WHO grade I meningiomas that show regrowth after gamma knife radiosurgery often show 1p36 loss

WHO grade I meningiomas occasionally show regrowth after radiosurgical treatment, which cannot be predicted by clinical features. There is increasing evidence that certain biomarkers are associated with regrowth of meningiomas. The aim of this retrospective study was to asses if these biomarkers could be of value to predict regrowth of WHO grade I meningiomas after additive radiosurgery. Forty-four patients with WHO grade I meningiomas who underwent additive radiosurgical treatment between 2002 and 2015 after Simpson IV resection were included in this study, of which 8 showed regrowth. Median follow-up time was 64 months (range 24–137 months). Tumors were analyzed for the proliferation marker Ki-67 by immunohistochemistry and for deletion of 1p36 by fluorescence in situ hybridization (FISH). Furthermore, genomic DNA was analyzed for promoter hypermethylation of the genes NDRG1–4, SFRP1, HOXA9 and MGMT. Comparison of meningiomas with and without regrowth after radiosurgery revealed that loss of 1p36 (p = 0.001) and hypermethylation of NDRG1 (p = 0.046) were correlated with regrowth free survival. Loss of 1p36 was the only parameter that was significantly associated with meningioma regrowth after multivariate analysis (p = 0.01). Assessment of 1p36 loss in tumor tissue prior to radiosurgery might be considered an indicator of prognosis/regrowth. However, this finding has to be validated in an independent larger set of tumors.

An inactivating mutation in HDAC2 leads to dysregulation of apoptosis mediated by APAF1

BACKGROUND & AIMS

Histone deacetylases (HDACs) are important regulators of chromatin involved in silencing tumor suppressor genes. We examined mutation of HDAC2 and examined consequences of HDAC2 loss.

METHODS

Colon cancer cell lines and primary cancers were examined for mutations in HDAC2 by direct sequencing and capillary electrophoresis. Promoter methylation was determined using methylation-specific polymerase chain reaction in primary tumors. Sensitivity to HDAC inhibitors and resistance in vitro used colon cancer cell lines.

RESULTS

HDAC2 mutations in the poly(A) tract in exon 1 result in a frameshift and premature stop codon. These were found in microsatellite instability (MSI) cell lines and 43% of MSI colon cancers, but only 7% of microsatellite stable cancers. Mutation was associated with complete or regional tumor specific loss of HDAC2 protein. Inactivation of HDAC2 was not associated with large-scale changes in promoter region methylation, but rather is a consequence of epigenetic MLH1 inactivation leading to MSI. HDAC2 mutation results in apoptotic resistance to HDAC inhibitors (trichostatin A or suberoylanilide hydroxamic acid), despite induction of global histone acetylation. Differential induction of apoptosis by HDAC inhibitors is mediated by the proapoptotic gene APAF1, as shown by specific APAF1 induction only in cell lines with functional HDAC2, HDAC2 protein localization to the APAF1 promoter by chromatin immunoprecipitation, siRNA knockdown of HDAC2 leading to up-regulation of APAF1, and stable knockdown of APAF1 reducing apoptotic response to HDAC inhibitors.

CONCLUSIONS

Frequent HDAC2 mutations are found in MSI tumors and HDAC2 plays a major role in mediating apoptotic response to HDAC inhibitors through direct regulation of APAF1.