5-diphenylacetamido-indirubin-3'-oxime as a novel mitochondria-targeting agent with anti-leukemic activities.

Current treatment for leukemia largely depends on chemotherapy. Despite the progress in treatment efficacy of chemotherapy, a poor outcome consequent upon chemoresistance against conventional anti-cancer drugs still remains to be solved. In this study, we report 5-diphenylacetamido-indirubin-3'-oxime (LDD398) as a novel mitochondria-targeting anti-leukemic agent, which is a derivative of indirubin used in traditional medicine. Treatment with LDD398 resulted in caspase activation, cell death, and growth arrest at G2/M phases in leukemia cells. Interestingly, LDD398 quickly collapsed mitochondrial membrane potential (MMP) within 1 h, accompanied by cytochrome c release into cytosol and severe depletion of cellular ATP. However, the LDD398-induced cellular events was significantly mitigated by blockage of mitochondrial permeability transition pore (MPTP) opening with chemical and genetic modifications, strongly supporting that LDD398 executes its anti-leukemic activity via an inappropriate opening of MPTP and a consequent depletion of ATP. The most meaningful finding was the prominent effectiveness of LDD398 on primary leukemia cells and also on malignant leukemia cells resistant to anticancer drugs. Our results demonstrate that, among a series of indirubin derivatives, LDD398 induces leukemia cell death via a different mode from indirubin or conventional chemotherapeutics, and can be employed as a potent anti-cancer agent in the treatment for newly diagnosed and relapsed leukemia.

Analysis of gene profiles involved in the enhancement of all-trans retinoic acid-induced HL-60 cell differentiation by sesquiterpene lactones identifies asparagine synthetase as a novel target for differentiation-inducing therapy.

All-trans retinoic acid (ATRA) is one of the most useful drugs in the treatment for acute promyelocytic leukemia (APL), but its adverse effects, which include drug resistance and hypercalcemia are obstacles to achieving complete remission. Our previous study showed that some sesquiterpene lactones (STLs), i.e., helenalin (HE) and parthenolide (PA) but not sclareolide (SC), enhance ATRA-induced differentiation of HL-60 APL cells with no unexpected effects, but the precise mechanism on underlying this synergism is not yet fully understood. In this study, we investigated the distinctive transcriptional profile of cells treated with effective STL compounds, which were identified by comparing the profile with that of cells treated with SC. Genome-wide approaches using cDNA microarrays showed that co-treatment with the differentiation-enhancing STLs HE and PA maximized the transcriptional variation regulated by the suboptimal concentration of ATRA in HL-60 cells. Of the genes of interest, asparagine synthetase was remarkably downregulated by ATRA co-treated with either HE or PA, but not with SC. In an additional analysis for the role of asparagine synthetase, ATRA-mediated HL-60 cell differentiation was enhanced when asparagine in the culture media was depleted by an addition of L-asparaginase, indicating that downregulation of asparagine synthetase gene expression may be involved in the enhanced cell differentiation by STL compounds. These results provide useful insight into differentiation-inducing therapy in the treatment of leukemia.