Sarah Short

Epoxyeicosanoids stimulate multiorgan metastasis and tumor dormancy escape in mice

Epoxyeicosatrienoic acids (EETs) are small molecules produced by cytochrome P450 epoxygenases. They are lipid mediators that act as autocrine or paracrine factors to regulate inflammation and vascular tone. As a result, drugs that raise EET levels are in clinical trials for the treatment of hypertension and many other diseases. However, despite their pleiotropic effects on cells, little is known about the role of these epoxyeicosanoids in cancer. Here, using genetic and pharmacological manipulation of endogenous EET levels, we demonstrate that EETs are critical for primary tumor growth and metastasis in a variety of mouse models of cancer. Remarkably, we found that EETs stimulated extensive multiorgan metastasis and escape from tumor dormancy in several tumor models. This systemic metastasis was not caused by excessive primary tumor growth but depended on endothelium-derived EETs at the site of metastasis. Administration of synthetic EETs recapitulated these results, while EET antagonists suppressed tumor growth and metastasis, demonstrating in vivo that pharmacological modulation of EETs can affect cancer growth. Furthermore, inhibitors of soluble epoxide hydrolase (sEH), the enzyme that metabolizes EETs, elevated endogenous EET levels and promoted primary tumor growth and metastasis. Thus, our data indicate a central role for EETs in tumorigenesis, offering a mechanistic link between lipid signaling and cancer and emphasizing the critical importance of considering possible effects of EET-modulating drugs on cancer.

Inhibition of endothelial cell migration by thrombospondin-1 type-1 repeats is mediated by β1 integrins

The anti-angiogenic effect of thrombospondin-1 has been shown to be mediated through binding of the type-1 repeat (TSR) domain to the CD36 transmembrane receptor. We now report that the TSR domain can inhibit VEGF-induced migration in human umbilical vein endothelial cells (HUVEC), cells that lack CD36. Moreover, we identified β1 integrins as a critical receptor in TSR-mediated inhibition of migration in HUVEC. Using pharmacological inhibitors of downstream VEGF receptor effectors, we found that phosphoinositide 3-kinase (PI3k) was essential for TSR-mediated inhibition of HUVEC migration, but that neither PLCγ nor Akt was necessary for this response. Furthermore, β1 integrins were critical for TSR-mediated inhibition of microvascular endothelial cells, cells that express CD36. Together, our results indicate that β1 integrins mediate the anti-migratory effects of TSR through a PI3k-dependent mechanism.

Platelet-derived thrombospondin-1 is a critical negative regulator and potential biomarker of angiogenesis

The sequential events leading to tumor progression include a switch to the angiogenic phenotype, dependent on a shift in the balance between positive and negative angiogenic regulators produced by tumor and stromal cells. Although the biologic properties of many angiogenesis regulatory proteins have been studied in detail, the mechanisms of their transport and delivery in vivo during pathologic angiogenesis are not well understood. Here, we demonstrate that expression of one of the most potent angiogenesis inhibitors, thrombospondin-1, is up-regulated in the platelets of tumor-bearing mice. We establish that this up-regulation is a consequence of both increased levels of thrombospondin-1 mRNA in megakaryocytes, as well as increased numbers of megakaryocytes in the bone marrow of tumor-bearing mice. Through the use of mouse tumor models and bone marrow transplantations, we show that platelet-derived thrombospondin-1 is a critical negative regulator during the early stages of tumor angiogenesis. Collectively, our data suggest that the production and delivery of the endogenous angiogenesis inhibitor thrombospondin-1 by platelets may be a critical host response to suppress tumor growth through inhibiting tumor angiogenesis. Further, this work implicates the use of thrombospondin-1 levels in platelets as an indicator of tumor growth and regression.

Suppression of heat shock protein 27 induces long-term dormancy in human breast cancer

The mechanisms underlying tumor dormancy have been elusive and not well characterized. We recently published an experimental model for the study of human tumor dormancy and the role of angiogenesis, and reported that the angiogenic switch was preceded by a local increase in VEGF-A and basic fibroblast growth factor. In this breast cancer xenograft model (MDA-MB-436 cells), analysis of differentially expressed genes revealed that heat shock protein 27 (HSP27) was significantly up-regulated in angiogenic cells compared with nonangiogenic cells. The effect of HSP27 down-regulation was further evaluated in cell lines, mouse models, and clinical datasets of human patients with breast cancer and melanoma. Stable down-regulation of HSP27 in angiogenic tumor cells was followed by long-term tumor dormancy in vivo. Strikingly, only 4 of 30 HSP27 knockdown xenograft tumors initiated rapid growth after day 70, in correlation with a regain of HSP27 protein expression. Significantly, no tumors escaped from dormancy without HSP27 expression. Down-regulation of HSP27 was associated with reduced endothelial cell proliferation and decreased secretion of VEGF-A, VEGF-C, and basic fibroblast growth factor. Conversely, overexpression of HSP27 in nonangiogenic cells resulted in expansive tumor growth in vivo. By clinical validation, strong HSP27 protein expression was associated with markers of aggressive tumors and decreased survival in patients with breast cancer and melanoma. An HSP27-associated gene expression signature was related to molecular subgroups and survival in breast cancer. Our findings suggest a role for HSP27 in the balance between tumor dormancy and tumor progression, mediated by tumor–vascular interactions. Targeting HSP27 might offer a useful strategy in cancer treatment.

