**Figure 3.**

*Malignant ascites has been shown to affect integrin expression and localization. Specifically, cellular and acellular factors in malignant ascites can promote increased integrin expression, leading to the upregulation of integrin-related survival pathways. Factors within malignant ascites can also promote integrin delocalization, which leads to cell clustering.*

*Integrins in Ovarian Cancer: Survival Pathways, Malignant Ascites and Targeted Photochemistry DOI: http://dx.doi.org/10.5772/intechopen.106725*

include integrins, which play a role in the formation of a tumor-promoting microenvironment. Although these adhesion-regulating factors are normally involved in cell differentiation, growth, and migration [11, 97, 98], aberrant integrin signaling frequently observed in cancers can influence cell invasiveness, drug resistance, and metastasis [14].

There are a multitude of integrins that are known to play a role in ovarian cancer. In the normal tumor microenvironment, activation of apoptosis by death receptors plays a key role in immune surveillance against tumor cells [99]. A study performed by Lane *et al.* demonstrated that malignant ascites protects against tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis through activation of the PI3K/Akt pathway in ovarian cancer cells. Normally, OVCAR3 and Caov-3 cell lines are sensitive to TRAIL-induced apoptosis and when exposed to TRAIL in the absence of ascites, only about 10% of cells remained viable. In contrast, Caov-3 cells exposed to TRAIL and patient-derived malignant ascites displayed a significant decrease in TRAIL-induced cell death. Similarly, OVCAR3 cells exposed to TRAIL and patient-derived malignant ascites demonstrated significantly increased cell viability compared to those treated only with TRAIL. A follow-up study performed by Lane *et al.* showed that ascites protects against TRAIL-induced apoptosis through αvβ5 integrin-mediated FAK and Akt activation [100]. Tumor cells in ascites from ovarian cancer often have higher expression of Akt compared to cells found in benign effusions, which suggests the role of ascites in the activation of the Akt pathway [101]. Akt activation may also occur due to the interactions between ECM proteins and cell surface integrins, integrin-mediated recruitment of FAK, or αvβ3 and αvβ<sup>5</sup> integrin ligation [102–104]. In the study described above by Lane *et al*., the use of αvβ3 and αvβ5 integrin-blocking antibodies on Caov-3 cells in the presence of ascites demonstrated a 50% reduction in the protective effect of ascites on TRAIL-induced apoptosis [100]. The addition of αvβ5 integrin-blocking antibody also prevented FAK phosphorylation, demonstrating that ascites-induced FAK phosphorylation is αvβ5-dependent and that survival factors present in malignant ascites can promote resistance to TRAIL-induced apoptosis through Akt activation in an αvβ5-dependent manner [99, 100].

Factors within ascites that engage αvβ5 integrins may include vitronectin and periostin, which are ECM proteins secreted by malignant ovarian epithelial cells [100, 103, 105]. Adhesion of ovarian cancer cells to the ECM is controlled by integrindependent and independent mechanisms, therefore changes in the ECM composition as well as integrin expression allow for the alteration of cancer cell adhesion and motility [26, 105–108]. Periostin is overexpressed in, and secreted by, epithelial ovarian cancer cells, and as a result, periostin accumulates in the malignant ascites [105, 109]. In a study by Gillan *et al.*, ~95% of ascites samples from ovarian cancer patients contained periostin [105]. Exploring the role of periostin in cell adhesion, Gillan *et al.* found that periostin-coated surfaces supported HOSE and SKOV3 cell attachment in a concentration-dependent manner. SKOV3 cell adhesion was enhanced after adding manganese, which increases the ligand-binding affinity of integrin αvβ3; however, adhesion was inhibited by anti-αvβ3 and anti-αvβ5 antibodies. When examining the role of periostin on ovarian cancer cell motility, Gillan *et al.* further showed that ovarian cancer cells grown on periostin formed less stress fibers and focal adhesion plaques than those grown on vitronectin or fibronectin. Based on these findings, Gillan *et al.* concluded that αvβ3 and αvβ5 integrin play important roles in periostininduced effects on cell adhesion and motility, which could promote intraperitoneal dissemination of ovarian cancer.

