Michael J. Coghlan

Spontaneous phasic activity of the pig urinary bladder smooth muscle: characteristics and sensitivity to potassium channel modulators.

A hallmark for unstable bladder contractions is hyperexcitability and changes in the nature of spontaneous phasic activity of the bladder smooth muscle. In this study, we have characterized the spontaneous activity of the urinary bladder smooth muscle from the pig, a widely used model for studying human bladder function. Our studies demonstrate that phasic activity of the pig detrusor is myogenic and is influenced by the presence of urothelium. Denuded strips exhibit robust spontaneous activity measured as mean area under the contraction curve (AUC=188.9±15.63 mNs) compared to intact strips (AUC=7.3±1.94 mNs). Spontaneous phasic activity, particularly the amplitude, is dependent on both calcium entry through voltage‐dependent calcium channels and release from ryanodine receptors as shown by inhibition of spontaneous activity by nifedipine and ryanodine respectively. Inhibition of BKCa channels by iberiotoxin (100 nM) resulted in an increase in contraction amplitude (89.1±20.4%) and frequency (92.5±31.0%). The SKCa channel blocker apamin (100 nM) also increased contraction amplitude (69.1±24.3%) and frequency (53.5±13.6%) demonstrating that these mechanisms are critical to the regulation of phasic spontaneous activity. Inhibition of KATP channels by glyburide (10 μM) did not significantly alter myogenic contractions (AUC=18.5±12.3%). However, KATP channel openers (KCOs) showed an exquisite sensitivity for suppression of spontaneous myogenic activity. KCOs were generally 15 fold more potent in suppressing spontaneous activity compared to contractions evoked by electrical field‐stimulation. These studies suggest that potassium channel modulation, particularly KATP channels, may offer a unique mechanism for controlling spontaneous myogenic activity especially those associated with the hyperexcitability occurring in unstable bladders.

Validation of FLIPR Membrane Potential Dye for High Throughput Screening of Potassium Channel Modulators

A fluorescence-based assay using the FLIPR Membrane Potential Assay Kit (FMP) was evaluated for functional characterization and high throughput screening (HTS) of potassium channel (ATP-sensitive Ki channel; KATP) modulators. The FMP dye permits a more sensitive evaluation of changes in membrane potential with a more rapid response time relative to DiBAC4(3). The time course of responses is comparable to ligand-evoked activation of the channel measured by patch-clamp studies. The pharmacological profile of the K+ channel evaluated by using reference KATP channel openers is in good agreement with that derived previously by DiBAC4(3)-based FLIPR assays. Improved sensitivity of responses together with the diminished susceptibility to artifacts such as those evoked by fluorescent compounds or quenching agents makes the FMP dye an alternative choice for HTS screening of potassium channel modulators.

The Pursuit of Differentiated Ligands for the Glucocorticoid Receptor

Glucocorticoids have a pervasive role in human health and physiology. The endogenous members of this family are involved in a breadth of endocrine functions including metabolism of lipids, carbohydrates and proteins, stress response, fluid and electrolyte balance, as well as maintenance of immunological, renal and skeletal homeostasis. The predominant mode of action of glucocorticoids involves regulation of gene expression via the glucocorticoid receptor (GR). Synthetic glucocorticoids have long been the standard for the treatment of inflammatory and immune disorders, yet the benefits of classic steroids such as dexamethasone and prednisolone are accompanied by well-characterized potentiation of homeostatic endocrine functions, leading to the side effects associated with prolonged treatment. In recent campaigns for safer analogs, compounds have been sought which differentiate functional repression of existing transcription factors such as AP-1 and NFkappaB from GR-mediated transcriptional activation arising from binding at glucocorticoid-receptor response elements (GREs). Such differentiated ligands would provide the desired immunoregulatory actions without the endogenous changes in gene expression associated with undifferentiated steroids. We detail the methods for the evaluation of selective GR modulators and describe the evolution of new compounds where varying degrees of selectivity have been reported.

