Farnesyl pyrophosphate synthase is the molecular target of nitrogen-containing bisphosphonates

Bisphosphonates (Bps), inhibitors of osteoclastic bone resorption, are used in the treatment of skeletal disorders. Recent evidence indicated that far nesyl pyrophosphate (FPP) synthase and/or isopentenyl pyrophosphate (IPP) i somerase is the intracellular target(s) of bisphosphonate action. To examin e which enzyme is specifically affected, we determined the effect of differ ent Bps on incorporation of [C-14]mevalonate(MVA), [C-14]IPP, and [C-14]dim ethylallyl pyrophosphate (DMAPP) into polyisoprenyl pyrophosphates in a hom ogenate of bovine brain. HPLC analysis revealed that the three intermediate s were incorporated into FPP and geranylgeranyl pyrophosphate (GGPP). In co ntrast to clodronate, the nitrogen-containing Bps (NBps), alendronate, rise dronate, olpadronate, and ibandronate, completely blocked FPP and GGPP form ation and induced in incubations with [C-14]MVA a 3- to 5-fold increase in incorporation of label into IPP and/or DMAPP. Using a method that could dis tinguish DMAPP from IPP on basis of their difference in stability in acid, we found that none of the NBps affected the conversion of [C-14]TPP into DM APP, catalyzed by IPP isomerase, excluding this enzyme as target of NBp act ion. On the basis of these and our previous findings, we conclude that none of the enzymes up- or downstream of FPP synthase are affected by NBps, and FPP synthase is, therefore, the exclusive molecular target of NBp action. (C) 1999 Academic Press.