Antiproliferative Effects on Tumour Cells and Promotion of Keratinocyte Wound Healing by Different Lichen Compounds

Five compounds representative of major structural classes of lichen polyketides, viz. (+)-usnic (1), salazinic (2), vulpinic (3), gyrophoric (4), and evernic acids (5), were investigated for their ability to affect cell proliferation or wound healing, two functional targets of relevance for research on cancer or tissue regeneration. The experiments were carried out on MM98 malignant mesothelioma cells, A431 vulvar carcinoma cells, and HaCaT keratinocytes. The NRU and CV cytotoxicity assays showed high toxicity for (+)-usnic acid, intermediate toxicity for vulpinic acid, and low toxicity for salazinic, gyrophoric and evernic acids. Scratch wounding experiments on HaCaT monolayers, in the presence of subtoxic doses of lichen compounds, showed strong wound closure effects by (+)-usnic and gyrophoric acid, an intermediate effect by vulpinic and salazinic acids, and no effect by evernic acid. A combination of (+)-usnic and gyrophoric acids gave a further increase in the wound closure rates. The results of a cell migration test correlated with the wound healing data. In conclusion, (+)-usnic acid might be a particularly interesting compound for the prevention of hyperproliferation syndromes, while (+)-usnic and gyrophoric acids qualify as interesting leads in the promotion of tissue regeneration.