Inhibition of 4EBP Phosphorylation Mediates the Cytotoxic Effect of Mechanistic Target of Rapamycin Kinase Inhibitors in Aggressive B-cell Lymphomas

Haematologica. 2017 Apr;102(4):755-764. doi: 10.3324/haematol.2016.159160. Epub 2017 Jan 19.

Abstract

Mechanistic target of rapamycin (mTOR) complex 1 is a central integrator of nutrient and growth factor inputs that controls cell growth in eukaryotes. The second generation of mTOR kinase inhibitors (TORKi), directly targeting the mTOR catalytic site, are more effective than rapamycin and its analogs in cancer treatment, particularly in inducing apoptosis. However, the mechanism underlying the cytotoxic effect of TORKi remains elusive. Herein, we demonstrate that TORKi-induced apoptosis is predominantly dependent on the loss of mTOR complex 1-mediated 4EBP activation. Knocking out RICTOR, a key component of mTOR complex 2, or inhibiting p70S6K has little effect on TORKi-induced apoptosis. Conversely, increasing the eIF4E:4EBP ratio by either overexpressing eIF4E or knocking out 4EBP1/2 protects lymphoma cells from TORKi-induced cytotoxicity. Furthermore, downregulation of MCL1 expression plays an important role in TORKi-induced apoptosis, whereas BCL-2 overexpression confers resistance to TORKi treatment. We further show that the therapeutic effect of TORKi in aggressive B-cell lymphomas can be predicted by BH3 profiling, and improved by combining it with pro-apoptotic drugs, especially BCL-2 inhibitors, both in vitro and in vivo Taken together, the study herein provides mechanistic insight into TORKi cytotoxicity and identified a potential way to optimize its efficacy in the clinical treatment of aggressive B-cell lymphoma.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • CRISPR-Cas Systems
  • Disease Progression
  • Ectopic Gene Expression
  • Eukaryotic Initiation Factor-4E / metabolism
  • Female
  • Gene Knockout Techniques
  • Gene Targeting / methods
  • Genetic Vectors / genetics
  • Humans
  • Lymphoma, B-Cell / drug therapy
  • Lymphoma, B-Cell / genetics
  • Lymphoma, B-Cell / metabolism*
  • Lymphoma, B-Cell / pathology
  • Mechanistic Target of Rapamycin Complex 2
  • Mice
  • Multiprotein Complexes / antagonists & inhibitors
  • Phosphorylation / drug effects
  • Protein Binding
  • Protein Kinase Inhibitors / pharmacology*
  • Retroviridae / genetics
  • Ribosomal Protein S6 Kinases, 70-kDa / antagonists & inhibitors
  • Signal Transduction / drug effects
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • Transduction, Genetic
  • Xenograft Model Antitumor Assays

Substances

  • Adaptor Proteins, Signal Transducing
  • Antineoplastic Agents
  • Eukaryotic Initiation Factor-4E
  • Multiprotein Complexes
  • Protein Kinase Inhibitors
  • TOR Serine-Threonine Kinases
  • Mechanistic Target of Rapamycin Complex 2
  • Ribosomal Protein S6 Kinases, 70-kDa