Rob Bristow - Translational Oncogenomics (based in the Manchester Cancer Research Centre)

Hypoxia-induced Genetic Instability in Prostate Cancer

Control of genome stability requires careful coordination between cell cycle checkpoint control and DNA repair mechanisms. Defects in the repair of DNA double-stranded breaks have been associated with acquiring genetic instability; particularly in genes responsible for homologous recombination (HR) such as BRCA1 and BRCA2. Defects in these genes lead to an increased risk of ovarian and breast cancer in women and prostate cancer in men. BRCA2- associated prostate cancers have a particular poor outcome with more than 50% of men dead at 5 years after local therapy. More recently, other DNA repair gene mutations or dysfunction have been linked to aggressive prostate cancer leading to castrate resistance and the metastatic phenotype.

All solid tumours, including prostate cancer, contain sub-regions of dynamic changes in nutrient and oxygen metabolism. Hypoxia (low oxygen tension) leads to a number of aggressive tumour cell phenotypes and genetic instability, in part, driven by the down regulation of gene expression and translation of HR genes (Bristow and Hill, Nat Rev Can, 2005). This can drive a microenvironment-induced "BRCAness" leading to a contextual synthetic lethality and a way forward using treatments that target HR-defective hypoxic cells. This includes the potential use of the chemotherapy drug, cisplatin, or PARP inhibitors, similar to their use in prostate or other cancers that have genetic defects in BRCA1 or BRCA2 (Luoto et al; Genome Integrity 2013).

Recently, our group, in collaboration with scientists in Melbourne, have used whole genome sequencing (WGS) to explore the genetic defects in the tissues derived from untreated localized prostate cancers that arise in men with familial BRCA2 mutation carrier status (Taylor et al; Nature Comm, Jan 2017; Boutros et al; Nature, 2017) compared to those that arise as sporadic prostate cancers. We observed activation of a number of pathways usually reserved solely for patients that acquire castrate resistance and metastasis during the progression of sporadic cancer including altered beta catenin- WNT signalling, defective mitotic control and DNA repair and altered androgen signalling. Together, these findings suggest that in untreated BRCA2-associated prostate cancers, pathways are already upregulated that herald resistance to hormone therapy and genetic instability. However the additional mechanistic role of hypoxia in the acquisition of these aggressive phenotypes on the background of BRCA1/BRCA2 genetic deficiency is not known (Lalonde et al; Lancet Oncology, 2014; Chan et al; Mol.Can Res; 2014; Chua at al; Eur Urol., 2017).

The project will develop and utilize isogenic defective in BRCA1 and BRCA2 and determine the additional effect of hypoxia on the generation of genetic instability, HR repair and sensitivity to inhibitors of DNA repair machinery including those targeting ATM, ATR and DNA-PKcs using both in vitro and in vivo systems. The effects of hypoxia on genetic instability will be explored using whole genome sequencing approaches and RNA seq. Understanding the mechanism by which hypoxia drives genetic instability in the absence and presnce of underlying DNA repair defects may allow for better patient stratification using precision medicine for optimal prostate cancer treatment.