Tumor angiogenesis and interstitial hypertension

Abstract

Due to the high permeability of tumor vessels to fluids and plasma proteins, the microvascular pressure (MVP) is the principal driving force for interstitial hypertension in solid tumors; as a result, hydrostatic pressures between the microvascular and interstitial space are close to equilibrium. Based on these observations, we hypothesized that the tumor interstitial fluid pressure (IFP) should increase following the onset of angiogenesis. To this end, the relationship between IFP and tumor neovascularization was determined in the human colon adenocarcinoma (LS174T) and the murine carcinoma (MCaIV) implanted in a transparent dorsal skin fold chamber in severe combined immunodeficient mice. Three stages in the development of the tumor neovasculature were characterized by intravital microscopy. Stage I tumors were avascular, stage II was characterized by vascular sprouts and loops, and in stage III, the tumor vasculature was completely developed and blood flow was obvious. The IFP was measured with micropipettes and a servo-null system. For both tumor types, the IFP in stage I tumors was close to 0 mm Hg, and IFP increased significantly from one stage to the next. To further confirm that interstitial hypertension was associated with the development of the tumor vasculature, IFP was measured in LS174T spheroids. The mean pressure in spheroids was 0.2 +/- 0.3 mm Hg. In stage III tumors, the IFP was compared to the MVP. In MCaIV, the MVP was comparable to the IFP; however, in LS174T the MVP was significantly higher than the IFP. In conclusion, the results demonstrate that avascular tumors have atmospheric pressures and that tumor interstitial hypertension is associated with the development of the neovasculature.