An overview of the therapeutic potential of understudied lichen species for novel drug discovery

Due to the emergence of new diseases, drug discovery is an ever-exciting field of science. Researchers have shifted their focus from chemical-based medicines to drugs of natural origin and their structural synthetic analogues to solve the problem of developing antibiotic resistance and the detrimental impacts of existing chemical medications. Lichens are still one of the least explored natural sources for drug discovery. These slow-growing forms are a rich source of some exceptional secondary metabolites known collectively as lichenochemicals. The significant proportion of these lichenochemicals are bioactive compounds with multiple pharmacological properties, including antimicrobial, anticancer, free radical scavenging, anti-inflammatory, antidiabetic and neuroprotective abilities and are also high in nutritional values, making this uncanny combination of algae and fungi, together with their metabolites, so well renowned in traditional and indigenous medicine. Although only oral knowledge was available about them earlier, studies over the last few decades have isolated and identified some unique bioactive compounds with high medicinal values, making lichen biology one of the most interesting and promising areas of pharmacological research. More than half of the lichen species and phytochemicals are yet to be explored. However, lichen-derived vitamin D3 is the only vegan source of vitamin D3. Likewise, studies have shown that lichenochemicals can significantly reduce the problem of antibiotic resistance developed by microorganisms. Advanced techniques in identification and isolation, combined with bioinformatics, predictive software, and databases, have greatly aided in understanding lichen chemistry. This review summarizes the use of lichens in drug discovery with a highlight on recent breakthroughs in lichen biology.