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L.F. Petersen
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MINI 35 - Biology (ID 161)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:T.A. Boyle, M.G. Kris
- Coordinates: 9/09/2015, 18:30 - 20:00, Mile High Ballroom 2c-3c
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MINI35.07 - ATM Mutations in Cancer Cell Lines Predict Higher Mutation Rates and Genetic Instability (ID 1704)
18:30 - 20:00 | Author(s): L.F. Petersen
- Abstract
- Presentation
Background:
Ataxia telangiectasia-mutated (ATM) is a critical first responder in the cell to DNA damage. Individuals lacking ATM are extremely sensitive to DNA-damaging ionizing radiation, and are predisposed to develop cancers. The mechanism for ATM dysfunction in A-T patients, or cancer patients that are ATM-deficient, is unknown. ATM has been sequenced in lung cancer patient samples, but no specific mutation hotspots have been linked with disease development, despite ATM being one of the most mutated genes in lung cancer. Our own quantitative analysis of ATM protein levels in patient samples suggests that expression is lost in 20-25% of cases and that this loss correlates with poor overall survival and increased response to adjuvant chemotherapy treatments. We believe that this may be the result of increased genomic instability within the cancer cells caused by a lack of adequate DNA repair. Given that ATM-deficient cancer cells may have higher genetic instability, and that ATM is so highly mutated in lung cancer, we sought to quantify the relationship between ATM mutations and genomic instability, as measured by total somatic mutations.
Methods:
Using data available from the Broad Institute’s Cancer Cell Line Encyclopedia (CCLE), we correlated mutations in ATM and other genes involved with the DNA repair response with the total number of mutations annotated in ~900 cancer cell lines. We also analyzed total mutations per cell line against the functional impact score of single nucleotide variations (SNVs) within ATM. To determine the clinical relevance of the cancer cell line observations, we partnered with the BC Genome Sciences Centre (BCGSC) to perform similar analyses on ~100 whole-genome-sequenced patient samples.
Results:
We show that in cell lines across all cancer types, mutations in ATM correlate with a significantly higher number of total mutations. When analyzed by site of origin, the greatest differences in total mutations were found in lung, breast, intestinal, and esophageal cancer cells. We examined additional genes associated with the DNA-repair response, including direct response genes (i.e. ATR, BRCA1&2) and downstream targets (i.e. p53). Only mutations in the direct response genes appeared to associate with total mutations, whereas p53 – while more commonly mutated – did not correlate with higher mutations. In 10 lung cancer patients, one had a truncating mutation and had the second highest number of somatic mutations, and highest among non-smokers.
Conclusion:
We have identified a potential relationship between ATM mutation and total somatic mutations in cancer cell lines and patient tumour genomes, which may be indicative of overall genetic instability in these samples. Analysis of the ATM mutations in cell lines and patient samples clearly shows that there are no specific hotspots for mutation in ATM that correlate with increased total mutations. Thus screening for ATM mutations alone may not be sufficient to indicate loss of function or instability. However, this data may prove useful in developing panels of targets to screen as mutation hotspots of instability, and ultimately to help identify patients that may benefit from targeted or modified therapy options based on ATM-deficiency or higher genetic instability.
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P2.04 - Poster Session/ Biology, Pathology, and Molecular Testing (ID 234)
- Event: WCLC 2015
- Type: Poster
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:
- Coordinates: 9/08/2015, 09:30 - 17:00, Exhibit Hall (Hall B+C)
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P2.04-100 - Platin-Induced ATM Activation in Non-Small Cell Lung Cancer (ID 2984)
09:30 - 17:00 | Author(s): L.F. Petersen
- Abstract
Background:
Platinum based antineoplastic therapies (platins) are a first line treatment prescribed for non-small cell lung cancer (NSCLC), but unfortunately have many adverse side effects. Cytotoxicity is caused by the generation of DNA adducts, which create single and double stranded DNA breaks and stimulate DNA damage response pathways. A key mediator of this response is ataxia telangiectasia mutated (ATM), which is responsible for the activation of several downstream targets involved in DNA repair, cell cycle arrest, and apoptosis. Of great interest are platin sensitivity markers that help identify patients more susceptible to these treatments. Previous research on predictive markers of platin sensitivity has focused on ERCC1 and RRM1 with varying levels of success. Our lab has shown that cells lacking ATM have increased sensitivity to some platin therapies. We hypothesize that ATM signaling may be invoked by platin exposure and that tumours deficient in ATM may have innate sensitivity to platin therapies. Here we assess the molecular action of ATM in response to different platin therapies to determine whether low activity in ATM-deficient cells is predictive of platin sensitivity.
Methods:
Six NSCLC cell lines were assessed for the presence of ATM by western blot. Those cell lines for which ATM was not found were deemed ATM-deficient. Cell lines were treated with varying concentrations of platinum based therapies (cisplatin, carboplatin and oxaloplatin) for two hours or overnight. ATM activation was determined by assessment of phosphorylated-ATM protein levels using western blots. Additionally, downstream targets of ATM were probed to determine ATM pathway activation.
Results:
NSCLC cell lines H226, H460 and H522 were found to be ATM-proficient whereas cell lines H23, H1373 and H1395 were found to be ATM-deficient. ATM-proficient cell lines demonstrated an increased level of phosphorylated-ATM in response to treatments with cisplatin, carboplatin, and oxaliplatin. In addition, downstream targets of ATM also showed increased levels of activation when compared to non-treated controls. ATM-deficient cell lines showed no increased levels of phosphorylated-ATM however, downstream targets of ATM showed some activation in ATM-deficient cell lines.
Conclusion:
We have shown that cisplatin, carboplatin and oxaliplatin treatments induce the phosphorylation of ATM, a prominent regulator of the DNA damage response. In addition, the ATM-deficient cell lines showed reduced activation of ATM to platin treatments. It is clear that platin exposure induced an ATM mediated signalling response, however its predictive capabilities of platin sensitivity is still unclear. Activation of DNA repair by platins may leave ATM-deficient tumours at a disadvantage when mounting repair responses to these treatments. This data suggests that individuals with low or non-functioning ATM may be candidates for precision low-dose therapies that exploit this deficiency.
