Mark E. Duggan

αvβ3 Integrin antagonists as inhibitors of bone resorption

The vβ3 integrin is a non-covalent, heterodimeric, cell-surface protein that is expressed with varying density on numerous cell types, including osteoclasts, vascular smooth muscle cells, endothelial cells and a variety of tumour cells. Functionally, vβ3 mediates a diverse range of biological events including the adhesion of osteoclasts to bone matrix, smooth muscle cell migration and angiogenesis. Specifically, there has been significant attention focused on the preparation of inhibitors of vβ3 for use as inhibitors of bone resorption, in recognition of the medical need for improved prevention and treatment of osteoporosis. Herein, we summarise the pertinent chemistry and biological advances in the medicinal design and biological evaluation of peptide and small molecule vβ3 antagonists as inhibitors of bone resorption.

Design, Synthesis, and In Vivo Efficacy of Glycine Transporter-1 (GlyT1) Inhibitors Derived from a Series of [4-Phenyl-1-(propylsulfonyl)piperidin-4-yl]methyl Benzamides

Design, Synthesis, and In Vivo Efficacy of Glycine Transporter-1 (GlyT1) Inhibitors Derived from a Series of [4-Phenyl-1(propylsulfonyl)piperidin-4-yl]methyl Benzamides Craig W. Lindsley,* Zhijian Zhao, William H. Leister, Julie O’Brien, Wei Lemaire, David L. Williams, Jr. , Tsing-Bau Chen, Raymond S. L. Chang, Maryann Burno, Marlene A. Jacobson, Cyrille Sur, Gene G. Kinney, Douglas J. Pettibone, Philip R. Tiller, Sheri Smith, Nancy N. Tsou, Mark E. Duggan, P. Jeffrey Conn, e] and George D. Hartman

Ligands to the integrin receptor αvβ3

The vitronectin receptor vβ3 is a member of the integrin superfamily of membrane bound glycoprotein receptors that is responsible for cell-cell and cell-matrix interactions and shares the same β subunit as the fibrinogen receptor IIbβ3 (also known as GPIIb/IIIa). Both these integrins recognise extracellular proteins that express the peptide sequence arginine-glycine-aspartic acid (RGD). Non-peptide RGD mimetics that bind with high affinity and selectivity to IIbβ3 were previously prepared as anti-thrombotic agents. More recently, medicinal chemistry groups have modified these non-peptide fibrinogen receptor antagonist lead structures to impart potency and integrin selectivity for vβ3. Numerous patent applications and issued patents have appeared throughout the last decade claiming structurally novel vβ3 antagonists as agents for the prevention and/or treatment of osteoporosis, cancer, diabetic retinopathy and rheumatoid arthritis. This review encompasses those issued patents and published patent applications that disclose ligands to vβ3.

Selective Activation of M4 Muscarinic Acetylcholine Receptors Reverses MK-801-Induced Behavioral Impairments and Enhances Associative Learning in Rodents

Positive allosteric modulators (PAMs) of the M4 muscarinic acetylcholine receptor (mAChR) represent a novel approach for the treatment of psychotic symptoms associated with schizophrenia and other neuropsychiatric disorders. We recently reported that the selective M4 PAM VU0152100 produced an antipsychotic drug-like profile in rodents after amphetamine challenge. Previous studies suggest that enhanced cholinergic activity may also improve cognitive function and reverse deficits observed with reduced signaling through the N-methyl-d-aspartate subtype of the glutamate receptor (NMDAR) in the central nervous system. Prior to this study, the M1 mAChR subtype was viewed as the primary candidate for these actions relative to the other mAChR subtypes. Here we describe the discovery of a novel M4 PAM, VU0467154, with enhanced in vitro potency and improved pharmacokinetic properties relative to other M4 PAMs, enabling a more extensive characterization of M4 actions in rodent models. We used VU0467154 to test the hypothesis that selective potentiation of M4 receptor signaling could ameliorate the behavioral, cognitive, and neurochemical impairments induced by the noncompetitive NMDAR antagonist MK-801. VU0467154 produced a robust dose-dependent reversal of MK-801-induced hyperlocomotion and deficits in preclinical models of associative learning and memory functions, including the touchscreen pairwise visual discrimination task in wild-type mice, but failed to reverse these stimulant-induced deficits in M4 KO mice. VU0467154 also enhanced the acquisition of both contextual and cue-mediated fear conditioning when administered alone in wild-type mice. These novel findings suggest that M4 PAMs may provide a strategy for addressing the more complex affective and cognitive disruptions associated with schizophrenia and other neuropsychiatric disorders.

Nonpeptide αvβ3 antagonists. Part 2: constrained glycyl amides derived from the RGD tripeptide

Abstract Mimetics of the RGD tripeptide are described that are potent, selective antagonists of the integrin receptor, αvβ3. The use of the 5,6,7,8-tetrahydro[1,8]naphthyridine group as a potency-enhancing N-terminus is demonstrated. Two 3-substituted-3-amino-propionic acids previously contained in αIIbβ3 antagonists were utilized to enhance binding affinity and functional activity for the targeted receptor. Further affinity increases were then achieved through the use of cyclic glycyl amide bond constraints.

