In the present study, the cytotoxicity of 30 diterpenoids with an abietane or a halimane skeleton was determined against five human tumor cell lines (HL-60, U937, Molt-3, SK-MEL-1, and MCF-7). Diterpenoids containing an abietane skeleton including taxodone (1) and taxodione (2), as well as the semisynthetic derivatives 12, 14, 15, 17, and 22, were the most cytotoxic compounds for human leukemia cells. Overexpression of the protective mitochondrial proteins Bcl-2 and Bcl-xL did not confer resistance to abietane diterpene-induced cytotoxicity. Studies performed on HL-60 cells indicated that growth inhibition triggered by compounds 1, 12, 14, and 15 was caused by induction of apoptosis. This was prevented by the nonspecific caspase inhibitor Z-VAD-FMK and, in the case of compounds 14 and 15, reduced by the selective caspase-8 inhibitor Z-IETD-FMK. Cell death induced by these abietane diterpenes was found to be associated with the release of mitochondrial proteins, including cytochrome c, Smac/DIABLO, and AIF (apoptosis-inducing factor), accompanied by dissipation of the mitochondrial membrane potential (ΔΨ), and modulated by inhibition of extracellular signal-regulated kinases signaling and the p38 mitogen-activated protein kinase pathway.

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Three new compounds, 2,4,4'-trihydroxydihydrochalcone (1), 3-(4-hydroxybenzyl)-5,7-dimethoxychroman (2), and 7-hydroxy-3-(4-hydroxybenzyl)chromone (3), were isolated from the resin "Dragon's blood" obtained from Dracaena draco along with 18 known compounds. The structures of 1, 2, and 3 were determined using MS and NMR techniques.

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Three new compounds, 5 alpha-lanosta-7,9(11),24-triene-3beta-hydroxy-26-al (1), 5 alpha-lanosta-7,9(11),24-triene-15 alpha-26-dihydroxy-3-one (2), and 8 alpha,9 alpha-epoxy-4,4,14 alpha-trimethyl-3,7,11,15,20-pentaoxo-5 alpha-pregnane (3), were isolated from Ganoderma concinna along with 12 known compounds. The structures of compounds 1 and 2 were determined on the basis of MS and NMR studies. The structure of 3 was determined by MS, NMR, and single-crystal X-ray diffraction. Compounds 1, 2, and 3 induce apoptosis in human promyelocytic leukemia HL-60 cells, as indicated by examining the morphological features of cells and detection of DNA fragmentation by gel electrophoresis.