Emergence of mismatch repair (MMR) deficiency is a frequent mechanism of acquired resistance to the alkylating chemotherapeutic temozolomide (TMZ) in gliomas. Poly(ADP-ribose) polymerase inhibitors ...(PARPi) have been shown to potentiate TMZ cytotoxicity in several cancer types, including gliomas. We tested whether PARP inhibition could re-sensitize MSH6-null MMR-deficient gliomas to TMZ, and assessed the role of the base excision repair (BER) DNA damage repair pathway in PARPi-mediated effects.
Isogenic pairs of MSH6 wild-type and MSH6-inactivated human glioblastoma (GBM) cells (including both
wild-type and
mutant), as well as MSH6-null cells derived from a patient with recurrent GBM were treated with TMZ, the PARPi veliparib or olaparib, and combination thereof. Efficacy of PARPi combined with TMZ was assessed
. We used genetic and pharmacological approaches to dissect the contribution of BER.
While having no detectable effect in MSH6 wild-type GBMs, PARPi selectively restored TMZ sensitivity in MSH6-deficient GBM cells. This genotype-specific restoration of activity translated
, where combination treatment of veliparib and TMZ showed potent suppression of tumor growth of MSH6-inactivated orthotopic xenografts, compared with TMZ monotherapy. Unlike PARPi, genetic and pharmacological blockage of BER pathway did not re-sensitize MSH6-inactivated GBM cells to TMZ. Similarly, CRISPR PARP1 knockout did not re-sensitize MSH6-inactivated GBM cells to TMZ.
PARPi restoration of TMZ chemosensitivity in MSH6-inactivated glioma represents a promising strategy to overcome acquired chemoresistance caused by MMR deficiency. Mechanistically, this PARPi-mediated synthetic phenotype was independent of BER blockage and was not recapitulated by loss of PARP1.
-mutant gliomas are dependent upon the canonical coenzyme NAD
for survival. It is known that PARP activation consumes NAD
during base excision repair (BER) of chemotherapy-induced DNA damage. We ...therefore hypothesized that a strategy combining NAD
biosynthesis inhibitors with the alkylating chemotherapeutic agent temozolomide could potentiate NAD
depletion-mediated cytotoxicity in mutant
cancer cells. To investigate the impact of temozolomide on NAD
metabolism, patient-derived xenografts and engineered mutant
-expressing cell lines were exposed to temozolomide,
and
, both alone and in combination with nicotinamide phosphoribosyltransferase (NAMPT) inhibitors, which block NAD
biosynthesis. The acute time period (<3 hours) after temozolomide treatment displayed a burst of NAD
consumption driven by PARP activation. In
-mutant-expressing cells, this consumption reduced further the abnormally lowered basal steady-state levels of NAD
, introducing a window of hypervulnerability to NAD
biosynthesis inhibitors. This effect was selective for
-mutant cells and independent of methylguanine methyltransferase or mismatch repair status, which are known rate-limiting mediators of adjuvant temozolomide genotoxic sensitivity. Combined temozolomide and NAMPT inhibition in an
-mutant cancer model exhibited enhanced efficacy compared with each agent alone. Thus, we find
-mutant cancers have distinct metabolic stress responses to chemotherapy-induced DNA damage and that combination regimens targeting nonredundant NAD
pathways yield potent anticancer efficacy
Such targeting of convergent metabolic pathways in genetically selected cancers could minimize treatment toxicity and improve durability of response to therapy.
.
Glioblastoma (GBM) is a devastating malignancy with few therapeutic options. We identify PRMT5 in an in vivo GBM shRNA screen and show that PRMT5 knockdown or inhibition potently suppresses in vivo ...GBM tumors, including patient-derived xenografts. Pathway analysis implicates splicing in cellular PRMT5 dependency, and we identify a biomarker that predicts sensitivity to PRMT5 inhibition. We find that PRMT5 deficiency primarily disrupts the removal of detained introns (DIs). This impaired DI splicing affects proliferation genes, whose downregulation coincides with cell cycle defects, senescence and/or apoptosis. We further show that DI programs are evolutionarily conserved and operate during neurogenesis, suggesting that they represent a physiological regulatory mechanism. Collectively, these findings reveal a PRMT5-regulated DI-splicing program as an exploitable cancer vulnerability.
