title: Pretargeted radioimmunotherapy using genetically engineered antibody-streptavidin fusion proteins for treatment of non-hodgkin lymphoma.
abstract: OBJECTIVE
  Pretargeted radioimmunotherapy (PRIT) using streptavidin (SAv)-biotin technology can deliver higher therapeutic doses of radioactivity to tumors than conventional RIT. However, "endogenous" biotin can interfere with the effectiveness of this approach by blocking binding of radiolabeled biotin to SAv. We engineered a series of SAv FPs that downmodulate the affinity of SAv for biotin, while retaining high avidity for divalent DOTA-bis-biotin to circumvent this problem.
  
  
  METHODS
  The single-chain variable region gene of the murine 1F5 anti-CD20 antibody was fused to the wild-type (WT) SAv gene and to mutant SAv genes, Y43A-SAv and S45A-SAv. FPs were expressed, purified, and compared in studies using athymic mice bearing Ramos lymphoma xenografts.
  
  
  RESULTS
  Biodistribution studies showed delivery of more radioactivity to tumors of mice pretargeted with mutant SAv FPs followed by (111)In-DOTA-bis-biotin [6.2 ± 1.7% of the injected dose per gram (%ID/gm) of tumor 24 hours after Y43A-SAv FP and 5.6 ± 2.2%ID/g with S45A-SAv FP] than in mice on normal diets pretargeted with WT-SAv FP (2.5 ± 1.6%ID/g; P = 0.01). These superior biodistributions translated into superior antitumor efficacy in mice treated with mutant FPs and (90)Y-DOTA-bis-biotin [tumor volumes after 11 days: 237 ± 66 mm(3) with Y43A-SAv, 543 ± 320 mm(3) with S45A-SAv, 1129 ± 322 mm(3) with WT-SAv, and 1435 ± 212 mm(3) with control FP (P < 0.0001)].
  
  
  CONCLUSIONS
  Genetically engineered mutant-SAv FPs and bis-biotin reagents provide an attractive alternative to current SAv-biotin PRIT methods in settings where endogenous biotin levels are high.
authors: Department of Medicine, University of North Carolina, Chapel Hill, USA.
authors: Steven I
authors: SI
authors: Park
authors: Jaideep
authors: J
authors: Shenoi
authors: Shani M
authors: SM
authors: Frayo
authors: Donald K
authors: DK
authors: Hamlin
authors: Yukang
authors: Y
authors: Lin
authors: D Scott
authors: DS
authors: Wilbur
authors: Patrick S
authors: PS
authors: Stayton
authors: Nural
authors: N
authors: Orgun
authors: Mark
authors: M
authors: Hylarides
authors: Franz
authors: F
authors: Buchegger
authors: Aimee L
authors: AL
authors: Kenoyer
authors: Amanda
authors: A
authors: Axtman
authors: Ajay K
authors: AK
authors: Gopal
authors: Damian J
authors: DJ
authors: Green
authors: John M
authors: JM
authors: Pagel
authors: Oliver W
authors: OW
authors: Press
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000235:genetics; D018951:Antigens, CD20 / Q000276:immunology; D045744:Cell Line, Tumor; D008228:Lymphoma, Non-Hodgkin / Q000276:immunology / Q000532:radiotherapy*; D051379:Mice; D008819:Mice, Nude; D015202:Protein Engineering; D016499:Radioimmunotherapy / Q000379:methods*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D057127:Single-Chain Antibodies / Q000235:genetics; D019809:Streptavidin / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D018951:Antigens, CD20; D011993:Recombinant Fusion Proteins; D057127:Single-Chain Antibodies; D019809:Streptavidin