Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35233, United States.
Department of Radiology, University of Alabama at Birmingham, Birmingham, Alabama 35233, United States.
Mol Pharm. 2023 May 1;20(5):2415-2425. doi: 10.1021/acs.molpharmaceut.2c00977. Epub 2023 Apr 4.
Tumor-associated macrophages (TAMs) are large phagocytic cells that play numerous roles in cancer biology and are an important component of the relationship between immune system response and tumor progression. The peptide, RP832c, targets the Mannose Receptor (CD206) expressed on M2-like macrophages and is cross-reactive to both human and murine CD206. Additionally, it exhibits therapeutic properties through its ability to shift the population of TAMs from an M2-like (protumor) toward an M1-like phenotype (antitumor) and has demonstrated promise in inhibiting tumor resistance in PD-L1 unresponsive melanoma murine models. In addition, it has shown inhibition in bleomycin-induced pulmonary fibrosis through interactions with CD206 macrophages. Our work aims to develop a novel CD206 positron emission tomography (PET) imaging probe based on RP832c ( = 5.64 μM) as a direct, noninvasive method for the assessment of TAMs in mouse models of cancer. We adapted RP832c to incorporate the chelator DOTA to allow for radiolabeling with the PET isotope Ga ( = 68 min; ß = 89%). In vitro stability studies were conducted in mouse serum up to 3 h. The in vitro binding characteristics of [Ga]RP832c to CD206 were determined by a protein plate binding assay and Surface Plasmon Resonance (SPR). PET imaging and biodistribution studies were conducted in syngeneic tumor models. Stability studies in mouse serum demonstrated that Ga remained complexed up to 3 h (less than 1% free Ga). Binding affinity studies demonstrated high binding of [Ga]RP832c to mouse CD206 protein and that the binding of the tracer was able to be blocked significantly when incubated with a blocking solution of native RP832c. PET imaging and biodistribution studies in syngeneic tumor models demonstrated uptake in tumor and CD206 expressing organs of [Ga]RP832c. A significant correlation was found between the percentage of CD206 present in each tumor imaged with [Ga]RP832c and PET imaging mean standardized uptake values in a CT26 mouse model of cancer. The data shows that [Ga]RP832c represents a promising candidate for macrophage imaging in cancer and other diseases.
肿瘤相关巨噬细胞（TAMs）是一种大型吞噬细胞，在癌症生物学中发挥着多种作用，是免疫系统反应与肿瘤进展之间关系的重要组成部分。肽 RP832c 靶向 M2 样巨噬细胞上表达的甘露糖受体（CD206），并与人源和鼠源 CD206 交叉反应。此外，它通过将 TAMs 从 M2 样（促肿瘤）表型转变为 M1 样（抗肿瘤）表型的能力发挥治疗特性，并在抑制 PD-L1 无反应性黑色素瘤小鼠模型中的肿瘤耐药方面显示出希望。此外，它通过与 CD206 巨噬细胞相互作用，在博来霉素诱导的肺纤维化中显示出抑制作用。我们的工作旨在开发一种新型的基于 RP832c 的 CD206 正电子发射断层扫描（PET）成像探针（=5.64μM），作为评估癌症小鼠模型中 TAMs 的直接、非侵入性方法。我们将 RP832c 改编为包含螯合剂 DOTA，以便用 PET 同位素 Ga（=68 分钟；β=89%）进行放射性标记。在小鼠血清中进行了长达 3 小时的体外稳定性研究。通过蛋白质平板结合测定和表面等离子体共振（SPR）测定，研究了[Ga]RP832c 与 CD206 的体外结合特性。在同种异体肿瘤模型中进行了 PET 成像和生物分布研究。在小鼠血清中的稳定性研究表明，Ga 直到 3 小时仍保持复合物状态（少于 1%的游离 Ga）。结合亲和力研究表明，[Ga]RP832c 与小鼠 CD206 蛋白具有高结合能力，并且当用天然 RP832c 的封闭溶液孵育时，示踪剂的结合能够被显著阻断。在同种异体肿瘤模型中的 PET 成像和生物分布研究表明，[Ga]RP832c 在肿瘤和表达 CD206 的器官中摄取。在 CT26 癌症小鼠模型中，用[Ga]RP832c 成像的每个肿瘤中 CD206 的百分比与 PET 成像平均标准化摄取值之间发现了显著相关性。数据表明，[Ga]RP832c 是癌症和其他疾病中巨噬细胞成像的有前途的候选物。
