Downregulation of Mcl-1 potentiates HDACi-mediated apoptosis in leukemic cells

Chidamide and venetoclax synergistically regulate the Wnt/β-catenin pathway by MYCN/DKK3 in B-ALL

B-cell acute lymphocytic leukemia (B-ALL) is a malignant proliferative B-lymphocyte disease. Although the outcome of B-ALL has greatly improved with combined chemotherapy, immunotherapy, and hematopoietic stem cell transplantation, some patients still experience drug resistance, relapse and a low long-term survival rate, therefore, finding novel approaches to improve the outcome of adult B-ALL patients is critical. Our previous studies revealed that the selective histone deacetylase inhibitor (HDACi) chidamide can inhibit the Wnt/β-catenin signaling pathway by inhibiting MYCN and increasing the expression of DKK3 in B-ALL cells. Some studies have indicated that histone deacetylase inhibitors (HDACis) can dysregulate the B-cell lymphoma-2 (BCL2) protein family, we speculate that chidamide and BCL2 inhibitor venetoclax synergistically inhibit the Wnt/β-catenin signaling pathway by inhibiting MYCN expression and increasing DKK3 expression. In our study, the in vitro and in vivo experiments confirmed that chidamide and venetoclax synergistically inhibited the expression of MYCN and increased the expression of DKK3 by inhibiting the activity of HDAC and BCL2, inhibiting the Wnt/β-catenin signaling pathway and B-ALL cell proliferation. These findings indicate that the HDACi chidamide and the BCL2 inhibitor venetoclax can be used in combination to treat B-ALL, providing a new method and strategy for treating B-ALL.

Chidamide and venetoclax synergistically exert cytotoxicity on multiple myeloma by upregulating BIM expression

Background

Multiple myeloma (MM) is the second most common hematologic malignancy with almost all patients eventually having relapse or refractory MM (RRMM), thus novel drugs or combination therapies are needed for improved prognosis. Chidamide and venetoclax, which target histone deacetylase and BCL2, respectively, are two promising agents for the treatment of RRMM.

Results

Herein, we found that chidamide and venetoclax synergistically exert an anti-myeloma effect in vitro in human myeloma cell lines (HMCLs) with a combination index (CI) < 1. Moreover, the synergistic anti-myeloma effect of these two drugs was demonstrated in primary MM cells and MM xenograft mice. Mechanistically, co-exposure to chidamide and venetoclax led to cell cycle arrest at G0/G1 and a sharp increase in DNA double-strand breaks. In addition, the combination of chidamide and venetoclax resulted in BCL-X_L downregulation and BIM upregulation, and the latter protein was proved to play a critical role in sensitizing HMCLs to co-treatment.

Conclusion

In conclusion, these results proved the high therapeutic potential of venetoclax and chidamide combination in curing MM, representing a potent and alternative salvage therapy for the treatment of RRMM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01306-7.

Long non-coding RNA long intergenic non-coding 00641 mediates cell progression with stimulating cisplatin-resistance in osteosarcoma cells via microRNA-320d/myeloid cell leukemia-1 axis

As a staple chemotherapy medicine, cisplatin (DDP) is extensively applied in cancer patients, but its drug resistance is limited. Numerous studies have elucidated that long non-coding RNA (lncRNA) performs as a pivotal agent in osteosarcoma (OS). Nevertheless, lncRNA long intergenic non-coding 00641 (LINC00641)’s functions in DDP resistance for OS remain obscure. The purpose of this study was to investigate the effect and mechanism of LINC00641 on drug resistance of OS. The tissues of both clinical cancer patients and the normal control were gathered. Detection of LINC00641, microRNA-320d (miR-320d) and myeloid cell leukemia-1 (MCL1) was conducted. After the selection of OS cell lines, the detection of cell advancement was applied. Series of experiments were conducted to verify the interaction of LINC00641, miR-320d and MCL1. Xenografted tumor model in vivo was utilized to determine the function of LINC00641. The data displayed, LINC00641 was prominently elevated in OS tissues and cells, especially in DDP-resistant tumors and cell lines. Knock-down LINC00641 was able to attenuate progression of DDP-resistant OS cells thus dampening their drug resistance toward DDP. Moreover, knock-downing LINC00641 gene was also able to manifest antagonism toward DDP-resistance in vivo. On the grounds of bioinformatics prediction, a direct binding of LINC00641 with miR-320d existed, whose target was MCL1. Meanwhile, LINC00641 modulated MCL1 via targeting miR-320d. Additionally, repressive LINC00641 blocked MCL1 via emulative interaction with miR-320d, thus expediting DDP-sensitivity of OS cells. All in all, it is found that LINC00641 is available to escalate drug resistance of DDP-resistant OS cells via mediation of miR-320d/MCL1 axis.

Combination of Chidamide-Mediated Epigenetic Modulation with Immunotherapy: Boosting Tumor Immunogenicity and Response to PD-1/PD-L1 Blockade

Improving tumor immunogenicity is critical for increasing the responsiveness of triple-negative breast cancer (TNBC) to anti-PD-(L)1 treatment. Here, we verified that chidamide (CHI), an epigenetic modulator, could elicit immunogenic cell death within TNBC to enhance cancer immunogenicity and elicit an antitumor immune response. Additionally, CHI increased the expression level of PD-L1, MHC I, and MHC II on cancer cells, which contributed to T-cell recognition and PD-1/PD-L1 blockade therapy response. The synergistic antitumor efficacy of CHI and PD-L1 blockade therapy was further explored through liposomes co-delivering CHI and BMS-202 (a small-molecule PD-L1 inhibitor). The liposomes possessed good biocompatibility, security, and controllable drug release and endowed therapeutics drugs with favorable tumor accumulation. Furthermore, the drug-loaded liposomes could obviously boost the antitumor immunity of TNBC through CHI-enhanced tumor immunogenicity and BMS-202-mediated PD-L1 blockade, thereby effectively inhibiting the growth of primary and metastatic tumors with an inhibitory rate of metastasis of up to 96%. In summary, this work provided a referable and optional approach for clinical antitumor therapy based on the combination of an epigenetic modulator and PD-1/PD-L1 blockade therapy.

Histone Deacetylase Inhibitor SAHA Induces Expression of Fatty Acid-Binding Protein 4 and Inhibits Replication of Human Cytomegalovirus

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor that shows marked efficacy against many types of cancers and is approved to treat severe metastatic cutaneous T-cell lymphomas. In addition to its anticancer activity, SAHA has significant effects on the growth of many viruses. The effect of SAHA on replication of human cytomegalovirus (HCMV) has not, however, been investigated. Here, we showed that the replication of HCMV was significantly suppressed by treatment with SAHA at concentrations that did not show appreciable cytotoxicity. SAHA reduced transcription and protein levels of HCMV immediate early genes, showing that SAHA acts at an early stage in the viral life-cycle. RNA-sequencing data mining showed that numerous pathways and molecules were affected by SAHA. Interferon-mediated immunity was one of the most relevant pathways in the RNA-sequencing data, and we confirmed that SAHA inhibits HCMV-induced IFN-mediated immune responses using quantitative Real-time PCR (qRT-PCR). Fatty acid-binding protein 4 (FABP4), which plays a role in lipid metabolism, was identified by RNA-sequencing. We found that FABP4 expression was reduced by HCMV infection but increased by treatment with SAHA. We then showed that knockdown of FABP4 partially rescued the effect of SAHA on HCMV replication. Our data suggest that FABP4 contributes to the inhibitory effect of SAHA on HCMV replication.

