Abstract

Background

Epithelial ovarian cancer (EOC) has a high mortality due to late presentation and variable treatment response. The development of resistance to combination chemotherapy with carboplatin and paclitaxel is common, but the underlying mechanisms remain poorly understood. Paclitaxel, a microtubule poison, causes cells to arrest in mitosis. Several proteins, including the oncogene c-MYC (Topham et al. 2015), affect the fate of breast cancer cells following taxol-induced arrest, although determinants of cell fate in ovarian cancer remain poorly characterised. We hypothesise that altered c-MYC degradation during mitosis may influence response to paclitaxel chemotherapy in ovarian cancer.

Method

HeLa FRT cells stably expressing doxycycline-inducible c-MYC-venus were generated by co-transfection of pOG44 Vector Flp-In System and pc5MYC-Venus.  Degradation of c-MYC following paclitaxel challenge was investigated by Western blot and live cell imaging in HeLa cells, A2780 and A1847 ovarian cancer cell lines. Transient c-MYC siRNA knockdown and over-expression were used to assess the effect of altered c-MYC expression on cell fate by live cell microscopy and Reverse Phase Protein Array (RPPA) analysis to compare c-MYC expression in A2780 and A2780pacR paclitaxel-resistant cells.

Results

In vitro exposure of paclitaxel during mitosis lead to consistent degradation of c-MYC in each cell line. The fate of mitotically arrested cells was altered by both loss and over-expression of c-MYC, with loss promoting cell survival, and over-expression increased cell death. A significant reduction in c-MYC protein expression (3.229-fold, p=0.037) was also seen in RPPA analysis of A2780pacR cells, consistent with a role for c-MYC as a determinant of mitotic cell fate.

Conclusion

In EOC cells treated with paclitaxel, reduced expression of c-MYC leads to increased cell survival. This may provide a potential novel therapeutic target to improve chemo-sensitivity or a predictive biomarker to guide treatment selection in ovarian cancer patients.  

Topham, C. et al., 2015. Cancer Cell, 28, pp.129–140.