Ivan Milicic

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.

Rotationally constrained 2,4-diamino-5,6-disubstituted pyrimidines: a new class of histamine H4 receptor antagonists with improved druglikeness and in vivo efficacy in pain and inflammation models.

A new structural class of histamine H 4 receptor antagonists (6-14) was designed based on rotationally restricted 2,4-diaminopyrimidines. Series compounds showed potent and selective in vitro H 4 antagonism across multiple species, good CNS penetration, improved PK properties compared to reference H 4 antagonists, functional H 4 antagonism in cellular and in vivo pharmacological assays, and in vivo anti-inflammatory and antinociceptive efficacy. One compound, 10 (A-943931), combined the best features of the series in a single molecule and is an excellent tool compound to probe H 4 pharmacology. It is a potent H 4 antagonist in functional assays across species (FLIPR Ca (2+) flux, K b < 5.7 nM), has high (>190x) selectivity for H 4, and combines good PK in rats and mice (t 1/2 of 2.6 and 1.6 h, oral bioavailability of 37% and 90%) with anti-inflammatory activity (ED 50 = 37 micromol/kg, mouse) and efficacy in pain models (thermal hyperalgesia, ED 50 = 72 micromol/kg, rat).

Structure−Activity Studies on a Series of a 2-Aminopyrimidine-Containing Histamine H4 Receptor Ligands

A series of 2-aminopyrimidines was synthesized as ligands of the histamine H4 receptor (H4R). Working in part from a pyrimidine hit that was identified in an HTS campaign, SAR studies were carried out to optimize the potency, which led to compound 3, 4- tert-butyl-6-(4-methylpiperazin-1-yl)pyrimidin-2-ylamine. We further studied this compound by systematically modifying the core pyrimidine moiety, the methylpiperazine at position 4, the NH2 at position 2, and positions 5 and 6 of the pyrimidine ring. The pyrimidine 6 position benefited the most from this optimization, especially in analogs in which the 6- tert-butyl was replaced with aromatic and secondary amine moieties. The highlight of the optimization campaign was compound 4, 4-[2-amino-6-(4-methylpiperazin-1-yl)pyrimidin-4-yl]benzonitrile, which was potent in vitro and was active as an anti-inflammatory agent in an animal model and had antinociceptive activity in a pain model, which supports the potential of H 4R antagonists in pain.

cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine (A-987306), A New Histamine H4R Antagonist that Blocks Pain Responses against Carrageenan-Induced Hyperalgesia

cis-4-(Piperazin-1-yl)-5,6,7a,8,9,10,11,11a-octahydrobenzofuro[2,3-h]quinazolin-2-amine, 4 (A-987306) is a new histamine H(4) antagonist. The compound is potent in H(4) receptor binding assays (rat H(4), K(i) = 3.4 nM, human H(4) K(i) = 5.8 nM) and demonstrated potent functional antagonism in vitro at human, rat, and mouse H(4) receptors in cell-based FLIPR assays. Compound 4 also demonstrated H(4) antagonism in vivo in mice, blocking H(4)-agonist induced scratch responses, and showed anti-inflammatory activity in mice in a peritonitis model. Most interesting was the high potency and efficacy of this compound in blocking pain responses, where it showed an ED(50) of 42 mumol/kg (ip) in a rat post-carrageenan thermal hyperalgesia model of inflammatory pain.

(−)-(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.

A-1048400 is a novel, orally active, state-dependent neuronal calcium channel blocker that produces dose-dependent antinociception without altering hemodynamic function in rats.

Blockade of voltage-gated Ca²⁺ channels on sensory nerves attenuates neurotransmitter release and membrane hyperexcitability associated with chronic pain states. Identification of small molecule Ca²⁺ channel blockers that produce significant antinociception in the absence of deleterious hemodynamic effects has been challenging. In this report, two novel structurally related compounds, A-686085 and A-1048400, were identified that potently block N-type (IC₅₀=0.8 μM and 1.4 μM, respectively) and T-type (IC₅₀=4.6 μM and 1.2 μM, respectively) Ca²⁺ channels in FLIPR based Ca²⁺ flux assays. A-686085 also potently blocked L-type Ca²⁺ channels (EC₅₀=0.6 μM), however, A-1048400 was much less active in blocking this channel (EC₅₀=28 μM). Both compounds dose-dependently reversed tactile allodynia in a model of capsaicin-induced secondary hypersensitivity with similar potencies (EC₅₀=300-365 ng/ml). However, A-686085 produced dose-related decreases in mean arterial pressure at antinociceptive plasma concentrations in the rat, while A-1048400 did not significantly alter hemodynamic function at supra-efficacious plasma concentrations. Electrophysiological studies demonstrated that A-1048400 blocks native N- and T-type Ca²⁺ currents in rat dorsal root ganglion neurons (IC₅₀=3.0 μM and 1.6 μM, respectively) in a voltage-dependent fashion. In other experimental pain models, A-1048400 dose-dependently attenuated nociceptive, neuropathic and inflammatory pain at doses that did not alter psychomotor or hemodynamic function. The identification of A-1048400 provides further evidence that voltage-dependent inhibition of neuronal Ca²⁺ channels coupled with pharmacological selectivity vs. L-type Ca²⁺ channels can provide robust antinociception in the absence of deleterious effects on hemodynamic or psychomotor function.