Anti-tumor effect of CT-322 as an Adnectin inhibitor of vascular endothelial growth factor receptor-2

CT-322 is a new anti-angiogenic therapeutic agent based on an engineered variant of the tenth type III domain of human fibronectin, i.e., an AdnectinTM, designed to inhibit vascular endothelial growth factor receptor (VEGFR)-2. This PEGylated Adnectin was developed using an mRNA display technology. CT-322 bound human VEGFR-2 with high affinity (KD, 11 nM), but did not bind VEGFR-1 or VEGFR-3 at concentrations up to 100 nM, as determined by surface plasmon resonance studies. Western blot analysis showed that CT-322 blocked VEGF-induced phosphorylation of VEGFR-2 and mitogen-activated protein kinase in human umbilical vascular endothelial cells. CT-322 significantly inhibited the growth of human tumor xenograft models of colon carcinoma and glioblastoma at doses of 15-60 mg/kg administered 3 times/week. Anti-tumor effects of CT-322 were comparable to those of sorafenib or sunitinib, which inhibit multiple kinases, in a colon carcinoma xenograft model, although CT-322 caused less overt adverse effects than the kinase inhibitors. CT-322 also enhanced the anti-tumor activity of the chemotherapeutic agent temsirolimus in the colon carcinoma model. The high affinity and specificity of CT-322 binding to VEGFR-2 and its anti-tumor activities establish CT-322 as a promising anti-angiogenic therapeutic agent. Our results further suggest that Adnectins are an important new class of targeted biologics that can be developed as potential treatments for a wide variety of diseases.

Mutant Anthrax Toxin B Moiety (Protective Antigen) Inhibits Angiogenesis and Tumor Growth

Bacillus anthracis protective antigen (PA), the B subunit of the binary anthrax toxin, binds to the cellular receptors capillary morphogenesis gene 2 protein and tumor endothelial marker 8 with high affinity. Both receptors are expressed on endothelial cells during angiogenesis. We sought to determine whether one could inhibit angiogenesis by interfering with the binding of these receptors to their endogenous ligands. Here, we show that wild-type PA inhibits both vascular endothelial growth factor-induced and basic fibroblast growth factor-induced angiogenesis at moderate but statistically significant levels. Structure-activity studies identified a PA mutant that exhibited markedly enhanced inhibition of angiogenesis and also inhibited tumor growth in vivo. This mutant, PASSSR, is unable to undergo normal cellular processing and, thus, remains bound to the surface receptor. Further mutation of PASSSR so that it does not bind to these cell surface receptors abolished its ability to inhibit angiogenesis. We conclude that high-affinity anthrax toxin receptor (ATR) ligands, such as PA and PASSSR, are angiogenesis inhibitors and that ATRs are useful targets for antiangiogenic therapy. These results also suggest that endothelial cell-binding proteins from additional pathogens may inhibit angiogenesis and raise the question of the role of such inhibition in pathogenesis.

Inhibition of neuroblastoma cell proliferation with omega-3 fatty acids and treatment of a murine model of human neuroblastoma using a diet enriched with omega-3 fatty acids in combination with sunitinib

Introduction:We investigated the use of dietary omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) in the treatment of neuroblastoma both as a sole agent and in combination with sunitinib, a broad-spectrum tyrosine kinase receptor inhibitor.Results:Substitution of all dietary fat with menhaden oil (ω-3 PUFA rich) resulted in a 40–70% inhibition of tumor growth and a statistically significant difference in the levels of several PUFAs (18:2 ω-6, 20:4 ω-6, 22:4 ω-6, 20:5 ω-3) as compared with a control diet. Furthermore, tumors from animals on the ω-3 fatty acid (FA)-enriched diet had an elevated triene/tetraene ratio suggestive of a change in local eicosanoid metabolism in these tissues similar to that seen with essential fatty acid deficiency. The ω-3 FA-enriched diet also decreased tumor-associated inflammatory cells and induced mitochondrial changes suggestive of mitochondrial damage. Combination treatment with sunitinib resulted in further reduction in tumor proliferation and microvessel density.Discussion:These findings suggest a potential role for ω-3 PUFAs in the combination treatment of neuroblastoma.Methods:We used a murine model of orthotopic and subcutaneous human neuroblastoma and diets that differ in the FA content to define the optimal dietary ω-3/omega-6 (ω-6) FA ratio required for the inhibition of these tumors.