2016;16:275C287. PD-L1 appearance (CHO-hPD-L1) and in handles (CHO). Specificity of [64Cu]atezolizumab was additional verified in orthotopic tumor types of individual breast cancer tumor (MDAMB231 and Amount149) and in a syngeneic mouse mammary carcinoma model (4T1). We noticed particular binding of [64Cu]atezolizumab to tumor cells in vitro, correlating with PD-L1 appearance levels. Specific deposition of [64Cu]atezolizumab Benzocaine hydrochloride was also seen in tumors with high PD-L1 appearance (CHO-hPD-L1 and MDAMB231) in comparison to tumors with low PD-L1 appearance (CHO, Amount149). Collectively, these research demonstrate the feasibility of using [64Cu]atezolizumab for the recognition of PD-L1 appearance in various tumor types. Graphical abstract INTRODUCTION Malignancy cells exploit multiple mechanisms to evade immune recognition and establish immune tolerance.1 This Benzocaine hydrochloride tolerance is facilitated and maintained by regulatory immune cells, immunosuppressive cytokines and chemokines, and immune checkpoint pathways that downregulate immune cells antitumor activity. Over the past decade, immune modulation therapies that are focused on either antagonizing coinhibitory or activating costimulatory pathways have resulted in improved patient survival.2, 3 Therapeutic antibodies targeting immune checkpoint proteins are at the forefront of those advances. A major therapeutic target in cancer immune modulation therapy is the axis between the two immune checkpoint proteins programmed death receptor 1 (PD-1, CD279) and its ligand PD-L1 (B7-H1, CD274).4 PD-1 is expressed on activated T, B, and NK cells, and PD-L1 is normally displayed as an autoimmune prevention mechanism on a subset of macrophages, endothelial cells, and other nonmalignant tissues. There is increased PD-L1 expression on a wide variety of tumors, including melanoma, nonsmall cell lung cancer, Merkel cell carcinoma, breast malignancy, and Klf1 squamous cell carcinomas.5C7 Promotion of PD-L1 expression in the tumor microenvironment Benzocaine hydrochloride (TME) is driven by both genetic and adaptive immune response mechanisms.8 Examples of the former include KRAS and PTEN mutations and translocation or amplification of the 9p24.1 gene in certain tumors.9C11 PD-L1 expression on tumor cells and immune cell infiltrates can also be induced as an adaptive mechanism in response to interferon- (INF-) secreted by antigen-bound tumor-infiltrating T cells.12 Increased expression of tumor and stromal cell PD-L1 leads to deactivation of PD-1-expressing tumor-infiltrating cytotoxic T cells, causing immune suppression in the TME.13 Clinical studies indicate that intratumoral PD-L1 expression, detected by immunohistochemistry (IHC), could be indicative of but not an effective biomarker of response to anti-PD-1 and anti-PD-L1 therapy.14, 15 Some of the contributing factors to the observed inconsistency are the unresolved issues with PD-L1 IHC, such as different antibodies for detection and variable criteria used Benzocaine hydrochloride for positive IHC in the evaluation of clinical trials14, 16 and the changes in PD-L1 expression in tumors induced by a dynamic TME. Obtaining repeated biopsies to evaluate PD-L1 expression in the TME is usually impractical, particularly in patients with metastatic disease, further limiting our ability to fully assess therapy-induced changes in PD-L1 expression in real time. Noninvasive imaging allows for repetitive measurements of target expression in all lesions in their entirety. Recent preclinical studies show that PD-L1 expression in tumors can be assessed by radionuclide imaging.17C21 We have previously shown in murine models that PD-L1 can be detected in the TME with 111In-radiolabeled atezolizumab using single photon emission computed tomography-computed tomography (SPECT-CT) imaging.19 Atezolizumab (MPDL3280a, PD-L1-mAb) is a humanized, human and mouse cross-reactive, PD-L1 antibody in clinical evaluation for treatment of advanced or metastatic bladder cancer,22 melanoma,23 nonsmall cell lung cancer,24 renal cell carcinoma, 25 and several other cancers. Atezolizumab binds both human and mouse PD-L1 with high affinity and provides an opportunity to evaluate PD-L1 expression in both human tumor xenografts and syngeneic mouse tumor models. Atezolizumab binds human and mouse PD-L1 with dissociation constants (= 0.997) with the flow cytometry mean fluorescence intensity (MFI) profile of the cells. The 4T1-Luc cells had low uptake, comparable to that of SUM149 cells. A blocking.