Hemodilution in isolated tumor perfusion

Structural, functional, and molecular MR imaging of the microvasculature

Magnetic resonance imaging (MRI) is widely applied for functional imaging of the microcirculation and for functional and structural studies of the microvasculature. The interest in the capabilities of MRI in noninvasively monitoring changes in vascular structure and function expanded over the past years, with specific efforts directed toward the development of novel imaging methods for quantification of angiogenesis. Molecular imaging approaches hold promise for further expansion of the ability to characterize the microvasculature. Exciting applications for MRI are emerging in the study of the biology of microvessels and in the evaluation of potential pharmaceutical modulators of vascular function and development, and preclinical MRI tools can serve for the design of mechanism-of-action-based noninvasive clinical methods for monitoring response to therapy. The aim of this review is to provide a current snapshot of recent developments in this rapidly evolving field.

Tumor-related angiogenesis

In recent years, tumor-related angiogenesis has become an important field of research in oncology. It could be stated that growth of solid tumors is completely dependent on neovascularization to provide the tumor with all required nutrients. Special compounds (tumor angiogenesis factor[s]) are released by tumor cells into the environment to stimulate different types of normal cells to become active for the tumor. In particular, endothelial cells of neighboring capillaries are induced to react. They disintegrate their own basal lamina, detach from their neighbors, enter the extracellular matrix, and migrate toward the tumor mass. Cell divisions occur within such sprouts, thereby increasing the number of migrating endothelial cells. Strands of such cells are formed, and inter- and intracellular lumina develop. Loops of these hollow strands anastomose to form a network of new vessels which become connected with the blood circulation. The tumor mass thus becomes vascularized and can continue to grow. The prevention of neoangiogenesis has an enormous impact on cancer treatment by inhibiting the growth of the tumor. In this review, all important aspects of tumor-related angiogenesis are presented.

Effect of anemia on tumor radiosensitivity under normo and hyperbaric conditions

The effect of chronic anemia on tumor radiosensitivity in a murine tumor has been investigated. Anemia was induced by bilateral kidney irradiation given several months before tumor implantation. Anemic, anemic transfused, and normal non-anemic age-matched tumor bearing animals were irradiated with X rays (2 F/24 hr) either in air, air plus misonidazole, or under hyperbaric oxygen. The most resistant response was that of tumors grown in normal mice treated in air. Anemia produced an increase in radiosensitivity which was further enhanced by red blood cell replacement. The most sensitive overall response was seen in the anemic-transfused group treated with HBO.

Improvement of tumor spheroid oxygenation by tetrachlorodecaoxide

The benefit of Tetrachlorodecaoxide (TCDO) in improving tumor tissue oxygenation has been tested using multicellular tumor spheroids. Measurements of oxygen tension (PO2) values with O2-sensitive microelectrodes revealed a distinct enhancement of the spheroid oxygenation after both, bolus injection or continuous infusion of TCDO into the medium surrounding the spheroids. The effect of TCDO on local oxygenation appeared to be less pronounced in spheroid regions with low initial PO2 values compared to well-oxygenated areas of these cellular aggregates. By continuously infusing TCDO into the measuring system, a sustained increase of local PO2 was obtained which was proportional to the local steady state concentration of TCDO in the medium surrounding the tumor spheroids. During experiments with TCDO in vivo, this substance should, therefore, be tested for its potential of improving the oxygenation status of solid tumors, and hence, of sensitizing tumors to classical treatments, such as radiotherapy.

Tetrachlorodecaoxide improves the oxygenation status of multicellular tumor spheroids

The benefit of Tetrachlorodecaoxide (TCDO) in improving tumor tissue oxygenation has been tested using multicellular tumor spheroids. Measurements of PO2 values with O2-sensitive microelectrodes revealed a distinct enhancement of the spheroid oxygenation after bolus injection of TCDO into the medium around the spheroid (peak concentration: 0.7 mM). Small spheroids exhibited a uniform, transient rise in PO2 at different locations within the spheroid. Larger spheroids showed a smaller, yet still significant increase in PO2 in inner parts compared to the spheroid periphery. The increase in PO2 after TCDO injection appeared to be less in spheroid areas with low initial PO2 values versus well-oxygenated spheroid regions. Continuous infusion of TCDO for 15 minutes at steady state concentrations in the medium of 33 microM resulted in a substantial and persistent elevation of the local PO2 within spheroids. The PO2 returned to the control level 20 minutes after the stoppage of the infusion.