Abstract
β-l-Dioxolane-cytidine (l-OddC, Troxacitabine, BCH-4556), a novel l-configuration deoxycytidine analog, is under clinical trials for treating cancer. The cytotoxicity of l-OddC is dependent on the amount of the triphosphate form (l-OddCTP) in nuclear DNA. Phosphoglycerate kinase (PGK), a downstream protein of hypoxia-inducible-factor-1α (HIF-1α), is responsible for the phosphorylation of the diphosphate to the triphosphate of l-OddC. In this study, we studied the impact of hypoxia on the metabolism and the cytotoxicity of l-OddC and β-d-2′,2′-difluorodeoxycytidine (dFdC) in several human tumor cell lines including HepG2, Hep3B, A673, Panc-1, and RKO. Hypoxic treatment induced the protein expression of PGK 3-fold but had no effect on the protein expression of APE-1, dCK, CMPK, and nM23 H1. Hypoxic treatment increased l-OddCTP formation and incorporation of l-OddC into DNA, but it decreased the uptake and incorporation of dFdC, which correlated with the reduction of hENT1, hENT2, and hCNT2 expression. Using a clonogenic assay, hypoxic treatment of cells made them 2- to 3-fold more susceptible to l-OddC but not to dFdC after exposure to drugs for one generation. Dimethyloxallyl glycine enhanced the cytotoxicity of l-OddC but not dFdC in Panc-1 cells under normoxic conditions. Overexpression or down-regulation of PGK using transient transfection of pcDNA5-PGK or inducible shRNA in RKO cells affected the cytotoxicity of l-OddC but not that of dFdC. The knockdown of HIF-1α in inducible shRNA in RKO cells reduced the cytotoxicity of l-OddC but not dFdC under hypoxic conditions. In conclusion, hypoxia is an important factor that may potentiate the activity of l-OddC.
Footnotes
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This work was supported by National Institutes of Health Grant No. RO1AI38204 and RO1CA63477 from the National Institutes of Health. Y.-C.C. is a fellow of the National Foundation for Cancer Research.
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Y.-C.C. is one of the inventors of l-OddC (troxacitabine) which was licensed to SGX Pharm by Yale University for the treatment of cancer. Y.-C.C. could have a financial stake in this compound.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.106.033472.
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ABBREVIATIONS:l-OddC, β-l-dioxolane-cytidine (troxacitabine); dFdC, β-d-2′,2′-difluorodeoxycytidine (gemcitabine); PGK, phosphoglycerate kinase; APE-1, apurinic/apyrimidinic endonuclease; dCK, deoxycytidine kinase; hENT, human equilibrative nucleoside transporter; hCNT, human concentrative nucleoside transporter; HRE, hypoxia response element; DMOG, dimethyloxallyl glycine; shRNA, short hairpin RNA; PBS, phosphate-buffered saline; HIF-1α, hypoxia-inducible factor-1α; ChIP, chromatin immunoprecipitation; RT-PCR, reverse transcription-polymerase chain reaction.
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received December 14, 2006.
- Accepted June 12, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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