Abstract
Iron is a critical nutrient for DNA synthesis and cellular proliferation. Targeting iron in cancer cells using specific chelators is a potential new strategy for the development of novel anticancer agents. One such chelator, 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), possesses potent and selective anticancer activity (J Med Chem 50:3716–3729, 2007). To elucidate the mechanisms of its potent antitumor activity, Bp4eT was labeled with 14C. Its efficacy was then compared with the 14C-labeled iron chelator pyridoxal isonicotinoyl hydrazone (PIH), which exhibits low anticancer activity. The ability of these ligands to permeate the cell membrane and their cellular retention was examined under various conditions using SK-N-MC neuroepithelioma cells. The rate of [14C]PIH uptake into cells was significantly (p < 0.001) lower than that of [14C]Bp4eT at 37°C, indicating that the increased hydrophilicity of [14C]PIH reduced membrane permeability. In contrast, the efflux of [14C]PIH was significantly (p < 0.05) higher than that of [14C]Bp4eT, leading to increased cellular retention of [14C]Bp4eT. In addition, the uptake and release of the 14C-labeled chelators was not reduced by metabolic inhibitors, indicating that these processes were energy-independent. No significant differences were evident in the uptake of [14C]Bp4eT at 37 or 4°C, demonstrating a temperature-independent mechanism. Furthermore, adjusting the pH of the culture medium to model the tumor microenvironment did not affect [14C]Bp4eT membrane transport. It can be concluded that [14C]Bp4eT more effectively permeated the cell membrane and evaded rapid efflux in contrast to [14C]PIH. This property, in part, accounts for the more potent anticancer activity of Bp4eT relative to PIH.
Footnotes
This work was supported by the National Health and Medical Research Council of Australia [Grant 570952]; the Australian Research Council [Discovery Grant DP0773027]; and by the Cancer Institute New South Wales [Early Career Development Fellowships 07/ECF/1-19, 08/ECF/1-30].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.066126.
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ABBREVIATIONS:
- RR
- ribonucleotide reductase
- 2,4-DNP
- 2,4-dinitrophenol
- BpT
- 2-benzoylpyridine thiosemicarbazone
- Bp4eT
- 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone
- DFO
- desferrioxamine
- DMEM + GLU
- Dulbecco's modified Eagle's medium with glucose
- DMEM − GLU
- Dulbecco's modified Eagle's medium without glucose
- HUVEC
- human umbilical vein endothelial cells
- MES
- 4-morpholine ethanesulfonic acid
- PIH
- pyridoxal isonicotinoyl hydrazone
- ROS
- reactive oxygen species
- Tf
- transferrin
- MEM
- minimal essential medium
- PBS
- phosphate-buffered saline
- ANOVA
- analysis of variance.
- Received May 26, 2010.
- Accepted July 6, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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