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PET of 89Zr-Pembrolizumab in Cynomolgus
PET/CT Imaging of 89Zr-N-sucDf-Pembrolizumab in Healthy Cynomolgus Monkeys
Wenping Li, Yuchuan Wang, Daniel Rubins, Idriss Bennacef, Marie Holahan, Hyking Haley, Mona Purcell, Liza Gantert, SuChun Hseih, Michael Judo, Wolfgang Seghezzi, Shuli Zhang, Elly L. van der Veen, Marjolijn N. Lub-de Hooge, Elisabeth G.E. de Vries, Jeffrey L. Evelhoch, Michael Klimas, Eric D. Hostetler
Molecular Imaging and Biology 2020 Oct 26. doi: 10.1007/s11307-020-01558-w
Programmed cell death-1 receptor (PD-1) and its ligand (PD-L1) are the targets for immunotherapy in many cancer types. Although PD-1 blockade has therapeutic effects, the efficacy differs between patients. Factors contributing to this variability are PD-L1 expression levels and immune cells present in tumors. However, it is not well understood how PD-1 expression in the tumor microenvironment impacts immunotherapy response. Thus, imaging of PD-1-expressing immune cells is of interest. This study aims to evaluate the biodistribution of Zirconium-89 (89Zr)-labeled pembrolizumab, a humanized IgG4 kappa monoclonal antibody targeting PD-1, in healthy cynomolgus monkeys as a translational model of tracking PD-1- positive immune cells.
Pembrolizumab was conjugated with the tetrafluorophenol-N-succinyl desferal- Fe(III) ester (TFP-N-sucDf) and subsequently radiolabeled with 89Zr. Four cynomolgus monkeys with no previous exposure to humanized monoclonal antibodies received tracer only or tracer co-injected with pembrolizumab intravenously over 5 min. Thereafter, a static whole-body positron emission tomography (PET) scan was acquired with 10 min per bed position on days 0, 2, 5, and 7. Image-derived standardized uptake values (SUVmean) were quantified by region of interest (ROI) analysis.
89Zr-N-sucDf-pembrolizumab was synthesized with high radiochemical purity (>99 %) and acceptable molar activity (>7 MBq/nmol). In animals dosed with tracer only, 89Zr-N-sucDf-pembrolizumab distribution in lymphoid tissues such as mesenteric lymph nodes, spleen, and tonsils increased over time. Except for the liver, low radiotracer distribution was observed in all non-lymphoid tissue including the lung, muscle, brain, heart, and kidney. When a large excess of pembrolizumab was co-administered with a radiotracer, accumulation in the lymph nodes, spleen, and tonsils was reduced, suggestive of target-mediated accumulation.
89Zr-N-sucDf-pembrolizumab shows preferential uptake in the lymphoid tissues including the lymph nodes, spleen, and tonsils. 89Zr-N-sucDf-pembrolizumab may be useful in tracking the distribution of a subset of immune cells in non-human primates and humans.