For immunoscintigraphic localization of human
breast cancer two
monoclonal antibodies (mabs) 12H12 (
immunoglobulin G1) and BM-2 (
immunoglobulin G3) were developed. The mabs, directed against two different
epitopes on the
mucin glycoprotein TAG-12, showed reactivity with 96% of all primary mammary
carcinomas. The
antibodies were labeled with either 125I or 131I. In addition, 12H12 was directly labeled with 99mTc according to the method of Schwarz and Steinsträsser (A. Schwarz and A. Steinsträsser, J. Nucl. Med., 28:721, 1987). Biodistribution was measured in female nude mice bearing the
human mammary carcinoma SF-15. Both radioiodinated mabs showed similar biodistribution with fast
tumor uptake (8.5% injected dose/g at 6 h postinjection), which increased to 10-11% injected dose/g at 24 h and subsequently remained constant up to 120 h. 99mTc-Labeling of the mab 12H12 led to an enhanced
tumor uptake of 10.5 and 14% injected dose/g at 6 and 24 h postinjection, respectively, and to significantly accelerated blood clearance of radioactivity. Similar results were obtained with a second mammary
tumor (AR-1), while an endometrial
tumor (EK-3) showed a 3-fold lower accumulation of radioactivity and no difference in uptake of radio-iodinated and 99mTc-labeled 12H12. Scintigraphic imaging of
tumor-bearing nude mice with the 99mTc 12H12 at 24 h postinjection clearly demonstrated a diagnostic potential of the new mab for
tumor localization and staging.