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 fre

Targeting DNA Replication before it Starts: Cdc7 as a Therapeutic Target in p53-Mutant Breast Cancers

Treatment options for triple-receptor negative (ER−/PR−/Her2−) and Her2-overexpressing (ER−/PR−/Her2+) breast cancers with acquired or de novo resistance are limited, and metastatic disease remains incurable. Targeting of growth signaling networks is often constrained by pathway redundancy or growth-independent cancer cell cycles. The cell-cycle protein Cdc7 regulates S phase by promoting DNA replication. This essential kinase acts as a convergence point for upstream growth signaling pathways and is therefore an attractive therapeutic target. We show that increased Cdc7 expression during mammary tumorigenesis is linked to Her2-overexpressing and triple-negative subtypes, accelerated cell cycle progression (P < 0.001), arrested tumor differentiation (P < 0.001), genomic instability (P = 0.019), increasing NPI score (P < 0.001), and reduced disease-free survival (HR = 1.98 [95% CI: 1.27–3.10]; P = 0.003), thus implicating its deregulation in the development of aggressive disease. Targeting Cdc7 with RNAi, we demonstrate that p53-mutant Her2-overexpressing and triple-negative breast cancer cell lines undergo an abortive S phase and apoptotic cell death due to loss of a p53-dependent Cdc7-inhibition checkpoint. In contrast, untransformed breast epithelial cells arrest in G1, remain viable, and are able to resume cell proliferation on recovery of Cdc7 kinase activity. Thus, Cdc7 appears to represent a potent and highly specific anticancer target in Her2-overexpressing and triple-negative breast cancers. Emerging Cdc7 kinase inhibitors may therefore significantly broaden the therapeutic armamentarium for treatment of the aggressive p53-mutant breast cancer subtypes identified in this study