title: Comparison of immunoscintigraphy, efficacy, and toxicity of conventional and pretargeted radioimmunotherapy in CD20-expressing human lymphoma xenografts.
abstract: Pretargeted radioimmunotherapy (RIT) using streptavidin (sAv)-conjugated antibodies before radiolabeled-biotin is a promising approach to improve absorbed dose ratios and achieve high durable remission rates with diminished systemic toxicity. This study compared the immunoscintigraphy, toxicity, and therapeutic efficacy of pretargeted RIT with conventional RIT using an anti-CD20 antibody.
  
  
  METHODS
  Athymic mice bearing Ramos human Burkitt's lymphoma xenografts were injected intraperitoneally with a 1F5-sAv conjugate followed 24 h later by a galactosylated, biotinylated clearing agent (CA) and, finally, 3 h later by (111)In- or (90)Y-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-biotin. The comparison groups consisted of mice injected with conventional, directly labeled (111)In- or (90)Y-1F5.
  
  
  RESULTS
  Rapid tumor uptake of radioactivity within 2 h was observed with the pretargeting approach, resulting in high-contrast tumor images at 24 h with minimal blood-pool radioactivity. Although conventional radiolabeled antibodies produced clear tumor images at 24 h, a large amount of radioactivity was present in the blood pool. The tumor-to-blood ratio was 3.5:1 with pretargeting compared with 0.4:1 with conventional (111)In-1F5. Pretargeted RIT with 29.6 MBq (800 micro Ci) (90)Y-DOTA-biotin cured 100% of mice with tolerable toxicity, whereas conventional RIT with (90)Y-1F5 at a dose of 14.8 MBq (400 micro Ci) produced no cures, induced profound pancytopenia, and was lethal to all mice.
  
  
  CONCLUSIONS
  These results suggest that anti-CD20 pretargeted RIT may be superior to conventional radiolabeled antibodies in terms of radioimmunoscintigraphy, toxicity, and therapeutic efficacy for treatment of B-cell lymphomas.
authors.affiliation: Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: Krishnan
authors.initials: K
authors.lastname: Subbiah
authors.forename: Don K
authors.initials: DK
authors.lastname: Hamlin
authors.forename: John M
authors.initials: JM
authors.lastname: Pagel
authors.forename: D Scott
authors.initials: DS
authors.lastname: Wilbur
authors.forename: Damon L
authors.initials: DL
authors.lastname: Meyer
authors.forename: Don B
authors.initials: DB
authors.lastname: Axworthy
authors.forename: Robert W
authors.initials: RW
authors.lastname: Mallett
authors.forename: Louis J
authors.initials: LJ
authors.lastname: Theodore
authors.forename: Pat S
authors.initials: PS
authors.lastname: Stayton
authors.forename: Oliver W
authors.initials: OW
authors.lastname: Press
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics / Q000627:therapeutic use* / Q000633:toxicity; D018951:Antigens, CD20 / Q000032:analysis / Q000276:immunology*; D001360:Avidin; D005260:Female; D006801:Humans; D018796:Immunoconjugates / Q000627:therapeutic use* / Q000633:toxicity; D016393:Lymphoma, B-Cell / Q000000981:diagnostic imaging / Q000276:immunology / Q000532:radiotherapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D016499:Radioimmunotherapy; D011877:Radionuclide Imaging; D019809:Streptavidin; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D018951:Antigens, CD20; D018796:Immunoconjugates; D001360:Avidin; D019809:Streptavidin