Abstract
Within the ovarian cancer tumor microenvironment, cancer stem-like cells (CSC) interact with carcinoma associated mesenchymal stem/stromal cells (CA-MSC) through multiple secreted cytokines and growth factors. These paracrine interactions have been revealed to cause enrichment of CSC and their chemoprotection; however, it is still not known if platelet-derived growth factor (PDGF) signaling is involved in facilitating these responses. In order to probe this undiscovered bidirectional communication, we created a model of ovarian malignant ascites in the three-dimensional (3D) hanging drop heterospheroid array, with CSC and CA-MSC. We hypothesized that PDGF secretion by CA-MSC increases self-renewal, migration, epithelial to mesenchymal transition (EMT) and chemoresistance in ovarian CSC. Our results indicate that PDGF signaling in the CSC-MSC heterospheroids significantly increased stemness, metastatic potential and chemoresistance of CSC. Knockdown of PDGFB in MSC resulted in abrogation of these phenotypes in the heterospheroids. Our studies also reveal a cross-talk between PDGF and Hedgehog signaling in ovarian cancer. Overall, our data suggest that when the stromal signaling via PDGF to ovarian CSC is blocked in addition to chemotherapy pressure, the tumor cells are significantly more sensitive to chemotherapy. Our results emphasize the importance of disrupting the signals from the microenvironment to the tumor cells, in order to improve response rates. These findings may lead to the development of combination therapies targeting stromal signaling (such as PDGF and Hedgehog) that can abrogate the tumorigenic, metastatic and platinum resistant phenotypes of ovarian CSC through additional investigations.
Highlights
Ovarian cancer is the fifth leading cause of cancer-related deaths in women in the United States, and has a low survival rate, due in part to the frequent late stage at diagnosis [1,2]
In order to test the presence of platelet-derived growth factor (PDGF)-BB as a soluble factor within the cancer stem-like cells (CSC)/MSC microenvironment, we performed an enzyme-linked immunosorbent assay (ELISA), where we found that OVCAR3 CSC cultures in CSC/MSC heterospheroids demonstrated an increased presence of PDGF-BB that was not statistically significant (Figure 4A)
We found that Hedgehog ligands SHH and IHH were significantly upregulated in CSC cultured in heterospheroids with WT MSC, and this upregulation was diminished in CSC cultured with siPDGFB
Summary
Ovarian cancer is the fifth leading cause of cancer-related deaths in women in the United States, and has a low survival rate, due in part to the frequent late stage at diagnosis [1,2]. Chemoresistance and new tumor growth following primary therapy has been ascribed to ovarian cancer stem cells (CSC), through a complex interplay with other cells within the tumor microenvironment (TME) [1,3,4,5,6,7]. Stromal cells within the TME, including carcinoma-associated mesenchymal stem/stromal cells (CA-MSC) play critical supportive roles aiding in CSC proliferation, metastasis and chemoresistance [22,23,24,25]. Co-culture of ovarian cancer cells with MSC leads to increased proliferation, invasiveness and platinum resistance of the cancer cells [29,30]. Within the framework of this dynamic CSC/CA-MSC relationship, we hypothesize that platelet-derived growth factor (PDGF) plays a critical role in CSC/CA-MSC pro-tumorigenic signaling
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