Antitumor effects of the molecule-downsized immunoconjugate composed of lidamycin and Fab' fragment of monoclonal antibody directed against type IV collagenase.

Type IV collagenase plays an important role in tumor invasion and metastasis through cleaving type IV collagen in the basement membrane and extracellular matrix. In this study a molecule-downsized immunoconjugate (Fab'-LDM) was constructed by linking lidamycin (LDM), a highly potent antitumor antibiotic, to the Fab' fragment of a monoclonal antibody directed against type IV collagenase and its antitumor effect was investigated. As assayed in 10% SDS-PAGE gel, the molecular weight of Fab'-LDM conjugate was 65 kD with a 1 : 1 molecular ratio of Fab' and LDM. The Fab'-LDM conjugate maintained most part of the immunoreactivity of Fab' fragment to both type IV collagense and mouse hepatoma 22 cells by ELISA. By MTT assay, Fab'-LDM conjugate showed more potent cytotoxicity to hepatoma 22 cells than that of LDM. Administered intravenously, Fab'-LDM conjugate proved to be more effective against the growth of subcutaneously transplanted hepatoma 22 in mice than free LDM in two experiment settings. In Experiment I, the drugs were given intravenously on day 1 and day 8. Fab'-LDM at the doses of 0.025 mg/kg, 0.05 mg/kg and 0.1 mg/kg inhibited tumor growth by 76.7%, 93.3% and 94.8%, while free LDM at 0.05 mg/kg inhibited tumor growth by 76.1%, respectively. In experiment II, the drugs were given intravenously on day 4 and day 11, Fab'-LDM at the doses of 0.025 mg/kg and 0.05 mg/kg inhibited tumor growth by 74.2%, 80.9%, while free LDM at 0.05 mg/kg inhibited tumor growth by 60.5%, respectively. In terms of survival time, Fab'-LDM was more effective than free LDM. The results suggest that the molecule-downsized immunoconjugate directed against type IV collagenase is of high efficacy in experimental cancer therapy.