Circulating Micro-RNAs as Biomarkers for Thoracic Radiation Therapy in Lung Cancer

Abstract

Risk of normal tissues toxicity limits the amount of thoracic radiation therapy that can be routinely prescribed for the treatment of non-small cell lung cancer (NSCLC). An early biomarker of response to thoracic radiation may provide a way to predict eventual toxicities during the multi-week treatment regimen. This enables dose adjustment before the symptomatic onset of late effects, such as radiation pneumonitis and esophagitis. Micro-RNAs (miRNAs) are small, non-coding RNAs that regulate gene expression by decreasing the translation of messenger RNAs. miRNAs constitute a major fraction of small RNAs reproducibly found in circulation, in part due to their protective encapsulation within exosomes. They are therefore attractive candidates as serological biomarkers. In this study, we performed miRNA profiling of the blood of 5 NSCLC patients at 5 dose-points during thoracic RT and found 10 miRNAs that correlated well with total radiation dose as well as other common dosimetric parameters. We then assessed these 10 miRNAs in samples from a separate cohort of 21 NSCLC patients receiving RT and identified miR-29a-3p and miR-150-5p as potential, reproducible biomarkers that decreased in circulation with increasing radiation dose. We also conducted in-vitro experiments to measure the expression levels of these miRNAs intracellularly and within exosomes in three NSCLC cell lines and two lung bronchoepithelial and fibroblast lines. The exosomal expression of miR-29a-3p and miR-150-5p decreased with radiation. However, this was concomitant with an increase in intracellular levels, suggesting that exosomal export of these miRNAs may be downregulated in NSCLC and stromal cells as a response to radiation. One may therefore hypothesize that outlier trends in levels of circulating miR-29a-3p and miR-150-5p may predict unexpected responses to radiation therapy, such as toxicity.