INCORPORATION OF BISPHOSPHONATES INTO ADENINE-NUCLEOTIDES BY AMEBAS OF THE CELLULAR SLIME-MOLD DICTYOSTELIUM-DISCOIDEUM

Bisphosphonates are a class of synthetic pyrophosphate analogues. Some are known to be potent inhibitors of osteoclast-mediated bone resorpt ion ir? vivo, but their mechanisms of action are unclear. The order of potency of bisphosphonates as inhibitors of bone resorption closely m atches the order of potency as inhibitors of growth of amoebae of the slime mould Dictyostelium discoideum, indicating that bisphosphonates may have a mechanism of action that is similar in both osteoclasts and Dictyostelium, Methylenebisphosphonate and several halogenated deriva tives, which have low potency as antiresorptive agents and as growth i nhibitors of Dictyostelium, are metabolized intracellularly by Dictyos telium amoebae into methylene-containing adenine nucleotides. We have used a combination of n.m.r. and f.p.l.c. analysis to determine whethe r incorporation into nucleotides is a feature of other bisphosphonates , especially those that are potent antiresorptive agents. Only bisphos phonates with short side chains or of low potency are incorporated int o adenine nucleotides, whereas those with long side chains or of high potency are not metabolized. Bisphosphonate metabolism in cell-free ex tracts of Dictyostelium was accompanied by inhibition of aminoacylatio n of tRNA by several aminoacyl-tRNA synthetases. These enzymes were ba rely affected by the bisphosphonates that were not metabolized. The re sults indicate that some bisphosphonates are not metabolically inert a nalogues of pyrophosphate and appear to be metabolized by aminoacyl-tR NA synthetases. The cellular effects of some bisphosphonates may be th e result of their incorporation into adenine nucleotides or inhibition of aminoacyl-tRNA synthetases, although the potent bisphosphonates ap pear to act by a different mechanism.