Histone Deacetylase Inhibitors as Multitarget-Directed Epi-Drugs in Blocking PI3K Oncogenic Signaling: A Polypharmacology Approach

Genetic mutations and aberrant epigenetic alterations are the triggers for carcinogenesis. The emergence of the drugs targeting epigenetic aberrations has provided a better outlook for cancer treatment. Histone deacetylases (HDACs) are epigenetic modifiers playing critical roles in numerous key biological functions. Inappropriate expression of HDACs and dysregulation of PI3K signaling pathway are common aberrations observed in human diseases, particularly in cancers. Histone deacetylase inhibitors (HDACIs) are a class of epigenetic small-molecular therapeutics exhibiting promising applications in the treatment of hematological and solid malignancies, and in non-neoplastic diseases. Although HDACIs as single agents exhibit synergy by inhibiting HDAC and the PI3K pathway, resistance to HDACIs is frequently encountered due to activation of compensatory survival pathway. Targeted simultaneous inhibition of both HDACs and PI3Ks with their respective inhibitors in combination displayed synergistic therapeutic efficacy and encouraged the development of a single HDAC-PI3K hybrid molecule via polypharmacology strategy. This review provides an overview of HDACs and the evolution of HDACs-based epigenetic therapeutic approaches targeting the PI3K pathway.

Resistance to histone deacetylase inhibitors confers hypersensitivity to oncolytic reovirus therapy

Despite the promising antilymphoma activity of histone deacetylase (HDAC) inhibitors as a drug class, resistance is a significant clinical issue. Elucidating the molecular mechanisms driving HDAC inhibitor resistance and/or the specific targets that are altered in drug-resistant cells may facilitate the development of strategies that overcome drug resistance and are more effective for refractory patients. We generated novel T-cell lymphoma (TCL) cell line models of acquired resistance to the HDAC inhibitor belinostat to identify potential effective therapies. Belinostat-resistant cells displayed significant cross-resistance to other HDAC inhibitors including romidepsin, panobinostat, and vorinostat. Consistent with a lack of sensitivity to HDAC inhibitors, the resistant cells failed to induce increased acetylated histones. Drug-resistant cells featured significantly decreased expression of the key antiviral mediators IRF1 and STAT1. On the basis of these findings, we investigated the efficacy of the clinical formulation of reovirus (Reolysin) in parental and drug-resistant models. Our investigation revealed that HDAC inhibitor-resistant cells displayed enhanced vulnerability to reovirus replication and cell death in both in vitro and in vivo models compared with their parental counterparts. Importantly, Reolysin also significantly increased the antilymphoma activity of belinostat in HDAC inhibitor-resistant cells. Our data demonstrate that Reolysin alone or in combination with belinostat is a novel therapeutic strategy to treat TCL patients who develop resistance to HDAC inhibitors.

LncRNA FGD5-AS1 promotes tumor growth by regulating MCL1 via sponging miR-153-3p in oral cancer

Purpose: To investigate the function of long noncoding RNA (lncRNA) FGD5-AS1 in oral cancer (OC) and to further clarify the regulation of FGD5-AS1 on miR-153-3p/MCL1 axis.

Results: FGD5-AS1 was significantly increased in OC tissues and cells. Loss of FGD5-AS1 inhibited the proliferation, migration and invasion of OC cells. FGD5-AS1 acted as a sponge of miR-153-3p, and MCL1 was direct target of miR-153-3p. Forced expression of miR-153-3p or inhibition of MCL1 reversed the promoted role of FGD5-AS1 on OC cells’ migration and invasion. The in vivo tumor growth assay showed that FGD5-AS1 promoted OC tumorigenesis by regulating miR-153-3p/MCL1 axis.

Conclusions: Our research revealed lncRNA FGD5-AS1 acted as an oncogene by regulating MCL1 via sponging miR-153-3p, thus providing some novel experimental basis for clinical treatment or prevention of OC.

Patients and Methods: The mRNA expression of FGD5-AS1, miR-153-3p and MCL1 was detected by qRT-PCR. CCK8 assay, Edu assay, wound healing assay and transwell assay were used to detect the FGD5-AS1/ miR-153-3p/MCL1 axis function on proliferation, migration and invasion in OC cells. Western blot was used to calculate protein level of MCL1. Luciferase assay was used to detect the binding of miR-153-3p and MCL1, FGD5-AS1and miR-153-3p.

Novel HDAC inhibitor MAKV-8 and imatinib synergistically kill chronic myeloid leukemia cells via inhibition of BCR-ABL/MYC-signaling: effect on imatinib resistance and stem cells

Background

Chronic myeloid leukemia (CML) pathogenesis is mainly driven by the oncogenic breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 (BCR-ABL) fusion protein. Since BCR-ABL displays abnormal constitutive tyrosine kinase activity, therapies using tyrosine kinase inhibitors (TKis) such as imatinib represent a major breakthrough for the outcome of CML patients. Nevertheless, the development of TKi resistance and the persistence of leukemia stem cells (LSCs) remain barriers to cure the disease, justifying the development of novel therapeutic approaches. Since the activity of histone deacetylase (HDAC) is deregulated in numerous cancers including CML, pan-HDAC inhibitors may represent promising therapeutic regimens for the treatment of CML cells in combination with TKi.

Results

We assessed the anti-leukemic activity of a novel hydroxamate-based pan-HDAC inhibitor MAKV-8, which complied with the Lipinski’s “rule of five,” in various CML cells alone or in combination with imatinib. We validated the in vitro HDAC-inhibitory potential of MAKV-8 and demonstrated efficient binding to the ligand-binding pocket of HDAC isoenzymes. In cellulo, MAKV-8 significantly induced target protein acetylation, displayed cytostatic and cytotoxic properties, and triggered concomitant ER stress/protective autophagy leading to canonical caspase-dependent apoptosis. Considering the specific upregulation of selected HDACs in LSCs from CML patients, we investigated the differential toxicity of a co-treatment with MAKV-8 and imatinib in CML versus healthy cells. We also showed that beclin-1 knockdown prevented MAKV-8-imatinib combination-induced apoptosis. Moreover, MAKV-8 and imatinib co-treatment synergistically reduced BCR-ABL-related signaling pathways involved in CML cell growth and survival. Since our results showed that LSCs from CML patients overexpressed c-MYC, importantly MAKV-8-imatinib co-treatment reduced c-MYC levels and the LSC population. In vivo, tumor growth of xenografted K-562 cells in zebrafish was completely abrogated upon combined treatment with MAKV-8 and imatinib.

Conclusions

Collectively, the present findings show that combinations HDAC inhibitor-imatinib are likely to overcome drug resistance in CML pathology.

Roscovitine enhances All-trans retinoic acid (ATRA)-induced leukemia cell differentiation: Novel effects on signaling molecules for a putative Cdk2 inhibitor

All-trans retinoic acid (ATRA)-based differentiation therapy has been unsuccessful in treating t(15;17) negative acute myeloid leukemia (AML) patients, motivating interest in combination therapies using ATRA plus other agents. Using the t (15, 17) negative HL-60 human myeloblastic leukemia model, we find that the cyclin-dependent kinase (CDK) inhibitor, roscovitine, augments signaling by an ATRA-induced macromolecular signalsome that propels differentiation and enhances ATRA-induced differentiation. Roscovitine co-treatment enhanced ATRA-induced expression of pS259- pS289/296/301- pS621-c-Raf, pS217/221-Mek, Src Family Kinases (SFKs) Lyn and Fgr and SFK Y416 phosphorylation, adaptor proteins c-Cbl and SLP-76, Vav, and acetylated 14-3-3 in the signalsome. Roscovitine enhanced ATRA-induced c-Raf interaction with Lyn, Vav, and c-Cbl. Consistent with signalsome hyper-activation, roscovitine co-treatment enhanced ATRA-induced G1/0 arrest and expression of differentiation markers, CD11b, ROS and p47 Phox. Because roscovitine regulated Lyn expression, activation and partnering, a stably transfected Lyn knockdown was generated from wt-parental cells to investigate its function in ATRA-induced differentiation. Lyn-knockdown enhanced ATRA-induced up-regulation of key signalsome molecules, c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, Vav1, SLP-76, and Fgr, but with essentially total loss of pY416-SFK. Compared to ATRA-treated wt-parental cells, differentiation markers p47 phox, CD11b, G1/G0 arrest and ROS production were enhanced in ATRA-treated Lyn-knockdown stable transfectants, and addition of roscovitine further enhanced these ATRA-inducible markers. The Lyn-knockdown cells expressed slightly higher c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, and SLP-76 than wt-parental cells, and this was associated with enhanced ATRA-induced upregulation of Fgr and cell differentiation, consistent with heightened signaling, suggesting that enhanced Fgr may have compensated for loss of Lyn to enhance differentiation in the Lyn-knockdown cells.

