Abstract
Bioassay-guided chromatographic fractionation of the active chloroform and methanolic extracts from the roots of Rhinacanthus nasutus led to the isolation of eight naphthoquinones, one lignan, two sterols and one triterpenoid: rhinacanthins-C, -D, -G, -O, -M, -N, -Q, rhinacanthone, heliobuphthalmin, sitosterol, β-sitosterol and lupeol, respectively. Their structures were elucidated on the basis of spectral and chemical analysis. This is first report of heliobuphthalmin isolated from this plant. The in vitro antiproliferative activity against panel of 10 kinds of cancer cells (e.g. KB, Hep-2, MCF-7, HepG2, HeLa, SiHa, C-32, LLC, Colon-26 and P388) and non-tumorigenic Vero cells were then analyzed by MTT assay. Antitumor activity of aqueous extracts of the roots and stems, chloroform extract and rhinacanthin-C in Meth-A Sarcoma-bearing BALB/c mice was also evaluated. All naphthoquinones showed apparent antiproliferative activity against cancer cells with the IC50 values of 0.29-54.4 μM, whereas they showed moderate activity against Vero cells (IC50 values of 4.2-41.1 μM). Heliobuphthalmin had weaker activity than naphthoquinone analogues. Two sterols and lupeol were inactive. Structure-activity relationship of the naphthoquinone esters revealed that the substitutes of phenolic groups in quinine and quinolate parts of these compounds may be important for increasing theirs antiproliferative activity. Regarding to in vivo antitumor activity, the chloroform extract and rhinacanthin-C (25 mg/kg/day) as well as aqueous extracts of the roots and stems (500 mg/kg/day) significantly suppressed the growth of Meth-A sarcoma bearing mice. Our findings conclude that the naphthoquinone compounds isolated from R. nasutus Kurz., a traditional Thai medicine for cancer treatment, are worth further investigation as lead compounds for the design of selective anticancer drug in cancer therapy.
