Antibacterial and anticancer activity of kaurenoic acid from root bark extract of Annona senegalensis
The antibacterial  and anticancer  activities of extract of Annona senegalensis Pers. (Annonaceae) have been reported. Bioactive-guided fractionation of the methanol-methylene chloride root bark extract of A. senegalensis afforded a potent antibacterial ethyl acetate fraction (EF) which on further fractionation, gave two active sub-fractions F1 and F2. F1 yielded a lipophilic liquid component while F2 on purification, precipitated a white crystalline compound, ASI, that was characterized by proton NMR and X-ray crystallography as kaur-16-en-19-oic acid. F1 was analyzed using GC-MS to obtain 6 major constituents: 1- dodecanol, kaur-16-en-18-oic acid, 1-Naphthalenemethanol, 6,6-dimethyl-bicyclo[3.1.1]hept-2-ene-2-ethanol, 3,3-dimethyl-2-(3-methylbuta-1,3-dienyl) cyclohexan-1-methanol and 3-hydroxyandrostan-17-carboxylic acid. Agar well diffusion method, using a 0.5 McFarland standard, was employed to obtain the MIC's for F1 and ASI. The MIC's against clinical isolates of Bacillus subtilis in µg/ml of the EF, F1 and ASI were 180, 60, and 30 respectively. However, ASI exhibited appreciable activity against Staphylococcus aureus with an MIC value of 150µg/ml while F1 was active against Pseudomonas aeruginosa with an MIC value of 40µg/ml. The standard agent ciprofloxacin exhibited MIC values of 0.28, 1.18 and 3.6µg/ml against B.subtilis, Staph aureus and Ps. aeruginosa respectively. Additionally, ASI was screened for cytotoxicity on 3 Cancer cell lines, human embryonic kidney cells expressing SV40 Large T-antigen (293 T), Pancreatic tumour (PANC-1) cell lines and Henrietta Lacks' cervical cancer cell line (HeLa), using the standard MTT assay method. 50% cellular toxicity (TC50) of ASI was calculated to be 125.89, 211.35, 266.07µg/ml for 293 T, Hela and PANC-1 cells respectively.
Acknowledgement: The authors are grateful to IOT World Bank assisted award grant of Step-B project of Federal Government of Nigeria.
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