KD5170, a novel mercaptoketone-based histone deacetylase inhibitor, exerts antimyeloma effects by DNA damage and mitochondrial signaling

Targeting the GCK pathway: a novel and selective therapeutic strategy against RAS-mutated multiple myeloma

In multiple myeloma (MM), frequent mutations of NRAS, KRAS, or BRAF are found in up to 50% of newly diagnosed patients. The majority of the NRAS, KRAS, and BRAF mutations occur in hotspots causing constitutive activation of the corresponding proteins. Thus, targeting RAS mutation in MM will increase therapeutic efficiency and potentially overcome drug resistance. We identified germinal center kinase (GCK) as a novel therapeutic target in MM with RAS mutation. GCK knockdown (KD) in MM cells demonstrated in vitro and in vivo that silencing of GCK induces MM cell growth inhibition, associated with blocked MKK4/7-JNK phosphorylation and impaired degradation of IKZF1/3, BCL-6, and c-MYC. These effects were rescued by overexpression of a short hairpin RNA (shRNA)-resistant GCK, thereby excluding the potential off-target effects of GCK KD. In contrast, overexpression of shRNA-resistant GCK kinase-dead mutant (K45A) inhibited MM cell proliferation and failed to rescue the effects of GCK KD on MM growth inhibition, indicating that GCK kinase activity is critical for regulating MM cell proliferation and survival. Importantly, the higher sensitivity to GCK KD in RASMut cells suggests that targeting GCK is effective in MM, which harbors RAS mutations. In accordance with the effects of GCK KD, the GCK inhibitor TL4-12 dose-dependently downregulated IKZF1 and BCL-6 and led to MM cell proliferation inhibition accompanied by induction of apoptosis. Here, our data identify GCK as a novel target in RASMut MM cells, providing a rationale to treat RAS mutations in MM. Furthermore, GCK inhibitors might represent an alternative therapy to overcome immunomodulatory drug resistance in MM.

Promising Anti-Mitochondrial Agents for Overcoming Acquired Drug Resistance in Multiple Myeloma

Multiple myeloma (MM) remains an incurable tumor due to the high rate of relapse that still occurs. Acquired drug resistance represents the most challenging obstacle to the extension of survival and several studies have been conducted to understand the mechanisms of this phenomenon. Mitochondrial pathways have been extensively investigated, demonstrating that cancer cells become resistant to drugs by reprogramming their metabolic assessment. MM cells acquire resistance to proteasome inhibitors (PIs), activating protection programs, such as a reduction in oxidative stress, down-regulating pro-apoptotic, and up-regulating anti-apoptotic signals. Knowledge of the mechanisms through which tumor cells escape control of the immune system and acquire resistance to drugs has led to the creation of new compounds that can restore the response by leading to cell death. In this scenario, based on all literature data available, our review represents the first collection of anti-mitochondrial compounds able to overcome drug resistance in MM. Caspase-independent mechanisms, mainly based on increased oxidative stress, result from 2-methoxyestradiol, Artesunate, ascorbic acid, Dihydroartemisinin, Evodiamine, b-AP15, VLX1570, Erw-ASNase, and TAK-242. Other agents restore PIs' efficacy through caspase-dependent tools, such as CDDO-Im, NOXA-inhibitors, FTY720, GCS-100, LBH589, a derivative of ellipticine, AT-101, KD5170, SMAC-mimetics, glutaminase-1 (GLS1)-inhibitors, and thenoyltrifluoroacetone. Each of these substances improved the efficacy rates when employed in combination with the most frequently used antimyeloma drugs.

Chidamide, a histone deacetylase inhibitor, induces growth arrest and apoptosis in multiple myeloma cells in a caspase-dependent manner

Chidamide, a novel histone deacetylase (HDAC) inhibitor, induces antitumor effects in various types of cancer. The present study aimed to evaluate the cytotoxic effect of chidamide on multiple myeloma and the underlying mechanisms involved. Viability of multiple myeloma cells upon chidamide treatment was determined by the Cell Counting Kit-8 assay. Apoptosis induction and cell cycle alteration were detected by flow cytometry. Specific apoptosis-associated proteins and cell cycle proteins were evaluated by western blot analysis. Chidamide suppressed cell viability in a time- and dose-dependent manner. Chidamide treatment markedly suppressed the expression of type I HDACs and further induced the acetylation of histones H3 and H4. In addition, it promoted G₀/G₁ arrest by decreasing cyclin D1 and c-myc expression, and increasing phosphorylated-cellular tumor antigen p53 and cyclin-dependent kinase inhibitor 1 (p21) expression in a dose-dependent manner. Treatment with chidamide induced cell apoptosis by upregulating the apoptosis regulator Bax/B-cell lymphoma 2 ratio in a caspase-dependent manner. In addition, the combination of chidamide with bortezomib, a proteasome inhibitor widely used as a therapeutic agent for multiple myeloma, resulted in enhanced inhibition of cell viability. In conclusion, chidamide induces a marked antimyeloma effect by inducing G₀/G₁ arrest and apoptosis via a caspase-dependent pathway. The present study provides evidence for the clinical application of chidamide in multiple myeloma.

DNMTi/HDACi combined epigenetic targeted treatment induces reprogramming of myeloma cells in the direction of normal plasma cells

Background

Multiple myeloma (MM) is the second most common hematologic malignancy. Aberrant epigenetic modifications have been reported in MM and could be promising therapeutic targets. As response rates are overall limited but deep responses occur, it is important to identify those patients who could indeed benefit from epigenetic-targeted therapy.

