Search

Structure-activity relationships were investigated on the tricyclic dihydropyridine (DHP) KATP openers 9-(3-bromo-4-fluorophenyl)-5,9-dihydro-3H,4H-2,6-dioxa-4-azacyclopenta[b]naphthalene-1,8-dione (6) and 10-(3-bromo-4-fluorophenyl)-9,10-dihydro-1H,8H-2,7-dioxa-9-azaanthracene-4,5-dione (65). Substitution off the core of the DHP, absolute stereochemistry, and aromatic substitution were evaluated for KATP channel activity using Ltk- cells stably transfected with the Kir6.2/SUR2B exon 17- splice variant and in an electrically stimulated pig bladder strip assay. A select group of compounds was evaluated for in vitro inhibition of spontaneous bladder contractions. Several compounds were found to have the unique characteristic of partial efficacy in both the cell-based and electrically stimulated bladder strip assays but full efficacy in inhibiting spontaneous bladder strip contractions. For compound 23b, this profile was mirrored in vivo where it was fully efficacious in inhibiting spontaneous myogenic bladder contractions but only partially able to reduce neurogenically mediated reflex bladder contractions.

The pharmacological profile of the novel dihydropyridine K channel opener (KCO), (9R)-9-(3-iodo-4-methylphenyl)-5,9-dihydro-3H-furo[3,4-b]pyrano[4,3-e]pyridine-1,8(4H,7H)-dione (A-325100), is described in numerous in vitro assays. Furthermore, the cardiovascular effects of A-325100 are characterized in both the anesthetized and conscious dog. In vitro, A-325100 selectively activated KATP currents and potently relaxed vascular smooth muscle (IC50 between 7.69x10 M and 7.78x10 M), an effect that was abolished by glyburide. Moreover, A-325100 did not interact with L-type Ca2+ channels at concentrations up to 30 microM. In anesthetized dogs A-325100 produced a dose-dependent reduction in systemic vascular resistance and mean arterial pressure concomitant with dose-dependent increases in dP/dtmax and heart rate. In conscious telemetry-instrumented dogs oral administration of A-325100 produced a similar response profile, including dose-dependent reductions in MAP and increases in heart rate and dP/dtmax. When concentration-dependent changes in MAP, heart rate, and dP/dtmax were compared relative to circulating plasma concentrations, A-325100 produced similar effects in both the anesthetized and conscious dog. In conclusion, the present study provides the first pharmacological description of the novel and selective tricyclic dihydropyridine KCO, A-325100. When studied in vivo, A-325100 produced similar concentration-dependent cardiovascular effects in both models consistent with its mode of action and independent of route of administration. Thus, these data demonstrate that the hemodynamic effects of vasoactive compounds, such as KCOs, can be effectively profiled in both the conscious and anesthetized dog.

Structure-activity relationships were investigated on a novel series of tricyclic dihydropyridine-containing K(ATP) openers. This diverse group of analogues, comprising a variety of heterocyclic rings fused to the dihydropyridine nucleus, was designed to determine the influence on activity of hydrogen-bond-donating and -accepting groups and their stereochemical disposition. Compounds were evaluated for K(ATP) activity in guinea pig bladder cells using a fluorescence-based membrane potential assay and in a pig bladder strip assay. The inhibition of spontaneous bladder contractions in vitro was also examined for a subset of compounds. All compounds studied showed greater potency to inhibit spontaneous bladder contractions relative to their potencies to inhibit contractions elicited by electrical stimulation.

1. 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. 2. 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 IC(50) values of 1.44 and 2.24 micro M respectively. 3. P1075-evoked relaxation of 25 mM K(+) stimulated aortic strips was inhibited by A-184209 in an apparently competitive fashion with a pA(2) value of 6.34. 4. The potencies of A-184209 to inhibit P1075-evoked decreases in membrane potential responses in cardiac myocytes (IC(50)=0.53 micro M) and to inhibit 2-deoxyglucose-evoked cation efflux pancreatic RINm5F cells (IC(50)=0.52 micro M) were comparable to the values for inhibition of smooth muscle K(ATP) channels. 5. 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 K(ATP) channel opener, evoking membrane potential responses in A10 smooth muscle cells (EC(50)=385 nM) and relaxing aortic smooth muscle strips (IC(50)=101 nM) in a glyburide-sensitive manner. 6. Radioligand binding studies demonstrated that A-184209 displaced SUR1 binding defined by [(3)H]glyburide binding to RINm5F cell membranes with a K(i) value of 0.11 micro M whereas A-184208 was ineffective. On the other hand, both A-184209 (K(i)=1.34 micro M) and A-184208 (K(i)=1.14 micro M) displaced binding of the KCO radioligand, [(125)I]A-312110 in guinea-pig bladder membranes with similar affinities. 7. These studies demonstrate that A-184209 is a novel and structurally distinct compound that inhibits K(ATP) 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 K(ATP) channel activation to inhibition.