Aherne G W, Ward E, Lawrence N, Dobinson D, Clarke S J, Musgrove H, Sutcliffe F, Stephens T, Jackman A L
CRC Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, UK.
Br J Cancer. 1998;77(2):221-6. doi: 10.1038/bjc.1998.37.
ZD1694 (Tomudex, raltitrexed) is a specific quinazoline antifolate thymidylate synthase inhibitor that relies on polyglutamation for high potency. Antibodies to ZD1694 have been used to establish a sensitive radioimmunoassay as an alternative to high-performance liquid chromatography (HPLC). The radioimmunoassay is reproducible, accurate and provides a means of determining low levels of ZD1694 in plasma (< 1 nM). By virtue of the high cross-reactivity of the antibodies with polyglutamated forms of ZD1694, it is also possible to measure the total concentration of drug in tissues. Results obtained in L1210 mouse leukaemia cells and in mouse tissues were similar to those previously determined using radiolabelled drug. Pharmacokinetic studies in mice have confirmed that the compound is rapidly eliminated from the plasma and that there is a prolonged terminal elimination phase. ZD1694 was measured in plasma (0.56 ng ml(-1); 1.2 pmol ml(-1)) up to 7 days after a single i.p. dose of 100 mg kg(-1) ZD1694. Liver, kidney and gut epithelium had a substantially higher level of ZD1694 immunoreactivity than plasma. For example, 24 h after a single i.p. dose at 1, 10 and 100 mg kg(-1), total drug levels in the liver were 480, 325 and 152 times higher than plasma levels respectively. In kidney and gut epithelium, total drug levels at these doses were approximately 55 and 34 times those of plasma. The high tissue to plasma ratios were maintained for at least 7 days after administration. Similarly, high tissue to plasma ratios (> 100) were found in dogs treated with a clinically relevant dose of ZD1694. These were maintained for 4 weeks in liver and kidney tissue (> 100). Total gastrointestinal concentrations of ZD1694 were approximately 10 times higher than plasma 3 days after administration, but levels were near to the limit of detection at 4 weeks. These results are consistent with extensive polyglutamation of ZD1694 within tissues in both mice and dog and provide further support for the infrequent schedule that has been used clinically. Although it has not been possible to measure individual polyglutamated forms of ZD1694, the radioimmunoassay provides a convenient means of assessing total drug levels in tissues and is currently the only method suitable for measuring the extent of drug retention in normal tissue and tumour biopsies obtained from patients treated with ZD1694.
ZD1694（托莫昔芬，雷替曲塞）是一种特异性喹唑啉抗叶酸胸苷酸合成酶抑制剂，其高效性依赖于多聚谷氨酸化。针对ZD1694的抗体已被用于建立一种灵敏的放射免疫测定法，作为高效液相色谱法（HPLC）的替代方法。该放射免疫测定法具有可重复性、准确性，并且提供了一种测定血浆中低水平ZD1694（<1 nM）的方法。由于抗体与ZD1694的多聚谷氨酸化形式具有高交叉反应性，因此也能够测量组织中药物的总浓度。在L1210小鼠白血病细胞和小鼠组织中获得的结果与先前使用放射性标记药物测定的结果相似。对小鼠的药代动力学研究证实，该化合物可迅速从血浆中清除，并且存在较长的终末消除期。在单次腹腔注射100 mg kg⁻¹ ZD1694后长达7天的时间里，血浆中均可检测到ZD1694（0.56 ng ml⁻¹；1.2 pmol ml⁻¹）。肝脏、肾脏和肠道上皮中的ZD1694免疫反应性水平显著高于血浆。例如，在单次腹腔注射1、10和100 mg kg⁻¹剂量后24小时，肝脏中的总药物水平分别比血浆水平高480、325和152倍。在肾脏和肠道上皮中，这些剂量下的总药物水平约为血浆的55倍和34倍。给药后至少7天内，组织与血浆的高比率一直维持。同样，在用临床相关剂量的ZD1694治疗的犬中也发现了高组织与血浆比率（>100）。在肝脏和肾脏组织中（>100），这种比率维持了4周。给药3天后，ZD1694在胃肠道中的总浓度约比血浆高10倍，但在4周时浓度接近检测限。这些结果与ZD1694在小鼠和犬的组织中广泛多聚谷氨酸化一致，并为临床使用的不频繁给药方案提供了进一步支持。尽管无法测量ZD1694的各个多聚谷氨酸化形式，但放射免疫测定法提供了一种评估组织中总药物水平的便捷方法，并且是目前唯一适用于测量接受ZD1694治疗的患者正常组织和肿瘤活检中药物保留程度的方法。
