An expedient approach to spot natural photosensitizers was established and with it were – for the first time – photosensitizers in mushrooms identified.

Mushrooms such as the dermocyboid Cortinarius rubrophyllus are characterized by strikingly colorful fruiting bodies. The molecular dyes responsible for such colors recently experienced a comeback as photoactive compounds with remarkable photophysical and photobiological properties. One of them—7,7′-biphyscion—is a dimeric anthraquinone that showed promising anticancer effects in the low nanomolar range under blue-light irradiation. Compared to acidic anthraquinones, 7,7′-biphyscion was more efficiently taken up by cells and induced apoptosis after photoactivation. However, seasonal collection of mushrooms producing this compound, low extraction yields, and tricky fungal identification hamper further developments to the clinics. To bypass these limitations, we demonstrate here an alternative approach utilizing a precursor of 7,7′-biphyscion, i.e., the pre-anthraquinone flavomannin-6,6′-dimethyl ether, which is abundant in many species of the subgenus Dermocybe. Controlled oxidation of the crude extract significantly increased the yield of 7,7′-biphyscion by 100%, which eased the isolation process. We also present the mycochemical and photobiological characterization of the yet chemically undescribed species, i.e. C. rubrophyllus. In total, eight pigments (1–8) were isolated, including two new glycosylated anthraquinones (1 and 2). Light-dependent generation of singlet oxygen was detected for the first time for emodin-1-O-β-d-glucopyranoside (3) [photophysical measurement: Φ∆ = 0.11 (CD3OD)]. Furthermore, emodin (7) was characterized as promising compound in the photocytotoxicity assay with EC50-values in the low micromolar range under irradiation against cells of the cancer cell lines AGS, A549, and T24. Graphical abstract

Antimicrobial resistance is one of the biggest health and subsequent economic threat humanity faces. Next to massive global awareness campaigns, governments and NGOs alike stress the need for new innovative strategies to treat microbial infections. One of such innovative strategies is the photodynamic antimicrobial chemotherapy (PACT) in which the synergistic effects of photons and drugs are exploited. While many promising reports are available, PACT – and especially the drug-design part behind – is still in its infancy. Common best-practice rules, such as the EUCAST or CLSI protocols for classic antibiotics as well as high-throughput screenings, are missing, and this, in turn, hampers the identification of hit structures. Hit-like structures might come from synthetic approaches or from natural sources. They are identified via activity-guided synthesis or isolation strategies. As source for new antimicrobials, fungi are highly ranked. They share the same ecological niche with many other microbes and consequently established chemical strategies to combat with the others. Recently, in members of the Cortinariaceae, especially of the subgenus Dermocybe, photoactive metabolites were detected. To study their putative photoantimicrobial effect, a photoantimicrobial high-throughput screening (HTS) based on The European Committee on Antimicrobial Susceptibility Testing (EUCAST) was established. After validation, the established HTS was used to evaluate a sample set containing six colorful representatives from the genus Cortinarius (i.e., Cortinarius callisteus, C. rufo-olivaceus, C. traganus, C. trivialis, C. venetus, and C. xanthophyllus). The assay is built on a uniform, light-emitting diode (LED)-based light irradiation across a 96-well microtiter plate, which was achieved by a pioneering arrangement of the LEDs. The validation of the assay was accomplished with well-known photoactive drugs, so-called photosensitizers, utilizing six distinct emission wavelengths (λexc = 428, 478, 523, 598, or 640 nm) and three microbial strains (Candida albicans, Staphylococcus aureus, and Escherichia coli). Evaluating the extracts of six Cortinarius species revealed two highly promising species, i.e., C. rufo-olivaceus and C. xanthophyllus. Extracts from the latter were photoactive against the Gram-positive S. aureus (c = 7.5 μg/ml, H = 30 J/cm2, λ = 478 nm) and the fungus C. albicans (c = 75 μg/ml, H = 30 J/cm2, λ = 478 nm).

<p><a>Pigments of mushrooms are a fertile ground of inspiration: they spread across various chemical backbones, absorption ranges, and bioactivities. While looking from a photochemical perspective, we discovered a new bioactivity, i.e., photoactivity. We revealed that singlet oxygen production is a common theme in one group of webcaps (i.e., dermocyboid Cortinarii, formerly called Dermocybe). This photoactivity was explored by bioactivity-based molecular networking and photo-activity guided isolation. As a result, three photosensitizers based on anthraquinone structures were isolated. All three were photochemically characterized and (photo)cytotoxically tested. For one of the three, i.e. (-)-7,7’-biphyscion (<b>1</b>), a promising photoyield of </a>f_D= 20 % (l_exc = 455 nm) and an excellent photocytotoxicity of approx. 64 nM against A549 lung cancer cell lines (l_exc = 468 nm, 9.3 J/cm²) was found, while no effect was observed in the dark. Several molecular biological methods proved the harmlessness of <b>1</b> in the dark while showing that apoptosis is dose-dependent induced by <b>1</b> under irradiation. Therewith, <b>1</b> is a promising candidate for photodynamic therapy, while the photoactivity theme in the subgenus hints towards a yet unthought bioactivity in fungi: photoactivated defense.</p>