The efficacy of treatment for
glioblastoma multiforme is currently limited by the development of resistance, particularly, but not exclusively, due to the expression of the
DNA repair enzyme O6-methylguanine methyltransferase (MGMT) in a significant proportion of astrocytic
tumors. MGMT is post-translationally regulated by the
26S proteasome, a multi-subunit organelle responsible for degradation of misfolded cellular
proteins. The
boronic acid dipeptide bortezomib is the first and only
proteasome inhibitor in clinical use so far, and has been reported as a strategy to restrict growth and promote apoptosis of
glioblastoma cells. In this study we investigated the effect of
bortezomib on MGMT expression in T98G cells, looking for an effect on the
nuclear factor kappa B (NFκB) pathway, which is a major player in MGMT regulation and is also under tight control by the
ubiquitin-
proteasome system. Administration of
bortezomib led to a significant reduction of T98G cell viability and induction of DNA fragmentation. These effects coincided with reduced expression of MGMT transcript levels, and a decrease in cellular amount and IκBα-mediated, proteasomal activity-dependent nuclear translocation of NFκB. In addition,
bortezomib-induced phosphorylation of the translation
initiation factor 2alpha (eIF2α) was in parallel with translational repression of MGMT. Taken together, these results suggest a novel role for
bortezomib as a potent MGMT inhibitor and support its ongoing testing as a chemosensitizer in
glioblastoma.