The DNA Replication Initiation Machinery as a Target for Cancer Diagnosis and Therapy

Cancer is a leading cause of death worldwide. Early, accurate detection of malignancy leads to better treatment decisions and there is consequently an urgent need for new cancer biomarkers. This thesis explores the use of the DNA replication initiation machinery as a target for the development of molecular biomarkers able to provide diagnostic and prognostic information in the clinical setting and to guide treatment decisions. In a large scale multicentre study, the DNA replicative helicase protein Mcm5 is shown to be a sensitive and specific biomarker for bladder cancer detection. Further clinical studies demonstrate that Mcm5 is potentially useful for the detection of prostate and pancreaticobiliary tract cancers. In conjunction with markers of mitotic progression and DNA ploidy status, replication initiation proteins are also shown to be able to provide prognostic information in the context of penile cancer. Mcm5 is a component of the DNA replicative helicase, which is phosphorylated by the cell cycle kinase Cdc7 as a crucial step during DNA replication initiation. The work described here demonstrates that depletion of Cdc7 in a normal human diploid cell line induces a novel origin activation checkpoint at the core of which there are a number of tumour suppressor and proto-oncogene proteins that are frequently lost in cancer cells. Depletion of Cdc7 in p53-mutant breast cancer cells, for example, is shown to result in cancer-cell-specific-killing, while untransformed cells engage a reversible cell cycle arrest. Together these results demonstrate the clinical utility of replication initiation proteins as biomarkers for cancer and identify Cdc7 as an important therapeutic target for cancer therapy.