Mcl-1 Phosphorylation without Degradation Mediates Sensitivity to HDAC Inhibitors by Liberating BH3-Only Proteins

Mcl-1, a prosurvival Bcl-2 family protein, is frequently overexpressed in cancer cells and plays a critical role in therapeutic resistance. It is well known that anticancer agents induce phosphorylation of Mcl-1, which promotes its binding to E3 ubiquitin ligases and subsequent proteasomal degradation and apoptosis. However, other functions of Mcl-1 phosphorylation in cancer cell death have not been well characterized. In this study, we show in colon cancer cells that histone deacetylase inhibitors (HDACi) induce GSK3β-dependent Mcl-1 phosphorylation, but not degradation or downregulation. The in vitro and in vivo anticancer effects of HDACi were dependent on Mcl-1 phosphorylation and were blocked by genetic knock-in of a Mcl-1 phosphorylation site mutant. Phosphorylation-dead Mcl-1 maintained cell survival by binding and sequestering BH3-only Bcl-2 family proteins PUMA, Bim, and Noxa, which were upregulated and necessary for apoptosis induction by HDACi. Resistance to HDACi mediated by phosphorylation-dead Mcl-1 was reversed by small-molecule Mcl-1 inhibitors that liberated BH3-only proteins. These results demonstrate a critical role of Mcl-1 phosphorylation in mediating HDACi sensitivity through a novel and degradation-independent mechanism. These results provide new mechanistic insights on how Mcl-1 maintains cancer cell survival and suggest that Mcl-1-targeting agents are broadly useful for overcoming therapeutic resistance in cancer cells.Significance: These findings present a novel degradation-independent function of Mcl-1 phosphorylation in anticancer therapy that could be useful for developing new Mcl-1-targeting agents to overcome therapeutic resistance. Cancer Res; 78(16); 4704-15. ©2018 AACR.

Characterization of TET and IDH gene expression in chronic lymphocytic leukemia: comparison with normal B cells and prognostic significance

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the most common hematological malignancy in western countries, characterized by a heterogeneous clinical course. Although genetic studies have identified chromosomal aberrations or specific mutations, epigenetic changes have been poorly characterized in CLL.

METHODS

We assessed ten-eleven translocations (TET) 1, 2, and 3, isocitrate dehydrogenase (IDH) 1, and 2 messenger RNA (mRNA) expression using real-time PCR on purified leukemic B cells from 214 CLL patients (median follow-up = 75 months, range 1-380), normal peripheral blood B cells (n = 20), and umbilical cord blood B cells (n = 21). The microenvironment influence was assessed after 24 h co-culture of CLL cells with bone marrow mesenchymal stromal cells (BMSC). Finally, 5-hydroxymethylcytosine level (%5-hmC) was assessed by ELISA in CLL cells alone or with microenvironment stimuli.

RESULTS

TET 1 and 3 and IDH2 were decreased in CLL cells compared with healthy B cells (P = 0.0221, 0.0013, <0.0001, respectively), while IDH1 was overexpressed (P = 0.0037). TET2 and IDH1 were significantly correlated with treatment-free survival (TFS); patients with high TET2/IDH1 expression had a higher median TFS (111 months) than patients with low expression (78 months, P = 0.0071/0.0123). Moreover, TET1 expression decreased (P = 0.0371), while TET3 and IDH2 expression increased (P = 0.0273/0.0039) in co-cultures. However, %5-hmC was not correlated with clinical data and was unchanged following microenvironment stimuli.

CONCLUSIONS

Despite a slight deregulation in CLL cells compared with normal B cells, we identified a significant association between TET/IDH gene expression and prognosis, suggesting that epigenetic changes could potentially be associated with disease progression. Moreover, despite an identical %5-hmC, TET gene expression was influenced by contact with BMSC confirming the crucial role of the microenvironment in CLL pathogenesis.

Maritoclax and dinaciclib inhibit MCL-1 activity and induce apoptosis in both a MCL-1-dependent and -independent manner

The anti-apoptotic BCL-2 family proteins are important targets for cancer chemotherapy. Specific and potent inhibitors of the BCL-2 family, such as ABT-263 (navitoclax) and ABT-199, are only effective against some members of the BCL-2 family but do not target MCL-1, which is commonly amplified in tumors and associated with chemoresistance. In this report, the selectivity and potency of two putative MCL-1 inhibitors, dinaciclib and maritoclax, were assessed. Although both compounds induced Bax/Bak- and caspase-9-dependent apoptosis, dinaciclib was more potent than maritoclax in downregulating MCL-1 and also in inducing apoptosis. However, the compounds induced apoptosis, even in cells lacking MCL-1, suggesting multiple mechanisms of cell death. Furthermore, maritoclax induced extensive mitochondrial fragmentation, and a Bax/Bak- but MCL-1-independent accumulation of mitochondrial reactive oxygen species (ROS), with an accompanying loss of complexes I and III of the electron transport chain. ROS scavengers, such as MitoQ, could not salvage maritoclax-mediated effects on mitochondrial structure and function. Taken together, our data demonstrate that neither dinaciclib nor maritoclax exclusively target MCL-1. Although dinaciclib is clearly not a specific MCL-1 inhibitor, its ability to rapidly downregulate MCL-1 may be beneficial in many clinical settings, where it may reverse chemoresistance or sensitize to other chemotherapeutic agents.

Dynamic Histone Acetylation of H3K4me3 Nucleosome Regulates MCL1 Pre-mRNA Splicing

Pre-mRNA splicing is a cotranscriptional process affected by the chromatin architecture along the body of coding genes. Recruited to the pre-mRNA by splicing factors, histone deacetylases (HDACs) and K-acetyltransferases (KATs) catalyze dynamic histone acetylation along the gene. In colon carcinoma HCT 116 cells, HDAC inhibition specifically increased KAT2B occupancy as well as H3 and H4 acetylation of the H3K4 trimethylated (H3K4me3) nucleosome positioned over alternative exon 2 of the MCL1 gene, an event paralleled with the exclusion of exon 2. These results were reproduced in MDA-MB-231, but not in MCF7 breast adenocarcinoma cells. These later cells have much higher levels of demethylase KDM5B than either HCT 116 or MDA-MB-231 cells. We show that H3K4me3 steady-state levels and H3K4me3 occupancy at the end of exon 1 and over exon 2 of the MCL1 gene were lower in MCF7 than in MDA-MB-231 cells. Furthermore, in MCF7 cells, there was minimal effect of HDAC inhibition on H3/H4 acetylation and H3K4me3 levels along the MCL1 gene and no change in pre-mRNA splicing choice. These results show that, upon HDAC inhibition, the H3K4me3 mark plays a critical role in the exclusion of exon 2 from the MCL1 pre-mRNA. J. Cell. Physiol. 231: 2196-2204, 2016. © 2016 Wiley Periodicals, Inc.

