E-cadherin loss is frequently associated with ovarian cancer metastasis. Given that adhesion to the abdominal peritoneum is the first step in ovarian cancer dissemination, we reasoned that down-regulation of E-cadherin would affect expression of cell matrix adhesion receptors. We show here that inhibition of E-cadherin in ovarian cancer cells causes up-regulation of A 5 -integrin protein expression and transcription. When E-cadherin was blocked, RMUG-S ovarian cancer cells were able to attach and invade more efficiently. This greater efficiency could, in turn, be inhibited both in vitro and in vivo with an A 5 B 1 -integrin-blocking antibody. When E-cadherin is silenced, A 5 -integrin is up-regulated through activation of an epidermal growth factor receptor/FAK/Erk1-mitogenactivated protein kinase-dependent signaling pathway and not through the canonical E-cadherin/B-catenin signaling pathway. In SKOV-3ip1 ovarian cancer xenografts, which express high levels of A 5 -integrin, i.p. treatment with an A 5 B 1 -integrin antibody significantly reduced tumor burden, ascites, and number of metastasis and increased survival by an average of 12 days when compared with IgG treatment (P < 0.0005). A 5 -Integrin expression was detected by immunohistochemistry in 107 advanced stage ovarian cancers using a tissue microarray annotated with disease-specific patient follow-up. Ten of 107 tissues (9%) had A 5 -integrin overexpression, and 39% had some level of A 5 -integrin expression. The median survival for patients with high A 5 -integrin levels was 26 months versus 35 months for those with low integrin expression (P < 0.05). Taken together, we have identified A 5 -integrin upregulation as a molecular mechanism by which E-cadherin loss promotes tumor progression, providing an explanation for how E-cadherin loss increases metastasis. Targeting this integrin could be a promising therapy for a subset of ovarian cancer patients.

c-Met receptor tyrosine kinase (RTK) has not been extensively studied in malignant pleural mesothelioma

Purpose: To understand the functional and preclinical efficacy of targeting the urokinase plasminogen activator receptor (u-PAR) in ovarian cancer.Experimental Design: Expression of u-PAR was studied in 162 epithelial ovarian cancers, including 77 pairs of corresponding primary and metastatic tumors. The effect of an antibody against u-PAR (ATN-658) on proliferation, adhesion, invasion, apoptosis, and migration was assessed in 3 (SKOV3ip1, HeyA8, and CaOV3) ovarian cancer cell lines. The impact of the u-PAR antibody on tumor weight, number, and survival was examined in corresponding ovarian cancer xenograft models and the mechanism by which ATN-658 blocks metastasis was explored.Results: Only 8% of all ovarian tumors were negative for u-PAR expression. Treatment of SKOV3ip1, HeyA8, and CaOV3 ovarian cancer cell lines with the u-PAR antibody inhibited cell invasion, migration, and adhesion. In vivo, anti-u-PAR treatment reduced the number of tumors and tumor weight in CaOV3 and SKOV3ip1 xenografts and reduced tumor weight and increased survival in HeyA8 xenografts. Immunostaining of CaOV3 xenograft tumors and ovarian cancer cell lines showed an increase in activecaspase 3 and TUNEL staining. Treatment with u-PAR antibody inhibited a 5 -integrin and u-PAR colocalization on primary human omental extracellular matrix. Anti-u-PAR treatment also decreased the expression of urokinase, u-PAR, b 3 -integrin, and fibroblast growth factor receptor-1 both in vitro and in vivo.Conclusions: This study shows that an antibody against u-PAR reduces metastasis, induces apoptosis, and reduces the interaction between u-PAR and a 5 -integrin. This provides a rationale for targeting the u-PAR pathway in patients with ovarian cancer and for further testing of ATN-658 in this indication.

The role of the vitronectin receptor (␣ v ␤ 3 -integrin) as a tumor promoter seems well established, and, consequently, therapies that block this integrin are currently in clinical testing. We undertook the current study to determine whether ␣ v ␤ 3 -integrin is an appropriate target in ovarian cancer treatment. Expression of ␤ 3 -integrin in SKOV3ip1 ovarian cancer cells led to the overexpression of ␣ v ␤ 3 -integrin on the cell surface and increased adhesion. However, ␣ v ␤ 3 -integrinoverexpressing cells showed impaired invasion, protease expression, and colony formation. These results were recapitulated in xenograft studies: ␣ v ␤ 3 -integrin-expressing cells showed increased adhesion to mouse peritoneum, but the overall number of metastatic nodules (105 versus 68 tumors) and tumor weight were significantly lower than those in the parental SKOV3ip1 cells. The ␣ v ␤ 3 -integrin-overexpressing cells had a decreased proliferation rate mediated by inhibition of cyclin B1 and induction of phosphoCdc2 and p53 expression, consistent with a G 2 M cell cycle arrest. Confirming the above results, inhibition of ␤ 3 -integrin in cultured or primary OvCa cells decreased adhesion but increased invasion and proliferation. Patients with tumors expressing high ␤ 3 -integrin had significantly better disease-free and overall survival (52 months versus 27 months, P < 0.05). This study shows that ␣ v ␤ 3 -integrin expression on tumor cells actually slows tumor progression and acts as a tumor suppressor. Therefore, the vitronectin receptor might not be an appropriate therapeutic target in ovarian cancer.

