CAM-Xenograft Model Provides Preclinical Evidence for the Applicability of [(68)Ga]Ga-Pentixafor in CRC Imaging

SIMPLE SUMMARY: The high mortality rate of colorectal cancer (CRC) is associated with metastasis to the liver, which is related to an increased expression of the C-X-C chemokine receptor 4 (CXCR4). We hereby report the first preclinical evaluation of [(68)Ga]Ga-Pentixafor, a radiotracer specifically targeting human CXCR4, for CRC imaging. We established the chorioallantoic membrane (CAM)-xenograft model for two different human colon cancer cell lines (HT29 and HCT116) in our facility and conducted a thorough histological characterisation of the obtained xenograft tissues. The subsequently performed simultaneous positron emission tomography and magnetic resonance (µPET/MR) scans demonstrated [(68)Ga]Ga-Pentixafor uptake in CAM-xenografts and provided novel insights into the radiotracer distribution in the chick embryonal organism. ABSTRACT: Colorectal cancer is one of the leading causes of cancer-related deaths worldwide. Increased expression of CXCR4 has been associated with liver metastasis, disease progression, and shortened survival. Using in vitro cell binding studies and the in ovo model, we aimed to investigate the potential of [(68)Ga]Ga-Pentixafor, a radiotracer specifically targeting human CXCR4, for CRC imaging. Specific membrane binding and internalisation of [(68)Ga]Ga-Pentixafor was shown for HT29 cells, but not for HCT116 cells. Accordingly, [(68)Ga]Ga-Pentixafor accumulated specifically in CAM-xenografts derived from HT29 cells, but not in HCT116 xenografts, as determined by µPET/MRI. The CAM-grown xenografts were histologically characterised, demonstrating vascularisation of the graft, preserved expression of human CXCR4, and viability of the tumour cells within the grafts. In vivo viability was further confirmed by µPET/MRI measurements using 2-[(18)F]FDG as a surrogate for glucose metabolism. [(68)Ga]Ga-Pentixafor µPET/MRI scans showed distinct radiotracer accumulation in the chick embryonal heart, liver, and kidneys, whereas 2-[(18)F]FDG uptake was predominantly found in the kidneys and joints of the chick embryos. Our findings suggest that [(68)Ga]Ga-Pentixafor is an interesting novel radiotracer for CRC imaging that is worth further investigation. Moreover, this study further supports the suitability of the CAM-xenograft model for the initial preclinical evaluation of targeted radiopharmaceuticals.