Withalutin, a new cytotoxic withanolide from Athenaea velutina (Sendtn.) D'Arcy.

Bioassay-guided fractionation of dichloromethane extract from Athenaea velutina leaves led to the isolation of three withanolides, all being reported for the first time in this species. They were identified as withacnistin (1), withacnistin acetate (2) and a new withanolide, designated as withalutin (3). The structures were established by spectral data analysis, including MS, 1D and 2D NMR. In addition, in silico ADMET studies were employed to understand the pharmacokinetic properties of these withanolides. The withanolides isolated from A. velutina reduced cancer cell viability with IC50 values ranging from 1.52 to 5.39 µM. In silico prediction revealed that withanolides have good gastrointestinal absorption or oral bioavailability properties; and are not likely to be mutagenic or hepatotoxic. These findings revealed that A. velutina is an important source of cytotoxic withanolides.

A Withanolide-rich Fraction of Athenaea velutina Induces Apoptosis and Cell Cycle Arrest in Melanoma B16F10 Cells.

Athenaea velutina is a promising Brazilian shrub with cytotoxic and antimigratory properties against cancer cells. However, the mechanism of induction of cancer cell death and the compounds involved remain unknown. To ascertain these bioactive compounds, bioassay-guided fractionation was performed, alongside the appropriate in vitro tests. A withanolide-rich fraction (FAv_5) from the dichloromethane extract increased cytotoxic activity by 1.5-fold (IC50 = 2.1 µg/mL). Fourteen withanolide steroids were tentatively identified for the first time for this species by mass spectrometry coupled to liquid chromatography (LC MS/MS), including withanolide A, aurelianolide A, and aurelianolide B. FAv_5 significantly decreased cell proliferation, migration, and invasion with a selectivity index greater than 8 for B16F10 cells. Furthermore, flow cytometry with annexin V fluorescein isothiocyanate/propidium iodide (V-FITC/PI) staining showed FAv_5 to promote cell cycle arrest at the G0/G1-phase as well as apoptotic cell death. Overall, these findings highlight A. velutina as a source of withanolide-steroids that inhibit cancer cell proliferation through apoptosis and cell cycle blockade mechanisms. Details on the geographic distribution of A. velutina and species conservation strategies have also been highlighted.