新型18F标记靶向CA-IX的肿瘤乏氧显像剂的研究

Hypoxia is ubiquity in solid tumors and has been linked to the development of treatment resistance, tumor progression and poor prognosis. It is essential to detect hypoxic area accurately for the implementation of individualized treatment and the prediction of the efficacy. At present, 18F-FMISO is the common hypoxia imaging agent used in clinic, but it is not satisfactory because of the defects of soft tissue absorption, high background value, complex labeling technique and the low yield. We would design and synthesize a novel hypoxia imaging agent to overcome the drawbacks. Our previous results have indicated: ①The carbonic anhydrase IX (CA-IX) is significantly negative correlated with oxygen partial pressure in hypoxic tumor microenvironment and can be used as a promising target for a novel tracer of PET imaging. ②Sulfonamide, CA-IX inhibitors, would be potential as the carrier of PET imaging agent. ③Al18F complex is attached to compounds like 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). The associated synthesis skills can shorten the span with the predigestion of flow and we have obtained national technical patents. Hence, the novel imaging tracer should be composed of sulfonamide and 18F as the nuclide with stable structure, high hydrophilicity and easy labeling method. We would testify the radiochemical purity, stability, uptake value of hypoxic cells, elimination half-life and the target/background ratio in the vitro and vivo experiment in order. We aim to obtain the high-quality imaging of hypoxic tumor that could provide reliable information to evaluate prognosis, outline biological target volume of radiotherapy and monitor curative effect.

乏氧参与肿瘤侵袭转移及放化疗抵抗，准确检测肿瘤的乏氧程度对于个体化诊疗至关重要。18F-FMISO是目前临床最常用的乏氧显像剂，但有浓聚慢、本底高、氟标复杂、产率低等缺陷，故亟待开发性能优良的新型肿瘤乏氧显像剂。我们前期研究发现：①乏氧相关蛋白碳酸酐酶-9（CA-IX）的表达量与细胞缺氧程度正相关，可作为探测肿瘤乏氧的受体靶蛋白；②在多种肿瘤细胞中，乙酰唑胺、苯磺酰胺等磺胺类药物可特异性结合并抑制CA-IX，其衍生物可作为靶向CA-IX的显像剂载体；③18F以氟铝配合物形式与NOTA基团螯合是高效且稳定的氟标方法，本课题组熟练掌握该技术并已申请相关国家发明专利。基于以上研究基础，本项目拟研发一系列18F标记、靶向CA-IX的磺胺类乏氧显像剂，通过体内外实验验证其放化纯度、稳定性及生物学活性等，以合成高标记率、高稳定性、高选择性的新型显像剂，为监测肿瘤乏氧、勾画放疗生物靶区提供新的思路。

乏氧参与肿瘤侵袭转移及放化疗抵抗，准确检测肿瘤的乏氧程度对于个体化诊疗及预后评估至关重要，精确勾画乏氧生物靶区是提高肿瘤放疗敏感性的关键，运用PET/CT技术结合解剖及功能显像可以实现肿瘤乏氧显像，我们的研究旨在开发高效PET乏氧显像剂。我们以肿瘤细胞膜上特异性高表达的CA-IX作为靶点，设计并合成了一种18F标记的新型乏氧显像剂18F-FAl-NOTA-MAL-GGGRDN-SA1，其中，乙酰唑胺为功能基团，NOTA为螯合基团，并引入亲水性结构GGGRDN。此新型显像剂具有高标记率、高稳定性、高放射化学纯度的特点，且有较明显的亲水性。在生物学功能方面，显像剂前体对食管癌ECa109细胞、鼻咽癌CNE-2细胞均有较明确的CA-IX抑制活性。显像剂在肿瘤细胞及组织内有特异性的高摄取。我们通过细胞摄取实验证实乏氧条件下ECa109及CNE-2细胞对新型显像剂的摄取率明显高于常氧细胞，乏氧及常氧下的摄取率比值高18F-MISO；细胞阻断实验通过乙酰唑胺竞争性抑制证实了乏氧显像原理与显像剂的CA-IX抑制作用有关。动物体内分布实验证实新型显像剂主要经肾脏代谢，血液及正常组织中清除较快，肿瘤区域有明显浓聚，显像剂注射后瘤血比（T/B）及瘤肌比（T/M）随时间增高，2小时后肿瘤摄取值、T/B及T/M达到理想状态。MicroPET显像实验建议新型显像剂适宜在注射后2小时采集清晰的肿瘤显像图像。