Cancer cells generally possess higher levels of reactive oxygen species than normal cells, and this can serve as a possible therapeutic target. In this proof-of-concept study, an antioxidant-inspired drug discovery strategy was evaluated using a hydroxycinnamic acid derivative. The processing of oxidized mixtures of p-coumaric acid methyl ester (pcm) revealed a new antitumor lead, graviquinone. Graviquinone bypassed ABCB1-mediated resistance, induced DNA damage in lung carcinoma cells but exerted DNA protective activity in normal keratinocytes, and modulated DNA damage response in MCF-7 cells. The cytotoxic effect of pcm in MCF-7 cells was potentiated under H 2 O 2 -induced oxidative stress, and the formation of graviquinone was confirmed by Fenton's reaction on pcm. In silico density functional theory calculations suggested graviquinone as a kinetic product of pcm-scavenging • OH radicals. Our results demonstrate the pharmacological value of an in situ-formed, oxidative stress-related metabolite of an antioxidant. This might be of particular importance for designing new strategies for antioxidant-based drug discovery.

Hydroxycinnamic acids represent a versatile group of dietary plant antioxidants. Oxidation of methyl-p-coumarate (pcm) and methyl caffeate (cm) was previously found to yield potent antitumor metabolites. Here, we report the formation of potentially bioactive products of pcm and cm oxidized with peroxynitrite (ONOO¯), a biologically relevant reactive nitrogen species (RNS), or with α,α′-azodiisobutyramidine dihydrochloride (AAPH) as a chemical model for reactive oxygen species (ROS). A continuous flow system was developed to achieve reproducible in situ ONOO¯ formation. Reaction mixtures were tested for their cytotoxic effect on HeLa, SiHa, MCF-7 and MDA-MB-231 cells. The reaction of pcm with ONOO¯ produced two fragments, an o-nitrophenol derivative, and a new chlorinated compound. Bioactivity-guided isolation from the reaction mixture of cm with AAPH produced two dimerization products, including a dihydrobenzofuran lignan that exerted strong antitumor activity in vitro, and has potent in vivo antimetastatic activity which was previously reported. This compound was also detected from the reaction between cm and ONOO¯. Our results demonstrate the ROS/RNS dependent formation of chemically stable metabolites, including a potent antitumor agent (5), from hydroxycinnamic acids. This suggests that diversity-oriented synthesis using ROS/RNS to obtain oxidized antioxidant metabolite mixtures may serve as a valid natural product-based drug discovery strategy.

No abstract

Melampyrum barbatum Waldst. & Kit. ex Willd. (Scrophulariaceae) has been used in traditional medicine for the treatment of rheumatic complaints and different skin diseases. In the course of our study the anti-inflammatory activity of the aerial parts of M. barbatum was evaluated. A MeOH extract was prepared and consecutively partitioned with CHCl 3 , EtOAc and n-BuOH. The fractions were assayed in in vivo carrageenan-induced rat paw oedema model. The intraperitoneally administered n-BuOH phase exerted marked inhibitory effect (33.6 %, p < 0.01). Multistep chromatographic separation afforded mussaenoside and aucubine from n-BuOH fraction. Moreover, 8-epiloganin, loganic acid and mussaenoside were obtained from EtOAc fraction and apigenin, luteolin, benzoic acid and galactitol from CHCl 3 fraction. These data validate the ethnomedicinal use of M. barbatum for the treatment of inflammatory diseases and reveal that iridoids and flavonoids could be responsible for the anti-inflammatory effect of this species.

No abstract