Recombinant ricin A chain conjugated to monoclonal antibodies: improved tumor cell inhibition in the presence of lysosomotropic compounds.
Recombinant ricin A chain was chemically linked to monoclonal antibodies directed toward human breast cancer cells, a human T-cell differentiation antigen, and mouse transferrin receptor. Three types of immunotoxins were prepared; in two of them the antibody was linked to recombinant ricin A chain by a disulfide bond and in the third, a nonreducible thioether bond was used. Immunotoxins containing a nonreducible linkage may have some advantage over conjugates containing a reducible linkage because of improved stability in vivo. Conjugation of recombinant ricin A chain through either the endogenous thiol group or through a derivatized amino group produced immunotoxins with comparable cytotoxicity. The thioether conjugate was 1000-fold less cytotoxic to target tumor cells than the respective disulfide-linked immunotoxin. However, addition of monensin, a monocarboxylic ionophore, greatly enhanced the cytotoxicity of the thioether-linked immunotoxin. Monensin increased the immunotoxin activity better than other lysosomotropic reagents that were tested. The increase in activity of recombinant ricin A chain-containing immunotoxins mediated by monensin argues against a role for contaminating ricin B chain in potentiation.
Ramakrishnan
S
S
Cetus Corporation, Emeryville, California 94608.
Bjorn
M J
MJ
Houston
L L
LL
D000911:Antibodies, Monoclonal; D001943:Breast Neoplasms / Q000473:pathology*; D002460:Cell Line; D006801:Humans; D007116:Immunization, Passive; D000922:Immunotoxins / Q000627:therapeutic use*; D008247:Lysosomes / Q000187:drug effects*; D008985:Monensin / Q000494:pharmacology; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology; D011994:Recombinant Proteins / Q000494:pharmacology; D012276:Ricin / Q000008:administration & dosage* / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D011994:Recombinant Proteins; D012276:Ricin; D008985:Monensin