Coleman D L, Canak N, Place G D, Shih C, Bowsher R R
Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA.
Clin Cancer Res. 1998 Jan;4(1):157-63.
LY309887, a reduced analogue of folic acid, is a potent inhibitor of glycinamide ribonucleotide formyltransferase and possesses a broad spectrum of antitumor activity. During preclinical studies using supplementation with oral folic acid, this second-generation inhibitor displayed both the desired safety profile and the pharmacology to warrant clinical investigation. A sensitive analytical method was needed to assess the pharmacokinetics of LY309887 due to the low doses planned for Phase I studies and the potential for low concentrations in plasma long after i.v. administration. We therefore undertook the development of a competitive RIA. A highly specific antiserum was raised in rabbits following immunization with LY309887 coupled to BSA. A RIA tracer was prepared by radioiodination of compound 389753, the adduct of LY309887 with p-tyramine. We developed a competitive-binding RIA procedure and used superparamagnetic particles coated with goat antirabbit IgG as a method for separating the bound and free forms of LY309887. The RIA is sensitive (0.5 ng/ml in serum and 25 ng/ml in urine), specific (negligible interference from endogenous folates), and reproducible (interassay coefficients of variation ranging from 8.1 to 15.4% and 7.6 to 8.3% for serum and urine controls, respectively). We used the RIA to assess the i.v. pharmacokinetics of LY309887 in both patients with metastatic cancer and dogs. The sensitivity of the RIA permitted the demonstration that serum concentrations of LY309887 decline in a multiexponential manner with a prolonged terminal elimination phase. We conclude that the RIA is a valid method for quantifying LY309887 in biological fluids.
LY309887是叶酸的一种还原类似物，是甘氨酰胺核糖核苷酸甲酰基转移酶的强效抑制剂，具有广泛的抗肿瘤活性。在使用口服叶酸补充剂的临床前研究中，这种第二代抑制剂显示出理想的安全性和药理特性，值得进行临床研究。由于I期研究计划使用低剂量药物，且静脉注射后很长时间血浆中可能出现低浓度情况，因此需要一种灵敏的分析方法来评估LY309887的药代动力学。因此，我们开展了竞争性放射免疫分析（RIA）的研发工作。用与牛血清白蛋白（BSA）偶联的LY309887免疫家兔，制备了高度特异性的抗血清。通过对化合物389753（LY309887与对酪氨酸的加合物）进行放射性碘化，制备了RIA示踪剂。我们开发了一种竞争性结合RIA程序，并使用包被有山羊抗兔IgG的超顺磁性颗粒作为分离LY309887结合型和游离型的方法。该RIA灵敏（血清中为0.5 ng/ml，尿液中为25 ng/ml）、特异（内源性叶酸的干扰可忽略不计）且可重复（血清和尿液对照的批间变异系数分别为8.1%至15.4%和7.6%至8.3%）。我们使用该RIA评估了LY309887在转移性癌症患者和犬体内的静脉药代动力学。RIA的灵敏性使得能够证明LY309887的血清浓度以多指数方式下降，终末消除相延长。我们得出结论，RIA是定量生物体液中LY309887的有效方法。
