Flavonoids are plant secondary metabolites with a broad spectrum of biological activities. In nature, they occur mainly in the form of glycosides, but their extraction is often difficult and expensive, as is chemical synthesis. We have shown that biotransformations are an excellent method for obtaining flavonoid glycosides. We are the first team to describe the use of Isaria microorganisms in biotransformations of flavonoid compounds. In the present study as biocatalysts, we used one strain of Isaria fumosorosea KCH J2 isolated from a spider carcass in green areas of Wroclaw and two strains of I. farinosa (J1.4 and J1.6) isolated from insects found in already unused mines in Lower Silesia. The substrates were 3-hydroxyflavone, 3-methoxyflavone, quercetin (3,3′,4′,5,7-pentahydroxyflavone), and baicalein (5,6,7-trihydroxyflavone). For all the substrates that were used in this study, we obtained 4-O-methylglucopyranosides. In the case of substrates with a hydroxyl group in the third position, O-β-d-glucopyranosides were also formed. Isoquercetin that was obtained by biotransformation was used as a substrate to check the kinetics of the formation of flavonoid 4-O-methylglucopyranosides in I. fumosorosea KCH J2 culture. We did not observe the attachment of the methyl group to glucose unit in isoquercetin. Our finding suggest that the attachment of 4-O-methylglucopyranose occurs in one step.

The resistance of cancer cells to a variety of structurally non-related cytotoxic drugs is known as multidrug resistance phenomenon (MDR). In cellular membranes an activity of MDR transporters such as P-glycoprotein (ABCB1) is affected by their lipid environment. Many various compounds have been examined for their ability to restore drug-sensitivity of resistant cancer cells. Statins, inhibitors of the key enzyme of mevalonate pathway HMG-CoA (3-hydroxy-3-methyl-glutaryl-coenzyme A) reductase are drugs commonly prescribed in order to reduce serum level of cholesterol and to diminish the risk of cardiovascular disease. Statins as drugs that influence lipid composition of cell membrane and in that way they also exert influence on lipid bilayer properties appear to be good candidates as MDR modulators. In this work it was shown that statins - mevastatin and simvastatin exert antiproliferative, pro-apoptotic and reversing drug resistance effect in human colon adenocarcinoma cell line LoVo and its drug-resistant subline LoVo/Dx. A hypothesis was also checked whether flavones, which as it is well known are able to influence the biosynthesis of cholesterol, may change the anticancer activity of statins. Our investigations have revealed that combined use of statins and studied flavonoids results in enhanced cell growth inhibition and apoptosis and lower cancer cell proliferation as compared to the application only statins alone. Moreover, in drug resistant LoVo/Dx cells a stronger decrease of resistance to doxorubicine was observed in the presence of statins in combination with flavones as compared to the effect observed for statins only.

Entomopathogenic fungi are known for their ability to carry out glycosylation of flavonoids, which usually results in the improvement of their stability and bioavailability. In this study we used a newly isolated strain of the entomopathogenic filamentous fungus Isaria fumosorosea KCH J2 as a biocatalyst. Our aim was to evaluate its ability to carry out the biotransformation of flavonoids and to obtain new flavonoid derivatives. The fungus was isolated from a spider’s carcass and molecularly identified using analysis of the ITS1-ITS2 rDNA sequence. As a result of biotransformation of 6-methylflavone two new products were obtained: 6-methylflavone 8-O-β-D-(4”-O-methyl)-glucopyranoside and 6-methylflavone 4’-O-β-D-(4”-O-methyl)-glucopyranoside. Chemical structures of the products were determined based on spectroscopic methods (¹H NMR, ¹³C NMR, COSY, HMBC, HSQC). Our research allowed us to discover a new species of filamentous fungus capable of carrying out glycosylation reactions and proved that I. fumosorosea KCH J2 is an effective biocatalyst for glycosylation of flavonoid compounds. For the first time we describe biotransformations of 6-methylflavone and the attachment of the sugar unit to the flavonoid substrate having no hydroxyl group. The possibility of using flavonoid aglycones is often limited by their low bioavailability due to poor solubility in water. The incorporation of a sugar unit improves the physical properties of tested compounds and thus increases the chance of using them as pharmaceuticals.

Entomopathogenic filamentous fungi of the genus Isaria are effective biocatalysts in the biotransformation of flavonoids as well as steroids. In the present study, the species Isaria fumosorosea and Isaria farinosa isolated from the environment were used. Their catalytic capacity to carry out biotransformations of flavones—unsubstituted, with hydroxy- and amino-substituents as well as a hydroxylated isoflavone—was investigated. Biotransformations of flavone, 5-hydroxyflavone, 6-hydroxyflavone, 7-hydroxyflavone, and daidzein resulted in the formation of O-methylglucosides, in the case of flavone and 5-hydroxyflavone with additional hydroxylations. 7-Aminoflavone was transformed into two acetamido derivatives. The following products were obtained: From flavone–flavone 2′-O-β-d-(4′′-O-methyl)-glucopyranoside, flavone 4′-O-β-d-(4′′-O-methyl)-glucopyranoside and 3′-hydroxyflavone 4′-O-β-d-(4′′-O-methyl)-glucopyranoside; from 5-hydroxyflavone–5-hydroxyflavone 4′-O-β-d-(4′′-O-methyl)-glucopyranoside; from 6-hydroxyflavone–flavone 6-O-β-d-(4′′-O-methyl)-glucopyranoside; from 7-hydroxyflavone–flavone 7-O-β-d-(4′′-O-methyl)-glucopyranoside; from daidzein–daidzein 7-O-β-d-(4′′-O-methyl)-glucopyranoside; and from 7-aminoflavone–7-acetamidoflavone and 7-acetamido-4′-hydroxyflavone. Seven of the products obtained by us have not been previously reported in the literature.