(−)-(9S)-9-(3-Bromo-4-fluorophenyl)-2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-Dioxide (A-278637): A Novel ATP-Sensitive Potassium Channel Opener Efficacious in Suppressing Urinary Bladder Contractions. I. In Vitro Characterization

Alterations in the myogenic activity of the bladder smooth muscle are thought to serve as a basis for the involuntary detrusor contractions associated with the overactive bladder. Activation of ATP-sensitive K+ (KATP) channels has been recognized as a potentially viable mechanism to modulate membrane excitability in bladder smooth muscle. In this study, we describe the preclinical pharmacology of (−)-(9S)-9-(3-bromo-4-fluorophenyl)-2,3,5,6,7,9-hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-dioxide (A-278637), a novel 1,4-dihydropyridine KATPchannel opener (KCO) that demonstrates enhanced bladder selectivity for the suppression of unstable bladder contractions in vivo relative to other reference KCOs. A-278637 activated KATP channels in bladder smooth muscle cells in a glyburide (glibenclamide)-sensitive manner as assessed by fluorescence membrane potential assays using bis-(1,3-dibutylbarbituric acid)trimethine oxonol (EC50 = 102 nM) and by whole cell patch clamp. Spontaneous (myogenic) phasic activity of pig bladder strips was suppressed (IC50 = 23 nM) in a glyburide-sensitive manner by A-278637. A-278637 also inhibited carbachol- and electrical field-stimulated contractions of bladder strips, although the respective potencies were 8- and 13-fold lower compared with inhibition of spontaneous phasic activity. As shown in the accompanying article [Brune ME, Fey TA, Brioni JD, Sullivan JP, Williams M, Carroll WA, Coghlan MJ, and Gopalakrishnan M (2002)J Pharmacol Exp Ther 303:387–394], A-278637 suppressed myogenic contractions in vivo in a model of bladder instability with superior selectivity compared with other KCOs, WAY-133537 [(R)-4-[3,4-dioxo-2-(1,2,2-trimethyl-propylamino)cyclobut-1-enylamino]-3-ethyl-benzonitrile] and ZD6169 [(S)-N-(4-benzoylphenyl)3,3,3-trifluro-2hydroxy-2-methyl-priopionamide]. A-278637 did not interact with other ion channels, including L-type calcium channels or other neurotransmitter receptor systems. The pharmacological profile of A-278637 represents an attractive basis for further investigations of selective KATP channel openers for the treatment of overactive bladder via myogenic etiology.

An Intra/Intermolecular Suzuki Sequence to Benzopyridyloxepines Containing Geometrically Pure Exocyclic Tetrasubstituted Alkenes

A route to enable the preparation of 5-benzylidenyl-benzopyridyloxepine analogues was developed to continue our research in the field of nuclear hormone receptor modulators. The key steps are 1) a syn-stereoselective diboration of a tethered aryl alkyne; 2) an intramolecular Suzuki cross-coupling reaction, which forms in a stereo- and regiocontrolled fashion, the 5-exoalkylidenyl 7-membered ring imbedded within the core of the scaffold and; 3) an intermolecular Suzuki to furnish the final tetra-substituted olefinic benzopyridyloxepines.

The discovery of a new class of large-conductance Ca2+-activated K+ channel opener targeted for overactive bladder: synthesis and structure-activity relationships of 2-amino-4-azaindoles.

2-Amino-4-azaindoles have been identified as a structurally novel class of BK(Ca) channel openers. Their synthesis from 2-chloro-3-nitropyridine is described together with their in vitro properties assessed by 86Rb(+) efflux and whole-cell patch-clamp assays using HEK293 cells stably transfected with the BK(Ca) alpha subunit. In vitro functional characterization of BK(Ca) channel opening activity was also assessed by measurement of relaxation of smooth muscle tissue strips obtained from Landrace pig bladders. The preliminary SAR data indicate the importance of steric bulk around the 2-amino substituent.

Glucocorticoid receptor modulators informed by crystallography lead to a new rationale for receptor selectivity, function, and implications for structure-based design.

