An enediyne-energized single-domain antibody-containing fusion protein shows potent antitumor activity.

Single-domain antibodies are attractive as tumor-targeting vehicles because of their much smaller size than intact antibody molecules. Lidamycin is a macromolecular antitumor antibiotic, which consists of a labile enediyne chromophore (AE) and a noncovalently bound apoprotein (LDP). An enediyne-energized fusion protein VH-LDP-AE composed of single-domain antibody directed against type IV collagenase and lidamycin was prepared by a novel two-step method including DNA recombination and molecular reconstitution. VH-LDP-AE demonstrated extremely potent cytotoxicity to cancer cells and marked antiangiogenic activity in vitro. In the mouse hepatoma 22 model, drugs were administered intravenously as a single dose on day 1 with maximal tolerated doses. VH-LDP-AE (0.25 mg/kg) suppressed the tumor growth by 95.9%, whereas lidamycin (0.05 mg/kg) and mitomycin (1 mg/kg) by 79.6 and 51.1%, respectively. In the HT-1080 xenograft model in nude mice, drugs were given intravenously as a single dose on day 4 after tumor implantation. VH-LDP-AE at 0.25 mg/kg suppressed tumor growth by 76% (P<0.05) compared with that of lidamycin at 0.05 mg/kg (53%) on day 18. No obvious toxic effects were observed in all groups during treatments. The results showed that energized fusion protein VH-LDP-AE was more effective than lidamycin and mitomycin. These properties, together with its much smaller size than conventional antibody-based agents, suggested that VH-LDP-AE would be a promising candidate for cancer-targeting therapy. In addition, the two-step approach could serve as a new technology platform for making a series of highly potent engineered antibody-based drugs for a variety of cancers.