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Blood, 6 August 2009, Vol. 114, No. 6, pp. 1226-1235. Prepublished online as a Blood First Edition Paper on June 10, 2009; DOI 10.1182/blood-2009-03-210344.
LYMPHOID NEOPLASIA Pretargeting CD45 enhances the selective delivery of radiation to hematolymphoid tissues in nonhuman primates1 Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA; 2 Department of Medicine, University of Washington, Seattle; 3 Department of Pediatrics, Oregon Health & Science University, Portland; 4 Department of Radiation Oncology, University of Washington, Seattle; 5 Pacific Northwest National Laboratory, Richland, WA; and 6 Department of Radiology, University of Washington, Seattle Pretargeted radioimmunotherapy (PRIT) is designed to enhance the directed delivery of radionuclides to malignant cells. Through a series of studies in 19 nonhuman primates (Macaca fascicularis), the potential therapeutic advantage of anti-CD45 PRIT was evaluated. Anti-CD45 PRIT demonstrated a significant improvement in target-to-normal organ ratios of absorbed radiation compared with directly radiolabeled bivalent antibody (conventional radioimmunotherapy [RIT]). Radio-DOTA-biotin administered 48 hours after anti-CD45 streptavidin fusion protein (FP) [BC8 (scFv)4SA] produced markedly lower concentrations of radiation in nontarget tissues compared with conventional RIT. PRIT generated superior target:normal organ ratios in the blood, lung, and liver (10.3:1, 18.9:1, and 9.9:1, respectively) compared with the conventional RIT controls (2.6:1, 6.4:1, and 2.9:1, respectively). The FP demonstrated superior retention in target tissues relative to comparable directly radiolabeled bivalent anti-CD45 RIT. The time point of administration of the second step radiolabeled ligand (radio-DOTA-biotin) significantly impacted the biodistribution of radioactivity in target tissues. Rapid clearance of the FP from the circulation rendered unnecessary the addition of a synthetic clearing agent in this model. These results support proceeding to anti-CD45 PRIT clinical trials for patients with both leukemia and lymphoma.
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