Methods

Since HDACi and DNMTi combination have potential therapeutic value in MM, we aimed to build a GEP-based score that could be useful to design future epigenetic-targeted combination trials. In addition, we investigated the changes in GEP upon HDACi/DNMTi treatment.

Results

We report a new gene expression-based score to predict MM cell sensitivity to the combination of DNMTi/HDACi. A high Combo score in MM patients identified a group with a worse overall survival but a higher sensitivity of their MM cells to DNMTi/HDACi therapy compared to a low Combo score. In addition, treatment with DNMTi/HDACi downregulated IRF4 and MYC expression and appeared to induce a mature BMPC plasma cell gene expression profile in myeloma cell lines.

Conclusion

In conclusion, we developed a score for the prediction of primary MM cell sensitivity to DNMTi/HDACi and found that this combination could be beneficial in high-risk patients by targeting proliferation and inducing maturation.

The Heme Oxygenase System in Hematological Malignancies

SIGNIFICANCE

Several lines of evidence suggest that hematological malignancies exhibit an altered redox balance homeostasis that can lead to the activation of various survival pathways that, in turn, lead to the progression of disease and chemoresistance. Among these pathways, the heme oxygenase-1 (HO-1) pathway is likely to play a major role. HO catalyzes the enzymatic degradation of heme with the simultaneous release of carbon monoxide (CO), ferrous iron (Fe²⁺), and biliverdin. This review focuses on the role of HO-1 in various hematological malignancies and the possibility of exploiting such targets to improve the outcome of well-established chemotherapeutic regimens. Recent Advances and Critical Issues: Interestingly, the inhibition of the expression of HO-1 (e.g., with siRNA) or HO activity (with competitive inhibitors) contributes to the increased efficacy of chemotherapy and improves the outcome in animal models. Furthermore, some hematological malignancies (e.g., chronic myeloid leukemia and multiple myeloma) have served to explore the non-canonical functions of HO-1, such as the association between nuclear compartmentalization and genetic instability and/or chemoresistance.

FUTURE DIRECTIONS

The HO system may serve as an important tool in the field of hematological malignancies because it can be exploited to counteract chemoresistance and to monitor the outcome of bone marrow transplants and may be an additional target for combined therapies. Antioxid. Redox Signal. 27, 363-377.

Combined expression of miR-34a and Smac mediated by oncolytic vaccinia virus synergistically promote anti-tumor effects in Multiple Myeloma

Despite great progress made in the treatment of multiple myeloma (MM), it is still incurable. Promising phase II clinical results have been reported recently for oncolytic vaccinia virus (OVV) clinic therapeutics. One reason for this has focused on the critical therapeutic importance of the immune response raised by these viruses. However, few studies have performed their applications as an optimal delivery system for therapeutic gene, especially miRNA in MM. In this study, we constructed two novel OVVs (TK deletion) that express anti-tumor genes, miR-34a and Smac, respectively, in MM cell lines and xenograft model. The results demonstrated that the novel OVV can effectively infect MM cell lines, and forcefully enhance the exogenous gene (miR-34a or Smac) expression. Furthermore, utilization of VV-miR-34a combined with VV-Smac synergistically inhibited tumor growth and induced apoptosis in vitro and in vivo. The underlying mechanism is proposed that blocking of Bcl-2 by VV-miR-34a increases the release of cytochrome c from mitochondria and then synergistically amplifies the antitumor effects of Smac-induced cell apoptosis. Our study is the first to utilize OVV as the vector for miR-34a or Smac expression to treat MM, and lays the groundwork for future clinical therapy for MM.

The combination of HDAC and aminopeptidase inhibitors is highly synergistic in myeloma and leads to disruption of the NFκB signalling pathway

There is a growing body of evidence supporting the use of epigenetic therapies in the treatment of multiple myeloma. We show the novel HDAC inhibitor CHR-3996 induces apoptosis in myeloma cells at concentrations in the nanomolar range and with apoptosis mediated by p53 and caspase pathways. In addition, HDAC inhibitors are highly synergistic, both in vitro and in vivo, with the aminopeptidase inhibitor tosedostat (CHR-2797). We demonstrate that the basis for this synergy is a consequence of changes in the levels of NFκB regulators BIRC3/cIAP2, A20, CYLD, and IκB, which were markedly affected by the combination. When co-administered the HDAC and aminopeptidase inhibitors caused rapid nuclear translocation of NFκB family members p65 and p52, following activation of both canonical and non-canonical NFκB signalling pathways. The subsequent up-regulation of inhibitors of NFκB activation (most significantly BIRC3/cIAP2) turned off the cytoprotective effects of the NFκB signalling response in a negative feedback loop. These results provide a rationale for combining HDAC and aminopeptidase inhibitors clinically for the treatment of myeloma patients and support the disruption of the NFκB signalling pathway as a therapeutic strategy.

