Goodwin D A, Meares C F, Osen M
Department of Nuclear Medicine, Veterans Affairs Palo Alto Health Care System, California 94304, USA.
J Nucl Med. 1998 Oct;39(10):1813-8.
Three-step pretargeting increases target-to-background ratios in radioimmunodetection and can potentially decrease harmful radiation to normal tissues in radioimmunotherapy. We studied four biotin-chelate conjugates (BCCs) for use in the avidin/biotin pretargeting system.
Pharmacokinetics and biodistribution were studied in normal BALB/c (IAk-negative), normal C3H (IAk-positive) and LS174T tumor-bearing BALB/c severe combined immunodeficient mice. Streptavidin alone and antibody-streptavidin conjugates [monoclonal antibody (MAb) 10-3.6 anti-IAk IgG2a] were used. Indium-111- or 88Y-BCCs were given alone intravenously; they were mixed with streptavidin or MAb-streptavidin conjugate and given intravenously; or streptavidin and MAb-streptavidin conjugate were pretargeted, and 2-3, 5 and 21 hr later, BCCs were injected intravenously. Samples were taken 2-3 hr after intravenous injection of labeled BCCs.
Three of the four BCCs were rapidly excreted by the kidneys, with <2.5%/g in any organ or tumor at 2-3 hr. Gut excretion eliminated biotinyl-(S)-1-p-aminobenzylethylenediaminetetraacetic acid (EDTA) for use in pretargeting. Ninety percent of BCCs were bound to circulating pretargeted streptavidin at 1-6 hr, and approximately 15% were bound to pretargeted streptavidin at 24 hr. Kidney uptakes were: preformed streptavidin-BCC given intravenously, approximately 80%/g (24 hr); streptavidin pretargeted for 2-3 hr, approximately 60%/g; and streptavidin pretargeted for 5-21 hr, approximately 10%-20%/g. Kidney uptake was dose-dependent: 0.2, 0.67 and 1.0 nmol of streptavidin pretargeted for 21 hr showed increasing concentrations (24 hr). Uptake of monoclonal anti-IAk-streptavidin-BCC complex into spleen (70% +/- 10%/g; p < 0.05) and lymph nodes (10% +/- 3.5%/g; p < 0.01) was higher in IAk-positive C3H mice than it was in IAk-negative control BALB/c mice, and it was much higher than that in streptavidin controls. No significant target uptake was seen with anti-IAk MAb-streptavidin pretargeted for 3 or 20 hr. Kidney uptake approximately 20%/g, which was lower than that of streptavidin alone.
Three biotinyl chelates bind the diagnostic and therapeutic radiometals 111In and 88Y (and, by analogy, 90Y) with the required in vivo stability and physiological properties for pretargeted diagnosis and therapy. Kidney uptake of streptavidin was decreased by conjugation to MAb. Failure of anti IAk MAb-streptavidin conjugate to bind BCC after pretargeting may be due to rapid internalization of MAb-streptavidin-IAk complex by the lymphocyte or to endogenous biotin. Either or both of these would make streptavidin unavailable to subsequent BCCs.
三步预靶向可提高放射免疫检测中的靶本底比，并有可能降低放射免疫治疗中对正常组织的有害辐射。我们研究了四种用于抗生物素蛋白/生物素预靶向系统的生物素螯合物共轭物（BCC）。
在正常BALB/c（IAk阴性）、正常C3H（IAk阳性）和携带LS174T肿瘤的BALB/c严重联合免疫缺陷小鼠中研究了药代动力学和生物分布。单独使用链霉抗生物素蛋白和抗体 - 链霉抗生物素蛋白共轭物[单克隆抗体（MAb）10 - 3.6抗 - IAk IgG2a]。单独静脉注射铟 - 111或88Y - BCC；将它们与链霉抗生物素蛋白或MAb - 链霉抗生物素蛋白共轭物混合后静脉注射；或者先进行链霉抗生物素蛋白和MAb - 链霉抗生物素蛋白共轭物的预靶向，然后在2 - 3小时、5小时和21小时后静脉注射BCC。在静脉注射标记的BCC后2 - 3小时采集样本。
四种BCC中的三种通过肾脏快速排泄，在2 - 3小时时任何器官或肿瘤中的含量均<2.5%/克。肠道排泄消除了用于预靶向的生物素基 - (S)-1 - 对氨基苄基乙二胺四乙酸（EDTA）。90%的BCC在1 - 6小时时与循环中的预靶向链霉抗生物素蛋白结合，在24小时时约15%与预靶向链霉抗生物素蛋白结合。肾脏摄取情况如下：静脉注射预先形成的链霉抗生物素蛋白 - BCC，约80%/克（24小时）；链霉抗生物素蛋白预靶向2 - 3小时，约60%/克；链霉抗生物素蛋白预靶向5 - 21小时，约10% - 20%/克。肾脏摄取呈剂量依赖性：预靶向21小时的0.2、0.67和1.0纳摩尔链霉抗生物素蛋白显示浓度增加（24小时）。IAk阳性的C3H小鼠中，单克隆抗 - IAk - 链霉抗生物素蛋白 - BCC复合物在脾脏（70%±10%/克；p<0.05）和淋巴结（10%±3.5%/克；p<0.01）中的摄取高于IAk阴性的对照BALB/c小鼠，且远高于链霉抗生物素蛋白对照组。预靶向3小时或20小时的抗 - IAk MAb - 链霉抗生物素蛋白未见明显的靶摄取。肾脏摄取约20%/克，低于单独使用链霉抗生物素蛋白的摄取。
三种生物素基螯合物能与诊断和治疗用放射性金属铟 - 111和88Y（类推还有钇 - 90）结合，具有预靶向诊断和治疗所需的体内稳定性和生理特性。与单克隆抗体共轭后，链霉抗生物素蛋白的肾脏摄取减少。预靶向后抗 - IAk MAb - 链霉抗生物素蛋白共轭物未能结合BCC，可能是由于淋巴细胞对MAb - 链霉抗生物素蛋白 - IAk复合物的快速内化或内源性生物素所致。其中之一或两者都可能使链霉抗生物素蛋白无法与后续的BCC结合。
