The purpose of the present study was to investigate the in vitro and in vivo activity of PLX9486, a tyrosine kinase inhibitor (TKI) targeting both primary KIT exon 9 and 11 and secondary exon 17 and 18 mutations in gastrointestinal stromal tumors (GISTs). Imatinib, a potent inhibitor of mutated KIT, has revolutionized the clinical management of advanced, metastatic GIST. However, secondary resistance develops mainly through acquired mutations in KIT exons 13/14 or exons 17/18. Second-line sunitinib potently inhibits KIT exon 13/14 mutants but is ineffective against exon 17 mutations. In our study, PLX9486 demonstrated in vitro nanomolar potency in inhibiting the growth and KIT phosphorylation of engineered BaF3 cells transformed with KIT exon 17 mutations (p.D816V) and with the double KIT exon 11/17 mutations (p.V560G/D816V). The in vivo efficacy of PLX9486 was evaluated using two imatinib-resistant GIST patient-derived xenograft (PDX) models. In UZLX-GIST9 (KIT: p.P577del;W557LfsX5;D820G), PLX9486 100 mg/kg/day resulted in significant inhibition of proliferation. Pharmacodynamic analysis showed a pronounced reduction in mitogen-activated protein kinase (MAPK) activation and other downstream effects of the KIT signaling pathway but no significant effect on KIT Y703 and Y719 phosphorylation. Similarly, in MRL-GIST1 (KIT: p.W557_K558del;Y823D) PLX9486 treatment led to significant tumor regression and strong inhibition of MAPK activation. Interestingly, the inhibitory effect on MAPK activation was evident even after a single dose of PLX9486. In conclusion, PLX9486 showed anti-tumor efficacy in patient-derived imatinib-resistant GIST xenograft models, mainly through inhibition of KIT signaling. These preclinical efficacy data encourage further testing of PLX9486 in the clinical setting.
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Plexxikon (Berkeley, CA, USA) provided PLX9486 and financial support for the study.
Compliance with ethical standards
Conflict of interest
Plexxikon provided PLX9486 and financial support for the study. EAB, BM, GH, JL, MN, GW, CZ and GB are employees of Plexxikon Inc. PS received institutional support from Plexxikon for advisory/consultancy, research funding and travel/accommodation/expenses.
Fig. S1Growth curves of BaF3 KIT p.V560G/D816V cells, treated with PLX9486, showing PLX9486-sensitive (IC50 = 7.1 nM) KIT-dependent growth inhibition in the absence of IL3 (No IL3) and PLX9486-resistant (IC50 2,070 nM) KIT-independent growth in the presence of IL3. Data are shown as mean values ± standard error of the mean (TIFF 349 kb)
Nishida T, Blay JY, Hirota S, Kitagawa Y, Kang YK. The standard diagnosis, treatment, and follow-up of gastrointestinal stromal tumors based on guidelines. Gastric Cancer. 2016;19:3–14.CrossRefGoogle Scholar
Joensuu H, Vehtari A, Riihimäki J, et al. Risk of recurrence of gastrointestinal stromal tumour after surgery: an analysis of pooled population-based cohorts. Lancet Oncol. 2012;13:265–74.CrossRefGoogle Scholar
Debiec-Rychter M, Sciot R, Le Cesne A, et al. KIT mutations and dose selection for imatinib in patients with advanced gastrointestinal stromal tumours. Eur J Cancer. 2006;42:1093–103.CrossRefGoogle Scholar
Antonescu CR, Besmer P, Guo T, et al. Acquired resistance to imatinib in gastrointestinal stromal tumor occurs through secondary gene mutation. Clin Cancer Res. 2005;11:4182–90.CrossRefGoogle Scholar
