Imaging and quantification of metastatic melanoma cells in lymph nodes with a ferritin MR reporter in living mice.

Cellular MRI with a reporter gene offers the opportunity to track small numbers of tumor cells and to study metastatic processes in their earliest developmental stages in the target organs of interest. This study demonstrates the feasibility of using the MR reporter ferritin for the noninvasive imaging and quantification of metastatic melanoma cells in the lymph nodes (LNs) of living mice. A B16F10 murine melanoma cell line expressing human ferritin heavy chain (hFTH) and green fluorescent protein (GFP) was constructed to allow the detection of cells by MRI and fluorescence imaging. Stable overexpression of hFTH and GFP in B16F10 murine melanoma cells was feasible and showed no cellular toxicity. In addition, hFTH cells were detectable by 9.4-T MRI in vitro and in vivo, yielding significant changes in T₂* relative to control cells. In BALB/c nude mice, the presence of hFTH- and GFP-expressing metastatic melanoma cells in deep-seated axillary LNs was demonstrated as areas of low T₂* on MRI, but the same LNs were not visible by fluorescence imaging because the light was unable to penetrate the tissue. Furthermore, the metastatic volume of each LN, which was assessed by cumulative histogram analysis of the T₂* MRI data, correlated well with tumor burden, which was determined by histology ( r = −0.8773, p = 0.0001). This study is the first to use MRI and an MR reporter gene for both the visualization and quantification of metastatic cancer cells in LNs. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]