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UNLABELLED: Multidrug resistance (MDR) is a major challenge to the successful treatment of acute myeloid leukemia (AML). Our purpose was to determine whether (111)In-HuM195 anti-CD33 antibodies modified with peptides harboring nuclear localizing sequences (NLS) could kill drug-resistant AML cell lines and primary AML patient specimens expressing MDR transporters through the emission of Auger electrons. METHODS: HuM195, M195, and irrelevant mouse IgG (mIgG) were conjugated to 10+/-3 NLS peptides and then labeled with (111)In by diethylenetriaminepentaacetic acid substitution to a specific activity of 1-8 MBq/microg. The binding affinity of HuM195 and M195 was determined for HL-60 and mitoxantrone-resistant HL-60-MX-1 cells. Nuclear localization of (111)In-NLS-HuM195, (111)In-NLS-M195, (111)In-HuM195, and (111)In-M195 was measured by subcellular fractionation. The antiproliferative effects of (111)In-NLS-HuM195, (111)In-NLS-M195, (111)In-HuM195, and (111)In-M195 (2.5-250 kBq/well) on HL-60 and HL-60-MX-1 were studied using the WST-1 assay. Clonogenic survival of HL-60 and HL-60-MX-1 leukemic cells and 10 primary AML specimens with MDR phenotype (assessed by flow cytometry) was determined after exposure for 3 h at 37 degrees C to 2.5-250 mBq/cell of (111)In-NLS-HuM195, (111)In-HuM195, or (111)In-NLS-mIgG. Clonogenic survival versus the amount of radioactivity incubated with the cells (mBq/cell) was plotted, and the mean lethal amount of radioactivity and the lower asymptote of the curve (plateau) were determined. RESULTS: The (111)In-labeled anti-CD33 monoclonal antibodies HuM195 and M195 modified with NLS were efficiently routed to the nucleus of HL-60 cells and their mitoxantrone-resistant clone after CD33-mediated internalization. The following are the principal findings of our study: (111)In-NLS-HuM195 was more effective at killing HL-60 and HL-60-MX-1 cells than was (111)In-HuM195, a strong correlation between the specific activity of the (111)In-labeled radioimmunoconjugates and their cytotoxicity toward AML cells existed, and leukemic cells from patients were killed by (111)In-NLS-M195 or (111)In-M195, but the cytotoxic response among specimens was heterogeneous. CONCLUSION: NLS conjugation enhanced the nuclear uptake and cytotoxicity of (111)In-HuM195 and (111)In-M195 toward drug-resistant AML cell lines as well as patient specimens expressing a diversity of MDR phenotypes, including Pgp-170, BCRP1, or MRP1 transporters. Targeted Auger electron radioimmunotherapy using (111)In-labeled anti-CD33 monoclonal antibodies modified with NLS may be able to overcome MDR and provide a means of treating chemotherapy-resistant myeloid leukemias in patients.

Original publication




Journal article


J Nucl Med

Publication Date





1546 - 1554


Antibodies, Monoclonal, Antineoplastic Agents, Cell Line, Tumor, Cell Survival, Drug Delivery Systems, Drug Resistance, Multiple, Humans, Indium Radioisotopes, Leukemia, Myeloid, Acute, Natural Cytotoxicity Triggering Receptor 2, Nuclear Localization Signals, Radionuclide Imaging, Receptors, Immunologic