Proapoptotic effects of the novel proteasome inhibitor b-AP15 on multiple myeloma cells and natural killer cells

Exp Hematol. 2014 Mar;42(3):172-82. doi: 10.1016/j.exphem.2013.11.010. Epub 2013 Nov 27.


The small molecule b-AP15 is a novel inhibitor of proteasome deubiquitination. Recent studies have shown that b-AP15 displays antitumor activity in several preclinical, solid tumor models. In this study, we show that b-AP15 triggers time- and dose-dependent apoptosis of the human multiple myeloma (MM) cell lines RPMI8226 and U266, as determined by phosphatidylserine exposure. Apoptosis was dependent on caspase activation and was partially dependent on cathepsin D. Furthermore, b-AP15 triggered processing of pro-caspase-3 and cleavage of poly (ADP-ribose) polymerase in MM cells. b-AP15 also induced caspase-independent apoptosis in primary human natural killer cells. We also demonstrate that b-AP15 induces activation of the mitochondrial apoptosis pathway in MM cells, with activation of the proapoptotic protein Bax and a pronounced loss of the mitochondrial transmembrane potential. The latter events, however, appeared largely independent of caspase activation. Our data suggest that proteasome deubiquitinase inhibitors may have potential for treatment of multiple myeloma patients.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Apoptosis / drug effects*
  • Blotting, Western
  • Caspase 3 / metabolism
  • Cathepsin D / metabolism
  • Cell Line, Tumor
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Enzyme Activation / drug effects
  • Flow Cytometry
  • Humans
  • Killer Cells, Natural / cytology
  • Killer Cells, Natural / drug effects*
  • Killer Cells, Natural / metabolism
  • Membrane Potential, Mitochondrial / drug effects
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • Mitochondria / physiology
  • Multiple Myeloma / metabolism
  • Multiple Myeloma / pathology
  • Phosphatidylserines / metabolism
  • Piperidones / pharmacology*
  • Poly(ADP-ribose) Polymerases / metabolism
  • Protease Inhibitors / pharmacology*
  • Time Factors
  • bcl-2-Associated X Protein / metabolism


  • 3,5-bis((4-nitrophenyl)methylidene)-1-prop-2-enoylpiperidin-4-one
  • Phosphatidylserines
  • Piperidones
  • Protease Inhibitors
  • bcl-2-Associated X Protein
  • Poly(ADP-ribose) Polymerases
  • Caspase 3
  • Cathepsin D