Cellular uptake and metabolism of clodronate and its derivatives in Caco-2 cells: a possible correlation with bisphosphonate-induced gastrointestinal side-effects.
OBJECTIVE
To investigate possible reasons for the low frequency of GI side-effects of clodronate, even though clodronate is known to be metabolised into a cytotoxic nucleotide analogue (AppCCl(2)p) by many cell types. The effects of some lipophilic prodrugs of clodronate were also studied.


METHODS
The effects of clodronate and its lipophilic derivatives on the proliferation and viability of Caco-2 cells were examined using an MTT assay. The intracellular uptake of 14C-clodronate and the accumulation of a clodronate metabolite (AppCCl(2)p) in Caco-2 cells were evaluated using ion-pairing HPLC-ESI-MS.


RESULTS
Clodronate had little effect on growth of proliferating, or the viability of confluent, Caco-2 cells. The uptake of clodronate by Caco-2 cells was only about 0.04% of total clodronate. The potentially cytotoxic clodronate metabolite, AppCCl(2)p, was detected in Caco-2 cell extracts after 3 h of exposure. Dianhydride- and triPOM-clodronate were metabolised to AppCCl(2)p more efficiently and also affected the viability of Caco-2 cells more than clodronate.


CONCLUSIONS
Clodronate appears to be metabolised into a cytotoxic ATP-analogue (AppCCl(2)p) by any cell type capable of internalising the drug. However, the cytotoxicity depends on the degree of uptake of clodronate. Due to the very low initial uptake of clodronate by epithelial Caco-2 cells, they do not accumulate sufficient intracellular concentrations of AppCCl(2)p to affect cell function. This explains the low frequency of gastrointestinal side-effects caused by oral clodronate therapy.
Department of Pharmaceutics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland. hannu.monkkonen@uku.fi
Hannu
H
Mönkkönen
Soili
S
Törmälehto
Kari
K
Asunmaa
Riku
R
Niemi
Seppo
S
Auriola
Jouko
J
Vepsäläinen
Jukka
J
Mönkkönen
D000284:Administration, Oral; D018712:Analgesics, Non-Narcotic / Q000009:adverse effects / Q000378:metabolism*; D018938:Caco-2 Cells; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002463:Cell Membrane Permeability; D002470:Cell Survival / Q000187:drug effects; D004002:Clodronic Acid / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000378:metabolism*; D005767:Gastrointestinal Diseases / Q000139:chemically induced*; D006801:Humans
D018712:Analgesics, Non-Narcotic; D004002:Clodronic Acid; D002118:Calcium