Immuno-PET imaging using 89Zr labeled PD-L1 antibody in non-small cell lung cancer Xenograft

Objectives The immune checkpoint, programmed cell death protein-1/ programmed cell death ligand-1 (PD-1/PD-L1) pathway has emerged as a critical target for cancer immunotherapy, and monoclonal antibodies that block either side of this inhibitory interaction have demonstrated impressive activity across a broad set of cancer subtypes, such as non-small cell lung cancer (NSCLC), melanoma, renal cell carcinoma (RCC), et al, even at advanced and metastatic stages of disease. Patients with tumors expressing PD-L1 are most likely to respond to anti-PD-1/PD-L1 treatment. The aim of our study was to develop a novel immune-PET technique to noninvasive determine tumor PD-L1 expression in vivo, which could help to select the patients who are most likely to benefit from anti-PD-1/PD-L1 treatment and monitor PD-L1 expression during therapy.

Methods KN035, an anti-PD-L1 heavy chain antibody selected from a large camel naïve phage display Nanobody library, was labeled with radionuclide 89Zr through conjugated to pisothiocyanatobenzyl-desferrioxamine (Df-Bz-NCS). The resulting probe, 89Zr-Df-KN035, was then evaluated by in vitro cell uptake and blocking studies using PD-L1 positive cell lines, human lung adenocarcinoma cell line A549. Next, serial immnuo-PET (at 1, 6, 24, 48, 72 and 120 h post-injection respectively, n=4) and biodistribution studies were performed in nude mice bearing A549 tumor xenografts to evaluate in vivo performance of 89Zr-Df-KN035.

Results Significant differences in uptake of 89Zr-Df-KN035 were observed in A549 tumor cells without and with unlabeled KN035 blocking (P < 0.05). Serial immnuo-PET imaging revealed that A549 tumors xenografts were clearly visible since 24h to 120h, while markedly reduced accumulations of 89Zr-Df-KN035 were noticed in blocking group. Moreover, biodistribution studies demonstrated tumor-to-background tissue ratios of 6.73 ± 3.07 (tumor-to-muscle) and 6.71 ± 2.18 (tumor-to-blood) at 24 h post-injection.

Conclusions 89Zr-Df-KN035 demonstrates promise for use as an immuno-PET agent to image tumor PD-L1 expression in living system, which warrants further selection of patients with NSCLC performing anti-PD-L1 antibody therapy.