Zoledronic acid induces formation of a pro-apoptotic ATP analogue and isopentenyl pyrophosphate in osteoclasts in vivo and in MCF-7 cells in vitro

Johanna Raikkonen, Julie C Crockett, Michael J Rogers, Hannu Monkkonen, Seppo Auriola, Jukka Monkkonen

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Bisphosphonates (BPs) are highly effective inhibitors of bone resorption. Nitrogen-containing bisphosphonates (N-BPs), such as zoledronic acid, induce the formation of a novel ATP analogue (1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester triphosphoric acid; ApppI), as a consequence of the inhibition of farnesyl pyrophosphate synthase and the accumulation of isopentenyl pyrophosphate (IPP). ApppI induces apoptosis, as do comparable metabolites of non-nitrogen-containing bisphosphonates (non-N-BPs). In order to further evaluate a pharmacological role for ApppI, we obtained more detailed data on IPP/ApppI formation in vivo and in vitro. Additionally, zoledronic acid-induced ApppI formation from IPP was compared with the metabolism of clodronate (a non-N-BP) to adenosine 5'(beta,gamma-dichloromethylene) triphosphate (AppCCl(2)p).

After giving zoledronic acid in vivo to rabbits, IPP/ApppI formation and accumulation was assessed in isolated osteoclasts. The formation of ApppI from IPP was compared with the metabolism of clodronate in MCF-7 cells in vitro. IPP/ApppI and AppCCl(2)p levels in cell extracts were analysed by mass spectrometry.

Isopentenyl pyrophosphate/ApppI were formed in osteoclasts in vivo, after a single, clinically relevant dose of zoledronic acid. Furthermore, exposure of MCF-7 cells in vitro to zoledronic acid at varying times and concentrations induced time- and dose-dependent accumulation of IPP/ApppI. One hour pulse treatment was sufficient to cause IPP accumulation and subsequent ApppI formation, or the metabolism of clodronate into AppCCl(2)p.

This study provided the first conclusive evidence that pro-apoptotic ApppI is a biologically significant molecule, and demonstrated that IPP/ApppI analysis is a sensitive tool for investigating pathways involved in BP action.

Original languageEnglish
Pages (from-to)427-435
Number of pages9
JournalBritish Journal of Pharmacology
Issue number3
Early online date3 Apr 2009
Publication statusPublished - Jun 2009


  • AppCCl(2)p
  • ApppI
  • bisphosphonate
  • cellular uptake
  • clodronate
  • IPP
  • osteoclast
  • zoledronic acid
  • nitrogen-containing bisphosphonates
  • HMG-COA reductase
  • bone-resorption
  • breast-cancer
  • inhibition
  • prenylation
  • mechanism
  • drugs
  • localization

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