37. Epigenetic reprogramming of brain development pathways during non-small cell lung cancer metastasis to brain

Non-small cell lung cancer (NSCLC) is one of the most common and deadliest cancers, with roughly half of all patients initially presenting with both primary and metastatic disease. While the major events in the metastatic cascade have been identified, a mechanistic understanding of how NSCLC routinely, successfully colonizes the brain is largely unknown. To better understand this process, we profiled a combination of genomic, transcriptomic, and methylomic landscapes of 45 paired NSCLC primary and brain metastasis samples. 75 genes displayed recurrent metastasis enriched variants, largely implicated in focal adhesion and extracellular matrix receptor interactions. Variant allele frequencies over a wide range of epigenetic regulators displayed an increase in metastases, suggesting that epigenetic misregulation may be selected for and possibly contribute to NSCLC metastasis to brain. Consistent with these observations, we observed widespread changes in DNA methylation throughout disease progression, many found within brain-specific active enhancers and correlated with increased nearby gene expression. The greatest recurrent methylation changes during metastatic progression occurred over a subset of DNA methylation valleys (DMVs) enriched for H3K9me3 and bivalent marks H3K27me3 and H3K4me1 in normal lung. Mapping EZH2, the catalytic subunit of polycomb repressive complex 2 (PCR2), binding locations in H1299, a lymph node-derived lung cancer cell line, revealed a pervasive loss of EZH2 binding within DMVs accompanied by an increase in DNA methylation, exemplifying epigenetic switching. The vast majority of these DMR-associated DMVs harbor developmental genes, suggesting that altered epigenetic regulation of developmentally important genes may confer a selective advantage during metastatic progression.