title: Tumor Uptake of Anti-CD20 Fabs Depends on Tumor Perfusion.
abstract: Antibodies have become an established treatment modality in cancer therapy during the last decade. However, these treatments often suffer from an insufficient and heterogeneous response despite validated antigen or target receptor expression in the tumor. In fact, therapeutic success depends on both the presence of the tumor antigen and its accessibility by the antibody. In search of a suitable preclinical animal model to evaluate the mechanisms of tumor heterogeneity and hemodynamics, we characterized two exemplary non-Hodgkin lymphoma subtypes with comparable CD20 expression and metabolism, SUDHL-4 and Granta-519, using multimodal imaging techniques.
  
  
  METHODS
  To investigate in vivo biodistribution, two differently modified αCD20 antigen-binding fragments (Fab), prepared by PASylation with a 200-residue polypeptide tag comprising Pro, Ala, and Ser (PAS200) and by fusion with an albumin-binding domain (ABD), were radiolabeled with125I and intravenously injected into immunocompromised mice bearing corresponding xenografts.
  
  
  RESULTS
  Validation with18F-FDG revealed a similar distribution in vital tumor tissue 1 h after injection. However, large differences in tumor uptake were observed when the CD20-specific radiotracers125I-Fab-ABD and125I-Fab-PAS200were applied (respective percentages injected dose per gram at 24 h after injection: 12.3 and 2.4 for Granta-519 vs. 5.8 and 1.2 for SUDHL-4). Three-dimensional light-sheet fluorescence microscopy with Cy5-Fab-PAS200confirmed better tracer extravasation in the Granta-519 tumors. Moreover, dynamic contrast-enhanced (DCE) MRI revealed significantly reduced perfusion in the SUDHL-4 tumors.
  
  
  CONCLUSIONS
  Tracer uptake was highly dependent on local tumor perfusion and Fab permeation in the SUDHL-4 and Granta-519 tumors. Thus, the SUDHL-4 xenograft offers an excellent model for investigating the influence of therapies affecting tumor angiogenesis.
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany claudia.mendler@wzw.tum.de.|Munich Center for Integrated Protein Science (CIPS-M) and Lehrstuhl für Biologische Chemie, Technische Universität München, Freising (Weihenstephan), Germany.
authors.forename: Claudia Theresa
authors.initials: CT
authors.lastname: Mendler
authors.affiliation: Research Unit Analytical Pathology, Institute of Pathology, Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Feuchtinger
authors.affiliation: Institute of Radiology, Klinikum rechts der Isar, Technische Universität München, München, Germany; and.
authors.forename: Irina
authors.initials: I
authors.lastname: Heid
authors.affiliation: Research Unit Analytical Pathology, Institute of Pathology, Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Aichler
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany.
authors.forename: Calogero
authors.initials: C
authors.lastname: D'Alessandria
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Pirsig
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Blechert
authors.affiliation: Pharmaceutical Radiochemistry, Technische Universität München, Garching, Germany.
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Wester
authors.affiliation: Institute of Radiology, Klinikum rechts der Isar, Technische Universität München, München, Germany; and.
authors.forename: Rickmer
authors.initials: R
authors.lastname: Braren
authors.affiliation: Research Unit Analytical Pathology, Institute of Pathology, Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Walch
authors.affiliation: Munich Center for Integrated Protein Science (CIPS-M) and Lehrstuhl für Biologische Chemie, Technische Universität München, Freising (Weihenstephan), Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Skerra
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, München, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
mesh_terms: D000818:Animals; D018951:Antigens, CD20 / Q000276:immunology*; D001775:Blood Circulation; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology* / Q000378:metabolism*; D051379:Mice; D055806:Microvessels / Q000378:metabolism / Q000503:physiopathology; D010539:Permeability; D021381:Protein Transport
chemical_list: D018951:Antigens, CD20; D007140:Immunoglobulin Fab Fragments
keywords: 3D light-sheet fluorescence microscopy; DCE MRI; Fab fragment; lymphoma; tumor perfusion