Selective Inhibition of KCC2 Leads to Hyperexcitability and Epileptiform Discharges in Hippocampal Slices and In Vivo

GABAA receptors form Cl− permeable channels that mediate the majority of fast synaptic inhibition in the brain. The K+/Cl− cotransporter KCC2 is the main mechanism by which neurons establish low intracellular Cl− levels, which is thought to enable GABAergic inhibitory control of neuronal activity. However, the widely used KCC2 inhibitor furosemide is nonselective with antiseizure efficacy in slices and in vivo, leading to a conflicting scheme of how KCC2 influences GABAergic control of neuronal synchronization. Here we used the selective KCC2 inhibitor VU0463271 [N-cyclopropyl-N-(4-methyl-2-thiazolyl)-2-[(6-phenyl-3-pyridazinyl)thio]acetamide] to investigate the influence of KCC2 function. Application of VU0463271 caused a reversible depolarizing shift in EGABA values and increased spiking of cultured hippocampal neurons. Application of VU0463271 to mouse hippocampal slices under low-Mg2+ conditions induced unremitting recurrent epileptiform discharges. Finally, microinfusion of VU0463271 alone directly into the mouse dorsal hippocampus rapidly caused epileptiform discharges. Our findings indicated that KCC2 function was a critical inhibitory factor ex vivo and in vivo.

Discovery of the Selective Androgen Receptor Modulator MK-0773 Using a Rational Development Strategy Based on Differential Transcriptional Requirements for Androgenic Anabolism Versus Reproductive Physiology

Selective androgen receptor modulators (SARMs) are androgen receptor (AR) ligands that induce anabolism while having reduced effects in reproductive tissues. In various experimental contexts SARMs fully activate, partially activate, or even antagonize the AR, but how these complex activities translate into tissue selectivity is not known. Here, we probed receptor function using >1000 synthetic AR ligands. These compounds produced a spectrum of activities in each assay ranging from 0 to 100% of maximal response. By testing different classes of compounds in ovariectomized rats, we established that ligands that transactivated a model promoter 40–80% of an agonist, recruited the coactivator GRIP-1 <15%, and stabilized the N-/C-terminal interdomain interaction <7% induced bone formation with reduced effects in the uterus and in sebaceous glands. Using these criteria, multiple SARMs were synthesized including MK-0773, a 4-aza-steroid that exhibited tissue selectivity in humans. Thus, AR activated to moderate levels due to reduced cofactor recruitment, and N-/C-terminal interactions produce a fully anabolic response, whereas more complete receptor activation is required for reproductive effects. This bimodal activation provides a molecular basis for the development of SARMs.

Identification of Anabolic Selective Androgen Receptor Modulators with Reduced Activities in Reproductive Tissues and Sebaceous Glands

Androgen replacement therapy is a promising strategy for the treatment of frailty; however, androgens pose risks for unwanted effects including virilization and hypertrophy of reproductive organs. Selective Androgen Receptor Modulators (SARMs) retain the anabolic properties of androgens in bone and muscle while having reduced effects in other tissues. We describe two structurally similar 4-aza-steroidal androgen receptor (AR) ligands, Cl-4AS-1, a full agonist, and TFM-4AS-1, which is a SARM. TFM-4AS-1 is a potent AR ligand (IC50, 38 nm) that partially activates an AR-dependent MMTV promoter (55% of maximal response) while antagonizing the N-terminal/C-terminal interaction within AR that is required for full receptor activation. Microarray analyses of MDA-MB-453 cells show that whereas Cl-4AS-1 behaves like 5α-dihydrotestosterone (DHT), TFM-4AS-1 acts as a gene-selective agonist, inducing some genes as effectively as DHT and others to a lesser extent or not at all. This gene-selective agonism manifests as tissue-selectivity: in ovariectomized rats, Cl-4AS-1 mimics DHT while TFM-4AS-1 promotes the accrual of bone and muscle mass while having reduced effects on reproductive organs and sebaceous glands. Moreover, TFM-4AS-1 does not promote prostate growth and antagonizes DHT in seminal vesicles. To confirm that the biochemical properties of TFM-4AS-1 confer tissue selectivity, we identified a structurally unrelated compound, FTBU-1, with partial agonist activity coupled with antagonism of the N-terminal/C-terminal interaction and found that it also behaves as a SARM. TFM-4AS-1 and FTBU-1 represent two new classes of SARMs and will allow for comparative studies aimed at understanding the biophysical and physiological basis of tissue-selective effects of nuclear receptor ligands.

Non-Peptide αvβ3 Antagonists. Part 4: Potent and Orally Bioavailable Chain-Shortened RGD Mimetics

Abstract Potent non-peptidic α v β 3 antagonists have been prepared where deletion of an amide bond from an earlier series of linear RGD-mimetics provides a novel series of chain-shortened α v β 3 antagonists with significantly improved oral pharmacokinetics. These chain-shortened α v β 3 antagonists represent structurally novel integrin inhibitors.

Non-Peptide αvβ3 antagonists. Part 6: Design and synthesis of αvβ3 antagonists containing a pyridone or pyrazinone central scaffold

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