Loss of the mismatch repair protein MSH6 in human glioblastomas is associated with tumor progression during temozolomide treatment.
OBJECTIVE
Glioblastomas are treated by surgical resection followed by radiotherapy [X-ray therapy (XRT)] and the alkylating chemotherapeutic agent temozolomide. Recently, inactivating mutations in the mismatch repair gene MSH6 were identified in two glioblastomas recurrent post-temozolomide. Because mismatch repair pathway inactivation is a known mediator of alkylator resistance in vitro, these findings suggested that MSH6 inactivation was causally linked to these two recurrences. However, the extent of involvement of MSH6 in glioblastoma is unknown. We sought to determine the overall frequency and clinical relevance of MSH6 alterations in glioblastomas.


METHODS
The MSH6 gene was sequenced in 54 glioblastomas. MSH6 and O(6)-methylguanine methyltransferase (MGMT) immunohistochemistry was systematically scored in a panel of 46 clinically well-characterized glioblastomas, and the corresponding patient response to treatment evaluated.


RESULTS
MSH6 mutation was not observed in any pretreatment glioblastoma (0 of 40), whereas 3 of 14 recurrent cases had somatic mutations (P = 0.015). MSH6 protein expression was detected in all pretreatment (17 of 17) cases examined but, notably, expression was lost in 7 of 17 (41%) recurrences from matched post-XRT + temozolomide cases (P = 0.016). Loss of MSH6 was not associated with O(6)-methylguanine methyltransferase status. Measurements of in vivo tumor growth using three-dimensional reconstructed magnetic resonance imaging showed that MSH6-negative glioblastomas had a markedly increased rate of growth while under temozolomide treatment (3.17 versus 0.04 cc/mo for MSH6-positive tumors; P = 0.020).


CONCLUSIONS
Loss of MSH6 occurs in a subset of post-XRT + temozolomide glioblastoma recurrences and is associated with tumor progression during temozolomide treatment, mirroring the alkylator resistance conferred by MSH6 inactivation in vitro. MSH6 deficiency may therefore contribute to the emergence of recurrent glioblastomas during temozolomide treatment.
Cahill
Daniel P
DP
Molecular Pathology Unit, Neurosurgical Service, Brain Tumor Center, and Center for Cancer Research, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Levine
Kymberly K
KK
Betensky
Rebecca A
RA
Codd
Patrick J
PJ
Romany
Candice A
CA
Reavie
Linsey B
LB
Batchelor
Tracy T
TT
Futreal
P Andrew
PA
Stratton
Michael R
MR
Curry
William T
WT
Iafrate
A John
AJ
Louis
David N
DN
D000328:Adult; D000368:Aged; D018906:Antineoplastic Agents, Alkylating / Q000009:adverse effects*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000096:biosynthesis / Q000187:drug effects; D045643:DNA Repair Enzymes / Q000096:biosynthesis / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics*; D003606:Dacarbazine / Q000009:adverse effects / Q000031:analogs & derivatives*; D018450:Disease Progression; D005260:Female; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009364:Neoplasm Recurrence, Local / Q000235:genetics; D016133:Polymerase Chain Reaction; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000187:drug effects
D018906:Antineoplastic Agents, Alkylating; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide