Prolonged mitotic arrest induced by Wee1 inhibition sensitizes breast cancer cells to paclitaxel

// Cody W. Lewis 1, 2, 3 , Zhigang Jin 1, 2, 3 , Dawn Macdonald 1, 2, 3 , Wenya Wei 1 , Xu Jing Qian 1 , Won Shik Choi 1 , Ruicen He 1 , Xuejun Sun 1, 2, 3 and Gordon Chan 1, 2, 3 1 Department of Oncology, University of Alberta, Edmonton, Alberta, Canada T6G 1Z2 2 Experimental Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada T6G 1Z2 3 Cancer Research Institute of Northern Alberta, University of Alberta, Edmonton, Alberta, Canada T6G 2J7 Correspondence to: Gordon Chan, email: gkc@ualberta.ca , gordonch@ahs.ca Keywords: cell cycle checkpoint, Wee1 kinase, paclitaxel, mitotic catastrophe, breast cancer Received: October 21, 2016      Accepted: April 27, 2017      Published: May 13, 2017 ABSTRACT Wee1 kinase is a crucial negative regulator of Cdk1/cyclin B1 activity and is required for normal entry into and exit from mitosis. Wee1 activity can be chemically inhibited by the small molecule MK-1775, which is currently being tested in phase I/II clinical trials in combination with other anti-cancer drugs. MK-1775 promotes cancer cells to bypass the cell-cycle checkpoints and prematurely enter mitosis. In our study, we show premature mitotic cells that arise from MK-1775 treatment exhibited centromere fragmentation, a morphological feature of mitotic catastrophe that is characterized by centromeres and kinetochore proteins that co-cluster away from the condensed chromosomes. In addition to stimulating early mitotic entry, MK-1775 treatment also delayed mitotic exit. Specifically, cells treated with MK-1775 following release from G1/S or prometaphase arrested in mitosis. MK-1775 induced arrest occurred at metaphase and thus, cells required 12 times longer to transition into anaphase compared to controls. Consistent with an arrest in mitosis, MK-1775 treated prometaphase cells maintained high cyclin B1 and low phospho-tyrosine 15 Cdk1. Importantly, MK-1775 induced mitotic arrest resulted in cell death regardless the of cell-cycle phase prior to treatment suggesting that Wee1 inhibitors are also anti-mitotic agents. We found that paclitaxel enhances MK-1775 mediated cell killing. HeLa and different breast cancer cell lines (T-47D, MCF7, MDA-MB-468 and MDA-MB-231) treated with different concentrations of MK-1775 and low dose paclitaxel exhibited reduced cell survival compared to mono-treatments. Our data highlight a new potential strategy for enhancing MK-1775 mediated cell killing in breast cancer cells.