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S. Kako
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MINI 09 - Drug Resistance (ID 107)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:L. Villaruz, J. Minna
- Coordinates: 9/07/2015, 16:45 - 18:15, 205+207
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MINI09.11 - Adaptor Re-Programming and Acquired Resistance in RET-Fusion Positive NSCLC (ID 2891)
17:45 - 17:50 | Author(s): S. Kako
- Abstract
- Presentation
Background:
RET gene fusions were identified as a novel oncogenic driver of ~1-2% of non-small cell lung cancer (NSCLC) patients and clinical trials investigating the use RET TKI therapy are underway. Like all NSCLC patients treated with TKI therapies, it is expected that drug resistance will emerge in this patient population. The mechanisms that drive acquired resistance to RET TKI therapy are still unknown. The objective of this study is to advance current understanding of RET signaling in NSCLC and to identify the cellular mechanisms of acquired RET TKI resistance that will eventually emerge in RET fusion positive NSCLC patients by using in vitro models of drug resistance.
Methods:
The LC-2/ad is a lung adenocarcinoma cell line that harbors the CCDC6-RET fusion. We created three distinct ponatinib resistant (PR) LC-2/ad cell lines (PR1, PR2, PR3) derived from three different dose-escalation strategies. RET break-apart fluorescence in situ hybridization (FISH) was performed on the parental LC-2/ad and PR-derivatives. Interactions between the RET kinase domain and known adaptor signaling molecules were assessed via proximity ligation assay (PLA) in parental LC-2/ad cells and resistant lines. Formation of RET-adaptor signaling complexes were confirmed via immunoprecipitation and western blot analysis. Next-generation RNA sequencing in conjunction with a high-throughput small molecule inhibitor screen were performed to elucidate the signaling pathways that drive resistance to RET-inhibition. Pathways and candidate molecules identified by these screens were validated using siRNA knockdown and pharmacologic inhibition in the context of a cell-proliferation MTS assay. Western blot analysis was utilized to identify the downstream signaling programs responsible for proliferation and survival in the RET-inhibition resistant cell lines.
Results:
MTS cell proliferation assay confirmed that all three ponatinib resistant cell lines are significantly less sensitive to ponatinib than parental LC-2/ad cells. RET FISH analysis demonstrated that the CCDC6-RET gene was retained in the PR1 and PR2 cell lines, but lost in the PR3 cell line. RT-PCR and western blot analysis confirmed the loss of the CCDC6-RET fusion in the PR3 cell line. DNA sequencing demonstrated no RET kinase domain mutations in either the PR1 or PR2 derivatives. Further, profound changes in the RET-signaling program have emerged in the PR1 and PR2 cell lines. Using a RET-GRB7 PLA, we have demonstrated that PR1 cells no longer form RET-GRB7 signaling complexes, while PR2 cells retain RET-GRB7 complexes even in the presence of ponatinib. Next-generation RNA sequencing of the PR1 cell line revealed an increase in expression of several known EMT markers including caveolin-1, vimentin, and ADAMTS1.
Conclusion:
Like many other targeted therapeutic strategies, resistance to small molecule Ret-inhibition in RET-fusion positive lung cancer cells can be driven by multiple mechanisms. Changes in the RET-adaptor programming appear to mitigate resistance in both the PR1 and PR2 cell lines, suggesting that RET-resistant cells may have successfully undergone an oncogenic switch to rely upon another known oncogenic driver in lieu of the CCDC6-RET fusion. Further, EMT reprogramming of the LC-2/ad cell may have contributed to the resistance phenotype in the PR1 cell line.
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MINI 12 - Biomarkers and Lung Nodule Management (ID 109)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Screening and Early Detection
- Presentations: 1
- Moderators:J.M. Siegfried, H.I. Pass
- Coordinates: 9/07/2015, 16:45 - 18:15, 401-404
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MINI12.02 - Clinical Utility of Chromosomal Aneusomy in High Risk Individuals (ID 1299)
16:50 - 16:55 | Author(s): S. Kako
- Abstract
- Presentation
Background:
In the context of CT screening in current and former smokers at high risk for lung cancer, the false positive rate is high (26% at first NLST screening; 13% with Lung-RADS criteria applied to NLST) and indeterminate nodules are frequently discovered. Noninvasive biomarkers are urgently needed to reduce false positives with screening CT and to improve risk stratification in those with indeterminate nodules. The Colorado (CO) Lung SPORE program performed a retrospective longitudinal evaluation (Pepe Phase 3 validation) to assess the potential of chromosomal aneusomy detected in sputum via fluorescence in situ hybridization (CA-FISH) as a biomarker for early detection in four nested case-control studies. Two of the cohorts (ACRIN/NLST and PLuSS) enrolled current and former smokers to investigate use of low dose CT to diagnose lung cancer. The other two were Colorado cohorts in which pulmonary clinic patients (mostly current and former smokers) were enrolled to investigate biomarkers to predict lung cancer. One of these cohorts (CO High Risk) was a COPD population and the other, still in the accrual phase, comprises patients referred for care of indeterminate lung nodules (CO Nodule).
Methods:
The cohorts were grouped into a Screening cohort (ACRIN/NLST (49 cases, 96 controls) and PLuSS (48 cases, 89 controls)) and a High Risk cohort (CO High Risk (55 cases, 59 controls) and CO Nodule (13 cases, 10 controls)). The CA-FISH assay was a 4-target panel including genomic sequences encompassing the EGFR and MYC genes, and the 5p15 and centromere 6 regions or the FGFR1 and PIK3CA genes. At the subject level, the assay was scored on a 4-category scale representing normal, probably normal, probably abnormal and abnormal. Operating characteristics (with 95% CI) of the assay were estimated for each group of cohorts overall and separately for COPD patients: sensitivity, specificity, likelihood ratio+ (LR+) and likelihood ratio- (LR-).
Results:
Using the cutoff of abnormal vs. not abnormal for CA-FISH, sensitivity and specificity for Screening subjects are 0.20 (0.13, 0.30) and 0.84 (0.78, 0.89), respectively; and for High Risk subjects are 0.67 (0.55, 0.78) and 0.94 (0.85, 0.98), respectively. Likelihood ratios for Screening subjects are LR+: 1.36 (0.81, 2.28) and LR-: 0.93 (0.83, 1.05), and for High Risk subjects are LR+: 11.66 (4.44, 30.63), and LR-: 0.34 (0.24, 0.48). Similar results were observed when only COPD subjects were analyzed.
Conclusion:
The high LR+ of sputum CA-FISH indicates that this noninvasive biomarker could be a clinically useful adjunct to CT among patients in high risk settings. Whether this same high level of LR+ will be reproducible in patients at high risk because of their indeterminate nodules remains to be seen. If so, a hypothetical patient with indeterminate nodules and a pre-test (CA-FISH) lung cancer risk of 20% would have a post-test probability of lung cancer of 78% if the CA-FISH test were positive. In the screening setting, however, the low LR+ of CA-FISH limits its clinical utility. Prospective assessment of sputum CA-FISH is ongoing in the Nodule Cohort of the CO Lung SPORE.
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