Targeting of immune checkpoint regulator V-domain Ig suppressor of T-cell activation (VISTA) with 89Zr-labelled CI-8993

• Published in: European journal of nuclear medicine and molecular imaging 2024-11, Vol.51 (13), p.3863-3873
• Main Authors: Burvenich, Ingrid Julienne Georgette, Wichmann, Christian Werner, McDonald, Alexander Franklin, Guo, Nancy, Rigopoulos, Angela, Huynh, Nhi, Vail, Mary, Allen, Stacey, O’Keefe, Graeme Joseph, Scott, Fiona Elizabeth, Soikes, Raul, Angelides, Steven, Roemeling, Reinhard von, Scott, Andrew Mark
• Format: Article
• Language: English
• Subjects: Binding; Biodistribution; Cancer; Cardiology; Cell activation; Chelating agents; Clinical trials; Conjugation; Deferoxamine; Enzyme-linked immunosorbent assay; Females; Flow cytometry; Gel electrophoresis; High-performance liquid chromatography; Imaging; Immune checkpoint; Immunoglobulin G; Immunoglobulins; Immunoreactivity; Lymphocytes T; Medical imaging; Medicine; Medicine & Public Health; Metal ions; Monoclonal antibodies; Nuclear Medicine; Oncology; Original; Original Article; Orthopedics; Pancreas; Pancreatic cancer; Pharmacokinetics; Positron emission; Radiochemistry; Radiolabelling; Radiology; Sodium lauryl sulfate; Tumors; Zirconium isotopes
• ISSN: 1619-7070; 1619-7089; 1619-7089
• DOI: 10.1007/s00259-024-06854-z

Background CI-8993 is a fully human IgG1κ monoclonal antibody (mAb) that binds specifically to immune checkpoint molecule VISTA (V-domain Ig suppressor of T-cell activation). Phase I safety has been established in patients with advanced cancer (NCT02671955). To determine the pharmacokinetics and biodistribution of CI-8993 in patients, we aimed to develop 89 Zr-labelled CI-8993 and validate PET imaging and quantitation in preclinical models prior to a planned human bioimaging trial. Methods CI-8993 and human isotype IgG1 control were conjugated to the metal ion chelator p -isothiocyanatobenzyl-desferrioxamine (Df). Quality of conjugates were assessed by SE-HPLC, SDS-PAGE, and FACS. After radiolabelling with zirconium-89 ( 89 Zr), radioconjugates were assessed for radiochemical purity, immunoreactivity, antigen binding affinity, and serum stability in vitro. [ 89 Zr]Zr-Df-CI-8993 alone (1 mg/kg, 4.6 MBq) or in combination with 30 mg/kg unlabelled CI-8993, as well as isotype control [ 89 Zr]Zr-Df-IgG1 (1 mg/kg, 4.6 MBq) were assessed in human VISTA knock-in female (C57BL/6 N-Vsir tm1.1(VSIR)Geno , huVISTA KI) or control C57BL/6 mice bearing syngeneic MB49 bladder cancer tumours; and in BALB/c nu / nu mice bearing pancreatic Capan-2 tumours. Results Stable constructs with an average chelator-to-antibody ratio of 1.81 were achieved. SDS-PAGE and SE-HPLC showed integrity of CI-8993 was maintained after conjugation; and ELISA indicated no impact of conjugation and radiolabelling on binding to human VISTA. PET imaging and biodistribution in MB49 tumour-bearing huVISTA KI female mice showed specific localisation of [ 89 Zr]Zr-Df-CI-8993 to VISTA in spleen and tumour tissues expressing human VISTA. Specific tumour uptake was also demonstrated in Capan-2 xenografted BALB/c nu / nu mice. Conclusions We radiolabelled and validated [ 89 Zr]Zr-Df-CI-8993 for specific binding to huVISTA in vivo. Our results demonstrate that 89 Zr-labelled CI-8993 is now suitable for targeting and imaging VISTA expression in human trials. Graphical Abstract