There is an urgent need to nominate biomarkers that are likely to predict the efficacy of radiotherapy and accelerate their clinical translation. Efforts thus far have been limited in large part because the genetic features regulating tumor cell survival and their frequency across and within individual cancer types had not been studied on a large-scale. Our group completed the largest profiling effort of survival after radiation in cancer cell lines, comprising a diverse collection of 533 genetically annotated tumor cell lines from 26 cancer types. To complement this work, we recently initiated the systematic profiling of >1000 genetic variants that could potentially contribute to the resistance of cancer cells to radiation. We combined results from our profiling efforts to identify features that predict the resistance of lung cancer cells to radiation. The objective in this investigation is to advance the clinical translation of two of the most important regulators of radiation resistance in lung cancer, Nrf2 and Braf. The Nrf2 pathway is genetically altered in ~28% of patients with non-small cell lung cancer (NSCLC) and cells with mutations in NFE2L2 or KEAP1 are the most highly correlated with resistance to radiation. To identify genetic dependencies of Nrf2-active tumors, we used computational and experimental approaches to demonstrate the frequent co-occurrence between Nrf2 and phosphoinositide 3-kinase (PI3K) alteration in NSCLCs. Using genetic and chemical means we show that antagonizing the catalytic subunit of PI3K, p110? (encoded by PIK3CA), decreases Nrf2 activity and reverses radiation resistance driven by this pathway. These results provide the rationale to advance a radiosensitization strategy for patients with Nrf2-active NSCLC by targeting PI3K. Our profiling efforts also demonstrate a critical role for BRAF, which is genetically altered in ~7% of patients with NSCLC, in the resistance of lung cancer cells to radiation. We show, for the first time, that BRAF kinase domain mutations confer resistance to radiation in lung cancers and that they, unlike Nrf2 pathway alterations, are almost invariably a minor component of the tumor (i.e. they are subclonal). We use mathematical and experimental models to show that clonal architecture has significant implications for the likelihood of response to targeted therapies and radiation. Together, these results provide a compelling rationale to examine the role of Nrf2 and Braf alterations in predicting outcomes after radiotherapy and advance a genomically-guided radiosensitization strategy for patients with these tumors. If these hypotheses are correct, our results will demonstrate that radiotherapeutic sensitizers can be selected based on both the identity and type (clonal v. subclonal) of genetic alterations identified in a patient's cancer, prompting an evolution in the use of radiation from a generic approach to one that is guided by the genetic composition of individual tumors.

Public Health Relevance

Radiotherapy regimens continue to be delivered using a ?one-size-fits-all? paradigm and therefore do not currently take into account the genetic content of individual tumors. Our results indicate the primacy of Nrf2 and Braf as regulators of radiation resistance in non-small cell lung cancer. The deliverables of this proposal include new biomarkers calibrated on the basis of radiotherapeutic efficacy and new drug-radiation therapeutic strategies that more precisely and effectively target the most resistant lung tumors to radiation.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Method to Extend Research in Time (MERIT) Award (R37)
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Radiation Therapeutics and Biology Study Section (RTB)
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Prasanna, Pat G
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Cleveland Clinic Lerner
Internal Medicine/Medicine
Schools of Medicine
United States
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