Demetri GD, van Oosterom AT, Garrett CR, et al. Efficacy and safety of sunitinib in patients with advanced gastrointestinal stromal tumour after failure of imatinib: a randomised controlled trial. Lancet. 2006;368:1329–38.CrossRefGoogle Scholar
Demetri GD, Reichardt P, Kang YK, et al. GRID study investigators. Efficacy and safety of regorafenib for advanced gastrointestinal stromal tumours after failure of imatinib and sunitinib (GRID): an international, multicentre, randomised, placebo-controlled, phase 3 trial. Lancet. 2013;381:295–302.CrossRefGoogle Scholar
Heinrich MC, Maki RG, Corless CL, et al. Primary and secondary kinase genotypes correlate with the biological and clinical activity of sunitinib in imatinib-resistant gastrointestinal stromal tumor. J Clin Oncol. 2008;26:5352–9.CrossRefGoogle Scholar
George S, Wang Q, Heinrich MC, et al. Efficacy and safety of regorafenib in patients with metastatic and/or unresectable GI stromal tumor after failure of imatinib and sunitinib: a multicenter phase II trial. J Clin Oncol. 2012;30:2401–7.CrossRefGoogle Scholar
Liegl B, Kepten I, Le C, et al. Heterogeneity of kinase inhibitor resistance mechanisms in GIST. J Pathol. 2008;216:64–74.CrossRefGoogle Scholar
Bollag G. Optimizing kinase inhibitors to treat cancer. Cancer Res. 2016;76 (abstract IA32).Google Scholar
Warmuth M, Kim S, Gu X, Xia G, Adrián F. Ba/F3 cells and their use in kinase drug discovery. Curr Opin Oncol. 2007;19:55–60.CrossRefGoogle Scholar
Van Looy T, Gebreyohannes YK, Wozniak A, et al. Characterization and assessment of the sensitivity and resistance of a newly established human gastrointestinal stromal tumour xenograft model to treatment with tyrosine kinase inhibitors. Clin Sarcoma Res. 2014;4:10.CrossRefGoogle Scholar
Mullins C, Ricono J, Carson P, et al. A patient derived xenograft (PDX) platform for development of next generation KIT kinase inhibitors in imatinib-resistant gastrointestinal stromal tumors (GIST). Cancer Res. 2014;74(Suppl 19) (Abstract 1224).Google Scholar
Gebreyohannes YK, Schöffski P, Van Looy T, et al. Cabozantinib is active against human gastrointestinal stromal tumor xenografts carrying different KIT mutations. Mol Cancer Ther. 2016;15:2845–52.CrossRefGoogle Scholar
Sciot R, Debiec-Rychter M. GIST under imatinib therapy. Semin Diagn Pathol. 2006;23:84–90.CrossRefGoogle Scholar
Choi H, Charnsangavej C, Faria SC, et al. Correlation of computed tomography and positron emission tomography in patients with metastatic gastrointestinal stromal tumor treated at a single institution with imatinib mesylate: proposal of new computed tomography response criteria. J Clin Oncol. 2007;25:1753–9.CrossRefGoogle Scholar
Ran L, Sirota I, Cao Z, et al. Combined inhibition of MAP kinase and KIT signaling synergistically destabilizes ETV1 and suppresses GIST tumor growth. Cancer Discov. 2015;5:304–15.CrossRefGoogle Scholar
Li F, Huynh H, Li X, et al. FGFR-mediated reactivation of MAPK signaling attenuates antitumor effects of imatinib in gastrointestinal stromal tumors. Cancer Discov. 2015;5:438–51.CrossRefGoogle Scholar
Miselli F, Negri T, Gronchi A, et al. Is autophagy rather than apoptosis the regression driver in imatinib-treated gastrointestinal stromal tumors? Transl Oncol. 2008;1:177–86.CrossRefGoogle Scholar
Bauer S, Joensuu H. Emerging agents for the treatment of advanced, imatinib-resistant gastrointestinal stromal tumors: current status and future directions. Drugs. 2015;75:1323–34.CrossRefGoogle Scholar