Epithelial ovarian carcinoma is the most common cause of death from gynecologic cancers largely due to advanced, relapsed, and chemotherapy-resistant peritoneal metastasis, which is refractory to the currently used treatment approaches. Mechanisms supporting advanced and relapsed peritoneal metastasis are largely unknown, precluding development of more effective targeted therapies. In this study we investigated the function of a potentially targetable fractalkine axis in the formation and the development of advanced and relapsed peritoneal metastasis and its impact on patients’ outcomes. Our mouse model studies support a role for the fractalkine receptor (CX3CR1) in the initiation of peritoneal adhesion important for recolonization of relapsed peritoneal metastasis. We show that downregulation of CX3CR1 results in reduction of metastatic burden at several peritoneal sites commonly colonized by advanced and relapsed metastatic ovarian carcinoma. We show that the chemokine fractalkine (CX3CL1), an activating ligand of CX3CR1, regulates organ-specific peritoneal colonization. High expression of CX3CR1 correlates with significantly shorter survival, specifically in post-menopausal patients with advanced and terminal stages of the disease. Taken together, our studies support a key regulatory role for the fractalkine axis in advanced and relapsed peritoneal metastasis in epithelial ovarian carcinoma.
Disseminating epithelial ovarian cancer cells often become assembled into spheroids prior to their arrival at metastatic sites within the peritoneal cavity. Although epithelial ovarian carcinoma (EOC) is the deadliest gynecologic malignancy, the mechanisms regulating formation and metastatic potential of spheroids are poorly understood. We show that expression of a cell surface glycoprotein CD44 is an important contributing factor for spheroid formation and spheroid adhesion to mesothelial cells, and its loss impairs mesenteric metastasis. In contrast, loss of CD44 resulted in significant increase of tumor burden at several locoregional sites, including liver, and unleashed distant metastases to the thoracic cavity. Altogether our studies suggest that CD44 regulates metastatic progression of EOC in an organ-specific manner. Implications: Expression of CD44 promotes spheroid formation, mesothelial adhesion, and formation of mesenteric metastasis, but it suppresses development of metastasis to several peritoneal sites, including liver, and the thoracic cavity.
Failure of currently used cytotoxic chemotherapy is one of the main reasons behind high mortality from metastatic high grade serous ovarian carcinoma. We found that high expression of a receptor for fractalkine (CX3CR1) significantly correlated with shorter survival of patients with serous ovarian carcinoma treated with cytotoxic DNA damage chemotherapies, and reduction of CX3CR1 expression resulted in sensitization to several DNA damaging modalities, including x-ray radiation and cisplatin. Here, we show that CX3CR1 plays a role in double-strand DNA break response and repair by regulating expression of RAD50 by a MYC-dependent mechanism. We demonstrate that downregulation of CX3CR1 alone and in a combination with irradiation affects peritoneal metastasis in an organ-specific manner; we show that CX3CR1 regulates lipid uptake which could control omental metastasis. This study identifies CX3CR1 as a novel potential target for sensitization of ovarian carcinoma to DNA damage therapies and reduction of peritoneal carcinomatosis.
Epithelial ovarian carcinoma (EOC) metastasis is characterized by the shedding of malignant cells from the surface of the primary tumor and their implantation onto the peritoneal surface lining the abdominal cavity in addition to more distant sites. This shedding of malignant cells from the primary site results as either single cells or free-floating multicellular aggregates, known as spheroids, in the ascites. Although single cells and spheroids may potentially seed metastases, considerable evidence now suggests that the aggregation of cells is important for anchorage-independent cell survival and growth, and spheroid formation may represent an important intermediate survival mechanism to facilitate EOC dissemination. Recent studies have uncovered human transmembrane cell adhesion molecule CD44 standard (CD44s) isoform expression correlating with high-grade and advanced-stage ovarian carcinoma. Moreover, it has also been suggested that CD44s may be an important mediator of ovarian cancer cell implantation in the peritoneal cavity, enhancing the metastatic potential of ovarian cancer cells. Thus, we investigated the functional significance of CD44 standard by means of in vitro culture experiments with ovarian cancer spheroids. After characterizing 8 EOC cell lines, a spectrum of CD44 expression was observed and two cell lines with high CD44s (ES-2 and SKOV-3) and two cell lines low in CD44s (OVCAR-4 and OVSAHO) were chosen for further testing. Interestingly, the high CD44s-expressing cell lines formed larger spheroids that adhered significantly faster to a monolayer of primary mesothelial cells. Stable knockdown of CD44 using CRISPR/Cas9 in these 2 cell lines reduced spheroid formation, suggesting that differential expression of CD44 standard plays a role in cell-cell adhesion. When ES-2 CD44-/- cells were injected i.p. into athymic nude mice, decreased ascites production and mesentery tumor burden were observed as well as increased overall survival. However, CD44 knockdown also significantly increased metastasis to the lung, suggesting a suppressive role for CD44 in EOC metastasis as well. These in vivo data imply that CD44 enhances the metastatic potential in ovarian cancer spheroids influencing peritoneal tumor growth while suppressing metastasis to lung tissue. Citation Format: Joelle D. Sacks, Hilal Gurler Main, Goda G. Muralidhar, Osama Elfituri, Hao-Liang Xu, Andre A. Kajdacsy-Balla, Maria V. Barbolina. Adhesion and beyond: CD44 in ovarian cancer spheroids. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B57.
<p>SUPPLEMENTARY FIGURE 10. Silencing of CD44 does not affect cell morphology (A), expression of mesenchymal markers (B), cell migration (C,D), or Matrigel invasion.</p>
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