Development and Preclinical Evaluation of CDH17-Specific ImmunoPET Imaging in Colorectal Cancers

Cadherin 17 (CDH17) is found to be abnormally expressed in colorectal cancer (CRC) and linked to a prognosis. Its consistent presence in both primary and metastatic CRC positions it as a promising biomarker. This study aims to develop CDH17-targeted immuno-positron emission tomography (immunoPET) probes and evaluate their potential for diagnosing CRC. Immunohistochemical (IHC) staining was performed on CRC tissue microarrays to analyze CDH17 expression. The CDH17 expression of CRC cells (LS174T, HCT116, and Caco-2) and pancreatic cancer cells (AsPC-1) was detected by flow cytometry. CDH17-specific nanobodies (i.e., CDH1) were produced and labeled with gallium-68 (⁶⁸Ga) and fluorine-18 (¹⁸F) to generate imaging probes. ImmunoPET imaging was conducted to evaluate the probes' diagnostic abilities in tumor models. IHC staining of CRC tissue microarrays demonstrated an elevated expression of CDH17 in malignant tissues relative to that in adjacent normal tissues. Flow cytometry showed that CDH17 was expressed on the surface of Caco-2 and AsPC-1 cells but not on the surface of HCT116 or LS174T cells. ImmunoPET imaging with [⁶⁸Ga]Ga-NOTA-CDH1 successfully visualized CDH17 expression in Caco-2 tumors, whereas no significant tracer uptake was observed in HCT116 tumors. [¹⁸F]AlF-RESCA-CDH1 immunoPET imaging demonstrated CDH17 expression in both LS174T and AsPC-1 tumors. IHC confirmed CDH17 expression on the membrane of Caco-2 and AsPC-1 cells with no significant expression on HCT116 cells. CDH17 expression was evident in the LS174T tumor capsule tissue. In this study, we developed three nanobody-based tracers targeting CDH17, of which [⁶⁸Ga]Ga-NOTA-CDH1 and [¹⁸F]AlF-RESCA-CDH1 noninvasively demonstrated CDH17 expression in preclinical models.