Affinity chromatography of the Walker carcinosarcoma 256 B tumor revealed a lactose-specific lectin of 24 kDa. In a chemotherapeutical experiment, B-D-lactosylisophosphoramide mustard (corresponding lectin present in tumor tissue) proved to be significantly more active than B-D-maltosylisophosphoramide mustard (no corresponding lectin present), although both compounds differ only marginally in their sugar parts. Whole body autoradiography after application of C-14-labeled B-D-lactosylisophosphoramide mustard in tumor bearing rats shows an accumulation of radioactivity in kidneys, thymus, central nervous system and in the tumor. Binding between the isolated lectin and the lactose-conjugated drug is shown in vitro; its activation outside tumor cells is experimentally excluded.

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