A Peptide Targeted To Fibrin-fibronectin Complexes With Colon Cancer In Mice By 7.0 T MRI

objective: To evaluate a new low molecular weight CREKA targeted contrast agent CREKA-(Gd-DOTA)4.CREKA is a small peptide that specifically binds to the fibrin-fibronectin complexes in tumor extracellular matrix.Fibronectins are found abundantly present in the extracellular matrix of a spectrum of malignant human tumors but not in normal human tissues.At present,this targeted contrast agent CREKA-(Gd-DOTA)4 has already been used in the research of prostate cancer,breast cancer.In this study,we investigated the imaging findings of CREKA-(Gd-DOTA)4 in nude mice bearing human colon cancer SW1116 cells.Methods:1.The nude mice model of colon cancer.Male athymic nu/nu mice(4-5 weeks old,n=20)weighing18-22 g were subcutaneously implanted in both flanks with 5×106/ml SW1116 cells until the tumor size reached 0.8-1.2 cm in diameter in 2-3 weeks.2.Experimental grouping and MR scanning.15 tumor-bearing mice were randomly divided into the experimental group(n=9)and the control group(n=6).MRI contrast agents were administered via a tail vein at a dose of 0.1mmol/L mice,the experimental group was injected with CREKA-(Gd-DOTA)4and the control group was injected with Gadopentetate dimeglumine(Gd-DTPA).The mice were placed in a nude mouse coil and scanned on a Bruker 7T MRI scanner before and at 5,10,20,30,40,50 and 60 min afterinjection using a 2D spin-echo sequence(TR=500 ms,TE=8.0 ms,90° flip angle,1.5mm slice thickness,FOV=3cm.)3.Pathological staining and Immunohistochemistry.Mice were sacrificed right now after injection,the tumor tissue were removed and fixed and used to hematoxylin-eosin staining and immunohistochemically staining.The primary antibody is Anti-Fibronectin antibody.4.Observation and statistics.(1)Degree of enhancement.Imaging analysis directly;Calculating contrast to noise ratio(CNR)and contrast ratio(CR),using the repeated measures analysis of variance(rmANOVA),assuming statistical significance at P < 0.05.(2)Duration of enhancement.Calculating contrast to noise ratio.(3)Enhancement of muscle tissue.Measuring the MR signal of muscle tissue before and after enhancement in experimental group and control group,using the paired t-test,assuming statistical significance at P < 0.05.(4)Image quality evaluation.Including image quality,image artifacts and spatial resolution.Results: 1.Degree of enhancement and duration of enhancement.CREKA-(Gd-DOTA)4 showed higher CNR at 10 min after injection in the tumor and decreased gradually at the peak value(CNR=14.8146).At the same time,CNR in tumor continuously maintain a high level during the period of 60 min post-injection.The CNR in tumor tissue with Gd-DTPA decreased rapidly after it reached the maximum values(CNR=10.2424)at 10 min post-injection.The CREKA-(Gd-DOTA)4showed significantly higher CNR than the control Gd-DTPA in tumor since 15 min post-injection(P < 0.05).2.Enhancement of muscle tissue.The experimental group was injected with contrast agent CREKA-(Gd-DOTA)4 5min,the signal values of muscle tissue lower than the pre-injection,but the difference was not statistically significant(P > 0.05);the control group was injected with Gd-DTPA 5 min,the signal values of muscle tissue more slightly increased than the pre-injection and the difference was statistically significant(P < 0.05).3.Pathological staining and Immunohistochemistry.The HEstaining was conform to the characteristics of colon cancer in nude mice.The IHC-staining clearly indicated the existence of fibronectin in extracellular spaces of tumor tissue,not in the normal muscle tissue.Conclusion: CREKA-(Gd-DOTA)4 is a targeted magnetic resonance contrast agent for colon cancer.Compared to Gd-DTPA,CREKA-(Gd-DOTA)4 has good relaxation and long duration.Targeted magnetic resonance contrast agent CREKA-(Gd-DOTA)4has potential pre-clinical application value,and provides the possibility for early detection and early diagnosis of colon cancer.