The structural basis of the pharmacology enabling the use of glucocorticoids as reliable treatments for inflammation and autoimmune diseases has been augmented with a new group of glucocorticoid receptor (GR) ligands. Compound 10, the archetype of a new family of dibenzoxepane and dibenzosuberane sulfonamides, is a potent anti-inflammatory agent with selectivity for the GR versus other steroid receptors and a differentiated gene expression profile versus clinical glucocorticoids (lower GR transactivation with comparable transrepression). A stereospecific synthesis of this chiral molecule provides the unique topology needed for biological activity and structural biology. In vivo activity of 10 in acute and chronic models of inflammation is equivalent to prednisolone. The crystal structure of compound 10 within the GR ligand binding domain (LBD) unveils a novel binding conformation distinct from the classic model adopted by cognate ligands. The overall conformation of the GR LBD/10 complex provides a new basis for binding, selectivity, and anti-inflammatory activity and a path for further insights into structure-based ligand design.

Tenidap, a novel anti-inflammatory agent, is an opener of the inwardly rectifying K+ channel hKir2.3.

We studied the effect of a novel anti-inflammatory agent, tenidap, on a cloned inwardly rectifying K+ channel, hKir2.3. Tenidap (a) potently potentiated 86Rb+ efflux through hKir2.3 channels expressed in Chinese hamster ovary cells (EC50=402 nM), (b) reversibly and dose-dependently increased whole-cell and macro-patch hKir2.3 currents (maximum whole-cell current response to tenidap was 230+/-27% of control; EC50=1.3 microM.), and (c) caused dose-dependent and Ba2+-sensitive membrane hyperpolarizations and concurrent decreases in input resistance. Potentiation of hKir2.3 by tenidap was unaffected by inhibitors of phospholipase A2, protein kinase C, or arachidonic acid metabolic pathways. The action of tenidap was not intracellular. Tenidap also had little or no effect on currents flowing through hKir2.1, Kv1.5, and micro1 Na+ channels. Our results demonstrate that tenidap is a potent opener of hKir2.3 and suggest that it can serve as a valuable pharmacological tool for studying physiological and pathological processes involving Kir2.3.

Dual Exosite-binding Inhibitors of Insulin-degrading Enzyme Challenge Its Role as the Primary Mediator of Insulin Clearance in Vivo.

Background: Insulin-degrading enzyme (IDE) is the best characterized catabolic enzyme implicated in insulin proteolysis. Results: Newly discovered dual exosite IDE inhibitors do not significantly affect insulin action or clearance. Conclusion: IDE catabolism does not appear to be the primary mechanism of insulin clearance in vivo. Significance: These IDE inhibitors will enable broader investigation of IDE function. Insulin-degrading enzyme (IDE, insulysin) is the best characterized catabolic enzyme implicated in proteolysis of insulin. Recently, a peptide inhibitor of IDE has been shown to affect levels of insulin, amylin, and glucagon in vivo. However, IDE−/− mice display variable phenotypes relating to fasting plasma insulin levels, glucose tolerance, and insulin sensitivity depending on the cohort and age of animals. Here, we interrogated the importance of IDE-mediated catabolism on insulin clearance in vivo. Using a structure-based design, we linked two newly identified ligands binding at unique IDE exosites together to construct a potent series of novel inhibitors. These compounds do not interact with the catalytic zinc of the protease. Because one of these inhibitors (NTE-1) was determined to have pharmacokinetic properties sufficient to sustain plasma levels >50 times its IDE IC50 value, studies in rodents were conducted. In oral glucose tolerance tests with diet-induced obese mice, NTE-1 treatment improved the glucose excursion. Yet in insulin tolerance tests and euglycemic clamp experiments, NTE-1 did not enhance insulin action or increase plasma insulin levels. Importantly, IDE inhibition with NTE-1 did result in elevated plasma amylin levels, suggesting the in vivo role of IDE action on amylin may be more significant than an effect on insulin. Furthermore, using the inhibitors described in this report, we demonstrate that in HEK cells IDE has little impact on insulin clearance. In total, evidence from our studies supports a minimal role for IDE in insulin metabolism in vivo and suggests IDE may be more important in helping regulate amylin clearance.

Trichloromethyl carbonate as a practical phosgene source: application to the synthesis of α-chloro chloroformates

Trichloromethyl carbonate 1 is used as a phosgene source in the preparation of α-chloro chloroformates. This stable, crystalline reagent smoothly delivers products 3 in good yield under mild conditions.