Cellular impedance assays for predictive preclinical drug screening of kinase inhibitor cardiovascular toxicity

Cardiovascular (CV) toxicity is a leading contributor to drug attrition. Implementing earlier testing has successfully reduced human Ether-à-go-go-Related Gene-related arrhythmias. How- ever, analogous assays targeting functional CV effects remain elusive. Demand to address this gap is particularly acute for kinase inhibitors (KIs) that suffer frequent CV toxicity. The drug class also presents some particularly challenging requirements for assessing functional CV toxicity. Specifically, an assay must sense a downstream response that integrates diverse kinase signaling pathways. In addition, sufficient throughput is essential for handling inherent KI nonselectivity. A new opportunity has emerged with cellular impedance technology, which detects spontaneous beating cardiomyocytes. Impedance assays sense morphology changes downstream of cardiomyocyte contraction. To evaluate cardiomyocyte impedance assays for KI screening, we investigated two distinct KI classes where CV toxicity was discovered late and target risks remain unresolved. Microtubule-associated protein/microtubule affinity regulating kinase (MARK) inhibitors decrease blood pressure in dogs, whereas checkpoint kinase (Chk) inhibitors (AZD7762, SCH900776) exhibit dose-limiting CV toxicities in clinical trials. These in vivo effects manifested in vitro as cardiomyocyte beat cessation. MARK effects were deemed mechanism associated because beat inhibition potencies correlated with kinase inhibition, and gene knockdown and microtubule-targeting agents suppressed beating. MARK inhibitor impedance and kinase potencies aligned with rat blood pressure effects. Chk inhibitor effects were judged off-target because Chk and beat inhibition potencies did not correlate and knockdowns did not alter beating. Taken together, the data demonstrate that cardiomyocyte impedance assays can address three unmet needs-detecting KI functional cardiotoxicity in vitro, determining mechanism of action, and supporting safety structure-activity relationships.

Phase I, dose-escalation study of AZD7762 alone and in combination with gemcitabine in Japanese patients with advanced solid tumours. Cancer Chemother Pharmacol. 2013;72:619-627. [PMID: 23892959 DOI: 10.1007/s00280-013-2234-6]

PURPOSE

AZD7762, a potent Chk1/Chk2 inhibitor, has shown chemosensitizing activity with gemcitabine in xenograft models.

METHODS

This open-label, Phase I, dose-escalation study evaluated the safety, pharmacokinetics (PK) and preliminary efficacy (RECIST) of AZD7762 alone and in combination with gemcitabine in Japanese patients with advanced solid tumours (NCT00937664). Patients received intravenous AZD7762 alone on days 1 and 8 of a 14-day cycle (cycle 0), followed by AZD7762 plus gemcitabine 1,000 mg/m(2) on days 1 and 8 of 22-day cycles, in ascending AZD7762 dose cohorts.

RESULTS

Twenty patients received AZD7762 at doses of 6 mg (n = 3), 9 mg (n = 3), 21 mg (n = 6) and 30 mg (n = 8). Dose-limiting toxicities occurred in 2/6 evaluable patients in the 30-mg cohort: one, CTCAE grade 3 elevated troponin T (cycle 0: AZD7762 monotherapy); one, neutropenia, thrombocytopenia, and elevated aspartate aminotransferase and alanine aminotransferase (cycle 1: combination therapy). The 30 mg dose was therefore regarded as non-tolerable. The most common adverse events (AEs) in cycle 0 (AZD7762 monotherapy) were bradycardia (50 %), hypertension (25 %) and fatigue (15 %). Overall, the most common AEs were bradycardia (55 %), neutropenia (45 %) and hypertension, fatigue and rash (30 % each). Grade ≥3 AEs were reported in 11 patients, the most common being neutropenia (45 %) and leukopenia (25 %). AZD7762 exposure increased approximately linearly. Gemcitabine did not appear to affect AZD7762 PK. There were no objective responses; five patients (all lung cancer) had stable disease.

CONCLUSIONS

The maximum tolerated dose of AZD7762 in combination with gemcitabine, 1,000 mg/m(2) was determined as 21 mg in Japanese patients.

Requirement for antiapoptotic MCL-1 in the survival of BCR-ABL B-lineage acute lymphoblastic leukemia

The response of Philadelphia chromosome (Ph(+)) acute lymphoblastic leukemia (ALL) to treatment by BCR-ABL tyrosine kinase inhibitors (TKIs) has been disappointing, often resulting in short remissions typified by rapid outgrowth of drug-resistant clones. Therefore, new treatments are needed to improve outcomes for Ph(+) ALL patients. In a mouse model of Ph(+) B-lineage ALL, MCL-1 expression is dysregulated by the BCR-ABL oncofusion protein, and TKI treatment results in loss of MCL-1 expression prior to the induction of apoptosis, suggesting that MCL-1 may be an essential prosurvival molecule. To test this hypothesis, we developed a mouse model in which conditional allele(s) of Mcl-1 can be deleted either during leukemia transformation or later after the establishment of leukemia. We report that endogenous MCL-1's antiapoptotic activity promotes survival during BCR-ABL transformation and in established BCR-ABL(+) leukemia. This requirement for MCL-1 can be overcome by overexpression of other antiapoptotic molecules. We further demonstrate that strategies to inhibit MCL-1 expression potentiate the proapoptotic action of BCL-2 inhibitors in both mouse and human BCR-ABL(+) leukemia cell lines. Thus, strategies focused on antagonizing MCL-1 function and expression would be predicted to be effective therapeutic strategies.

