Targeted isolation of photoactive pigments from mushrooms yielded a highly potent new photosensitizer: 7,7′-biphyscion

Pigments of fungi are a fertile ground of inspiration: they spread across various chemical backbones, absorption ranges, and bioactivities. However, basidiomycetes with strikingly colored fruiting bodies have never been explored as agents for photodynamic therapy (PDT), even though known photoactive compound classes (e.g., anthraquinones or alkaloids) are used as chemotaxonomic markers. In this study, we tested the hypothesis that the dyes of skin-heads (dermocyboid Cortinarii) can produce singlet oxygen under irradiation and thus are natural photosensitizers. Three photosensitizers based on anthraquinone structures were isolated and photopharmaceutical tests were conducted. For one of the three, i.e., (–)-7,7′-biphyscion (1), a promising photoyield and photocytotoxicity of EC(50) = 0.064 µM against cancer cells (A549) was found under blue light irradiation (λ(exc) = 468 nm, 9.3 J/cm(2)). The results of molecular biological methods, e.g., a viability assay and a cell cycle analysis, demonstrated the harmlessness of 1 in the dark and highlighted the apoptosis-inducing PDT potential under blue light irradiation. These results demonstrate for the first time that pigments of dermocyboid Cortinarii possess a so far undescribed activity, i.e., photoactivity, with significant potential for the field of PDT. The dimeric anthraquinone (–)-7,7′-biphyscion (1) was identified as a promising natural photosensitizer.