title: Induction of thymidine kinase 1 after 5-fluorouracil as a mechanism for 3'-deoxy-3'-[18F]fluorothymidine flare.
abstract: Imaging the pharmacodynamics of anti-cancer drugs may allow early assessment of anti-cancer effects. Increases in 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) uptake early after thymidylate synthase inhibition (TS) inhibition, the so-called flare response, is considered to be largely due to an increase in binding sites for type-1 equilibrative nucleoside transporter. We investigated the induction of thymidine kinase 1 (TK1) after 5-fluorouracil (5-FU) treatment as one of mechanisms for [(18)F]FLT flare. Exposure of nine cancer cell lines to 5-FU for 24h induced a 2.5- to 3.5-fold increase in [(18)F]FLT uptake, significantly higher than the 1.5-fold increase observed 2h after treatment. The increase of [(18)F]FLT uptake 24h after 5-FU exposure accompanied TK1 induction in most cell lines. In representative cell lines (A431 and HT29), 5-FU time-dependently increased [(18)F]FLT uptake, kinase activity and the levels of protein and mRNA for TK1, sequential cyclin E and A induction, and G(1)-S phase transition. Cycloheximide treatment and knockdown of TK1 completely inhibited 5-FU-induced [(18)F]FLT flare. On the other hand, HCT8 cells showed a biphasic [(18)F]FLT flare with lacked TK1 induction in response to the dosage of 5-FU. Cycloheximide did not inhibit 5-FU-induced [(18)F]FLT flare in this cells. In vivo dynamic [(18)F]FLT-PET and ex vivo analysis in HT29 tumor-bearing mice showed significantly increased [(18)F]FLT flux and TK1 activity of tumor tissue 24h after 5-FU administration (P<0.05). Conclusively, 5-FU induced TK1 and TK1-mediated high [(18)F]FLT flare in most of cell lines. [(18)F]FLT-PET may be used to assess pharmacodynamics of TS inhibitor by a mechanism involving TK1 induction.
authors: Institute for Innovative Cancer Research, Asan Medical Center, Asanbyeongwon-gil 86, Songpa-gu, Seoul 138-736, Republic of Korea.
authors: Seung Jin
authors: SJ
authors: Lee
authors: Seog Young
authors: SY
authors: Kim
authors: Jin Hwa
authors: JH
authors: Chung
authors: Seung Jun
authors: SJ
authors: Oh
authors: Jin Sook
authors: JS
authors: Ryu
authors: Yong Sang
authors: YS
authors: Hong
authors: Tae Won
authors: TW
authors: Kim
authors: Dae Hyuk
authors: DH
authors: Moon
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D015224:Dideoxynucleosides / Q000493:pharmacokinetics*; D004790:Enzyme Induction; D005434:Flow Cytometry; D005462:Fluorine Radioisotopes; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D049268:Positron-Emission Tomography; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013937:Thymidine Kinase / Q000096:biosynthesis* / Q000235:genetics; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*
chemical_list: D000964:Antimetabolites, Antineoplastic; D015224:Dideoxynucleosides; D005462:Fluorine Radioisotopes; D013940:Thymidylate Synthase; D013937:Thymidine Kinase; C092717:thymidine kinase 1; C002854:alovudine; D005472:Fluorouracil