Cytotoxicity-guided isolation of acacetin derivatives from Cirsium rhizocephalum C.A.Mey. (Asteraceae) and their in silico investigation for androgen receptor inhibition against prostate cancer

Bioactivity-guided investigation of Cirsium rhizocephalum against the human androgen-sensitive prostate cancer cell line (LnCAP) led to the isolation of six flavonoids: nicotiflorin (CRE_1), rutin (CRE_2), isoquercetin (CRE_4), linarin (CRE_5), acacetin (CRE_6a), 6-methoxy acacetin (CRE_6b), and chlorogenic acid (CRE_3). The chemical structures of the compounds were determined by examining their ¹H NMR spectra, comparing them with existing literature, and by authentication with thin-layer chromatography (TLC) for rutin and chlorogenic acid. To rationalize and support the obtained cytotoxicity data against human androgen-sensitive prostate cancer cells, purified molecules were docked into the binding site of the human androgen receptor (AR), a validated therapeutic target for the treatment of prostate cancer. In line with the biological results, the isolated flavones acacetin and 6-methoxy acacetin, with the strongest cytotoxic activity against prostate cancer cell lines, interacted with AR in a similar way to the native ligand, metribolone. The stability of the binding modes of both compounds within the active pocket of AR was confirmed by applying molecular dynamic simulations and the dynamic 3D pharmacophore (dynophore) method. Furthermore, the molecular descriptors indicating drug-likeness were calculated for all compounds isolated from C. rhizocephalum.