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•DI splicing is a regulated pathway promoting proliferation gene expression•GBMs assume control of the DI pathway, creating an exploitable vulnerability•PRMT5 inhibition induces DI inclusion and yields potent anti-tumor activity•CLNS1A/RIOK1 ratio is a predictive biomarker for PRMT5 inhibitor sensitivity
Braun et al. show that glioblastoma is selectively sensitive to the inhibition of PRMT5 and identify a predictive biomarker for this sensitivity. PRMT5 inhibition primarily disrupts the removal of detained introns, which results in the reduction of functional transcripts of mainly proliferation-associated genes.
The Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) update 3 recommends that histologic grade II and III
IDH
-wildtype diffuse astrocytic gliomas that ...harbor
EGFR
amplification, the combination of whole chromosome 7 gain and whole chromosome 10 loss (7 + /10 −), or
TERT
promoter (p
TERT
) mutations should be considered as glioblastomas (GBM), World Health Organization grade IV. In this retrospective study, we examined the utility of molecular classification based on p
TERT
status and copy-number alterations (CNAs) in
IDH
-wildtype lower grade gliomas (LGGs, grade II, and III). The impact on survival was evaluated for the p
TERT
mutation and CNAs, including
EGFR
gain/amplification,
PTEN
loss,
CDKN2A
homozygous deletion, and
PDGFRA
gain/amplification. We analyzed 46 patients with
IDH
-wildtype/p
TERT
-mutant (mut) LGGs and 85 with
IDH
-wildtype/p
TERT
-wildtype LGGs.
EGFR
amplification and a combination of
EGFR
gain and
PTEN
loss (
EGFR
+ /
PTEN
−) were significantly more frequent in p
TERT
-mut patients (
p
< 0.0001). Cox regression analysis showed that the p
TERT
mutation was a significant predictor of poor prognosis (hazard ratio HR 2.79, 95% confidence interval CI 1.55–4.89,
p
= 0.0008), but neither
EGFR
amplification nor
EGFR
+ /
PTEN
− was an independent prognostic factor in
IDH
-wildtype LGGs.
PDGFRA
gain/amplification was a significant poor prognostic factor in
IDH
-wildtype/p
TERT
-wildtype LGGs (HR 2.44, 95% CI 1.09–5.27,
p
= 0.03, Cox regression analysis). The
IDH
-wildtype LGGs with either p
TERT
-mut or
PDGFRA
amplification were mostly clustered with GBM by DNA methylation analysis. Thus, our study suggests that analysis of p
TERT
mutation status is necessary and sufficient to diagnose
IDH
-wildtype diffuse astrocytic gliomas with molecular features of glioblastoma. The
PDGFRA
status may help further delineate
IDH
-wildtype/p
TERT
-wildtype LGGs. Methylation profiling showed that
IDH
-wildtype LGGs without molecular features of GBM were a heterogeneous group of tumors. Some of them did not fall into existing categories and had significantly better prognoses than those clustered with GBM.
NAD
is an essential cofactor metabolite and is the currency of metabolic transactions critical for cell survival. Depending on tissue context and genotype, cancer cells have unique dependencies on ...NAD
metabolic pathways. PARPs catalyze oligomerization of NAD
monomers into PAR chains during cellular response to alkylating chemotherapeutics, including procarbazine or temozolomide. Here we find that, in endogenous IDH1-mutant tumor models, alkylator-induced cytotoxicity is markedly augmented by pharmacologic inhibition or genetic knockout of the PAR breakdown enzyme PAR glycohydrolase (PARG). Both
and
, we observe that concurrent alkylator and PARG inhibition depletes freely available NAD
by preventing PAR breakdown, resulting in NAD
sequestration and collapse of metabolic homeostasis. This effect reversed with NAD
rescue supplementation, confirming the mechanistic basis of cytotoxicity. Thus, alkylating chemotherapy exposes a genotype-specific metabolic weakness in tumor cells that can be exploited by PARG inactivation. SIGNIFICANCE: Oncogenic mutations in the isocitrate dehydrogenase genes
or
initiate diffuse gliomas of younger adulthood. Strategies to maximize the effectiveness of chemotherapy in these tumors are needed. We discover alkylating chemotherapy and concurrent PARG inhibition exploits an intrinsic metabolic weakness within these cancer cells to provide genotype-specific benefit.
