In vivo magnetic resonance imaging of mice liver tumors using a new gadolinium-based contrast agent

Abstract

We compared the enhancement effect between a newly synthesized tissue-specific contrast agent, [Gd-DOTA-FPβG], and a commercially available agent, [Gd(DOTA)](-), in a murine model of liver tumor using a clinical magnetic resonance imaging scanner. The colon cancer cell lines with and without β-glucuronidase (βG) expression were implanted into the liver of mice. Self-synthesized gadolinium-based magnetic resonance contrast agent, [Gd(DOTA-FPβG)], was administered to measure enhancement on magnetic resonance images using a commercially available agent, [Gd(DOTA)](-), as control in a clinical 3.0 tesla (T) magnetic resonance scanner. In vivo fluorescence imaging and histopathology of the liver were also performed to compare and correlate with the magnetic resonance studies. The in vivo fluorescence imaging failed to depict a sufficiently intense signal for liver or liver tumor of mice without exposure of the liver following an incision on the abdominal wall. The tissue-specific magnetic resonance agent, [Gd(DOTA-FPβG)], caused significantly stronger enhancement in tumors expressing βG (CT26/mβG-eB7) than in tumors not expressing βG (CT26) (p < 0.05). In the magnetic resonance imaging studies using control agent [Gd(DOTA)](-), the tumors with and without βG expression depicted no significant difference in enhancement on the T1-weighted images. The [Gd(DOTA-FPβG)] also provided significantly more contrast uptake in the CT26/mβG-eB7 tumor than in the normal liver parenchyma, whereas the [Gd(DOTA)](-) did not. This study confirms that better contrast enhancement can be readily detected in vivo by the use of a tissue-specific magnetic resonance contrast agent to target tumor cells with specific biomarkers in a clinical magnetic resonance imaging scanner.

Figure 1

Time course curve, signal intensity of fluorescent images of CT26 and CT26/mβG‐eB7. The overall signal before exposing liver is low. The signal intensity of fluorescence does not demonstrate significant difference between CT26/mβG‐eB7(■) and CT26 tumors(◆). After the incision of the abdominal wall and exposure of the liver, the signal is significantly higher than that of the animal without exposure of liver at 35 minutes after the injection of fluorescent probes FDGlcU(B).

Figure 2

Fluorescent images of CT26 and CT26/mβG‐eB7 before (left in A and B) and after (right in A and B) the excision of the abdominal wall. There was no significant signal from the liver tumor before the excision. The signals can be detected after the exposure of the liver. The CT26/mβG‐eB7 tumor depicts a stronger fluorescent signal than the CT26 tumor after abdominal wall excision (right in B). There are some autofluorescent signals expressed on the hairs of the limbs and head.

Figure 3

Photograph of the excised CT26/mβG‐eB7 and CT26 tumors in the left lateral lobe of the liver. No significant gross difference was seen between these two lesions.

Figure 4

Gd‐DOTA‐FPβG enhanced T1‐weighted MR images in mice. Pre = Pre‐contrast image. The numbers indicate time (minutes) after intravenous administration of the contrast medium. The images show higher signal intensity in the CT26/mβG‐eB7 tumor than in the CT26 tumor and liver from 10 minutes after the contrast agent, and the obvious difference remained constant until 90 minutes. As the time passed, the signal intensity in livers and CT26 tumors decreased. The signal intensity in the CT26/mβG‐eB7 tumor remains higher than the other until the end of the scan.

Figure 5

Time‐enhancement change of tumors and livers after intravenous injections of contrast medium [Gd(DOTA‐FPβG)]. The CT26/mβG‐eB7 tumor shows a stronger signal intensity from 5 to 90 minutes. The highest average signal of the CT26/mβG‐eB7 tumor was at 10 minutes. It was about 25% more enhanced than an average signal of the CT26 tumor, and 20% more than an average signal of liver tissues. The signals obtained from CT26/mβG‐eB7 and CT26 tumors were statistically different (p < 0.001, N = 6).

Figure 6

[(Gd‐DOTA)]⁻ enhanced T1‐weighted MR images in mice. The numbers indicate time (minutes) after intravenous administration of contrast medium. Both tumors are relatively less enhanced than the liver. Pre = Pre‐contrast image.

Figure 7

Time‐enhancement curves of the tumors and livers after intravenous injections of contrast medium [Gd(DOTA)]⁻. The signals of the CT26/mβG‐eB7 and the CT26 tumors reveal no significant difference (p = 0.67, N = 6). Both were less enhanced than the liver.

Figure 8

Histology demonstrates CT26/mβG‐eB7 tumor (T = tumor), CT26 tumor and liver tissues stained by hematoxylin and eosin (A, C), and X‐ GlcA (B, D). The area of CT26/mβG‐eB7 tumor reveals blue stain (B) because of βG expression. The CT26 tumor reveals no blue stain (D).