Cytotoxic compounds from Iris tectorum

Extracts of several Chinese plant species used traditionally to treat cancer were tested for cytotoxicity using the SRB assay [1] with three cancer cell lines (COR-L23, C32 and MCF-7) and a mammalian non-cancer cell line Hep G2. A chloroform extract of the rhizomes of Iris tectorum Maxim. gave the greatest cytotoxicity with 100µg/ml giving less than 15% survival with all three cancer cell lines. The SRB assay was used for bioassay-guided fractionation of this extract and yielded two novel iridogermanal triterpenes IT4C and IT4D, two known iridogermanal triterpenes iridobelamal 1 and isoiridogermanal and two flavonoids, 7-OMe-aromadendrin and tectorigenin, whose structures were determined by advanced MS and NMR spectroscopy. The compounds were tested for cytotoxicity using the SRB assay against the four cell lines with iridobelamal 1 having the greatest activity (Table).

Table: Cytotoxicity (IC₅₀ µM±SEM) of isolated compounds n=3

Compound	Cell line
COR-L23	MCF-7		C32		HepG2
IT4C	35±1	18±1		40±2	29±2
IT4D	19±1	11±1		25±2	20±1
Iridobelamal 1	14±0	11±1		23±1	18±0
Isoiridogermanal	16±2	11±2		24±1	22±2
7-OMe-Aromadendrin	33±1	21±1		33±3	25±2
Tectorigenin	189±6	105±2		207±14	149±2

References: [1] Itharat, I. et al. (2004) J. Ethnopharmacology 90: 33–38.