Bioconjugate Chem. 1990, 1, 431-437
431
Enhanced Kidney Clearance with an Ester-Linked 99mTc-Radiolabeled Antibody Fab'-Chelator Conjugate Robert W. Weber,' Raymond H. Boutin, Mark A. Nedelman, John Lister-James,+ and Richard T. Dean+ Chemistry Research, Centocor, Incorporated, 244 Great Valley Parkway, Malvern, Pennsylvania 19355. Received April 9, 1990
Bifunctional chelators for labeling antibodies with ggmTcbased on the N3S core of (mercaptoacety1)triglycine having ester or amide linking moieties were synthesized and site-specifically attached to the sulfhydryl groups of the Fab' fragment of antimyosin. Protein labeling was quantitative after 15 min; postlabeling purification was not necessary. The radiolabeled conjugates exhibited no loss of immunoreactivity. Under basic conditions, the ester-linked conjugate lost 95% of the radiolabel in the form of the 9 9 m T complex ~ of (mercaptoacety1)triglycine as determined by RP-HPLC, while the radioactivity in the amide-linked conjugate remained completely bound to the protein. In a mouse biodistribution study, the ester-linked conjugate showed a 2-fold enhancement in clearance from the kidney when compared to the amide-linked product.
INTRODUCTION The use of monoclonal antibodies as carriers of radioisotopes for diagnosis or therapy requires labeling methodologies which result in stable products with uncompromised immunoreactivity. Ideally, the radiolabeled product should be nonimmunogenic and exhibit rapid clearance from the blood, nontarget tissues, and excretory organs. For radiopharmaceuticals, the use of Fab or Fab' fragments of the monoclonal antibody offer several advantages over the IgG. These smaller fragments lack the Fc region of the IgG molecule and thus circumvent possible adverse effects due to this region. The fragments are better able to penetrate the target tissues, are less immunogenic, and are cleared from the circulation more rapidly than the intact IgG. The major route of clearance for these -50,000 Da species is via the renal system, making the kidneys the critical organs in regard to absorbed radiation dosimetry. I t would be advantageous if a mechanism to facilitate clearance from this organ could be constructed into the radiopharmaceutical product. The goal of our research was to develop labeling ~ radionuclide of choice for methodology with 9 9 m T(the diagnostic imaging) of antibody fragments which would allow quantitative, stable labeling with preservation of immunoreactivity in a short period of time (
