| Abstract: | This study investigates the influence of antibody protein dose on the radioimmunodetection of a CEA-producing, human colonic tumor xenograft (GW-39) using affinity-purified goat anti-carcinoembryonic antigen (CEA) antibody and a murine monoclonal anti-CEA antibody (NP-2). Hamsters bearing GW-39 tumors were given an equal mixture of 131I-labelled antibody and 125I-labelled irrelevant IgG at doses varying from 0.01 to 1.0 mg (0.1 to 10 mg/kg body weight) for each antibody preparation. No differences were found in the percentage of antibody in the tumor or the clearance rate from the blood as the antibody dose was increased. The concentration of antibody in the tumor increased proportionally with the antibody dose and maintained a linear relationship with increasing dose, indicating that antigenic sites in the tumor were not saturated with antibody. The concentration of irrelevant IgG in the tumor also increased proportionally as the dose was increased, but the concentration of irrelevant IgG in the tumor was less than the antibody and was removed more rapidly from the tumor than the antibody. By considering the amount of irrelevant IgG in the tumor as a measure of the amount of antibody non-specifically bound, we determined that there was no change in the amount of antibody in the tumor between days 3 and 7, and the amount of antibody increased uniformly for both the tumor and non-tumor tissues, resulting in no improvement in the tumor/non-tumor ratios with increasing antibody dose. External scintigraphy verified that the dose of the antibody did not influence tumor imaging. Thus, tumor accretion of antibody in this model is not dependent principally on the antibody protein dose, and other factors such as accessibility to antigen and antibody metabolism may play important roles in regulating the uptake of antibody in tumor. |
