Molecular characterization of PS-341 (bortezomib) resistance: implications for overcoming resistance using lysophosphatidic acid acyltransferase (LPAAT)-beta inhibitors

Oncogene. 2005 Apr 28;24(19):3121-9. doi: 10.1038/sj.onc.1208522.


PS-341 (bortezomib, Velcadetrade mark) is a promising novel agent for treatment of advanced multiple myeloma (MM); however, 65% of patients with relapsed refractory disease in a phase II study do not respond to PS-341. We have previously shown that lysophosphatidic acid acyltransferase (LPAAT)-beta inhibitor CT-32615 triggers caspase-dependent apoptosis, and can overcome resistance to conventional therapeutics (i.e., dexamethasone, doxorubicin, melphalan) in MM cells. In this study, we therefore determined whether CT-32615 could also overcome resistance to PS-341. We first characterized molecular mechanisms of resistance to PS-341 in DHL-4 cells. DHL-4 cells express low levels of caspase-3 and caspase-8; furthermore, no cleavage in caspase-8, caspase-9, caspase-3, poly ADP-ribose polymerase (PARP), or DNA fragmentation factor 45 was triggered by PS-341 treatment. We have previously shown that PS-341 treatment triggers phosphorylation of c-Jun NH(2)-terminal kinase (JNK), which subsequently induces caspase-dependent apoptosis; conversely, JNK inhibition blocks PS-341-induced apoptosis. We here show that phosphorylation of SEK-1, JNK, and c-Jun are not induced by PS-341 treatment, suggesting that PS-341 does not trigger a stress response in DHL-4 cells. Importantly, CT-32615 inhibits growth of DHL-4 cells in a time- and dose-dependent fashion: a transient G2/M cell cycle arrest induced by CT-32615 is mediated via downregulation of cdc25c and cdc2. CT-32615 triggered swelling and lysis of DHL-4 cells, without caspase/PARP cleavage or TUNEL-positivity, suggesting a necrotic response. Our studies therefore demonstrate that LPAAT-beta inhibitor CT-32615 triggers necrosis, even in PS-341-resistant DHL-4 cells, providing the framework for its evaluation to overcome clinical PS-341 resistance and improve patient outcome.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acyltransferases / antagonists & inhibitors*
  • Adenosine Triphosphate / metabolism
  • Apoptosis
  • Apoptosis Regulatory Proteins
  • Boronic Acids / pharmacology*
  • Bortezomib
  • CDC2 Protein Kinase / metabolism
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases / metabolism
  • Cell Cycle Proteins / metabolism
  • Cell Division
  • Cell Line, Tumor
  • Cell Proliferation
  • Dose-Response Relationship, Drug
  • Down-Regulation
  • Drug Resistance, Neoplasm*
  • Enzyme Inhibitors / pharmacology*
  • Flow Cytometry
  • G2 Phase
  • Humans
  • Immunoblotting
  • In Situ Nick-End Labeling
  • Multiple Myeloma / drug therapy
  • Multiple Myeloma / metabolism
  • Necrosis
  • Phosphorylation
  • Poly(ADP-ribose) Polymerases / metabolism
  • Protease Inhibitors / pharmacology*
  • Proteasome Inhibitors
  • Proteins / metabolism
  • Pyrazines / pharmacology*
  • Time Factors
  • Treatment Outcome
  • cdc25 Phosphatases / metabolism


  • Apoptosis Regulatory Proteins
  • Boronic Acids
  • Cell Cycle Proteins
  • Enzyme Inhibitors
  • Protease Inhibitors
  • Proteasome Inhibitors
  • Proteins
  • Pyrazines
  • caspase-activated DNase inhibitor
  • Bortezomib
  • Adenosine Triphosphate
  • Acyltransferases
  • 2-acylglycerophosphate acyltransferase
  • Poly(ADP-ribose) Polymerases
  • CDC2 Protein Kinase
  • CDC25C protein, human
  • cdc25 Phosphatases
  • CASP3 protein, human
  • CASP8 protein, human
  • CASP9 protein, human
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases