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By using a novel profiling analysis of protein tyrosine kinases differentially expressed in the sensitive and refractory leukemia from the same patients we found that AXL was upregulated in drug-resistant leukemia. Furthermore, AXL could be induced by chemotherapy drugs in the acute myeloid leukemia U937 cells and this induction was dependent on the CCWGG methylation status of the AXL promoter. In U937 cells ectopically overexpressing AXL, addition of exogenous Gas6 induced AXL phosphorylation and activation of the Akt and ERK1/2 survival pathways. The Gas6-AXL activation pathway of drug resistance was associated with increased expression of Bcl-2 and Twist. These results show that upregulation of AXL by chemotherapy might induce drug resistance in acute myeloid leukemia in the presence of Gas6 stimulation.

Five lanostane (2, 3, 4, 6 and 8) and three ergostane-type (1, 5 and 7) triterpenes isolated from the fruiting bodies of Antrodia camphorata were evaluated for their in vitro cytotoxic data against various cancer cell types. The three zhankuic acids, 1, 5 and 7 displayed the most potent cytotoxic effect with an IC(50) value of 22.3-75.0microM. The compound 3 was selectively cytotoxic in three colon cancer cell lines (HT-29, HCT-116 and SW-480) and a breast cancer model (MDA-MB-231), whereas 8 only showed its cytotoxicity against MDA-MB-231. None of these isolates was toxic to mammary epithelial (MCF10A) and primary foreskin fibroblast (HS68) cells, two human normal cell lines. The compounds 1, 5 and 7 were also demonstrated to induce apoptosis in HT-29 and SW-480 cells, as confirmed by sub-G1 cell cycle arrest. In HT-29 cells, the expression of apoptosis-associated proteins poly-(ADP-ribose) polymerase cleavage, Bcl-2 and procaspase-3 were suppressed by compounds 1, 5 and 7. A mixture containing 4microM each of compounds 1, 5 and 7 also showed a synergistic cytotoxic effect in HT-29 cells.

Isocostunolide is a sesquiterpene lactone isolated from the roots of Inula helenium. Its chemical structure was determined by NMR and FAB-MS spectra. No biological activities of this compound have yet been reported. In this study, we found isocostunolide could effectively induce cytotoxicity in three cancer cell lines (A2058, HT-29, and HepG2), with an IC(50) of 3.2, 5.0, and 2.0 micro g/mL, respectively. DNA flow cytometric analysis indicated that isocostunolide actively induced apoptosis of cancer cells accompanied by a marked loss of G0/G1 phase cells. To address the mechanism of the apoptotic effect of isocostunolide, we analyzed the induction of apoptosis-related proteins in A2058. The levels of pro-caspase-8, Bid, pro-caspase-3, and poly(ADP-ribose) polymerase (PARP) decreased. However, the level of Fas was increased markedly in a dose-dependent manner. Furthermore, this compound markedly induced a depolarization of mitochondrial membranes to facilitate cytochrome c release into cytosol. The findings suggest that isocostunolide may activate a mitochondria-mediated apoptosis pathway. To address this, we found that isocostunolide-induced loss of mitochondrial membrane potential occurred via modulation of the Bcl-2 family proteins. The production of intracellular reactive oxygen species (ROS) in A2058 was not elicited. In summary, for the first time, we have isolated and characterized isocostunolide from I. helenium. This compound induces apoptosis through a mitochondria-dependent pathway in A2058 cells.