title: ImmunoPET Imaging of CTLA-4 Expression in Mouse Models of Non-small Cell Lung Cancer.
abstract: Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is expressed on the surface of activated T cells and some tumor cells, and is the target of the clinically approved monoclonal antibody ipilimumab. In this study, we investigate specific binding of radiolabeled ipilimumab to CTLA-4 expressed by human non-small cell lung cancer cells in vivo using positron emission tomography (PET). Ipilimumab was radiolabeled with64Cu (t1/2= 12.7 h) through the use of the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to formulate64Cu-DOTA-ipilimumab. CTLA-4 expression in three non-small cell lung cancer (NSCLC) cell lines (A549, H460, and H358) was verified and quantified by Western blot and enzyme-linked immunosorbent assays (ELISA). A receptor binding assay was utilized to monitor the binding and internalization of64Cu-DOTA-ipilimumab in the NSCLC cell lines. Next, the biodistribution of64Cu-DOTA-ipilimumab was mapped by longitudinal PET imaging up to 48 h after injection. Ex vivo biodistribution and histological studies were employed to verify PET results. By in vitro analysis, CTLA-4 was found to be expressed on all three NSCLC cell lines with A549 and H358 showing the highest and lowest level of expression, respectively. PET imaging and quantification verified these findings as the tracer accumulated highest in the A549 tumor model (9.80 ± 0.22%ID/g at 48 h after injection; n = 4), followed by H460 and H358 tumors with uptakes of 9.37 ± 0.26%ID/g and 7.43 ± 0.05%ID/g, respectively (n = 4). The specificity of the tracer was verified by injecting excess ipilimumab in A549 tumor-bearing mice, which decreased tracer uptake to 6.90 ± 0.51%ID/g at 48 after injection (n = 4). Ex vivo analysis following the last imaging session also corroborated these findings.64Cu-DOTA-ipilimumab showed enhanced and persistent accumulation in CTLA-4-expressing tissues, which will enable researchers further insight into CTLA-4 targeted therapies in the future.
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Emily B
authors.initials: EB
authors.lastname: Ehlerding
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: England
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Majewski
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Hector F
authors.initials: HF
authors.lastname: Valdovinos
authors.affiliation: Department of Radiology, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Dawei
authors.initials: D
authors.lastname: Jiang
authors.affiliation: Department of Medicine, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Glenn
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Medicine, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Douglas G
authors.initials: DG
authors.lastname: McNeel
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Nickles
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.|Department of Biomedical Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.|Department of Radiology, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Weibo
authors.identifier: 0000-0003-4641-0833
authors.initials: W
authors.lastname: Cai
mesh_terms: D000818:Animals; D060908:CTLA-4 Antigen / Q000378:metabolism*; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D007167:Immunotherapy; D000074324:Ipilimumab / Q000378:metabolism; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*
chemical_list: D060908:CTLA-4 Antigen; D000074324:Ipilimumab
keywords: CTLA-4 (cytotoxic T-lymphocyte-associated protein 4); PET (positron emission tomography); immune checkpoint inhibitor; immunotherapy; lung cancer