A comparative proteomic study of Homoharringtonine-induced apoptosis in leukemia K562 cells

Synergistic cytotoxicity of homoharringtonine and etoposide in acute myeloid leukemia cells involves disrupted antioxidant defense

Background/Aims

Cytotoxicity induced by reactive oxygen species (ROS) is critical for the effectiveness of chemotherapeutic drugs used in the treatment of acute myeloid leukemia (AML). This study aimed to investigate whether ROS contributes to cytotoxicity in AML cells when treated with homoharringtonine (HHT) and etoposide (ETP) in combination.

Methods

AML cell lines THP1 and HL60 and primary AML cells from patients were treated with HHT and ETP alone or in combination, and cell viability was determined by trypan blue exclusion test, and apoptosis was analyzed by annexin-V/propidium iodide double staining as well as Western blot for measuring expression of cleaved caspase-9 and cleaved caspase-3. Intracellular ROS level was detected by DCFH-DA fluorescence assay, and N-Acetyl-L-cysteine (NAC) was used to scavenge intracellular ROS. Retroviral infection was applied to mediate stable overexpression in AML cells.

Results

We show that HHT and ETP exhibit synergistic cytotoxicity in AML cell lines and primary AML cells in vitro, and meanwhile, HHT causes elevated ROS generation in ETP-treated AML cells. We next reveal that the elevated ROS is a critical factor for the synergistic cytotoxicity, since ROS scavenge by NAC remarkably diminishes this effect. Mechanistically, we demonstrate that HHT causes elevated ROS generation by disabling thioredoxin-mediated antioxidant defense. Finally, similar to HHT treatment, depletion of thioredoxin sensitizes AML to ETP treatment.

Conclusion

These results provide the foundation for augmenting the efficacy of ETP in treating AML with HHT, and also highlight the importance of targeting ROS in improving treatment outcome in AML.

Homoharringtonine could induce quick protein synthesis of PSMD11 through activating MEK1/ERK1/2 signaling pathway in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most devastating disease with the 5-year survival rate less than 6%. In this study, we investigated if inhibiting protein synthesis directly with homoharringtonine (HHT) could induce acute apoptosis in pancreatic cancer cells through quick depletion of multiple short-lived critical members of the central proteome, example, PSMD11(26S proteasome non-ATPase regulatory subunit 11). It was shown that although HHT could inhibit proliferation and growth of MiaPaCa-2 and PANC-1 cells in a time- and dose-dependent manner, only part of pancreatic cancer cells could be induced to die through acute apoptosis. Mechanistic studies showed that HHT could induce quick protein synthesis of PSMD11 through activating MEK1/ERK1/2 signaling pathway in pancreatic cancer cells. Inhibiting MEK1/ERK1/2 pathway with sorafenib could improve the cytotoxity of HHT in vitro and in a genetically engineered mouse model of pancreatic cancer. These results suggest that quick induction of PSMD11 or other acute apoptosis inhibitors through activation of the MEK1/ERK1/2 signaling pathway may be one of the important surviving mechanism which can help pancreatic cancer cells avoid acute apoptosis, it may have significant implications for the targeted therapy of pancreatic ductal adenocarcinoma.

The combination effect of homoharringtonine and ibrutinib on FLT3-ITD mutant acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous disease and internal tandem duplication mutation in FMS-like tyrosine-kinase-3 (FLT3-ITD) has a negative impact on outcome. Finding effective treatment regimens is desperately needed. In this study, we explored the inhibitory effect and mechanism of homoharringtonine (HHT) in combination with ibrutinib on FLT3-ITD mutant AML cells. Consequently, we observed a synergistic inhibitory effect when ibrutinib was combined with HHT to inhibit cell proliferation, induce apoptosis and arrest cell cycle at G0/G1 phase in MV4-11 and MOLM-13 leukemia cells. Our results indicate that the mechanisms of the combination effect are mainly via regulating the STAT5/Pim-2/C-Myc pathway, AKT pathway and Bcl-2 family, activating p21WAF1/CIP1 and inhibiting CCND/CDK complex protein. Interestingly, synergistic cytotoxicity of ibrutinib and HHT was dependent on both FLT3 and BTK. Here we provide a novel effective therapeutic approach for the treatment of AML patients with FLT3-ITD mutation.

