2-substituted indazolinones: orally active and selective 5-lipoxygenase inhibitors with anti-inflammatory activity

1. This paper describes the pharmacological profile of ICI207968, a novel, orally-active and selective inhibitor of 5-lipoxygenase. 2. Inhibition of leukotriene B4 (LTB4) synthesis by 2-substituted indazolinones was not directly related to redox potential but was critically dependent on the nature of the N2 substituent. 2-(3-Pyridylmethyl)-indazolinone (ICI207968) combined selectivity and oral potency. 3. In several in vitro systems ICI207968 exhibited similar lipoxygenase inhibitory potency (IC50 values from 1.5 microM to 6.0 microM) and was approximately 300 times less potent against cyclo-oxygenase, as measured by inhibition of prostaglandin E2 (PGE2) synthesis. 4. ICI207968 also produced selective lipoxygenase inhibition following oral administration in the rat. ED50 values of 2.5, 10 and 25 mg kg-1 p.o. for inhibition of LTB4 release from A23187-stimulated blood were obtained 1, 3 and 5 h after dosing. The compound did not inhibit PGE2 synthesis at oral doses up to 300 mg kg-1. 5. Co-administration of ICI207968 with arachidonic acid, into rabbit dermis, potently inhibited both plasma extravasation and polymorphonuclear leucocyte (PMNL) infiltration induced by this inflammatory fatty acid. The anti-inflammatory potency of a number of intradermally administered indazolinones, with similar redox potentials, was related to their inhibitory potency against leukotriene generation in blood. Oral administration of ICI207968 (100 mg kg-1) in the rabbit inhibited ex vivo leukotriene generation in blood and arachidonic acid-induced skin inflammation. 6. These data demonstrate that ICI207968 is an orally active and selective inhibitor of 5-lipoxygenase which has anti-inflammatory properties. IC1207968 will be a valuable agent for clarifying the biological roles of leukotrienes and the therapeutic potential of 5-lipoxygenase inhibitors.