PET Imaging of Spontaneous Colorectal Cancer in Mice with 64Cu-Labeled TCP-1 Peptide

Background: Patients with inflammatory bowel disease (IBD) are at increased risk for colorectal cancer (CRC) and require close monitoring. However, distinguishing dysplasia from inflammatory tissues remains challenging. We developed a molecular PET imaging probe, TCP-1 (c[CTPSPFSHC]OH), for CRC detection. This study evaluates the feasibility of ⁶⁴Cu-labeled TCP-1, [⁶⁴Cu]Cu-NODAGA-TCP-1, for PET imaging of spontaneous CRC associated with colorectal inflammation in mice.

Methods: The TCP-1 peptide was conjugated with 1-glutaric acid-4,7-acetic acid (NODAGA) and radiolabeled with 64Cu to produce [64Cu]Cu-NODAGA-TCP-1. Binding assays were conducted to assess the specific binding properties of [64Cu]Cu-NODAGA-TCP-1 to human HT-29 and CaCo-2 CRC cells. PET imaging was performed in mice (n=5) with spontaneous CRC induced by azoxymethane (AOM) and dextran sodium sulfate (DSS) treatment, and 4 control mice with DSS-induced colitis without malignancy.

Results: The cell binding of [64Cu]Cu-NODAGA-TCP-1 was positively verified in CRC cell lines. Competition assays using non-radioactive TCP-1 significantly reduced [64Cu]Cu-NODAGA-TCP-1 radioactivity in the cells, confirming cell binding specificity. IC50 values for [64Cu]Cu-NODAGA-TCP-1 binding were determined to be 4.09 nM for CaCo-2 cells and 3.83 nM for HT-29 cells. In AOM/DSS-treated mice, spontaneous malignant lesions in the distal colon were effectively detected by [64Cu]Cu-NODAGA-TCP-1 PET imaging from 1 h up to 21 h post-injection. No detectable uptake of [64Cu]Cu-NODAGA-TCP-1 was observed in inflamed colorectal tissues in animals with colitis. Cancerous lesions identified by PET imaging were confirmed via postmortem histology.

Conclusions: [⁶⁴Cu]Cu-NODAGA-TCP-1 PET imaging enables sensitive detection and quantifiable assessment of inflammation-associated colorectal malignancy, effectively distinguishing tumors from inflammatory tissues.