Angela Garofalo

Distinct Role of Fibroblast Growth Factor-2 and Vascular Endothelial Growth Factor on Tumor Growth and Angiogenesis

Tumors express more than a single angiogenic growth factor. To investigate the relative impact of fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF) on tumor growth and neovascularization, we generated tumor cell transfectants differing for VEGF and/or FGF-2 expression. Human endometrial adenocarcinoma HEC-1-B-derived Tet-FGF-2 cells that express FGF-2 under the control of the tetracycline-responsive promoter (Tet-off system) were further transfected with a VEGF(121) anti-sense (AS-VEGF) cDNA. Next, Tet-FGF-2 and AS-VEGF/Tet-FGF-2 cells were transplanted subcutaneously in nude mice that received tetracycline or not in the drinking water. Simultaneous expression of FGF-2 and VEGF in Tet-FGF-2 cells resulted in fast-growing lesions characterized by high blood vessel density, patency and permeability, and limited necrosis. Blood vessels were highly heterogeneous in size and frequently associated with pericytes. Inhibition of FGF-2 production by tetracycline caused a significant decrease in tumor burden paralleled by a decrease in blood vessel density and size. AS-VEGF expression resulted in a similar reduction in blood vessel density associated with a significant decrease in pericyte organization, vascular patency, and permeability. The consequent decrease in tumor burden was paralleled by increased tumor hypoxia and necrosis. A limited additional inhibitory effect was exerted by simultaneous down-regulation of FGF-2 and VEGF expression. These findings demonstrate that FGF-2 and VEGF stimulate vascularization synergistically but with distinctive effects on vessel functionality and tumor survival. Blockade of either one of the two growth factors results in a decrease in blood vessel density and, consequently, in tumor burden. However, inhibition of the expression of VEGF, but not of FGF-2, affects also vessel maturation and functionality, leading to tumor hypoxia and necrosis. Our experimental model represents an unique tool to investigate anti-neoplastic therapies in different angiogenic environments.

Vascular Endothelial Growth Factor Stimulates Organ-Specific Host Matrix Metalloproteinase-9 Expression and Ovarian Cancer Invasion

Vascular endothelial growth factor (VEGF) and matrix metalloproteinases (MMP) regulate each other, contributing to tumor progression. We have previously reported that MMP9 induces the release of tumor VEGF, promoting ascites formation in human ovarian carcinoma xenografts. The aim of this study was to investigate whether tumor-derived VEGF regulated the expression of gelatinase by the stroma, influencing the invasive properties of ovarian tumors. Tumor variants derived from 1A9 human ovarian carcinoma, stably expressing VEGF121 in the sense (1A9-VS-1) and antisense orientations (1A9-VAS-3), were used. In vivo, zymographic analysis of tumors from 1A9-VS-1 implanted in the peritoneal cavity of nude mice showed higher levels of gelatinases, particularly murine MMP9, indicating that VEGF stimulates host expression of the matrix-degrading enzyme. Murine MMP9 expression was also high in the ovaries of mice bearing 1A9-VS-1 tumors. The effect on host MMP9 activity was organ-specific. The levels of host pro-MMP9 in ovaries correlated with the plasma levels of tumor VEGF and with the selective invasion of the ovaries. Induction of host MMP9 expression in tumors and ovaries was independent of the site of tumor growth as it was seen in mice carrying both intraperitoneal and subcutaneous tumors. The anti-VEGF antibody bevacizumab (Avastin) inhibited MMP9 expression and tumor invasion in the ovaries of mice bearing 1A9-VS-1 tumors. These findings point to a complex cross-talk between VEGF and MMPs in the progression of ovarian tumor and suggest the possibility of using VEGF inhibitors to affect MMP-dependent tumor invasion. (Mol Cancer Res 2008;6(4):525–34)

The Vascular Targeting Property of Paclitaxel Is Enhanced by SU6668, a Receptor Tyrosine Kinase Inhibitor, Causing Apoptosis of Endothelial Cells and Inhibition of Angiogenesis

