title: The gunmetal mouse reveals Rab geranylgeranyl transferase to be the major molecular target of phosphonocarboxylate analogues of bisphosphonates.
abstract: The described ability of phosphonocarboxylate analogues of bisphosphonates (BPs) to inhibit Rab geranylgeranyl transferase (RGGT) is thought to be the mechanism underlying their cellular effects, including their ability to reduce macrophage cell viability and to inhibit osteoclast-mediated resorption. However, until now the possibility that at least some of the effects of these drugs may be mediated through other targets has not been excluded. Since RGGT is the most distal enzyme in the process of Rab prenylation, it has not proved possible to confirm the mechanism underlying the effects of these drugs by adding back downstream intermediates of the mevalonate pathway, the approach used to demonstrate that bisphosphonates act through this pathway. We now confirm that RGGT is the major pharmacological target of phosphonocarboxylates by using several alternative approaches. Firstly, analysis of several different phosphonocarboxylate drugs demonstrates a very good correlation between the ability of these drugs to inhibit RGGT with their ability to: (a) reduce macrophage cell viability; (b) induce apoptosis; and (c) induce vacuolation in rabbit osteoclasts. Secondly, we have found that cells from the gunmetal (gm/gm) mouse, which bear a homozygous mutation in RGGT that results in ~80% reduced activity of this enzyme compared to wild-type or heterozygous mice, are more sensitive to the effects of active phosphonocarboxylates (including reducing macrophage cell viability, inhibiting osteoclast formation and inhibiting fluid-phase endocytosis), confirming that these effects are mediated through inhibition of RGGT. In conclusion, these data demonstrate that all of the pharmacological effects of phosphonocarboxylates found thus far appear to be mediated through the specific inhibition of RGGT, highlighting the potential therapeutic value of this class of drugs.
authors.affiliation: Musculoskeletal Programme, Division of Applied Medicine, Institute of Medical Sciences, University of Aberdeen, Foresterhill, UK. f.p.coxon@abdn.ac.uk
authors.forename: Fraser P
authors.initials: FP
authors.lastname: Coxon
authors.forename: Adam
authors.initials: A
authors.lastname: Taylor
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Stewart
authors.forename: Rudi
authors.initials: R
authors.lastname: Baron
authors.forename: Miguel C
authors.initials: MC
authors.lastname: Seabra
authors.forename: F Hal
authors.initials: FH
authors.lastname: Ebetino
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rogers
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002452:Cell Count; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004164:Diphosphonates / Q000378:metabolism* / Q000494:pharmacology*; D004224:Diterpenes / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006579:Heterozygote; D008264:Macrophages / Q000187:drug effects / Q000201:enzymology; D051379:Mice; D008815:Mice, Inbred Strains; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology; D010010:Osteoclasts / Q000187:drug effects / Q000201:enzymology; D017368:Protein Prenylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism
chemical_list: C410028:2-(3-pyridinyl)-1-hydroxyethylidene-1,1-phosphonocarboxylic acid; D004164:Diphosphonates; D004224:Diterpenes; D004791:Enzyme Inhibitors; D011725:Pyridines; C017338:geranylgeraniol; D019883:Alkyl and Aryl Transferases; C075607:Rab geranylgeranyltransferase