Homoharringtonine-induced apoptosis of MDS cell line MUTZ-1 cells is mediated by the endoplasmic reticulum stress pathway

Apoptotic and cell cycle response to homoharringtonine and harringtonine in wild and mutant p53 hepatocarcinoma cells

This study aimed to evaluate the modes of action of harringtonine (HT) and homoharringtonine (HHT) alkaloids in cell with wild (HepG2/C3A) and mutant p53 (HuH-7.5). We performed assays for cytotoxicity, genotoxicity, induction of apoptosis, cell cycle phase, and membrane integrity. Obtained data were compared with the relative expression of mRNA of genes related to proliferation, apoptosis, cell cycle control, metabolism of xenobiotics, and reticulum endoplasmic stress. The relative expression of the genes showed an increase in apoptosis-inducing mRNAs, such as TNF and BBC3, as well as a reduction in BCL2 and BAK. The mRNAs of CYP2E1 and CYP2C19 xenobiotic metabolism genes increased in both lineages, while CYP3A4 increased only in the HuH-7.5 lineage. The mRNA expression of endoplasmic reticulum (ER) stress genes (ERN1 and EIF2AK3) was shown to increase in HHT and HT treatments. A similar increase was recorded in the mRNA expression of the TRAF2 gene. The changes observed in this study support the hypothesis that ER stress was more strongly associated with TNF induction, causing cell death by apoptosis in p53 mutant cells. This result with wild and mutant p53 cells may have clinical implications in the use of these compounds.

The efficacy and toxicity of the CHG priming regimen (low-dose cytarabine, homoharringtonine, and G-CSF) in higher risk MDS patients relapsed or refractory to decitabine

PURPOSE

Myelodysplastic syndromes (MDSs) refractory or relapsed after hypomethylating agents (HMAs) remain a therapeutic challenge. The CHG regimen has been demonstrated to be effective in initially treating higher risk MDS. The current study evaluated the efficacy and toxicity of the CHG regimen in patients who were resistant to decitabine.

METHODS

Patients with higher risk MDS relapsed or refractory to decitabine were enrolled in this study. Each patient received the CHG regimen (cytarabine (25 mg/day, days 1-14) and homoharringtonine (1 mg/day, days 1-14) intravenously with G-CSF (300 μg/day) subcutaneously from day 0 until neutrophil count recovery to 2.0 × 109 cells/L). Next gene sequencing with a 31-gene panel was carried out in patients.

RESULTS

Thirty-three patients were enrolled, including 12 relapsed and 21 refractory cases. The overall response rate (ORR) was 39.4% (13 of 33), with 9 (27.3%) achieving complete remission (CR), 2 having marrow CR (mCR), and 2 achieving partial remission (PR). The CR rate was higher in patients harboring fewer gene mutations (0-1) (55.6%) than in those with more gene mutations (> 1) (12.5%) (p = 0.021). The median overall survival (OS) of the 33 patients was 7.0 months. Patients who achieved a response had significantly longer survival times than were found in those without a response (21.0 M vs. 4.0 M, p < 0.0001). The regimen was endurable for most of the patients.

CONCLUSIONS

The CHG priming regimen provided a safe and effective salvage regimen for higher risk MDS patients who were resistant to decitabine. Further studies involving larger samples will be needed. Clinical trial No. ChiCTR-ONC-11001501.

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.

Efficacy and safety of homoharringtonine plus cytarabine and aclarubicin for patients with myelodysplastic syndrome-RAEB

The aim of the present study was to evaluate the treatment outcome of homoharringtonine, cytarabine (AraC) and aclarubicin combination therapy as induction treatment for myelodysplastic syndromes-refractory anemia with excess blasts (MDS-RAEB). A total of 24 patients with MDS-RAEB who were aged between 18 and 66 years were treated with homoharringtonine, AraC and aclarubicin (HAA regimen). The HAA regimen consisted of homoharringtonine (2 mg/m² intramuscularly twice daily, days 1-3), AraC (75 mg/m² injected subcutaneously twice daily, days 1-7) and aclarubicin (12 mg/m², days 1-7). The overall response rate was 79% with a complete remission rate of 58.3% and partial remission rate of 20.7%. There was no evidence of early mortality in this group of patients. The median overall survival (OS) was 36.2 months (95% confidence interval, 24.6-47.4 months), and the estimated three year overall survival rate was 45.8%. In conclusion, HAA combination therapy is a suitable induction regimen for patients with MDS-RAEB, which may improve the outcome for de novo higher-risk MDS patients, particularly of those with favorable and intermediate cytogenetics.