.
.
The Jarvik 2000, with a postauricular cable, is a left ventricular assistance device with a driveline that is passed to the postauricular region subcutaneously. A titanium pedestal base that holds a ...3-pin connector is fixed to the parietal bone, posterior to the auricle. Essentially, the device is fixed in the same position as a cochlear implant; however, the disadvantages include continuous mechanical stress on the cable by neck rotations, and the visibility of the apparatus. To improve such concerns, we adjusted the location of the pedestal of the lower parietal bone to just above the transverse sinus and closer to the mastoid process. To reach this point, the internal cable was passed through the retromastoid pathway commonly used in ventriculoperitoneal shunting. The thickness of the skull at this location is sufficient for safe fixation; however, preoperative evaluation by a neurosurgeon using CT is necessary.
Mismatch repair (MMR) deficiency through
inactivation has been identified in up to 30% of recurrent high-grade gliomas, and represents a key molecular mechanism underlying the acquired resistance to ...the alkylating agent temozolomide (TMZ). To develop a therapeutic strategy that could be effective in these TMZ-refractory gliomas, we first screened 13 DNA damage response modulators for their ability to suppress viability of MSH6-inactivated, TMZ-resistant glioma cells. We identified a PLK1 selective inhibitor, Volasertib, as the most potent in inhibiting proliferation of glioblastoma cells. PLK1 inhibition induced mitotic catastrophe, G
-M cell-cycle arrest, and DNA damage, leading to caspase-mediated apoptosis in glioblastoma cells. Importantly, therapeutic effects of PLK1 inhibitors were not influenced by MSH6 knockdown, indicating that their action is independent of MMR status of the cells. Systemic treatment with Volasertib potently inhibited tumor growth in an MMR-deficient, TMZ-resistant glioblastoma xenograft model. Further
testing in established and patient-derived cell line panels revealed an association of PLK1 inhibitor efficacy with cellular Myc expression status. We found that cells with deregulated Myc are vulnerable to PLK1 inhibition, as Myc overexpression sensitizes, whereas its silencing desensitizes, glioblastoma cells to PLK1 inhibitors. This discovery is clinically relevant as glioma progression post-TMZ treatment is frequently accompanied by
genomic amplification and/or pathway activation. In conclusion, PLK inhibitor represents a novel therapeutic option for recurrent gliomas, including those TMZ-resistant from MMR deficiency. Genomic
alteration may serve as a biomarker for PLK inhibitor sensitivity, as Myc-driven tumors demonstrated pronounced responses.
The prognostic impact of TERT mutations has been controversial in IDH-wild tumors, particularly in glioblastomas (GBM). The controversy may be attributable to presence of potential confounding ...factors such as MGMT methylation status or patients' treatment. This study aimed to evaluate the impact of TERT status on patient outcome in association with various factors in a large series of adult diffuse gliomas. We analyzed a total of 951 adult diffuse gliomas from two cohorts (Cohort 1, n = 758; Cohort 2, n = 193) for IDH1/2, 1p/19q, and TERT promoter status. The combined IDH/TERT classification divided Cohort 1 into four molecular groups with distinct outcomes. The overall survival (OS) was the shortest in IDH wild-type/TERT mutated groups, which mostly consisted of GBMs (P < 0.0001). To investigate the association between TERT mutations and MGMT methylation on survival of patients with GBM, samples from a combined cohort of 453 IDH-wild-type GBM cases treated with radiation and temozolomide were analyzed. A multivariate Cox regression model revealed that the interaction between TERT and MGMT was significant for OS (P = 0.0064). Compared with TERT mutant-MGMT unmethylated GBMs, the hazard ratio (HR) for OS incorporating the interaction was the lowest in the TERT mutant-MGMT methylated GBM (HR, 0.266), followed by the TERT wild-type-MGMT methylated (HR, 0.317) and the TERT wild-type-MGMT unmethylated GBMs (HR, 0.542). Thus, patients with TERT mutant-MGMT unmethylated GBM have the poorest prognosis. Our findings suggest that a combination of IDH, TERT, and MGMT refines the classification of grade II-IV diffuse gliomas.
