High performance liquid chromatography (HPLC) with UV detection has been employed for the quantitative determination of ursolic acid in the ethyl acetate extract of the aerial parts of Plectranthus amboinicus. The antiproliferative activity of the extract and ursolic acid against MCF-7 was tested in vitro by MTT assay. Molecular modeling using MOE was employed to check the binding mode of ursolic acid (UA) with the crystal structures of the Protein tyrosine phosphatase 1B (PTP1B) enzyme complexed with the orthosteric sulfamic acid inhibitor (PDB: 2F71). Ursolic acid was detected in the ethyl acetate extract at 203 nm with retention time 6.98 min and the HPLC analytical methodology for standard curve was developed and validated to quantify ursolic acid as 3.96 mg/g DW. The ursolic acid and extract were highly active against MCF-7 cell line with IC50 22.4± 0.64 µg/ml and 43.1± 2.3 µg/ml respectively. Molecular study emphasized the influential ursolic acid fitting in the binding site of PTP1B enzyme suggesting its inhibition to be responsible for the in vitro anticancer activity.
These findings justify the use of Plectranthus amboinicus against cancer and strengthen its selection for the discovery of natural anticancer agents. Also, the results provide important guidance for the potential pathway of ursolic acid as anticancer compound.