理由：抗体通过血脑屏障 (BBB) 和血肿瘤屏障 (BTB) 的通道不仅决定着提高免疫检查点抑制剂的功效，而且还决定着监测预后和预测生物标志物，例如程序性死亡配体 1 (PD-L1) 通过免疫PET。尽管新生儿 Fc 受体 (FcRn) 参与抗体分布已被证明，但其在 BBB 中的功能仍存在争议，而在 BTB 中的功能尚不清楚。在这种情况下，我们在临床前原位胶质母细胞瘤模型中使用未修饰的 FcRn 低亲和力 IgG 靶向 PD-L1，通过药代动力学免疫 PET 成像结合聚焦超声 (FUS) 评估 FcRn 的作用。方法：在同基因胶质母细胞瘤小鼠模型 (GL261-绿色荧光蛋白）。通过注射后 7 天的 PET 扫描测量大脑摄取情况。进行动力学建模以比较两种 C4 格式的大脑动力学。结果：FUS 有效增强了两种 C4 放射性配体在大脑中的递送，且具有高重现性。注射后 1 小时，大脑中 89Zr-DFO-C4Fc-MUT 的平均浓度在使用 FUS 时显着达到 3.75±0.41%ID/cc，而没有使用 FUS 时则达到 1.92±0.45%ID/cc。在 10.4±4.6 分钟内，观察到两种 C4 放射性配体以 0.163±0.071 mL/h/g 组织的速率大量且相似地进入。与未突变的 IgG 相比，89Zr-DFO-C4Fc-MUT 与 FcRn 的相互作用受损，显着降低了从健康脑组织到血浆的流出常数。消除 FcRn 相互作用可以在注射后 12 小时立即确定与特异性结合相关的靶点接合。结论：消除 Fc-FcRn 相互作用可改善 89Zr-DFO-C4Fc-MUT 的免疫 PET 成像动力学特性。 FUS 辅助的 BBB/BTB 破坏能够对大脑内胶质母细胞瘤肿瘤的 PD-L1 表达进行定量成像。© 作者。

Rationale: The passage of antibodies through the blood-brain barrier (BBB) and the blood-tumoral barrier (BTB) is determinant not only to increase the immune checkpoint inhibitors efficacy but also to monitor prognostic and predictive biomarkers such as the programmed death ligand 1 (PD-L1) via immunoPET. Although the involvement of neonatal Fc receptor (FcRn) in antibody distribution has been demonstrated, its function at the BBB remains controversial, while it is unknown at the BTB. In this context, we assessed FcRn's role by pharmacokinetic immunoPET imaging combined with focused ultrasounds (FUS) using unmodified and FcRn low-affinity IgGs targeting PD-L1 in a preclinical orthotopic glioblastoma model. Methods: Transcranial FUS were applied over the whole brain in mice shortly before injecting the anti-PD-L1 IgG 89Zr-DFO-C4 or its FcRn low-affinity mutant 89Zr-DFO-C4Fc-MUT in a syngeneic glioblastoma murine model (GL261-GFP). Brain uptake was measured from PET scans acquired up to 7 days post-injection. Kinetic modeling was performed to compare the brain kinetics of both C4 formats. Results: FUS efficiently enhanced the delivery of both C4 radioligands in the brain with high reproducibility. 89Zr-DFO-C4Fc-MUT mean concentrations in the brain reached a significant uptake of 3.75±0.41%ID/cc with FUS against 1.92±0.45%ID/cc without, at 1h post-injection. A substantial and similar entry of both C4 radioligands was observed at a rate of 0.163±0.071 mL/h/g of tissue during 10.4±4.6min. The impaired interaction with FcRn of 89Zr-DFO-C4Fc-MUT significantly decreased the efflux constant from the healthy brain tissue to plasma compared with non-mutated IgG. Abolishing FcRn interaction allows determining the target engagement related to the specific binding as soon as 12h post-injection. Conclusion: Abolishing Fc-FcRn interaction confers improved kinetic properties to 89Zr-DFO-C4Fc-MUT for immunoPET imaging. FUS-aided BBB/BTB disruption enables quantitative imaging of PD-L1 expression by glioblastoma tumors within the brain.© The author(s).