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Tumor blood supply was related to the morphology of the tumor microvasculature and the supplying arteries (SAs) of A-07-GFP and D-12-GFP melanoma xenografts growing in window chamber preparations in BALB/c nu/nu mice. Blood supply and morphologic parameters were determined from first-pass imaging movies and vascular maps recorded after a bolus of 155-kDa tetramethylrhodamine isothiocyanate-labeled dextran had been administered intravenously. Poorly supplied tumors showed microvascular networks that did not differ from those of well-supplied tumors in vessel tortuosity, diameter, and density. Conversely, the SAs of poorly supplied tumors were more tortuous and had a smaller diameter than those of well-supplied tumors, resulting in lower plasma velocities in the downstream tumor vessels. Consequently, the blood supply of A-07-GFP and D-12-GFP tumors was governed by the geometric resistance of the SAs rather than by the geometric resistance or the vessel density of the tumor microvasculature. The present study suggests that the SAs may represent an important target for physiological interventions of tumors and that it may be beneficial to focus on the tumor SAs rather than the tumor microvasculature when searching for novel therapeutic strategies for modifying tumor blood supply.

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.

The purpose of the study was to investigate vascularization, oxygenation, and the effect of sunitinib treatment in pancreatic ductal adenocarcinoma (PDAC). BxPC-3 and Capan-2 xenografts grown in dorsal window chambers were used as preclinical models of human PDAC. Tumor angiogenesis and the morphology and function of tumor vascular networks were studied by intravital microscopy, and tumor hypoxia was assessed by immunohistochemistry. The PDAC models differed in vessel distribution and oxygenation, and the differences were induced by the initial tumor angiogenesis. In both models, sunitinib treatment reduced intratumor and peritumor vessel densities by selectively removing small-diameter vessels. Sunitinb treatment resulted in a general decrease in vessel density and scattered hypoxia in BxPC-3 tumors, and depleted most vessels and induced massive hypoxia in central parts of Capan-2 tumors. The study demonstrates that PDAC xenografts can differ in vascularization, and the differences can impact oxygenation and effects of treatment. Neoadjuvant sunitinib treatment is inappropriate in combination with conventional therapy for human PDACs resembling the PDAC xenografts used here, because sunitinib-induced hypoxia can impair the effect of most conventional therapies.

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 a major cause of treatment resistance and poor survival in locally-advanced cervical carcinoma (LACC). It has been suggested that Ktrans and ve maps derived by dynamic contrast-enhanced magnetic resonance imaging can provide information on the oxygen supply and oxygen consumption of tumors, but it is not clear whether and how these maps can be combined to identify tumor hypoxia. The aim of the current study was to find the optimal strategy for calculating hypoxic fraction and predicting survival from Ktrans and ve maps in cervical carcinoma. Ktrans and ve maps of 98 tumors of four patient-derived xenograft models of cervical carcinoma as well as 80 patients with LACC were investigated. Hypoxic fraction calculated by using Ktrans maps correlated strongly (P < 0.0001) to hypoxic fraction assessed with immunohistochemistry using pimonidazole as a hypoxia marker and was associated with disease-free and overall survival in LACC patients. Maps of ve did not provide information on hypoxic fraction and patient outcome, and combinations of Ktrans and ve were not superior to Ktrans alone for calculating hypoxic fraction. These observations imply that Ktrans maps reflect oxygen supply and may be used to identify hypoxia and predict outcome in cervical carcinoma, whereas ve is a poor parameter of oxygen consumption and does not provide information on tumor oxygenation status.

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