A single-chain immunotoxin against carcinoembryonic antigen that suppresses growth of colorectal carcinoma cells

Y. Akamatsu, J. C. Murphy, K. F. Nolan, P. Thomas, R. J. Kreitman, S. O. Leung, R. P. Junghans

    Research output: Contribution to journalArticlepeer-review


    We have engineered an anti-carcinoembryonic antigen (CEA) single-chain immunotoxin derived from humanized anti-CEA antibody (hMN14) and a truncated Pseudomonas exotoxin (PE), PE40. The purified anti-CEA immunotoxin (hMN14(Fv)-PE40) was first measured for binding affinity against a CEA- positive colorectal carcinoma cell line and compared with its parental IgG and the monovalent Fab fragment. The K(a) of sFv-PE40, Fab, and IgG were 5 x 107, 6 x 107, and 3 x 108 M-1, respectively. There was no significant affinity loss by conversion of Fab to the single-chain Fv, but these monovalent forms were 5-6-fold reduced in affinity compared with the parental IgG. In cytotoxicity assays, the hMN14(Fv)-PE40 showed specific growth suppression of CEA-expressing colon cancer cell lines MIP-CEA (high CEA) and LS174T (moderate CEA) with IC50s of 12 ng/ml (0.2 nM) and 69 ng/ml (1.1 nM). These IC50s correlated inversely with the surface expression of CEA, such that 50% killing was equivalent for each cell type when expressed in toxin molecules bound/cell (3000-5000). The presence of soluble CEA up to 1000 ng/ml did not affect the cytotoxicity against CEA-expressing cells, with 50% suppression only at 4000 ng/ml that correlated with the binding K(d) of the single-chain Fv. The stability of the hMN14(Fv)-PE40 molecule at 37°C was confirmed by bioassay and by lack of aggregation. Our hMN14(Fv)-PE40 may be clinically useful for tumors with high CEA expression without affecting normal tissues with low or absent CEA, even in patients with high soluble antigen levels.
    Original languageEnglish
    Pages (from-to)2825-2832
    Number of pages7
    JournalClinical Cancer Research
    Issue number11
    Publication statusPublished - Nov 1998


    • *ADP Ribose Transferases
    • Antibody Affinity
    • Antibody Specificity
    • Antineoplastic Agents/chemistry/*pharmacology
    • *Bacterial Toxins
    • Carcinoembryonic Antigen/biosynthesis/*immunology
    • Cell Count/drug effects
    • Colorectal Neoplasms/immunology/pathology/*therapy
    • Exotoxins/*therapeutic use
    • Humans
    • Immunotoxins/chemistry/*therapeutic use
    • Tumor Cells, Cultured
    • *Virulence Factors


    Dive into the research topics of 'A single-chain immunotoxin against carcinoembryonic antigen that suppresses growth of colorectal carcinoma cells'. Together they form a unique fingerprint.

    Cite this