Clinical use and applications of histone deacetylase inhibitors in multiple myeloma

The incorporation of various novel therapies has resulted in a significant survival benefit in newly diagnosed and relapsed patients with multiple myeloma (MM) over the past decade. Despite these advances, resistance to therapy leads to eventual relapse and fatal outcomes in the vast majority of patients. Hence, there is an unmet need for new safe and efficacious therapies for continued improvement in outcomes. Given the role of epigenetic aberrations in the pathogenesis and progression of MM and the success of histone deacetylase inhibitors (HDACi) in other malignancies, many HDACi have been tried in MM. Various preclinical studies helped us to understand the antimyeloma activity of different HDACi in MM as a single agent or in combination with conventional, novel, and immune therapies. The early clinical trials of HDACi depicted only modest single-agent activity, but recent studies have revealed encouraging clinical response rates in combination with other antimyeloma agents, especially proteasome inhibitors. This led to the approval of the combination of panobinostat and bortezomib for the treatment of relapsed/refractory MM patients with two prior lines of treatment by the US Food and Drug Administration. However, it remains yet to be defined how we can incorporate HDACi in the current therapeutic paradigms for MM that will help to achieve longer disease control and significant survival benefits. In addition, isoform-selective and/or class-selective HDAC inhibition to reduce unfavorable side effects needs further evaluation.

Histone deacetylase inhibitor-induced cell death in bladder cancer is associated with chromatin modification and modifying protein expression: A proteomic approach

The Cancer Genome Atlas (TCGA) project recently identified the importance of mutations in chromatin remodeling genes in human carcinomas. These findings imply that epigenetic modulators might have a therapeutic role in urothelial cancers. To exploit histone deacetylases (HDACs) as targets for cancer therapy, we investigated the HDAC inhibitors (HDACIs) romidepsin, trichostatin A, and vorinostat as potential chemotherapeutic agents for bladder cancer. We demonstrate that the three HDACIs suppressed cell growth and induced cell death in the bladder cancer cell line 5637. To identify potential mechanisms associated with the anti-proliferative and cytotoxic effects of the HDACIs, we used quantitative proteomics to determine the proteins potentially involved in these processes. Our proteome studies identified a total of 6003 unique proteins. Of these, 2472 proteins were upregulated and 2049 proteins were downregulated in response to HDACI exposure compared to the untreated controls (P<0.05). Bioinformatic analysis further revealed that those differentially expressed proteins were involved in multiple biological functions and enzyme-regulated pathways, including cell cycle progression, apoptosis, autophagy, free radical generation and DNA damage repair. HDACIs also altered the acetylation status of histones and non-histone proteins, as well as the levels of chromatin modification proteins, suggesting that HDACIs exert multiple cytotoxic actions in bladder cancer cells by inhibiting HDAC activity or altering the structure of chromatin. We conclude that HDACIs are effective in the inhibition of cell proliferation and the induction of apoptosis in the 5637 bladder cancer cells through multiple cell death-associated pathways. These observations support the notion that HDACIs provide new therapeutic options for bladder cancer treatment and thus warrant further preclinical exploration.

Elevated Translation Initiation Factor eIF4E Is an Attractive Therapeutic Target in Multiple Myeloma

eIF4E is the key regulator of protein translation and critical for translation. The oncogenic potential of tumorigenesis, which is highly contingent on cap-dependent eIF4E, also arises from the critical role in the nuclear export and cytosolic translation of oncogenic transcripts. Inhibition of Exportin1 (XPO1), which is the major nuclear export protein for eIF4E-bound oncoprotein mRNAs, results in decreased tumor cell growth in vitro and in vivo, suggesting that eIF4E is critical in multiple myeloma. Indeed, we found that eIF4E is overexpressed in myeloma cell lines and primary myeloma cells compared with normal plasma cells. Although stable overexpression of eIF4E in multiple myeloma cells significantly increases tumorigenesis, knockdown of eIF4E impairs multiple myeloma tumor progression in a human xenograft mouse model. Using a tet-on-inducible eIF4E-knockdown system, eIF4E downregulation blocks multiple myeloma tumor growth in vivo, correlating with decreased eIF4E expression. Further overexpression and knockdown of eIF4E revealed that eIF4E regulates translation of mRNAs with highly complex 5'-untranslated regions, such as c-MYC and C/EBPβ, and subsequently proliferation in multiple myeloma cells, but not in nonmalignant bone marrow stromal cells. Because many transcription factors that are critical for multiple myeloma proliferation exhibit a higher dependency on protein translation, eIF4E is an ideal and selective tool to target multiple myeloma cell growth. Mol Cancer Ther; 15(4); 711-9. ©2016 AACR.

Oxidative stress and proteasome inhibitors in multiple myeloma

Multiple myeloma is a form of plasma cell neoplasm that accounts for approximately 10% of all hematological malignancies. Recently, several novel drugs have been discovered that almost doubled the overall survival of multiple myeloma patients. One of these drugs, the first-in-class proteasome inhibitor bortezomib (Velcade) has demonstrated remarkable response rates in multiple myeloma patients, and yet, currently this disease remains incurable. The major factor undermining the success of multiple myeloma treatment is a rapidly emerging resistance to the available therapy. Thus, the development of stand-alone or adjuvant anti-myeloma agents becomes of paramount importance. Overproduction of intracellular reactive oxygen species (ROS) often accompanies malignant transformation due to oncogene activation and/or enhanced metabolism in tumor cells. As a result, these cells possess higher levels of ROS and lower levels of antioxidant molecules compared to their normal counterparts. Unbalanced production of ROS leads to oxidative stress which, if left unchecked, could be toxic for the cell. In multiple myeloma cells where high rates of immunoglobulin synthesis is an additional factor contributing to overproduction of ROS, further induction of oxidative stress can be an effective strategy to cope with this disease. Here we will review the available data on the role of oxidative stress in the cytotoxicity of proteasome inhibitors and the use of ROS-inducing compounds as anti-myeloma agents.

