Effect of local anti-VEGF antibody treatment on tumor microvessel permeability.

Recent studies have shown that systemic injection of anti-VEGF antibody into tumor-bearing mice results in decreases in tumor vascular permeability, vessel diameters, and tumor regression. Using a similar animal model, we have applied anti-VEGF antibody directly to the tumor tissue growing in transparent window chambers in SCID mice. Similar to the results obtained with systemic injection, vascular permeability was greatly reduced, but the response was reached at much lower concentrations with local application. Implications of these findings on local control of tumors are discussed.

Angiogenic potential of malignant and non-malignant human breast tissues in an in vivo angiogenesis model.

Tumors need to acquire an angiogenic phenotype for outgrowth and metastasis formation. Limited information on the angiogenic potential of specific tissues, especially human breast tissues is available. Here we describe an in vivo model, using the dorsal skin fold chamber in immunodeficient nude mice, where various tissues of human breast origin were xenografted and evaluated for their angiogenesis-inducing potential. We found that angiogenesis was abundantly induced by all breast carcinoma tissue samples. Similar angiogenesis was induced by tissue samples from breasts with hyperplasia and apocrine metaplasia. Histologically normal tissues adjacent to the tumor induced angiogenesis in 66% of the cases. Angiogenesis was not induced by control tissues from normal healthy breasts, obtained after cosmetic breast reduction. Angiogenesis induction parallelled VEGF production by the tumor cells. The tissue induced neovascularization, found both around and in the human tissue, was functional since a tail vein injection of albumin-FITC revealed positive tumor microcirculation within 5 min, while the tumor tissue still consisted of vital human epithelial cells after 14 days.

Solid stress inhibits the growth of multicellular tumor spheroids.

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.

Perfusion of single tumor microvessels: application to vascular permeability measurement.

OBJECTIVE: To develop a new method for determining the relative importance of convection versus diffusion in macromolecular transport across tumor microvessel walls. METHODS: The human colon adenocarcinoma LS174T was transplanted in the dorsal skinfold chamber in a severe combined immunodeficient (SCID) mouse. The vasculature at the tumor surface was exposed by carefully removing the glass window of the chamber. A tumor microvessel was randomly selected, which was approximately 20-40 microns in diameter, embedded in the connective tissue 10-12 microns below the surface of the tumor. The vessel was cannulated with a micropipette and perfused with fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) at different perfusion pressures. The fluorescence intensity was recorded on videotapes via a video system attached to the fluorescence microscope for offline analysis. The apparent vascular permeability was determined based on the time-dependence of fluorescence intensity and the vessel diameter. RESULTS: The apparent vascular permeability of single vessels to FITC-labeled BSA was quantified at perfusion pressures of 20-45 cmH2O. The pressure dependence of vascular permeability in LS174T tumors was heterogeneous. On average, there was no correlation between the apparent vascular permeability and the perfusion pressure in the range of 20-35 cmH2O (p = 0.73), even though the apparent permeability increased significantly when the pressure was increased from 20 to 45 cmH2O (p = 0.008). CONCLUSIONS: These results indicate that convection in the transvascular transport of albumin is not significant in non-peripheral regions of solid tumors in which the pressure difference across the vessel wall is small or even negligible. In addition to the permeability studies, this preparation can be used to study cell-cell interactions in single tumor vessels under defined flow conditions.

Tumor cell spheroids induce a mitogenic response in endothelial cells.

Conditioned media from spheroids of human colorectal tumor cell lines HT29, SW620, SW480 and CaCo-2 were tested for their mitogenic activity on human umbilical vein endothelial (HUVE) and bovine capillary endothelial (BCE) cells. All spheroid-conditioned media were capable of increasing the labeling indices in both endothelial cell populations, with the mitogenic activity decreasing in the following order: SW620, HT29/SW480 and CaCo-2. The endothelial cell mitogenic activity of the spheroids was not dependent on the presence of necrosis nor on their in vivo cytokinetic characteristics. We conclude that tumor spheroids release mitogenic activity for endothelial cells, but this stimulation depends on the age of the tumor spheroid as well as on the type of tumor used.