Design and SAR of novel potassium channel openers targeted for urge urinary incontinence. 2. Selective and potent benzylamino cyclobutenediones.

A novel series of benzylamine, potassium channel openers (KCOs) is presented as part of our program toward designing new, bladder-selective compounds for the treatment of urge urinary incontinence (UUI). We have found that the in vitro potency of (R)-4-[3,4-dioxo-2-(1,2, 2-trimethyl-propylamino)-cyclobut-1-enylamino]-3-ethyl-benzo nitrile 1 in the relaxation of precontracted rat detrusor strips can also be obtained with cyanobenzylamine derivative 4 (IC(50) = 0.29 microM) (Figure 3). Addition of a 2-Cl substituted benzylamine moiety and changing the alkylamino substituent of 4 to a t-Bu amine gives 31 (IC(50) = 0.14 microM)-a compound with similar in vitro potency as 4 as well as relaxant activity on bladder smooth muscle in vivo when administered orally (31, ED(50) = 3 mg/kg) in a rodent model of bladder instability. Further modifications, particularly the replacement of the t-Bu amino substituent with a tert-amylamine, gave a similarly active compound 60 (IC(50) = 0.10 microM) which shows excellent in vivo efficacy (ED(50) = 0.6 mg/kg). Moreover, 60, 3-(2,4-dichloro-6-methyl-benzylamino)-4-(1, 1-dimethyl-propylamino)-cyclobut-3-ene-1,2-dione (WAY-151616), shows excellent tissue selectivity for bladder K channels over arterial tissue (60, MAP ED(20) = 100 mg/kg; selectivity: MAP ED(20)/bladder ED(50) = 166). Other manipulations of the benzylamino cyclobutenediones, acylation of the benzylamine, conversion of the benzylamine substituent to a benzamide, homologation of the benzylamine to a phenethylamine, and incorporation of a methyl group at the benzyl carbon, all led to substantial loss of in vitro activity, although some in vivo activity was maintained in the acylated analogues. Compound 60 represents an attractive candidate for development in the treatment of UUI.

Design and SAR of novel potassium channel openers targeted for urge urinary incontinence. 1. N-Cyanoguanidine bioisosteres possessing in vivo bladder selectivity.

A structurally novel series of adenosine 5'-triphosphate-sensitive potassium (K(ATP)) channel openers is described. As part of our efforts directed toward identifying novel, bladder-selective potassium channel openers (KCOs) targeted for urge urinary incontinence (UUI), we found that bioisosteric replacement of the N-cyanoguanidine moiety of pinacidil (1, Figure 1) with a diaminocyclobutenedione template afforded squaric acid analogue 2, the prototype of a novel series of K(ATP) channel openers with unique selectivity for bladder smooth muscle in vivo. Further modification of the heterocyclic ring to give substituted aryl derivatives (3) afforded potent KCOs that possessed the desired detrusor selectivity when administered orally. The effects of these potassium channel agonists on bladder contractile function was studied in vitro using isolated rat detrusor strips. Potent relaxants were evaluated in vivo in a rat model of bladder instability. Lead compounds were evaluated concomitantly in normotensive rats for their effects on mean arterial blood pressure (MAP) and heart rate as a measure of in vivo bladder selectivity. (R)-4-[3,4-Dioxo-2-(1,2, 2-trimethyl-propylamino)-cyclobut-1-enylamino]-3-ethyl-benzo nitrile (79) met our potency and selectivity criteria and represents an attractive development candidate for the treatment of UUI. Electrophysiological studies using isolated rat bladder detrusor myocytes have demonstrated that compound 79 produces significant hyperpolarization which is glyburide-reversed, thus consistent with the activation of K(ATP). The design, synthesis, structure-activity relationships (SAR), and pharmacological activity associated with this series of novel KCOs will be discussed.

Comparison of the potassium channel openers, WAY-133537, ZD6169, and celikalim on isolated bladder tissue and In vivo bladder instability in rat.

