Cytotoxic constituents of cymbidium finlaysonianum and paphiopedilum dianthum

Abstract

Chemical investigation of two orchids native to Thailand led to the isolation of eighteen compounds. From the whole plants of Cymbidium finlaysonianum Wall. ex Lindl, a new dihydrophenanthrene, 1-(4-hydroxybenzyl)-2,7-dihydroxy-4,6-dimethoxy-9,10-dihydrophenan-threne, and nine known stilbenoids, including a phenanthrenequinone, cymbinodin-A, a dihydrophenanthrenequinone, ephemeranthoquinone B, a bibenzyl, batatasin III, two phenanthrenes, 2,4-dimethoxy-3,7-dihydroxyphenanthrene and 3,7-dihydroxy-2,4,6-trimethoxyphenanthrene, and four dihydrophenanthrenes i.e. coelonin, 6-methoxycoelonin, flavanthridin and lusianthridin, were obtained. From the roots and leaves of Paphiopedilum dianthum Tang & Wang, two new stilbene dimers, paphiodianthins A and B, were isolated along with three known stilbenes i.e. pinosylvin monomethyl ether, 2,3'-dihydroxy-5'-methoxystilbene and (E)-2,5'-dihydroxy-2'-(4-hydroxybenzyl)-3'-methoxystilbene, and three known flavonoids i.e. isalpinin, pinocembrin and galangin. The chemical structures of these compounds were determined by spectroscopic techniques including UV, IR, MS and NMR, as well as comparison with previously reported data. These isolated compounds were assayed for their cytotoxicity against colon (Caco-2), breast (MCF-7) and lung (NCI-H187) cancer cell lines, as well as two resistant sublines of MCF-7 cells (MCF-7/DOX and MCF-7/MX), by MTT and resazurin microplate assays. Among compounds isolated from C. finlaysonianum, cymbinodin-A displayed the strongest cytotoxicity against almost all cancer cell lines tested (Caco-2, NCI-H187, MCF-7/DOX and MCF-7/MX), whereas coelonin was the most cytotoxic constituent against MCF-7 cell line. Other compounds from this orchid were moderately cytotoxic. From P. dianthum, (E)-2,5'-dihydroxy-2'-(4-hydroxybenzyl)-3'-methoxystilbene and paphiodianthin A exhibited the strongest cytotoxic effect against all cell lines tested, while pinosylvin monomethyl ether and paphiodianthin B were strongly cytotoxic to MCF-7 cells, but were moderately toxic or non-toxic to normal cells (NIH/3T3). Moreover, isalpinin was more cytotoxic to MCF-7/DOX subline than to MCF-7 cell line and was non-toxic to normal cell line.