Purpose

The unsatisfactory efficacy of PD-L1 antibodies in glioblastoma (GBM) is largely due to the temporal and spatial heterogeneity of PD-L1 expression. Molecular imaging can enhance understanding of the tumor immune microenvironment and guide immunotherapy. However, highly sensitive imaging agents capable of effectively visualizing PD-L1 heterogeneity are limited. This study introduces a novel PET tracer, offering improved imaging of PD-L1 heterogeneity in GBM xenografts, with a comparative analysis to [¹⁸F]AlF-NOTA-WL12.

Methods

[¹⁸F]AlF-NOTA-PCP2 was synthesized with high purity and its affinity for PD-L1 was characterized using surface plasmon resonance (SPR) and cell binding assays. Its specificity for PD-L1 was evaluated both in vitro using various cell lines and in vivo with GBM xenograft models in NOD/SCID mice. PET/CT imaging was conducted to evaluate the tracer’s biodistribution, pharmacokinetics, and ability to quantify tumoral spatial heterogeneity of PD-L1 expression. A focused comparative analysis between [¹⁸F]AlF-NOTA-PCP2 and [¹⁸F]AlF-NOTA-WL12 was conducted, examining binding affinity, biodistribution, pharmacokinetics, and imaging effectiveness in GBM xenografts. Additionally, human radiation dosimetry estimates compared the safety profiles of both tracers.

Results

[¹⁸F]AlF-NOTA-PCP2 demonstrated high radiochemical purity (> 95%) and a strong affinity for PD-L1, comparable to [¹⁸F]AlF-NOTA-WL12. In vitro and in vivo studies confirmed its specificity for PD-L1, with increased uptake in PD-L1 expressing cells and tumors. Toxicological profiles indicated no significant abnormalities in serum biochemical indicators or major organ tissues. MicroPET/CT imaging showed [¹⁸F]AlF-NOTA-PCP2’s effectiveness in visualizing PD-L1 expression levels and spatial heterogeneity in GBM xenografts. Comparative studies revealed [¹⁸F]AlF-NOTA-PCP2’s improved pharmacokinetic properties, including higher tumor-to-blood ratios and lower nonspecific liver uptake, as well as reduced radiation exposure compared to [¹⁸F]AlF-NOTA-WL12.

Conclusion

[¹⁸F]AlF-NOTA-PCP2 distinguishes itself as an exceptionally sensitive PET/CT tracer, adept at non-invasively and accurately quantifying PD-L1 expression and its spatial heterogeneity in tumors, especially in GBM. Its favorable pharmacokinetic properties, safety profile, and high affinity for PD-L1 highlight its potential for enhancing the precision of cancer immunotherapy and guiding individualized treatment strategies. While promising, its clinical translation, especially in brain imaging, necessitates further validation in clinical trials.

中文翻译：

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[18F]AlF-NOTA-PCP2：一种新型PET/CT示踪剂，用于增强胶质母细胞瘤异种移植物中的PD-L1异质性成像并与[18F]AlF-NOTA-WL12进行比较分析

目的

PD-L1抗体在胶质母细胞瘤（GBM）中的疗效不理想很大程度上是由于PD-L1表达的时间和空间异质性造成的。分子成像可以增强对肿瘤免疫微环境的了解并指导免疫治疗。然而，能够有效观察 PD-L1 异质性的高灵敏度成像剂是有限的。本研究介绍了一种新型 PET 示踪剂，可改善 GBM 异种移植物中 PD-L1 异质性的成像，并与 [ ¹⁸ F]AlF-NOTA-WL12进行比较分析。

方法

[ ¹⁸ F]AlF-NOTA-PCP2 以高纯度合成，并使用表面等离子共振（SPR）和细胞结合测定来表征其对 PD-L1 的亲和力。其对 PD-L1 的特异性在体外使用各种细胞系进行评估，并在体内使用 NOD/SCID 小鼠的 GBM 异种移植模型进行评估。进行 PET/CT 成像以评估示踪剂的生物分布、药代动力学以及量化 PD-L1 表达的肿瘤空间异质性的能力。对[ ¹⁸ F]AlF-NOTA-PCP2和[ ¹⁸ F]AlF-NOTA-WL12之间进行了集中比较分析，检查了GBM异种移植物中的结合亲和力、生物分布、药代动力学和成像有效性。此外，人体辐射剂量测定估计还比较了两种示踪剂的安全性。

结果

[ ¹⁸ F]AlF-NOTA-PCP2 表现出高放射化学纯度（> 95%）和对PD-L1的强亲和力，与[ ¹⁸ F]AlF-NOTA-WL12相当。体外和体内研究证实了其对 PD-L1 的特异性，增加了表达 PD-L1 的细胞和肿瘤的摄取。毒理学特征表明血清生化指标或主要器官组织未见明显异常。 MicroPET/CT成像显示[ ¹⁸ F]AlF-NOTA-PCP2在可视化GBM异种移植物中的PD-L1表达水平和空间异质性方面的有效性。比较研究显示，与[ ^{18 F]AlF-NOTA-WL12相比，[ 18} F ]AlF-NOTA-PCP2改善了药代动力学特性，包括更高的肿瘤与血液比率和更低的非特异性肝脏摄取，以及减少的辐射暴露。

结论

[ ¹⁸ F]AlF-NOTA-PCP2 是一种异常敏感的 PET/CT 示踪剂，擅长非侵入性且准确地量化肿瘤（尤其是 GBM）中的 PD-L1 表达及其空间异质性。其良好的药代动力学特性、安全性和对 PD-L1 的高亲和力凸显了其提高癌症免疫治疗精度和指导个体化治疗策略的潜力。虽然前景广阔，但其临床转化，特别是在脑成像方面，需要在临床试验中进一步验证。