Soluble angiogenesis markers in gastric tumor patients

Emerging roles of endoglin/CD105 and angiogenic cytokines for disease development and progression in multiple myeloma patients

Angiogenesis is an essential process for the expansion of multiple myeloma (MM), in which many angiogenic factors participate. Endoglin (CD105) is a transforming growth factor-β co-receptor, being mainly expressed in angiogenic endothelial cells and has been used as a marker of tumor angiogenesis, having prognostic potential. The aim of the study was to evaluate serum levels of soluble CD105 (sCD105) in MM patients, both during diagnosis and after effective conventional chemotherapy, in the plateau phase, and to correlate them with the clinical stage of the disease, as well as with the known angiogenic factors vascular endothelial growth factor, angiogenin and interleukin-18 (IL-18). Serum levels of the aforementioned factors were measured, by enzyme-linked immunosorbent assay, in 56 newly diagnosed MM patients, in 35 of them who entered plateau phase and in 24 healthy controls. Bone marrow aspirations were also performed in all patients to determine plasma cell infiltration. All measured cytokines were higher in MM patients compared with controls and with advancing disease stage (p < 0.001 for all cases). Furthermore, the values of all factors decreased significantly in the plateau phase (p < 0.001 for all cases). Serum levels of sCD105 correlated with the other angiogenic cytokines, whereas only serum levels of angiogenin had prognostic value for the survival. In conclusion, CD105 and the angiogenic cytokines vascular endothelial growth factor, angiogenin and IL-18, seem to have emerging roles both in angiogenesis and tumor growth in MM.

ENDOGLIN/CD105 is expressed in KIT positive cells in the gut and in gastrointestinal stromal tumours

ENDOGLIN/CD105 (ENG) is a transmembrane glycoprotein and an auxiliary unit of the transforming growth factor-β (TGF-β); receptor, expressed predominantly in vascular endothelium. Noteworthy, Eng mRNA expression has been reported also in Kit⁺ interstitial cells of Cajal (ICC) in the mouse intestine. Gastrointestinal stromal tumours (GIST) are thought to derive from ICC. Here we have investigated Eng expression in the Kit^K641E mouse GIST model, in human GIST and in the Ba/F3 cell model. In wild type (WT) mouse antrum, Eng immunoreactivity (-ir) was detected in CD34⁺/CD31⁺ endothelium and in Kit⁺ ICC. In Kit^K641E mice, hyperplasia of Kit⁺ cells made Eng-ir even more evident. Quantitative PCR confirmed the increased expression of Eng transcript in Kit^K641E mice. On human GIST TMA, 26/49 cases stained positive for ENG. Strong ENG staining was associated with malignant and high-risk tumours. ENG negative cases were predominantly of the epithelioid type or harboured PDGFRA mutation. In vitro, Eng mRNA was up-regulated in Ba/F3 cell lines stably expressing various oncogenic Kit mutations (K641E, del559, del814). This effect appeared to be independent of Kit activation, as neither the stimulation of WT Kit by its ligand SCF, nor the inhibition of Kit autophosphorylation by imatinib mesylate in oncogenic mutants, altered Eng expression. Elevated Eng expression in Kit oncogenic mutants appeared rather to be indirectly mediated by DNA hypomethylation, because treatment with the demethylating agent 5-Aza/dC increased Eng mRNA expression in Kit^WT cells. ENG expression in ICC and in GIST deserves further consideration as ENG is emerging as a potential target for cancer therapy.

mTOR inhibition by everolimus counteracts VEGF induction by sunitinib and improves anti-tumor activity against gastric cancer in vivo

VEGF receptor blockage has been reported to increase serum VEGF. We hypothesized that mTOR inhibition by everolimus counteracts VEGF induction by sunitinib resulting in an improved anti-tumor activity of sunitinib. In vitro, sunitinib in combination with everolimus did not outperform the respective monotherapies. In vivo, monotherapies reduced tumor growth by 60%, whereas the combination of sunitinib and everolimus led to an almost complete tumor growth inhibition. This superior anti-tumor activity coincided with attenuation of VEGF peaks. In conclusion mTOR inhibition by everolimus counteracts VEGF induction by sunitinib and results in significant reduction of tumor burden and long-lasting tumor growth control.

Matrix metalloproteinase-14 (MT1-MMP)-mediated endoglin shedding inhibits tumor angiogenesis

Endoglin is a transforming growth factor-beta coreceptor with a crucial role in angiogenesis. A soluble form of endoglin is present in the circulation, but the role of soluble endoglin (sEndoglin) is poorly understood. In addition, the endoglin shedding mechanism is not known. Therefore, we examined the role of sEndoglin in tumor angiogenesis and the mechanism by which the extracellular domain of endoglin is released from the membrane.In colorectal cancer specimens, we observed high endothelial endoglin protein expression, accompanied with slightly lower sEndoglin levels in the circulation, compared with healthy controls. In vitro analysis using endothelial sprouting assays revealed that sEndoglin reduced spontaneous and vascular endothelial growth factor-induced endothelial sprouting. Human umbilical vascular endothelial cells were found to secrete high levels of sEndoglin. Endoglin shedding was inhibited by matrix metalloproteinase (MMP) inhibitors and MMP-14 short hairpin RNA, indicating MMP-14 as the major endoglin shedding protease. Coexpression of endoglin and membrane-bound MMP-14 led to a strong increase in sEndoglin levels. Endoglin shedding required a direct interaction between endoglin and membrane-localized MMP-14. Using cleavage site mutants, we determined that MMP-14 cleaved endoglin at a site in close proximity to the transmembrane domain. Taken together, this study shows that MMP-14 mediates endoglin shedding, which may regulate the angiogenic potential of endothelial cells in the (colorectal) tumor microenvironment.

The role of angiogenesis in solid tumours: an overview

Angiogenesis is the physiological process of the formation of new blood vessels from pre-existing ones. Multiple molecules regulate angiogenesis, such as the vascular endothelial growth factor, angiopoietins, the fibroblast growth factor, the platelet-derived growth factor and the transforming growth factor-beta. Angiogenesis plays an important role in the growth, progression and metastasis of a tumour. Inhibiting the angiogenic process or targeting existing tumour vessels can be used for treatment of tumours as an alternative or in parallel with conventional chemotherapy. Many anti-angiogenic factors are under investigation and some are already being used in clinical practice with various results.