McGuire J J, Magee K J, Russell C A, Canestrari J M
Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Oncol Res. 1997;9(3):139-47.
Thymidylate synthase (TS) inhibitor effects on growth of human head and neck squamous cell carcinoma (HNSCC) cell lines and CCRF-CEM human leukemia cells and sublines with acquired methotrexate (2,4-diamino-10-methylpteroylglutamic acid) (MTX) resistance were studied. During 120-h treatment, HNSCC cell lines A253 and FaDu are equally sensitive to MTX, whereas the polyglutamylatable TS inhibitors ZD1694 and BW1843U89 are 5- to 35-fold more potent than MTX and the lipophilic AG331 is approximately 10(2)-fold less potent than MTX. A253 is intrinsically resistant to intermittent (24 h) MTX and BW1843U89 exposure (higher EC50 values and shallower slopes of concentration-response curves relative to FaDu); AG331 and ZD1694 largely overcome this intrinsic resistance to intermittent exposure. Thymidine (TdR) protects against growth inhibition by these inhibitors, confirming that TS is their target in HNSCC; at high AG331 levels, TdR only partially protects, implying that a second site of action exists. Growth inhibition of HNSCC by ZD1694 and BW1843U89 is protected by leucovorin (LV) at > or = 10(-7) and > 10(-3) M, respectively; 10(-4) M LV cannot protect HNSCC cells against AG331. Results similar to protection studies are obtained if LV addition is delayed < or = 24 h after ZD1694 or BW1843U89 exposure. CCRF-CEM sublines with acquired MTX resistance resulting from dihydrofolate reductase (DHFR) overexpression, defective MTX transport, or defective MTX polyglutamylation retain full sensitivity to AG331. Cells with defective MTX transport are highly cross-resistant to ZD1694 and BW1843U89, implicating the reduced folate/MTX carrier in their transport. Minor cross-resistance of the DHFR overexpressing line to ZD1694 and BW1843U89 is observed. A subline with highly defective MTX polyglutamylation is cross-resistant to 120-h exposure to ZD1694, but not to BW1843U89, suggesting a profound contribution of polyglutamylation to the mechanism of action of ZD1694.
研究了胸苷酸合成酶（TS）抑制剂对人头颈鳞状细胞癌（HNSCC）细胞系以及获得性甲氨蝶呤（2,4 - 二氨基 - 10 - 甲基蝶酰谷氨酸）（MTX）耐药的CCRF - CEM人白血病细胞及其亚系生长的影响。在120小时的治疗过程中，HNSCC细胞系A253和FaDu对MTX的敏感性相同，而可聚谷氨酸化的TS抑制剂ZD1694和BW1843U89的效力比MTX高5至35倍，亲脂性的AG331的效力比MTX低约100倍。A253对间歇性（24小时）MTX和BW1843U89暴露具有内在抗性（相对于FaDu，其半数有效浓度（EC50）值更高，浓度 - 反应曲线斜率更平缓）；AG331和ZD1694在很大程度上克服了这种对间歇性暴露的内在抗性。胸腺嘧啶核苷（TdR）可防止这些抑制剂对细胞生长的抑制，证实TS是它们在HNSCC中的作用靶点；在高AG331水平下，TdR仅提供部分保护，这意味着存在第二个作用位点。ZD1694和BW1843U89对HNSCC的生长抑制分别在亚叶酸（LV）浓度≥10^(-7) M和＞10^(-3) M时受到保护；10^(-4) M的LV不能保护HNSCC细胞免受AG331的影响。如果在ZD1694或BW1843U89暴露后≤24小时添加LV，可得到与保护研究相似的结果。因二氢叶酸还原酶（DHFR）过表达、MTX转运缺陷或MTX聚谷氨酸化缺陷而获得MTX耐药性的CCRF - CEM亚系对AG331仍保持完全敏感性。MTX转运缺陷的细胞对ZD1694和BW1843U89具有高度交叉抗性，这表明其转运过程中涉及的叶酸/MTX载体减少。观察到DHFR过表达的细胞系对ZD1694和BW
