Abstract 4178: The novel PLK1 inhibitor, CYC140: Identification of pharmacodynamic markers, sensitive target indications and potential combinations

Introduction: CYC140 is a selective and potent ATP-competitive inhibitor of PLK1, which has completed IND-enabling studies. The aim of this translational project was to inform the clinical development path of CYC140. Esophageal cancer was investigated as a potential target indication based on unmet medical need and the observation that PLK1 is frequently overexpressed in esophageal tumors and carries a poor prognosis. Experimental procedures: The anticancer activity of CYC140 was examined across multiple tumor types to identify sensitive target indications or tumor subsets. 6 h pulse exposure to CYC140 was used to determine sensitivity in a panel of over 250 cancer cell lines, including 15 esophageal cancer cell lines, using CellTiter Glo and resazurin-based assays. Candidate pharmacodynamic markers were examined in malignant and non-malignant cells. Drug combination testing was undertaken in several esophageal cell lines using approved and targeted agents. Solid tumor and leukemia xenograft models were performed to assess CYC140 dosing schedules and efficacy. Summary: Inhibition of PLK1 by CYC140 perturbs the entry into and exit from mitosis. In malignant cells, CYC140 treatment leads to the appearance of mitotic cells with monopolar spindles and a persistent increase in the proportion of cells in G2 and M phase, resulting in complete growth inhibition and induction of cell death. In non-malignant cells, the growth arrest is transient, and cells resume cycling once compound is removed. Short (6 h) pulse treatments of CYC140 maximise the difference in cellular response between malignant esophageal cell lines and cells of a non-malignant origin. In the esophageal cell line panel, CYC140 cellular IC50 correlates with induction of apoptosis. The effect of CYC140 on pharmacodynamic markers of PLK-1 activity such as phospho-nucleophosmin and phospho-histone H3 was characterized in malignant and non-malignant cells. Several promising combinations of CYC140 with targeted agents were identified, including EGFR inhibitors, HDAC inhibitors and PI3K pathway inhibitors, and CYC140 can also be combined with cytotoxic agents approved for use in esophageal cancer, such as cisplatin or irinotecan. CYC140 anti-tumor efficacy was demonstrated in solid tumor and leukemic xenograft models with responses including tumor regression and tumor-free cures. Conclusions: CYC140 is a promising anti-cancer agent with potent anti-proliferative activity and therapeutic potential in a variety of cancers, including esophageal cancer and acute leukemia. The mode of action of CYC140 is consistent with PLK1 inhibition and cell death is preferentially triggered in sensitive malignant cells. Suitable pharmacodynamic markers and several promising combinations have been identified that could assist clinical development of CYC140. Citation Format: Sylvie Moureau, Craig MacKay, Chiara Saladino, Elizabeth Pohler, Karin Kroboth, Jonathan Hollick, Daniella Zheleva, Sheelagh Frame, David Blake. The novel PLK1 inhibitor, CYC140: Identification of pharmacodynamic markers, sensitive target indications and potential combinations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4178. doi:10.1158/1538-7445.AM2017-4178