Influence of cocktails of labeled monoclonal antibodies on the localization of antibodies in human tumor xenografts

In order to evaluate the usefulness of cocktails of labeled monoclonal antibodies (MoAbs) recognizing different antigen molecules to localize human cancer xenografts, we have compared the potential of three MoAbs recognizing representative cancer-associated CA 19-9, 17-1A and CEA antigens when administered alone or in combination. Specific binding of radioiodinated F(ab')2 fragments of these three MoAbs was observed to human colorectal cancer cell lines SW1116, LS180 and Co-3. The percentage of in vitro cell binding of a cocktail of any two MoAbs to cancer cells was equal to the average of those obtained with the two MoAbs alone. The three MoAbs were preferentially localized in tumor tissues xenografted in nude mice. When cocktails of any two MoAbs were used, the obtained tumor-to-normal tissue ratios and percent of injected dose per gram of tumor were between the levels obtained for each MoAb when administered alone, in all three tumors transplanted in nude mice. These data suggest that, although cocktails of labeled MoAbs recognizing different antigens may extend the spectrum of tumor specificities, their use does not improve the tumor localization ability of MoAb-conjugates.