Evaluation of [Gd(Bz-TTDA)]2- as a potential contrast agent in MR imaging of the hepatobiliary system: An animal study

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

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.

Comparison of Gd-Bz-TTDA, Gd-EOB-DTPA, and Gd-BOPTA for dynamic MR imaging of the liver in rat models

To evaluate the competitive potential of a new lipophilic paramagnetic complex, Gd-Bz-TTDA [4-benzyl-3,6,10-tri (carboxymethyl)-3,6,10-triazado-decanedioic acid] compared with two other commercially available MR hepatobiliary contrast agents, gadobenate dimeglumine (Gd-BOPTA) and gadoxetic acid (Gd-EOB-DTPA), dynamic MR imaging studies were performed on normal and hepatocellular carcinoma (HCC) rat models using a 1.5-Tesla MR scanner. The results indicate that normal rats that were injected with 0.1 mmol/kg Gd-Bz-TTDA showed significantly more intense and persistent liver enhancement than those that were injected with the same dose of Gd-EOB-DTPA or Gd-BOPTA. All of these agents showed similar enhancement patterns in the implanted HCC. The liver-lesion contrast-to-noise ratios were higher and more persistent in rats that were injected with Gd-Bz-TTDA. These results indicate that Gd-Bz-TTDA is comparable with the commercially available hepatobiliary agents, Gd-EOB-DTPA and Gd-BOPTA, and can result in more intense and prolonged liver enhancement while still providing better liver-lesion discrimination. These results warrant further large-scale studies.

Evaluation of CH3-DTPA-Gd (NMS60) as a new MR contrast agent: early phase II study in brain tumors and dual dynamic contrast-enhanced imaging

PURPOSE

A newly developed contrast material, CH3-DTPA-Gd (NMS60), a trimer containing 3 Gd(3+) atoms per molecule, has been shown to offer greater enhancement and longer vascular retention than gadopentetate dimeglumine (Gd-DTPA) in animals. We report on our early phase II study on NMS60 in brain tumor patients together with supplementary investigations.

METHODS AND MATERIALS

The longitudinal relaxation rate (R(1)=1/T(1)) and the transverse relaxation rate (R(2)*=1/T(2)*) of NMS60 and Gd-DTPA were determined at 20 degrees C in water at 1.5 T. An NMS60 dose of 0.1 or 0.2 mmol (Gd)/kg was randomly assigned and administered to 10 patients (five women, five men; mean age: 49 years) with brain tumors. Safety and contrast-enhancing ability of NMS60 were evaluated. Dual dynamic contrast-enhanced T(1) and R(2)* studies (DUCE imaging) were also carried out in two patients.

RESULTS

Regarding the relaxivity per Gd, R(1) and R(2)* of NMS60 were 9.5 and 11.0 (mmol/L x s)(-1), respectively, compared to 4.8 and 7.2 (mmol/L x s)(-1) for Gd-DTPA. Although a transient slight increase of alanine aminotransferase was observed in one case, no other adverse reactions were observed after administration of NMS60. Contrast enhancement by NMS60 was excellent at both concentrations, and when tumor detectability was assessed with a five-point scale, the diagnostic usefulness was 4 or higher in all cases. In DUCE imaging, NMS60 appeared to show high signal intensity, when compared with the data obtained separately for Gd-DTPA.

CONCLUSION

NMS60 had a high contrasting effect and little toxicity, and is expected to be clinically useful.

Cellular MR Imaging

Cellular MR imaging is a young field that aims to visualize targeted cells in living organisms. In order to provide a different signal intensity of the targeted cell, they are either labeled with MR contrast agents in vivo or prelabeled in vitro. Either (ultrasmall) superparamagnetic iron oxide [(U)SPIO] particles or (polymeric) paramagnetic chelates can be used for this purpose. For in vivo cellular labeling, Gd3+- and Mn2+- chelates have mainly been used for targeted hepatobiliary imaging, and (U)SPIO-based cellular imaging has been focused on imaging of macrophage activity. Several of these magneto-pharmaceuticals have been FDA-approved or are in late-phase clinical trials. As for prelabeling of cells in vitro, a challenge has been to induce a sufficient uptake of contrast agents into nonphagocytic cells, without affecting normal cellular function. It appears that this issue has now largely been resolved, leading to an active research on monitoring the cellular biodistribution in vivo following transplantation or transfusion of these cells, including cell migration and trafficking. New applications of cellular MR imaging will be directed, for instance, towards our understanding of hematopoietic (immune) cell trafficking and of novel guided (stem) cell-based therapies aimed to be translated to the clinic in the future.