Abstract PO-032: Mechanistic studies of hypoxia as a driver of genomic instability in prostate cancer
Authors: Ashton Jack , Rebello Richard , Lyons Stephen , Bristow Robert G. 
Published: April 2021

Abstract
Prostate cancer (PCa) is the 2nd most prevalent cancer in men and has poor patient outcome upon transition from localized disease to the castration-resistant and metastatic state. Numerous studies have indicated intratumoral hypoxia as a key driver in disease progression across multiple cancers and in prostate cancer. Hypoxia is associated with local recurrence, metastatic capacity, androgen independence and neuroendocrine differentiation (Ashton and Bristow, Brit.J.Rad, 2020). Crucially, among localized PCa patients, hypoxia and genomic instability have an independent and additive effect on biochemical relapse and bioinformatic studies suggest that hypoxia co-segregates mutation signatures representing defects in homologous recombination (HR) and mismatch repair (MMR) DNA repair pathways (Bhandari et al., Nat Comms, 2020). In order to investigate whether hypoxia directly drives genome instability in prostate cancer, mechanistic studies using hTERT-immortalized, primary prostate epithelial cells isogenic for c-MYC, BRCA2, or TP53/RB (SV40-transduced as PNT2 cells) were studied as to the relationship between hypoxia, inherent versus acquired genetic instability, and DNA repair capacity in-vitro and in-situ. Chronic hypoxia (20 generation doublings at 0.2% O2) was sufficient to drive increased copy number alterations (CNAs; based on low-pass whole genome sequencing - WGS) in selected clones by up to 30% in TP53/RB null cells, but not hTERT immortalized models. This finding is now being quantitated within a clonal evolution model and genotype-phenotype associations are being validated using functional transformation and invasion assays. Associated mechanistic studies have revealed that the hypoxic suppression of homologous recombination (HR) factor transcript and protein abundance (e.g up to ~60% reduction of RAD51/BRCA2 in PC3, DU145 and PNT2 cells) and associated with reduced RAD51 nuclear foci induction or defective DR-GFP reconstitution, is highly-dependent on cell density. This suggests that reduced HR and MMR repair capacity may exist in situ within hypoxic tumor oxygen gradients with close cell-cell interactions; in situ studies of RAD51 and other DNA repair proteins across hypoxic gradients in primary human tumors will be presented. These translational studies will accompany the HYPROGEN trial in Manchester in which patients who present with treatment-naïve M1 bone metastatic disease are given oral pimonidazole prior to prostate and bone metastasis biopsies to directly study genomic instability (using WGS) and hypoxia (pimonidazole staining and RNA hypoxic signatures) to understand these relationships in paired primary-metastatic samples. This data will provide a mechanistic basis for the adverse prognosis seen in patients whose tumors have both hypoxia and genome instability, as well as fresh evidence for stratification and treatment intensification of localized PCa patients with hypoxic tumors. (Supported by a core grant from Cancer Research UK to RGB)
Citation Format: Jack Ashton, Richard Rebello, Stephen Lyons, Robert G. Bristow. Mechanistic studies of hypoxia as a driver of genomic instability in prostate cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-032.