Discovery of novel INK4C small-molecule inhibitors to promote human and murine hematopoietic stem cell ex vivo expansion

Hematopoietic stem cells (HSCs) have emerged as promising therapeutic cell sources for high-risk hematological malignancies and immune disorders. However, their clinical use is limited by the inability to expand these cells ex vivo. Therefore, there is an urgent need to identify specific targets and effective probes that can expand HSCs. Here we report a novel class of INK4C (p18^INK4C or p18) small molecule inhibitors (p18SMIs), which were initially found by in silico 3D screening. We identified a lead p18 inhibitor, XIE18-6, confirmed its p18-targeting specificity and bioactivity of promoting HSCs expansion, and then performed structure-activity relationship (SAR) studies by synthesizing a series of analogs of XIE18–6. Among these, compound 40 showed the most potent bioactivity in HSCs expansion (ED₅₀ = 5.21 nM). We confirmed that compound 40 promoted expansion of both murine and human HSCs, and also confirmed its p18-targeting specificity. Notably, compound 40 did not show significant cytotoxicity toward 32D cells or HSCs, nor did it augment leukemia cell proliferation. Taken together, our newly discovered p18SMIs represent novel chemical agents for murine and human HSCs ex vivo expansion and also can be used as valuable chemical probes for further HSC biology research towards promising utility for therapeutic purposes.

Targeting cannabinoid receptor-2 pathway by phenylacetylamide suppresses the proliferation of human myeloma cells through mitotic dysregulation and cytoskeleton disruption

Cannabinoid receptor-2 (CB2) is expressed dominantly in the immune system, especially on plasma cells. Cannabinergic ligands with CB2 selectivity emerge as a class of promising agents to treat CB2-expressing malignancies without psychotropic concerns. In this study, we found that CB2 but not CB1 was highly expressed in human multiple myeloma (MM) and primary CD138+ cells. A novel inverse agonist of CB2, phenylacetylamide but not CB1 inverse agonist SR141716, inhibited the proliferation of human MM cells (IC50 : 0.62 ∼ 2.5 μM) mediated by apoptosis induction, but exhibited minor cytotoxic effects on human normal mononuclear cells. CB2 gene silencing or pharmacological antagonism markedly attenuated phenylacetylamide's anti-MM effects. Phenylacetylamide triggered the expression of C/EBP homologous protein at the early treatment stage, followed by death receptor-5 upregulation, caspase activation, and β-actin/tubulin degradation. Cell cycle related protein cdc25C and mitotic regulator Aurora A kinase were inactivated by phenylacetylamide treatment, leading to an increase in the ratio inactive/active cdc2 kinase. As a result, phosphorylation of CDK substrates was decreased, and the MM cell mitotic division was largely blocked by treatment. Importantly, phenylacetylamide could overcome the chemoresistance of MM cells against dexamethasone or melphalan. Thus, targeting CB2 may represent an attractive approach to treat cancers of immune origin.

Overcoming inherent resistance to histone deacetylase inhibitors in multiple myeloma cells by targeting pathways integral to the actin cytoskeleton

Histone deacetylase inhibitors (HDACi) are novel chemotherapeutics undergoing evaluation in clinical trials for the potential treatment of patients with multiple myeloma (MM). Although HDACi have demonstrable synergy when combined with proteasome inhibitors (PIs), recent evidence indicates that combination of HDACi and PI is beneficial only in a subset of patients with advanced MM, clearly indicating that other rational combinations should be explored. In this context we hypothesized that understanding the molecular signature associated with inherent resistance to HDACi would provide a basis for the identification of therapeutic combinations with improved clinical efficacy. Using human myeloma cell lines (HMCL) categorized as sensitive, intermediate or resistant to HDACi, gene expression profiling (GEP) and gene ontology enrichment analyses were performed to determine if a genetic signature associated with inherent resistance to HDACi-resistance could be identified. Correlation of GEP to increasing or decreasing sensitivity to HDACi indicated a unique 35-gene signature that was significantly enriched for two pathways – regulation of actin cytoskeleton and protein processing in endoplasmic reticulum. When HMCL and primary MM samples were treated with a combination of HDACi and agents targeting the signaling pathways integral to the actin cytoskeleton, synergistic cell death was observed in all instances, thus providing a rationale for combining these agents with HDACi for the treatment of MM to overcome resistance. This report validates a molecular approach for the identification of HDACi partner drugs and provides an experimental framework for the identification of novel therapeutic combinations for anti-MM treatment.

Gene expression-based prediction of myeloma cell sensitivity to histone deacetylase inhibitors

Background:

Multiple myeloma (MM) is still a fatal plasma cell cancer. Novel compounds are currently clinically tested as a single agent in relapsing patients, but in best cases with partial response of a fraction of patients, emphasising the need to design tools predicting drug efficacy. Histone deacetylase inhibitors (HDACi) are anticancer agents targeting epigenetic regulation of gene expression and are in clinical development in MM.

Methods:

To create a score predicting HDACi efficacy, five MM cell lines were treated with trichostatin A (TSA) and gene expression profiles were determined.

Results:

The expression of 95 genes was found to be upregulated by TSA, using paired supervised analysis with Significance Analysis of Microarrays software. Thirty-seven of these 95 genes had prognostic value for overall survival in a cohort of 206 newly diagnosed MM patients and their prognostic information was summed up in a histone acetylation score (HA Score); patients with the highest HA Score had the shorter overall survival. It is worth noting that MM cell lines or patients' primary MM cells with a high HA Score had a significant higher sensitivity to TSA, valproic acid, panobinostat or vorinostat.

