Bioactive Monoterpenes fromMonarda fistulosa(Lamiaceae)

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Abstract
Bioactivity-guided fractionation of Monarda fistulosa L. (F005), using the brine shrimp lethality test (BST) and crown gall tumor potato disc assay (PD), led to the isolation of the bioactive monoterpenes, thymoquinone (1), and thymol (2). 1, surprisingly, exhibited selective cytotoxicities against certain cell lines. Of over 60 human tumor cell lines evaluated, 1 was very selective for SF-539 (CNS) with an LC50 < 2.51 × 10−2 μg/ml. Other cell lines targeted by 1 were PC-3 (prostate), M-14 (melanoma), OVCAR-5 (ovarian), and MCF-7 (breast). The reduction of 1 to thymohydroquinone (3) resulted in a 1.7 fold decrease in the cytotoxic potency for PC-3. Thymol (2), although not significantly cytotoxic, demonstrated strong pesticidal activity, more potent than rotenone, in the yellow fever mosquito larvae assay (YFM). None of the compounds, 1–3, approached the IC50 value of rotenone in inhibiting oxygen uptake in the rat liver mitochondrial bioassay, suggesting that they must have another mode of action.