结直肠癌（CRC）是全球第三大常见癌症。仅在美国，2023 年结直肠癌就造成约 52,550 例死亡，估计新增病例 153,020 例。 CRC 在 5-10% 的患者中呈现同步腹膜扩散，高达 20-50% 的复发性疾病患者将发展为异时结直肠癌腹膜转移 (CRC-PM) 疾病。根除肿瘤、肿瘤边缘和微观残留病灶至关重要，因为微观残留病灶与局部复发相关，5年生存率低于35%。切除和减少残留病灶的成功取决于术中区分癌细胞和正常组织的准确性。荧光分子成像（IFMI）和肿瘤靶向造影剂代表了术中检测和手术干预的一种有前途的方法。正确的靶点选择、可扩展成像剂的开发以及增强的实时肿瘤和肿瘤微环境成像对于增强手术切除至关重要。 LGR5（富含亮氨酸重复序列的 G 蛋白偶联受体 5）是一种结肠隐窝干细胞标记物，也是 Wnt 信号通路中 R-spondins (RSPO) 的受体，也在结直肠癌干细胞 (CSC) 上表达）以及结直肠癌肿瘤和转移，表明它可能是结直肠癌成像的有用靶点。然而，关于 LGR5 在 CRC 治疗和结果中的作用有许多不同的报告。在此，我们报告了 37 个氨基酸的 RSPO1 模拟肽（称为 RC18）的合成和验证，该肽专门设计用于访问 LGR5 的 R-spondin 结合位点，有可能用于 CRC-PM 的互操作成像。 RC18的受体结合能力表明，与LGR5的直接相互作用既不会显着增加LGR5信号传导，也不会阻断RSPO1结合和信号转导，这表明RSPO1模拟物在功能上是惰性的，使其成为术中CRC-PM成像的有吸引力的造影剂。

Colorectal cancer (CRC) is the third most common cancer worldwide. In the United States alone, CRC was responsible for approximately 52,550 deaths in 2023, with an estimated 153,020 new cases. CRC presents with synchronous peritoneal spread in 5-10% of patients, and up to 20-50% of patients with recurrent disease will develop metachronous colorectal cancer peritoneal metastatic (CRC-PM) disease. Eradication of the tumor, tumor margins and microscopic residual disease is paramount, as microscopic residual disease is associated with local recurrences, with 5-year survival rates of less than 35%. The success of resection and reduction of residual disease depends on the accuracy with which cancer cells and normal tissue can be intra-operatively distinguished. Fluorescence Molecular Imaging (IFMI) and tumor-targeted contrast agents represent a promising approach for intraoperative detection and surgical intervention. Proper target selection, the development of scalable imaging agents and enhanced real-time tumor and tumor microenvironment imaging are critical to enabling enhanced surgical resection. LGR5 (leucine-rich repeat-containing G-protein-coupled receptor 5), a colonic crypt stem cell marker and the receptor for the R-spondins (RSPO) in the Wnt signaling pathway, is also expressed on colorectal cancer stem cells (CSC) and on CRC tumors and metastases, suggesting it could be a useful target for imaging of CRC. However, there are numerous diverging reports on the role of LGR5 in CRC therapy and outcomes. Herein, we report on the synthesis and validation of a 37 amino acid RSPO1-mimetic peptide, termed RC18, that was specifically designed to access the R-spondin binding site of LGR5 to potentially be used for interoperative imaging of CRC-PM. The receptor-binding capabilities of the RC18 indicate that direct interactions with LGR5 neither significantly increased LGR5 signaling nor blocked RSPO1 binding and signal transduction, suggesting that the RSPO1-mimetic is functionally inert, making it an attractive contrast agent for intraoperative CRC-PM imaging.