Conclusion:

In conclusion, the HA Score allows identification of MM patients with poor survival, who could benefit from HDACi treatment.

Epigenetic modulating agents as a new therapeutic approach in multiple myeloma

Multiple myeloma (MM) is an incurable B-cell malignancy. Therefore, new targets and drugs are urgently needed to improve patient outcome. Epigenetic aberrations play a crucial role in development and progression in cancer, including MM. To target these aberrations, epigenetic modulating agents, such as DNA methyltransferase inhibitors (DNMTi) and histone deacetylase inhibitors (HDACi), are under intense investigation in solid and hematological cancers. A clinical benefit of the use of these agents as single agents and in combination regimens has been suggested based on numerous studies in pre-clinical tumor models, including MM models. The mechanisms of action are not yet fully understood but appear to involve a combination of true epigenetic changes and cytotoxic actions. In addition, the interactions with the BM niche are also affected by epigenetic modulating agents that will further determine the in vivo efficacy and thus patient outcome. A better understanding of the molecular events underlying the anti-tumor activity of the epigenetic drugs will lead to more rational drug combinations. This review focuses on the involvement of epigenetic changes in MM pathogenesis and how the use of DNMTi and HDACi affect the myeloma tumor itself and its interactions with the microenvironment.

Novel triaryl sulfonamide derivatives as selective cannabinoid receptor 2 inverse agonists and osteoclast inhibitors: discovery, optimization, and biological evaluation

Cannabinoid receptors have gained increasing attention as drug targets for developing potential therapeutic ligands. Here, we report the discovery and optimization of triaryl sulfonamides as a novel series possessing significant CB2 receptor affinity and selectivity. Four sets of triaryl ligands were designed and synthesized for further structural modifications and led to the identification of eight compounds as potent and selective CB2 inverse agonists with high binding affinity (CB2K(i) < 10 nM). Especially, compound 57 exhibited the strongest binding affinity on the CB2 receptor (CB2K(i) of 0.5 nM) and the best selectivity over the CB1 receptor (selectivity index of 2594). Importantly, 57 also showed potent inhibitory activity on osteoclast formation, and it was confirmed by a cell viability assay that the inhibition effects were not derived from the cytotoxicity. Finally, 3D QSAR studies confirmed our SAR findings that three bulky groups play an important role for CB2 receptor binding affinity.

Lead discovery, chemistry optimization, and biological evaluation studies of novel biamide derivatives as CB2 receptor inverse agonists and osteoclast inhibitors

N,N'-((4-(Dimethylamino)phenyl)methylene)bis(2-phenylacetamide) was discovered by using 3D pharmacophore database searches and was biologically confirmed as a new class of CB(2) inverse agonists. Subsequently, 52 derivatives were designed and synthesized through lead chemistry optimization by modifying the rings A-C and the core structure in further SAR studies. Five compounds were developed and also confirmed as CB(2) inverse agonists with the highest CB(2) binding affinity (CB(2)K(i) of 22-85 nM, EC(50) of 4-28 nM) and best selectivity (CB(1)/CB(2) of 235- to 909-fold). Furthermore, osteoclastogenesis bioassay indicated that PAM compounds showed great inhibition of osteoclast formation. Especially, compound 26 showed 72% inhibition activity even at the low concentration of 0.1 μM. The cytotoxicity assay suggested that the inhibition of PAM compounds on osteoclastogenesis did not result from its cytotoxicity. Therefore, these PAM derivatives could be used as potential leads for the development of a new type of antiosteoporosis agent.

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.

Apaf-1 deficiency confers resistance to ultraviolet-induced apoptosis in mouse embryonic fibroblasts by disrupting reactive oxygen species amplification production and mitochondrial pathway

Apoptosis requires tightly regulated cell death pathways. The signaling pathways that trigger a cell to undergo apoptosis after UV radiation are cell type specific and are currently being defined. Here, we have used pharmacological and genetic tools to demonstrate the decisive part of the mitochondrial pathway in UVC-induced apoptosis in mouse embryo fibroblasts (MEFs). UVC-induced apoptosis proceeded independent of the activation of death receptor components. In contrast, soon after UV radiation, MAPK activation and generation of reactive oxygen species (ROS) increased, followed by a decline in mitochondrial membrane potential (MMP) and cytochrome c release, as well as activation of caspase-9 and -3 and the upregulation of p47-phox. Deficiency of apaf-1, a critical member of the apoptosome, dramatically abolished all the UV-induced signal deterioration and cell death. In parallel, UVC-induced apoptosis was largely attenuated by either DN-caspase-9 or Bcl-X(L) overexpression. Pretreatment of cells with N-acetylcysteine or catalase but not Tempol decreased UVC-induced MAPK activation and apoptosis. Inhibition of JNK and caspase attenuated p47-phox upregulation. Altogether, we have for the first time demonstrated the critical role of Apaf-1 in the regulation of MAPK, ROS, and MMP in UVC-radiated MEFs and propose that the amplification feedback loop among mitochondrial signal molecules culminates in the demise of the cell.

