Abstract 4926: Molecular imaging of colorectal cancer in the setting of colitis

Abstract

Abstract Introduction: Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is defined by chronic inflammation of the gastrointestinal tract. In the colon, persistent colitis is a major risk factor in IBD-associated colorectal cancer (CRC). While primary and metastatic CRC can often be visualized using radiotracers such as 18F-FDG for PET imaging, the sensitivity for detection of primary CRC is decreased in the setting of IBD due to increased glucose metabolism at sites of inflammation. EGFR overexpression is reported in up to 97% of CRCs. The lower expression in inflammatory cells makes it a valuable imaging target to identify CRC in the setting of colitis. Objective: The goal of this effort is to develop and test in murine models an EGFR targeted PET imaging probe for the detection of CRC, with the ability to differentiate neoplasia from colonic inflammation. Methods: The F(ab')2 fragment of cetuximab was generated by enzymatic digestion. After the integrity and purity of the F(ab')2 was evaluated with SDS-PAGE and FPLC, the F(ab')2 fragment was conjugated with the p-SCN-Bn-DOTA chelate, and then radiolabeled with 64Cu. The receptor binding affinity and specificity of the 64Cu-DOTA-F(ab')2 was evaluated using EGFR expressing CT26 murine colon cancer cells. Tumor to bowel ratio of the EGFR PET imaging probe was compared with 18F-FDG using DSS-treated CT26 tumor-bearing BALB/c mice at 24 h. The in vivo behavior of the probe was demonstrated with PET-CT in two different mouse models of CRC (ApcCKOp53flox/flox and ApcLoxP/ LoxPMsh2null/LoxP). Histochemical examination were also performed. Results: F(ab')2 fragments of cetuximab can be generated efficiently and with high purity. The radioligand binding assay revealed that 64Cu labeled EGFR-DOTA-F(ab')2 conjugate bound specifically to EGFR on CT26 xenografts, with KD and Bmax values in vitro of 6.6 0.7 nM and 3.3 0.1 x 106 receptors/cell respectively. DSS-induced colitis was confirmed with relative change in body weight, 18F-FDG PET imaging, and histological examination. 64Cu-DOTA-F(ab')2 showed a significantly higher (p < 0.001) tumor to bowel ratio (TBR = 3.8 0.10) in comparison with 18F-FDG (TBR =1.5 0.05) during inflammation in the colon. Colon tumors in GEMM were successfully visualized and showed high correlation with ex-vivo PET imaging results and IHC examination. Conclusions: The developed EGFR targeted PET imaging probe demonstrated high target specificity for colonic tumors in the setting of colitis as compared to 18F-FDG. Future clinical translation of this paradigm is promising for the detection of CRC in IBD. Citation Format: N. Selcan Turker, Umar Mahmood, Melani H. Kucherlapati, Raju Kucherlapati. Molecular imaging of colorectal cancer in the setting of colitis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4926. doi:10.1158/1538-7445.AM2014-4926