Lichen secondary metabolites inhibit Wnt/β-catenin pathway in glioblastoma cells and improve the anticancer effects of temozolomide

Lichens are a source of secondary metabolites with significant pharmacological potential. Data regarding their possible application in glioblastoma (GBM) treatment are, however scarce. The study aimed to analyze the mechanism of action of six lichen secondary metabolites: atranorin, caperatic acid, physodic acid, squamatic acid, salazinic acid, and lecanoric acid using two- and three-dimensional GBM cell line models. The Parallel Artificial Membrane Permeation Assay was used to predict the blood-brain barrier penetration ability of the tested compounds. Their cytotoxicity was analyzed using MTT test on A-172, T98G, and U-138 MG cells. Flow cytometry was applied for the analysis of oxidative stress, cell cycle distribution, and apoptosis, whereas qPCR and microarrays detected the induced transcriptomic changes. Our data confirm the ability of lichen secondary metabolites to cross the blood-brain barrier and exert cytotoxicity against GBM cells. Moreover, the compounds generated oxidative stress, interfered with the cell cycle, and induced apoptosis in T98G cells. They also inhibited Wnt/β-catenin pathway, and this effect was even stronger in case of a co-treatment with temozolomide. Transcriptomic changes in cancer related genes induced by caperatic acid and temozolomide were the most pronounced. Lichen secondary metabolites, in particular caperatic acid should be further analyzed as potential anti-GBM agents. The T98G spheroids were exposed to the influence of lichen secondary metabolites for 48 h and subjected to microarray analysis. A pairwise scatter plot analysis was performed to determine the general profiles of the whole gene expression in the control (1), TMZ 100 μM (2), atranorin 25 μM + TMZ 100 μM (3), caperatic acid 50 μM + TMZ 100 μM (4), physodic acid 25 μM + TMZ 100 μM (5), squamatic acid 25 μM + TMZ 100 μM (6), salazinic acid 50 μM + TMZ 100 μM (7) and lecanoric acid 100 μM + TMZ 100 μM (8) experimental groups.