IDH‐mutant gliomas are classified into astrocytic or oligodendroglial tumors by 1p/19q status in the WHO 2016 classification, with the latter presenting with characteristic morphology and better ...prognosis in general. However, the morphological and genetic features within each category are varied, and there might be distinguishable subtypes. We analyzed 170 WHO grade II‐IV gliomas resected in our institution. 1p/19q status was analyzed by microsatellite analysis, and genetic mutations were analyzed by next‐generation sequencing and Sanger sequencing. For validation, the Brain Lower Grade Glioma dataset of The Cancer Genome Atlas was analyzed. Of the 42 grade III IDH‐mutated gliomas, 12 were 1p‐intact/19q‐intact (anaplastic astrocytomas AA), 7 were 1p‐intact/19q‐loss (AA), and 23 showed 1p/19q‐codeletion (anaplastic oligodendrogliomas). Of the 88 IDH‐wild type glioblastomas (GBMs), 14 showed 1p‐intact/19q‐loss status. All of the seven 1p‐intact/19q‐loss AAs harbored TP53 mutation, but no TERT promotor mutation. All 19q‐loss AAs had regions presenting oligodendroglioma‐like morphology, and were associated with significantly longer overall survival compared to 19q‐intact AAs (P = .001). This tendency was observed in The Cancer Genome Atlas Lower Grade Glioma dataset. In contrast, there was no difference in overall survival between the 19q‐loss GBM and 19q‐intact GBM (P = .4). In a case of 19q‐loss AA, both oligodendroglial morphology and 19q‐loss disappeared after recurrence, possibly indicating correlation between 19q‐loss and oligodendroglial morphology. We showed that there was a subgroup, although small, of IDH‐mutated astrocytomas harboring 19q‐loss that present oligodendroglial morphology, and also were associated with significantly better prognosis compared to other 19q‐intact astrocytomas.
Even after the introduction of the WHO 2016 classification, heterogeneity within each category still exists, and the next challenges would include whether we can further refine subtyping of gliomas. Our analysis of 170 diffuse gliomas suggested that there appeared to be a subgroup of IDH‐mutated astrocytomas characterized by isolated 19q‐loss, oligodendroglial morphology and significantly better prognosis compared to other 19q‐intact astrocytomas, providing with a new genetic‐morphological‐clinical association that may characterize a small but distinct subtype within anaplastic astrocytoma.
Purpose
We previously reported that there was a subgroup of
IDH
-mutated astrocytomas harboring only 19q-loss showing oligodendroglioma-like morphology and significantly longer overall survival (OS) ...compared with 19q-intact astrocytomas. The aim of this study was to further explore the biological characteristics of this possible subgroup and obtain insight into the mechanism of their relatively benign clinical behavior.
Methods
We compared gene expression pattern between five 19q-loss and five 19q-intact
IDH
-mutated astrocytomas by microarray analysis.
Results
By comparing expression levels of genes of 19q-loss astrocytomas to those of 19q-intact astrocytomas, 102 up-regulated genes and 162 down-regulated genes were extracted. The down-regulated genes clustered heavily to 19q and 4p while the up-regulated genes clustered to 4q. It was noteworthy that fibroblast growth factor 1 associated with stem cell maintenance and multiple genes associated with glioma progression were down-regulated in 19q-loss astrocytomas, and these results were validated with the independent TCGA data set. On t-SNE analysis of the 19q-loss astrocytomas with other
IDH
-mutant glioma subgroups from the TCGA datasets, the expression pattern of the 19q-loss astrocytomas showed no shift toward oligodendrogliomas with 1p/19q codeletion but rather constituted a subgroup of astrocytoma.
Conclusions
These findings suggested that 19q-loss in astrocytomas is more likely acquired event rather than an early event in oncogenesis like the 1p/19q-codeletion in oligodendrogliomas, and that the biological features of 19q-loss astrocytomas are possibly related to differentially expressed genes associated with stem cell maintenance and glioma progression.
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