title: Basis of FLT as a cell proliferation marker: comparative uptake studies with [3H]thymidine and [3H]arabinothymidine, and cell-analysis in 22 asynchronously growing tumor cell lines.
abstract: The usefulness of radiolabeled 3'-fluoro-3'-deoxythymidine (FLT), a thymidine derivative with affinity to cytoplasmic thymidine kinase 1 (TK1), as a tumor proliferation marker was evaluated using [3H]FLT and 22 cultured tumor cell lines. Asynchronously growing tumor cells were used for studies to mimic in vivo status of tumors. FLT uptake in each cell line was compared with [3H]thymidine ([3H]Thd) uptake and %S-phase fraction, both known as acceptable markers of proliferation. Uptake of the mitochondrial TK2 specific substrate [3H]arabinothymidine ([3H]AraT) was studied as a reference. Metabolic fate of FLT in tumor cells was also analyzed to elucidate the retention mechanism of FLT. [3H]FLT uptake was mildly correlated with the %S-phase fraction (r=0.76, p<0.0001) and correlated better with [3H]Thd uptake (r=0.88, p<0.0001). In contrast, the TK(2) specific substrate, [3H]AraT, was not significantly correlated with the %S-phase fraction (r=0.19, p=0.39), although it showed some correlation with the [3H]Thd uptake (r=0.47, p<0.05). Over 90% of radioactivity of [3H]Thd was found in the DNA fraction after 60 minutes incubation. In contrast, most of the radioactivity of [3H]FLT was found in the acid-soluble fraction (95%). [3H]FLT incorporation into the DNA fraction was negligible (0.2%). The [3H]AraT was mainly distributed in the acid-soluble fraction (70%) and the DNA fraction (20%). From our results, we concluded that FLT uptake in tumor cells reflects tumor cell proliferation. However, much more convincing validation is needed to clarify the difference between FLT and true substrates for DNA synthesis, like thymidine.
authors.affiliation: Research Center, Research and Development Division, Nihon Medi-Physices, Co, Ltd, Chiba, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Toyohara
authors.forename: Atsuo
authors.initials: A
authors.lastname: Waki
authors.forename: Shinji
authors.initials: S
authors.lastname: Takamatsu
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Yonekura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Magata
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Fujibayashi
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000502:physiology; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D051379:Mice; D019275:Radiopharmaceuticals; D013936:Thymidine / Q000378:metabolism*; D013937:Thymidine Kinase / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D004273:DNA, Neoplasm; D019275:Radiopharmaceuticals; C105339:thymidine kinase 2; D013937:Thymidine Kinase; D013936:Thymidine