Upregulation of the MCL-1S protein variant following dihydroartemisinin treatment induces apoptosis in cholangiocarcinoma cells

The aim of the present study was to determine whether dihydroartemisinin (DHA) induces apoptosis in the human cholangiocarcinoma QBC939 cell line through the regulation of myeloid cell leukemia-1 (MCL-1) expression. The inhibitory rates of DHA on QBC939 cell proliferation and the effects of DHA on the cell death rates at various DHA concentrations and following various treatment times were examined. The rate of apoptosis and cell cycle changes following DHA treatment were examined and the changes in the expression of MCL-1 mRNAs and MCL-1 proteins following DHA treatment were also examined. The MTT assay and trypan blue staining demonstrated that DHA significantly inhibited the proliferation (P<0.05) and promoted the death of QBC939 cells (P<0.05). The DNA ladder assay and flow cytometry (FCM) analysis demonstrated that the rate of apoptosis in the experimental group was significantly increased following DHA treatment (P<0.01). FCM analysis also demonstrated that DHA treatment led to a reduction in the percentage of QBC939 cells in the G₀/G₁ and G₂/M phases, and the majority of the DNA-treated cells were arrested in the S phase of the cell cycle (P<0.01). Western blot analysis demonstrated that DHA treatment significantly upregulated the expression of the pro-apoptotic MCL-1S protein. In contrast, no significant difference in the expression of the anti-apoptotic MCL-1L protein was observed following DHA treatment. DHA affected the expression of the apoptosis-associated protein MCL-1 through multiple mechanisms. DHA treatment increased the ratio of MCL-1S/MCL-1L protein, thus inducing apoptosis in cholangiocarcinoma cells.

Effective elimination of chronic lymphocytic leukemia cells in the stromal microenvironment by a novel drug combination strategy using redox-mediated mechanisms

Chronic lymphocytic leukemia (CLL) is the most common type of adult leukemia, and is currently incurable due to drug resistance. A previous study indicated that the redox interaction between bone marrow stromal cells and leukemia cells profoundly affected CLL cell viability and drug response. The present study aimed to further investigate the effect of the redox interaction on drug resistance of CLL cells in the bone marrow microenvironment, and to assess a novel redox-mediated strategy to eliminate stromal-protected CLL cells, and thus to achieve maximum therapeutic efficacy of antileukemic drugs. Histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) is a potent novel anticancer agent, however, it exerts limited activity in patients with CLL. The results of the present study demonstrated that SAHA facilitated stromal‑mediated glutathione upregulation in the CLL cells, contributing to drug resistance. The addition of β‑phenylethyl isothiocyanate (PEITC) induced severe depletion of stromal and SAHA‑upregulated glutathione, enhanced SAHA‑mediated reactive oxygen species accumulation in the CLL cells and caused oxidation of mitochondrial cardilopin, leading to substantial cell death. The results further demonstrated that stromal cells and SAHA markedly upregulated antiapoptotic protein expression levels of myeloid cell leukemia 1 (Mcl1) in CLL the cells. By inducing protein deglutathionylation and degradation, PEITC suppressed the expression of Mcl1 in co‑cultured CLL cells, and increased SAHA sensitivity. The combination of SAHA and PEITC enabled the induction of marked apoptosis of CLL cells co‑cultured with bone marrow stromal cells. The present study provided a preclinical rationale, which warrants further clinical investigation for the potential use of SAHA/PEITC as a novel combination treatment strategy for CLL.

Apoptosis inducers in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by a typical defect in apoptosis and is still an incurable disease. Numerous apoptosis inducers have been described. These synthetic compounds and natural products (mainly derived from plants) display antileukemic properties in vitro and in vivo and some have even been tested in the clinic in CLL. They act through several different mechanisms. Most of them involve proteins of the Bcl-2 family, which are the key regulators in triggering the mitochondrial pathway of caspase-dependent apoptosis. Thus, the Mcl-1/Noxa axis appeared as a target. Here I overview natural and synthetic apoptosis inducers and their mechanisms of action in CLL cells. Opportunities for developing novel, apoptosis-based therapeutics are presented.

Noxa and cancer therapy: Tuning up the mitochondrial death machinery in response to chemotherapy

Biochemical analyses have characterized the BH3-only protein family member Noxa as a “sensitizer” with weak pro-apoptotic activity. Investigations into cancer cell responses to chemotherapeutic agents have identified Noxa as a pivotal factor mediating the cytotoxic effect of a plethora of anticancer treatments independent of its own pro-apoptotic activity. Accumulating evidence now suggests that tumor cells exert a number of strategies to counteract Noxa function by exploiting diverse cellular regulatory circuits that normally govern Noxa expression during cellular stress responses. Here, we summarize data concerning the role of Noxa in cancer chemosensitivity and highlight the potential of this enigmatic BH3-only protein family member in current and novel anticancer therapies.

SAHA and S116836, a novel tyrosine kinase inhibitor, synergistically induce apoptosis in imatinib-resistant chronic myelogenous leukemia cells

Limited treatment options are available for chronic myelogenous leukemia (CML) patients who develop imatinib mesylate (IM) resistance. Here we proposed a novel combination regimen, a co-administration of S116836, a novel small molecule multi-targeted tyrosine kinase inhibitor that was synthesized by rational design, and histone deacetylases inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA), to overcome IM resistance in CML. S116836 at low concentrations used in the present study mildly downregulates auto-tyrosine phosphorylation of Bcr-Abl. SAHA, an FDA-approved HDACi drug, at 1 μM has modest anti-tumor activity in treating CML. However, we found a synergistic interaction between SAHA and S116836 in Bcr-Abl-positive CML cells that were sensitive or resistant to IM. Exposure of KBM5 and KBM5-T315I cells to minimal or non-toxic concentrations of SAHA and S116836 synergistically reduced cell viability and induced cell death. Co-treatment with SAHA and S116838 repressed the expressions of anti-apoptosis proteins, such as Mcl-1 and XIAP, but promoted Bim expression and mitochondrial damage. Of importance, treatment with both drugs significantly reduced cell viability of primary human CML cells, as compared with either agent alone. Taken together, our findings suggest that SAHA exerts synergistically with S116836 at a non-toxic concentration to promote apoptosis in the CML, including those resistant to imatinib or dasatinib.

Synergistic interaction between the HDAC inhibitor, MPT0E028, and sorafenib in liver cancer cells in vitro and in vivo

PURPOSE

To investigate the antitumor activities of a histone deacetylase (HDAC) inhibitor, MPT0E028, plus sorafenib in liver cancer cells in vitro and in vivo.

EXPERIMENTAL DESIGN

Different liver cancer cell lines were exposed to sorafenib in the presence or absence of MPT0E028, and cell viability was determined by MTT assay. Effects of combined treatment on cell cycle and intracellular signaling pathways were assessed by flow cytometry and Western blot analysis. The Hep3B xenograft model was used to examine the antitumor activity in vivo.

RESULTS

Our data indicate that sorafenib and MPT0E028 synergistically reduced cell viability in liver cancer cells, and also markedly induced apoptotic cell death in these cells, as evidenced by the cleavage of caspase-3, PARP, and DNA fragmentation. MPT0E028 altered the global modifications of histone and nonhistone proteins regardless of the presence of sorafenib. However, sorafenib blocked MPT0E028-induced Erk activation and its downstream signaling cascades, such as Stat3 phosphorylation (Ser(727)) and Mcl-1 upregulation. Ectopic expression of constitutively active Mek successively reversed the apoptosis triggered by the combined treatment. Pharmacologic inhibition of Mek by PD98059 potentiated MPT0E028-induced apoptosis, suggesting that the synergistic interaction between MPT0E028 and sorafenib occurs at least partly through inhibition of Erk signaling. The data demonstrated that transcriptional activation of fibroblast growth factor receptor 3 (FGFR3) contributes to MPT0E028-mediated Erk phosphorylation. Finally, MPT0E028 plus sorafenib significantly improved the tumor growth delay (TGD) in a Hep3B xenograft model.

CONCLUSIONS

These findings suggest that MPT0E028 in combination with sorafenib has significant anti-hepatocellular carcinoma activity in preclinical models, potentially suggesting a novel therapeutic strategy for patients with advanced hepatocellular carcinoma.