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

The objective of this study was to determine the changes in protein profiles of K562 chronic myeloid leukemia (CML) cells in response to Homoharringtonine (HHT). HHT treatment significantly increased apoptosis of K562 cells. Proteomic analyses indicated 32 differentially expressed proteins, 13 of which were identified by mass spectrometry (nine down-regulated and four up-regulated). Aside from alterations in apoptotic proteins and proteins associated with transcription and translation, our data also revealed changes in oxidative stress response and redox reaction-related proteins, such as heat shock proteins (Hsps), DJ-1 and thioredoxin. Specifically, these proteins were validated to decrease after HHT treatment in K562 cells and in primary CML cells by immunoblot analysis. Additionally, Hsps, DJ-1 and thioredoxin, which were also shown to decrease in primary cells from imatinib-resistant patients, may be promising potential targets for mechanistic research and new clinical treatments.

Homoharringtonine increases intestinal epithelial permeability by modulating specific claudin isoforms in Caco-2 cell monolayers

Homoharringtonine (HHT), a natural alkaloid produced by various Cephalotaxus species, has antileukemic activity in acute and chronic myelogenous leukemia. However, HHT can also induce unanticipated effects in the gastrointestinal tract, such as diarrhea and nausea/vomiting, but the mechanism behind these adverse effects has not been clarified. In the present study, we show that HHT affects the epithelial permeability of intestinal Caco-2 cell monolayers. HHT reduced the transepithelial electrical resistance (TER) of Caco-2 cells in a dose- and time-dependent manner. The HHT effect was reversible and no cytotoxicity was observed at the concentrations used. HHT simultaneously increased the paracellular flux of the 4 kDa and 40 kDa FITC-dextrans associated with the TER reduction. Immunoblotting analysis revealed that HHT decreased the protein expression of TJ components such as claudin-3, -5, and -7. However, the transcription levels of these claudins were not repressed by HHT treatment. HHT also disturbed the cellular localization of claudin-1 and -4. These changes coincided with the reduced barrier function. Our findings suggest that HHT enhances the paracellular permeability of Caco-2 cell monolayers by modulating the protein expression and localization of claudin isoforms; these actions might be responsible for the gastrointestinal effects of HHT.

Homoharringtonine and omacetaxine for myeloid hematological malignancies

Homoharringtonine (HHT), a plant alkaloid with antitumor properties originally identified nearly 40 years ago, has a unique mechanism of action by preventing the initial elongation step of protein synthesis. HHT has been used widely in China for the treatment of chronic myeloid leukemia (CML), acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Omacetaxine, a semisynthetic form of HHT, with excellent bioavailability by the subcutaneous route, has recently been approved by FDA of the United States for the treatment of CML refractory to tyrosine kinase inhibitors. This review summarized preclinical and clinical development of HHT and omacetaxine for myeloid hematological malignancies.

A phase II open-label study of the intravenous administration of homoharringtonine in the treatment of myelodysplastic syndrome

Homoharringtonine is an alkaloid inhibitor of protein synthesis with activity in myeloid malignancies. We report a phase II pilot study of homoharringtonine in myelodysplastic syndrome (MDS). Induction consisted of homoharringtonine at 2.5 mg/m(2) via continuous infusion for 7 days. Maintenance was given every 4 weeks. Nine patients were enrolled: five with refractory anaemia with excess blasts, two with refractory anaemia with excess blasts in transformation, one each with refractory anaemia and chronic myelomonocytic leukaemia respectively. Median age was 70 years (55-84) and 6 (66%) were male. Per International Prognostic Scoring System (IPSS) two patients were intermediate-1, five intermediate-2 and two high-risk. Median chemotherapy courses were one (1-3). One patient (11%) responded with complete haematological and cytogenetic remission after one course. Eight patients did not respond (four had stable disease, two progressed to acute leukaemia and two died during induction - from aspergillus pneumonia and intracerebral haemorrhage respectively). Grade 3/4 myelosuppression seen in 56% (5/9). Serious non-haematological toxicities included one case of grade 4 left bundle branch heart block and one grade 3 nephrotoxicity. Median time between courses was 42 days (35-72 days). In conclusion homoharringtonine might have clinical activity in some patients with MDS.

