Wolf in sheep's clothing: Effect of primary lung tumor cells equipped with elevated neuron-like properties on brain metastases formation.

e14009 Background: It is clinically significant to decipher the mechanisms underlying lung cancer-associated brain metastases. However, comparative studies on primary tumors between patients with and without brain metastases failed to unveil such mechanisms. Moreover, the clinical observation that the incidence of brain metastases after resection of the primary tumor was as high in lymph node-negative (non-LNM) patients as in those with lymph node metastases (LNM) challenges our established knowledge that lymph node staging correlates with distant metastases. Here, we hypothesized that tumor cells in non-LNM patients might acquire a unique mechanism to develop brain metastases. Methods: We ran whole-transcriptome sequencing and methylation sequencing on paired primary tumor and brain metastases samples from 15 NSCLC patients. We compared the differentially expressed genes (DEGs) between patients with LNM and non-LNM patients. Results: Pathway enrichment analysis showed that GO and KEGG pathways associated with neuronal transmission and synaptic signaling were upregulated in primary tumors of the non-LNM group vs. that of the LNM group. In contrast, brain metastases revealed an inversed trend of differential expression for these pathways between non-LNM and LNM groups. Exploratory validation at methylation level revealed that high expression of the neuronal transmission-associated gene GABRG3 correlated with hypomethylation of this gene (R=-0.39, p=0. 042), responsive to increased expression of GABRG3 in brain metastases. Brain metastases expressed higher neuronal transmission-related signatures than paired primary tumors. Intriguingly, this upregulation of tumor-neuron interactions was more pronounced in patients with lymph node metastases, suggesting that i) lymph node metastases might aid primary tumor to develop brain metastases by promoting the adaptation of tumor cells to the brain microenvironment, while ii) non-LNM patients already acquired neuron-like traits at primary sites, heralding the potential of brain metastases. Conclusions: The hypothetical mechanism of lymph node-negative lung cancer developing brain metastases might be that these tumor cells acquired properties of brain cells as early as in primary sites, masking themselves as ‘sheep’ to communicate with the host’s brain cells, and eventually unmasked as ‘wolf’: brain metastases. Further functional studies are warranted to validate this hypothesis.