Institute for Innovative Cancer Research, Asan Medical Center, Asanbyeongwon-gil 86, Songpa-gu, Seoul 138-736, Republic of Korea.
Biochem Pharmacol. 2010 Nov 15;80(10):1528-36. doi: 10.1016/j.bcp.2010.08.004. Epub 2010 Aug 17.
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.
成像抗肿瘤药物的药效动力学可能允许对抗肿瘤作用进行早期评估。胸苷酸合酶抑制（TS）抑制后早期 3'-脱氧-3'-[(18)F]氟代胸苷 ([(18)F]FLT) 摄取的增加，所谓的闪光反应，被认为主要是由于结合位点的增加用于 1 型平衡核苷转运体。我们研究了胸苷激酶 1 (TK1) 在氟尿嘧啶 (5-FU) 治疗后作为 [(18)F]FLT 闪光的一种机制。将九种癌细胞系暴露于 5-FU 24h 可引起 [(18)F]FLT 摄取增加 2.5-3.5 倍，明显高于治疗后 2h 观察到的 1.5 倍增加。大多数细胞系在 5-FU 暴露 24h 后 [(18)F]FLT 摄取的增加伴随着 TK1 的诱导。在代表性细胞系（A431 和 HT29）中，5-FU 时间依赖性地增加 [(18)F]FLT 摄取、激酶活性和 TK1 的蛋白和 mRNA 水平、顺序细胞周期蛋白 E 和 A 的诱导以及 G(1)-S 期转变。环已亚胺处理和 TK1 敲低完全抑制 5-FU 诱导的 [(18)F]FLT 闪光。另一方面，HCT8 细胞在响应 5-FU 剂量时表现出双相 [(18)F]FLT 闪光，缺乏 TK1 诱导。环已亚胺不抑制这些细胞中 5-FU 诱导的 [(18)F]FLT 闪光。HT29 荷瘤小鼠的体内动态 [(18)F]FLT-PET 和离体分析显示，5-FU 给药后 24h 肿瘤组织的 [(18)F]FLT 通量和 TK1 活性显著增加（P<0.05）。总之，5-FU 诱导大多数细胞系中的 TK1 和 TK1 介导的高 [(18)F]FLT 闪光。[(18)F]FLT-PET 可用于通过涉及 TK1 诱导的机制评估 TS 抑制剂的药效动力学。
