111In or 125I Labeled Epidermal Growth Factor for The In Vivo Localization of EGF Receptors: In Vivo Stability

Radio iodinated epidermal growth factor (125I-EGF) used for the detection EGF receptors in implanted tumors in mice showed rapid in vivo de-iodination. To increase its stability EGF was labeled with 111In and its biodistribution in normal NMRI mice was determined and compared to 125I-EGF. The highest accumulation was observed in the thyroid (max at 6 h: 1045.2 ± 376.4 % /g) with 125I-EGF. 111In-EGF demonstrated prolonged blood clearance and whole body retention compared to 125I-EGF. High renal activity (23.79 ± 3.41% /g) indicated excretion via kidneys. 111In labeling increased the stability of the radiotracer. Further studies in tumor implanted nude mice are warranted to demonstrate the biological efficacy of 111In labeling.