Tumor uptake of intravenously administered radiolabeled antibodies in ovarian carcinoma patients in relation to antigen expression and other tumor characteristics

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Abstract
To study factors that possibly influence the heterogeneous tumor uptake of radiolabeled antibodies, tissues from 34 ovarian‐carcinoma patients were obtained 2 to 8 days after i.v. injection with radiolabeled murine OV‐TL 3 or chimeric MOv 18 (cMOv18). The tumor uptake and the ratio of tumor to normal tissue (T/NT) were studied in relation to the histopathological classification, prior treatment, site of tumor, time interval, antigen expression, volume percentage of (malignant) epithelium in the tumor tissue, and the size of the tumor. The results of immuno‐scintigraphy were also included. In addition, autoradiography using storage phosphor technology was performed on tissue sections from patients injected with iodine‐labeled cMOv18.Tumor uptake varied largely, not only between patients, but also between tumor deposits within the same patient. Uptake of OV‐TL 3 F(ab')2 was higher than of cMOv18 F(ab')2, but the T/NT ratios were similar. The antibody uptake was positively correlated with the pattern of antigen expression and inversely correlated with the time interval between injection and surgery. No correlation was observed with any of the other factors studied. The visibility with immunoscintigraphy was related to the size of the detected lesion, but not to the other factors studied. Autoradiography showed that antibodies preferentially localized in areas with cancer cells, which were immunohisto‐chemically positive for MOv18. In areas with weak antigen expression, autoradiography revealed less activity. The antigen expression by the tumor is an important factor for estimation of the tumor uptake of radiolabeled antibodies.

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