Abstract 4000: Cellular MRI of human breast cancer cells labeled with gadofluorine M

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The ability to non-invasively locate and quantify tumor cell number at a metastatic site would be of considerable interest in pre-clinical and clinical metastasis research. To this end, our objective is to develop positive-contrast cellular magnetic resonance imaging (MRI) for use in quantifying tumor cell number at a metastatic site in vivo. The goals of the current study were to characterize the in vitro labeling of MDA-MB-231-luc-D3H2LN human breast cancer cells with a novel positive contrast MR agent Gadofluorine M (GdF), and to demonstrate the detectability of GdF-labeled cells in vitro at clinical strength MRI (1.5 and 3Tesla) scanners. Briefly, cells (1.5 × 107cells) were loaded by simple incubation for 24h with GdF at concentrations ranging from 25μM to 10mM. GdF-loading from 25μM to 1000μM did not result in significant changes in metabolic activity. Higher GdF-loading concentrations, 2500μM and 10mM, resulted in a 16% and 21% reduction in metabolic activity, respectively. The lowest GdF-loading concentration used (25μM) resulted in a significant (9-fold) increase in MR signal enhancement which then plateaued from 100μM to 1000μM. T1-relaxometry of cell pellets demonstrated a similar statistical trend in relaxation rates of cell pellets for all loading conditions, and at both field strengths. Inductively-coupled plasma atomic emission spectroscopy was performed on the cell pellet extracts to assess the average amount of GdF that had accumulated per cell at each incubating concentration. Since the relaxivity of an MR contrast agent can be affected by its intracellular location, we assessed whether internalized GdF-cc (GdF analog where the mannose moiety was replaced with carbocyanine) was cytosolic or compartmentalized into endosomes, via immunostaining for mannose-6-phosphate receptor. Using confocal fluorescence microscopy, we found that GdF is largely cytosolic and did not co-localize to late endosomes, an optimal situation for achieving maximum positive-contrast by T1-shortening since endosomal compartmentalization can lessen the enhancement seen in MR images. From these results, we have determined that the GdF loading concentration of 1000μM permits the highest payload for detection by cellular MRI in clinical field strength scanners. Information from this proof-of-principle study will support future work to develop positive-contrast cellular MRI as a new approach to quantitative imaging of metastatic cells in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4000.