Glioblastoma (GBM) is the most frequent and aggressive primary malignant brain tumor and PI3K/Akt signaling pathway is activated in almost 90% of cases. The aim of this study was to evaluate the capacity of natural compounds to potentiate the activity of temozolomide (TMZ) - the standard pharmacological drug for GBM.
U-87 MG (ATCC HTB-14) cells were treated with quercetin, resveratrol, curcumin and TMZ, alone or in combination of TMZ with either of them, for 30 minutes (for signaling protein phosphorylation) and 48 hours (for total signaling protein expression). LDH-based cytotoxicity and MTS assays were performed for dose selection. Signaling molecular patterns were studies by xMAP array technology. The effect of treatments was evaluated by assessing a 9-plex panel of total and phosphorylated signaling proteins.
Based on the cytotoxicity testing, selected working concentrations were 30 μM for quercetin, 30 μM for resveratrol, 15 μM for curcumin and 50 μM temozolomide. We found strong increase in JNK Thr183/Tyr185, p38 Thr180/Tyr182 and STAT3 Ser727 phosphorylation and a moderate increase for ERK1/2 Thr185/Tyr187 phosphorylation after 30 minutes of treatment. Resveratrol treatment reduced Akt Ser473 phosphorylation, whereas the other treatments had no effect. After 48 hours treatment of U87 cells, the expression of most signaling proteins analyzed (CREB, JNK, ERK1/2, Akt and STAT3) was decreased upon treatment with natural products alone. When the natural compounds were combined with TMZ, an even stronger decrease in protein expression was observed: CREB fold-regulation 0.63-0.78), NFkB (fold-regulation 0.81-0.86) and p38 (fold-regulation 0.68-0.85).
Our results revealed that quercetin and resveratrol performed best in potentiating TMZ effects on signaling protein expression. Natural compounds could be used as therapeutic adjuvants in GBM therapy. Given the complexity of signaling pathways in GBM treatment approaches, further studies are required to unravel the mechanisms for precision therapy.
Victor Babes National Institute of Pathology.
Ministry of Research, Innovation and Digitization, project no. COP A 1.2.3., ID: P_40_197/2016, PN 19.29.01.04, PN 19.41.50.01, PED 382 and 31PFE/2021.
All authors have declared no conflicts of interest.