Sulforaphane synergistically enhances the cytotoxicity of arsenic trioxide in multiple myeloma cells via stress-mediated pathways

Oncol Rep. 2012 Nov;28(5):1851-8. doi: 10.3892/or.2012.1977. Epub 2012 Aug 22.

Abstract

Persistent paraprotein production in plasma cells necessitates a highly developed rough endoplasmic reticulum (ER) that is unusually susceptible to perturbations in protein synthesis. This biology is believed to account for the exquisite sensitivity of multiple myeloma (MM) to the proteasomal inhibitor bortezomib (BTZ). Despite remarkable response rates to BTZ in MM, BTZ carries the potential for serious side-effects and development of resistance. We, therefore, sought to identify therapeutic combinations that effectively disrupt proteostasis in order to provide new potential treatments for MM. We found that sulforaphane, a dietary isothiocyanate found in cruciferous vegetables, inhibits TNFα-induced Iκβ proteasomal degradation in a manner similar to BTZ. Like BTZ, sulforaphane synergistically enhances the cytotoxicity of arsenic trioxide (ATO), an agent with clinical activity in MM. ATO and sulforaphane co-treatment augmented apoptotic induction as demonstrated by cleavage of caspase-3, -4 and PARP. The enhanced apoptotic response was dependent upon production of reactive oxygen species (ROS) as demonstrated by glutathione depletion and partial inhibition of the apoptotic cascade after pretreatment with the radical scavenger N-acetyl-cysteine (NAC). Combination treatment resulted in enhanced ER stress signaling and activation of the unfolded protein response (UPR), indicative of perturbation of proteostasis. Specifically, combination treatment caused elevated expression of the molecular chaperone HSP90 (heat shock protein 90) along with increased PERK (protein kinase RNA-like endoplasmic reticulum kinase) and eIF2α phosphorylation and XBP1 (X-box binding protein 1) splicing, key indicators of UPR activation. Moreover, increased splicing of XBP1 was apparent upon combination treatment compared to treatment with either agent alone. Sulforaphane in combination with ATO effectively disrupts protein homeostasis through ROS generation and induction of ER stress to culminate in inhibition of protein secretion and apoptotic induction in MM. Our results suggest that sulforaphane deserves further investigation in combination with ATO in the treatment of MM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Arsenic Trioxide
  • Arsenicals / pharmacology*
  • Caspase 3 / metabolism
  • Caspases, Initiator / metabolism
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • DNA-Binding Proteins / metabolism
  • Drug Synergism
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum Stress / drug effects*
  • Eukaryotic Initiation Factor-2 / metabolism
  • Glutathione / metabolism
  • HSP90 Heat-Shock Proteins / biosynthesis
  • HSP90 Heat-Shock Proteins / metabolism
  • Humans
  • I-kappa B Kinase / metabolism
  • Isothiocyanates
  • Multiple Myeloma / drug therapy*
  • Multiple Myeloma / metabolism
  • Oxides / pharmacology*
  • Phosphorylation / drug effects
  • Poly(ADP-ribose) Polymerases / metabolism
  • Reactive Oxygen Species / metabolism
  • Regulatory Factor X Transcription Factors
  • Signal Transduction / drug effects
  • Thiocyanates / pharmacology*
  • Transcription Factors / metabolism
  • Tumor Necrosis Factor-alpha / metabolism
  • Unfolded Protein Response / drug effects
  • X-Box Binding Protein 1
  • eIF-2 Kinase / biosynthesis

Substances

  • Antineoplastic Agents
  • Arsenicals
  • DNA-Binding Proteins
  • Eukaryotic Initiation Factor-2
  • HSP90 Heat-Shock Proteins
  • Isothiocyanates
  • Oxides
  • Reactive Oxygen Species
  • Regulatory Factor X Transcription Factors
  • Thiocyanates
  • Transcription Factors
  • Tumor Necrosis Factor-alpha
  • X-Box Binding Protein 1
  • XBP1 protein, human
  • Poly(ADP-ribose) Polymerases
  • PERK kinase
  • eIF-2 Kinase
  • I-kappa B Kinase
  • CASP4 protein, human
  • Caspase 3
  • Caspases, Initiator
  • sulforafan
  • Glutathione
  • Arsenic Trioxide