Abstract
1019
Purpose: The programmed death protein 1 and programmed death-ligand 1 (PD-1/PD-L1) have been widely studied as one of the most important immuno-checkpoint pairs in cancer microenvironment. In breast cancer (BCa), the expression of PD-L1 are believed to be a determinant biomarker for patient stratification and prediction of inhibition response. The quantitative positron emission tomography (PET) imaging of PD-L1 profile in tumors with therapeutic antibody, which is in clinical application, seems to be a promising solution that can complement the conventional histopathological methods for the assay of PD-L1 expression to overcome the heterogeneities in the specificity between antibodies, sampling representativeness and the thresholds of positive value. In the study, we synthesized and evaluated the 89Zr-labeled Avelumab for the in vivo characterization of PD-L1 Expression in BCa.
Methods: The immuno-fluorescent confocal imaging of cell culture and flow cytometry were employed to assay the expression of PD-L1 in the MDA-MB-231 BCa cell line. A fully humanized monoclonal PD-L1 antibody newly approved by FDA, i.e. Avelumab, was connected to 1-(4-isothiocyanatophenyl)-3-[6,17-dihydroxy-7,10,18,21-tetraoxo-27-(N-acetylhydroxylamino)-6,11,17,22-tetraazaheptaeicosine]thiourea (p-SCN-Df) via conjugation chemistry and labeled with 89Zr. After the 89Zr-Df-Avelumab was intravenously administrated to the athymic nude mice bearing the MDA-MB-231 subcutaneous tumors, the PET imaging with or without the blockade of cold Avelumab and the bio-distribution study was performed. The expression of PD-L1 expression in tumor, spleen and lymph tissues were validated by histopathological test. Finally, the radiation burden based on major organs was estimated.
Results: The high expression of PD-L1 on the MDA-MB-231 cells are confirmed by the in vitro immuno-fluorescent staining and flow cytometry. The PET images indicate the prominent deposition of 89Zr-Df-Avelumab in tumor (6.4±1.0 %ID/g), spleen (10.2±0.7 %ID/g) and lymph node (6.9±1.0 %ID/g) at 48 h (n=4), and the blockade of cold Avelumab can reduce the uptake in these tissues (5.2±1.0 %ID/g in tumor, 4.9±0.5 %ID/g in spleen and 5.8±1.1 %ID/g in lymph node at 48 h, n=4), which demonstrate the specificity of 89Zr-Df-Avelumab. The results of bio-distribution and immuno-fluorescent staining are in consistence with the quantitative data of PET imaging. The dosimetry shows that the total radiation burden is acceptable.
Conclusions: In this research, we have offered the evidence of the value and safety in the immuno-PET with 89Zr-Df-Avelumab for the in vivo characterization of PD-L1 expression in BCa. They support the applicability of 89Zr-Df-Avelumab in BCa for the evaluation of effective therapy of immuno-checkpoint inhibition.