Uptake of radiolabeled alpha-fetoprotein by mouse mammary carcinomas and its usefulness in tumor scintigraphy.

The ability to internalize alpha-fetoprotein (AFP) and serum albumin, which is characteristic of embryonic and fetal elements undergoing differentiation, may reappear in some cultured neoplastic cells (i.e., the MCF-7 human breast cancer cell line). The in vivo uptake of AFP by spontaneous carcinomas of the CH3/Bi mouse was investigated. Nineteen mice were given i.v. injections of approximately 10 muCi of mouse 125I-AFP (0.6 to 4 micrograms of AFP according to the specific ratio of the preparation used). Four to 7 days later, the animals were sacrificed. The radioactivity concentration in the tumor was the highest among all solid tissues examined. Tumor:liver radioactivity ratios were clearly positive [3.6 +/- 0.3 (S.E.)] in 27 of 31 specimens studied. Microscopy examination of autoradiograms from various tissue sections confirmed the selective accumulation of radioactive AFP in the tumors. In order to assess the specificity of AFP uptake by mammary tumors, 4 mice were given simultaneous injections of 125I-AFP and 131I-ovalbumin, respectively. Compared to AFP, the retention of ovalbumin was very low in all tissues studied, including the tumor. The possibility of tumor localization of radiolabeled AFP by external photoscanning was also explored. Two mice were given injections of 131I-AFP, one mouse received 131I-serum albumin, and one was given 131I-ovalbumin. Images were obtained 6 days after with a standard gamma-camera linked to a computer with data display. About 50% of the total radioactivity retained was concentrated in the tumor areas of mice given injections of iodinated AFP, while it was only 15% in the mouse that received 131I-serum albumin. No tumor image could be detected in the mouse given ovalbumin. These results show that the ability to internalize AFP, common to many tissues during ontogenesis, may also be shared by neoplastic cells which develop later in life. They also prove the preferential uptake of AFP by the tumors compared to normal tissues and the usefulness of AFP as a radiotracer for mammary carcinomas. The latter represents a novel approach to tumor detection.