Abstract
1189
Objectives Cancer immunotherapy utilizes the immune system to identify cancer cells and stimulate immune responses unlike traditional chemotherapeutic treatments. When T-cells recognize cancer antigens, they activate producing cytotoxic T-lymphocytes (CTL) that seek out and destroy cancer cells. CTLs upregulate expression of the Programmed Death-1 (PD-1) protein that binds to its natural ligands, Programmed Death-Ligand 1 (PD-L1) and 2 (PD-L2) on neighboring cells as an immune system checkpoint, resulting in negative regulation of T-cell activation. Many cancers express and upregulate PD-L1 and PD-L2 as an immune escape mechanism. Nivolumab is a fully human IgG4 anti-PD-1 monoclonal antibody (mAb) approved for the treatment of advanced melanoma and advanced squamous non-small cell lung cancer. This study reports the preparation and in vivo evaluation of 89Zr-nivolumab in healthy non-human primates (NHP) as a baseline study of biodistribution and clearance.
Methods Nivolumab was modified with the chelator desferrioxamine (DFO) by conjugation to lysine residues, followed with 89Zr-labeling yielded the PET tracer 89Zr-nivolumab. Three naïve NHPs were intravenously injected with tracer only or co-injected with 1 or 3 mg/kg nivolumab. Combination PET/MRI images in each NHP were acquired on 1, 4, 6, and 8 days after injection, and image-derived standardized uptake values (SUV) were quantified by region of interest analysis.
Results Nivolumab-DFO was produced in high purity (>95%) with a chelator to antibody ratio of 1.14 and a KD of 3.75 nM. 89Zr-labeling yielded 225 - 341 MBq of 89Zr-nivolumab (radiochemical yield 53 ± 8% non-decay-corrected) with specific activity of 352 ± 87 MBq/mg and good purity (>87%). Binding in the spleen was significantly reduced by addition of unlabeled nivolumab compared to the carrier-free NHP at all imaging time points (82.5 ± 4.6%; range: 75.2 - 87.0%). Liver uptake was consistent as a clearance organ with minimal signal from other tissues: lung, muscle, brain, heart, and kidney.
Conclusions Nivolumab can be labeled with 89Zr at good purity and moderate-to-high radiochemical yield. Our results indicate specific biodistribution to NHP spleen, which can be blocked by co-administration of excess nivolumab. Distribution to other organs is consistent with excretion pathways of antibodies, with primary clearance through the liver.