Abstract: AimTo study the antitumor effects of an immunoconjugate composed of lidamycin (LDM) and monoclonal antibody 3G11 (3G11-LDM conjugate). Methods3G11-LDM conjugate was prepared by using 2-iminothiolane (2-IT) and m-maleimidobenzoyl-n-hydroxy-succimide ester (MBS) as crosslinkers. The molecular weight of the conjugate was measured on non-reduced SDS-PAGE gel. Immunoreactivity of 3G11-LDM conjugate to type IV collagenase or to hepatoma 22 cells was determined by ELISA. The cytotoxicity of the immunoconjugate to hepatoma 22 cells was examined by MTT assay. Antitumor effects of the 3G11-LDM conjugate in vivo were evaluated using subcutaneously transplanted hepatoma 22 tumor model in mice. ResultsThe molecular weight of 3G11-LDM conjugate was approximately 160 kDa. 3G11-LDM conjugate retained part of the immunoreactivity of 3G11 to type IV collagenase and hepatoma 22 cells. As compared with free LDM, 3G11-LDM conjugate showed stronger cytotoxicity to hepatoma 22 cells. When administered intravenously (iv×2 on day 1 and 8), 3G11-LDM conjugate, at doses of 0.05 and 0.10 mg·kg^-1, inhibited the growth of hepatoma 22 in mice by 87.8% and 97.2% on day 11, respectively, whereas the unconjugated LDM at 0.05 mg·kg^-1 inhibited tumor growth by 67.1%. The median survival times for tumor-bearing mice of untreated control, LDM at 0.05 mg·kg^-1, 3G11-LDM at 0.05 mg·kg^-1, and 3G11-LDM at 0.10 mg·kg^-1 were 34, 41.5, 60.5 and 94 d, respectively. Evidently 3G11-LDM was more effective than free LDM in suppressing tumor growth and prolonging the life span of tumor-bearing mice. Conclusion3G11-LDM conjugate shows much stronger antitumor effects than equivalent dose of free LDM and may have promising therapeutic potential in cancer treatment.