title: Cytotoxic Properties of a DEPTOR-mTOR Inhibitor in Multiple Myeloma Cells.
abstract: DEPTOR is a 48 kDa protein that binds to mTOR and inhibits this kinase in TORC1 and TORC2 complexes. Overexpression of DEPTOR specifically occurs in a model of multiple myeloma. Its silencing in multiple myeloma cells is sufficient to induce cytotoxicity, suggesting that DEPTOR is a potential therapeutic target. mTORC1 paralysis protects multiple myeloma cells against DEPTOR silencing, implicating mTORC1 in the critical role of DEPTOR in multiple myeloma cell viability. Building on this foundation, we interrogated a small-molecule library for compounds that prevent DEPTOR binding to mTOR in a yeast-two-hybrid assay. One compound was identified that also prevented DEPTOR-mTOR binding in human myeloma cells, with subsequent activation of mTORC1 and mTORC2. In a surface plasmon resonance (SPR) assay, the compound bound to recombinant DEPTOR but not to mTOR. The drug also prevented binding of recombinant DEPTOR to mTOR in the SPR assay. Remarkably, although activating TORC1 and TORC2, the compound induced apoptosis and cell-cycle arrest in multiple myeloma cell lines and prevented outgrowth of human multiple myeloma cells in immunodeficient mice. In vitro cytotoxicity against multiple myeloma cell lines was directly correlated with DEPTOR protein expression and was mediated, in part, by the activation of TORC1 and induction of p21 expression. Additional cytotoxicity was seen against primary multiple myeloma cells, whereas normal hematopoietic colony formation was unaffected. These results further support DEPTOR as a viable therapeutic target in multiple myeloma and suggest an effective strategy of preventing binding of DEPTOR to mTOR. Cancer Res; 76(19); 5822-31. ©2016 AACR.
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California.
authors.forename: Yijiang
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Department of Surgery, University of California at Los Angeles, Los Angeles, California.
authors.forename: Tracy R
authors.initials: TR
authors.lastname: Daniels-Wells
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California.
authors.forename: Patrick
authors.initials: P
authors.lastname: Frost
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California.
authors.forename: Jihye
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Finn
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California.
authors.forename: Carolyne
authors.initials: C
authors.lastname: Bardeleben
authors.affiliation: Department of Surgery, University of California at Los Angeles, Los Angeles, California. Department of Microbiology, Immunology, and Molecular Genetics, University of California at Los Angeles, Los Angeles, California.
authors.forename: Manuel L
authors.initials: ML
authors.lastname: Penichet
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Jung
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California.
authors.forename: Joseph
authors.initials: J
authors.lastname: Gera
authors.affiliation: Department of Hematology-Oncology, University of California at Los Angeles, Los Angeles, California. alan.lichtenstein@med.va.gov.
authors.forename: Alan
authors.initials: A
authors.lastname: Lichtenstein
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000473:pathology; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors*; D008113:Liver Neoplasms / Q000188:drug therapy / Q000473:pathology; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000473:pathology; D046912:Multiprotein Complexes / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D019253:Proto-Oncogene Proteins c-bcl-2; C556139:DEPTOR protein, human; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases