Five sesquiterpene lactones were isolated and identified from Ambrosia maritima L. Hymenin showed highest cytotoxic activity against HCT-116, A-549, and MCF-7 cell lines (IC50= 3.83 ± 0.2, 5.48 ± 0.3, 10.1 ± 0.6 µg/mL, respectively). Damsin has significant COX-2 inhibitory activity (IC50=33.97 ± 1.62 µg/mL) while hymenin showed highest selectivity to COX-1 (IC50 = 18.21 µg/mL) and significant inhibition of NO (IC50=18.19 ± 0.75 µg/mL). The docking study revealed nice fitting into COX-1/2 and a

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... igher binding affinity for maritimolide towards human Src kinase compared to the native ligand, Bosutinib. Results suggested that both COXs/Src kinase inhibition could contribute even partially to the overall mechanism of cytotoxic activity of the five compounds. The structure-activity relationship revealed that α-methylene-γ-lactone moiety enhances the cytotoxic activity, OH group at C-1 increase activity of hymenin. However, the reduction of the double bond at C-2 as in damsin resulted in a significant decrease in activity against HCT-116 and MCF-7 cells.