The procoagulatory serine protease, thrombin, is known to induce invasion and metastasis in various cancers, but the mechanisms by which it promotes tumorigenesis are poorly understood. Because the 92-kDa gelatinase (MMP-9) is a known mediator of tumor cell invasion, we sought to determine whether and how thrombin regulates MMP-9. The thrombin receptor, PAR-1, and MMP-9 are expressed in osteosarcomas, as determined by immunohistochemistry. Stimulation of U2-OS osteosarcoma cells with thrombin and a thrombin receptor-activating peptide induced pro-MMP-9 secretion as well as cell surface-associated pro-MMP-9 expression and proteolytic activity. This was paralleled by an increase in MMP-9 mRNA and MMP-9 promoter activity. Thrombin-induced invasion of U2-OS cells through Matrigel was mediated by the phosphatidylinositol 3-kinase signaling pathway and could be inhibited with an MMP-9 antibody. The stimulation of MMP-9 by thrombin was paralleled by an increase in ␤1-integrin mRNA and ␤1-integrin expression on the cell surface, which was also mediated by phosphatidylinositol 3-kinase and was required for invasion. Thrombin activation induced and co-localized both ␤1-integrin and pro-MMP-9 on the cell membrane, as evidenced by co-immunoprecipitation, confocal microscopy, and a protein binding assay. The thrombin-mediated association of these two proteins, as well as thrombin-mediated invasion of U2-OS cells, could be blocked with a cyclic peptide and with an antibody preventing binding of the MMP-9 hemopexin domain to ␤1-integrin. These results suggest that thrombin induces expression and association of ␤1-integrin with MMP-9 and that the cell surface localization of the protease by the integrin promotes tumor cell invasion.

Colonic carcinogenesis involves the progressive dysregulation of homeostatic mechanisms that control growth. The epidermal growth factor (EGF) receptor (EGFR) regulates colonocyte growth and differentiation and is overexpressed in many human colon cancers. A requirement for EGFR in colonic premalignancy, however, has not been shown. In the current study, we used a specific EGFR antagonist, gefitinib, to investigate this role of the receptor in azoxymethane colonic premalignancy. The azoxymethane model shares many clinical, histologic, and molecular features of human colon cancer. Mice received azoxymethane i.p. (5 mg/kg/wk) or saline for 6 weeks. Animals were also gavaged with gefitinib (10 mg/kg body weight) or vehicle (DMSO) thrice weekly for 18 weeks, a dose schedule that inhibited normal receptor activation by exogenous EGF. Compared with control colonocytes [bromodeoxyuridine (BrdUrd), 2.2 F 1.2%], azoxymethane significantly increased proliferation (BrdUrd, 12.6 F 2.8%), whereas gefitinib inhibited this hyperproliferation (BrdUrd, 6.2 F 4.0%; <0.005). Azoxymethane significantly induced pro-transforming growth factor-A (6.4 F 1.3-fold) and increased phospho-(active) EGFR (5.9 F 1.1-fold), phospho-(active) ErbB2 (2.3 F 0.2-fold), and phospho-(active) extracellular signal-regulated kinase (3.3 F 0.4-fold) in premalignant colonocytes. Gefitinib inhibited activations of these kinases by >75% (P < 0.05). Gefitinib also significantly reduced the number of large aberrant crypt foci and decreased the incidence of colonic microadenomas from 75% to 33% (P < 0.05). Gefitinib concomitantly decreased cell cycle-regulating cyclin D1 and prostanoid biosynthetic enzyme cyclooxygenase-2 in microadenomas, suggesting that these regulators are key targets of EGFR in colonic carcinogenesis. These results show for the first time that EGFR signaling is required for early stages of colonic carcinogenesis. Our findings suggest, moreover, that inhibitors of EGFR might be useful in chemopreventive strategies in individuals at increased risk for colonic malignancies. [Cancer Res 2007;67(2):827-35]

