RT Journal Article SR Electronic T1 Tumor uptake of anti-CD20 Fabs depends on tumor perfusion JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP jnumed.116.176784 DO 10.2967/jnumed.116.176784 A1 Claudia T Mendler A1 Annette Feuchtinger A1 Irina Heid A1 Michaela Aichler A1 Calogero D'Alessandria A1 Sabine Pirsig A1 Birgit Blechert A1 Hans-Jürgen Wester A1 Rickmer Braren A1 Axel Walch A1 Arne Skerra A1 Markus Schwaiger YR 2016 UL http://jnm.snmjournals.org/content/early/2016/07/11/jnumed.116.176784.abstract AB Antibodies have become an established treatment modality in cancer therapy during the last decade. However, these treatments often suffer from insufficient and heterogeneous response despite validated antigen or target receptor expression in the tumor. In fact, therapeutic success depends both on the presence and accessibility of the tumor antigen 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, using multimodal imaging techniques. Methods: To investigate in vivo biodistribution, two differently modified αCD20 antigen-binding fragments (Fab), prepared (i) by PASylation and (ii) by fusion with an albumin-binding domain (ABD), were radiolabeled with 125I and intravenously injected into immunocompromised mice bearing corresponding xenografts. Results: Validation with 18F-FDG revealed similar distribution of vital tumor tissue 1 h p.i. However, large differences in tumor uptake were observed when applying the CD20-specific radiotracers 125I-Fab-ABD and 125I-Fab-PAS200 with 12.3 and 2.4 % ID/g, respectively, for Granta in comparison with 3.5 and 0.75 % ID/g, respectively, for SUDHL-4 xenografts 24 h p.i. 3D light-sheet fluorescence microscopy with Cy5-Fab-PAS200 confirmed better tracer extravasation in the Granta tumors. Moreover, dynamic contrast enhanced MRI imaging revealed significantly reduced tumor perfusion in the SUHDL-4 xenografts. Conclusion: Tracer uptake was highly dependent on local tumor perfusion as well as Fab permeation in the SUDHL-4 and Granta tumors. Thus, the SUDHL-4 xenograft offers an excellent model system to investigate the influence of therapies affecting tumor angiogenesis.