Uptake of a monoclonal antibody against CEA (Tumak 431/31) in a human colon tumor (Co-112) xenografted in the nude mouse. Dependence on tumor size and injected dose.

A monoclonal antibody (Tumak) against carcinoembryonic antigen (CEA) was injected into nude mice bearing a human colon carcinoma (Co-112). The tumor uptake was found to be dependent on the size of the tumors: relative uptake (percentage of the injected dose/gram tumor (% i.d./g) decreased for tumors with weights up to approximately 1 g, although the absolute uptake (% i.d./tumor) still increased over the same weight range. In the constant region (greater than or equal to 1 g) mean relative tumor uptake was approximately 4% i.d./g. The same tumor size dependence was found for the relative Tumak uptake in the other mouse organs studied (e.g., blood, liver, spleen and muscle). Consequently tumor/organ ratios were found to be independent of tumor size. Tumor uptake was also studied for various doses of Tumak (0.07-120 micrograms) in tumors of approximately 1 g. Evidence was found for a threshold dose of 0.1 microgram under which no serious tumor uptake appeared. From 1 to 120 micrograms no further dependence of Tumak distribution on applied dose was found: the relative uptake of all organs remained the same but the absolute uptake increased with dose.