Combining [¹¹C]-AnxA5 PET Imaging with Serum Biomarkers for Improved Detection in Live Mice of Modest Cell Death in Human Solid Tumor Xenografts

BackgroundIn vivo imaging using Annexin A5-based radioligands is a powerful technique for visualizing massive cell death, but has been less successful in monitoring the modest cell death typically seen in solid tumors after chemotherapy. Here we combined dynamic positron emission tomography (PET) imaging using Annexin A5 with a serum-based apoptosis marker, for improved sensitivity and specificity in assessment of chemotherapy-induced cell death in a solid tumor model. Methodology/Principal FindingsModest cell death was induced by doxorubicin in a mouse xenograft model with human FaDu head and neck cancer cells. PET imaging was based on 11C-labeled Sel-tagged Annexin A5 ([11C]-AnxA5-ST) and a size-matched control. 2-deoxy-2-[18F]fluoro-D-glucose ([18F]-FDG) was utilized as a tracer of tissue metabolism. Serum biomarkers for cell death were ccK18 and K18 (M30 Apoptosense® and M65). Apoptosis in tissue sections was verified ex vivo for validation. Both PET imaging using [11C]-AnxA5-ST and serum ccK18/K18 levels revealed treatment-induced cell death, with ccK18 displaying the highest detection sensitivity. [18F]-FDG uptake was not affected by this treatment in this tumor model. [11C]-AnxA5-ST gave robust imaging readouts at one hour and its short half-life made it possible to perform paired scans in the same animal in one imaging session. Conclusions/SignificanceThe combined use of dynamic PET with [11C]-AnxA5-ST, showing specific increases in tumor binding potential upon therapy, with ccK18/K18 serum measurements, as highly sensitive markers for cell death, enabled effective assessment of modest therapy-induced cell death in this mouse xenograft model of solid human tumors.背景：基于膜联蛋白A5（Annexin A5）的放射性配体体内成像技术，是可视化大规模细胞死亡的有力手段，但在监测化疗后实体瘤中常见的轻度细胞死亡方面效果欠佳。本研究将基于膜联蛋白A5的动态正电子发射断层显像（positron emission tomography, PET）与血清源性细胞凋亡标志物相结合，以提升实体瘤模型中化疗诱导细胞死亡评估的灵敏度与特异性。 方法与主要结果：采用阿霉素（doxorubicin）在携带人类FaDu头颈癌细胞的小鼠异种移植模型中诱导轻度细胞死亡。PET成像采用¹¹C标记的Sel标签修饰膜联蛋白A5（[¹¹C]-AnxA5-ST）及尺寸匹配的对照探针；以2-脱氧-2-[¹⁸F]氟-D-葡萄糖（[¹⁸F]-FDG）作为组织代谢示踪剂。细胞死亡的血清生物标志物为ccK18与K18（对应M30 Apoptosense®与M65检测试剂盒）。通过体外检测组织切片中的细胞凋亡以完成实验验证。无论是采用[¹¹C]-AnxA5-ST的PET成像，还是血清ccK18/K18水平检测，均能反映治疗诱导的细胞死亡，其中ccK18展现出最高的检测灵敏度。本肿瘤模型中，[¹⁸F]-FDG的摄取不受该治疗的影响。[¹¹C]-AnxA5-ST在注射后1小时即可获取稳定可靠的成像读数，且其较短的半衰期使得单次成像流程中可对同一动物开展配对扫描。 结论与意义：将基于[¹¹C]-AnxA5-ST的动态PET成像——其可反映治疗后肿瘤结合潜能的特异性升高——与作为高灵敏度细胞死亡标志物的ccK18/K18血清检测相结合，可有效评估人类实体瘤小鼠异种移植模型中轻度治疗诱导的细胞死亡。