Jahangiri, M

Jahangiri, M.K. failure and in xenograft models of bevacizumab resistance. Inhibition of 1 1 in tumor cells with stable gene knockdown or treatment with OS2966, a neutralizing 1 integrin monoclonal antibody, attenuated aggressive tumor phenotypesin vitroand blocked growth of bevacizumab-resistant tumor xenograftsin vivo. Thus, 1 integrins promote resistance to antiangiogenic therapy through potentiation of multiple malignant programs facilitated by interactions with the tumor microenvironment. The elucidation of this mechanism creates an outstanding opportunity for improving patient outcomes in cancer. == Introduction == Aggressive cancers require adequate vasculature to support continued tumor progression. Tumor vasculature can be derived from preexisting host blood vessels (vessel cooption) or through new vessel growth (angiogenesis). There is likely to be a spectrum of vessel utilization along this continuum depending on various contexts (1). The recognition of the critical importance of vascularization in cancer progression has led to the hope for a new standard of care through the development of antiangiogenic agents such as bevacizumab. However, these drugs, mostly focused on the VEGF pathway, have not produced the clinical outcomes expected on the basis of the dramatic preclinical results in mice. This was most recently demonstrated in a randomized phase III trial in patients with newly diagnosed glioblastoma (2). The reasons for the disparity between preclinical and clinical results with this therapeutic modality are multiple; however, the use of animal models, which themselves rely heavily upon angiogenesis for growth, ARV-825 such as subcutaneous cell linederived xenografts, likely represents a selection bias for highly angiogenic, VEGF-dependent tumors. == Integrins and Their Role in Cellular Interaction with the Microenvironment in Inflammation and Cancer == Although angiogenesis during wound healing is tightly regulated and ARV-825 self-limiting, angiogenesis associated with chronic inflammation and ARV-825 cancer is often persistent and abnormal. However, many of the molecules that regulate angiogenesis in wound healing, such as integrin v3, also regulate pathologic angiogenesis associated with chronic inflammation and cancer. Increasing evidence points to causative links between inflammation and cancer and suggests that inflammation promotes the angiogenic switch in tumors (3). This connection between inflammation and cancer underscores the complexity of tumorigenesis and the fact that models that define cancer as driven primarily by a minor population of genetically aberrant cells violates the basic notions of systems biology, evolution, and pathophysiology. Cancer is a systems-level process defined by growth of malignant ARV-825 cells in an organ, which breaches normal tissue boundaries established by the basement membrane. In other words, cancer requires tumor cells directly interacting with cellular and structural components of the surrounding stroma. Dolberg and Bissell demonstrated the importance of this tumor microenvironment when they studied cells infected with the rous sarcoma virus (4).In vitroand in early embryonic-stage eggs, the cells grew ARV-825 aggressively. However, when transplanted into late-stage eggs, the genetically malignant program was overridden by the microenvironmental context and the cells incorporated into normal tissue. Integrins are a major mediator of these interactions between the cells comprising a tumor and their microenvironment. The cells engaging in these interactions include monocytes, in which intratumoral trafficking and subsequent promotion of angiogenesis are mediated by integrin 41 (VLA4; ref.5). Integrins also contribute to macrophage polarization, with 3 integrin promoting the M1 cytotoxic immunostimulating macrophage phenotype rather than the M2 immunosuppressive, proinvasive phenotype (6). For tumor cells, these interactions with the microenvironment are crucial to the development of malignant features, with reversion of the malignant phenotype demonstrated in breast cancer cells by inhibition of 1 1 integrin in culture andin vivo(7). These findings emphasize the importance of interactions between the cells comprising a tumor Rabbit polyclonal to COXiv with microenvironmental integrin ligands in the extracellular matrix for tumor progression. Integrins are also crucial to VEGF-dependent and VEGF-independent angiogenesis. On endothelial cells, reciprocal interactions between integrin v3 and VEGFR2 are particularly important during tumor vascularization (8). The v integrin expression on endothelial cells is also stimulated by VEGF-independent angiogenic growth factors such as bFGF, TNF-, and interleukin (IL)-8 (9). Finally, mesenchymal aspects of angiogenesis, including endothelial cell invasion and vascular redesigning, rely on 51 integrin (10). We now understand the multiple parallel signaling pathways downstream of integrin engagement that promote tumor growth, including FAK, ERK/MAP kinase, Src, Akt, and Ras (1114). These pathways are upregulated as 1 levels increase. Indeed, several studies have shown the expression of 1 1 integrin to correlate with malignant features, including metastasis (1517). Accordingly, 1 integrin signaling in tumor cells offers been shown to.