Purpose: Different antiangiogenic approaches have been proposed in cancer treatment where therapeutic efficacy has been shown with the addition of cytotoxic agents. Here, we used SU6668, a small-molecule receptor tyrosine kinase inhibitor, to investigate the combinatorial effect with paclitaxel on the cellular populations of the developing vasculature. Experimental Design: The effect of this combination was evaluated in vitro in a 72-hour proliferation assay on human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells derived from lungs, endothelial cells, aortic smooth muscle cells, and human ovarian carcinoma cells sensitive (1A9) and resistant (1A9-PTX22) to paclitaxel. Combination data were assessed by isobologram analysis. Cell survival was determined by terminal deoxyribonucleotide transferase–mediated nick-end labeling and Annexin V staining. The activity of the combination in vivo was evaluated in fibroblast growth factor-2–induced angiogenesis in Matrigel plugs s.c. implanted in mice. The 1A9-PTX22, paclitaxel-resistant xenograft model was used to evaluate tumor response. Results: Combination index values and isobologram analysis showed synergy in inhibition of proliferation of HUVEC, human microvascular endothelial cells derived from lungs, and aortic smooth muscle cells. The combination induced greater apoptosis in HUVEC than the single agents. The addition of paclitaxel to the treatment with SU6668 significantly decreased the hemoglobin content and the number of CD31-positive vessels in Matrigel plugs in vivo. The combination of the drugs was more active than either single agent against 1A9-PTX22 xenografts; the tumor growth delay was accompanied by a significant reduction of vascular density. Conclusions: These findings show that the activity of angiogenesis inhibitors on vascular cells could be potentiated when administered in combination with chemotherapeutic agents that themselves have vascular targeting properties.

Circulating plasma vascular endothelial growth factor in mice bearing human ovarian carcinoma xenograft correlates with tumor progression and response to therapy

Vascular endothelial growth factor (VEGF) performs as an angiogenic and permeability factor in ovarian cancer, and its overexpression has been associated with poor prognosis. However, models to study its role as a marker of tumor progression are lacking. We generated xenograft variants derived from the A2780 human ovarian carcinoma (1A9), stably transfected with VEGF121 in sense (1A9-VS-1) and antisense orientation (1A9-VAS-3). 1A9, 1A9-VS-1, and 1A9-VAS-3 disseminated in the peritoneal cavity of nude mice, but only 1A9-VS-1, the VEGF121-overexpressing tumor variant, produced ascites. Tumor biopsies from 1A9-VS-1 showed alterations in the vascular pattern and caused an angiogenic response in the chorioallantoic membrane assay. A significant level of soluble VEGF was detectable in the plasma of mice bearing 1A9-VS-1 even at an early stage of tumor growth. Plasma VEGF correlated positively with tumor burden in the peritoneal cavity and ascites accumulation. Cisplatin reduced the tumor burden and ascites in mice bearing 1A9-VS-1; the response was associated with a significant decrease of VEGF in plasma. This 1A9-VS-1 xenograft model reproduces the behavior of human ovarian cancer by growing in the peritoneal cavity, being highly malignant, and producing ascites. Plasma VEGF as a marker of tumor progression offers a valuable means of detecting early tumor response and following up treatments in an animal model.

Inhibition of matrix metalloproteinases by over-expression of tissue inhibitor of metalloproteinase-2 inhibits the growth of experimental hemangiomas

Inhibitors of proteases prevent tumor‐associated matrix degradation, affecting tumor growth, angiogenesis and metastasis. Our study was designed to investigate the effect of inhibition of matrix metalloproteinases (MMPs) on the growth of experimental hemangiomas, using the model of murine endothelioma eEnd.1 cells. In nude mice, these cells generate hemangiomas, consisting mostly of host‐recruited endothelial cells, whose growth requires the activity of MMPs. In vitro, eEnd.1 cells produce factors that recruit endothelial cells and stimulate them to release MMPs. Over‐expression of TIMP‐2, following retrovirus‐mediated gene transfer, decreased tumor growth in vivo. The infected clone CR1, which produces high levels of TIMP‐2 (as assessed by Northern blot, ELISA and reverse zymography), formed slow‐growing tumors that did not grow beyond 0.4 g, while clone 1H, which produces little TIMP‐2, grew not dissimilarly to mock‐infected cells and parental e.End.1 cells. Histologically, control tumors presented the features of cavernous hemangiomas, while CR1 tumors had a more solid pattern, showing foci of apoptotic cells. In vitro, TIMP‐2 over‐expression had no autocrine anti‐proliferative effect on endothelioma cells but reduced their ability to recruit endothelial cells. CR1 cells lacked the capacity of mock‐infected or parental eEnd.1 cells to stimulate endothelial cell motility and invasiveness. Antibodies against TIMP‐2 restored the ability of CR1 to induce endothelial cell invasion. We conclude that, in this model, genetic increase of TIMP‐2 inhibits tumor growth, apparently by affecting the recruitment and organization of host endothelial cells by the transformed cells.

