Ovarian Carcinoma: Quantitative Biexponential MR Imaging Relaxometry Reveals the Dynamic Recruitment of Ferritin-expressing Fibroblasts to the Angiogenic Rim of Tumors

Abstract

Purpose:To quantitatively monitor the dynamic perivascular recruitment of ferritin heavy chain (FHC)-overexpressing fibroblasts to ovarian carcinoma xenografts by using R2 mapping and biexponential magnetic resonance (MR) relaxometry. Materials andMethods:In vivo studies of female mice were approved by the institutional animal care and use committee. In vitro analysis included MR-based R2 relaxation measurements of monkey kidney cell line (CV1) fibroblasts that overexpress FHC, followed by inductively coupled plasma mass spectrometry to assess cellular iron content. For in vivo analysis, CV1-FHC fibroblasts were either mixed with fluorescent human ovarian carcinoma cells before subcutaneous implantation (coinjection) or injected intraperitoneally 4 days after the cancer cells were injected (remote recruitment). Dynamic changes in tumor R2 were used to derive CV1-FHC cell fraction in both models. In coinjection tumors, dynamic contrast material-enhanced MR imaging was used to measure tumor fractional blood volume. Whole-body fluorescence imaging and immunohistochemical staining were performed to validate MR results. One-way repeated measures analysis of variance was used to assess MR and fluorescence imaging results and tumor volume, and one-way analysis of variance was used to assess spectrometric results, fractional blood volume, and immunohistochemical evaluation. Results:CV1-FHC fibroblasts (vs CV1 fibroblasts) showed enhanced iron uptake (1.8 mmol 6 0.5 3 10 28 vs 0.9 mmol 6 0.5 3 10 28 ; P , .05), retention (1.6 mmol 6 0.5 3 10 28 vs 0.5 mmol 6 0.5 3 10 28 , P , .05), and cell density-dependent R2 contrast. R2 mapping in vivo revealed preferential recruitment of CV1-FHC cells to the tumor rim in both models. Measurement of fractional blood volume was similar in all tumors (2.6 AU 6 0.5 3 10 23 for CV1, 2.3 AU 6 0.3 3 10 23 for CV1-FHC, 2.9 6 0.3 3 10 23 for CV1-FHC-ferric citrate). Dynamic changes in CV1-FHC cell fraction determined at MR relaxometry in both models were confirmed at immunohistochemical analysis. Conclusion:FHC overexpression, when combined with R2 mapping and MR relaxometry, enabled in vivo detection of the dynamic recruitment of exogenously administered fibroblasts to the vasculature of solid tumors.

Evaluation of Tumor-associated Stroma and Its Relationship with Tumor Hypoxia Using Dynamic Contrast-enhanced CT and18F Misonidazole PET in Murine Tumor Models

“…Previously, some studies have reported on the imaging of tumor-associated stroma (9,13,22,30,31). Ko et al (4) showed that apparent diffusion coefficient values were lower in the stroma-poor group than in the stroma-rich quantified with immunohistochemistry; this finding supported our hypothesis that DCE CT had the potential to depict a similar spatial distribution of tumor-associated stroma to that confirmed with histopathologic analysis.…”

“…Thus, there is a strong need for reliable biomarkers and noninvasive in vivo imaging strategies for the stromal components. However, to date, it has not been possible to use conventional imaging techniques to assess tumor stromal components in clinical practice even though considerable efforts have been devoted to the development of novel imaging techniques (4,8,9).…”

“…Furthermore, with DCE MR imaging, the concentration of the gadoliniumcontaining agent is considered not to be proportional to the detected signal changes (32), while it is assumed that the concentration of the iodinated agent is proportional to the measured attenuation at DCE CT (33). Vandsburger et al (9) described an experimental study using ferritin heavy chain-overexpressing fibroblasts detected with MR imaging and targeting cancer-associated fibroblasts, although the technique may not be adopted in clinical practice because it requires genetic manipulation of a fibroblast (8), while our method requires only an iodinated contrast agent and a CT scanner. In our study, we observed that tumor-associated stroma was not always hypoxic, at least as long as tumorassociated stroma contained vascular endothelium.…”

Ferritin Iron Mineralization and Storage: From Structure to Function

“…Ftn reporter genes were applied in a wide range of MRI studies including the detection of viral-based gene transfer as a surrogate of gene therapy, monitoring of stem cells and migration of other cells in the context of regenerative medicine for the heart and brain, and monitoring recruitment of cells in cancer [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]. As an endogenous protein, which can be used for generating detectable MRI contrast when expressed at physiological levels, Ftn offers the hope for its utilization for detection of transcriptional activation of gene expression, for detection of cell differentiation, and for longitudinal tracking of cell proliferation and migration.…”

Molecular Imaging of the Tumor Microenvironment for Precision Medicine and Theranostics

“…More recently, fibroblasts overexpressing ferritin heavy chain (FHC) were engineered and used to quantitatively monitor the dynamic perivascular recruitment in ovarian carcinoma xenografts (Vandsburger et al, 2013). FHC overexpression combined with R 2 mapping and MR relaxometry enabled in vivo imaging of the recruitment of exogenously administered fibroblasts to the vasculature of ovarian tumor xenografts (Vandsburger et al, 2013).…”