title: Improvement of the Targeting of Radiolabeled and Functionalized Liposomes with a Two-Step System Using a Bispecific Monoclonal Antibody (Anti-CEA × Anti-DTPA-In).
abstract: This study proposes liposomes as a new tool for pretargeted radioimmunotherapy (RIT) in solid tumors. Tumor pretargeting is obtained by using a bispecific monoclonal antibody [BsmAb, anti-CEA × anti-DTPA-indium complex (DTPA-In)] and pegylated radioactive liposomes containing a lipid-hapten conjugate (DSPE-PEG-DTPA-In). In this work, the immunospecificity of tumor targeting is demonstrated both in vitro by fluorescence microscopy and in vivo by biodistribution studies.
  
  
  METHODS
  Carcinoembryonic antigen (CEA)-expressing cells (LS174T) were used either in cell culture or as xenografts in nude mice. Doubly fluorescent liposomes or doubly radiolabeled liposomes were, respectively, used for in vitro and in vivo studies. In each case, a tracer of the lipid bilayer [rhodamine or indium-111 ((111)In)] and a tracer of the aqueous phase [fluorescein or iodine-125 ((125)I)] were present. The targeting of liposomes was assessed with BsmAb for active targeting or without for passive targeting.
  
  
  RESULTS
  Data obtained with the lipid bilayer tracer showed a fluorescent signal on cell membranes two to three times higher for active than for passive targeting. This immunospecificity was confirmed in vivo with tumor uptake of 7.5 ± 2.4% ID/g (percentage of injected dose per gram of tissue) for active targeting versus 4.5 ± 0.45% ID/g for passive targeting (p = 0.03). Regarding the aqueous phase tracer, results are slightly more contrasted. In vitro, the fluorescent tracer seems to be released in the extracellular matrix, which can be correlated with the in vivo data. Indeed, the tumor uptake of (125)I is lower than that of (111)In: 5.1 ± 2.5% ID/g for active targeting and 2.7 ± 0.6% ID/g for passive targeting, but resulted in more favorable tumor/organs ratios.
  
  
  CONCLUSIONS
  This work demonstrated the tumor targeting immunospecificity of DSPE-PEG-DTPA-In liposomes by two different methods. This original and new approach suggests the potential of immunospecific targeting liposomes for the RIT of solid tumors.
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France ; Nuclear Medicine Department, Institut de Cancérologie de l'Ouest , Saint Herblain , France.
authors.forename: Aurore
authors.initials: A
authors.lastname: Rauscher
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France ; Nuclear Medicine Department, University Hospital Nantes , Nantes , France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Frindel
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France.
authors.forename: Holisoa
authors.initials: H
authors.lastname: Rajerison
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Gouard
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Maurel
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France ; GIP Arronax , Saint Herblain , France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Barbet
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France ; Nuclear Medicine Department, University Hospital Nantes , Nantes , France.
authors.forename: Alain
authors.initials: A
authors.lastname: Faivre-Chauvet
authors.affiliation: Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), 6299 CNRS, UMR 892 - INSERM, Université de Nantes , Nantes , France ; Nuclear Medicine Department, University Hospital Nantes , Nantes , France.
authors.forename: Marie
authors.initials: M
authors.lastname: Mougin-Degraef
keywords: bispecific antibody; pegylated liposomes; pretargeting; radioimmunotherapy; solid tumors