Tumor-Specific Labeling of Pancreatic Cancer Using a Humanized Anti-CEA Antibody Conjugated to a Near-Infrared Fluorophore

Background/Purpose: Development of a humanized fluorophore-conjugated antibody that can improve contrast for fluorescence-guided oncologic surgeries. Methods: BxPC-3-GFP pancreatic cancer cells were injected into flanks of nude mice. Fragments of subcutaneous tumors were grafted onto the pancreatic tail of recipient mice to create orthotopic xenograft models of pancreatic cancer. After tumors developed for 4 weeks, a humanized anti-carcinoembryonic antigen antibody conjugated to an 800 nm near-infrared fluorescent dye (hM5A-IR800) was injected intravenously. Mice were imaged at 6, 12, 24, 48, and 72 h after injection. Results: Fluorescence imaging showed that hM5A-IR800 specifically localized to BxPC-3 human pancreatic cancer cells. The fluorescent probe localized to cell surfaces in vitro and specifically co-localized with green fluorescent protein-labeled tumors in an orthotopic pancreatic xenograft model in vivo. Serial imaging at specific time points showed peak signal intensity of the orthotopic pancreatic tumor at 48 h; this time point corresponded with a maximal tumor-to-background ratio (TBR) of 16.6 at 48 h. Discussion: hM5A-IR800 was successfully able to specifically label orthotopic pancreatic tumors in situ. The longer wavelength allowed deeper tissue penetration, particularly in tumor areas covered by normal pancreatic parenchyma. The probe had expected kinetics for an antibody-fluorophore conjugate, with the peak signal intensity reached at 48 h. A clear tumor signal was observed with a TBR CloseSPigtSPi 5 at all time points, with high contrast (TBR of 16.6) at 48 h. Conclusion: hM5A-IR800 demonstrated excellent tumor localization and a very bright signal. It is a promising agent for future clinical fluorescence-guided surgery applications.