PLK4 inhibition as a strategy for non-small cell lung cancer radiosensitization

Background/Purpose: Lung cancer remains the leading cause of cancer-related death. Concurrent chemoradiation is the standard of care for locally advanced non-small cell lung cancer (NSCLC). Despite advancements in treatment, local control remains an issue and survival is suboptimal, highlighting the need for novel therapeutic approaches. Polo-like kinase 4 (PLK4) is a serine/threonine kinase that controls centriole duplication. PLK4 is highly expressed in multiple malignancies including lung cancer. CFI-400945 is a specific PLK4 inhibitor currently undergoing clinical trial evaluation. As radiation causes cell death primarily via a mitotic death, we hypothesized that disruption of the mitotic machinery by inhibition of PLK4 would enhance the effects of radiation. Methods: The effects of CFI-400945 on cell survival and radiation sensitivity were examined using the clonogenic survival assay in two KRAS-mutant lung cancer cell lines (H460 and A549). Confocal microscopy was utilized to determine the effects of PLK4 inhibition on radiation-induced mitotic catastrophe (defined as the presence of 2 or more distinct nuclear lobes within a single cell). Cell cycle distribution by flow cytometry was determined after treatment with CFI-400945 and radiation. Results: Exposure of H460 and A549 lung cancer cell lines to 10nM CFI-400945 for 48h reduced clonogenic survival to 63.9% and 83.1% respectively. CFI-400945 treatment of H460 and A549 cells resulted in radiosensitization of both cell lines with dose enhancement factors (DEF) of 1.60 and 1.31. To understand the mechanism of enhanced radiosensitivity with CFI-400945 treatment the effects on radiation-induced mitotic catastrophe were determined. In both H460 and A549 cells the combination of radiation and PLK4 inhibition enhanced the proportion of cells undergoing mitotic catastrophe. The combination of CFI-400945 and radiation resulted in increased G2/M arrest and appearance of >4N populations by flow cytometric analysis when compared to drug or radiation treatment alone. Conclusion: PLK4 inhibition with CFI-400945 enhances the radiosensitivity of lung cancer cell lines via mitotic catastrophe and G2/M arrest and these data support additional pre-clinical testing. Citation Format: Thomas J. Hayman, Mark R. Bray, Jacqueline M. Mason, Tak W. Mak, Joseph N. Contessa. PLK4 inhibition as a strategy for non-small cell lung cancer radiosensitization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3935.