Sebastian, Nikhil

AbstractIntroductionIncreasingly, early‐stage non–small cell lung cancer (NSCLC) is treated with stereotactic body radiation therapy (SBRT). Although treatment is generally effective, a small subset of tumors will recur because of radioresistance. Preclinical studies suggested PI3K‐AKT‐mTOR activation mediates radioresistance. This study sought to validate this finding in tumor samples from patients who underwent SBRT for NSCLC.MethodsPatients with T1‐3N0 NSCLC treated with SBRT at our institution were included. Total RNA of formalin‐fixed paraffin‐embedded tumor biopsy specimens (pretherapy) was isolated and analyzed using the Clariom D assay. Risk scores from a PI3K activity signature and four published NSCLC signatures were generated and dichotomized by the median. Kaplan–Meier curves and Cox regressions were used to analyze their association with recurrence and overall survival (OS). The PI3K signature was also tested in a data set of resected NSCLC for additional validation.ResultsA total of 92 patients were included, with a median follow‐up of 18.3 months for living patients. There was no association of any of the four published gene expression signatures with recurrence or OS. However, high PI3K risk score was associated with higher local recurrence (hazard ratio [HR], 11.72; 95% CI, 1.40–98.0; p = .023) and worse disease‐free survival (DFS) (HR, 3.98; 95% CI, 1.57–10.09; p = .0035), but not OS (p = .49), regional recurrence (p = .15), or distant recurrence (p = .85). In the resected NSCLC data set (n = 361), high PI3K risk score was associated with decreased OS (log‐rank p = .013) but not DFS (p = 0.54).ConclusionsThis study validates that higher PI3K activity, measured by gene expression, is associated with local recurrence and worse DFS in early‐stage NSCLC patients treated with SBRT. This may be useful in prognostication and/or tailoring treatment, and merits further validation.

Background: Optimal patient selection for radiotherapy in pancreatic ductal adenocarcinoma (PDAC) is unestablished. Molecular profiling may select patients at high risk for locoregional recurrence (LRR) who would benefit from radiation. Methods: We included resectable pancreatic cancer (R-PDAC) patients, divided into training and validation cohorts, treated among three institutions with surgery and adjuvant chemotherapy, and borderline resectable or locally advanced pancreatic cancer (BR/LA-PDAC) patients treated with chemotherapy with or without radiation at the primary study institution. We isolated RNA from R-PDAC surgical specimens. Using NanoString, we identified miRNAs differentially expressed between normal and malignant pancreatic tissue. ElasticNet regression identified two miRNAs most predictive of LRR in the training cohort, miR-181b/d and miR-575, which were used to generate a risk score (RS). We evaluated the association of the median-dichotomized RS with recurrence and overall survival (OS). Results: We identified 183 R-PDAC and 77 BR/LA-PDAC patients with median follow up of 37 months treated between 2001 and 2014. On multivariable analysis of the R-PDAC training cohort (n = 90), RS was associated with worse LRR (HR = 1.34; 95%CI 1.27–11.38; p = 0.017) and OS (HR = 2.89; 95%CI 1.10–4.76; p = 0.027). In the R-PDAC validation cohort, RS was associated with worse LRR (HR = 2.39; 95%CI 1.03–5.54; p = 0.042), but not OS (p = 0.087). For BR/LA-PDAC, RS was associated with worse LRR (HR = 2.71; 95%CI 1.14–6.48; p = 0.025), DR (HR = 1.93; 95%CI 1.10–3.38; p = 0.022), and OS (HR = 1.97; 95%CI 1.17–3.34; p = 0.011). Additionally, after stratifying by RS and receipt of radiation in BR/LA-PDAC patients, high RS patients who did not receive radiation had worse LRR (p = 0.018), DR (p = 0.006), and OS (p < 0.001) compared to patients with either low RS or patients who received radiation, irrespective of RS. Conclusions: RS predicted worse LRR and OS in R-PDAC and worse LRR, DR, and OS in BR/LA-PDAC. This may select patients who would benefit from radiation and should be validated prospectively.

Abstract KRAS-activating mutations are oncogenic drivers and are correlated with radioresistance of multiple cancers, including colorectal cancer, but the underlying precise molecular mechanisms remain elusive. Herein we model the radiosensitivity of isogenic HCT116 and SW48 colorectal cancer cell lines bearing wild-type or various mutant KRAS isoforms. We demonstrate that KRAS mutations indeed lead to radioresistance accompanied by reduced radiotherapy-induced mitotic catastrophe and an accelerated release from G2/M arrest. Moreover, KRAS mutations result in increased DNA damage response and upregulation of 53BP1 with associated increased non-homologous end-joining (NHEJ) repair. Remarkably, KRAS mutations lead to activation of NRF2 antioxidant signaling to increase 53BP1 gene transcription. Furthermore, genetic silencing or pharmacological inhibition of KRAS, NRF2 or 53BP1 attenuates KRAS mutation-induced radioresistance, especially in G1 phase cells. These findings reveal an important role for a KRAS-induced NRF2-53BP1 axis in the DNA repair and survival of KRAS-mutant tumor cells after radiotherapy, and indicate that targeting NRF2, 53BP1 or NHEJ may represent novel strategies to selectively abrogate KRAS mutation-mediated radioresistance.