PT  - JOURNAL ARTICLE
AU  - Kyung-Ho Jung
AU  - Jin Won Park
AU  - Jin Hee Lee
AU  - Seung Hwan Moon
AU  - Young Seok Cho
AU  - Kyung-Han Lee
TI  - <sup>89</sup>Zr-Labeled Anti-PD-L1 Antibody PET Monitors Gemcitabine Therapy-Induced Modulation of Tumor PD-L1 Expression
AID  - 10.2967/jnumed.120.250720
DP  - 2021 May 10
TA  - Journal of Nuclear Medicine
PG  - 656--664
VI  - 62
IP  - 5
4099  - http://jnm.snmjournals.org/content/62/5/656.short
4100  - http://jnm.snmjournals.org/content/62/5/656.full
SO  - J Nucl Med2021 May 10; 62
AB  - We developed an 89Zr-labeled anti–programmed death ligand 1 (anti-PD-L1) immune PET that can monitor chemotherapy-mediated modulation of tumor PD-L1 expression in living subjects. Methods: Anti-PD-L1 underwent sulfohydryl moiety–specific conjugation with maleimide-deferoxamine followed by 89Zr radiolabeling. CT26 colon cancer cells and PD-L1–overexpressing CT26/PD-L1 cells underwent binding assays, flow cytometry, and Western blotting. In vivo pharmacokinetics, biodistribution, and PET imaging were evaluated in mice. Results: 89Zr-anti-PD-L1 synthesis was straightforward and efficient. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that reduction produced half-antibody fragments, and matrix-assisted laser desorption ionization time-of-flight analysis estimated 2.18 conjugations per antibody, indicating specific conjugation at the hinge-region disulfide bonds. CT26/PD-L1 cells showed 102.2 ± 6.7-fold greater 89Zr-anti-PD-L1 binding than that of weakly expressing CT26 cells. Excellent target specificity was confirmed by a drastic reduction in binding by excess cold antibody. Intravenous 89Zr-anti-PD-L1 followed biexponential blood clearance. PET/CT image analysis demonstrated decreases in major organ activity over 7 d, whereas high CT26/PD-L1 tumor activity was maintained. Again, this was suppressed by excess cold antibody. Treatment of CT26 cells with gemcitabine for 24 h augmented PD-L1 protein to 592.4% ± 114.2% of the control level and increased 89Zr-anti-PD-L1 binding, accompanied by increased AKT (protein kinase B) activation and reduced phosphatase and tensin homolog (PTEN). In CT26 tumor–bearing mice, gemcitabine treatment substantially increased tumor uptake from 1.56% ± 0.48% to 6.24% ± 0.37% injected dose per gram (tumor-to-blood ratio, 34.7). Immunoblots revealed significant increases in tumor PD-L1 and activated AKT and a decrease in PTEN. Conclusion: 89Zr-anti-PD-L1 showed specific targeting with favorable imaging properties. Gemcitabine treatment upregulated cancer cell and tumor PD-L1 expression and increased 89Zr-anti-PD-L1 uptake. 89Zr-anti-PD-L1 PET may thus be useful for monitoring chemotherapy-mediated tumor PD-L1 modulation in living subjects.