Endoplasmic reticulum stress contributes to arsenic trioxide-induced apoptosis in drug-sensitive and -resistant leukemia cells

This study characterized the role of endoplasmic reticulum stress (ERS)-related pathways in arsenic trioxide-induced apoptosis in multidrug-resistant leukemia K562/ADM cells. Arsenic trioxide exposure led to much significant induction of apoptosis in K562/ADM cells than the parental K562 cells, and the chaperone proteins glucose-regulated protein 78, CHOP/GADD153, X-box binding protein-1 and caspase-12 were activated to varying degrees. Furthermore, arsenic trioxide stimulation led to inhibition of P-glycoprotein and Bcl-2 expression. This study demonstrates a missing link between arsenic trioxide and ERS-induced apoptosis, and suggests that the greater effects obtained in drug-resistant K562/ADM cells may be mediated by downregulation of P-glycoprotein and Bcl-2 expression.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

Bcl-xL is a dominant antiapoptotic protein that inhibits homoharringtonine-induced apoptosis in leukemia cells

Homoharringtonine (HHT) has been reported to be effective in a portion of patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). To investigate its mechanism of action, cell growth inhibition and cytotoxicity of HHT were investigated in three AML cell lines, HL-60, NB4, and U937, and in three CML cell lines, K562, KU812, and KCL22. AML cells were more sensitive than CML cells to HHT-induced cytotoxicity. Using HL-60 cells, it was revealed that HHT decreased the levels of myeloid cell leukemia 1 (Mcl-1), X-linked inhibitor of apoptosis protein (XIAP), survivin, and B-cell lymphoma 2 (Bcl-2)-homology domain 3 (BH3)-only proteins as well as the mitochondrial membrane potential. The levels of Bcl-2, Bcl-2-associated X protein (Bax), and Bcl-2 homologous antagonist/killer (Bak) proteins in HL-60 cells were not changed after HHT treatment. U937, K562, KU812, and KCL22 cells expressed B-cell lymphoma-extra large (Bcl-xL) and were less responsive to HHT-induced apoptosis than HL-60 cells. Silencing Mcl-1 or Bcl-xL, but not XIAP or survivin, enhanced HHT-induced apoptosis in U937 cells. The levels of HHT-induced apoptosis in K562, KCL22, and KU812 cells were inversely correlated with the levels of Bcl-xL but not those of Bcl-2 or Mcl-1. K562 cells expressing high levels of Bcl-xL but no Bcl-2 were less responsive to HHT-induced apoptosis than KCL22 cells that expressed lower levels of Bcl-xL and higher levels of Bcl-2 protein. In K562 cells, knockdown of Bcl-xL, but not of Mcl-1, enhanced HHT-induced apoptosis. Transfection of Bcl-xL into KCL22 cells attenuated HHT-induced apoptosis. These data suggest that Bcl-xL plays a more important role than Bcl-2 and Mcl-1 in protecting against HHT-induced apoptosis.

Effect of low-dose cytarabine, homoharringtonine and granulocyte colony-stimulating factor priming regimen on patients with advanced myelodysplastic syndrome or acute myeloid leukemia transformed from myelodysplastic syndrome

A total of 32 patients (25 with advanced MDS and 7 with t-AML) were enrolled in this study to evaluate the efficacy and toxicity of the low-dose cytarabine and homoharringtonine in combination with granulocyte colony-stimulating factor (G-CSF) (CHG protocol) in patients with advanced myelodysplastic syndromes (MDS) or MDS-transformed acute myeloid leukemia (t-AML). All the patients were administered the CHG regimen comprising low-dose cytarabine (25 mg/day, intravenous continuous infusion, days 1-14), homoharringtonine (1 mg/day, intravenous continuous infusion, days 1-14), and G-CSF (300 microg/day, subcutaneous injection, days 0-14, interrupted when the peripheral white blood cell count reached >20 x 10(9)/L). The overall response rate was 71.9% after the administration of one course of the CHG regimen. Of the 32 patients, 15 (46.9%) achieved complete remission (CR) and 8 (25%) achieved partial remission (PR). This regimen was followed by a post-remission therapy that included conventional chemotherapy, when CR was achieved. Of the patients with CR who just received post-remission regimens as homoharringtonine and cytarabine (HA) and daunorubicin and cytarabine (DA) 6 relapsed rapidly and just had a mean 6.1 months of CR. Otherwise, the other 8 out of 14 patients with CR alternatively received subsequent chemotherapy, which combined mitoxantrone, idarubicin, pirarubicin, or aclarubicin with cytarabine. The mean CR duration of the 8 patients had reached 10.6 months, and 5 of the 8 still kept a continuous CR. The median overall survival (OS) was 18.2 months. There were no statistically significant differences for CR, PR, and OS when the patients were grouped by age, blasts in bone marrow, and karyotypes, respectively. No treatment-related deaths were observed. Myelosuppression was mild to moderate, and no severe non-hematological toxicity was observed. Thus, a CHG priming regimen as an induction therapy was well tolerated and effective in patients with advanced MDS or t-AML. Stronger and alternative subsequent chemotherapy is necessary for patients with CR to maintain longer CR and better OS.

