Bijnsdorp I V, Comijn E M, Padron J M, Gmeiner W H, Peters G J
Department of Medical Oncology, VU University Medical Center, 1007 MB Amsterdam, The Netherlands.
Oncol Rep. 2007 Jul;18(1):287-91. doi: 10.3892/or.18.1.287.
FdUMP[10] is a multimer of FdUMP, a suicide inhibitor of thymidylate synthase (TS), and was designed to bypass resistance to 5-fluorouracil (5FU). The aim of the study was to compare the effect of FdUMP[10] with 5FU and 5-fluoro-2-deoxyuridine (FUdR) in their efficacy to inhibit their target TS in resistant cells. Therefore cell lines FM3A/0, FM3A/TK- (deficient in thymidine kinase) and FM3A/TS- (deficient in thymidylate synthase) were used to determine TK dependency and specificity for TS inhibition. FdUMP[10] inhibited cell growth with greater potency than 5FU and FdUMP. Direct folate-based inhibitors Raltitrexed, GW1843U89 and Pemetrexed were also evaluated using these cell lines. In TK-deficient cells these folate-based inhibitors had greater potency than the fluoropyrimidines (FPs). Surprisingly, Pemetrexed even inhibited cell growth in TS-deficient cells. Incubation with nucleotidase and phosphatase inhibitors resulted in a reduction of cytotoxicity of FdUMP[10], indicating that the drug can be degraded outside the cells. In the TS in situ inhibition assay (TSIA) 24 h exposure of FM3A cells to 0.5 microM FdUMP and 0.05 microM FdUMP[10] decreased TSIA to 7 and 1% of control. Inhibition of nucleotidase and phosphatase activities reduced the effect of FdUMP[10], while the inhibitory effect was lower in cells lacking TK. FdUMP[10] can enter the cells intact, but also to some extent after dephosphorylation. In conclusion, FdUMP[10] can bypass resistance to FUdR by direct inhibition of TS.
FdUMP[10]是FdUMP的多聚体，FdUMP是胸苷酸合成酶（TS）的自杀性抑制剂，其设计目的是绕过对5-氟尿嘧啶（5FU）的耐药性。本研究的目的是比较FdUMP[10]与5FU和5-氟-2-脱氧尿苷（FUdR）在耐药细胞中抑制其靶标TS的效果。因此，使用细胞系FM3A/0、FM3A/TK-（胸苷激酶缺陷）和FM3A/TS-（胸苷酸合成酶缺陷）来确定对TS抑制的胸苷激酶依赖性和特异性。FdUMP[10]抑制细胞生长的效力高于5FU和FdUMP。还使用这些细胞系评估了直接基于叶酸的抑制剂雷替曲塞、GW1843U89和培美曲塞。在胸苷激酶缺陷的细胞中，这些基于叶酸的抑制剂比氟嘧啶（FPs）具有更高的效力。令人惊讶的是，培美曲塞甚至能抑制胸苷酸合成酶缺陷细胞的生长。用核苷酸酶和磷酸酶抑制剂孵育导致FdUMP[10]的细胞毒性降低，表明该药物可在细胞外降解。在TS原位抑制试验（TSIA）中，FM3A细胞暴露于0.5微摩尔FdUMP和0.05微摩尔FdUMP[10]24小时后，TSIA分别降至对照的7%和1%。抑制核苷酸酶和磷酸酶活性降低了FdUMP[10]的作用，而在缺乏胸苷激酶的细胞中抑制作用较低。FdUMP[10]可以完整进入细胞，但在去磷酸化后也能在一定程度上进入。总之，FdUMP[10]可通过直接抑制TS绕过对FUdR的耐药性。