Cephalotaxus Alkaloids

Cephalotaxus alkaloids represent a family of plant secondary metabolites known for 60 years. Significant activity against leukemia in mice was demonstrated for extracts of Cephalotaxus. Cephalotaxine (CET) (1), the major alkaloid of this series was isolated from Cephalotaxus drupacea species by Paudler in 1963. The subsequent discovery of promising antitumor activity among new Cephalotaxus derivatives reported by Chinese, Japanese, and American teams triggered extensive structure elucidation and biological studies in this family. The structural feature of this cephalotaxane family relies mainly on its tetracyclic alkaloid backbone, which comprises an azaspiranic 1-azaspiro[4.4]nonane unit (rings C and D) and a benzazepine ring system (rings A and B), which is linked by its C3 alcohol function to a chiral oxygenated side chain by a carboxylic function alpha to a tetrasubstituted carbon center. The botanical distribution of these alkaloids is limited to the Cephalotaxus genus (Cephalotaxaceae). The scope of biological activities of the Cephalotaxus alkaloids is mainly centered on the antileukemic activity of homoharringtonine (HHT) (2), which in particular demonstrated marked benefits in the treatment of orphan myeloid leukemia and was approved as soon as 2009 by European Medicine Agency and by US Food and Drug Administration in 2012. Its exact mechanism of action was partly elucidated and it was early recognized that HHT (2) inhibited protein synthesis at the level of the ribosome machinery. Interestingly, after a latency period of two decades, the topic of Cephalotaxus alkaloids reemerged as a prolific source of new natural structures. To date, more than 70 compounds have been identified and characterized. Synthetic studies also regained attention during the past two decades, and numerous methodologies were developed to access the first semisynthetic HHT (2) of high purity suitable for clinical studies, and then high grade enantiomerically pure CET (1), HHT (2), and analogs.

Identification of potential targets for differentiation in human leukemia cells induced by diallyl disulfide

Diallyl disulfide (DADS) is a primary component of garlic, which has chemopreventive potential. We previously found that moderate doses (15-120 µM) of DADS induced apoptosis and G2/M phase cell cycle arrest. In this study, we observed the effect of low doses (8 µM) of DADS on human leukemia HL-60 cells. We found that DADS could inhibit proliferation, migration and invasion in HL-60 cells, and arrested cells at G0/G1 stage. Then, cell differentiation was displayed by morphologic observation, NBT reduction activity and CD11b evaluation of cytometric flow. It showed that DADS induced differentiation, reduced the ability of NBT and increased CD11b expression. Likewise, DADS inhibited xenograft tumor growth and induced differentiation in vivo. In order to make sure how DADS induced differentiation, we compared the protein expression profile of DADS-treated cells with that of untreated control. Using high resolution mass spectrometry, we identified 18 differentially expressed proteins after treatment with DADS, including four upregulated and 14 downregulated proteins. RT-PCR and western blot assay showed that DJ-1, cofilin 1, RhoGDP dissociation inhibitor 2 (RhoGDI2), Calreticulin (CTR) and PCNA were decreased by DADS. These data suggest that the effects of DADS on leukemia may be due to multiple targets for intervention.

Common mechanisms of onset of cancer and neurodegenerative diseases

Onset of cancer and neurodegenerative disease occurs by abnormal cell growth and neuronal cell death, respectively, and the number of patients with both diseases has been increasing in parallel with an increase in mean lifetime, especially in developed countries. Although both diseases are sporadic, about 10% of the diseases are genetically inherited, and analyses of such familial forms of gene products have contributed to an understanding of the molecular mechanisms underlying the onset and pathogenesis of these diseases. I have been working on c-myc, a protooncogene, for a long time and identified various c-Myc-binding proteins that play roles in c-Myc-derived tumorigenesis. Among these proteins, some proteins have been found to be also responsible for the onset of neurodegenerative diseases, including Parkinson's disease, retinitis pigmentosa and cerebellar atrophy. In this review, I summarize our findings indicating the common mechanisms of onset between cancer and neurodegenerative diseases, with a focus on genes such as DJ-1 and Myc-Modulator 1 (MM-1) and signaling pathways that contribute to the onset and pathogenesis of cancer and neurodegenerative diseases.