Endoplasmic reticulum stress and BCL-2 family members

In the eukaryotic cell, the endoplasmic reticulum (ER) plays an important role as the site of lipid synthesis, protein folding and protein maturation. Stringent regulation of redox and calcium homeostasis is paramount, failure of which leads accumulation of unfolded and aggregating proteins resulting in a condition known as ER stress. Eukaryotic cells deal with ER stress by eliciting the unfolded protein response (UPR). This pathway splits into two streams depending on the severity and longevity of the ER stress, where the cell must make a choice for the good of the organism between survival and programmed cell death. The BCL-2 family of proteins is central to the cell death arm of the UPR pathway. This chapter discusses the recent findings on the involvement of BCL-2 family members in the apoptotic process initiated by ER stress and a related process called autophagy. Understanding the molecular mechanisms involved in ER stress and autophagy could have a profound implications developing new therapies for many ER stress associated diseases and cancer.

Dual involvement of caspase-4 in inflammatory and ER stress-induced apoptotic responses in human retinal pigment epithelial cells

PURPOSE

To investigate the functional involvement of caspase-4 in human retinal pigment epithelial (hRPE) cells.

METHODS

Expression and activation of caspase-4 in hRPE cells were measured after stimulation with proinflammatory agents IL-1beta (2 ng/mL), TNF-alpha (20 ng/mL), lipopolysaccharide (1000 ng/mL), interferon-gamma (500 U/mL), or monocyte coculture in the absence or presence of immunomodulating agent cyclosporine (3 or 30 ng/mL), dexamethasone (10 microM), or IL-10 (100 U/mL) and endoplasmic reticulum (ER) stress inducer thapsigargin (25 nM) or tunicamycin (3 or 10 microM). The onset of ER stress was determined by expression of GRP78. The involvement of caspase-4 in inflammation and apoptosis was further examined by treating the cells with caspase-4 inhibitor Z-LEVD-fmk, caspase-1 and -4 inhibitor Z-YVAD-fmk, and pan-caspase inhibitor Z-VAD-fmk.

RESULTS

Caspase-4 mRNA expression and protein activation were induced by all the proinflammatory agents and ER stress inducers tested in this study. Caspase-4 activation was blocked or reduced by dexamethasone and IL-10. Elevated ER stress by proinflammatory agents and ER stress inducers was shown by increased expression of the ER stress marker GRP78. The induced caspase-4 and caspase-3 activities by tunicamycin and the stimulated IL-8 protein expression by IL-1beta were markedly reduced by caspase-4 inhibitor Z-LEVD-fmk. Although caspase-4 inhibitor Z-LEVD-fmk and caspase-1 and -4 inhibitor Z-YVAD-fmk reduced tunicamycin-induced hRPE apoptotic cell death by 59% and 86%, respectively, pan-caspase inhibitor Z-VAD-fmk completely abolished the induced apoptosis.

CONCLUSIONS

Caspase-4 is dually involved in hRPE proinflammatory and proapoptotic responses. Various proinflammatory stimuli and ER stress induce hRPE caspase-4 mRNA synthesis and protein activation. ER stress-induced hRPE cell death is caspase and, in part, caspase-4 dependent.

Homoharringtonine inhibits the AKT pathway and induces in vitro and in vivo cytotoxicity in human multiple myeloma cells

Involvement of phosphatidylinositol 3-kinase/Akt-1 in cell survival and proliferation of multiple myeloma (MM) has been well established. In this study, we demonstrate that homoharringtonine (HHT), an antileukemic drug first isolated from the Chinese evergreen Cephalotaxus harringtonia, induces significant cytotoxicity in dexamethasone-sensitive and -resistant and chemotherapy-sensitive MM cell lines in a time and dose-dependent manner. HHT also triggers apoptosis in chemotherapy-resistant patient's myeloma cells. Contrary to dexamethasone, the cytotoxicity of HHT on myeloma is independent of interleukin-6. The mechanism of HHT cytotoxicity is related to down-regulation of Akt phosphorylation/activation and various target genes of Akt including nuclear factor kappa B, XIAP, cIAP and cyclin D1. Moreover, in vivo antitumor activity of HHT is demonstrated in RPMI8226 myeloma xenograft model. Importantly, an additive effect of antitumor is confirmed in the myeloma cells treated with HHT and bortezomib concomitantly with inhibition of phosphorylated Akt. Together, these findings obtained with HHT should give useful insights into a novel antimyeloma chemotherapy.