The pan-histone deacetylase inhibitor CR2408 disrupts cell cycle progression, diminishes proliferation and causes apoptosis in multiple myeloma cells

In view of the fact that histone deacetylases (HDACs) are promising targets for myeloma therapy, we investigated the effects of the HDAC inhibitor CR2408 on multiple myeloma (MM) cells in vitro. CR2408 is a direct pan-HDAC inhibitor and inhibits all known 11 HDACs with a 50% inhibitory concentration (IC(50) ) of 12 nmol/l (HDAC 6) to 520 nmol/l (HDAC 8). Correspondingly, CR2408 induces hyperacetylation of histone H4, inhibits cell growth and strongly induces apoptosis (IC(50) =0.1-0.5 μmol/l) in MM cell lines and primary MM cells. CR2408 leads to fragmentation of cells and induces an accumulation in the subG1 phase accompanied with moderately decreased levels of cyclin D1 and cdk4 and strongly decreased levels of cdc25a, pRb and p53. Interruption of the cell cycle is reflected by inhibition of cell proliferation and is accompanied by decreased phosphorylation of 4E-BP1 and p70S6k. Treatment with CR2408 results in increased protein levels of Bim and pJNK and downregulation of Bad and Bcl-xL and activation of Caspases 3, 8 and 9. Furthermore, as HDAC inhibitors have shown synergism with other drugs, these effects were investigated and synergism was observed for combinations of CR2408 with doxorubicin and bortezomib. In conclusion, we have identified potent anti-myeloma activity for this novel HDAC inhibitor that gives further insights into the biological sequelae of HDAC inhibition in MM.

Targeting the microtubular network as a new antimyeloma strategy

We identified nocodazole as a potent antimyeloma drug from a drug screening library provided by the Multiple Myeloma Research Foundation. Nocodazole is a benzimidazole that was originally categorized as a broad-spectrum anthelmintic drug with antineoplastic properties. We found that nocodazole inhibited growth and induced apoptosis of primary and multiresistant multiple myeloma cells cultured alone and in the presence of bone marrow stromal cells. Nocodazole caused cell-cycle prophase and prometaphase arrest accompanied by microtubular network disarray. Signaling studies indicated that increased expression of Bim protein and reduced X-linked inhibitor of apoptosis protein and Mcl-1(L) levels were involved in nocodazole-induced apoptosis. Further investigation showed Bcl-2 phosphorylation as a critical mediator of cell death, triggered by the activation of c-jun-NH(2) kinase (JNK) instead of p38 kinase or extracellular signal-regulated kinases. Treatment with JNK inhibitor decreased Bcl-2 phosphorylation and subsequently reduced nocodazole-induced cell death. Nocodazole combined with dexamethasone significantly inhibited myeloma tumor growth and prolonged survival in a human xenograft mouse model. Our studies show that nocodazole has potent antimyeloma activity and that targeting the microtubular network might be a promising new treatment approach for multiple myeloma.

Use of the hollow fiber assay for the evaluation of DNA damaging agents

INTRODUCTION

The preclinical development and clinical progression of potential anticancer agents are highly time and resource-intensive. Traditionally, promising compounds in vitro undergo further screening in xenograft models, a long process that uses large numbers of animals. In order to hasten compound progression, the hollow fiber assay (HFA) was developed by the US National Cancer Institute as an additional filtering step in drug development, bridging the gap between in vitro and xenograft compound screening. The HFA demonstrates a good correlation in terms of clinical predictivity, and has significant reduction and refinement benefits for animal usage. In addition, the assay enables the study of basic pharmacological properties of compounds under investigation. The HFA has been mainly used as a rapid in vivo cytotoxicity screen, but has also been shown to be amenable to study drug/target interactions in vivo. One of the challenges of the HFA is the small sample sizes obtained, which can limit sensitivity.

METHODS

Here we specifically focus on the detection of DNA double-strand breaks, monitoring the effects of standard and novel anti-cancer agents on human lung, colon and breast cancer cell lines using immunoblotting and flow cytometry techniques for γ-H2A.X. This presented a further challenge due to the low abundance of the target event.

RESULTS

We found a good correlation between techniques in terms of rate of detection and sensitivity confirming the ability to use the HFA for detection of these specific drug-target interactions.

DISCUSSION

The results demonstrate good sensitivity and predictability for drug behavior in an assay where cell number is limited. In contrast to conventional xenograft studies, this short-term assay also enables analysis of pharmacodynamic endpoints in tumor cells in vivo. Importantly, there is a significant impact on reduction and refinement of the use of animals in incorporating this assay into the drug development process.

Pathogenesis and management of myeloma bone disease

Osteolytic bone disease is a frequent complication of multiple myeloma, resulting in skeletal complications that are a significant cause of morbidity and mortality. It is the result of increased activity of osteoclasts that is not followed by reactive bone formation by osteoblasts. Recent studies have revealed novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition, including the RANKL/osteoprotegerin pathway, macrophage inflammatory proteins and the wingless type signaling pathway. These molecules also appear to interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma. Currently, bisphosphonates are the mainstay of treatment for myeloma bone disease, although several novel agents appear promising. This review focuses on recent advances in understanding the biology of bone disease in multiple myeloma, diagnosis and recent progress in treatment options.

