SYNTHETIC DOSAGE LETHAL INTERACTIONS OF POLO-LIKE KINASE 1 AND THEIR APPLICATION IN CANCER THERAPEUTICS
Targeted therapies are crucial for personalizing cancer treatment, but tumour heterogeneity presents a challenge in the identification of effective targets. Polo-like kinase 1 is overexpressed near ubiquitously across cancer types and dysregulation of polo-like kinase 1 is closely tied to chromosomal instability and tumour heterogeneity. Despite promising pre-clinical studies, clinical trials of polo-like kinase 1 inhibitors as cancer drugs have generally displayed poor response or adverse side-effects leading to trial termination. Genetic interactions, such as synthetic dosage lethality can overcome these issues and identify targets that kill only tumour cells that overexpress polo-like kinase 1. A genome-wide shRNA screen identified 960 synthetic dosage lethal interactions in an inducible polo-like kinase 1 model cell line. Computational prioritization using a combination of available databases with data on patient tumour gene expression and survival and gene essentiality in cell lines narrowed the list of polo-like kinase 1 synthetic dosage lethal hits to 105. These 105 genes were extensively experimental validated by using a robust set of different techniques. Specifically, an in vivo CRISPR pooled screen and matching in vitro CRISPR arrayed screen in a patient-derived xenograft model of triple negative breast cancer was used and found 65 genes that were essential in this model of polo-like kinase 1 overexpression. Further testing of these 65 polo-like kinase 1 synthetic dosage lethal hits in a variety of polo-like kinase 1-overexpressing cell line types with siRNA and non-malignant cell line controls found 5 synthetic dosage lethal hits in breast cancer, 4 in pancreatic cancer, and 13 in prostate cancer. Characterization of two of the validated targets, KIF5B and PPP2R5D, showed that the interactions of these two genes can also be modelled using chemical inhibition rather than genetic inhibition. KIF5B and other kinesin proteins may underly a role of polo-like kinase 1 in centrosome clustering and PPP2R5D as part of the protein phosphatase 2A complex works with polo-like kinase 1 to maintain chromosome segregation, which may be exploited as a therapeutic approach. The highly validated set of therapeutic targets in this work provide potential for identification of compounds for pre-clinical studies for a variety of solid tumours in the context of polo-like kinase 1 overexpression and set the stage for future successful application.
Polo-like kinase 1, synthetic dosage lethality, chromosomal instability, tumour heterogeneity
Doctor of Philosophy (Ph.D.)