RNA-dependent dynamic histone acetylation regulates MCL1 alternative splicing

Histone deacetylases (HDACs) and lysine acetyltransferases (KATs) catalyze dynamic histone acetylation at regulatory and coding regions of transcribed genes. Highly phosphorylated HDAC2 is recruited within corepressor complexes to regulatory regions, while the nonphosphorylated form is associated with the gene body. In this study, we characterized the nonphosphorylated HDAC2 complexes recruited to the transcribed gene body and explored the function of HDAC-complex-mediated dynamic histone acetylation. HDAC1 and 2 were coimmunoprecipitated with several splicing factors, including serine/arginine-rich splicing factor 1 (SRSF1) which has roles in alternative splicing. The co-chromatin immunoprecipitation of HDAC1/2 and SRSF1 to the gene body was RNA-dependent. Inhibition of HDAC activity and knockdown of HDAC1, HDAC2 or SRSF1 showed that these proteins were involved in alternative splicing of MCL1. HDAC1/2 and KAT2B were associated with nascent pre-mRNA in general and with MCL1 pre-mRNA specifically. Inhibition of HDAC activity increased the occupancy of KAT2B and acetylation of H3 and H4 of the H3K4 methylated alternative MCL1 exon 2 nucleosome. Thus, nonphosphorylated HDAC1/2 is recruited to pre-mRNA by splicing factors to act at the RNA level with KAT2B and other KATs to catalyze dynamic histone acetylation of the MCL1 alternative exon and alter the splicing of MCL1 pre-mRNA.

Hydroxyquinoline-derived compounds and analoguing of selective Mcl-1 inhibitors using a functional biomarker

Anti-apoptotic Bcl-2 family proteins are important oncology therapeutic targets. To date, BH3 mimetics that abrogate anti-apoptotic activity have largely been directed at Bcl-2 and/or Bcl-xL. One observed mechanism of resistance to these inhibitors is increased Mcl-1 levels in cells exposed to such therapeutics. For this reason, and because Mcl-1 is important in the onset of lymphoid, myeloid, and other cancers, it has become a target of great interest. However, small molecule inhibitors displaying potency and selectivity for Mcl-1 are lacking. Identifying such compounds has been challenging due to difficulties in translating the target selectivity observed at the biochemical level to the cellular level. Herein we report the results of an HTS strategy coupled with directed hit optimization. Compounds identified have selective Mcl-1 inhibitory activity with greater than 100-fold reduced affinity for Bcl-xL. The selectivity of these compounds at the cellular level was validated using BH3 profiling, a novel personalized diagnostic approach. This assay provides an important functional biomarker that allows for the characterization of cells based upon their dependencies on various anti-apoptotic Bcl-2 proteins. We demonstrate that cells dependent on Mcl-1 or Bcl-2/Bcl-xL for survival are commensurately responsive to compounds that genuinely target those proteins. The identification of compound 9 with uniquely validated and selective Mcl-1 inhibitory activity provides a valuable tool to those studying the intrinsic apoptosis pathway and highlights an important approach in the development of a first-in-class cancer therapeutic.

Suberoylanilide hydroxamic acid (SAHA) causes tumor growth slowdown and triggers autophagy in glioblastoma stem cells

Although suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, has been used in clinical trials for cancer therapies, its pharmacological effects occur through a poorly understood mechanism. Here, we report that SAHA specifically triggers autophagy and reduces cell viability via promotion of apoptosis in the late phase of glioblastoma stem cells (GSCs). Using a cell line cultured from a glioblastoma biopsy, we investigated the properties and effects of GSCs under SAHA treatment in vitro. In vivo xenograft assays revealed that SAHA effectively caused tumor growth slowdown and the induction of autophagy. SAHA was sufficient to increase formation of intracellular acidic vesicle organelles, recruitment of LC3-II to the autophagosomes, potentiation of BECN1 protein levels and reduced SQSTM1 levels. We determined that SAHA triggered autophagy through the downregulation of AKT-MTOR signaling, a major suppressive cascade of autophagy. Interestingly, upon depletion or pharmacological inhibition of autophagy, SAHA facilitates apoptosis and results in cell death at the early phase, suggesting that SAHA-induced autophagy functions probably act as a prosurvival mechanism. Furthermore, our results also indicated that the inhibition of SAHA-induced autophagy using chloroquine has synergistic effects that further increase apoptosis. Moreover, we found that a reduced dose of SAHA functioned as a potent modulator of differentiation and senescence. Taken together, our results provide a new perspective on the treatment of GSCs, indicating that SAHA is a promising agent for targeting GSCs through the induction of autophagy.

Intrinsic and extrinsic apoptotic pathway signaling as determinants of histone deacetylase inhibitor antitumor activity

Histone deacetylase inhibitors (HDACi) can elicit a range of biological responses that impede the growth and/or survival of tumor cells. Depending on the physiological context, HDACi can induce apoptosis via two well-defined apoptotic pathways; the intrinsic/mitochondrial pathway and the death receptor (DR)/extrinsic pathway. A number of groups have demonstrated that overexpression of prosurvival Bcl-2 family members significantly reduces HDACi-mediated tumor cell death and therapeutic efficacy in preclinical models. In many cases, HDACi activate the intrinsic pathway via upregulation of a number of proapoptotic BH3-only Bcl-2 family genes including Bim, Bid, and Bmf. Additionally, HDACi can engage the extrinsic pathway through upregulation of DR expression, reductions in c-FLIP, and upregulation of ligands such as TRAIL. Overall, it appears that activation of the intrinsic apoptotic pathway is the predominant mechanism of HDACi-induced tumor cell death; however, the DR pathway may also be engaged, either to amplify the apoptotic signal through the intrinsic pathway or to directly induce cell death.

MYC directs transcription of MCL1 and eIF4E genes to control sensitivity of gastric cancer cells toward HDAC inhibitors

Histone deacetylases (HDACs) control fundamental physiological processes such as proliferation and differentiation. HDAC inhibitors (HDACi) induce cell cycle arrest and apoptosis of tumor cells. Therefore, they represent promising cancer therapeutics that appear particularly useful in combination therapies. Although HDACi are tested in current clinical trials, the molecular mechanisms modulating the cellular responses toward HDACi are incompletely understood. To gain insight into pathways that limit HDACi efficacy in gastric cancer, we treated a panel of gastric cancer cells with the clinically relevant HDACi suberoylanilide hydroxamic acid (SAHA). We report that higher expression levels of the anti-apoptotic BCL2 family members MCL1 and BCL(XL) were detectable in cells with high inhibitory concentration 50 (IC(50)) values for SAHA. Using RNAi, we show that MCL1 and BCL(XL) lower the efficacy of SAHA. To find strategies to interfere with MCL1 and BCL(XL) expression, we investigated molecular regulation of both proteins. We show that specific siRNAs against c-MYC as well as pharmacological inhibition of this cancer-relevant transcription factor reduced MCL1 and BCL(XL) expression. Subsequently, we observed an increase in SAHA efficacy. Our data furthermore demonstrate that two different molecular mechanisms are responsible for the modulation of these factors. Whereas c-MYC controls transcription of MCL1 directly, regulation of BCL(XL) was due to c-MYC's capability to regulate the eIF4E gene, which encodes a rate-limiting factor of eukaryotic translation. Our data reveal a new molecular mechanism for how c-MYC controls cell autonomous apoptosis and provide a rationale for a concerted inhibition of HDACs and c-MYC in gastric cancer.

