Original Article
Translational Oncology
RET Solvent Front Mutations Mediate Acquired Resistance to Selective RET Inhibition in RET-Driven Malignancies

https://doi.org/10.1016/j.jtho.2020.01.006Get rights and content
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open access

Abstract

Introduction

Novel rearranged in transfection (RET)-specific tyrosine kinase inhibitors (TKIs) such as selpercatinib (LOXO-292) have shown unprecedented efficacy in tumors positive for RET fusions or mutations, notably RET fusion-positive NSCLC and RET-mutated medullary thyroid cancer (MTC). However, the mechanisms of resistance to these agents have not yet been described.

Methods

Analysis was performed of circulating tumor DNA and tissue in patients with RET fusion-positive NSCLC and RET-mutation positive MTC who developed disease progression after an initial response to selpercatinib. Acquired resistance was modeled preclinically using a CCDC6-RET fusion-positive NSCLC patient-derived xenograft. The inhibitory activity of anti-RET multikinase inhibitors and selective RET TKIs was evaluated in enzyme and cell-based assays.

Results

After a dramatic initial response to selpercatinib in a patient with KIF5B-RET NSCLC, analysis of circulating tumor DNA revealed emergence of RET G810R, G810S, and G810C mutations in the RET solvent front before the emergence of clinical resistance. Postmortem biopsy studies reported intratumor and intertumor heterogeneity with distinct disease subclones containing G810S, G810R, and G810C mutations in multiple disease sites indicative of convergent evolution on the G810 residue resulting in a common mechanism of resistance. Acquired mutations in RET G810 were identified in tumor tissue from a second patient with CCDC6-RET fusion-positive NSCLC and in plasma from patients with additional RET fusion-positive NSCLC and RET-mutant MTC progressing on an ongoing phase 1 and 2 trial of selpercatinib. Preclinical studies reported the presence of RET G810R mutations in a CCDC6-RET patient-derived xenograft (from a patient with NSCLC) model of acquired resistance to selpercatinib. Structural modeling predicted that these mutations sterically hinder the binding of selpercatinib, and in vitro assays confirmed loss of activity for both anti-RET multikinase inhibitors and selective RET TKIs.

Conclusions

RET G810 solvent front mutations represent the first described recurrent mechanism of resistance to selective RET inhibition with selpercatinib. Development of potent inhibitor of these mutations and maintaining activity against RET gatekeeper mutations could be an effective strategy to target resistance to selective RET inhibitors.

Keywords

RET fusion
RET mutation
Acquired resistance
Multikinase inhibitor
Selective tyrosine kinase inhibitor

Cited by (0)

Drs. Solomon, Tan, Lin, Wong, and Hollizeck equally contributed to this work.

Disclosure: Dr. Solomon reports personal fees and other from Loxo Oncology, during the conduct of the study; personal fees from Novartis, Pfizer, Roche-Genentech, AstraZeneca, Merck & Co., Bristol-Myers Squibb, and Gritstone Oncology, outside the submitted work, Dr. Lin reports other from Pfizer, C4 Therapeutics, Novartis, Hengrui, Turning Point Therapeutics, Neon Therapeutics, Nuvalent, OncLive, and MedScape, outside the submitted work; Dr. Ebata reports other from Loxo Oncology, during the conduct of the study; Dr. Tuch reports other from Loxo Oncology, during the conduct of the study; Dr. Yoda reports grants from Lung Cancer Research Foundation, during the conduct of the study; Dr. Gainor reports personal fees from Bristol-Myers Squibb, Genentech-Roche, Takeda, Loxo Oncology-Eli Lilly, Pfizer, Incyte, Novartis, Merck & Co., Agios, Amgen, Regeneron, Oncorus, Array, and Jounce; and other from Ironwood Pharmaceuticals, outside the submitted work; Dr. Sequist reports grants from Loxo Oncology, during the conduct of the study; grants and personal fees from AstraZeneca, Merrimack Pharmaceuticals and Blueprint Medicines; grants from Novartis, Genentech, and Boehringer Ingelheim; and personal fees from Janssen, outside the submitted work; Dr. Oxnard reports personal fees from Loxo Oncology, AstraZeneca, Janssen, AbbVie, Foundation Medicine, Inivata, Illumina, Blueprint Medicines, Takeda, and Guardant, outside the submitted work.; Dr. Drilon reports other from Ignyta/Genentech/Roche, Eli Lilly, Takeda/Ariad/Millenium, TP Therapeutics, AstraZeneca, Pfizer, Blueprint Medicines, Helsinn, Beigene, BergenBio, Hengrui, Exelixis, Tyra, Verastem, MORE Health, AbbVie, and Loxo Oncology/Bayer, outside the submitted work, and Associated Research Paid to Institution (Pfizer, Exelixis, GlaxoSmithKlein, Teva, Taiho, PharmaMar), Research (Foundation Medicine), Royalties (Wolters Kluwer), Other (Merck/Puma), and CME Honoraria (Medscape, OncLive, PeerVoice, Physicians Education Resources, Targeted Oncology, Research to Practice, Oncology); Dr. Subbiah reports grants from Loxo Oncology/Eli Lilly, Novartis, GlaxoSmithKline, during the conduct of the study; grants from Bayer, Nano Carrier, Vegenics, Celgene, Northwest Biotherapeutics, Berghealth, Incyte, Fujifilm, Pharmamar, D3, Pfizer Multivir, Amgen, AbbVie, Alfa-sigma, Agensys, Boston Biomedical, Idera Pharma, Inhibrx, Exelixis, and Blueprint Medicines, outside the submitted work; and travel support from Novartis, Pharmamar, American Society for Clinical Oncology, European Society for Clinical Oncology, Helsin, and Incyte; Dr. Zhu reports other from Loxo Oncology, outside the submitted work; Dr. Nguyen reports other from Loxo Oncology, outside the submitted work; Ms. Henry reports other from Loxo Oncology, outside the submitted work; Dr. Condroski reports other from Loxo Oncology, outside the submitted work; Ms. Kolakowski reports other from Loxo Oncology and Array BioPharma, outside the submitted work. In addition, Ms. Kolakowski has three patents issued: WO2018071447, WO2019075092, and WO2019075108; Dr. Gomez reports other from Loxo Oncology, outside the submitted work; Mr. Ballard reports other from Loxo Oncology, outside the submitted work; Mr. Metcalf reports other from Loxo Oncology and Array BioPharma, outside the submitted work. In addition, Mr. Metcalf has three patents issued: WO2018071447, WO2019075092, and WO2019075108; Dr. Dawson reports grants from Genentech and Pfizer, outside the submitted work; Dr. Stancato reports other from Eli Lilly, outside the submitted work; Dr. Brandhuber reports employment at Loxo Oncology and previous equity in Loxo Oncology; Dr. Andrews reports other from Loxo Oncology and Array BioPharma, outside the submitted work. In addition, Dr. Andrews has three patents issued: WO2018071447, WO2019075092, and WO2019075108; Dr. Robinson reports personal fees from Loxo Oncology, during the conduct of the study, personal fees from Eisai, outside the submitted work; Dr. Rothenberg reports other from Loxo Oncology, outside the submitted work. The remaining authors declare no conflict of interest.