9734

HDAC9

HD7|HD7b|HD9|HDAC|HDAC7|HDAC7B|HDAC9B|HDAC9FL|HDRP|MITR;histone deacetylase 9;HDAC9;histone deacetylase 9

MEF-2 interacting transcription repressor (MITR) protein|histone deacetylase 4/5-related protein|histone deacetylase 7B

7p21.1

protein-coding

PURPOSE: Medulloblastomas are the most common malignant brain tumors in childhood. Survivors suffer from high morbidity because of therapy-related side effects. Thus, therapies targeting tumors in a specific manner with small molecules such as histone deacetylase (HDAC) inhibitors are urgently warranted. This study investigated the expression levels of individual human HDAC family members in primary medulloblastoma samples, their potential as risk stratification markers, and their roles in tumor cell growth. EXPERIMENTAL DESIGN: Gene expression arrays were used to screen for HDAC1 through HDAC11. Using quantitative real time reverse transcriptase-PCR and immunohistochemistry,we studied the expression of HDAC5 and HDAC9 in primary medulloblastoma samples.In addition, we conducted functional studies using siRNA-mediated knockdown of HDAC5 and HDAC9 in medulloblastoma cells. RESULTS: HDAC5 and HDAC9 showed the highest expression in prognostically poor subgroups. This finding was validated in an independent set of medulloblastoma samples. High HDAC5 and HDAC9 expression was significantly associated with poor overall survival, with high HDAC5 and HDAC9 expression posing an independent risk factor. Immunohistochemistry revealed a strong expression of HDAC5 and HDAC9 proteins in most of ALL primary medulloblastomas investigated. siRNA-mediated knockdown of HDAC5 or HDAC9 in medulloblastoma cells resulted in decreased cell growth and cell viability. CONCLUSION: HDAC5 and HDAC9 are significantly upregulated in high-risk medulloblastoma in comparison with low-risk medulloblastoma, and their expression is associated with poor survival. Thus, HDAC5 and HDAC9 may be valuable markers for risk stratification. Because our functional studies point toward a role in medulloblastoma cell growth, HDAC5 and HDAC9 may potentially be novel drug targets.#CI- (c) 2010 AACR.

Altered expression of histone deacetylases (HDACs) is a common feature in several human malignancies and may represent an interesting target for cancer treatment,including haematological malignancies. We evaluated the mRNA gene expression profile of 12 HDAC genes by quantitative real-time polymerase chain reaction in 94 consecutive childhood acute lymphoblastic leukaemia (ALL) samples and its association with clinical/biological features and survival. ALL samples showed higher expression levels of HDAC2, HDAC3, HDAC8, HDAC6 and HDAC7 when compared to normal bone marrow samples. HDAC1 and HDAC4 showed high expression in T-ALL and HDAC5 was highly expressed in B-lineage ALL. Higher than median expression levels of HDAC3 were associated with a significantly lower 5-year event-free survival (EFS) in the overall group of patients (P = 0.03) and in T-ALL patients (P = 0.01). HDAC7 and HADC9 expression levels higher than median were associated witha lower 5-year EFS in the overall group (P = 0.04 and P = 0.003, respectively) and in B-lineage CD10-positive patients (P = 0.009 and P = 0.005, respectively).Our data suggest that higher expression of HDAC7 and HDAC9 is associated with poor prognosis in childhood ALL and could be promising therapeutic targets for the treatment of refractory childhood ALL.#CI- (c) 2010 Blackwell Publishing Ltd.

Medulloblastomas are the most common malignant brain tumors in childhood. Emerging evidence suggests that medulloblastoma comprises at least four distinctdiseases (WNT, SHH, Group 3 and 4) with different biology, clinical presentation, and outcome, with especially poor prognosis in Group 3. The tight connection of biology and clinical behavior in patients emphasizes the need for subgroup-specific preclinical models in order to develop treatments tailored to each subgroup. Herein we report on the novel cell line HD-MB03, isolated from tumor material of a patient with metastasized Group 3 medulloblastoma, and preclinical testing of different histone deacetylase inhibitors (HDACis) in thismodel. HD-MB03 cells grow long term in vitro and form metastatic tumors in vivo upon orthotopic transplantation. HD-MB03 cells reflect the original Group 3 medulloblastoma at the histological and molecular level, showing large cell morphology, similar expression patterns for markers Ki67, p53, and glial fibrillary acidic protein (GFAP), a gene expression profile most closely matching Group 3 medulloblastomas, and persistence of typical molecular alterations, i.e., isochromosome 17q [i(17q)] and MYC amplification. Protein expression analysis ofHDACs 2, 5, 8, and 9 as well as the predictive marker HR23B showed intermediate to strong expression, suggesting sensitivity to HDACis. Indeed, treatment with HDACis Helminthosporium carbonum (HC)-toxin, vorinostat, and panobinostat revealed high sensitivity to this novel drug class, as well as a radiation-sensitizing effect with significantly increased cell death upon concomitant treatment. In summary, our data indicate that HD-MB03 is a suitable preclinical model for Group 3 medulloblastoma, and HDACis could represent a therapeutic option for this subgroup.