Abstract A29: Anticancer effects of polo-like kinase-4 inhibitor (CFI-400945) in ovarian cancer
Authors: Tse Ka Yu , Chan Kin Tak , Yuen Vincent , Zhang Misty Shuo , Ip Philip Pun Ching , Ngan Hextan Yeung Sheung , Bray Mark , Wong Carmen Chai Lui , Mak Tak Wah 
Published: September 2020

Abstract
Background: Dysregulation of cell cycle and mitosis plays a pivotal role in carcinogenesis. Polo-like kinase (PLK) regulates centriole duplication and mitosis and is crucial in maintaining the genomic stability in cancer cells. Disruption of this process may affect cancer cell growth and so PLK represents a druggable target in cancer therapy. CFI-400945 is a small molecule against PLK4 activity, and this study aims to investigate its anticancer efficacy and mechanisms in ovarian cancer cells.
Methods: Expression of PLK4 in ovarian cancer patients was determined by Taqman quantitative PCR (qPCR) at transcriptional level. To assess the in vitro growth inhibition effect of CFI-400945, XTT cell viability assay was employed to compare the IC50 of CFI-400945 in a panel of 25 ovarian cancer cell lines of different histologic origins, and the antiproliferative results were assessed by direct cell counting assay. The anticancer activity of CFI-400945 in ovarian cancer cells were further studied by (1) propidium iodide (PI) staining to assess its impact on cell cycle and cell division, (2) annexin V staining to determine the level of apoptosis, (3) gH2AX Western blotting and gH2AX/RAD51 co-immunofluorescence to reveal its effect on DNA damage and repair, and (4) beta-galactosidase activity staining to study the outcome of senescence induced by CFI-400945. To study the change of gene expression induced by CFI-400945 at molecular level, poly-A capture RNA sequencing (RNAseq) was performed in OCC1 and ES2.
Results: The qPCR assay significantly demonstrated overexpression of PLK4 in ovarian cancer tumor tissue when compared to nontumor. The growth inhibition effect of CFI-400945 varied among different ovarian cancer cell lines, with IC50 ranging from 0.7 to 68.2nmol. PI-based cell cycle analysis clearly demonstrated the presence of aneuploidy up to 16N, indicating the failure of cell division after S phase DNA duplication. In addition to its impact on cell division, gH2AX immunofluorescent staining and Western blotting also revealed CFI-400945 induced DNA damage. However, induction of apoptosis was only rarely seen in the cell lines tested. The aneuploidy formation and low level of apoptosis was followed by cellular senescence, which was evidenced by 3-fold increase in the number of cells having positive beta-galactosidase staining after CFI-400945 treatment as compared to control. RNAseq of OCC1 and ES2 showed an induction of senescence-associated secretory phenotypes, like IL6 and P21, and suppression of DNA repair gene expression, like RAD51 and BRCA1, which were in agreement with our in vitro observation.
Conclusion: CFI-400945 had antiproliferative effect in ovarian cancer cell lines of different histologic origins, and its anticancer activity was attributable to DNA damage, its suppressive effect on DNA repair, failure of cell division, and subsequent cell senescence. Further study would focus on enhancing the anticancer activity of CFI-400945 through drug combination against DNA damage repair.
Citation Format: Ka Yu Tse, Kin Tak Chan, Vincent Yuen, Misty Shuo Zhang, Philip Pun Ching Ip, Hextan Yeung Sheung Ngan, Mark Bray, Carmen Chai Lui Wong, Tak Wah Mak. Anticancer effects of polo-like kinase-4 inhibitor (CFI-400945) in ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A29.