Aberrant crypt foci (ACF) are collections of abnormal colonic crypts with heterogeneous molecular and pathologic characteristics. Large and dysplastic ACF are putative precursors of colon cancer with neoplastic risk related to increased proliferation. In this study, we examined the role of epidermal growth factor receptor (EGFR) signaling in regulating ACF proliferation. Using magnification chromoendoscopy, we collected large ACF with endoscopic features of dysplasia and separately biopsied adjacent mucosa. Transcript levels were measured by real-time PCR, proteins were assessed by Western blotting, and levels were expressed as fold changes of adjacent mucosa. K-ras and B-Raf mutations were assessed by PCR and Ras activation by the ratio Ras-GTP / (Ras-GTP + Ras-GDP). At the RNA level, 38% of ACF were hyperproliferative, with proliferating cell nuclear antigen (PCNA) mRNA z2-fold of adjacent mucosa. Hyperproliferative ACF had significantly increased mRNA levels of EGFR (6.0 F 1.7-fold), transforming growth factor-A (14.4 F 5.0-fold), heparin-binding EGF-like growth factor (4.5 F 1.4-fold), cyclin D1 (4.6 F 0.7-fold), and cyclooxygenase-2 (COX-2; 9.3 F 4.2-fold; P < 0.05). At the protein level, 46% of ACF were hyperproliferative (PCNA, 3.2 F 1.2-fold). In hyperproliferative ACF, 44% possessed significant increases in four EGFR signaling components: EGFR (9.5 F 1.3-fold), phosphoactive ErbB2 (2.6 F 0.4-fold), phosphoactive extracellular signal-regulated kinase (3.7 F 1.1-fold), and cyclin D1 (3.4 F 0.8-fold; P < 0.05). Ras was activated in 46% of ACF (3.2 F 0.4-fold; P < 0.05), but K-ras mutations were present in only 7% of ACF. In contrast to COX-2 mRNA, the protein was not increased in hyperproliferative ACF. In summary, we have shown that ACF with up-regulated PCNA possess increased EGFR signaling components that likely contribute to the enhanced proliferative state of

Purpose: Colonic carcinogenesis deranges growth-regulating epidermal growth factor receptors (EGFR). We previously showed that EGFR signals were up-regulated in human aberrant crypt foci (ACF), putative colon cancer precursors. The azoxymethane model of colon cancer recapitulates many aspects of human colonic tumors. Recent studies indicate that flat dysplastic ACF with increased h-catenin are tumor precursors in this model. We asked, therefore, if EGFR signals are required for flat dysplastic ACF development and cancer progression. Experimental Design: Rats received azoxymethane or saline, and standard chow or chow supplemented with gefitinib, an EGFR inhibitor, for 44 weeks. EGFR signals were quantified in normal colon, flat ACF, and tumors by computerized analysis of immunostains and Western blots. K-ras mutations were assessed by PCR and mRNA for egfr ligands by quantitative real-time PCR. Results: EGFR inhibition with gefitinib decreased the incidence of flat dysplastic ACF from 66% to 36% and tumors from 71% to 22% (P < 0.05). This inhibitor also reduced the overexpressions of cyclin D1 and Cox-2 in flat ACF. Furthermore, in flat ACF, EGFR blockade decreased the upregulation of c-Jun, FosB, phosphorylated active signal transducers and activators of transcription 3, and CCAAT/enhancer binding protein-h, potential regulators of cyclin D1 and Cox-2. In colonic tumors, EGFR blockade significantly decreased angiogenesis, proliferation, and progression while also increasing apoptosis (P < 0.05). Gefitinib also inhibited the activations of extracellular signal^regulated kinase, Src, and AKT pathways in tumors. Conclusions: We have shown for the first time that EGFR promotes the development of flat dysplastic ACF and the progression of malignant colonic tumors. Furthermore, we have mechanistically identified several transcription factors and their targets as EGFR effectors in colonic carcinogenesis.Colonic carcinogenesis is characterized by the accumulation of activating mutations in proto-oncogenes and inhibiting mutations in tumor suppressor genes. These mutations dysregulate pathways, including epidermal growth factor receptor (EGFR) signals that control cell growth, maturation, and cell death. Up-regulations of EGFRs and ligands have been described in many tumors, including colon cancers (1). Recently, we reported that EGFR signals were up-regulated in human aberrant crypt foci (ACF) identified in situ using image magnification chromoendoscopy (2). ACF are the earliest identifiable lesions in experimental colonic carcinogenesis and dysplastic ACF are believed to be precursors of colon cancer (3).EGFR (ErbB1) is a member of the ErbB family of receptor tyrosine kinases which also includes ErbB2, ErbB3, and ErbB4 (4). Ligand binding induces a conformational change, causing receptors to dimerize and activating the receptor's intrinsic tyrosine kinase. ErbB2 is unique in that it has no identified ligand, but is the preferred heterodimeric partner for other members. EGFR signals activate multiple pathways i...