Different cytotoxic activity and intracellular fate of an anti-CD5-momordin immunotoxin in normal compared to tumour cells.
We investigated the different sensitivity of peripheral blood mononuclear cells (PBMC) and human T cell leukaemias (Jurkat and CEM) to an anti-CD5-momordin immunotoxin. In a short-term assay, the immunotoxin displayed different cytotoxic activity on normal and tumour cells: for leukaemic cell lines an incubation time of 72 h was necessary for the immunotoxin to reach the IC50 of 41-53 pM, compared to the 1 h sufficient for 6 pM immunotoxin to inhibit 50% of PBMC protein synthesis. In a long-term clonogenic assay (15 days), the immunotoxin demonstrated a comparable efficacy of clonogenic cell killing for both cell types. We investigated the immunotoxin internalization pathway by a flow-cytometric method and our data seem to indicate that the molecules meet a different intracellular fate in the two cell populations. It may be assumed that the low cytotoxic activity of immunotoxins on tumour cells, detected in the short-term assay, is due to inefficient delivery to their cytoplasmatic target, while a longer exposure of the cells to the immunotoxin promotes adequate intracellular distribution.
Porro
G
G
Italfarmaco Research Centre, Cinisello Balsamo (MI), Italy.
Lento
P
P
Marcucci
F
F
Gromo
G
G
Modena
D
D
D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism; D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics* / Q000633:toxicity*; D018956:CD5 Antigens; D002478:Cells, Cultured; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000493:pharmacokinetics; D006801:Humans; D000922:Immunotoxins / Q000493:pharmacokinetics* / Q000633:toxicity*; D007424:Intracellular Fluid / Q000378:metabolism; D015458:Leukemia, T-Cell / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism*; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000493:pharmacokinetics* / Q000633:toxicity*; D054790:Ribosome Inactivating Proteins, Type 2; D012680:Sensitivity and Specificity; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000964:Antimetabolites, Antineoplastic; D018956:CD5 Antigens; D000922:Immunotoxins; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D009699:N-Glycosyl Hydrolases; D016650:Fluorescein-5-isothiocyanate