Theranostics. 2016 Sep 9;6(12):2028-2038.
Purpose: To assess optical imaging of Mesenchymal-Epithelial Transition factor (MET) for delineation and characterization of intrahepatic models of human hepatocellular carcinoma (HCC) and metastatic colorectal cancer (CRC), and thereby demonstrate its potential use in precision oncology.
Materials and Methods: MET expression in human CRC and HCC was assessed in tissue microarrays. We used GE-137, a modified cyanine 5-tagged peptide for MET targeting. HepG2 and Huh-7 (HCC) and HT-29 (CRC) cells with MET overexpression, and LNCaP cells (negative control) with minimal MET expression were incubated with the probe. Correlation between the relative fluorescence signal intensity and cellular MET expression level was assessed. Flow cytometry was used to assess probe specific binding and dissociation constant (Kd). Orthotopic xenograft models of human HCC and metastatic CRC were generated in nu/nu mice by subcapsular implantation of cells. Epifluorescence imaging was performed to capture the changes in deferential probe accumulation at different time points after injection. Target-to-liver background ratio (TBR) was calculated and the probe biodistribution within different organs was assessed. Histopathologic analysis of extracted xenografts was performed to correlate the tumors MET expression with probe uptake by cancer cells.
Results: Approximately 91.5% of HCC and 81% of CRC microarray cores showed MET expression. HCC and CRC cells incubated with the probe showed substantial fluorescence compared to control LNCaP, with strong correlation between fluorescence signal and MET expression (R2 = 0.99, p < 0.001). Probe binding affinity to MET (Kd) was measured to be 2.9 ± 0.36 nM. Epifluorescence imaging showed intense uptake in subcapsular tumors with peak TBR of 5.46 ± 0.46 in Huh-7, 3.55 ± 0.38 in HepG2, and 15.93 ± 0.61 in HT-29 orthotopic xenografts at 4 hours post-injection (mean ± standard deviation). We demonstrated that in vivo probe uptake in xenografts is specific and can be blocked when co-injected with unlabeled peptide; for instance the epifluorescence TBR is reduced from 13.5 ± 1.2 to 1.7 ± 0.3 (p < 0.05) in HT-29 and from 5.3 ± 0.8 to 1.4 ± 0.2 (p < 0.05) in Huh-7 xenografts after co-injection with unlabeled peptides. Biodistribution studies showed predominantly renal clearance of the probe.
Conclusion: Optical imaging of MET resulted in high TBR in animal models of primary and metastatic hepatic tumors suggesting its utility for procedural guidance.