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Human Biodistribution of ¹¹¹In-labeled B72.3 Monoclonal Antibody¹

Departments of Nuclear Medicine, Pharmacy, and Medicine, Bay Pines Veterans Administration Medical Center, Bay Pines, Florida 33504; College of Pharmacy, University of Florida, Gainesville, Florida 32610; and Department of Radiology, University of South Florida School of Medicine, Tampa, Florida 33612

The murine IgG1 monoclonal antibody B72.3 reacts with human colorectal, breast, lung, pancreatic, gastric, and ovarian tumors. Human biodistribution studies using intact ¹³¹I-B72.3 have been reported by Carrasquillo et al. (J. Nucl. Med., 29: 1022–1030, 1988). We have performed similar studies on five patients using i.v. infusion of 20 mg of intact ¹¹¹In-B72.3 (Cytogen Corp.). Serum clearance is similar with a t of 64.2 h (range, 44–80) for ¹¹¹In-B72.3 and 65 h (range, 32–106) for ¹³¹I-B72.3 (J. A. Carrasquillo et al., J. Nucl. Med., 29: 1022–1030, 1988). However, organ biodistribution is markedly different. For ¹³¹I-B72.3, hepatic and splenic clearance mirrors blood pool clearance (J. A. Carrasquillo et al., J. Nucl. Med., 29: 1022–1030, 1988). For ¹¹¹In-B72.3, there is rapid uptake in tumor, liver, spleen, kidney, lumbar spine, and testes by 2–6 h with no significant clearance over the next 9 days. For ¹¹¹In-B72.3, quantitative analysis of liver (from biopsy specimens), spleen, kidney, and lumbar spine (from scintiphoto regions of interest after background subtraction and attenuation correction) shows the following peak organ biodistributions in percentage infused dose: liver, 32%; spleen, 3.9%; kidneys, 3.5%; and lumbar vertebral bodies (marrow sample), 2.7%. For both ¹¹¹In-B72.3 and ¹³¹I-B72.3, the principal route of excretion from the body is urinary with excretion rate of ¹³¹I faster than ¹¹¹In. The marked differences between ¹¹¹In-B72.3 and ¹³¹I-B72.3 biodistribution and clearance strongly influence the dosimetry, immunodetection, and immunotherapeutic potentials of B72.3 MoAb.