BAG3 protects bovine papillomavirus type 1-transformed equine fibroblasts against pro-death signals

In human cancer cells, BAG3 protein is known to sustain cell survival. Here, for the first time, we demonstrate the expression of BAG3 protein both in equine sarcoids in vivo and in EqS04b cells, a sarcoid-derived fully transformed cell line harbouring bovine papilloma virus (BPV)-1 genome. Evidence of a possible involvement of BAG3 in equine sarcoid carcinogenesis was obtained by immunohistochemistry analysis of tumour samples. We found that most tumour samples stained positive for BAG3, even though to a different grade, while normal dermal fibroblasts from healthy horses displayed very weak staining pattern for BAG3 expression. By siRNA technology, we demonstrate in EqS04b the role of BAG3 in counteracting basal as well as chemical-triggered pro-death signals. BAG3 down-modulation was indeed shown to promote cell death and cell cycle arrest in G₀/G₁. In addition, we found that BAG3 silencing sensitized EqS04b cells to phenethylisothiocyanate (PEITC), a promising cancer chemopreventive/chemotherapeutic agent present in edible cruciferous vegetables. Notably, such a pro-survival role of BAG3 was less marked in E. Derm cells, an equine BPV-negative fibroblast cell line taken as a normal counterpart. Altogether our findings might suggest a mutual cooperation between BAG3 and viral oncoproteins to sustain cell survival.

Efficacy of histone deacetylase and estrogen receptor inhibition in breast cancer cells due to concerted down regulation of Akt

Hormonal therapy resistance remains a considerable barrier in the treatment of breast cancer. Activation of the Akt-PI3K-mTOR pathway plays an important role in hormonal therapy resistance. Our recent preclinical and clinical studies showed that the addition of a histone deacetylase inhibitor re-sensitized hormonal therapy resistant breast cancer to tamoxifen. As histone deacetylases are key regulators of Akt, we evaluated the effect of combined treatment with the histone deacetylase inhibitor PCI-24781 and tamoxifen on Akt in breast cancer cells. We demonstrate that while both histone deacetylase and estrogen receptor inhibition down regulate AKT mRNA and protein, their concerted effort results in down regulation of AKT activity with induction of cell death. Histone deacetylase inhibition exerts its effect on AKT mRNA through an estrogen receptor-dependent mechanism, primarily down regulating the most abundant isoform AKT1. Although siRNA depletion of AKT modestly induces cell death, when combined with an anti-estrogen, cytotoxicity is significantly enhanced. Thus, histone deacetylase regulation of AKT mRNA is a key mediator of this therapeutic combination and may represent a novel biomarker for predicting response to this regimen.

Environmental epigenetics: from novelty to scientific discipline

Epigenetic phenomena have sparked much interest resulting in an exponential increase in scientific investigation in the last two decades. While growing, the field of environmental epigenetics remains small when compared to other areas of epigenetic inquiry such as cancer research. In this paper, our objective is to describe the status of the field of environmental epigenetics and lay out our vision for its future. While environmental epigenetic studies represent fewer than 5% of all epigenetic publications, the National Institute of Environmental Health Sciences ranks second in proportion of dollars spent on epigenetics of all NIH Institutes. Such investment highlights the hypothesis that epigenetic marks are modified by environmental exposures and the hope that interventions targeted at epigenetic mechanisms may ultimately lead to improved health outcomes. The road to achieve this vision will require: (1) attention to tissue specificity; (2) focused interventional studies; (3) collaboration among cohorts; (4) inclusion of environmental exposures in new large-scale epigenomic studies; and (5) understanding of multiple mechanisms beyond DNA methylation and histone modifications. The investment in environmental epigenetic inquiry will lead to great rewards if we can understand the biology of how phenotype results from environmental stimuli and genetic code. Understanding the epigenetic implications of our actions and exposures may benefit generations to come.

