THE SELECTION OF ANTIBODIES FOR TARGETED THERAPY OF SMALL-CELL LUNG-CANCER (SCLC) USING A HUMAN TUMOR SPHEROID MODEL TO COMPARE THE UPTAKE OF CLUSTER-1 AND CLUSTER-W4 ANTIBODIES

Spheroids of a small-cell lung cancer (SCLC) cell line POC were used t o evaluate the uptake and penetration of two antibodies recognising di fferent SCLC antigens. Spheroids approximately 300-400 mu m in diamete r were incubated with 1 mu g ml(-1) I-125-labelled NY.3D11, an antibod y which reacts with the cluster 1 group antigen (neural cell adhesion molecule; NCAM) and [I-125]SWA11, which binds to the cluster w4 antige n. The rate of uptake of both antibodies was similar, an initially rap id phase was seen during the first X h and maximum uptake occurred by 24 h. The mean uptake per spheroid at 24 h was 0.97 ng for [I-125]NY.3 D11 and 0.45 ng for [I-125]SWA11. An objective measurement of antibody penetration into spheroids was developed using a computerised image a nalysis of immunostained sections of spheroids. The concentration of a ntibody and incubation times were varied. Both antibodies penetrated t he spheroids to a depth of 50 mu m after 30 min. This increased to abo ut 100 mu m after 4 h incubation with 1 or 100 mu g ml(-1) SWA11. The results with 1 mu g ml(-1) NY.3D11 were similar, but in the presence o f 100 mu g ml(-1) NY.3D11 penetration into the spheroid was deep and d iffuse. These results demonstrate a major concentration-dependent diff erence in the uptake and penetration of cluster 1 and cluster w4 antib odies in this spheroid model and they have implications for the select ion of antibodies for targeted therapy of SCLC.