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Radioimmunoassay of Neocarzinostatin, an Antitumor Protein¹

The Sidney Farber Cancer Center, Harvard Medical School, Boston, Massachusetts 02115

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.

¹ This investigation was supported by National Cancer Institute Research Grants CA 17305 and CA 06516.

Received 6/30/76. Accepted 8/23/76.