Similar to periostin, vitronectin and fibronectin are also important in shaping the tumor-promoting microenvironment of malignant ascites. Specifically, fibronectin has been shown to promote cell migration and spheroid formation, anchorage, and disaggregation in ovarian cancer [25, 27, 110, 111], while vitronectin has been found to play key roles in cancer cell adhesion, proliferation, and migration [112–115]. Fibronectin and vitronectin can also enhance metastasis when they are cleaved into smaller fragments by matrix metalloproteinase-2 (MMP-2) [111, 116]. A study by Carduner *et al*. found that, in 14 patient-derived ascites samples, both vitronectin and fibronectin were detected. When cells were grown on patient-derived ascites, their morphology changed to clusters of rounded cells varying in thickness [111]. Purified vitronectin and fibronectin from patient-derived ascites also supported the adhesion and migration of ovarian cancer cells alongside altered integrin organization. Vitronectin-exposed IGROV1, OVCAR3, and SKOV3 cells displayed altered localization and/or organization patterns of αv and β1 integrins. In fibronectin-exposed cells, co-localization between β1 integrin and fibronectin fibrils was observed, suggesting a role for integrins in fibrillation.

Since EMT behavior can also be modulated by ascites in an integrin-dependent manner, Carduner *et al.* examined the EMT status of cells based on cell-cell contact, modification of cell-matrix adhesion, elongation of cell shape, and cell migration [117]. After treatment with ascites, cell shape was altered in IGROV1, SKOV3, and OVCAR3 cells, as cells become clustered, spindle-like, and heterogenous, respectively. Ascites also induced changes in localization and the expression of epithelial and mesenchymal markers that differed by cell line, but were nonetheless associated with an ascites-associated shift towards an intermediate epithelial or mesenchymal phenotype. In IGROV1 and SKOV3 cells, Carduner *et al.* reported that αv integrins were involved in the observed shift towards a mesenchymal phenotype, since ascites induced the partial delocalization of αv integrins to favor the formation of IGROV1 aggregates and SKOV3 migration. Overall, this study found that exposure to ascites stimulates integrin trafficking and is associated with a shift towards a mesenchymal phenotype in ovarian cancer cells.

Additional studies have implicated αv integrins in ovarian cancer progression by promoting an ascites-associated invasive and mesenchymal phenotype. For example, αvβ6 integrin has been correlated with increased urokinase plasminogen (uPA) expression, MMP-2 and MMP-9 secretion, and protease-dependent matrix degradation [23, 32]. Increased uPA and MMP-9 expression are associated with a poor prognosis because they contribute to ovarian cancer progression and enhanced metastatic potential [23, 118, 119]. uPA and its receptor (uPAR) are often found at high concentrations in both the tumors and ascitic fluid of advanced-stage ovarian cancer patients [120, 121]. It has been shown that increased uPAR expression in cancer cells is maintained by ERK MAP kinase pathway activity, which is associated with tumor cell growth and proliferation [122–125]. The ERK MAP kinase pathway, a downstream target of the Ras pathway, is often activated upon integrin binding and activation [122, 123]. Since integrins, uPA, and MMPs are all present in malignant ascites, and are associated with a poor prognosis, Ahmed *et al*. examined the role of ascites in regulating integrin-mediated changes in ovarian cancer growth and function [122]. Results showed that, in the presence of ascites, α6 integrin expression was enhanced in OVHS1, PEO.36, OVCA 433 and HEY cell lines while uPAR expression was only enhanced in invasive OVCA 433 and HEY cell lines. Additionally, while malignant and high-grade tumors displayed epithelial uPAR staining, uPAR expression was absent in normal and benign tumor samples. α6 integrin staining was also much lower
