Cancer chemopreventive effects and cytotoxic activities of the triterpene acids from the resin of Boswellia carteri

Fifteen triterpene acids, viz,, seven of the P-boswellic acids (ursane-type) (1-7), two of the a-boswellic acids (oleanane-type) (8, 9), two of the lupeolic acids (lupane-type) (10, 11), and four of the tirucallane-type (12-14, 16), and two cembrane-type diterpenes (17, 18), isolated from the MeOH extract of the resin of Boswellia carteri (Burseraceae), together with a triterpene acid 15 (the acetyl derivative of 14), were examined for their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells and on activation of (+/-)-(E)-methyl-2[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexemide (NOR 1), a nitrogen oxide (NO) donor, and cytotoxic activities against three human neuroblastoma cell lines, IMR-32, NB-39, and SK-N-SH in vitro. On evaluation against the EBV-EA activation induced by TPA, seven compounds, 2, 10, 11, and 13-16, showed potent inhibitory effects on EBV-EA induction. Upon evaluation against activation of NOR 1, five compounds, 7, 13, and 14-16, showed potent inhibitory effects. Further, fifteen compounds, 1-7, 9-11, 13-15, 17, and 18, exhibited potent cytotoxic activities with IC50 values of 4.1-82.4 mu m against all of the three human neuroblastoma cells tested.