Bortezomib administered prior to temozolomide depletes MGMT, chemosensitizes glioblastoma with unmethylated MGMT promoter and prolongs animal survival

Br J Cancer. 2019 Oct;121(7):545-555. doi: 10.1038/s41416-019-0551-1. Epub 2019 Aug 15.


Background: Resistance to temozolomide (TMZ) is due in part to enhanced DNA repair mediated by high expression of O6-methyl guanine DNA methyltransferase (MGMT) that is often characterised by unmethylated promoter. Here, we investigated pre-treatment of glioblastoma (GBM) cells with the 26S-proteasome inhibitor bortezomib (BTZ) as a strategy to interfere with MGMT expression and thus sensitise them to TMZ.

Methods: Cell lines and patient GBM-derived cells were examined in vitro, and the latter also implanted orthotopically into NOD-SCID C.B.-Igh-1b/lcrTac-Prkdc mice to assess efficacy and tolerability of BTZ and TMZ combination therapy. MGMT promoter methylation was determined using pyrosequencing and PCR, protein signalling utilised western blotting while drug biodistribution was examined by LC-MS/MS. Statistical analysis utilised Analysis of variance and the Kaplan-Meier method.

Results: Pre-treatment with BTZ prior to temozolomide killed chemoresistant GBM cells with unmethylated MGMT promoter through MGMT mRNA and protein depletion in vitro without affecting methylation. Chymotryptic activity was abolished, processing of NFkB/p65 to activated forms was reduced and corresponded with low MGMT levels. BTZ crossed the blood-brain barrier, diminished proteasome activity and significantly prolonged animal survival.

Conclusion: BTZ chemosensitized resistant GBM cells, and the schedule may be amenable for temozolomide refractory patients with unmethylated MGMT promoter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / administration & dosage*
  • Bortezomib / administration & dosage*
  • Brain Neoplasms / diagnostic imaging
  • Brain Neoplasms / drug therapy*
  • Brain Neoplasms / enzymology
  • Cell Line, Tumor
  • Drug Administration Schedule
  • Drug Resistance, Neoplasm / drug effects
  • Glioblastoma / diagnostic imaging
  • Glioblastoma / drug therapy*
  • Glioblastoma / enzymology
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Kaplan-Meier Estimate
  • Methylation
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Neoplasm Transplantation
  • O(6)-Methylguanine-DNA Methyltransferase / drug effects
  • O(6)-Methylguanine-DNA Methyltransferase / metabolism*
  • Polymerase Chain Reaction
  • Promoter Regions, Genetic
  • RNA, Messenger / metabolism
  • Temozolomide / administration & dosage*
  • Transcription Factor RelA / metabolism


  • Antineoplastic Agents
  • RNA, Messenger
  • Transcription Factor RelA
  • Bortezomib
  • O(6)-Methylguanine-DNA Methyltransferase
  • Temozolomide