| Since 1999, no new drugs have been approved for the treatment of ovarian cancer even though it continues to be the most lethal gynecologic malignancy. Most ovarian cancer patients are diagnosed having advanced stage disease with metastasis to the omentum. At this metastatic site, more than half of the tumor microenvironment is composed of fibroblasts. It is now understood that cancer-associated fibroblasts (CAFs) play a key role in tumorigenesis by promoting tumor growth, invasion, and metastasis. However, the mechanism for how CAFs promote metastatic disease in ovarian cancer is not known.;MicroRNA's play an important role in cellular programming and little is known about their role in the context of stromal cells, specifically in carcinoma-associated fibroblasts (CAFs). RNA was extracted from fibroblasts isolated from both omental tumors (CAF) and the normal adjacent tissue (aNOF) from 7 patients with metastatic serous ovarian carcinoma. Candidate miRNAs were identified using a miRNA array; two of which expression goes down (miR-31 and miR-214) in CAFs and one of which expression goes up (miR-155). Altering the miRNA expression levels in fibroblasts using transfection of LNAs or pre-miRs changed their ability to stimulate invasion and colony formation of ovarian cancer cells. In addition, CAFs stably expressing pre-miR-31 were significantly less proficient in promoting tumor growth as compared to the CAFs expressing the empty vector when co-injected with HeyA8's. These results suggest that changes in miRNA expression mediate the reprogramming of NOFs to CAFs.;CAFs are known to secrete growth factors which can promote tumor growth. Using a receptor tyrosine kinase array to analyze phosphorylation of 42 different receptor tyrosine kinases (RTKs), we found that c-Met was the only RTK that was phosphorylated in cancer cells upon co-culture with CAFs. Further analysis of the co-culture revealed that cell-to-cell contact was required for activation of c-Met and this was HGF-independent because CAFs that were transiently transfected with HGF siRNA were still able to activate c-Met in the human ovarian cancer cell line SKOV3ip1. Interestingly, membrane fragments isolated from CAFs were sufficient to stimulate phosphorylation of c-Met in cancer cells. Collectively, these results suggest a potentially novel mechanism whereby CAFs activate c-Met in cancer cells by direct contact.;c-Met is widely expressed in ovarian cancer and is known to be a negative prognostic indicator of ovarian cancer patient survival. Two small-molecule inhibitors of c-Met, PF-2341066 and GSK1363089 (foretinib), currently under clinical development were tested for efficacy in reducing ovarian cancer growth and metastasis in preclinical studies and their mechanism elucidated. Both inhibitors were shown to be effective inhibitors of c-Met activation in vitro and inhibited ovarian cancer growth and metastasis in vivo very efficiently. Notably, in a genetic mouse model of endometrioid ovarian cancer, treatment with the c-Met inhibitor, foretinib, prevented primary tumors from progressing to invasive adenocarcinoma blocking invasion through the basement membrane. To determine the mechanism of inhibition, we analyzed the inhibitor's effect in vitro and found that foretinib effectively inhibited c-Met activation and downstream signaling, causing; (1) a reduction in cell adhesion to a model of the human omentum, (2) a block in migration and invasion, (3) reduced proliferation mediated by a G2/M cell cycle arrest, and (4) induction of anoikis. Overall, these preclinical data strongly suggest that c-Met inhibitors should be considered for further clinical development in the treatment of ovarian cancer. |
