Abstract: C1027, a new macromolecular peptide antitumor antibiotic producedby Streptomyces globisporus C1027, shows extremely potent cytotoxicity to cultured cancercells. The antibiotic is composed of an apoprotein and a chromophore and the latter servesas the active part of the compound. C1027 was separated into apoprotein andchromophore by methanol extraction and the separated parts can be reconstituted to formthe active C1027 molecule in phosphate buffer. For determiation of the specificity ofC1027 reconstitution, the apoprotein was incubated with epirubicin and the chromophorewas incubated with H16, a McAb directed against hepatoma cells. Notably, thereconstitution of C1027 occurred neither between apoprotein and epirubicin nor betweenchromophore and IgG molecule. In addition, bovine serum albumin showed no competi-tion with C1027 apoprotein in binding to the chromophore. Various methods for linkingC1027 to McAb were studied and two kinds of immunoconjugates have been preparted: (1)direct conjugate was made by linking C1027 to McAb, using SPDP as a linker agent, (2)assembled conjugate was made by linking and reconstitution, including 3 steps. Firstly,the chromophore was extracted with methanol and stored at-70°C in drak. Secondly, theapoprotein was conjugated to McAb by SPDP and finally the extracted chromophore wasadded to the McAb-apoprotein conjugate. Determined by clonogenic assay, the IC₅₀valuesfor hopatoma cells were 42 pmol/L, and 5. 5 pmol/L, respectively, for direct conjugate andassembled conjugate. The IC₅₀ value of M3-MC1027 assembled conjugate prepared bylinking the irrelevant McAb M3 to C1027 was 1 400 pmol/L. The results indicate that thecytotoxicity of assembled conjugate is much stronger than that of direct conjugate and thatH16-C1027 assembled conjugate showed highly selective effect on hepatoma cells.