Siderol Inhibits Proliferation of Glioblastoma Cells and Acts Synergistically with Temozolomide

Abstract

Glioblastoma (GBM) is the most aggressive primary central nervous system (CNS) tumor in adults with dismal prognosis. Currently, the therapeutic interventions include gross total resection, when possible, followed by radiotherapy and chemotherapy. However, despite treatment, tumor usually recurs within 7–9 months. The presence of glioma cells with stem-like properties and tumor’s heterogeneity have been identified as the most important factors driving recurrence. Recently, research efforts have been focused on the use of natural substances as treatment for GBM. Siderol is an ent-kaurane diterpenoid, isolated from the genus Sideritis. Sideritis extracts have already been investigated for their anti-inflammatory, antioxidant, and anticancer effects. In this study, we investigated the antitumoral effects of siderol in GBM T98 and U87 cell lines, as well as the effects of combined treatment with temozolomide (TMZ). Cell viability was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and trypan blue exclusion assay. Different concentrations of siderol were used in order to calculate the IC50 values at 72 h after treatment. Flow cytometry used for the DNA cell cycle analysis after treatment with siderol in concentrations of IC50 and twice the IC50 values for 72 h. Furthermore, the effect of siderol in cell’s migratory ability was tested using wound healing assay. Cell viability and proliferation, after combined treatment with siderol and TMZ, also were evaluated with the trypan blue exclusion assay and the effects of the combination treatment were analyzed with CompuSyn software. Treatment with siderol significantly reduced cell viability in T98 and U87 cell lines in a dose-dependent manner and IC50 values were calculated, 18 μM and 13 μM, respectively. Moreover, siderol induced G0/G1 cell cycle arrest in a dose-dependent manner and inhibited the migration in both cell lines. In addition, siderol and TMZ seem to have synergistic action in the majority of tested concentrations in both T98 and U87 cells. In conclusion, siderol may represent an innovative strategy for the treatment of GBM, and further studies are needed on siderol’s efficacy and mode of action.

Antineoplastic Activity of 9″-Lithospermic Acid Methyl Ester in Glioblastoma Cells

“…For these reasons, it is imperative that new, more effective drugs are discovered. So far, a plethora of active compounds from plants and herbs have been found with potential cytotoxic properties against various types of cancer [14,[16][17][18][19]. For this reason, we undertook the study of a natural compound, 9 ′′ -lithospermic acid methyl ester, isolated from the methanolic extract of Thymus thracicus Velen or thyme.…”

“…The cytotoxicity assay was performed in triplicate, and the results represent the mean of the three assays. Additionally, the Trypan Blue exclusion assay was used to assess the viability of the cells following co-treatment with TMZ and 9 ′′ -lithospermic acid methyl ester [19].…”

“…The cells were incubated for 72 h, washed twice with phosphate-buffered saline (PBS), and then Crystal Violet solution 0.2% (0.2 g Crystal Violet Powder, MERCK in 80 mL ddH 2 O and 20 mL Methanol, MERCK GLOBAL, Athens, Greece) was added in each well and the plates were placed on a rocking shaker for 2-3 min. Subsequently, the plates were rinsed with running water twice and left to dry for 24 h, after which pictures of every well-plate were obtained by phase-contrast microscopy [19].…”

Iloperidone and Temozolomide Synergistically Inhibit Growth, Migration and Enhance Apoptosis in Glioblastoma Cells

“…Multiple combination doses of ILO and TMZ were tried and tested in order to select the most effective combination dose at which cell growth inhibition was synergistic. The doses were selected considering previous studies where IC 50 of 80 µM was reported for ILO; a range of 10 µM to 100 µM was used for TMZ [ 38 , 39 , 40 , 41 ]. ILO and TMZ were dissolved in 100% sterile DMSO at a stock concentration of 50 mM and carefully stored at −20 °C until further use.…”

Antioxidant and Antitumor Potential of Micropropagated Balkan Endemic Sideritis scardica Griseb

“…The high concentration of phenolic compounds, and especially of some flavonoids, is one reason for its cytotoxic effect against cancer cells [19,27,28]. An antitumor effect of siderol (diterpenoid) has been demonstrated in glioblastoma GBM T98 and U87 cell lines [29] and in C6 rat glioma cells [23].…”