The effects of the ATP-dependent potassium channel agonists ZD6169, celikalim, and WAY-133537 on bladder contractile function were examined in vitro on isolated bladder strips and in vivo on spontaneous bladder contractions. All three compounds produced a concentration-dependent relaxation of isolated rat detrusor strips (IC50 values = 0.93, 0.03, and 0.09 microM, respectively for ZD6169, celikalim, and WAY-133537. Contractile inhibition by all three compounds was fully reversed by 6 microM glyburide. These compounds also effectively inhibited spontaneous bladder contractions in the rat hypertrophied bladder model of detrusor instability. We also examined the electrophysiological properties of WAY-133537 on isolated rat bladder detrusor myocytes. Myocytes had an average resting membrane potential of -40 mV. Under patch current-clamp conditions, WAY-133537 (0.3 and 1.0 microM, n = 4-5) produced a significant hyperpolarization of 21 and 26 mV, respectively. Hyperpolarization was reversed by the addition of 5 microM glyburide. In patch voltage-clamp studies, WAY-133537 (0.3 microM, n = 3) significantly increased outward current in response to both voltage step and ramp protocols consistent with activation of the ATP-dependent potassium channel. In the detrusor instability model, WAY-133537 and celikalim had similar oral potencies (ED50 = 0.13 and 0.3 mg/kg, respectively), whereas ZD6169 was less potent (ED50 = 2.4 mg/kg). The antihypertensive agent celikalim exerted effects on the bladder at doses that significantly reduced systemic blood pressure. In contrast, both WAY-133537 and ZD6169 inhibited bladder hyperactivity at doses that produced minimal changes in both mean arterial blood pressure and heart rate. These data suggest that both WAY-133537 and ZD6169 may be useful in the treatment of bladder instability at doses associated with minimal hemodynamic side effects.

Antihypertensive and hypotensive actions of atiprosin (AY-28,228) in rats, dogs, and monkeys.

Atiprosin, a chemically novel octahydro-pyrazino-pyrido-indole, exerts antihypertensive effects in spontaneously hypertensive, deoxycorticosterone acetate hypertensive, and renal-hypertensive rats over a dose range of 0.1-10 mg/kg per os (p.o.). In terms of relative potency, atiprosin was calculated to be seven to fifteen times less potent than prazosin, five to sixteen times more potent than ketanserin, and 14-25 times more potent than indoramin, depending on the hypertensive model examined. Atiprosin had good oral bioavailability (p.o./i.v. ratio = 1.25), and there was no evidence from rat studies for tolerance on repeated administration. The compound also exerted hypotensive effects in normotensive rats and monkeys at 1-10 mg/kg p.o.; in neither species was there evidence of drug-induced tachycardia. Experiments in anesthetized dogs suggest that atiprosin may be similar to prazosin with respect to its liability to produce orthostatic hypotension as a side effect.

Indole-phenol bioisosterism. Synthesis and antihypertensive activity of a pyrrolo analogue of labetalol.

The synthesis of 5-[hydroxy-2-[(1-methyl-3-phenylpropyl)amino]ethyl]-1H-indole-7- carboxamide, 5, a pyrrolo analogue of labetalol, is described. Compound 5 was found to reduce blood pressure in spontaneously hypertensive rats with an ED50 of 5 mg/kg po, without causing any decrease in heart rate. Isolated tissue studies with 5 shows that it is a nonselective beta-adrenoceptor antagonist and that it is a weaker alpha-adrenoceptor antagonist with a relative selectivity for alpha 1-receptors. Additionally, the compound displayed significant beta-adrenoceptor intrinsic sympathomimetic activity. Evidence is presented that the beta-adrenoceptor antagonist and agonist properties of 5 are mediated via hydrogen-bond formation with the receptor.

In vitro studies on cetamolol, a new potent cardioselective beta-adrenoceptor blocking agent with intrinsic sympathomimetic activity.

In vitro studies on the new beta-adrenoceptor antagonist, cetamolol (Betacor), have demonstrated that the compound is a potent antagonist of the chronotropic effects of isoproterenol on guinea pig atria. The pA2 value (8.05) of cetamolol was slightly lower than that of propranolol (8.44). The compound was shown to possess a moderate degree of cardioselectivity as indicated by a lower pA2 value for the antagonism of isoproterenol-induced relaxation of the isolated guinea pig trachea (pA2 = 7.67) compared with that derived from atrial experiments (pA2 = 8.05). Up to concentrations of 10(-4) M, cetamolol displayed negligible negative inotropic activity relative to propranolol in the electrically stimulated guinea pig left atrial preparation. When applied to isolated right atria from reserpinized rats, cetamolol had a positive chronotropic effect (approximately 75% of that displayed by practolol) which was antagonized by pretreatment with propranolol, thus indicating intrinsic sympathomimetic activity. Specificity experiments in a number of isolated tissues indicated that cetamolol had very little antihistaminic, anticholinergic, alpha 1-adrenergic blocking, or calcium antagonistic properties. Biochemical receptor binding studies are in general agreement with the observations from the isolated tissue experiments.