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Development of a 68Gallium-Labeled D-Peptide PET Tracer for Imaging Programmed Death-Ligand 1 Expression
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A Gallium-67/68-Labeled Antibody Fragment for Immuno-SPECT/PET Shows Low Renal Radioactivity Without Loss of Tumor

Tomoya Uehara1, Miki Yokoyama2, Hiroyuki Suzuki2

  • 1Graduate School of Pharmaceutical Sciences, Chiba University, Chiba, Japan. tuehara@chiba-u.jp.

Clinical Cancer Research : an Official Journal of the American Association for Cancer Research
|April 19, 2018
PubMed

Purpose: This study was undertaken to evaluate the renal radioactivity levels of a newly designed 67Ga-labeled antibody fragment with a linkage cleaved by enzymes present on the brush border membrane (BBM) lining the lumen of the renal tubule.Experimental Design:67Ga-labeled S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bn-NOTA) was conjugated with an antibody Fab fragment through a Met-Val-Lys linkage (67Ga-NOTA-MVK-Fab) considering that a Met-Val sequence is a substrate of enzymes on the renal BBM and 67Ga-NOTA-Met is excreted from the kidney into the urine. The enzymatic recognition of the linkage was evaluated with a low-molecular-weight 67Ga-NOTA-Met-Val-Lys derivative. Biodistribution of radioactivity after injection of 67Ga-NOTA-MVK-Fab into mice was compared with 67Ga-NOTA-conjugated Fab fragments through a Met-Ile linkage that liberates 67Ga-NOTA-Met (67Ga-NOTA-MI-Fab) or a conventional thiourea linkage (67Ga-NOTA-Fab).Results: The MVK linkage remained stable in plasma and was recognized by enzymes on renal BBM to liberate 67Ga-NOTA-Met. When injected into mice, all three 67Ga-labeled Fab exhibited similar blood clearance rates and tumor accumulation. Significant differences were observed in the kidney where 67Ga-NOTA-MVK-Fab registered the lowest renal radioactivity levels from early postinjection time (P < 0.05), followed by 67Ga-NOTA-MI-Fab, which was well reflected in the SPECT/CT images.Conclusions: These findings indicated that our proposal of liberating a radiolabeled compound to urinary excretion from antibody fragments at the renal BBM to reduce the renal radioactivity levels was applicable to 67/68Ga-labeled antibody fragments. Because antibody fragments and constructs share similar metabolic fates in the kidney, the present labeling procedure would also apply to a variety of antibody fragments and constructs of interest. Clin Cancer Res; 24(14); 3309-16. ©2018 AACR.

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