Abstract 2136: Entrectinib is effective against the gatekeeper and other emerging resistance mutations in NTRK-, ROS1- and ALK- rearranged cancers
Authors: Wei Ge , Ardini Elena , Patel Roopal , Cam Nicholas , Harris Jason , Vernier Jean-Michel , Zhu Nanqun , Yeh Litain , Shoemaker Robert , Multani Pratik , Hornby Zachary , Wild Robert , Li Gary G. 
Published: July 2016

Abstract
Gene rearrangements involving NTRK1, NTRK2, NTRK3, ROS1 and ALK result in oncogenic fusion proteins that have been identified in many types of cancer, including lung, colorectal, salivary gland, sarcoma, papillary thyroid, glioblastoma, melanoma and other histologies. Entrectinib (RXDX-101) is an orally available, highly potent and selective ATP-competitive pan-Trk, ROS1 and ALK inhibitor. In preclinical studies, entrectinib effectively inhibits target kinase activity and cancer cell proliferation and in vivo tumor growth across various fusion partners and cancer types. More importantly, entrectinib's activity has been validated clinically in patients across multiple fusion partners and tissue histologies.
Trk inhibitors, including entrectinib, have shown promising clinical activity in molecularly selected patients. Predictably, potential resistance mechanisms have also begun to emerge. For example, mutations in the Trk kinase domain were identified as one of the in vitro induced resistance mechanisms to the Trk inhibitor, Loxo-101. The three reported resistance mutations in the Ba/F3-MPRIP-NTRK1 cell line model treated with Loxo-101 were F589, G667 and V573. The F589 location on TrkA is equivalent to the gatekeeper mutations, L1196 location on ALK and L2026 location on ROS1. These gatekeeper mutations often arise as resistance mechanisms in patients treated with ALK and ROS1 inhibitors. To test the activity of entrectinib against these three reported NTRK1 mutations, we introduced mutated Trk proteins into Ba/F3 and cancer cell lines and performed dose-dependent proliferation studies. Entrectinib was able to inhibit proliferation of cells harboring each of these three mutations that confer resistance to other Trk inhibitors. Particularly, the IC50 values of entrectinib against kinase domain wildtype and gatekeeper mutated (F589) are essentially unchanged (low single-digit nM), which is consistent with the observation that entrectinib is also able to inhibit the gatekeeper mutation in ALK (L1196) in both cell based assays and in vivo tumor growth inhibition studies.
In conclusion, our preclinical data suggest that entrectinib is an effective treatment for patients with NTRK-rearranged tumors, including cancers that harbor certain resistance mutations to other Trk inhibitors.
Citation Format: Ge Wei, Elena Ardini, Roopal Patel, Nicholas Cam, Jason Harris, Jean-Michel Vernier, Nanqun Zhu, Litain Yeh, Robert Shoemaker, Pratik Multani, Zachary Hornby, Robert Wild, Gary G. Li. Entrectinib is effective against the gatekeeper and other emerging resistance mutations in NTRK-, ROS1- and ALK- rearranged cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2136.