title: MCL-1 and BCL-xL-dependent resistance to the BCL-2 inhibitor ABT-199 can be overcome by preventing PI3K/AKT/mTOR activation in lymphoid malignancies.
abstract: Overexpression of anti-apoptotic BCL-2 family members is a hallmark of many lymphoid malignancies, including chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) that can be targeted with small molecule inhibitors. ABT-199 is a rationally designed BCL-2 homology (BH)-3 mimetic that specifically binds to BCL-2, but not to MCL-1 and BCL-xL. Although the thrombocytopenia that occurs with navitoclax treatment has not been a problem with ABT-199, clinical trials in CLL could benefit by lowering the ABT-199 concentration through targeting other survival pathways. In this study, we investigated the mechanisms of resistance that develops to ABT-199 therapy by generating ABT-199-resistant (ABT199-R) cell lines via chronic exposure of NHL cell lines to ABT-199. Acquired resistance resulted in substantial AKT activation and upregulation of MCL-1 and BCL-xL levels that sequestered BIM. ABT199-R cells exhibited increased MCL-1 stability and failed to activate BAX in response to ABT-199. The ABT-199 acquired and inherent resistant cells were sensitized to treatment with ABT-199 by inhibitors of the PI3K, AKT, and mTOR pathways, NVP-BEZ235 and GS-1101. NVP-BEZ235, a dual inhibitor of p-AKT and mTOR, reduced MCL-1 levels causing BIM release from MCL-1 and BCL-xL, thus leading to cell death by BAX activation. The PI3Kδ inhibitor GS-1101 (idelalisib) downregulated MCL-1 and sensitized ABT199-R cells through AKT-mediated BAX activation. A genetic approach, through siRNA-mediated down-regulation of AKT, MCL-1, and BCL-xL, significantly decreased cell survival, demonstrating the importance of these cell survival factors for ABT-199 resistance. Our findings suggest a novel mechanism that modulates the expression and activity of pro-survival proteins to confer treatment resistance that could be exploited by a rational combination therapeutic regimen that could be effective for treating lymphoid malignancies.
authors.affiliation: 1] Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA [2] Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Choudhary
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: S
authors.initials: S
authors.lastname: Al-Harbi
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: S
authors.initials: S
authors.lastname: Mazumder
authors.affiliation: Department of Hematology and Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: B T
authors.initials: BT
authors.lastname: Hill
authors.affiliation: Department of Hematology and Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Smith
authors.affiliation: Department of Clinical Pathology, Institute of Pathology and Laboratory Medicine, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: J
authors.initials: J
authors.lastname: Bodo
authors.affiliation: Department of Clinical Pathology, Institute of Pathology and Laboratory Medicine, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: E D
authors.initials: ED
authors.lastname: Hsi
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
authors.forename: A
authors.initials: A
authors.lastname: Almasan
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology*; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008223:Lymphoma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D052999:Quinazolinones / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D019086:Bridged Bicyclo Compounds, Heterocyclic; D007093:Imidazoles; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019869:Phosphatidylinositol 3-Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011687:Purines; D052999:Quinazolinones; D011804:Quinolines; D012333:RNA, Messenger; D013449:Sulfonamides; D058570:TOR Serine-Threonine Kinases; D051020:bcl-X Protein; C000606775:BCL2L11 protein, human; C579095:MCL1 protein, human; C579720:venetoclax; C531198:dactolisib; C552946:idelalisib