Abstract
177
Objectives: Inhibiting PD-1/PD-L1 pathway using antiPD-1 or antiPD-L1 antibody has shown great success on cancer treatment. However, only 20~25% cancer patients exhibit positive response to PD-L1 immunotherapy. Though immunohistochemistry (IHC) is the gold standard for patient classification, a non-invasive method is highly favored for clinical diagnosis. Herein, we report a new antiPD-L1 monoclonal antibody (Ab1881), of which Copper-64 labelled derivative exhibited significantly different tumor uptake on PD-L1 positive and negative types of xenografts. In addition, the xenografts of high Ab1881 uptake demonstrated notable therapeutic efficacy, while the xenografts of low Ab1881 uptake kept growing rapidly till scarification, demonstrating a strong correlation between PET imaging and therapeutic efficacy. METHODAb1881 was conjugated with a bifunctional chelator 2-S-(4-Isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) to give NOTA-Ab-1881. Copper-64 radiolabeling was conducted in sodium acetate buffer (pH=4), and quality control was performed by radio-HPLC equipped with size-exclusion column. The metabolic stability of 64Cu-NOTA-Ab1881 was assessed under both in vitro and in vivo conditions. PET imaging and bio-distribution studies were performed in mice bearing MC38 (PDL1 positive) and 4T1 (PDL1 negative) xenografts on the left and right shoulder, respectively. Ab1881 treatment was performed 3 days a time, 0.25 mg for each therapy.RESULT Cu-NOTA-Ab1881 and Ab1881 bound to PD-L1 with the binding affinity of 0.47 ± 0.12 nM and 0.92 ± 0.33 nM, respectively. 64Cu-NOTA-Ab1881 exhibited 4.7 ± 2.1, 10.3 ± 3.2, 14.3 ± 4.1, 19.7 ± 3.7 %ID/g uptake in MC38 xenografts at 2.0, 4.0, 12.0, 24.0 hours post injection, respectively. Meanwhile, 64Cu-NOTA-Ab1881 exhibited 3.7 ± 1.3, 4.3 ± 1.2, 5.3 ± 2.1, 6.8 ± 2.7 %ID/g uptake in 4T1 xenografts at 2.0, 4.0, 12.0, 24.0 hours post injection, respectively. The rest of radiotracer was excreted mainly through hepatobiliary system, and liver uptake reached to maximum at around 12 hours post injection, which is 17 ± 4.3%ID/g. In regards to treatment, xenografts of MC38 kept the same size if did not shrink at day 21 post therapy. In contrast, at day 21, xenografts of 4T1 were 12.7 ± 1.2 times larger than them of day 0. CONCLUSIONA Copper-64 labelled Ab1881 was reported that successfully distinguished PD-L1 positive and negative xenografts in mouse model with PET imaging. Moreover, Ab1881 also demonstrate impressive therapeutic efficacy, which is highly correlated to the tumor uptake of its radioactive derivative.