Abstract 2486: Tumor hypoxia induces DNA repair vulnerabilities through contextual loss of heterozygosity
Bibliographic record
Abstract
Abstract Introduction: Intratumoural hypoxia leads to decreased expression in DNA damage response (DDR) and repair pathways. Given the ‘two-hit’ model for loss of gene function, we hypothesize that hypoxia-mediated down-regulation of gene expression and function, coupled with an already inactive allele contributes to an exploitable contextual ‘loss-of- heterozygosity’ phenotype. Method: To interrogate this relationship, isogenic DLD-1 cells heterozygous and homozygous null for BRCA2, were placed under normoxic (21%) or hypoxic (0.2%) conditions for 72 hours. Hypoxia-mediated changes in DDR response and DNA repair were evaluated by cell proliferation, cell cycle analysis, western blots, qPCR, immunofluorescence, clonogenic assays and functional repair assays. Results: No differences in proliferation and cell survival were observed between oxic and hypoxic cells (72 hours - 0.2% O2). Under chronic hypoxic conditions, confirmed by the up-regulation of VEGF and HIF1a, mRNA and protein expression of key homologous recombination (HR) genes (BRCA1, BRCA2, RAD51) were down-regulated. Functionally, BRCA2-/- null cells proved unable to recruit Rad51 foci and were profoundly sensitivity to PARP inhibition. Conversely, heterozygote BRCA2+/- cells retained the ability to recruit Rad51 foci under both oxic and hypoxic conditions. However, exposure to chronic hypoxia resulted in a reduction of foci formation. Chronically hypoxic BRCA2+/- cells exhibited a 30-40% increase in sensitivity to PARP inhibition compared to their oxic counterparts. Preliminary data shows a similar synthetically lethal relationship in genetic (BRCA2-/- ) and tumor microenvironment induced (BRCA2+/-) HR deficient cells, when challenged with DNA damage response (DDR) kinase inhibitors ATRi and DNAPKi. Conclusions: Herein, we demonstrate a novel mechanism of contextual ‘loss-of heterozygosity’, which marries the tumour microenvironment and innate genetic alterations. The resultant increased sensitivity to DDR kinase inhibitors and PARPi highlights the therapeutic significance of this phenomenon. Citation Format: Osman Mahamud, Melvin Chua, Winnie Lo, Gaetano Zafarana, Robert Bristow. Tumor hypoxia induces DNA repair vulnerabilities through contextual loss of heterozygosity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2486. doi:10.1158/1538-7445.AM2017-2486
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".