Development and Characterization of the Metastatic Niche in Ovarian Carcinoma

Ovarian carcinoma has a unique pattern of metastasis, it remains largely restricted to the abdominal cavity, where the omentum; a large fat pad in front of the bowel, is a major site of the metastasis. The development and progression of cancer is closely associated with the tumor microenvironment. Tumor cells exist in a microenvironment composed of fibroblasts, epithelial cells, leukocytes, lymphocytes, extracellular matrices, etc. Interaction between the disseminating tumor cells and the local microenvironment at that site, the pre-metastatic niche, makes it a major site for metastasis.

The metastatic niche is composed of a variety of cells including immune cells, endothelial cells and activated fibroblasts and adipocytes; the Cancer Associate Fibroblasts (CAFs). CAFs contribute to tumor cell proliferation, invasion and progression. They are characterized with the expression of alpha-smooth muscle actin (α-SMA) and fibroblast activation protein-alpha (FAP-α). There are two major sites for CAFs in ovarian cancer, both the tumor stroma and the omentum. In ovarian cancer, it was recently reported that several lncRNA have been shown to be overexpressed in CAFs and contribute to their ability to promote metastasis. To further explore the role of CAFs in the metastatic niche, we conducted a study to characterize them. For isolation of primary CAFs, fresh material from primary omentum of ovarian cancer were obtained from patients undergoing surgery at Hadassah Medical Organization (n = 18). Normal fibroblasts (NF) were isolated from patients undergoing non-cancerous prophylactic surgery (n=11). The study was approved by the local ethics committee and informed consent was obtained from the patients. Both sets of fibroblasts were cultured and mRNA levels were tested for several lncRNAs using qPCR. CAFs and NFs were characterized by the expression of FAP-1α, α-SMA and Periostin; potential markers of activated fibroblasts. Remarkably, various lncRNAs were found to be differentially expressed in CAFs and NFs. GAS5, known as a potential tumor suppressor, was upregulated in NFs samples compared to CAFs, while FLJ22447, a yet uncharacterized lncRNA, was found to be upregulated in CAFs compared to NFs. Migration of the CAF or NF samples towards OVCAR3-an ovarian cancer cell line, was tested using cell culture chamber slide and the results revealed that CAFs show an increased motility towards ovarian cancer cells compared to NFs. Furthermore, we found that MRC-5, a NF cell line, can be activated and transformed to CAF, when exposed to CAFs conditioned media. These results demonstrate that targeting the activation of CAFs in the omentum of ovarian cancer patients could serve a novel appealing approach to inhibit the metastatic niche formation.