Inhibition of histone deacetylation potentiates the evolution of acquired temozolomide resistance linked to MGMT upregulation in glioblastoma xenografts.
OBJECTIVE
The therapeutic benefit of temozolomide in glioblastoma multiforme (GBM) is limited by resistance. The goal of this study was to elucidate mechanisms of temozolomide resistance in GBM.


METHODS
We developed an in vivo GBM model of temozolomide resistance and used paired parental and temozolomide-resistant tumors to define the mechanisms underlying the development of resistance and the influence of histone deacetylation (HDAC) inhibition.


RESULTS
Analysis of paired parental and resistant lines showed upregulation of O6-methylguanine-DNA methyltransferase (MGMT) expression in 3 of the 5 resistant xenografts. While no significant change was detected in MGMT promoter methylation between parental and derivative-resistant samples, chromatin immunoprecipitation showed an association between MGMT upregulation and elevated acetylation of lysine 9 of histone H3 (H3K9-ac) and decreased dimethylation (H3K9-me2) in GBM12 and GBM14. In contrast, temozolomide resistance development in GBM22 was not linked to MGMT expression, and both parental and resistant lines had low H3K9-ac and high H3K9-me2 within the MGMT promoter. In the GBM12TMZ-resistant line, MGMT reexpression was accompanied by increased recruitment of SP1, C-JUN, NF-κB, and p300 within the MGMT promoter. Interestingly, combined treatment of GBM12 flank xenografts with temozolomide and the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) favored the evolution of temozolomide resistance by MGMT overexpression as compared with treatment with temozolomide alone.


CONCLUSIONS
This study shows, for the first time, a unique mechanism of temozolomide resistance development driven by chromatin-mediated MGMT upregulation and highlights the potential for epigenetically directed therapies to influence the mechanisms of resistance development in GBM.
Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota 55905, USA. kitange.gaspar@mayo.edu
Gaspar J
GJ
Kitange
Ann C
AC
Mladek
Brett L
BL
Carlson
Mark A
MA
Schroeder
Jenny L
JL
Pokorny
Ling
L
Cen
Paul A
PA
Decker
Wenting
W
Wu
Gwen A
GA
Lomberk
Shiv K
SK
Gupta
Raul A
RA
Urrutia
Jann N
JN
Sarkaria
D000107:Acetylation / Q000187:drug effects; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D015153:Blotting, Western; D019175:DNA Methylation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000235:genetics / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005909:Glioblastoma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D053208:Kaplan-Meier Estimate; D008745:Methylation / Q000187:drug effects; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects; D000077337:Vorinostat; D023041:Xenograft Model Antitumor Assays
D018906:Antineoplastic Agents, Alkylating; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D025521:Tumor Suppressor Proteins; D000077337:Vorinostat; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide