Epithelial ovarian cancer stem­like cells are resistant to the cellular lysis of cytokine­induced killer cells via HIF1A­mediated downregulation of ICAM­1.

ABSTRACT

Epithelial ovarian cancer (EOC) is the most lethal of all gynecologic tumors. Cancer spheroid culture is a widely used model to study cancer stem cells. Previous studies have demonstrated the effectiveness of cytokine­induced killer (CIK) cell­based therapies against cancer and cancer stem cells. However, it is not clear how EOC spheroid cells respond to CIK­mediated cellular lysis, and the mechanisms involved have never been reported before. A flow cytometry­based method was used to evaluate the anti­cancer effects of CIK cells against adherent A2780 cells and A2780 spheroids. To demonstrate the association between hypoxia inducible factor­1α (HIF1A) and intercellular adhesion molecule­1 (ICAM­1), two HIF1A short hairpin RNA (shRNA) stable transfected cell lines were established. Furthermore, the protein expression levels of hypoxia/HIF1A­associated signaling pathways were evaluated, including transforming growth factor­ß1 (TGF­ß1)/mothers against decapentaplegic homologs (SMADs) and nuclear factor­κB (NF­κB) signaling pathways, comparing A2780 adherent cells and cancer spheroids. Flow cytometry revealed that A2780 spheroid cells were more resistant to CIK­mediated cellular lysis, which was partially reversed by an anti­ICAM­1 antibody. HIF1A was significantly upregulated in A2780 spheroids compared with adherent cells. Using HIF1A shRNA stable transfected cell lines and cobalt chloride, it was revealed that hypoxia/HIF1A contributed to downregulation of ICAM­1 in A2780 spheroid cells and adherent cells. Furthermore, hypoxia/HIF1A­associated signaling pathways, TGF­ß1/SMADs and NF­κB, were activated in A2780 spheroid cells by using western blotting. The findings indicate that EOC stem­like cells resist the CIK­mediated cellular lysis via HIF1A­mediated downregulation of ICAM­1, which may be instructive for optimizing and enhancing CIK­based therapies.