Histone deacetylase inhibitor-mediated sensitization to TRAIL-induced apoptosis in childhood malignancies is not associated with upregulation of TRAIL receptor expression, but with potentiated caspase-8 activation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has great potential for the treatment of cancer because it targets tumor cells while sparing normal cells. Several cancers, however, fail to respond to TRAIL's antineoplastic effects. These resistant tumors require cotreatment with sensitizing agents in order for TRAIL to exert anticancer activity. Histone deacetylase inhibitors (HDACi) have been recognized as potent TRAIL sensitizers. In searching for the determinants of TRAIL responsiveness, HDACi-mediated TRAIL sensitization has been predominantly attributed to TRAIL receptor upregulation. This explanation, however, has been challenged by a few studies. The aim of the present study was to explore the relevance of TRAIL receptor expression for HDACi-mediated TRAIL sensitization in childhood tumors, i.e., in medulloblastoma, Ewing's sarcoma and osteosarcoma. In previous studies, we had shown that TRAIL and HDACi were synergistic in inducing apoptosis in medulloblastoma and Ewing's sarcoma. In the present study, we demonstrate that HDACi cooperated with TRAIL in eliciting cell death in osteosarcoma. However, HDACi treatment did not alter or even reduced cell surface expression of TRAIL receptors in the three childhood tumors. In gaining insight into the apoptotic pathway involved in TRAIL sensitization, HDACi were found to potentiate TRAIL-induced caspase-8 activation. Taken together, our findings suggest that HDACi-mediated TRAIL sensitization is not the result of TRAIL receptor upregulation, but the result of a receptor-proximal event in childhood tumor cells.

Development of Noxa-like BH3 mimetics for apoptosis-based therapeutic strategy in chronic lymphocytic leukemia

Despite real advances made in chemoimmunotherapy, chronic lymphocytic leukemia (CLL) is still an incurable disease. New therapeutic strategies based on the restoration of the cell death program seemed relevant. Some members of the Bcl-2 family are critical players in the defective apoptotic program in CLL cells and/or targets of apoptosis inducers in vitro. The concept of BH3 mimetics has led to the characterization of small molecules mimicking proapoptotic BH3-only members of the Bcl-2 family by their ability to bind and antagonize the prosurvival members. Some putative or actual BH3 mimetics are already being tested in clinical trials with somewhat promising results. However, none of them has a high enough interaction affinity with Mcl-1, a crucial antiapoptotic factor in CLL. It has been suggested that resistance to BH3 mimetics can be overcome by using inhibitors of Mcl-1 expression. An alternative and more direct strategy is to design mimetics of the Noxa BH3 domain, which is a specific antagonistic Mcl-1 ligand. The development of such Noxa-like BH3 mimetics, capable of directly interacting with Mcl-1 and efficiently neutralizing its antiapoptotic activity, is extremely important to evaluate their impact on the clinical outcome of patients with CLL.

Design of novel BH3 mimetics for the treatment of chronic lymphocytic leukemia

Impaired programmed cell death is an important factor in the pathogenesis of chronic lymphocytic leukemia (CLL) and in the development of resistance to chemoimmunotherapy. Hence, the reactivation of apoptotic processes is likely to be a pertinent strategy for circumventing this resistance. Proteins from the Bcl-2 family are critical elements in defective apoptosis. Some compounds induce the apoptosis of CLL cells ex vivo by downregulation of prosurvival members of this family (for example, Bcl-2 and Mcl-1), whereas others act by upregulation of proapoptotic Bcl-2 homology (BH) 3-only members (for example, Noxa and Bim). The concept of BH3 mimetics was prompted by the fact that BH3-only proteins are specific antagonistic ligands of prosurvival Bcl-2 family members. This led to the design of small molecules capable of inhibiting the activity of prosurvival Bcl-2 proteins and inducing apoptosis in leukemia cells in vitro and antileukemic effects in animal models. Several putative or actual BH3 mimetics are currently being trialed in the clinic. Two novel BH3 mimetics that can specifically bind to and antagonize Mcl-1 (a crucial antiapoptotic factor in CLL) have recently been discovered. The evaluation of this type of compound's clinical impact in CLL can now be considered.

[Cell cycle and molecular targets: CDK inhibition]

Protein phosphorylation is a fundamental post-translational modification. It regulates a large number of critical cellular processes (differentiation, division, proliferation, apoptosis). Cell division is a process including a series of phases by which a parent cell divides into two daughter cells. The cells enter these stages then progress within the cell division under an accurate control by many proteins. These proteins are activated by phosphorylation. Cyclin-dependent kinases are responsible for this phosphorylation and therefore represent potential therapeutic targets especially in oncology.

Mechanisms of resistance to histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are a new class of anticancer agents. HDAC inhibitors induce acetylation of histones and nonhistone proteins which are involved in regulation of gene expression and in various cellular pathways including cell growth arrest, differentiation, DNA damage and repair, redox signaling, and apoptosis (Marks, 2010). The U.S. Food and Drug Administration has approved two HDAC inhibitors, vorinostat and romidepsin, for the treatment of cutaneous T-cell lymphoma (Duvic & Vu, 2007; Grant et al., 2010; Marks & Breslow, 2007). Over 20 chemically different HDAC inhibitors are in clinical trials for hematological malignancies and solid tumors. This review considers the mechanisms of resistance to HDAC inhibitors that have been identified which account for the selective effects of these agents in inducing cancer but not normal cell death. These mechanisms, such as functioning Chk1, high levels of thioredoxin, or the prosurvival BCL-2, may also contribute to resistance of cancer cells to HDAC inhibitors.

Deregulated expression of A1, Bcl-2, Bcl-xL, and Mcl-1 antiapoptotic proteins and Bid, Bad, and Bax proapoptotic genes in polycythemia vera patients

Apoptosis deregulation might have a role in the pathophysiology of polycythemia vera (PV). This study evaluated Bcl-2 molecule expression in CD34+ cells and leukocytes in 12 PV patients. Gene expression was investigated by real time PCR using SybrGreen Quantitect kit and protein expression was evaluated by western-blotting. JAK2 V617F mutation was detected according to Baxter et al (2005). CD34+ cells from PV patients presented higher levels of A1 and Mcl-1 expression (median: 22.6 and 5.2, respectively) in comparison with controls (0.9 and 0.5, p=0.004 and p=0.020); while Bcl-2 and Bcl-xL expression decreased in PV patients (0.18 and 1.19) compared with controls (1.39 and 2.01, p=0.006 and p=0.020). CD34+ cells in PV patients showed an elevated Bid expression (14.4) in comparison with healthy subjects (1.0; p=0.002). Patients' leukocytes showed an A1 augmentation (7.41, p=0.001) and a reduced expression of Bax (0.19; p=0.040) and Bad (0.2; p=0.030). There was no correlation between JAK2 V617F allele burden and molecular expression. PV patients showed alterations in Bcl-2 members' expression, which may interfere with control of apoptotic machinery and contribute to disease pathogenesis.

Histone deacetylases mediate the silencing of miR-15a, miR-16, and miR-29b in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) demonstrates a global down-regulation of miR-15a and miR-16 and a selective silencing of the related miR-29b in aggressive disease. Deletions in chromosome 13 [del(13q14)] partially account for the loss of expression of miR-15a and miR-16, but the mechanisms by which miR-29b becomes silenced is unknown. In the present study, we show that the histone deacetylases (HDACs) are overexpressed in CLL and mediate the epigenetic silencing of miR-15a, miR-16, and miR-29b. HDAC inhibition triggered the accumulation of the transcriptionally activating chromatin modification H3K4me2 and restored the expression of miR-15a, miR-16, and miR-29b in approximately 35% of samples. Ectopic expression of miR-15a and miR-16 and HDAC inhibition-induced expression of miR-15a, miR-16, or miR-29b in primary CLL cells was associated with declines in the levels of Mcl-1, but not Bcl-2, mitochondrial dysfunction, and induction of cell death. Therefore, our results show that HDACs aberrantly silence the expression of the critical tumor suppressors miR-15a, miR-16, and miR-29b in CLL. Deacetylase inhibition may be a therapeutic strategy that restores the expression of these miRs to antagonize Mcl-1, an important survival protein in these cells. Consequently, CLL patients who exhibit such epigenetic silencing may benefit from HDAC inhibitor-based therapy.

