A monoclonal antibody, 6D7, reactive with cytokeratin-8, the most abundant type of cytokeratin in normal and malignant epithelial cells, was examined for its binding in DU 145 prostatic carcinoma spheroids. It was found that 6D7 bound in the intermediate, quiescent cell layers of the spheroids while no binding was observed either in the outer layers, which comprises mainly proliferating cells, or in the central necrotic core of the spheroids. Even within the quiescent cell layers, binding was only observed in certain cells that appeared to have incorporated the anticytokeratin antibody. It is likely that these cells had a disturbance in cell membrane permeability and therefore permitted the transmembrane passage of 6D7. The disturbed cell membrane permeability was due to the local environmental conditions in the spheroids, since quiescent monolayer cells did not incorporate 6D7. A complementary binding of 6D7 and E4, a prostatic carcinoma reactive monoclonal antibody, was found in the DU 145 spheroids. While E4 bound strongly in the outer viable cell layers, 6D7 bound in the quiescent cell layers close to the necrotic core. A combination of radiolabelled 6D7 and E4, therefore appears efficient in targeting both proliferating and quiescent cells.

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