HETEROCYCLE-CONTAINING BISPHOSPHONATES CAUSE APOPTOSIS AND INHIBIT BONE-RESORPTION BY PREVENTING PROTEIN PRENYLATION - EVIDENCE FROM STRUCTURE-ACTIVITY-RELATIONSHIPS IN J774 MACROPHAGES

Recent evidence suggests that bisphosphonates (BPs) may inhibit bone r esorption by mechanisms that lead to osteoclast apoptosis, We have pre viously shown that BPs also reduce cell viability and induce apoptosis in the macrophage-like cell line J774, To determine whether BPs inhib it osteoclast-mediated bone resorption and affect J774 macrophages by the same molecular mechanism, we examined the potency to reduce J774 c ell viability of pairs of nitrogen-containing BPs that differ slightly in the structure of the heterocycle-containing side chain but that di ffer markedly in antiresorptive potency. In all cases, the most potent antiresorptive BP of each pair also caused the greatest loss of J774 viability, while the less potent antiresorptive BPs were also less pot ent at reducing J774 cell viability. Similarly, the bisphosphinate, ph osphonoalkylphosphinate and monophosphonate analogs of BPs (in which o ne or both phosphonate groups are modified, giving rise to much less p otent or inactive antiresorptive agents) were much less potent or inac tive at reducing J774 cell viability, Thus, the structure-activity rel ationships of BPs for inhibiting bone resorption match those for causi ng loss of cell viability in J774 cells, indicating that BPs inhibit o steoclast-mediated bone resorption and reduce J774 macrophage viabilit y by the same molecular mechanism, Loss of J774 cell viability after t reatment with BPs was associated with a parallel increase in apoptotic cell death, We have recently proposed that nitrogen-containing BPs re duce cell viability and cause J774 apoptosis as a consequence of inhib ition of enzymes of the mevalonate pathway and hence loss of prenylate d proteins. In this study, the BPs that were potent inducers of J774 a poptosis and potent antiresorptive agents were also found to be effect ive inhibitors of protein prenylation in J774 macrophages, whereas the less potent BP analogs did not inhibit protein prenylation, This prov ides strong evidence that BPs with a heterocyclic, nitrogen-containing side chain, such as risedronate, inhibit osteoclast-mediated bone res orption and induce J774 apoptosis by preventing protein prenylation.