Molecular dissection of the valproic acid effects on glioma cells

Abstract

Many glioblastoma patients suffer from seizures why they are treated with antiepileptic agents. Valproic acid (VPA) is a histone deacetylase inhibitor that apart from its anticonvulsive effects in some retrospective studies has been suggested to lead to a superior outcome of glioblastoma patients. However, the exact molecular effects of VPA treatment on glioblastoma cells have not yet been deciphered. We treated glioblastoma cells with VPA, recorded the functional effects of this treatment and performed a global and unbiased next generation sequencing study on the chromatin (ChIP) and RNA level. 1) VPA treatment clearly sensitized glioma cells to temozolomide: A protruding VPA-induced molecular feature in this context was the transcriptional upregulation/reexpression of numerous solute carrier (SLC) transporters that was also reflected by euchromatinization on the histone level and a reexpression of SLC transporters in human biopsy samples after VPA treatment. DNA repair genes were adversely reduced. 2) VPA treatment, however, also reduced cell proliferation in temozolomide-naive cells: On the molecular level in this context we observed a transcriptional upregulation/reexpression and euchromatinization of several glioblastoma relevant tumor suppressor genes and a reduction of stemness markers, while transcriptional subtype classification (mesenchymal/proneural) remained unaltered. Taken together, these findings argue for both temozolomide-dependent and -independent effects of VPA. VPA might increase the uptake of temozolomide and simultaneously lead to a less malignant glioblastoma phenotype. From a mere molecular perspective these findings might indicate a surplus value of VPA in glioblastoma therapy and could therefore contribute an additional ratio for clinical decision making.

Cellular Effects of the Antiepileptic Drug Valproic Acid in Glioblastoma

“…In addition, VPA at a concentration of 750 µM did not radiosensitize the three human glioblastoma cell lines and three primary glioblastoma spheroid cultures studied in delayed plating colony formation assays and pre-plating limited dilution assays, respectively. These results were unexpected in light of the reported chromatin remodeling action of VPA [18, 48-50] and contradictory to previous in vitro studies [10-15, 17, 48, 51, 52] which clearly show VPA-induced cell death or radio- or chemosensitization in cancer cells including glioma. Unlike the present work, VPA concentrations of 1-5 mM [52], 1.5-2 mM [10], 1-5 mM [51], 2.5-5 mM [11], 1.5-3 mM [12], 1-15 mM [13], 2-16 mM [14], 7.5 mM [18], 2 mM [19], 5-20 mM [53], 1-10 mM [21], or 4.8 mM [22] were applied in these studies.…”

“…DNA demethylation, however, might induce up-regulation of MGMT expression and might confer resistance to temozolomide. In contrast to this assumption, VPA has been shown to down-regulate MGMT expression in glioma cells [17] and to sensitize glioblastoma cells to temozolomide in vitro in some [11, 17, 18] but not all [19] studies (for review see [20]. …”

The first-in-class alkylating deacetylase inhibitor molecule tinostamustine shows antitumor effects and is synergistic with radiotherapy in preclinical models of glioblastoma

“…While vorinostat (suberoylanilide hydroxamic acid, SAHA) and panobinostat have undergone equal evaluation as combination therapies for TMZ in glioblastoma [ 20 , 21 ], of the potential for HDACi may be as a radio-sensitizer inducing chromatin relaxation, altering transcription of DNA damage repair genes and common cell death pathway synergisms [ 22 ]. Furthermore, despite increasing the efficacy of chemotherapeutic agents such as TMZ [ 22 , 23 ], HDAC inhibitors may potentiate the evolution of acquired TMZ resistance linked to MGMT upregulation in glioblastoma xenografts [ 24 ]. Tinostamustine (EDO-S101; TINO) is the first-in-class alkylating deacetylase inhibitor (AK-DACi) molecule which was designed to create a very potent cytotoxic agent for systemic use, with the aim of increasing the efficacy of the alkylating DNA damage through deacetylase-mediated chromatin relaxation.…”

Effects of siRNA Targeting Interference of APE1 Gene on Proliferation and Apoptosis of Glioma Cells

“…As a speed limiting enzyme in the DNA excision repair (base, excision, repair, BER) pathway, APE1 was an extremely important repair factor for genotoxic drugs (such as alkylating agents) and radiation damage of cells. In addition, APE1 still has redox (reductionoxidation) function (Riemenschneider et al, 2016). Through the regulation of dependent and non-dependent redox, it can be used to maintain the organization including unique transcription factors (such as p53, Egr-1, AP-1), tissue-specific transcription factors (such as TTF-1, PAX-8, PEBP-2), and transcription factor activation reduced state.…”