Mechanisms of Resistance to NTRK Inhibitors and Therapeutic Strategies in NTRK1-Rearranged Cancers.

Neurotrophic receptor tyrosine kinase 1 (NTRK1) gene rearrangement leads to constitutive activation of NTRK1, which induces high-transforming ability. NTRK-rearranged cancers have been identified in several cancer types, such as glioblastoma, non-small cell lung cancer, and colorectal cancer. Although there are currently no clinically approved inhibitors that target NTRK1, several tyrosine kinase inhibitors (TKI), such as entrectinib and LOXO-101, are in clinical trials. The purpose of this study was to identify potential mechanisms of resistance to NTRK inhibitors and find potential therapeutic strategies to overcome the resistance. We examined the sensitivity of TPM3-NTRK1-transformed Ba/F3 cells and TPM3-NTRK1-harboring KM12 cells to multiple NTRK inhibitors. Acquired NTRK inhibitor-resistant mutations were screened by N-ethyl-N-nitrosourea mutagenesis with Ba/F3-TPM3-NTRK1 cells or by the establishment of NTRK-TKI-resistant cells from KM12 cells continuously treated with NTRK-TKIs. We identified multiple novel NTRK-TKI resistance mutations in the NTRK1 kinase domain, including G595R, and insulin growth factor receptor type 1 (IGF1R) bypass pathway-mediated resistance. After identifying the resistance mechanisms, we performed drug screening with small-molecule inhibitors to overcome the resistance. As a result, we found that ponatinib and nintedanib effectively inhibited the survival of TPM3-NTRK1-G667C but not G595R mutants, both of which showed resistance to entrectinib or larotrectinib (LOXO-101). Furthermore, cabozantinib with an IGF1R inhibitor such as OSI-906 could overcome bypass pathway-mediated resistance. We developed a comprehensive model of acquired resistance to NTRK inhibitors in cancer with NTRK1 rearrangement and identified cabozantinib as a therapeutic strategy to overcome the resistance. Mol Cancer Ther; 16(10); 2130-43. ©2017 AACR. ©2017 American Association for Cancer Research.