A peripherally acting, selective T-type calcium channel blocker, ABT-639, effectively reduces nociceptive and neuropathic pain in rats

Activation of T-type Ca²⁺ channels contributes to nociceptive signaling by facilitating action potential bursting and modulation of membrane potentials during periods of neuronal hyperexcitability. The role of T-type Ca²⁺ channels in chronic pain is supported by gene knockdown studies showing that decreased Ca(v)3.2 channel expression results in the loss of low voltage-activated (LVA) currents in dorsal root ganglion (DRG) neurons and attenuation of neuropathic pain in the chronic constriction injury (CCI) model. ABT-639 is a novel, peripherally acting, selective T-type Ca²⁺ channel blocker. ABT-639 blocks recombinant human T-type (Ca(v)3.2) Ca²⁺ channels in a voltage-dependent fashion (IC₅₀ = 2 μM) and attenuates LVA currents in rat DRG neurons (IC₅₀ = 8 μM). ABT-639 was significantly less active at other Ca²⁺ channels (e.g. Ca(v)1.2 and Ca(v)2.2) (IC₅₀ > 30 μM). ABT-639 has high oral bioavailability (%F = 73), low protein binding (88.9%) and a low brain:plasma ratio (0.05:1) in rodents. Following oral administration ABT-639 produced dose-dependent antinociception in a rat model of knee joint pain (ED₅₀ = 2 mg/kg, p.o.). ABT-639 (10-100 mg/kg, p.o.) also increased tactile allodynia thresholds in multiple models of neuropathic pain (e.g. spinal nerve ligation, CCI, and vincristine-induced). [corrected]. ABT-639 did not attenuate hyperalgesia in inflammatory pain models induced by complete Freunds adjuvant or carrageenan. At higher doses (e.g. 100-300 mg/kg) ABT-639 did not significantly alter hemodynamic or psychomotor function. The antinociceptive profile of ABT-639 provides novel insights into the role of peripheral T-type (Ca(v)3.2) channels in chronic pain states.

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.

Effects of Selective and Nonselective Alpha-1-Adrenoceptor Antagonists on Intraurethral and Arterial Pressures in Intact Conscious Dogs

In this study, we used a novel conscious dog model to evaluate the uroselectivity of selected alpha 1-antagonists either approved for human use or in clinical development for the treatment of symptomatic benign prostatic hyperplasia (BPH) and compared those results to their in vitro binding and functional affinities at alpha 1A, alpha 1B and alpha 1D receptor subtypes. Conscious dogs were instrumented acutely with a balloon catheter for the measurement of changes in prostatic intraurethral pressure (IUP) and chronically with implantable telemetry devices for the measurement of arterial pressure. The pressor effects of the alpha 1-agonist phenylephrine (PE) on IUP and mean arterial pressure (MAP) were compared before and at various time points after oral doses of either terazosin, doxazosin, tamsulosin or Rec 15/2739 (SB 216469). At submaximal doses, terazosin and doxazosin blocked PE-induced increases in MAP to a greater extent than increases in IUP. Tamsulosin blocked both parameters equally at the lowest and highest doses; however, at the intermediate dose, IUP was blocked more than MAP. Rec 15/2739 at each dose always blocked IUP to a greater extent than MAP. While the in vivo uroselectivity of these agents was predicted by radioligand binding and in vitro functional selectivity for the alpha 1A subtype over alpha 1B and alpha 1D subtypes, results from conscious dog experiments indicate that estimates of in vivo uroselectivity also depend upon dose and the time after administration. Our conscious canine model provides the basis for frequent and repeated evaluation of uroselectivity parameters over many hours, thus providing a pharmacological profile of compound effects perhaps more relevant to clinical practice.

Pharmacological characterization of a 1,4‐dihydropyridine analogue, 9‐(3,4‐dichlorophenyl)‐3,3,6,6‐tetramethyl‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184209) as a novel KATP channel inhibitor

This study reports on the identification and characterization of a 1,4‐dihydropyridine analogue, 9‐(3,4‐dichlorophenyl)‐3,3,6,6‐tetramethyl‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184209) as a novel inhibitor of ATP‐sensitive K+ channels. A‐184209 inhibited membrane potential changes evoked by the prototypical cyanoguanidine ATP‐sensitive K+ channel opener (KCO) P1075 in both vascular (A10) and urinary bladder smooth muscle cells with IC50 values of 1.44 and 2.24 μM respectively. P1075‐evoked relaxation of 25 mM K+ stimulated aortic strips was inhibited by A‐184209 in an apparently competitive fashion with a pA2 value of 6.34. The potencies of A‐184209 to inhibit P1075‐evoked decreases in membrane potential responses in cardiac myocytes (IC50=0.53 μM) and to inhibit 2‐deoxyglucose‐evoked cation efflux pancreatic RINm5F cells (IC50=0.52 μM) were comparable to the values for inhibition of smooth muscle KATP channels. On the other hand, a structural analogue of A‐184209 that lacked the gem‐dimethyl substituent, 9‐(3,4‐dichlorophenyl)‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184208), was found to be a KATP channel opener, evoking membrane potential responses in A10 smooth muscle cells (EC50=385 nM) and relaxing aortic smooth muscle strips (IC50=101 nM) in a glyburide‐sensitive manner. Radioligand binding studies demonstrated that A‐184209 displaced SUR1 binding defined by [3H]glyburide binding to RINm5F cell membranes with a Ki value of 0.11 μM whereas A‐184208 was ineffective. On the other hand, both A‐184209 (Ki=1.34 μM) and A‐184208 (Ki=1.14 μM) displaced binding of the KCO radioligand, [125I]A‐312110 in guinea‐pig bladder membranes with similar affinities. These studies demonstrate that A‐184209 is a novel and structurally distinct compound that inhibits KATP channels in smooth muscle with potencies comparable to glyburide. The structural overlap between DHP openers and blockers, together with their differential interaction with ligand binding sites, support the notion that both openers and blockers bind to similar or very closely coupled sites on the sulfonylurea receptor and that subtle changes in the pharmacophore itself could switch functional properties from KATP channel activation to inhibition.