Purpose

Despite remarkable clinical responses and prolonged survival across several cancers, not all patients benefit from PD-1/PD-L1 immune checkpoint blockade. Accordingly, assessment of tumour PD-L1 expression by immunohistochemistry (IHC) is increasingly applied to guide patient selection, therapeutic monitoring, and improve overall response rates. However, tissue-based methods are invasive and prone to sampling error. We therefore developed a PET radiotracer to specifically detect PD-L1 expression in a non-invasive manner, which could be of diagnostic and predictive value.

Methods

Anti-PD-L1 (clone 6E11, Genentech) was site-specifically conjugated with DIBO-DFO and radiolabelled with ⁸⁹Zr (⁸⁹Zr-DFO-6E11). ⁸⁹Zr-DFO-6E11 was optimized in vivo by longitudinal PET imaging and dose escalation with excess unlabelled 6E11 in HCC827 tumour-bearing mice. Specificity of ⁸⁹Zr-DFO-6E11 was evaluated in NSCLC xenografts and syngeneic tumour models with different levels of PD-L1 expression. In vivo imaging data was supported by ex vivo biodistribution, flow cytometry, and IHC. To evaluate the predictive value of ⁸⁹Zr-DFO-6E11 PET imaging, CT26 tumour-bearing mice were subjected to external radiation therapy (XRT) in combination with PD-L1 blockade.

Results

⁸⁹Zr-DFO-6E11 was successfully labelled with a high radiochemical purity. The HCC827 tumours and lymphoid tissue were identified by ⁸⁹Zr-DFO-6E11 PET imaging, and co-injection with 6E11 increased the relative tumour uptake and decreased the splenic uptake. ⁸⁹Zr-DFO-6E11 detected the differences in PD-L1 expression among tumour models as evaluated by ex vivo methods. ⁸⁹Zr-DFO-6E11 quantified the increase in PD-L1 expression in tumours and spleens of irradiated mice. XRT and anti-PD-L1 therapy effectively inhibited tumour growth in CT26 tumour-bearing mice (p < 0.01), and the maximum ⁸⁹Zr-DFO-6E11 tumour-to-muscle ratio correlated with response to therapy (p = 0.0252).

Conclusion

PET imaging with ⁸⁹Zr-DFO-6E11 is an attractive approach for specific, non-invasive, whole-body visualization of PD-L1 expression. PD-L1 expression can be modulated by radiotherapy regimens and ⁸⁹Zr-DFO-6E11 PET is able to monitor these changes and predict the response to therapy in an immunocompetent tumour model.

中文翻译：

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使用位点特异性标记的PD-L1抗体对异种移植和同基因肿瘤模型中PD-L1表达的定量PET成像

目的

尽管有出色的临床反应并能在多种癌症中延长生存期，但并非所有患者都能从PD-1 / PD-L1免疫检查点封锁中受益。因此，通过免疫组织化学（IHC）对肿瘤PD-L1表达的评估越来越多地用于指导患者选择，治疗监测和提高总体应答率。但是，基于组织的方法具有侵入性，并且容易出现采样错误。因此，我们开发了一种PET放射性示踪剂，以非侵入性方式特异性检测PD-L1表达，这可能具有诊断和预测价值。

方法

Anti-PD-L1（克隆6E11，Genentech）与DIBO-DFO进行位点特异性偶联，并用⁸⁹ Zr（⁸⁹ Zr-DFO-6E11）进行放射性标记。通过在HCC827荷瘤小鼠中通过纵向PET成像和剂量递增以及过量未标记的6E11对体内的⁸⁹ Zr-DFO-6E11进行了优化。在具有不同水平PD-L1表达的NSCLC异种移植物和同基因肿瘤模型中评估了⁸⁹ Zr-DFO-6E11的特异性。体内成像数据得到离体生物分布，流式细胞仪和IHC的支持。为了评估⁸⁹ Zr-DFO-6E11 PET成像的预测价值，对CT26荷瘤小鼠进行了外部放射治疗（XRT）和PD-L1阻断治疗。

结果

⁸⁹ Zr-DFO-6E11被成功标记为高放射化学纯度。通过⁸⁹ Zr-DFO-6E11 PET成像鉴定出HCC827肿瘤和淋巴样组织，并与6E11共注射增加了相对肿瘤摄取，并降低了脾脏摄取。⁸⁹ Zr-DFO-6E11通过离体方法评估了肿瘤模型之间PD-L1表达的差异。⁸⁹ Zr-DFO-6E11量化了照射小鼠的肿瘤和脾脏中PD-L1表达的增加。XRT和抗PD-L1治疗有效抑制了CT26荷瘤小鼠的肿瘤生长（p  <0.01），最大⁸⁹ Zr-DFO-6E11肿瘤与肌肉的比例与对治疗的反应相关（p  = 0.0252）。

结论

使用⁸⁹ Zr-DFO-6E11进行PET成像是一种有吸引力的方法，可用于PD-L1表达的特异性，非侵入性全身观察。PD-L1的表达可以通过放疗方案进行调节，并且⁸⁹ Zr-DFO-6E11 PET能够监测这些变化并预测在具有免疫能力的肿瘤模型中对治疗的反应。