Medical Chemistry and Bioinformatics Center, College of Basic Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
Bioconjug Chem. 2024 Apr 17;35(4):528-539. doi: 10.1021/acs.bioconjchem.4c00040. Epub 2024 Mar 21.
Cancer which causes high mortality globally threatens public health seriously. There is an urgent need to develop tumor-specific near-infrared (NIR) imaging agents to achieve precise diagnosis and guide effective treatment. In recent years, imaging probes that respond to acidic environments such as endosomes, lysosomes, or acidic tumor microenvironments (TMEs) are being developed. However, because of their nonspecific internalization by both normal and tumor cells, resulting in a poor signal-to-noise ratio in diagnosis, these pH-sensitive probes fail to be applied to tumor imaging. To address this issue, a cholecystokinin-2 receptor (CCK2R)-targeted TME-sensitive NIR fluorescent probe R2SM was synthesized by coupling pH-sensitive heptamethine cyanine with a CCK2R ligand, minigastrin analogue 11 (MG11) for imaging, in which MG11 would target overexpressed CCK2Rs in gastrointestinal stromal tumors (GISTs). Cell uptake assay demonstrated that R2SM exhibited a high affinity for CCK2R, leading to receptor-mediated internalization and making probes finally accumulated in the lysosomes of tumor cells, which suggested in the tumor tissues, the probes were distributed in the extracellular acidic TME and intracellular lysosomes. With a p of 6.83, R2SM can be activated at the acidic TME (pH = 6.5-6.8) and lysosomes (pH = 4.5-5.0), exhibiting an apparent pH-dependent behavior and generating more intense fluorescence in these acidic environments. imaging showed that coupling of MG11 with a pH-sensitive NIR probe facilitated the accumulation of probe and enhanced the fluorescence in CCK2R-overexpressed HT-29 tumor cells. A high signal was observed in the tumor region within 0.5 h postinjection, indicating its potential application in intraoperative imaging. Fluorescence imaging of R2SM exhibited higher tumor-to-liver and tumor-to-kidney ratios (2.1:1 and 2.3:1, respectively), compared separately with the probes that are lipophilic, pH-insensitive, or MG11-free. and studies demonstrated that the synergistic effect of tumor targeting with pH sensitivity plays a vital role in the high signal-to-noise ratio of the NIR imaging probe. Moreover, different kinds of tumor-targeting vectors could be conjugated simultaneously with the NIR dye, which would further improve the receptor affinity and targeting efficiency.
癌症在全球范围内导致高死亡率，严重威胁着公众健康。因此迫切需要开发肿瘤特异性的近红外（NIR）成像剂，以实现精确诊断和有效治疗。近年来，人们正在开发针对内体、溶酶体或酸性肿瘤微环境（TME）等酸性环境的成像探针。然而，由于正常和肿瘤细胞的非特异性内化，导致诊断中的信噪比较差，这些 pH 敏感探针未能应用于肿瘤成像。为了解决这个问题，通过将 pH 敏感的七甲川花菁与 CCK2R 配体、最小胃泌素类似物 11（MG11）偶联，合成了胆囊收缩素 2 受体（CCK2R）靶向的 TME 敏感 NIR 荧光探针 R2SM，用于成像，其中 MG11 靶向胃肠道间质瘤（GISTs）中过表达的 CCK2R。细胞摄取实验表明，R2SM 对 CCK2R 具有高亲和力，导致受体介导的内化，使探针最终积聚在肿瘤细胞的溶酶体中，这表明在肿瘤组织中，探针分布在细胞外酸性 TME 和细胞内溶酶体中。R2SM 的 p 值为 6.83，可在酸性 TME（pH = 6.5-6.8）和溶酶体（pH = 4.5-5.0）中被激活，表现出明显的 pH 依赖性行为，并在这些酸性环境中产生更强的荧光。NIR 成像显示，MG11 与 pH 敏感 NIR 探针的偶联促进了探针的积累，并增强了 CCK2R 过表达 HT-29 肿瘤细胞中的荧光。在注射后 0.5 小时内，在肿瘤区域观察到高信号，表明其在术中成像中的潜在应用。与亲脂性、pH 不敏感或无 MG11 的探针相比，R2SM 的荧光成像显示出更高的肿瘤与肝脏和肿瘤与肾脏的比值（分别为 2.1:1 和 2.3:1）。细胞摄取和 实验表明，肿瘤靶向与 pH 敏感性的协同作用在 NIR 成像探针的高信噪比中起着至关重要的作用。此外，还可以同时将不同种类的肿瘤靶向载体与 NIR 染料缀合，从而进一步提高受体亲和力和靶向效率。