Histone deacetylase inhibitors: emerging mechanisms of resistance

The histone deacetylase inhibitors (HDIs) have shown promise in the treatment of a number of hematologic malignancies, leading to the approval of vorinostat and romidepsin for the treatment of cutaneous T-cell lymphoma and romidepsin for the treatment of peripheral T-cell lymphoma by the U.S. Food and Drug Administration. Despite these promising results, clinical trials with the HDIs in solid tumors have not met with success. Examining mechanisms of resistance to HDIs may lead to strategies that increase their therapeutic potential in solid tumors. However, relatively few examples of drug-selected cell lines exist, and mechanisms of resistance have not been studied in depth. Very few clinical translational studies have evaluated resistance mechanisms. In the current review, we summarize many of the purported mechanisms of action of the HDIs in clinical trials and examine some of the emerging resistance mechanisms.

Vorinostat-induced apoptosis in mantle cell lymphoma is mediated by acetylation of proapoptotic BH3-only gene promoters

PURPOSE

Mantle cell lymphoma (MCL) is an aggressive B-cell neoplasm with generally poor prognosis, for which current therapies have shown limited efficacy. Vorinostat is a histone deacetylase inhibitor (HDACi) that has been approved for the treatment of cutaneous T-cell lymphoma. Our purpose was to describe the molecular mechanism whereby vorinostat induces apoptosis in MCL with particular emphasis on the role of proapoptotic BH3-only proteins.

EXPERIMENTAL DESIGN

The sensitivity to vorinostat was analyzed in eight MCL cell lines and primary cells from 10 MCL patients. Determination of vorinostat mechanism of action was done by flow cytometry, immunoblotting, HDAC activity assay kit, quantitative reverse transcription PCR, chromatin immunoprecipitation, and siRNA-mediated transfection.

RESULTS

Vorinostat inhibited total histone deacetylase activity leading to selective toxicity toward tumor cells. Vorinostat-mediated cell death implied the activation of mitochondrial apoptosis, as attested by BAX and BAK conformational changes, mitochondrial depolarization, reactive oxygen species generation, and subsequent caspase-dependent cell death. This phenomenon was linked to H4 hyperacetylation on promoter regions and consequent transcriptional activation of the proapoptotic BH3-only genes BIM, BMF, and NOXA. Selective knockdown of the three corresponding proteins rescued cells from vorinostat-induced apoptosis. Moreover, vorinostat enhanced the activity of the BH3-mimetic ABT-263 in MCL cells, leading to synergistic apoptosis induction.

CONCLUSION

These results indicated that transcriptional upregulation of BH3-only proteins plays an important role in the antitumoral activity of vorinostat in MCL, and that HDACi alone or in combination with BH3-mimetizing agents may represent a promising therapeutic approach for MCL patients.

PRL-3, a metastasis associated tyrosine phosphatase, is involved in FLT3-ITD signaling and implicated in anti-AML therapy

Combination with other small molecule drugs represents a promising strategy to improve therapeutic efficacy of FLT3 inhibitors in the clinic. We demonstrated that combining ABT-869, a FLT3 inhibitor, with SAHA, a HDAC inhibitor, led to synergistic killing of the AML cells with FLT3 mutations and suppression of colony formation. We identified a core gene signature that is uniquely induced by the combination treatment in 2 different leukemia cell lines. Among these, we showed that downregulation of PTP4A3 (PRL-3) played a role in this synergism. PRL-3 is downstream of FLT3 signaling and ectopic expression of PRL-3 conferred therapeutic resistance through upregulation of STAT (signal transducers and activators of transcription) pathway activity and anti-apoptotic Mcl-1 protein. PRL-3 interacts with HDAC4 and SAHA downregulates PRL-3 via a proteasome dependent pathway. In addition, PRL-3 protein was identified in 47% of AML cases, but was absent in myeloid cells in normal bone marrows. Our results suggest such combination therapies may significantly improve the therapeutic efficacy of FLT3 inhibitors. PRL-3 plays a potential pathological role in AML and it might be a useful therapeutic target in AML, and warrant clinical investigation.

Aberrantly activated anti-apoptotic signalling mechanisms in chronic lymphocytic leukaemia cells: clues to the identification of novel therapeutic targets

Chronic lymphocytic leukaemia (CLL) is the commonest haematological malignancy in the western world and is incurable by cytotoxic therapy. Considerable research effort has identified the signal transduction pathways in CLL cells that contribute to anti-apoptotic signalling. Some pathways are constitutively activated in CLL cells but upregulated in normal cells only when protein tyrosine kinases (PTKs) are activated by ligands. This review describes which PTKs are aberrantly activated in CLL cells and are potential targets for inhibition. Additional potential targets within pathways downstream of these PTKs include Mek/Erk, mTorc1, protein kinase C, PI-3 kinase/Akt, nuclear factor-κB and cyclin-dependent protein kinase. Numerous studies have identified chemical agents and antibodies that selectively kill CLL cells, irrespective of their genetic resistance to conventional chemotherapeutic agents, and which can overcome cytoprotective microenvironmental signalling. These studies have resulted in identification of novel therapies, some of which are currently undergoing clinical trials. In vitro and animal model studies and clinical trials could determine which inhibitors of which targets are the likely to be most effective and least toxic either singly or in combination.

Role of alternative splicing events in gastric carcinogenesis

Alternative splicing affects many essential biologic processes and is the basis for a number of pathologic conditions, including cancer. Inherited and acquired changes in pre-mRNA splicing have been documented to play a significant role in human disease development. Many cancer-associated genes are regulated by alternative splicing. In this review, we will summarize the evidence supporting the association between alternative splicing and gastric carcinogenesis. The potential significance of alternative splicing events as a target for the diagnosis and treatment of gastric cancer will also be discussed.

Role of NOXA and its ubiquitination in proteasome inhibitor-induced apoptosis in chronic lymphocytic leukemia cells

BACKGROUND

Bortezomib has been successfully used in the treatment of multiple myeloma and has been proposed as a potential treatment for chronic lymphocytic leukemia. In this study we investigated the mechanism by which bortezomib induces apoptosis in chronic lymphocytic leukemia cells.

DESIGN AND METHODS

Using western blot analysis, we monitored the regulation of BCL2 family members, proteins of the unfolded protein response (endoplasmic reticulum stress response) and activation of caspases in relation to induction of apoptosis (measured by annexin-propidium iodide staining and loss of mitochondrial membrane potential) by bortezomib in chronic lymphocytic leukemia cells.

RESULTS

Bortezomib induced apoptosis through activation of the mitochondrial pathway independently of changes associated with endoplasmic reticulum stress. Perturbation of mitochondria was regulated by a rapid and transcription-independent increase of NOXA protein, which preceded release of cytochrome c, HtrA2, Smac and activation of caspase-9 and -3. NOXA had a short half life (approximately 1-2 h) and was ubiquitinated on at least three primary lysine residues, resulting in proteasomal-dependent degradation. Down-regulation of NOXA, using short interfering RNA in chronic lymphocytic leukemia cells, decreased bortezomib-induced apoptosis. Finally bortezomib when combined with seliciclib resulted in a stronger and earlier increase in NOXA protein, caspase-3 cleavage and induction of apoptosis in chronic lymphocytic leukemia cells.

CONCLUSIONS

These results highlight a critical role for NOXA in bortezomib-induced apoptosis in chronic lymphocytic leukemia cells and suggest that this drug may become more efficient for the treatment of chronic lymphocytic leukemia if combined with other agents able to interfere with the basal levels of MCL1.

Apoptosis in cancer: key molecular signaling pathways and therapy targets

Apoptosis is a physiological process vital for embryologic development and the maintenance of homeostasis in multicellular organisms, but it is also involved in a wide range of pathological processes, including cancer. In mammalian cells, apoptosis has been divided into two major pathways: the extrinsic pathway, activated by proapoptotic receptor signals at the cellular surface, and the intrinsic pathway, which involves the disruption of mitochondrial membrane integrity. Although many of the proteins vital for apoptosis have been identified, the molecular pathways of cellular death still remain to be elucidated. This review provides references concerning the apoptotic molecules, their interactions, the mechanisms involved in apoptosis resistance, and also the modulation of apoptosis for the treatment of cancer.

