DR-04 * VALPROIC ACID AND HEDGEHOG PATHWAY: A POSSIBLE DRUG RESISTANCE MECHANISM IN MEDULLOBLASTOMA?

Abstract

BACKGROUND: Medulloblastoma (MB) is a malignant neuroepithelial embryonal tumor of cerebellum. In children, they comprise the most frequent embryonal brain tumor. This study aim to investigate the role of valproic acid (VA) and cisplatin (CDDP) in the cytotoxicity, viability, and expression of hedgehog pathway (HH) in MB DAOY cell line. METHODS: The treatment of DAOY cells was distributed in four groups: (1) VA single, (2) CDDP single, (3) VA sensibilization + CDDP, (4) untreated. Cell viability was measured by Presto Blue assay, qPCR was performed to quantify HH genes and two PTCH1 punctual mutations were investigated by direct sequencing. RESULTS: VA and CDDP affected the viability of DAOY cell line (IC50= 6mM and 10mM, respectively). VA sensibilization followed by CDDP exposure (group 3) caused the most significant reduction of cell viability. Interestingly, we observed higher expression levels of PTCH1, SMO, GLI1 and GLI2 genes in the cells treated with VA (single or combined), than the cells submitted to the others treatments (groups 2 and 4). We identified the presence of H408N mutation, in PTCH1 gene in DAOY cells. CONCLUSIONS: The HH pathway is considered to be crucially involved in the development of MB. Our study showed that MB cells resistant to treatment with VA, single or combined, presented high expression of HH genes. Recent studies have demonstrated that the chronic use of VA is associated with reactivation of AKT pathway, which may be involved in resistance development. Additionally, AKT activates HH pathway in an independent-manner. In this way, we suggest that the resistance of MB cells submitted to VA treatment may be related to the activation of HH pathway via AKT. The MB treatment with VA should be cautious and deserves further investigation about the role of this HDAC inhibitor in the drug resistance development in MB.