IMiD immunomodulatory compounds block C/EBP{beta} translation through eIF4E down-regulation resulting in inhibition of MM

Immunomodulatory derivatives of thalidomide (IMiD compounds), such as pomalidomide and lenalidomide, are highly active in multiple myeloma (MM) treatment. However, the precise mechanisms of action and resistance in MM are unresolved. Here we show that IMiD compounds down-regulate CCAAT/enhancer-binding protein-β (C/EBPβ) resulting in abrogation of cell proliferation. Overexpression of C/EBPβ rescued MM cells from IMiD-induced inhibition of proliferation, indicating that C/EBPβ is critical in mediating antiproliferative effects. IMiD-induced decrease of C/EBPβ protein led to impaired transcription of interferon regulatory factor 4 (IRF4). Down-regulation of IRF4 by lenalidomide was confirmed by longitudinal studies of bone marrow samples from 23 patients obtained before and during lenalidomide treatment using CD138⁺/IRF4⁺ double labeling. In contrast to down-regulation of C/EBPβ protein, IMiD compounds did not alter C/EBPβ mRNA levels or protein stability, suggesting translational regulation of C/EBPβ. We could demonstrate that C/EBPβ protein expression is under eIF4E-translational control in MM. Furthermore, inhibition of the eIF4E-C/EBPβ axis by IMiD compounds was not observed in IMiD-resistant MM cells. However, targeting translation at a different level by inhibiting eukaryotic translation initiation factor 4E-binding protein 1 phosphorylation overcame resistance, suggesting that this pathway is critical and might be a target to overcome drug resistance.

The DAC system and associations with multiple myeloma

Despite the clear progress achieved in recent years in the treatment of MM, most patients eventually relapse and therefore novel therapeutic options are still necessary for these patients. In this regard, several drugs that target specific mechanisms of the tumor cells are currently being explored in the preclinical and clinical setting. This manuscripts offers a review of the rationale and current status of the antimyeloma activity of one of the most relevant examples of these targeted drugs: deacetylase inhibitors (DACi). Several studies have demonstrated the prooncogenic activity of deacetylases (DACs) through the targeting not only of histones but also of non histone proteins relevant to tumor progression, such as p53, E2F family members, Bcl-6, Hsp90, HIF-1α or Nur77. This fact together with the DACs overexpression present in several tumors, has prompted the development of some DACi with potential antitumor effect. This situation is also evident in the case of MM as two mechanisms of DACi, the inhibition of the epigenetic inactivation of p53 and the blockade of the unfolded protein response, through the inhibition of the aggressome formation (by targeting DAC6) and the inactivation of the chaperone system (by acetylating HSP-90), provides the rationale for the exploration of the potential antimyeloma activity of these compounds. Several DACi with different chemical structure and different selectivity for targeting the DAC families have been tested in MM. Their preclinical activity in monotherapy has been quite exciting and has been described to be mediated by various mechanisms: the induction of apoptosis and cell cycle arrest mainly by the upregulation of p21; the interferece with the interaction between plasma cells and the microenvironment, by reducing the expression and signalling of several cytokines or by inhibiting angiogenesis. Finally they also have a role in protecting murine models from myeloma bone disease. Neverteless, the clinical activity in monotherapy of these drugs in relapsed/refractory MM patients has been very modest. This has prompted the development of combinations such as the one with bortezomib or lenalidomide and dexamethasone, which have already been taken into the clinics with positive preliminary results.

Antitumor effects of (S)-HDAC42, a phenylbutyrate-derived histone deacetylase inhibitor, in multiple myeloma cells

PURPOSE

Epigenetic agents are among the newly targeted therapeutic strategies being studied with intense interest for patients with multiple myeloma. Here, we demonstrate the antitumor activity of a phenylbutyrate-based histone deacetylase (HDAC) inhibitor, (S)-HDAC42, and identify its possible targets in myeloma cells.

METHODS

The antiproliferative effect of (S)-HDAC42 was compared with suberoylanilide hydroxamic acid (SAHA) in three myeloma cell lines, IM-9, RPMI-8226, and U266. Flow cytometry and terminal transferase dUTP nick-end labeling (TUNEL) assay were used to demonstrate the induction of apoptosis by (S)-HDAC42. Moreover, the proposed mechanisms of action, such as modulation of Akt, NF-κB pathway, and cell cycle-related proteins, were investigated by western blotting.

RESULTS

(S)-HDAC42 exhibited four- to sevenfold higher potency relative to SAHA in suppressing myeloma cell viabilities. The apoptotic effect induced by (S)-HDAC42 was through both intrinsic and extrinsic pathways, as evidenced by increased cleavage of caspase-3, caspase-8, and caspase-9 and release of cytochrome c from mitochondria. In addition to HDAC inhibition, (S)-HDAC42 also disturbed signaling pathways governing cell survival, including downregulating Akt phosphorylation and NF-κB signaling. The modulation of cell cycle-related proteins by (S)-HDAC42 suggested its inhibitory effect on cell cycle propagation.

CONCLUSION

These data suggest the translational value of (S)-HDAC42 in developing new therapeutic strategies for myeloma, which warrants further investigations.

