Induction of thymidine kinase 1 after 5-fluorouracil as a mechanism for 3'-deoxy-3'-[18F]fluorothymidine flare.
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.
Lee
Seung Jin
SJ
Institute for Innovative Cancer Research, Asan Medical Center, Asanbyeongwon-gil 86, Songpa-gu, Seoul 138-736, Republic of Korea.
Kim
Seog Young
SY
Chung
Jin Hwa
JH
Oh
Seung Jun
SJ
Ryu
Jin Sook
JS
Hong
Yong Sang
YS
Kim
Tae Won
TW
Moon
Dae Hyuk
DH
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*
D000964:Antimetabolites, Antineoplastic; D015224:Dideoxynucleosides; D005462:Fluorine Radioisotopes; D013940:Thymidylate Synthase; D013937:Thymidine Kinase; C092717:thymidine kinase 1; C002854:alovudine; D005472:Fluorouracil