Effect of Potent Urease Inhibitor, Fluorofamide, on Helicobacter sp. in Vivo and in Vitro

Abstract

The therapeutic potential of urease inhibitionof Helicobacter pylori has been studied by examining theeffect of the potent urease inhibitor, fluorofamide(N-(diaminophosphinyl)-4-fluorobenzenamide), on urease activity and bacterial survival invivo and in vitro. In culture, acid protection in H.pylori was shown to be due to changes in the pH of themedium brought about by the release of ammonia. Both the acid protection and the ammoniarelease were completely blocked by fluorofamide at lowdoses (ED₅₀ = ~100 nM). However, fluorofamidewas unstable under acidic conditions (T_1/25.7 min at pH 2). Despite this, fluorofamide was the best availablecompound to test in vivo. In ferrets naturally infectedwith H. mustelae, a single dose (50 mg/kg, per os ) offluorofamide completely inhibited bacterial urease. In repeat dosing studies, fluorofamide(50 mg/kg per os, three times a day) was compared withthe Helicobacter triple therapy regime (amoxycillin,metronidazole, and bismuth subcitrate). Fluorofamide failed to eradicate the H. mustelae infection,compared to 80% eradication with triple therapy.However, histological samples showed a profoundreduction in bacterial numbers following fluorofamidetreatment. A combination of fluorofamide and amoxycillinwas dosed to ferrets (seven days of treatment with 50mg/kg fluorofamide plus 10 mg/kg amoxycillin per ostwice a day); however, this failed to eradicate the infection, despite there being a reduction inbacterial numbers in 3/5 ferrets after 21 days afterdosing stopped. It was concluded that urease inhibitors(either alone or in combination with antibiotics) are unlikely to have therapeutic potential forHelicobacter pylori infections. This is probablybecause, in vivo, some bacteria (perhaps dormant forms)are not entirely dependent upon urease for survival. However, given the acid instability offluorofamide, the possibility that more stable ureaseinhibitors might have therapeutic potential, cannot beexcluded.