Abstract
The taxanes are effective microtubule-stabilizing chemotherapy drugs that inhibit mitosis, induce apoptosis, and produce regression in a fraction of cancers that arise at many sites including the ovary. Novel therapeutic targets that augment taxane effects are needed to improve clinical chemotherapy response in CCNE1-amplified high grade serous ovarian cancer (HGSOC) cells. In this study, we conducted an siRNA-based kinome screen to identify modulators of mitotic progression in CCNE1-amplified HGSOC cells that may influence clinical paclitaxel response. PLK1 is overexpressed in many types of cancer, which correlates with poor prognosis. Here, we identified a novel synthetic lethal interaction of the clinical PLK1 inhibitor BI6727 and the microtubule-targeting drug paclitaxel in HGSOC cell lines with CCNE1-amplification and elucidated the underlying molecular mechanisms of this synergism. BI6727 synergistically induces apoptosis together with paclitaxel in different cell lines including a patient-derived primary ovarian cancer culture. Moreover, the inhibition of PLK1 reduced the paclitaxel-induced neurotoxicity in a neurite outgrowth assay. Mechanistically, the combinatorial treatment with BI6727/paclitaxel triggers mitotic arrest, which initiates mitochondrial apoptosis by inactivation of anti-apoptotic BCL-2 family proteins, followed by significant loss of the mitochondrial membrane potential and activation of caspase-dependent effector pathways. This conclusion is supported by data showing that BI6727/paclitaxel-co-treatment stabilizes FBW7, a component of SCF-type ubiquitin ligases that bind and regulate key modulators of cell division and growth including MCL-1 and Cyclin E. This identification of a novel synthetic lethality of PLK1 inhibitors and a microtubule-stabilizing drug has important implications for developing PLK1 inhibitor-based combination treatments in CCNE1-amplified HGSOC cells.
Highlights
High grade serous ovarian cancer (HGSOC) accounts for 70-80% of ovarian cancer-related deaths.Despite major improvements in the understanding of ovarian cancer carcinogenesis, most patients relapse after primary treatment and succumb to disease progression
For the subsequent analysis we selected an ovarian cancer cell line with CCNE1-amplification like OVCAR-3 cells exhibiting strong Cyclin E expression and a reasonable doubling time, which is an important prerequisite for a www.oncotarget.com successful siRNA screening
We used a multi-step strategy to identify novel therapeutic targets in ovarian cancer cells that induce cell death and might improve taxane-based effects: (1) screening of 711 pools of siRNAs (Dharmacon kinome library) targeting individual human kinases; (2) specific hits were validated using single siRNAs that made up the pool in the primary screening; and (3) assays for cell viability, cell death (Caspase-3/7 activity, Annexin staining) and cell cycle distribution (FACS measurements) of siRNA-treated OVCAR-3 cells (Supplementary Figure 2A)
Summary
Despite major improvements in the understanding of ovarian cancer carcinogenesis, most patients relapse after primary treatment and succumb to disease progression. The toxicity profile favoring the carboplatin/paclitaxel regimen has established this as standard of care in the first-line setting. Changes to both chemotherapy schedules and routes of administration are associated with improved survival, it appears that a therapeutic ceiling with these drugs has been reached. Despite a good chemosensitivity of HGSOC, a significant frequency of these patients fails to respond to the primary treatment with taxanes. Bevacizumab, a humanized monoclonal antibody targeting vascular endothelial growth factor, showing improvement in progression-free survival in combination with standard chemotherapy has enriched the modern armament targeting HGSOC [3]
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