Biorefining Research Institute, Lakehead University, 1294 Balmoral Street, Thunder Bay, Ontario P7B 5Z5, Canada.
Curr Pharm Biotechnol. 2020;21(14):1516-1527. doi: 10.2174/1389201021666200504114515.
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.
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.
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.
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%.
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.
地衣作为具有药物应用前景的生物活性的新兴天然来源，越来越受到关注。本研究旨在进一步了解地衣 U. muhlenbergii 作为具有潜在药用价值的抗癌和抗生土地衣化学物质的来源。
U. muhlenbergii 的粗丙酮提取物对乳腺癌细胞（MCF-7）的细胞毒性（EC50）为 13.3μg mL-1，而顺铂阳性对照的 EC50 为 5.8μg mL-1。粗提取物对革兰氏阳性菌金黄色葡萄球菌的抗生素活性为 22.5μg mL-1（MIC）。采用硅胶 60（SG60）柱层析法，将粗提取物分离成 8 个馏分，进一步评价其对 MCF-7 细胞的抗癌活性。通过碘化丙啶流式细胞术，发现 8 个 SG60 馏分中的两个导致 MCF-7 细胞发生细胞周期阻滞（G2 期 73.14%的细胞），表明细胞凋亡和细胞增殖抑制。
利用薄层色谱法（TLC）和地衣代谢产物数据库（Wintabolites）对这两种 SG60 馏分中存在的化学成分进行了鉴定。发现这两个馏分（SG60-5 和 SG60-6）含有属于地衣酚、地衣酮、蒽醌和黄烷酮类化学家族的化合物。
SG60-5 和 SG60-6 馏分进一步用 Sephadex LH-20 进行了分离。从 SG60-5 馏分获得的 46 个 LH-20 馏分中的 15%以上导致细胞死亡 100%，而 SG60-6 馏分中获得的 32%的 LH-20 馏分使细胞存活率降低到 20%以下。
这项工作将地衣次生代谢物的细胞毒性和抗生素活性的评价扩展到 U. muhlenbergii 物种。它提供了具有药物应用前景的令人鼓舞的结果，使地衣成为新的生物活性天然产物的有效来源。目前正在进行进一步的研究，以揭示 U. muhlenbergii 的全部生物制药潜力。
