Alendronate is a specific, nanomolar inhibitor of farnesyl diphosphate synthase

Alendronate, a nitrogen-containing bisphosphonate, is a potent inhibitor of bone resorption used for the treatment and prevention of osteoporosis, Rec ent findings suggest that alendronate and other N-containing bisphosphonate s inhibit the isoprenoid biosynthesis pathway and interfere with protein pr enylation, as a result of reduced geranylgeranyl diphosphate levels. This s tudy identified farnesyl disphosphate synthase as the mevalonate pathway en zyme inhibited by bisphosphonates, HPLC analysis of products from a liver c ytosolic extract narrowed the potential targets for alendronate inhibition (IC50 = 1700 nM) to isopentenyl diphosphate isomerase and farnesyl diphosph ate synthase, Recombinant human farnesyl diphosphate synthase was inhibited by alendronate with an IC50 of 460 nM (following 15 min preincubation), Al endronate did not inhibit isopentenyl diphosphate isomerase or GGPP synthas e, partially purified from liver cytosol. Recombinant farnesyl diphosphate synthase was also inhibited by pamidronate (IC50 = 500 nM) and risedronate (IC50 = 3.9 nM), negligibly by etidronate (IC50 = 80 mu M), and not at all by clodronate, In osteoclasts, alendronate inhibited the incorporation of [ H-3]mevalonolactone into proteins of 18-25 kDa and into nonsaponifiable lip ids, including sterols, These findings (i) identify farnesyl diphosphate sy nthase as the selective target of alendronate in the mevalonate pathway, (i i) show that this enzyme is inhibited by other N-containing bisphosphonates , such as risendronate, but not by clodronate, supporting a different mecha nism of action for different bisphosphonates, and (iii) document in purifie d osteoclasts alendronate inhibition of prenylation and sterol biosynthesis . (C) 2000 Academic Press.