IMPROVED TUMOR TARGETING OF TC-99M FAB BY CHEMICAL MODIFICATIONS

该项目由C.H. Paik博士我们一直在开发化学方法来放射性标记单克隆抗体及其片段，以用作荧光成像剂来检测表达IL-2受体的血液恶性肿瘤。对于FY 99，我们已经扩展了我们的努力，用Tc-99 m标记抗Tac单克隆抗体的Fab片段，使用Tc-99 m-mercaptoacetyltriglycine作为螯合剂。标记的Fab定位在IL-2受体阳性的ATAC肿瘤迅速，但清除迅速从血液和所有器官，除了肾脏。为了改善其高肾摄取的药代动力学性质，我们通过用乙醇酸的四氟苯基酯酰化其氨基来降低Fab的等电点（pI >9.3）。该反应中和Fab的氨基上的一个正电荷，同时向Fab添加一个羟基。pI范围为4.6-6.6的乙醇酸化Tc-99 m标记的Fab在注射后15分钟将肾脏蓄积降低至对照Tc-99 m标记的Fab的14%，并将其峰值肿瘤摄取从对照的7% ID/g增加至14%注射剂量/g（ID/g）。这项研究表明，肾脏摄取的Fab涉及带正电荷的Fab和带负电荷的磷脂双分子层的肾实质细胞膜之间的电荷相互作用和降低的pI减少肾摄取。通过用乙醇酸酯分子酰化中和Fab的正电荷和使用Tc-99 m-巯基乙酰基三甘氨酸进行放射性标记提高了肿瘤摄取峰值，但降低了肾摄取。

This project was developed and is directed by C.H. Paik, Ph.D. We have been developing chemical methods to radiolabel monoclonal antibodies and their fragments to use as scintigraphic imaging agents to detect hematologic malignancies that express IL-2 receptors. For FY 99 we have extended our efforts to label Fab fragments of anti-Tac monoclonal antibody with Tc-99m using Tc-99m-mercaptoacetyltriglycine as a chelator. The labeled Fab localized in IL-2 receptor-positive ATAC tumors rapidly but cleared rapidly from blood and all organs except kidneys. To improve its pharmacokinetic property with respect to its high renal uptake, we lowered the isoelectric point (pI >9.3) of Fab by acylation of its amino groups with tetrafluorophenyl ester of glycolic acid. This reaction neutralizes one positive charge on an amino group of Fab and at the same time adds one hydroxyl group to Fab. The glycolated Tc-99m-labeled Fab with a pI range of 4.6-6.6 decreased the renal accumulation to 14 percent of that of the control Tc-99m-labeled Fab at 15 min postinjection and increased its peak tumor uptake to 14 percent injected dose per gram (ID/g) from 7 percent ID/g for the control. This study suggests that the renal uptake of Fab involves charge interactions between positively charged Fab and negatively charged phospholipid bilayers of renal parenchymal cell membranes and that the lowering of the pI decreases the renal uptake. The neutralization of the positive charges of Fab by acylation with glycolate molecules and the use of Tc-99m-mercaptoacetyltriglycine for radiolabeling improved the peak tumor uptake value but it reduced the renal uptake.