Involvement of marrow-derived endothelial cells in vascularization.

Until recently, the adult neovasculature was thought to arise only through angiogenesis, the mechanism by which new blood vessels form from preexisting vessels through endothelial cell migration and proliferation. However, recent studies have provided evidence that postnatal neovasculature can also arise though vasculogenesis, a process by which endothelial progenitor cells are recruited and differentiate into mature endothelial cells to form new blood vessels. Evidence for the existence of endothelial progenitors has come from studies demonstrating the ability of bone marrow-derived cells to incorporate into adult vasculature. However, the exact nature of endothelial progenitor cells remains controversial. Because of the lack of definitive markers of endothelial progenitors, the in vivo contribution of progenitor cells to physiological and pathological neovascularization remains unclear. Early studies reported that endothelial progenitor cells actively integrate into the adult vasculature and are critical in the development of many types of vascular-dependent disorders such as neoplastic progression. Moreover, it has been suggested that endothelial progenitor cells can be used as a therapeutic strategy aimed at promoting vascular growth in a variety of ischemic diseases. However, increasing numbers of studies have reported no clear contribution of endothelial progenitors in physiological or pathological angiogenesis. In this chapter, we discuss the origin of the endothelial progenitor cell in the embryo and adult, and we discuss the cell's link to the primitive hematopoietic stem cell. We also review the potential significance of endothelial progenitor cells in the formation of a postnatal vascular network and discuss the factors that may account for the current lack of consensus of the scientific community on this important issue.

Growth of V79 cells as xenograft tumors promotes multicellular resistance but does not increase spontaneous or radiation-induced mutant frequency.

A Chinese hamster V79 xenograft model was developed to determine whether cells subjected to a hypoxic tumor microenvironment would be more likely to undergo mutation at the HPRT locus. V79-171b cells stably transfected with VEGF and EGFP were grown subcutaneously in immunodeficient NOD/ SCID mice. V79-VE tumors were characterized for host cell infiltration, doubling time, hypoxic fraction, vascular perfusion, and response to ionizing radiation. When irradiated in vitro, the mutant frequency for a given surviving fraction did not differ for cells grown in vivo or in vitro. Similar results were obtained using HCT116 human colorectal carcinoma cells grown as xenografts. However, V79-VE cells grown as xenografts were significantly more resistant to killing than monolayers. The background mutant frequency and the radiation-induced mutant frequency did not differ for tumor cells close to or distant from blood vessels. Similarly, tumor cells from well-perfused regions showed the same rate of strand break rejoining and the same rate of loss of phosphorylated histone H2AX as cells sorted from poorly perfused regions. Therefore, deleterious effects of the tumor microenvironment on DNA repair efficiency or mutation induction could not be demonstrated in these tumors. Rather, development of multicellular resistance in V79-VE tumors acted to reduce mutant frequency for a given dose of radiation.

Signaling pathways induced by vascular endothelial growth factor (review).

Vasculogenesis and angiogenesis are the mechanisms responsible for the development of the blood vessels. Angiogenesis refers to the formation of capillaries from pre-existing vessels in the embryo and adult organism, while vasculogenesis is the development of new blood vessels from the differentiation of endothelial precursors (angioblasts) in situ. Vascular endothelial growth factor (VEGF) family members are major mediators of vasculogenesis and angiogenesis both during development and in pathological conditions. VEGF has a variety of effects on vascular endothelium, including the ability to promote endothelial cell viability, mitogenesis, chemotaxis, and vascular permeability. It mediates its activity mainly via two tyrosine kinase receptors, VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR), although other receptors, such as neuropilin-1 and -2, can also bind VEGF. Another tyrosine kinase receptor, VEGFR-3 (flt-4) binds VEGF-C and VEGF-D and is more important in the development of lymphatic vessels. While the functional effects of VEGF on endothelial cells has been well studied, not as much is known about VEGF signaling. This review summarizes the different pathways known to be involved in VEGF signal transduction and the biological responses triggered by the VEGF signaling cascade.

Modulation of adriamycin cytotoxicity and transport in drug-sensitive and multidrug-resistant Chinese hamster ovary cells by hyperthermia and cyclosporin A.