The novel inhibitor of histone deacetylase resminostat (RAS2410) inhibits proliferation and induces apoptosis in multiple myeloma (MM) cells

Inhibition of histone deacetylase (HDAC) is a promising mechanism for novel, anti-myeloma agents. We investigated the effects of the novel HDAC inhibitor resminostat on multiple myeloma (MM) cells in vitro. Resminostat is a potent inhibitor of HDACs 1, 3 and 6 [50% inhibitory concentration (IC50)=43-72 nmol/l] representing HDAC classes I and II and induces hyperacetylation of histone H4 in MM cells. Low micromolar concentrations of resminostat abrogated cell growth and strongly induced apoptosis (IC50=2.5-3 micromol/l in 3 out of 4 MM cell lines) in MM cell lines as well as primary MM cells. At 1 micromol/l, resminostat inhibited proliferation and induced G0/G1 cell cycle arrest in 3 out of 4 MM cell lines accompanied with decreased levels of cyclin D1, cdc25a, Cdk4 and pRb as well as upregulation of p21. Resminostat decreased phosphorylation of 4E-BP1 and p70S6k indicating an interference with Akt pathway signalling. Treatment with resminostat resulted in increased protein levels of Bim and Bax and decreased levels of Bcl-xL. Caspases 3, 8 and 9 were activated by resminostat. Furthermore, synergistic effects were observed for combinations of resminostat with melphalan and the proteasome inhibitors bortezomib and S-2209. In conclusion, we have identified potent anti-myeloma activity for this novel HDAC inhibitor.

New patented histone deacetylase inhibitors

IMPORTANCE OF THE FIELD

Following FDA approval of vorinostat in 2006, several novel HDAC inhibitors (HDACis) have entered clinical trials, and there are numerous published patent applications claiming novel HDACis which were optimized as potential drug candidates, designed for regional or systemic release, and created as dual or multifunctional inhibitors. Given the breadth and depth of recent reporting of novel HDACis, there has emerged a need to review the field from a chemist's perspective in one compact article.

AREAS COVERED IN THIS REVIEW

This review provides a summary of published patent applications claiming novel HDACis from 2007 until mid-2009, covering mainly classes I, II and IV anticancer HDACis including those that have recently advanced to the clinic.

WHAT THE READER WILL GAIN

Readers will rapidly gain an overview of the majority of HDACi scaffolds with representative structure-activity relationships; they will learn how these new compounds were created, how their drug like properties were improved and which companies are the main players in the field.

TAKE HOME MESSAGE

Although competition in this field is intense, the future application of HDACis to treat human disease either as single agents or in combination with existing drugs holds real promise.

The potential role of epigenetic therapy in multiple myeloma

This review describes the role that epigenetic changes play in the pathogenesis of cancer, concentrating on the plasma cell malignancy multiple myeloma, and highlights recent findings regarding the efficacy of epigenetic therapeutic agents in laboratory studies and clinical trials. DNA methylation is altered in a wide range of cancers with hypermethylation of CpG islands associated with silencing of tumour suppressor genes. Genes found to be silenced by methylation in myeloma samples include VHL, TP53, CDKN2A, and TGFBR2. Myeloma is linked to the overexpression of a histone methylatransferase (MMSET) and inactivating mutations of a histone demethylase (UTX), suggesting that the regulation of histone methylation is a potential therapeutic target. Abnormal expression of histone deacetylases (HDACs) has been widely described in solid tumours and haematological malignancies. In myeloma, histone deacetylase inhibitors show promising results both in laboratory-based cell culture studies and in clinical trials, where they demonstrate particularly good therapeutic outcome when administered in combination with other standard chemotherapeutic agents. The study of epigenetics shows great promise for understanding the alterations in gene expression that underlie malignancies and provides exciting novel drugable targets.

Etoposide induces protein kinase Cdelta- and caspase-3-dependent apoptosis in neuroblastoma cancer cells

In this report, we reveal that etoposide inhibits the proliferation of SK-N-AS neuroblastoma cancer cells and promotes protein kinase Cdelta (PKCdelta)- and caspase-dependent apoptosis. Etoposide induces the caspase-3-dependent cleavage of PKCdelta to its active p40 fragment, and active PKCdelta triggers the processing of caspase-3 by a positive-feedback mechanism. Treatment of cells with the caspase-3-specific inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone or caspase-3-specific small interacting RNA (siRNA) prevented the etoposide-induced activation of caspase-8 and inhibited apoptosis. The silencing of the caspase-2 or caspase-8 genes using siRNAs did not affect the etoposide-induced processing of caspase-3, indicating that these caspases lie downstream of caspase-3 in this signaling pathway. Furthermore, the etoposide-induced processing of caspase-2 required the expression of caspase-8, and the etoposide-mediated processing of caspase-8 required the expression of caspase-2, indicating that these two caspases activate each other after etoposide treatment. We also observed that etoposide-mediated apoptosis was decreased by treating the cells with the caspase-6-specific inhibitor benzyloxycarbonyl-Val-Glu(OMe)-Ile-Asp-(OMe)-fluoromethyl ketone and that caspase-6 was activated by a caspase-8-dependent mechanism. Finally, we show that rottlerin blocks etoposide-induced apoptosis by inhibiting the PKCdelta-mediated activation of caspase-3 and by degrading caspase-2, which prevents caspase-8 activation. Our results add important insights into how etoposide mediates apoptotic signaling and how targeting these pathways may lead to the development of novel therapeutics for the treatment of neuroblastomas.

Targeted therapies in multiple myeloma

Increasing knowledge of the biology of multiple myeloma led the way for the development of novel drugs that have changed the management of the disease. New treatments target not only to the malignant plasma cell but also target the interactions of myeloma cells with their microenvironment. Several preclinical studies have identified potential targets and drugs are developed that act on pathways crucial for myeloma cell survival, proliferation, migration and drug resistance. The identification of active agents in the laboratory is followed by rationally designed clinical studies that validate these drugs, either as single agents or in combinations with other active drugs. These novel agents may be either small molecules or monoclonal antibodies targeting receptors, kinase activity of receptors or key molecules within critical pathways, intracellular maintenance mechanisms and immune modulation.