title: Development, characterization, and reversal of acquired resistance to the MEK1 inhibitor selumetinib (AZD6244) in an in vivo model of childhood astrocytoma.
abstract: OBJECTIVE
  The BT-40 low-grade childhood astrocytoma xenograft model expresses mutated BRAF(V600E) and is highly sensitive to the MEK inhibitor selumetinib (AZD6244). In this study, we developed and characterized selumetinib resistance and explored approaches to circumventing the mechanisms of acquired resistance.
  
  
  METHODS
  BT-40 xenografts were selected in vivo for selumetinib resistance. Resistant tumors were obtained and characterized, as were tumors that reverted to sensitivity. Characterization included expression profiling, assessment of MEK signature and compensatory pathways, MEK inhibition, BRAF expression, and cytokine levels. Combination treatment of BT-40/AZD-resistant tumors with the MEK inhibitor and a STAT3 inhibitor (LLL12) was assessed.
  
  
  RESULTS
  Resistance was unstable, tumors reverting to selumetinib sensitivity when passaged in untreated mice, and MEK was equally inhibited in sensitive and resistant tumors by selumetinib. Drug resistance was associated with an enhanced MEK signature and increased interleukin (IL)-6 and IL-8 expression. Selumetinib treatment induced phosphorylation of STAT3 (Y705) only in resistant xenografts, and similar results were observed in BRAF(V600E) astrocytic cell lines intrinsically resistant to selumetinib. Treatment of BT-40-resistant tumors with selumetinib or LLL12 had no significant effect, whereas combined treatment induced complete regressions of BT-40/AZD-resistant xenografts.
  
  
  CONCLUSIONS
  Resistance to selumetinib selected in vivo in BT-40 tumor xenografts was unstable. In resistant tumors, selumetinib activated STAT3, and combined treatment with selumetinib and LLL12 induced complete responses in resistant BT-40 tumors. These results suggest dual targeting BRAF (V600E) signaling and STAT3 signaling may be effective in selumetinib-resistant tumors or may retard or prevent onset of resistance.
authors.affiliation: Authors' Affiliations: Center for Childhood Cancer & Blood Diseases, Nationwide Children's Hospital; Center for Biostatistics, The Ohio State University, Columbus, Ohio; Institut of Pathology, Department Neuropathology, Ruprecht-Karls University and Clinical Cooperation Unit Neuropathology, German Cancer Research Center (DKFZ), Heidelberg, Germany; and Astrazeneca Ltd., Oncology iMed, Macclesfield, United Kingdom.
authors.forename: Hemant K
authors.initials: HK
authors.lastname: Bid
authors.forename: Aaron
authors.initials: A
authors.lastname: Kibler
authors.forename: Doris A
authors.initials: DA
authors.lastname: Phelps
authors.forename: Sagymbek
authors.initials: S
authors.lastname: Manap
authors.forename: Linlin
authors.initials: L
authors.lastname: Xiao
authors.forename: Jiayuh
authors.initials: J
authors.lastname: Lin
authors.forename: David
authors.initials: D
authors.lastname: Capper
authors.forename: Duane
authors.initials: D
authors.lastname: Oswald
authors.forename: Brian
authors.initials: B
authors.lastname: Geier
authors.forename: Mariko
authors.initials: M
authors.lastname: DeWire
authors.forename: Paul D
authors.initials: PD
authors.lastname: Smith
authors.forename: Raushan T
authors.initials: RT
authors.lastname: Kurmasheva
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Mo
authors.forename: Soledad
authors.initials: S
authors.lastname: Fernandez
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Houghton
mesh_terms: D000818:Animals; D000880:Anthraquinones / Q000494:pharmacology; D001254:Astrocytoma / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D001562:Benzimidazoles / Q000008:administration & dosage*; D045744:Cell Line, Tumor; D002648:Child; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D064593:Heterografts; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis; D016209:Interleukin-8 / Q000096:biosynthesis; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics*; D051379:Mice; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D050796:STAT3 Transcription Factor / Q000235:genetics; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C517975:AZD 6244; D000880:Anthraquinones; D001562:Benzimidazoles; C508600:IL6 protein, human; D015850:Interleukin-6; D016209:Interleukin-8; C549232:LLL12 compound; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D013449:Sulfonamides; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1