Biotransformation of quercetin by Bacillus subtilis and anticancer activity evaluation: in vitro and in Silico

Biotransformation of quercetin by Bacillus subtilis ATCC 23,857 yielded a major metabolite; apigenin-7-O-pentoside (A7P) and 9 other phenolic metabolites. They were elucidated by LC-ESI-TOF-MS/MS analysis. Furthermore, the cytotoxic potential of the biotransformed products was compared to their parent substrate (S) using MTT assay against 2 cancer cell lines; A549 and Caco-2. After 72 h. incubation, the BPs showed concentration-dependent cytotoxic activity against Caco-2 and A549 with IC₅₀ equal to 0.32 and 0.78 mg/ml, respectively. Both BPs and S were safe on the normal human skin fibroblast (hFB) cell line. Molecular docking confirmed the high binding affinity of A7P towards phosphatidyl inositide 3-kinase delta (PI3Kδ) and Cathepsin B protein (CatB) expressed in lung and colorectal cancer cells compared to quercetin suggesting higher anticancer activity. The present findings suggest that the application of biotransformation techniques using bacteria as B. subtilis can enhance the biological activity of flavonoids by generating bioactive metabolites.