The role of angiogenesis, vascular maturation, regression and stroma infiltration in dormancy and growth of implanted MLS ovarian carcinoma spheroids

Abstract

MLS ovarian epithelial carcinoma multicellular spheroids xenografted subcutaneously in CD-1 nude mice displayed growth delay, or dormancy, of up to 52 days. In the study reported here, implanted MLS spheroids were used for testing the role of angiogenesis and vascular maturation in triggering the initiation of tumor progression. The kinetics and impact of neovascular maturation and functionality, in dormancy, and growth of MLS spheroid xenografts were studied noninvasively by BOLD contrast MRI. MR data were supported by histologic staining for biotinylated albumin as a blood pool marker and alpha-smooth muscle actin (alpha-SMA) as marker for perivascular mural cells. Although the tumor periphery showed higher levels of total and mature vasculature than normal skin, the fraction of mature out of the total vessels as detected by MRI vascular maturation index (VMI MRI ) was significantly lower in the tumor both before and after tumor exit from dormancy. The neovasculature induced by the implanted spheroid was unstable and showed cycles of vessel growth and regression. Surprisingly, this instability was not restricted to the immature vessels, but rather included also regression of mature vessels. During dormancy, neovasculature was predominantly peripheral with no infiltration into the implanted spheroid. Infiltration of alpha-SMA positive stroma cells into the spheroid was associated with functional vascularization and tumor growth. Thus, stroma infiltration and vascular maturation are an important checkpoint linking the angiogenic switch with initiation of tumor progression.

Labeling fibroblasts with biotin‐BSA‐GdDTPA‐FAM for tracking of tumor‐associated stroma by fluorescence and MR imaging

“…It is well known, however, that both endothelial cells and fibroblasts are located in close association in many epithelial tumors, i.e., in those expressing a desmoplastic response. We recently reported the critical role of myofibroblasts in the initiation of growth of dormant MLS ovarian epithelial tumor xenografts (14), and in the stabilization and maturation of the tumor vasculature (22). These tumor xenografts are not only massively infiltrated by ␣SMA-positive stromal cells (myofibroblasts/pericytes), they are also characterized by a moderate and nonleaky vasculature.…”

“…Additionally, in a xenograft model of human fibroblasts and human ovarian cancer cells, after intravenous administration of biotin-BSA-GdDTPA, immunohistochemical staining detected the contrast material intracellularly in myofibroblasts. This model is of particular interest since in a previous study we reported that the exit of implanted human MLS ovarian carcinoma spheroids from dormancy correlated with the infiltration of ␣-SMA-positive (myo)fibroblasts into the tumor mass, suggesting a critical role for these cells in the initiation of tumor progression (14). Moreover, we recently showed that these stroma myofibroblasts contributed to vascular stabilization and maturation in ovarian tumors by the expression of angiopoietin-1 (22).…”

“…Recent studies have suggested that fibroblastic tumor stroma, particularly myofibroblasts, essentially contribute to both the angiogenic process and cancer progression (13,14). It was suggested that fibroblasts at the tumor-host interface differentiate into myofibroblasts and then into pericyte-like cells, which are proposed to guide endothelial sprouts (15).…”

Macrophages promote angiogenesis in human breast tumour spheroids in vivo

“…Implantation of the chamber with human breast tumour cells or spheroids permits accurate, serial, noninvasive monitoring of tumour growth, and angiogenesis using in vivo micro-scopy, facilitating accurate spatial and temporal quantification (Borgstrom et al, 1998;Gilead et al, 2004). Using this model, the requirement of VEGF for tumour angiogenesis and maintenance of vessel integrity has been demonstrated (Borgstrom et al, 1996;Lichtenbeld et al, 1998).…”

Magnetic resonance imaging as a biomarker in renal cell carcinoma

“…[80][81][82] BOLD studies in humans have focused primarily on gliomas, suggesting utility in monitoring vascular reactivity. 83,84 The mechanistic elements of RCC, its hypervascular nature, and its oxygen deregulation provide a rationale for the pursuit of BOLD imaging.…”