Inhibition of catabolism of radiolabeled antibodies by tumor cells using lysosomotropic amines and carboxylic ionophores

• Published in: Cancer research (Chicago, Ill.) Vol. 50; no. 4; pp. 1243 - 1250
• Main Authors: PRESS, O. W, DE SANTES, K, ANDERSON, S. K, GEISSLER, F
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15.02.1990
• Subjects: Acid Phosphatase - analysis; Amantadine - pharmacology; Ammonium Chloride - pharmacology; Animals; Antibodies, Monoclonal - analysis; Antibodies, Monoclonal - metabolism; Antibodies, Neoplasm - analysis; Antibodies, Neoplasm - metabolism; Antineoplastic agents; Biological and medical sciences; Chloroquine - pharmacology; Chromatography, High Pressure Liquid; General aspects; Humans; Iodine Radioisotopes; Lysosomes - enzymology; Lysosomes - metabolism; Medical sciences; Mice; Monensin - pharmacology; Nigericin - pharmacology; Pharmacology. Drug treatments; Temperature; Tumor Cells, Cultured - metabolism; Verapamil - pharmacology; Human; Cell culture; Calcium antagonist; Lysosome; Enzyme inhibitor; Malignant hemopathy; Monoclonal antibody; Radioisotope; Metabolism; Drug targeting; Drug interaction; Ionophore; Tumor cell
• ISSN: 0008-5472; 1538-7445

The rates of degradation of radioiodinated monoclonal antibodies (MoAbs) by malignant T- and B-lymphoid cells were studied in the presence and absence of a variety of pharmacological agents known to affect the intracellular metabolism of internalized ligands. 125I-MoAbs directed against the CD2, CD3, CD5, and anti-mu surface antigens underwent rapid endocytosis, followed by prompt degradation with release of greater than or equal to 50% of the initially bound radioactivity as free, trichloroacetic acid-soluble 125I within 24 h. Lysosomotropic amines (chloroquine, ammonium chloride, amantadine), carboxylic ionophores (monensin, nigericin), calcium channel blockers (verapamil), thionamides (propylthiouracil), lysosomal enzyme inhibitors (leupeptin), and colchicine all inhibited metabolism of radioiodinated MoAbs and enhanced retention of 125I-MoAbs by tumor cells. The most effective agents (e.g., monensin, nigericin) diminished the release of free 125I by greater than 90% and enhanced retention of radioactivity by greater than 300% at 24 h. Experiments with immunoperoxidase electron microscopy and Percoll gradient fractionation of organelles from disrupted cells suggested that high concentrations of monensin (10-20 microM) delayed transfer of 125I-MoAbs to lysosomes, but other mechanisms (e.g., pH neutralization) were operative at lower concentrations (1-3 microM). Clinical administration of these agents may enhance retention of radioimmunoconjugates by tumor cells, resulting in improved radioimmunoscintigraphy and radioimmunotherapy.