Quantitative Whole-Body Autoradiography of Radiolabeled Antibody Distribution in a Xenografted Human Cancer Model

Abstract Quantitative whole-body autoradiography (WBAR) was used to study the biodistribution of goat anti-carcinoembryonic antigen and normal goat IgG, each labeled with 125 I, in hamsters bearing the carcinoembryonic antigen-producing GW-39 human colonic carcinoma xenograft. Comparisons between computer-assisted videodensitometric profiles of WBARs and tissue radioactivity counts were made at 1, 3, and 7 days following administration of the radiolabeled IgGs. The results indicated that maximal tumor accretion of the radiolabeled antibody and normal IgG occurred within 1–3 days, with a marked selective accretion of antibody in the tumor being evidenced at 3–7 days because of clearance of normal IgG. Radioactivity derived from antibody IgG showed 6.5 to 118.7 times that found in other tissues, as measured by videodensitometry, whereas organ radioactivity counting revealed ratios of only 6.7 to 29.6. Specificity of tumor-cell accretion of the radiolabeled antibody was confirmed by microscopic autoradiography, showing intense labeling of the proliferating perimeters of GW-39 tumors. WBAR was found to have a resolution of 0.10 to 0.25 mm in 100-g hamsters, which appears to be greater than the resolving power of external body imaging by gamma camera scintigraphy. These studies suggest the use of WBAR and microautoradiography to complement external imaging methods for the analysis of antibody distribution and localization in cancer radioimmunodetection models.