title: Mechanistic Target of Rapamycin (mTOR) Inhibition Synergizes with Reduced Internal Ribosome Entry Site (IRES)-mediated Translation of Cyclin D1 and c-MYC mRNAs to Treat Glioblastoma.
abstract: Our previous work has demonstrated an intrinsic mRNA-specific protein synthesis salvage pathway operative in glioblastoma (GBM) tumor cells that is resistant to mechanistic target of rapamycin (mTOR) inhibitors. The activation of this internal ribosome entry site (IRES)-dependent mRNA translation initiation pathway results in continued translation of critical transcripts involved in cell cycle progression in the face of global eIF-4E-mediated translation inhibition. Recently we identified compound 11 (C11), a small molecule capable of inhibiting c-MYC IRES translation as a consequence of blocking the interaction of a requisite c-MYC IRES trans-acting factor, heterogeneous nuclear ribonucleoprotein A1, with its IRES. Here we demonstrate that C11 also blocks cyclin D1 IRES-dependent initiation and demonstrates synergistic anti-GBM properties when combined with the mechanistic target of rapamycin kinase inhibitor PP242. The structure-activity relationship of C11 was investigated and resulted in the identification of IRES-J007, which displayed improved IRES-dependent initiation blockade and synergistic anti-GBM effects with PP242. Mechanistic studies with C11 and IRES-J007 revealed binding of the inhibitors within the UP1 fragment of heterogeneous nuclear ribonucleoprotein A1, and docking analysis suggested a small pocket within close proximity to RRM2 as the potential binding site. We further demonstrate that co-therapy with IRES-J007 and PP242 significantly reduces tumor growth of GBM xenografts in mice and that combined inhibitor treatments markedly reduce the mRNA translational state of cyclin D1 and c-MYC transcripts in these tumors. These data support the combined use of IRES-J007 and PP242 to achieve synergistic antitumor responses in GBM.
authors.affiliation: Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California 90048; Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
authors.forename: Brent
authors.initials: B
authors.lastname: Holmes
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90048.
authors.forename: Jihye
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
authors.forename: Kenna A
authors.initials: KA
authors.lastname: Landon
authors.affiliation: Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
authors.forename: Angelica
authors.initials: A
authors.lastname: Benavides-Serrato
authors.affiliation: Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343.
authors.forename: Tariq
authors.initials: T
authors.lastname: Bashir
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90048; Jonnson Comprehensive Cancer Center, University of California, Los Angeles, California 90048; Molecular Biology Institute, University of California, Los Angeles, California 90048.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Jung
authors.affiliation: Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California 90048; Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343; Jonnson Comprehensive Cancer Center, University of California, Los Angeles, California 90048.
authors.forename: Alan
authors.initials: A
authors.lastname: Lichtenstein
authors.affiliation: Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California 90048; Department of Research and Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343; Jonnson Comprehensive Cancer Center, University of California, Los Angeles, California 90048; Molecular Biology Institute, University of California, Los Angeles, California 90048. Electronic address: jgera@mednet.ucla.edu.
authors.forename: Joseph
authors.initials: J
authors.lastname: Gera
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000378:metabolism / Q000628:therapy*; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000235:genetics*; D005260:Female; D016259:Genes, myc; D005909:Glioblastoma / Q000378:metabolism / Q000628:therapy*; D064593:Heterografts; D006801:Humans; D000067556:Internal Ribosome Entry Sites; D051379:Mice; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: D000067556:Internal Ribosome Entry Sites; D012333:RNA, Messenger; D019938:Cyclin D1; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases
keywords: IRES; ITAF; Myc (c-Myc); cyclin D1; glioblastoma; heterogeneous nuclear ribonucleoprotein (hnRNP); mRNA translation; mechanistic target of rapamycin (mTOR); translation