Targeted Isolation of Photoactive Pigments from Mushrooms Yielded a Highly Potent New Photosensitizer: 7,7’-Biphyscion

Abstract

<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<sub>D</sub>= 20 % (l<sub>exc</sub> = 455 nm) and an excellent photocytotoxicity of approx. 64 nM against A549 lung cancer cell lines (l<sub>exc</sub> = 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>

Does the chemistry of fungal pigments demand the existence of photoactivated defense strategies in basidiomycetes?

“…Furthermore, we were also able to isolate and to describe new AQ-like PSs from Cortinarius i.a. the dimeric AQ 7,7′-Biphyscion (60) which under irradiation exhibits antitumor activities in the nanomolar range (60), which is photoactive [112]. Another chemotaxonomic marker of the Cortinarius subgenus Dermocybe is hypericin (11), underlining further the hypothesis of a general phototoxicity in dermocyboid Cortinarii.…”

Feature-Based Molecular Networking—An Exciting Tool to Spot Species of the Genus Cortinarius with Hidden Photosensitizers

“…Molecular structures were selected hierarchically, whereby the conformity of the annotation results (spectral matching against GNPS, ISDB-DNP, and an in-house library) was more trusted than the result of solely the in-house library (fungal origin) or solely the in silico annotation. Anthraquinone-rich fractions from a previous study (i.e., the mycochemical investigation of C. uliginosus [8]) were integrated into the FBMN to attain the marker compounds dermolutein (ID3), dermorubin (ID5), 5-chlorodermorubin (ID23), and 7,7 -biphyscion (ID31) (Figure 5). By manually propagating the structural information provided by these markers, the dependability of the annotation for features clustering with these compounds can be greatly increased.…”

“…Based on matching MS 2 spectral data and the use of authentic reference compounds, two features were identified as the AQs dermolutein (ID3, Cluster A) and dermorubin (ID5, Cluster A). Both exhibited light-induced activity (i.e., production of 1 O 2 ) [8]. These AQ-carboxylic acids are known secondary metabolites of dermocyboid Cortinarii [9], but are unlikely to contribute to its photocytotoxic effect due to their insufficient cellular uptake [8].…”

“…Recently, hints of an overlooked chemical defense mechanism in the kingdom Fungi were discovered: photoactive metabolites in dermocyboid Cortinarii [7,8]. Fungi from this phylogenetic lineage are characterized by brightly colored fruiting bodies, which owe their hues to polyketide pigments [9].…”

“…Fungi from this phylogenetic lineage are characterized by brightly colored fruiting bodies, which owe their hues to polyketide pigments [9]. Some of these fungal anthraquinones, e.g., 7,7 -biphyscion, exhibited a promising singlet oxygen production yield and were highly phototoxic, as they induced light-dependent apoptosis in the nanomolar range [8]. Therefore, a thorough investigation of the photoactivity phenomenon occurring in the genus Cortinarius combined with the identification and isolation of photoactive compounds could contribute to a more comprehensive understanding of fungal defense strategies (i.e., ecological role).…”