Clodronate and Liposome‐Encapsulated Clodronate Are Metabolized to a Toxic ATP Analog, Adenosine 5′‐(β,γ‐Dichloromethylene) Triphosphate, by Mammalian Cells In Vitro

• Published in: Journal of bone and mineral research Vol. 12; no. 9; pp. 1358 - 1367
• Main Authors: Frith, Julie C., Mönkkönen, Jukka, Blackburn, G. Michael, Russell, R. Graham G., Rogers, Michael J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Washington, DC John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR) 01.09.1997; American Society for Bone and Mineral Research
• Subjects: Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - metabolism; Adenosine Triphosphate - toxicity; Alendronate - metabolism; Alendronate - pharmacology; Analgesics, Non-Narcotic - administration & dosage; Analgesics, Non-Narcotic - metabolism; Analgesics, Non-Narcotic - pharmacology; Apoptosis - drug effects; Biological and medical sciences; Bones, joints and connective tissue. Antiinflammatory agents; Cell Survival - drug effects; Cells, Cultured; Clodronic Acid - administration & dosage; Clodronic Acid - metabolism; Clodronic Acid - pharmacology; Diphosphonates - pharmacology; Humans; Liposomes; Medical sciences; Microscopy, Fluorescence; Pharmacology. Drug treatments; Human; Toxicity; Rodentia; Metabolism; Bisphosphonates; Clodronic acid; Vertebrata; Cell line; Mammalia; Mouse; Cell death; Osteosarcoma; Analog; Mechanism of action; ATP; Tumor cell; Macrophage
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.1997.12.9.1358

Clodronate, alendronate, and other bisphosphonates are widely used in the treatment of bone diseases characterized by excessive osteoclastic bone resorption. The exact mechanisms of action of bisphosphonates have not been identified but may involve a toxic effect on mature osteoclasts due to the induction of apoptosis. Clodronate encapsulated in liposomes is also toxic to macrophages in vivo and may therefore be of use in the treatment of inflammatory diseases. It is generally believed that bisphosphonates are not metabolized. However, we have found that mammalian cells in vitro (murine J774 macrophage‐like cells and human MG63 osteosarcoma cells) can metabolize clodronate (dichloromethylenebisphosphonate) to a nonhydrolyzable adenosine triphosphate (ATP) analog, adenosine 5′‐(β,γ‐dichloromethylene) triphosphate, which could be detected in cell extracts by using fast protein liquid chromatography. J774 cells could also metabolize liposome‐encapsulated clodronate to the same ATP analog. Liposome‐encapsulated adenosine 5′‐(β,γ‐dichloromethylene) triphosphate was more potent than liposome‐encapsulated clodronate at reducing the viability of cultures of J774 cells and caused both necrotic and apoptotic cell death. Neither alendronate nor liposome‐encapsulated alendronate were metabolized. These results demonstrate that the toxic effect of clodronate on J774 macrophages, and probably on osteoclasts, is due to the metabolism of clodronate to a nonhydrolyzable ATP analog. Alendronate appears to act by a different mechanism.