A human acute lymphoblastic leukemia line with the t(4;11) translocation as a model of minimal residual disease in SCID mice

This study describes a new human acute lymphoblastic leukemia (ALL) cell line (ALL-PO) with the t(4;11) translocation established in SCID mice. The ALL-PO line can be maintained by serial transplant in SCID mice with stable immunophenotypic, molecular and karyotypic features. After intravenous (i.v.) injection ALL-PO spread systemically involving the hematopoietic organs and the central nervous system (CNS) of all mice. The homing and the progression of the disease are evaluated by histological analysis and reverse-transcriptase polymerase chain reaction (RT-PCR) amplification of the t(4;11) translocation in the bone marrow, spleen and CNS of SCID mice at different times after engraftment. Occult leukemia was detectable by PCR in the bone marrow of SCID mice as early as three days after the i.v. injection of leukemic cells whereas the first signs of involvement of the spleen and CNS appeared after 14 days; after 24 days all the mice were euthanized because they were moribund and the bone marrow, spleen and CNS showed ample infiltration by leukemic cells. The sensitivity to conventional chemotherapy was tested in this model. ALL-PO in SCID mice did not respond to treatment with vincristine or idarubicin but cyclophosphamide (150 mg kg(-1) i.v., single injection) significantly increased the survival of the mice. The efficacy of such a treatment was more evident when cyclophosphamide was given in the early stages of the disease (detectable only by molecular analysis) but much less effective when the drug was administered when the disease could be detected by conventional histological analysis. The biological behavior and molecular characteristics of ALL-PO make it a good model for studying novel therapeutic strategies for a better control of minimal residual disease.

Syngeneic Murine Metastasis Models

Animal studies are costly, time consuming, and subject to several restrictive regulations. However, the metastatic process is one of the research areas in which the in vivo studies remain most relevant (1). In fact, the in vitro studies are not fully predictive of the metastatic behavior of a tumor cell, probably because in vitro, it is difficult to reproduce the complexity of the metastatic process in itself and the interaction with the host.

Endothelial-Tumor Cell Interactions in Vitro and in Vivo

The development of a viable metastasis is a complex multi-step process (Poste, G. and Fidler, LL, 1980). A metastasizing cell must first detach from the primary tumor, degrade and invade the surrounding tissue before hematogenous and lymphatic dissemination can occur. Neoplastic cells are released into the circulation in large numbers, but only a few will establish a metastasis; many cells will die because they are unable to survive the hemodynamic pressure and host defense mechanisms. The arrest in the capillary bed of secondary organs is the next step, followed by extravasation into the organ parenchyma and establishment as micro-metastases. Once growth and neovascularization have occurred, metastatic lesions can produce further metastases. A major mechanism of tumor cell extravasation consists of the rapid attachment to the endothelium, followed by endothelial cell retraction, migration of tumor cells to the subendothelial matrix with the dissolution of the basement membrane (Crissman et al., 1988; Kramer and Nicolson, 1979; Lapis et al., 1988; Liotta, 1986). Disruption of the endothelial layer (Kawaguchi and Nakamura, 1986) during extravasation has also been described. The initial endothelial cell recognition precedes the extravasation of circulating tumor cells (Kawaguchi and Nakamura, 1986; Kramer and Nicolson, 1979). The location of the first capillary bed encountered only partially explains the site of metastasis formation, and tumor types that selectively disseminate to certain organs have been found in experimental and human systems (Fidler, 1990; Nicolson, 1988; Sugarbaker, 1979).