The investigation of circulating biomarkers and potential mechanisms of resistance in the ATR/CHK1 signalling pathway in response to CHK1 inhibitor therapy

Abstract

The DNA damage response is a network of cell checkpoints leading to cellular repair and genome integrity when DNA insults have occurred. In cancers, enhanced tumour replication stress and genomic instability along with mutations in oncogenes and tumour suppressor genes can lead to disruption of the DNA damage response. Tumour survival becomes dependant on critical checkpoint controls. Drugs to target intact pathways, such as CHK1 inhibitors are therefore desirable and are being evaluated in clinical trials as prospective anticancer therapies. Cancer treatments have moved to a personalised approach based on tumour profiling and circulating biomarkers, such as circulating cell free DNA to predict patient response to targeted treatments. The mechanisms underpinning sensitivity and resistance to CHK1 inhibitor treatment are still unclear. This project explores three distinct strands of research to examine both primary and acquired mechanisms of CHK1i resistance. Firstly, investigating gene and protein expression changes in Eμ-Myc mouse models of B-Cell lymphoma. Wild type Eμ-Myc mice are sensitive to CHK1i treatment, however by contrast Eμ-Myc NF-κB c-Rel -/- and RelA T505A lymphomas are CHK1i resistant. Secondly, the generation and characterisation of U2OS osteosarcoma cells with acquired CHK1i resistance. Lastly, investigating if DNA damage response mutations can be isolated from patient cfDNA samples on a CHK1 inhibitor clinical trial. Results have shown that resistance to CHK1 is complex and that there are multiple resistance mechanisms in place. The Eμ-Myc NF-κB c-Rel -/- mice completely downregulate the DNA damage response and this pattern is shared with some resistant cell lines, but alternative mechanisms developed in other models. DDR mutations can be detected and tracked in cfDNA samples and show a large degree of heterogeneity between patients. This study highlights the importance of the ATR/CHK1 DNA damage checkpoint and how drug resistance mechanisms can vary between diverse tumour mutational profiles.