Honokiol enhances temozolomide-induced apoptotic insults to malignant glioma cells via an intrinsic mitochondrion-dependent pathway

Phytomedicine. 2018 Oct 1;49:41-51. doi: 10.1016/j.phymed.2018.06.012. Epub 2018 Aug 8.


Background: Temozolomide (TMZ) is a first-line chemotherapeutic drug for malignant gliomas. Nonetheless, TMZ-induced side effects and drug resistance remain challenges. Our previous study showed the suppressive effects of honokiol on growth of gliomas.

Purpose: This study was further aimed to evaluate if honokiol could enhance TMZ-induced insults toward malignant glioma cells and its possible mechanisms.

Methods: Human U87 MG glioma cells were exposed to TMZ, honokiol, and a combination of TMZ and honokiol. Cell survival, apoptosis, necrosis, and proliferation were successively assayed. Fluorometric substrate assays were conducted to determine activities of caspase-3, -6, -8, and -9. Levels of Fas ligand, Bax, and cytochrome c were immunodetected. Translocation of Bax to mitochondria were examined using confocal microscopy. Mitochondrial function was evaluated by assaying the mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and complex I enzyme activity. Caspase-6 activity was suppressed using specific peptide inhibitors. The honokiol-induced effects were further confirmed using human U373 MG and murine GL261 cells.

Results: Exposure of human U87 MG glioma cells to honokiol significantly increased TMZ-induced DNA fragmentation and cell apoptosis. Interestingly, honokiol enhanced intrinsic caspase-9 activity without affecting extrinsic Fas ligand levels and caspase-8 activity. Sequentially, TMZ-induced changes in Bax translocation, the MMP, mitochondrial complex I enzyme activity, intracellular ROS levels, and cytochrome c release were enhanced by honokiol. Consequently, honokiol amplified TMZ-induced activation of caspases-3 and -6 in human U87 MG cells. Fascinatingly, suppressing caspase-6 activity concurrently decreased honokiol-induced DNA fragmentation and cell apoptosis. The honokiol-involved improvement in TMZ-induced intrinsic apoptosis was also confirmed in human U373 MG and murine GL261 glioma cells.

Conclusions: This study showed that honokiol can enhance TMZ-induced apoptotic insults to glioma cells via an intrinsic mitochondrion-dependent mechanism. Our results suggest the therapeutic potential of honokiol to attenuate TMZ-induced side effects.

Keywords: Apoptosis; Honokiol; Intrinsic pathway; Malignant glioma; Temozolomide.

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Biphenyl Compounds / pharmacology*
  • Caspases / metabolism
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Cytochromes c / metabolism
  • DNA Fragmentation
  • Dacarbazine / analogs & derivatives*
  • Dacarbazine / pharmacology
  • Drugs, Chinese Herbal / pharmacology*
  • Fas Ligand Protein / metabolism
  • Glioma / drug therapy
  • Glioma / pathology*
  • Humans
  • Lignans / pharmacology*
  • Membrane Potential, Mitochondrial
  • Mice
  • Mitochondria / physiology*
  • Reactive Oxygen Species / metabolism
  • Signal Transduction / drug effects
  • Temozolomide


  • Biphenyl Compounds
  • Drugs, Chinese Herbal
  • FASLG protein, human
  • Fas Ligand Protein
  • Lignans
  • Reactive Oxygen Species
  • honokiol
  • Dacarbazine
  • Cytochromes c
  • Caspases
  • Temozolomide