NITROGEN-CONTAINING BISPHOSPHONATES INHIBIT THE MEVALONATE PATHWAY AND PREVENT POSTTRANSLATIONAL PRENYLATION OF GTP-BINDING PROTEINS, INCLUDING RAS

Bisphosphonates are currently the most important class of antiresorpti ve drags used for the treatment of metabolic bone diseases, Although t he molecular targets of bisphosphonates have not been identified, thes e compounds inhibit bone resorption by mechanisms that can lead to ost eoclast apoptosis, Bisphosphonates also induce apoptosis in mouse J774 macrophages in vitro, probably by the same mechanisms that lead to os teoclast apoptosis, We have found that, in J774 macrophages, nitrogen- containing bisphosphonates (such as alendronate, ibandronate, and rise dronate) inhibit post-translational modification (prenylation) of prot eins, including the GTP-binding protein Ras, with farnesyl or geranylg eranyl isoprenoid groups, Clodronate did not inhibit protein prenylati on, Mevastatin, an inhibitor of 3-hydroxy-3-methylglutatyl (HMG)-CoA r eductase and hence the biosynthetic pathway required for the productio n of farnesyl pyrophosphate and geranylgeranyl pyrophosphate, also cau sed apoptosis in J774 macrophages and murine osteoclasts in vitro, Fur thermore, alendronate-induced apoptosis, like mevastatin-induced apopt osis, could be suppressed in J774 cells by the addition of farnesyl py rophosphate or geranylgeranyl pyrophosphate, while the effect of alend ronate on osteoclast number and bone resorption in murine calvariae in vitro could be overcome by the addition of mevalonic acid, These obse rvations suggest that nitrogen-containing bisphosphonate drugs cause a poptosis following inhibition of post-translational prenylation of pro teins such as Ras, It is likely that these potent antiresorptive bisph osphonates also inhibit bone resorption by preventing protein prenylat ion in osteoclasts and that enzymes of the mevalonate pathway or preny l protein transferases are the molecular targets of the nitrogen-conta ining bisphosphonates. Furthermore, the data support the vie cv that c lodronate acts by a different mechanism.