Exploiting cellular pathways to develop new treatment strategies for AML

The standard approaches to the treatment of acute myeloid leukemia (AML) have been predominantly based on cytarabine and anthracyclines. Yet, the outcomes associated with AML continue to be poor, especially for those patients who are older or carry higher-risk disease. In recent years, extensive research has led to the development and study of novel agents which target AML by diverse and varied mechanisms. Among these are targeted therapeutics such as kinase inhibitors and oligonucleotide constructs. These aim to suppress the production or activity of proteins, such as FLT3 and BCL2, among others, and thus disrupt related signaling cascades essential for leukemogenesis and proliferation. In addition, other agents like flavopiridol appear to target the myeloid blast by various mechanisms including suppression of cyclin-dependent kinases and interference with nucleotide synthesis. Another class of novel therapies includes inhibitors of histone deacetylase, which cause growth arrest and apoptosis through histone acetylation and resultant conformational changes. Clinical trials are now studying these and other agents alone and in combination with traditional cytotoxic therapies, with some encouraging results. In this review, we aim to provide a summary of the preclinical and clinical investigations of selected promising agents currently under study.

Enhanced Fas-associated death domain recruitment by histone deacetylase inhibitors is critical for the sensitization of chronic lymphocytic leukemia cells to TRAIL-induced apoptosis

Chronic lymphocytic leukemia (CLL) is an incurable disease characterized by failure of mature lymphocytes to undergo apoptosis. CLL cells are inherently resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Pretreatment with histone deacetylase inhibitors (HDACi) sensitizes CLL cells to TRAIL-mediated apoptosis primarily via TRAIL-R1 and offers a novel approach for the therapy of CLL and other malignancies. Depsipeptide (romidepsin), a HDACi, did not enhance TRAIL binding to TRAIL-R1, TRAIL-R1 aggregation, or internalization of TRAIL-R1, but it enhanced Fas-associated death domain protein (FADD) recruitment to TRAIL-R1 in the death-inducing signaling complex. Cotreatment with phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, dramatically inhibited the HDACi-mediated increase in FADD recruitment and sensitization to TRAIL-induced apoptosis and both of these were reversed by PKC inhibitors. Thus, enhanced FADD recruitment is a critical step in HDACi-mediated sensitization of CLL cells to TRAIL-induced apoptosis and this step is differentially affected by HDACi and phorbol 12-myristate 13-acetate. Using biotinylated TRAIL and streptactin-tagged TRAIL, we have identified several novel TRAIL receptor interacting proteins, including PKCbeta, lymphocyte-specific protease-1, Lyn, and Syk. These molecules may play an as yet unappreciated role in TRAIL signaling in CLL cells and inhibition of one or more of these kinases/phosphatases may provide a novel target to overcome TRAIL resistance.

Histone deacetylase inhibitors: current status and overview of recent clinical trials

Histone deacetylase (HDAC) inhibitors are a new group of anticancer agents that have a potential role in the regulation of gene expression, induction of cell death, apoptosis and cell cycle arrest of cancer cells by altering the acetylation status of chromatin and other non-histone proteins. In clinical trials, HDAC inhibitors have demonstrated promising antitumour activity as monotherapy in cutaneous T-cell lymphoma and other haematological malignancies. In solid tumours, several HDAC inhibitors have been shown to be efficacious as single agents; however, results of most clinical trials were in favour of using HDAC inhibitors either prior to the initiation of chemotherapy or in combination with other treatments. Currently, the molecular basis of response to HDAC inhibitors in patients is not fully understood. In this review, we summarize the current status of HDAC inhibitors, as single agents or in combination with other agents in different phases of clinical trials. In most of the clinical trials, HDAC inhibitors were tolerable and exerted biological or antitumor activity. HDAC inhibitors have been studied in phase I, II and III clinical trials with variable efficacy. The combination of HDAC inhibitors with other anticancer agents including epigenetic or chemotherapeutic agents demonstrated favourable clinical outcome.

Differential effects of anti-apoptotic Bcl-2 family members Mcl-1, Bcl-2, and Bcl-xL on celecoxib-induced apoptosis

The cyclooxygenase-2 inhibitor Celecoxib is a potent inducer of apoptosis in tumor cells. In most cellular systems Celecoxib induces apoptosis via an intrinsic, mitochondrial apoptosis pathway. We recently showed that in Bax-negative Jurkat cells expression of pro-apoptotic Bak is essential for Celecoxib-induced mitochondrial damage and apoptosis induction. Aim of the present study was to identify specific pro- and anti-apoptotic members of the Bcl-2 family involved in the regulation of Bak activation, and subsequent apoptosis upon treatment with Celecoxib in the Jurkat cell model. Our results show that apoptosis in response to Celecoxib required the presence of Noxa and downregulation of the anti-apoptotic protein Mcl-1. Celecoxib-induced Bak activation and subsequent apoptosis could be inhibited by overexpression of Bcl-xL but not by the very similar Bcl-2. In Bcl-xL-overexpressing cells neutralization of both, Mcl-1 and Bcl-xL, was prerequisite for an efficient induction of apoptosis. Our data reveal an important role of the Mcl-1/Noxa axis for Celecoxib-induced apoptosis and suggest that Celecoxib may be of value for treatment of tumors addicted to Mcl-1 and for combined treatment approaches targeting anti-apoptotic Bcl-2 family members.

Ordering of caspases in cells undergoing apoptosis by the intrinsic pathway

Caspases are a family of aspartate-specific cysteine proteases responsible for the biochemical and morphological changes that occur during the execution phase of apoptosis. The hierarchical ordering of caspases has been clearly established using dATP-activated cell lysates to model the intrinsic pathway induced by initial mitochondrial perturbation. In this model, caspase-9, the apical caspase, directly processes and activates the effector caspases, caspase-3 and -7, and then active caspase-3 but not caspase-7, processes caspase-2 and -6, and subsequently the activated caspase-6 processes caspase-8 and -10. To address the possibility that this model in vitro system might not reflect the precise ordering of caspases in intact cells, we have examined this possibility in cells induced to undergo apoptosis by activation of the intrinsic pathway. We have used caspase deficient cells, small interference RNA for caspase-6 and -7, and a specific caspase-3 inhibitor. In contrast to the earlier in vitro studies, we now show that in intact cells caspase-7 can also directly process and activate caspase-2 and -6. The processing of caspase-2 and -6 occurs within the cytoplasm and active caspase-6 is then responsible for both the processing of caspase-8 and the cleavage of caspase-6 substrates, including lamin A/C.

Simultaneous targeting of MCL1 and ABCB1 as a novel strategy to overcome drug resistance in human leukaemia

Drug resistance is a major obstacle to chemotherapy success in leukaemia. Although ABCB1 (MDR1) overexpression represents a critical mechanism of drug resistance, modulation of ABCB1 shows unsatisfactory clinical outcome. Recent studies showed that MCL1 was upregulated in numerous haematological and solid tumour malignancies. The present study found that patients with newly diagnosed or relapsed/refractory leukaemia expressed higher MCL1 levels than patients that were in complete remission. We demonstrated that overexpression of MCL1 decreased sensitivity of human leukaemia cell lines to cytotoxic drugs and inhibited drug-induced apoptosis. Specific downregulation of MCL1 via RNA interference sensitized multidrug resistant leukaemia cells towards chemotherapy and induced apoptosis. Our study also demonstrated that MCL1 and ABCB1 mediated drug resistance through different mechanisms and the depletion of both MCL1 and ABCB1 showed an additive effect in reversing drug resistance and promoting drug-induced apoptosis. Thus, this study documented an important role of MCL1 in drug resistance and apoptosis. Simultaneous targeting of MCL1 and ABCB1 could be a novel approach to overcome drug resistance in leukaemia.