Targeting wild type NTRK decreases brain metastases of lung cancers non-driven by NTRK fusions
The central nervous system (CNS) is a common site of metastatic spread for both non-small cell and small cell lung cancer, yet the therapeutic strategies to prevent and decrease lung cancer brain metastases remain limited. Tyrosine kinase inhibitors have shown promising results in increasing the overall response in brain metastases, owing to their brain penetrance and increased effectiveness; however, their use is limited to the small group of tumors carrying specific oncogenic drivers. Among these, inhibitors with activity against neurotrophic tyrosine receptor kinases (NTRKs) are showing promising effects in reducing CNS metastases in cancers driven by gene rearrangements of these drugs targets. However, wild-type NTRKs are susceptible to activation by their canonical ligands, which are expressed throughout the brain metastatic niche and can, in a paracrine manner, activate NTRK function in cancer cells. Here we show that NTRKs are expressed in primary tumors, brain metastases, and lung cancer cells with various driver mutations expressing wild-type NTRK2 (WT-TrkB). We demonstrate that WT-TrkB activates downstream signaling and proliferation in response to exogenous BDNF and conditioned media from reactive astrocytes known to secrete BDNF in the brain niche. Importantly, the FDA-approved NTRK inhibitor entrectinib blocked BDNF and astrocyte-induced survival pathways in multiple lung cancer cell lines, decreased their proliferation in vitro, and effectively prevented brain metastatic colonization and progression in vivo without significant effects on extracranial disease. Thus, these studies suggest that brain-dependent activation of NTRK is critical for brain metastases of WT-NTRK+ lung cancers, and therefore, NTRK inhibitors can be used to target non-fusion NTRK function to prevent or decrease brain metastases. SIGNIFICANCEThese studies demonstrate that NTRK wild-type receptors are important drivers of brain metastatic colonization and progression in different subtypes of lung cancer, independent of their driver alterations. Thus, they provide rationale to expand the use of FDA-approved NTRK inhibitors with brain penetrance for the prevention of CNS metastases.