In normal tissues, the processes of growth, remodeling, and morphogenesis are tightly regulated by the stress field; conversely, stress may be generated by these processes. We demonstrate that solid stress inhibits tumor growth in vitro, regardless of host species, tissue of origin, or differentiation state. The inhibiting stress for multicellular tumor spheroid growth in agarose matrices was 45 to 120 mm Hg. This stress, which greatly exceeds blood pressure in tumor vessels, is sufficient to induce the collapse of vascular or lymphatic vessels in tumors in vivo and can explain impaired blood flow, poor lymphatic drainage, and suboptimal drug delivery previously reported in solid tumors. The stress-induced growth inhibition of plateau-phase spheroids was accompanied, at the cellular level, by decreased apoptosis with no significant changes in proliferation. A concomitant increase in the cellular packing density was observed, which may prevent cells from undergoing apoptosis via a cell-volume or cell-shape transduction mechanism. These results suggest that solid stress controls tumor growth at both the macroscopic and cellular levels, and thus influences tumor progression and delivery of therapeutic agents.

Localization of activated natural killer (A-NK) cells in the microvasculature of growing tumors is the result of recognition of the intracellular and vascular cell-adhesion molecules ICAM-1 and VCAM-1 on the tumor endothelium, mediated by lymphocyte function-associated protein LFA-1 and vascular lymphocyte function-associated protein VLA-4. In vitro and in vivo studies of A-NK cell adhesion to endothelial cells showed that vascular endothelial growth factor (VEGF) promotes adhesion, whereas basic fibroblast growth factor (bFGF) inhibits adhesion through the regulation of these molecules on tumor vasculature. Thus, some angiogenic factors may facilitate lymphocyte recognition of angiogenic vessels, whereas others may provide such vessels with a mechanism that protects them from cytotoxic lymphocytes.

These data provide the rationale for investigation of an optimized approach for RDN in future clinical studies. This may have profound implications for the clinical application of RDN, as this approach may not only achieve greater reductions in sympathetic activity but also reduce treatment effect variability.

The binding of circulating cells to the vascular wall is a central process in inflammation, metastasis, and therapeutic cell delivery. Previous in vitro studies have identified the adhesion molecules on various circulating cells and the endothelium that govern the process under static conditions. Other studies have attempted to simulate in vivo conditions by subjecting adherent cells to shear stress as they interact with the endothelial cells in vitro. These experiments are generally performed with the cells suspended in Newtonian solutions. However, in vivo conditions are more complex because of the non-Newtonian flow of blood, which is a suspension consisting of 20-40% erythrocytes by volume. The forces imparted by the erythrocytes in the flow can contribute to the process of cell adhesion. A number of experimental and theoretical studies have suggested that the rheology of blood can influence the binding of circulating leukocytes by increasing the normal and axial forces on leukocytes or the frequency of their collision with the vessel wall, but there have been no systematic investigations of these phenomena to date. The present study quantifies the contribution of red blood cells (RBCs) in cell capture and adhesion to endothelial monolayers using a combination of mathematical modeling and in vitro studies. Mathematical modeling of the flow experiments suggested a physical mechanism involving RBC-induced leukocyte dispersion and/or increased normal adhesive contact. Flow chamber studies performed with and without RBCs in the suspending medium showed increases in wall collision and binding frequencies, and a decrease in rolling velocity in the presence of erythrocytes. Increased fluid viscosity alone did not influence the binding frequency, and the differences could not be attributed to large near-wall excesses of the lymphocytes. The results indicate that RBCs aid in the transport and initial engagement of lymphocytes to the vascular wall, modifying the existing paradigm for immune cell surveillance of the vascular endothelium by adding the erythrocyte as an essential contributor to this process.

Lymphocyte adhesion and trafficking is difficult to observe in vivo over

The parallel plate flow chamber provides a controlled environment for determinations of the shear stress at which cells in suspension can bind to endothelial cell monolayers. By decreasing the flow rate of cell-containing media over the monolayer and assessing the number of cells bound at each wall shear stress, the relationship between shear force and binding efficiency can be determined. The rate of binding should depend on the delivery of cells to the surface as well as the intrinsic cell-surface interactions; thus, only if the cell flux to the surface is known can the resulting binding curves be interpreted correctly. We present the development and validation of a mathematical model based on the sedimentation rate and velocity profile in the chamber for the delivery of cells from a flowing suspension to the chamber surface. Our results show that the flux depends on the bulk cell concentration, the distance from the entrance point, and the flow rate of the cell-containing medium. The model was then used in a normalization procedure for experiments in which T cells attach to TNF-alpha-stimulated HUVEC monolayers, showing that a threshold for adhesion occurs at a shear stress of about 3 dyn/cm2.

Results from these studies suggest that the therapeutic efficacy of rIL-2 is improved in mice by prolonging its in vivo half-life through genetic fusion to albumin. Albuleukin, the fusion protein, had pronounced anti-tumor effects in Renca and hepatic melanoma tumor models without an increase in mortality. On the basis of its preclinical effects, Albuleukin was brought to the clinic to assess its therapeutic benefit in a variety of cancers.

The adhesive and hemodynamic forces that lead to lymphocyte rolling and arrest on activated endothelium and the biophysical role of various adhesion molecules and blood elements in this process are poorly understood. By quantifying their behaviour both in vivo and in vitro, we show here that erythrocytes facilitate selectin- and integrin-mediated rolling and binding of T-lymphocytes on tumor necrosis factor alpha-activated endothelium. The relative contribution of selectins and integrins to this process can be distinguished by using a simple mathematical expression of lymphocyte capture within the range of physiological shear stress. The need for selectin participation in lymphocyte capture increases with shear stress (> 1 dyn/cm2), and both beta 1 and beta 2 integrins act in synergy to produce adhesive drag on captured cells. These findings are potentially useful in developing strategies for intervening with T-cells in a variety of normal and pathological responses as well as for the delivery of genetically modified T-cells to their targets in vivo.