Vasorelaxant and antiplatelet activity of 4,7‐dimethyl‐1,2,5‐oxadiazolo[3,4‐d]pyridazine 1,5,6‐trioxide: role of soluble guanylate cyclase, nitric oxide and thiols

Abstract

1 Certain heterocyclic N-oxides are vasodilators and inhibitors of platelet aggregation. The pharmacological activity of the furoxan derivative condensed with pyridazine di-N-oxide 4,7-dimethyl-1,2,5-oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide (FPTO) and the corresponding furazan (FPDO) was studied. 2 FPTO reacted with thiols generating nitrite (NO), S-nitrosoglutathione and hydroxylamine (nitroxyl) and converted oxyHb to metHb. FPDO did not generate detectable amounts of NO-like species but reacted with thiols and oxyHb. 3 FPTO and FPDO haem-dependently stimulated the activity of soluble guanylate cyclase (sGC) and this stimulation was inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and by 0.1 mM dithiothreitol. 4 FPTO relaxed noradrenaline-precontracted aortic rings and its concentration-response curve was biphasic (pIC 50 =9.03+0.13 and 5.85+0.06). FPDO was signi®cantly less potent vasodilator (pIC 50 =5.19+0.14). The vasorelaxant activity of FPTO and FPDO was inhibited by ODQ. oxyHb signi®cantly inhibited only FPTO-dependent relaxation. 5 FPTO and FPDO were equipotent inhibitors of ADP-induced platelet aggregation (IC 50 =0.63+0.15 and 0.49+0.05 mM, respectively). The antiplatelet activity of FPTO (but not FPDO) was partially suppressed by oxyHb. The antiaggregatory eects of FPTO and FPDO were only partially blocked by sGC inhibitors. 6 FPTO and FPDO (10 ± 20 mM) signi®cantly increased cyclic GMP levels in aortic rings and platelets and this increase was blocked by ODQ. 7 Thus, FPTO can generate NO and, like FPDO, reacts with thiols and haem. The vasorelaxant activity of FPTO and FPDO is sGC-dependent and a predominant role is played by NO at FPTO concentrations below 1 mM. On the contrary, inhibition of platelet aggregation is only partially related to sGC activation.

Nitric Oxide and Cyclic GMP Signaling Pathway as a Focus for Drug Development

“…Apparently, their potency is increased in the case of electron-withdrawing substitutions (CHF 2206) [39] and upon condensation with pyridazine-di-N-oxide moiety (FPTO; Fig. 2) [40].…”

The First Synthesis of Furoxan and 1,3,4‐Oxadiazole Ring Ensembles

“…Vasodilating and antiaggregatory activity was also reported for the furoxan analog of Nefedipine . Some furoxan derivatives are potential nitric oxide donors ; various nitrofuroxans can act as propellants and explosives . 1,3,4‐Oxadiazole derivatives also display different kinds of biological activity: antibacterial, insecticidal, antifungal, analgesic, anti‐inflammatory, anti‐HIV, anticonvulsant, etc .…”

Synthesis, structural characterization and cytotoxic activity of heterocyclic compounds containing the furoxan ring

“…It is well-known that furoxans behave as NO donors in presence of thiol cofactors. 5,10,11 At the same time, the formation of nitrite-anion as a result of NO oxidation may be quantified according to Griess assay and thus may serve as a reliable tool for measuring the amount of NO release. The amounts of NO 2 -produced of the selected hetarylfuroxan structures under physiological conditions (pH 7.4; 37 °C) after 1 h incubation were measured via the Griess reaction using a spectrophotometric technique.…”

“…), [7][8][9] including the 1,2,5-oxadiazole 2-oxides (furoxans) which are capable of exogenous NO release at the presence of thiol cofactors. 10,11 Furoxans comprise a valuable class of five-membered heterocycles and can serve as a privileged motif in medicinal and pharmaceutical chemistry owing to their significant biological activities, for example neuroprotective and precognitive, 12 cytotoxic, 13,14 antihelmintic, 15 antibacterial 16 and fungicidal 17 , connected with the high capacity of furoxans to produce a large flux of NO. It was established that NO exerts a cytotoxic effect at high concentrations, while low levels of NO are potentially protective, particularly in the CNS.…”