Cytotoxic and Antibiotic Potential of Secondary Metabolites from the Lichen Umbilicaria muhlenbergii.

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.

Lichenochemicals: extraction, purification, characterization, and application as potential anticancer agents.

Introduction: To date, over 1,000 lichen secondary metabolites have been identified. Despite their promising cytotoxic properties, the number of literature reports on anticancer evaluation of lichenochemicals is limited. As cancer prevalence among the human population increases, there is growing interest in lichens as a natural source of secondary metabolites for anti-cancer drug discovery and development.Areas covered: The lack of significant progress in lichen anticancer research is due to the low levels of cytotoxic compounds contained in lichens, the technical difficulties associated with their isolation and characterization, and the insufficient understanding of their mechanism of action on different cancer cell lines. In this review, the authors discuss these challenges and provide systematically organized information on the limitations and advantages of commonly used and newly developed methods for lichen exploration and screening of lichen secondary metabolites for their anticancer potential.Expert opinion: Recent research activities have demonstrated that lichen secondary metabolites possess chemotherapeutic properties. A systematic and multidisciplinary approach is required to advance lichen research and improve our understanding of the mechanisms responsible for the potent cytotoxic properties of lichenochemicals. More efforts need to focus on screening and discovery of new lichen-derived compounds with unique anticancer properties.