Objective: Lichens are emerging as a promising natural source of bioactivities of pharmaceutical
interest. The present study aims to contribute to the knowledge of the lichen Umbilicaria muhlenbergii
as a potential source of pharmaceutically relevant anticancer and antibiotic lichen chemicals.
Methods: The crude acetone extract of U. muhlenbergii exhibited 13.3 μg mL-1 cytotoxic activity
(EC50) against breast cancer cells (MCF-7), as compared to a cisplatin positive control with EC50 of
5.8 μg mL-1. The antibiotic activity of the crude extract against a gram-positive Staphylococcus aureus
was 22.5 μg mL-1
as MIC. Using silica gel 60 (SG60) column chromatography, the crude extract was
then separated into eight fractions, which were further evaluated for their anticancer activities against
MCF-7 cells. By means of propidium iodide flow cytometry, two of the eight SG60 fractions were
found to cause cell cycle arrest in MCF-7 cells (73.14% of cells) at the G2 phase, which is indicative
of apoptosis and inhibition of cellular proliferation.
Results: Identification of chemical constituents present in these two SG60 fractions was carried out
with Thin-Layer Chromatography (TLC) and a lichen metabolite database (Wintabolites). The two
fractions (SG60-5 and SG60-6) were found to contain compounds belonging to the chemical families
depsides, depsidones, anthraquinones, and xanthones.
Discussion: The SG60-5 and SG60-6 fractions were further fractionated with Sephadex LH-20. Over
15% of the 46 LH-20 fractions obtained from the SG60-5 fraction caused 100% cell death, whereas
32% of the LH-20 fractions derived from SG60 6 fraction reduced cell survival to below 20%.
Conclusion: This work extends the evaluation of the cytotoxic and antibiotic activities of lichen secondary
metabolites to the species U. muhlenbergii. It presents encouraging results of pharmaceutical
interest that set up lichens as an effective source of new bioactive natural products. Further investigations
are underway to reveal the full biopharmaceutical potential of U. muhlenbergii.