In vivo characterization of PD-L1 expression in breast cancer by immuno-PET with 89Zr-labeled avelumab

Miao Li; Emily B Ehlerding; Dawei Jiang; Todd E Barnhart; Weiyu Chen; Tianye Cao; Jonathan W Engle; Weibo Cai

In vivo characterization of PD-L1 expression in breast cancer by immuno-PET with ⁸⁹Zr-labeled avelumab

Am J Transl Res. 2020 May 15;12(5):1862-1872. eCollection 2020.

Authors

Miao Li^{1

2}, Emily B Ehlerding², Dawei Jiang², Todd E Barnhart², Weiyu Chen², Tianye Cao², Jonathan W Engle², Weibo Cai²

Affiliations

¹ Department of Radiology, The First Affiliated Hospital of Xi'an Jiaotong University 277 West Yanta Road, Xi'an 710061, Shaanxi, China.
² Departments of Radiology and Medical Physics, University of Wisconsin-Madison 1111 Highland Avenue, Madison 53705, Wisconsin, United States.

PMID: 32509182
PMCID: PMC7270013

Abstract

Programmed death protein 1 and programmed death-ligand 1 (PD-1/PD-L1) have been widely studied as one of the most critical immune check-point pairs in the cancer microenvironment. In breast cancer (BrCa), the expression of PD-L1 is regarded as a determinant biomarker for patient stratification and prediction of inhibition response. Quantitative positron emission tomography (PET) imaging of PD-L1 expression in tumors using a therapeutic antibody in the clinic seems to be a promising approach that can complement conventional histopathological methods and overcome several issues, such as the tumor heterogeneities, sampling representativeness and clear differentiation of positive and negative results. In this study, we synthesized and evaluated ⁸⁹Zr-labeled avelumab (Ave) for the in vivo characterization of PD-L1 expression in BrCa. Confocal imaging of BrCa cells and flow cytometry were employed to evaluate PD-L1 expression in MDA-MB-231 cells. The intact human monoclonal antibody targeting PD-L1, i.e., Ave, was conjugated to p-SCN-Deferoxamine (Df) and labeled with ⁸⁹Zr. After intravenous injection of ⁸⁹Zr-Df-avelumab (⁸⁹Zr-Df-Ave), PET imaging of MDA-MB-231 tumor-bearing mice, with or without blocking, was performed. High PD-L1 expression of MDA-MB-231 cells was confirmed by in vitro immuno-fluorescent staining and flow cytometry. PET imaging indicated the peak uptake of ⁸⁹Zr-Df-Ave in the tumor (6.4±1.0 %ID/g), spleen (10.2±0.7 %ID/g) and lymph nodes (6.9±1.0 %ID/g) at 48 h after injection (n=4). Blocking study using unlabeled Ave could reduce the tracer uptake in these tissues (5.2±1.0 %ID/g in the tumor, 4.9±0.5 %ID/g in the spleen and 5.8±1.1 %ID/g in lymph nodes at 48 h, n=4), which demonstrated the specificity of ⁸⁹Zr-Df-Ave. Biodistribution study and immuno-fluorescent staining were consistent with the quantitative data from PET imaging. Herein, we offer the evidence supporting the value of immuno-PET imaging using ⁸⁹Zr-Df-Ave for non-invasive characterization of PD-L1 expression in BrCa and the applicability of this tracer in BrCa for treatment evaluation after immunotherapy.

Keywords: PD-L1; Positron emission tomography; avelumab; breast cancer; zirconium-89.