Tumor hypoxia is associated with resistance to treatment, aggressive growth, metastatic dissemination, and poor clinical outcome in many cancer types. The potential of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to assess the extent of hypoxia in tumors has been investigated in several studies in our laboratory. Cervical carcinoma, melanoma, and pancreatic ductal adenocarcinoma (PDAC) xenografts have been used as models of human cancer, and the transfer rate constant (Ktrans) and the extravascular extracellular volume fraction (ve) have been derived from DCE-MRI data by using Tofts standard pharmacokinetic model and a population-based arterial input function. Ktrans was found to reflect naturally occurring and treatment-induced hypoxia when hypoxia was caused by low blood perfusion, radiation responsiveness when radiation resistance was due to hypoxia, and metastatic potential when metastasis was hypoxia-induced. Ktrans was also associated with outcome for patients with locally-advanced cervical carcinoma treated with cisplatin-based chemoradiotherapy. Together, the studies imply that DCE-MRI can provide valuable information on the hypoxic status of cervical carcinoma, melanoma, and PDAC. In this communication, we review and discuss the studies and provide some recommendations as to how DCE-MRI data can be analyzed and interpreted to assess tumor hypoxia.

Preclinical studies have suggested that interstitial fluid pressure (IFP) is uniformly elevated in the central region of tumors, whereas clinical studies have revealed that IFP may vary among different measurement sites in the tumor center. IFP measurements are technically difficult, and it has been claimed that the intratumor heterogeneity in IFP reported for human tumors is due to technical problems. The main purpose of this study was to determine conclusively whether IFP may be heterogeneously elevated in the central tumor region, and if so, to reveal possible mechanisms and possible consequences. Tumors of two xenograft models were included in the study: HL-16 cervical carcinoma and Panc-1 pancreatic carcinoma. IFP was measured with Millar SPC 320 catheters in two positions in each tumor and related to tumor histology or the metastatic status of the host mouse. Some tumors of both models showed significant intratumor heterogeneity in IFP, and this heterogeneity was associated with a compartmentalized histological appearance (i.e., the tissue was divided into compartments separated by thick connective tissue bands) in HL-16 tumors and with a dense collagen-I-rich extracellular matrix in Panc-1 tumors, suggesting that these connective tissue structures prevented efficient interstitial convection. Furthermore, some tumors of both models developed lymph node metastases, and of the two IFP values measured in each tumor, only the higher value was significantly higher in metastatic than in non-metastatic tumors, suggesting that metastatic propensity was determined by the tumor region having the highest IFP.

Purpose The purpose of the study was to demonstrate the performance and possible applications of an intravital microscopy assay using a standard fluorescence microscope. Methods Melanoma and pancreatic ductal adenocarcinoma xenografts were initiated in dorsal window chambers and subjected to repeated intravital microscopy. The entire tumor vasculature as well as the normal tissue surrounding the tumor was imaged simultaneously with high spatial and temporal resolution. Vascular morphology images were recorded by using transillumination, and vascular masks were produced to quantify vessel density, vessel diameter, vessel segment length, and vessel tortuosity. First-pass imaging movies were recorded after an intravenous injection of a fluorescent marker and were used to investigate vascular function. Lymphatics were visualized by intradermal injections of a fluorescent marker. Results The intravital microscopy assay was used to study tumor growth and vascularization, tumor vessel morphology and function, tumor-associated lymphatics, and vascular effects of acute cyclic hypoxia and antiangiogenic treatment. The assay was sensitive to tumor-line differences in vascular morphology and function and detected tumor-induced lymphatic dilation. Acute cyclic hypoxia induced angiogenesis and increased the density of small diameter vessels and blood supply times, whereas antiangiogenic treatment selectively removed small-diameter vessels, reduced blood supply times, and induced hypoxia. Moreover, the window chamber was compatible with magnetic resonance imaging (MRI), and parametric images derived by dynamic contrast-enhanced MRI were shown to reflect vascular morphology and function. Conclusions The presented assay represents a useful and affordable alternative to intravital microscopy assays using confocal and multi-photon microscopes.

Tumor hypoxia is associated with resistance to treatment, aggressive growth, and poor clinical outcome in many cancer types, and is a result of an imbalance between oxygen supply and oxygen consumption. We have previously shown that Ktrans and ve images derived by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) reflect blood perfusion and cell density which are important determinants of oxygen supply and oxygen consumption respectively. The purpose of the current study was to investigate whether Ktrans and/or ve images can be used to produce images of tumor hypoxia. Cervical carcinoma and pancreatic ductal adenocarcinoma xenografts were used as models of human cancer, and xenografted tumors were subjected to antiangiogenic treatment or left untreated. Ktrans and ve images were derived from DCE-MRI data by using Tofts standard pharmacokinetic model, and images of tumor hypoxia were produced by applying threshold values to Ktrans and/or ve. Tumor hypoxia was also assessed by immunohistochemistry by using pimonidazole as a hypoxia marker. Ktrans and ve images were highly heterogeneous. Strong correlations were found between hypoxic fractions determined by immunohistochemistry and hypoxic fractions calculated by using Ktrans but not ve images. Importantly, hypoxia images produced by using Ktrans images reflected both naturally occurring and treatment-induced hypoxia. Moreover, hypoxia images produced by combining Ktrans and ve images were not superior to the hypoxia images produced by using only Ktrans images. These observations imply that Ktrans images reflected blood perfusion and oxygen supply, and that the heterogeneity in hypoxia was caused by heterogeneity in oxygen supply rather than heterogeneity in cell density and oxygen consumption in these tumor models. Citation Format: Jon-Vidar Gaustad, Anette Hauge, Catherine S. Wegner, Lise Mari K. Hansem, Einar K. Rofstad. DCE-MRI of tumor hypoxia in cervical carcinoma and pancreatic ductal adenocarcinoma xenografts [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-038.