reversed tone established in the rat aorta by prior exposure to hU‐II (Kapp∼20 nM). 5 SB‐706375 was a selective U‐II antagonist with 100‐fold selectivity for the human UT receptor compared to 86 distinct receptors, ion channels, enzymes, transporters and nuclear hormones (Ki/IC50>1 μM). Accordingly, the contractile responses induced in isolated aortae by KCl, phenylephrine, angiotensin II and endothelin‐1 were unaltered by SB‐706375 (1 μM). 6 In summary, SB‐706375 is a high‐affinity, surmountable, reversible and selective nonpeptide UT receptor antagonist with cross‐species activity that will assist in delineating the pathophysiological actions of U‐II in mammals.

Enantiospecific synthesis of SB 214857, a potent, orally active, nonpeptide fibrinogen receptor antagonist

Abstract An enantiospecific synthesis of SB 214857, a potent, nonpeplide fibrinogen receptor antagonist, is reported. The synthetic route employs as a key step an intramolecular aryl fluoride displacement to form the sevenmembered ring of the 1,4-benzodiazepine system.

Orally bioavailable nonpeptide vitronectin receptor antagonists with efficacy in an osteoporosis model

A new series of potent nonpeptide vitronectin receptor antagonists, based on a novel carbocyclic Gly-Asp mimetic, has been discovered. A representative of this series, SB 265123 (4), has 100% oral bioavailability in rats, and is orally active in vivo in the ovariectomized rat model of osteoporosis.

Discovery of potent and selective phenylalanine derived CCR3 receptor antagonists. Part 2.

Highly potent CCR3 antagonists have been developed from a previously reported series of phenylalanine ester-based leads. Solution-phase, parallel synthesis optimization was utilized to identify highly potent, functional CCR3 antagonists.

Substituted benzothiadizine inhibitors of Hepatitis C virus polymerase.

The synthesis and optimisation of HCV NS5B polymerase inhibitors with improved potency versus the existing compound 1 is described. Substitution in the benzothiadiazine portion of the molecule, furnishing improvement in potency in the high protein Replicon assay, is highlighted, culminating in the discovery of 12h, a highly potent oxyacetamide derivative.

Design of a potent and orally active nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist.

The direct design of the potent nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist, 8-[[[4- (aminoiminomethyl)phenyl]amino]carbonyl]-2,3,4,5-tetrahydro-3-oxo- 4- (2-phenylethyl)-1H-1,4-benzodiazepine-2-acetic acid, (3) (SB 207448), based on the structure and conformation of the potent and highly constrained cyclic peptide antagonist SK&F 107260 (2), has been reported [Ku et al., J. Am. Chem. Soc. 1993, 115, 8861]. While 3 displayed in vivo activity in the conscious dog following intravenous administration, it was not active following intraduodenal administration; activity was measured with an ex vivo platelet aggregation assay. The secondary amide in 3 was N-methylated in the expectation of increased absorption and bioavailability. The resulting tertiary amide, 4 (SB 208651), also showed high binding affinity for human GPIIb/IIIa and potent antiaggregatory activity in human platelet-rich plasma. Most importantly, 4 was active in vivo following intravenous and intraduodenal administration. Comparison of the iv and id inhibition curves suggests an apparent bioavailability of approximately 10%. Thus, 4 represents the first orally active compound in this series of potent, nonpeptide fibrinogen receptor antagonists.

Benzothiopyran-4-one based reversible inhibitors of the human cytomegalovirus (HCMV) protease

A novel class of CMV protease inhibitors based on a benzothiopyran-S,S-dioxide nucleus has been discovered. Enzyme kinetic data supports a reversible mode of inhibition for a representative member of this class, 2-(3-pyridyl-N-oxide)benzothiopyran-4-one-S,S-dioxide, 1. Experiments in the presence and absence of the disulfide reducing agent DTT suggest that the inhibition by 1 is not due to oxidative inactivation of the enzyme. Also presented are results of some SAR studies of the benzothiopyranone ring system.

Discovery of potent and selective phenylalanine derived CCR3 antagonists. Part 1.

The discovery of a series of phenylalanine derived CCR3 antagonists is reported. Parallel, solution-phase library synthesis has been utilized to delineate the structure-activity relationship leading to the synthesis of highly potent, CCR3-selective antagonists.