The anti-CD25 monoclonal antibody 7G7/B6, armed with the α-emitter 211At, provides effective radioimmunotherapy for a murine model of leukemia

Radioimmunotherapy of cancer with radiolabeled antibodies has shown promise. alpha-Particles are very attractive for cancer therapy, especially for isolated malignant cells, as is observed in leukemia, because of their high linear energy transfer and short effective path length. We evaluated an anti-CD25 [interleukin-2 receptor alpha (IL-2R alpha)] monoclonal antibody, 7G7/B6, armed with At-211 as a potential radioinummotherapeutic agent for CD25-expressing leukemias and lymphomas. Therapeutic studies were done in severe combined immunodeficient/nonobese diabetic mice bearing the karpas299 leukemia and in nude mice bearing the SUDHL-1 lymphoma. The results from a pharmacokinetic study showed that the clearance of At-211-7G7/B6 from the circulation was virtually identical to I-125-7G7/B6. The biodistributions of At-211-7G7/B6 and I-125-7G7/B6 were also similar with the exception of a higher stomach uptake of radioactivity with At-211-7G7/B6. Therapy using 15 mu Ci of At-211-7G7/B6 prolonged survival of the karpas299 leukemia-bearing mice significantly when compared with untreated mice and mice treated with At-211- 111711, a radiolabeled nonspecific control antibody (P < 0.01). All of the mice in the control and At-211-11F11 groups died by day 46 whereas > 70% of the mice in the At-211-7G7/B6 group still survived at that time. In summary, At-211-7G7/B6 could serve as an effective therapeutic agent for patients with CD25-expressing leukemias.