Radioimmunoassay of neocarzinostatin, an antitumor protein

Antibodies directed toward the antitumor protein neocarzinostatin (NCS) have been produced in a rabbit by immunization with a highly purified NCS preparation. The antiserum was monospecific and reversed the antibacterial activity of NCS against Sarcina lutea. It cross-reacted with chemically modified derivatives of NCS and mitomalcin but failed to cross-react with macromomycin. A radioimmunoassay procedure has been developed utilizing the antiserum and a biologically active 125I-labeled derivative of NCS. The lower limit of detection by this radioimmunoassay, which involves a double antibody technique for the separation of antibody-bound and free antigen, was 1 X 10(-13) mole. The sensitivity of the assay is such that serum levels of NCS can be determined accurately after administration of the drug to rats at a single dose of 2 mg/kg. Since NCS is now undergoing clinical trial, the radioimmunoassay of the drug will be a valuable tool in clinical pharmacological studies.