Distribution of 1-(2-Deoxy-2-fluoro-β-d-arabinofuranosyl) Uracil in Mice Bearing Colorectal Cancer Xenografts

• Published in: Clinical cancer research 2004-10, Vol.10 (19), p.6669-6676
• Main Authors: Eiseman, Julie L., Brown-Proctor, Clive, Kinahan, Paul E., Collins, Jerry M., Anderson, Lawrence W., Joseph, Erin, Hamburger, Deborah R., Pan, Su-shu, Mathis, Chester A., Egorin, Merrill J., Klecker, Raymond W.
• Format: Article
• Language: English
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.CCR-03-0686

Purpose: In colorectal, breast, and head and neck cancers, response to 5-fluorouracil is associated with low expression of thymidylate synthase. In contrast, tumors with high expression of thymidylate synthase may be more sensitive to prodrugs such as 1-(2-deoxy-2-fluoro-β- d -arabinofuranosyl) uracil (FAU) that are activated by thymidylate synthase. These studies were designed to evaluate FAU as a potential therapeutic and diagnostic probe. Experimental Design: [ 18 F]-FAU and [ 3 H]-FAU were synthesized with >97% radiochemical purity. [ 3 H]-FAU or [ 18 F]-FAU was administered intravenously to severe combined immunodeficient mice bearing either HT29 (low thymidylate synthase) or LS174T (high thymidylate synthase) human colon cancer xenografts. Four hours after [ 3 H]-FAU dosing, tissue distribution of total radioactivity and incorporation of 1-(2-deoxy-2-fluoro-β- d -arabinofuranosyl) 5-methyluracil (FMAU), derived from thymidylate synthase activation of FAU, into tumor DNA was measured. Positron emission tomography (PET) images were obtained for 90 minutes after injection of [ 18 F]-FAU. Thymidylate synthase activity was determined in vitro in tumors from untreated mice by [ 3 H] release from [ 3 H]dUMP. Each cell line was incubated in vitro with [ 3 H]-FAU or [ 3 H]-FMAU in the absence or presence of 5-fluoro-2′-deoxyuridine (FdUrd) and then was analyzed for incorporation of radiolabel into DNA. Results: Thymidylate synthase enzymatic activity in LS174T xenografts was ∼3.5-fold higher than in HT29 xenografts, and incorporation of radioactivity derived from [ 3 H]-FAU into LS174T DNA was ∼2-fold higher than into HT29 DNA. At 240 minutes, radioactivity derived from [ 3 H]-FAU was ∼2-fold higher in tumors than in skeletal muscle. At times up to 90 minutes, PET imaging detected only small differences in uptake of [ 18 F]-FAU between the tumor types. Fluorine-18 in skeletal muscle was higher than in tumor for the first 90 minutes and plateaued earlier, whereas [ 18 F] in tumor continued to increase during the 90-minute imaging period. For both cell lines in vitro , FdUrd decreased the rate of incorporation of [ 3 H]-FAU into DNA, whereas the incorporation of [ 3 H]-FMAU was increased. Conclusions: These results for FAU incorporation into DNA in vitro and in vivo further support clinical evaluation of FAU as a therapeutic agent in tumors with high concentrations of thymidylate synthase that are less likely to respond to 5-fluorouracil treatment. The high cir