Disposition and metabolism of Ro 24-4736 in the rat

Ro 24-4736, a new platelet activating factor antagonist, is currently under preclinical and clinical development. The tissue distribution of the 14C-label in male rats following a single intravenous dose of 1.0 mg/kg of 14C-Ro 24-4736 indicated appreciable uptake by the liver, kidney, heart and gastrointestinal tract. Peak plasma and tissue concentrations were seen at 5 minutes after dosing except for the small intestine (4 hrs) and abdominal fat, stomach and large intestine (4 hrs). Thereafter, the 14C-label rapidly declined in all tissues. At 48 hours, only 3.5% of the dose was present in the tissues, and 6.1% in the lumen of the gastrointestinal tracts. The excretion of 14C was essentially completed; 94% of the administered 14C was excreted in the feces and 4.0% in the urine. Overall recoveries of the administered 14C label ranged from 96 to 116%. The purified major 14C-labelled component in the fecal extracts yielded essentially the same NMR spectrum as authentic Ro 24-4736 which accounted for 11% of the dose. In vitro incubations of Ro 24-4736 with rat liver 9S supernatant in an NADPH generating system produced two metabolites. NMR spectra indicated that one metabolite was hydroxylated at carbon-1 while the other one contained a hydroxyl at carbon-10 of the parent molecule. Interestingly, the sites of hydroxylation were at carbons C 1, and C 10 bearing the protons guarding the bay area of the phenanthrenoid ring, rather than carbons of the phenyl-methyl-thienotriazolodiazepine moiety.