Tetrahydroxy Flavone from Acacia auriculiformis A. Cunn Ex Benth. (Fabaceae) with Novel Kinase Activity

Background: The decoctions of the bark of Acacia auriculiformis are used in folkloric medicine to relieve pain and inflammation and as remedy for cancer. Objective: The aim of this work is to screen the extract and fractions of Acacia auriculiformis for protein kinase inhibitory activity and also to isolate and characterize chemical entities from this plant and evaluate their protein kinase inhibitory activity. Materials and Methods: Kinase inhibitory activity were assayed in appropriate buffer, with either protein or peptide as substrate in the presence of 15μM (33-P) ATP (3,000Ci/mmol; 10mCi/ml) in a final volume of 30μL. Controls were performed with appropriate dilutions of dimethyl sulphoxide. A portion of the Chloroform extract, ethylacetate and n-butanol soluble fractions of the stem bark of Acacia auriculiformis were screened against a panel of disease-related protein kinases and the active fractions was tested over a wide range of concentrations from 0.016 to 50μg/ml and the IC₅₀ values were determined from the dose response curve. The most active fraction was subjected to chromatographic separation using Silica gel G column chromatography and sephadex LH-20 to give compound I. The structure of the isolated compound was elucidated using NMR and LCMS. Results: The Primary screening of the extract and fractions showed that the chloroform extract was inactive against all the protein kinases investigated, while the ethylacetate and n-butanol soluble fractions inhibited all the protein kinases tested. Compound I also inhibited all the kinases tested. The IC₅₀ of the active fractions and compound were also evaluated. Ethylacetate fraction inhibited all the kinases tested with the highest activity against Haspine kinase with IC₅₀ of 1.0 μg/ml, while n-butanol also gave the highest activity against Haspine kinase with 1C₅₀ of 1.3 μg/ml. From the active ethylacetate fractions 3, 4’, 7, 8- tetrahydroxy flavone was isolated. The Compound exhibited the maximal activity against DYRK1A kinase with an IC₅₀ of 2.05 μg/ml followed by CDK9 with an IC₅₀ of 2.28 μg/ml. Conclusion: 3, 4’,7, 8- tetrahydroxy flavone was isolated was found to be a DYRK1A and CDK9 inhibitor which might justify the anticancer potential of this plant.