Fungi have received much attention as a source of bioactive compounds with variety of therapeutic properties such as antioxidant, antibacterial, antiviral, antiparasitic and anticancer activities. With great biomedical potential, these pharmacologically-active natural products tend to replace the currently used synthetic drugs. The objective of this study was to evaluate the antioxidant potential, aldo-keto reductase (AKR) inhibition, and estrogen receptor binding affinity of two different extract types (70% ethanolic and hot water) derived from one indigenous fungal species, namely Fomes fomentarius sampled from Uzbekistan.

Evaluation of antioxidant activity in the tested fungal extracts was conducted using established in vitro assays, including ABTS, DPPH, and FRAP. Fungal extracts were tested in vitro for binding affinity to ligand-binding domains of estrogen receptor α and estrogen receptor β using fluorescencent screen in yeast and their potential to inhibit aldo-keto reductases, valuable targets for the treatment of hormone-dependent diseases. The results revealed that the highest scavenging activity and reducing power potential was observed for the analyzed 70% EtOH extract (DPPH: 12.11 mg TE/g d.w., ABTS: 124.24 mg TA/g d.w. and FRAP: 350.52 mg TE/g d.w.).

Similarly, the 70% EtOH extract of F. fomentarius exhibited higher inhibition potential against AKR1C3 (91.9%) than the hot water extract (35.7%). These fungal extracts showed weak inhibition against AKR1C4 isoform and no estrogenicity, making them promising candidates for the design of anticancer therapeutics against estrogen-dependent breast cancer.

In conclusion, our study highlights the promising potential of F. fomentarius extracts as a basis for additional study in the searching for novel natural anticancer drugs.