A humanized antibody for imaging immune checkpoint ligand PD-L1 expression in tumors

// Samit Chatterjee 1,* , Wojciech G. Lesniak 1,* , Matthew Gabrielson 1 , Ala Lisok 1 , Bryan Wharram 1 , Polina Sysa-Shah 1 , Babak Behnam Azad 1 , Martin G. Pomper 1,2 and Sridhar Nimmagadda 1,2 1 Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, USA 2 Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, MD, USA * These authors have contributed equally to this work Correspondence to: Sridhar Nimmagadda, email: // Keywords : MPDL3280A, immunotherapy, immune escape, molecular imaging, personalized medicine Received : January 02, 2016 Accepted : January 16, 2016 Published : February 02, 2016 Abstract Antibodies targeting the PD-1/PD-L1 immune checkpoint lead to tumor regression and improved survival in several cancers. PD-L1 expression in tumors may be predictive of response to checkpoint blockade therapy. Because tissue samples might not always be available to guide therapy, we developed and evaluated a humanized antibody for non-invasive imaging of PD-L1 expression in tumors. Radiolabeled 111 InPD-L1-mAb and near-infrared dye conjugated NIR-PD-L1-mAb imaging agents were developed using the mouse and human cross-reactive PD-L1 antibody MPDL3280A. We tested specificity of 111 InPD-L1-mAb and NIR-PD-L1-mAb in cell lines and in tumors with varying levels of PD-L1 expression. We performed SPECT/CT imaging, biodistribution and blocking studies in NSG mice bearing tumors with constitutive PD-L1 expression (CHO-PDL1) and in controls (CHO). Results were confirmed in triple negative breast cancer (TNBC) (MDAMB231 and SUM149) and non-small cell lung cancer (NSCLC) (H2444 and H1155) xenografts with varying levels of PD-L1 expression. There was specific binding of 111 InPD-L1-mAb and NIR-PD-L1-mAb to tumor cells in vitro , correlating with PD-L1 expression levels. In mice bearing subcutaneous and orthotopic tumors, there was specific and persistent high accumulation of signal intensity in PD-L1 positive tumors (CHO-PDL1, MDAMB231, H2444) but not in controls. These results demonstrate that 111 InPD-L1-mAb and NIR-PD-L1-mAb can detect graded levels of PD-L1 expression in human tumor xenografts in vivo . As a humanized antibody, these findings suggest clinical translation of radiolabeled versions of MPDL3280A for imaging. Specificity of NIR-PD-L1-mAb indicates the potential for optical imaging of PD-L1 expression in tumors in relevant pre-clinical as well as clinical settings.