EPIGENETIC MODULATION OF STEMNESS AND DIFFERENTIATION BY VALPROIC ACID IN MEDULLOBLASTOMA

Abstract

Abstract AIMS Changes in epigenetic processes, including histone acetylation, are proposed as key events affecting tumor cell function and the initiation and progression of pediatric brain cancers. Valproic acid (VPA) is an antiepileptic drug that acts partially by inhibiting histone deacetylases (HDACs) and could be repurposed as an epigenetic anticancer therapy. Here, we report VPA-induced alterations in features related to stemness and differentiation in medulloblastoma (MB) cells. METHOD Human MB cells were treated with different concentrations of VPA and cell viability was measured with a trypan exclusion assay. Cell cycle was evaluated with flow cytometry. Expansion of MB cancer stem cells (CSCs) was evaluated by a neurosphere formation assay. Reverse transcriptase polymerase chain reaction (RT-qPCR) was used to analyze mRNA expression and Western Blot to analyze protein levels. H3K9 histone acetylation (H3K9ac) was measured with immunofluorescence, and chromatin Immunoprecipitation (ChIP) was used to evaluate the occupancy of gene promoter regions by H3K9ac. RESULTS VPA reduced MB cell viability and expansion of MB CSCs, induced morphological changes consistent with neuronal differentiation, and increased expression of differentiation markers tubulin beta 3 class III (TUBB3) and enolase 2 (ENO2). Expression of stemness markers SOX2 and Nestin was differentially affected by VPA in cells representative of SHH or Group 3/4 MB molecular subgroups. VPA increased H3K9ac and its occupancy of promoter regions of TP53 and CDKN1A genes. CONCLUSION Our results indicate that VPA may exert antitumor effects in MB by influencing histone acetylation, which may result in modulation of stemness and stimulation of neuronal differentiation.