PURPOSE: Chemosensitizers such as cyclosporin A can increase intracellular accumulation of chemotherapeutic agents such as Adriamycin in certain multidrug-resistant (MDR) cell lines with overexpression of P-glycoprotein. It is likely that, when combined with cyclosporin A, hyperthermia could increase membrane permeability to Adriamycin and enhance its cytotoxic effects. The ability of both hyperthermia and cyclosporin A to modulate the cytotoxicity, transport and subcellular distribution pattern of Adriamycin was studied in a pleiotropic MDR Chinese hamster ovary cell line (CH(R)C5) and in the drug-sensitive parent line (AuxB1). METHODS: Adriamycin cytotoxicity was evaluated by clonogenic cell survival, drug transport using [(14)C]-labeled Adriamycin and intracellular drug distribution by fluorescence microscopy. RESULTS: Adriamycin cytotoxicity was increased in both drug-sensitive and MDR cells by cyclosporin A (5 microM) alone, and by hyperthermia alone (41-43 degrees C) only in sensitive cells. However, when cyclosporin A and 42 degrees C hyperthermia were used in combination, a large increase in drug cytotoxicity occurred in both cell lines. This effect increased with time and was temperature-dependent. The increase in Adriamycin cytotoxicity caused by cyclosporin A and hyperthermia was accompanied by alterations in membrane permeability to the drug. Cyclosporin A increased [(14)C]Adriamycin uptake, while drug efflux decreased, for both AuxB1 and CH(R)C5 cells and nuclei. For AuxB1 cells only, drug distribution studies showed that cyclosporin A promoted an increase in both nuclear and cytoplasmic drug accumulation. Hyperthermia, combined with cyclosporin A, increased [(14)C]Adriamycin uptake. This effect was seen as an increase in intensity of nuclear and cytosolic drug fluorescence in both cell lines. Cyclosporin A alone diminished drug efflux and caused Adriamycin to remain firmly bound in the nucleus of AuxB1 cells, while it remained primarily in the cytoplasm of CH(R)C5 cells. CONCLUSIONS: Hyperthermia alone had little effect on Adriamycin cytotoxicity and transport in MDR cells, in contrast to drug-sensitive cells. This suggests that P-glycoprotein is fully functional in these MDR cells. Our findings suggest that cyclosporin A and hyperthermia could be beneficial by increasing intracellular drug accumulation, thus improving the effectiveness of Adriamycin against both drug-sensitive and MDR cells within a localized target region.

Melphalan resistance and photoaffinity labelling of P-glycoprotein in multidrug-resistant Chinese hamster ovary cells: reversal of resistance by cyclosporin A and hyperthermia.

The multidrug resistance phenotype is often associated with overexpression of P-glycoprotein, an energy-dependent efflux pump responsible for decreased intracellular accumulation of chemotherapeutic agents. The role of P-glycoprotein in the mechanism of cross-resistance to melphalan in multidrug-resistant Chinese hamster ovary cells (CH(R)C5) was investigated by photoaffinity labelling of P-glycoprotein using [3H]azidopine. We investigated whether the chemosensitiser cyclosporin A and hyperthermia, either used alone or combined, could reverse melphalan resistance and alter transport processes for [14C]melphalan in CH(R)C5 cells. Melphalan inhibited azidopine photolabelling of P-glycoprotein, implicating drug efflux mediated by P-glycoprotein in the mechanism of melphalan resistance in CH(R)C5 cells. Azidopine photolabelling also was inhibited by the chemosensitiser cyclosporin A, which binds to P-glycoprotein. Cyclosporin A alone reversed melphalan resistance in CH(R)C5 cells, but had no effect in drug-sensitive AuxB1 cells. Hyperthermia (40-45 degrees) alone increased melphalan cytotoxicity in both cell lines. When hyperthermia was combined with cyclosporin A, a large increase in melphalan cytotoxicity occurred, but only in CH(R)C5 cells. This effect increased with temperature and exposure time. Sensitisation to melphalan cytotoxicity by heat and cyclosporin A in CH(R)C5 cells appeared to be explained by altered drug transport processes. Lower accumulation of melphalan occurred in CH(R)C5 cells than in drug-sensitive cells. At 37 degrees, cyclosporin A increased drug accumulation in CH(R)C5 cells, but not in AuxB1 cells, by slowing drug efflux from cells. Heat alone increased both melphalan uptake and drug efflux for both cell lines. Our findings suggest that the combination of cyclosporin A and hyperthermia could be very useful in overcoming melphalan resistance by increasing intracellular drug accumulation in multidrug-resistant cells.

Hyperthermia, cyclosporine A and melphalan cytotoxicity and transport in multidrug resistant cells.

The ability of hyperthermia and cyclosporine A to modulate melphalan cytotoxicity and transport processes was investigated in a pleiotropic MDR Chinese hamster ovary cell line (CH(R)C5) and in the drug-sensitive parent line (AuxB1). Cyclosporine A increased cytotoxicity of melphalan in MDR cells, but not in drug-sensitive cells. In MDR cells, hyperthermia caused marked enhancement of melphalan cytotoxicity when cyclosporine A was present. The increased melphalan cytotoxicity in MDR cells was accompanied by changes in membrane permeability to the drug. Cyclosporine A caused an increase in melphalan uptake in MDR cells and a decrease in melphalan efflux out of cells, leading to an overall increase in intracellular drug accumulation. Drug transport processes were not affected by cyclosporine A in drug-sensitive cells.

Factor structure of classroom behavior problems for mainstreamed and regular students.

The purpose of this study was twofold: (1) to examine the factor structure of behavior exhibited in the regular classroom in order to provide a conceptual framework for classifying problem behavior relevant to the classroom setting, and (2) to determine the extent to which the factors generated from ratings of regular classroom children are similar to those generated from ratings of mainstreamed special education children. Thirty-five elementary-school teachers completed behavior ratings for all of their 876 students utilizing a group-administered adapted version of the Devereux Elementary School Behavior Rating Scale. The factor analysis yielded five factors defined as Conduct Problem, Personality Problem, Adaptive Classroom Behavior, Inadequacy-Immaturity, and Achievement Anxiety. Coefficients of factorial congruence confirmed the similarity between the pattern generated from ratings of regular students and that of mainstreamed students.

Behavior rating scales: need for refining normative data.

The purpose of this study was to generate normative data by grade and sex to accompany behavior rating scales. Teachers rate 483 boys and girls in Grades 1 through 4. The findings suggest rating scales be re-examined since norms by grade level and sex may be desirable attributes.