Cytotoxic and apoptosis-inducing activities of triterpene acids from Poria cocos.
Kikuchi T, Uchiyama E, Ukiya M, Tabata K, Kimura Y, Suzuki T, Akihisa T.
Six lanostane-type triterpene acids (1a-6a), isolated from Poria cocos , and their methyl ester (1b-6b) and hydroxy derivatives (1c-6c) were prepared. Upon evaluation of the cytotoxic activity of these compounds against leukemia (HL60), lung (A549), melanoma (CRL1579), ovary (NIH:OVCAR-3), breast (SK-BR-3), prostate (DU145), stomach (AZ521), and pancreas (PANC-1) cancer cell lines, 11 compounds (5a, 6a, 2b-5b, 1c, and 3c-6c) exhibited activity with single-digit micromolar IC(50) values against one or more cell lines. Poricotriol A (1c), a hydroxy derivative of poricoic acid A (1a), exhibited potent cytotoxicities against six cell lines with IC(50) values of 1.2-5.5 μM. Poricotriol A induced typical apoptotic cell death in HL60 and A549 cells on evaluation of the apoptosis-inducing activity by flow cytometric analysis. Western blot analysis in HL60 cells showed that poricotriol A activated caspases-3, -8, and -9, while increasing the ratio of Bax/Bcl-2. This suggested that poricotriol A induced apoptosis via both mitochondrial and death receptor pathways in HL60. On the other hand, poricotriol A did not activate caspases-3, -8, and -9, but induced translocation of apoptosis-inducing factor (AIF) from mitochondria and increased the ratio of Bax/Bcl-2 in A549. This suggested that poricotriol A induced apoptosis via the mitochondrial pathway mostly by translocation of AIF, independent from the caspase pathway in A549. Furthermore, poricotriol A was shown to possess high selective toxicity in lung cancer cells since it exhibited only weak cytotoxicity against a normal lung cell line (WI-38).