Inhibition of growth of Dictyostelium discoideum amoebae by bisphosphonate drugs is dependent on cellular uptake.
OBJECTIVE
The aim of the study was to determine whether bisphosphonates are internalised by Dictyostelium amoebae and whether cellular uptake is required for their growth-inhibitory effects. Bisphosphonates inhibit growth of amoebae of the slime mould Dictyostelium discoideum, by mechanisms that appear to be similar to those that cause inhibition of osteoclastic bone resorption.


METHODS
Cell-free extracts prepared from amoebae that had been incubated with bisphosphonates were analysed by 31P-n.m.r, spectroscopy or ion-exchange f.p.l.c., to identify the presence of bisphosphonates or bisphosphonate metabolites respectively. The growth-inhibitory effect of bisphosphonates towards Dictyostelium amoebae was also examined under conditions in which pinocytosis was inhibited.


RESULTS
All of the bisphosphonates studied were internalised by Dictyostelium amoebae, probably by fluid-phase pinocytosis, and could be detected in cell-free extracts. Amoebae that were prevented from internalising bisphosphonates by pinocytosis were markedly resistant to the growth-inhibitory effects of these compounds. In addition, bisphosphonates encapsulated within liposomes were more potent growth inhibitors of Dictyostelium owing to enhanced intracellular delivery of bisphosphonates.


CONCLUSIONS
All bisphosphonates inhibit Dictyostelium growth by intracellular mechanisms following internalisation of bisphosphonates by fluid-phase pinocytosis. It is therefore likely that bisphosphonates also affect osteoclasts by interacting with intracellular, rather than extracellular, processes.
Rogers
M J
MJ
Department of Human Metabolism and Clinical Biochemistry, University of Sheffield Medical School, UK. m.j.rogers@sheffield.ac.uk
Xiong
X
X
Ji
X
X
Mönkkönen
J
J
Russell
R G
RG
Williamson
M P
MP
Ebetino
F H
FH
Watts
D J
DJ
D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D000935:Antifungal Agents / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D002852:Chromatography, Ion Exchange; D004023:Dictyostelium / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D004164:Diphosphonates / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D004337:Drug Carriers; D004339:Drug Compounding; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy
D000227:Adenine Nucleotides; D000935:Antifungal Agents; D004164:Diphosphonates; D004337:Drug Carriers; D008081:Liposomes