In vivo localization of radioiodinated peanut lectin in a murine TA3/Ha mammary carcinoma model

Peanut lectin (PNA) binds avidly to oligosaccharides containing the terminal sequence β-D-Gal(1->3)α-D-GAlAc. This disaccharide is the immunodeterminant group of the Thomsen-Friedenreich (T) antigen which is present in an exposed form on a number of human and animal adenocarcinomas and can be identified in tumor tissue sections by histochemical PNA staining techniques. We have studied the in vivo uptake of radioiodinated PNA in a murine Ta3/Ha mammary adenocarcinoma model to evaluate the potential applications of radiolabeled PNA for the immunodetection of T antigen expressing carcinoma. We have found that PNA has a high in vitro binding affinity for the Ta3/Ha tumor cells as well as for epiglycanin, a glycoprotein fraction shed by the Ta3/Ha cells. Tissue biodistribution studies after IV 125I-PNA injection into Ta3/Ha tumor-bearing mice indicated tumor: blood ratios of 7:1 and 55:1 at 24 and 48 h with corresponding tumor:muscle ratios of 33:1 and 77:1. The high tumor uptake and rapid blood clearance allowed clear scintigraphic delineation of tumor by 24 and 48 h without the necessity for background subtraction techniques. Rapid in vivo deiodination of 125I-PNA also contributed to localization of radioactivity in the stomach, salivary glands, thyroid, and kidney. (orig.)