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Thesis Format



Master of Science


Anatomy and Cell Biology


Parsyan, Armen

2nd Supervisor

Allan, Alison L.



Breast cancer is a leading cause of death in women and development of new treatments is essential. Polo-like Kinase 4 (PLK4) controls centriole duplication and its inhibition by CFI-400945 induces genomic instability and aneuploidy. Radiation therapy (RT) also induces aneuploidy leading to cell death, although development of radioresistance is common. We hypothesized that CFI-400945 and RT act synergistically in breast cancer. Colony formation assays identified synergistic anticancer effects of CFI-400945 and RT, with combinatorial effects also observed for RT with either siRNA inhibition of PLK4 or with the PLK4 inhibitor Centrinone B. This suggests that the antiproliferative effect of these combinations are, at least partly, mediated through PLK4. Immunocytochemistry for Centrin showed significant overamplification of centrioles in combination compared to single agent treatment, suggesting a possible combined mechanism of action. These results support further translational studies of CFI-400945 and RT as a combination treatment to improve breast cancer outcomes.

Summary for Lay Audience

Despite recent advances in breast cancer diagnostics and treatment, poor outcomes are still frequently observed once cancer has spread, or metastasized, to distant organs. Developing new therapeutic strategies to treat advanced or metastatic disease is therefore of significant importance. A promising anti-breast cancer drug called CFI-400945 has been developed to target a protein called Polo-Like Kinase 4 (PLK4) that is involved in the regulation of cancer growth. This project investigated CFI-400945 as a combination therapy with radiation therapy in an effort to develop novel and more effective treatment strategies. We used both breast cancer cell lines and patient-derived organoids, the latter of which are clinically relevant models developed from individual breast cancer patients. We found that CFI-400945 and radiation had a much greater anticancer effect when used as a combined treatment versus individually, regardless of the various sequencing of drug and radiation treatments. CFI-400945 predominantly acts by inhibition of PLK4, but can also inhibit other proteins, such as Aurora Kinase B. By comparing results of combining CFI-400945 with radiation to combinations with other inhibitors of PLK4 or other proteins, we identified that the combination effect of CFI-400945 and radiation is due, at least partially, to the PLK4 inhibition effect, though other inhibitory effects could also be involved, including targeting of Aurora Kinase B. To examine the anticancer mechanisms of the combination of CFI-400945 and radiation, we investigated the cell machinery needed for division and tumour growth. We found that the cells treated with CFI-400945 or radiation individually had amplified centrioles (needed for proper cell division), and that this was further increased when the treatments were used in combination. By enhancing this overamplification, cell division occurred abnormally in cancer cells leading to cell death. Future studies are aimed at delving into these findings further. The results of these studies will also support the development of clinical trials and eventual clinical use of this combination to improve outcomes in breast cancer patients.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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