Analysis of hematopoietic stem cells using a composite approach

The hedgehog pathway regulates cancer stem cells in serous adenocarcinoma of the ovary

PURPOSE

Signaling by cancer stem cells (CSCs) is known to occur at least in part through conserved developmental pathways. Here, the role of one of these pathways, i.e., the hedgehog pathway, was evaluated in high-grade serous ovarian carcinoma (HGSOC).

METHODS AND RESULTS

We found that in HGSOC, hedgehog inhibitors (HHIs) GANT61, LDE225 and GDC0449 reduced or inhibited the formation of spheroids enriched in CSCs. Primary malignant cells (PMCs) in ascites from HGSOC patients cultured in the presence of HHIs showed significant reduction in CSCs. Sonic hedgehog (SHH) significantly increased the expression of ALDH1A1, which was inhibited by GANT61. In the presence of a SHH neutralizing antibody (5E1), a significant reduction in the number of spheroids was observed in HGSOC-derived cell lines. Further, the motility, migration and clonogenic growth of the cells were significantly reduced by HHIs. In the presence of GANT61, a reduction of cells from PMCs in the G0 phase of the cell cycle was observed. The magnitude of difference in expression of Gli1 in tumors from the same HGSOC patients at presentation and at interval debulking surgery was greater in patients who had a recurrence on follow up. GANT61 also significantly inhibited the growth of CSCs in nude mice. Finally, RNA sequencing of HGSOC cells treated with GANT61 showed a significantly reduced expression of CSC markers.

CONCLUSIONS

Our results indicate that the hedgehog pathway plays an important role in maintaining the integrity of CSCs in HGSOC and could be a potential therapeutic target.

ALDH1A1+ ovarian cancer stem cells co-expressing surface markers CD24, EPHA1 and CD9 form tumours in vivo

One of the reasons for recurrence following treatment of high grade serous ovarian carcinoma (HGSOC) is the persistence of residual cancer stem cells (CSCs). There has been variability between laboratories in the identification of CSC markers for HGSOC. We have identified new surface markers (CD24, CD9 and EPHA1) in addition to those previously known (CD44, CD117 and CD133) using a bioinformatics approach. The expression of these surface markers was evaluated in ovarian cancer cell lines, primary malignant cells (PMCs), normal ovary and HGSOC. There was no preferential expression of any of the markers or a combination. All the markers were expressed at variable levels in ovarian cancer cell lines and PMCs. Only CD117 and CD9 were expressed in the normal ovarian surface epithelium and fallopian tube. Both ALDEFLUOR (ALDH1A1) and side population assays identified a small proportion of cells (<3%) separately that did not overlap with little variability in cell lines and PMCs. All surface markers were co-expressed in ALDH1A1+ cells without preference for one combination. The cell cycle analysis of ALDH1A1+ cells alone revealed that majority of them reside in G0/G1 phase of cell cycle. Further separation of G0 and G1 phases showed that ALDH1A1+ cells reside in G1 phase of the cell cycle. Xenograft assays showed that the combinations of ALDH1A1 + cells co-expressing CD9, CD24 or EPHA1 were more tumorigenic and aggressive with respect to ALDH1A1-cells. These data suggest that a combined approach could be more useful in identifying CSCs in HGSOC.