Chk1/2 inhibition overcomes the cisplatin resistance of head and neck cancer cells secondary to the loss of functional p53

Despite the use of multimodality therapy using cisplatin to treat patients with advanced stage squamous cell carcinoma of the head and neck (HNSCC), there is an unacceptably high rate of treatment failure. TP53 is the most commonly mutated gene in HNSCC, and the impact of p53 mutation on response to cisplatin treatment is poorly understood. Here, we show unambiguously that wild-type TP53 (wtp53) is associated with sensitivity of HNSCC cells to cisplatin treatment, whereas mutation or loss of TP53 is associated with cisplatin resistance. We also show that senescence is the major cellular response to cisplatin in wtp53 HNSCC cells and that cisplatin resistance in p53-null or -mutant TP53 cells is due to their lack of senescence. Given the dependence on checkpoint kinase (Chk)1/2 kinases to mediate the DNA damage response in p53-deficient cells, there is potential to exploit this to therapeutic advantage through targeted inhibition of the Chk1/2 kinases. Treatment of p53-deficient HNSCC cells with the Chk inhibitor AZD7762 sensitizes them to cisplatin through induction of mitotic cell death. This is the first report showing the ability of a Chk kinase inhibitor to sensitize TP53-deficient HNSCC to cisplatin in a synthetic lethal manner, which has significance given the frequency of TP53 mutations in this disease and because cisplatin has become part of standard therapy for aggressive HNSCC tumors. These preclinical data provide evidence that a personalized approach to the treatment of HNSCC based on Chk inhibition in p53-mutant tumors may be feasible.

Chromatin remodeling by polyamines and polyamine analogs

Natural polyamines are involved in many molecular processes, including maintenance of DNA structure and RNA processing and translation. Our aim here is to present an overview of the literature concerning the significance of polyamines in the modulation of chromatin arrangement and the transcriptional regulation of gene expression. The pleiotropic picture emerging from the published data highlights that these polycations take part in apparently diverging effects, possibly depending on the heterogeneous experimental settings described, and on a methodological approach aimed at the evaluation of the global levels of the histone chemical modifications. Since the relevant changes observed appear to be rather local and gene specific, investigating histone modifications at the level of specific gene promoters of interest is thus to be recommended for future studies. Furthermore, decoding the multiple regulatory mechanisms by which polyamines exert their influence on chromatin-modifier enzymes will reasonably require focus on selected individual polyamine-regulated genes. The evaluation of the many known chromatin-remodeling enzymes for their individual susceptibility to polyamines or polyamine derivatives will also be helpful: determining how they discriminate between the different enzyme isoforms is expected to be a fruitful line of research for drug discovery, e.g., in cancer prevention and therapy. Indeed, polyamine derivatives acting as epigenetic modulators appear to be molecules with great potential as antitumor drugs. All these novel polyamine-based pharmacologically active molecules are thus promising tools, both as a stand-alone strategy and in combination with other anticancer compounds.

The anticancer potential of flavonoids isolated from the stem bark of Erythrina suberosa through induction of apoptosis and inhibition of STAT signaling pathway in human leukemia HL-60 cells

Erythrina suberosa is an ornamental tall tree found in India, Pakistan, Nepal, Bhutan, Burma, Thailand and Vietnam. We have isolated four known distinct metabolites designated as α-Hydroxyerysotrine, 4'-Methoxy licoflavanone (MLF), Alpinumisoflavone (AIF) and Wighteone. Among the four isolated metabolites the two flavonoids, MLF and AIF were found to be the most potent cytotoxic agent with IC50 of ∼20μM in human leukemia HL-60 cells. We are reporting first time the anticancer and apoptotic potential of MLF and AIF in HL-60 cells. Both MLF and AIF inhibited HL-60 cell proliferation and induce apoptosis as measured by several biological endpoints. MLF and AIF induce apoptosis bodies formation, enhanced annexinV-FITC binding of the cells, increased sub-G0 cell fraction, loss of mitochondrial membrane potential (Δψm), release of cytochrome c, Bax, activation of caspase-9, caspase-3 and PARP (poly ADP Ribose polymers) cleavage in HL-60 cells. MLF and AIF also increase the expression of apical death receptor, Fas, with inhibition of anti-apoptotic protein Bid. All the above parameters revealed that these two flavonoids induce apoptosis through both extrinsic and intrinsic apoptotic pathways in HL-60 cells. In spite of apoptosis, these two flavonoids significantly inhibit nuclear transcription factor NF-κB and STAT (Signal Transducer and Activator of Transcription) signaling pathway, which are highly expressed in leukemia. The present study provide an insight of molecular mechanism of cell death induced by MLF and AIF in HL-60 cells which may be useful in managing and treating leukemia.

Evaluation and critical assessment of putative MCL-1 inhibitors. Cell Death Differ. 2013;20:1475-1484. [PMID: 23832116 DOI: 10.1038/cdd.2013.79]

High levels of BCL-2 family proteins are implicated in a failed/ineffective apoptotic programme, often resulting in diseases, including cancer. Owing to their potential as drug targets in cancer therapy, several inhibitors of BCL-2 family proteins have been developed. These primarily target specific members of the BCL-2 family, particularly BCL-2 and BCL-XL but are ineffective against MCL-1. Major efforts have been invested in developing inhibitors of MCL-1, which is commonly amplified in human tumours and associated with tumour relapse and chemoresistance. In this report, the specificity of several BCL-2 family inhibitors (ABT-263, UCB-1350883, apogossypol and BH3I-1) was investigated and compared with putative MCL-1 inhibitors designed to exhibit improved or selective binding affinities for MCL-1 (TW-37, BI97C1, BI97C10, BI112D1, compounds 6 and 7, and MCL-1 inhibitor molecule (MIM-1)). ABT-263, BI97C1, BI112D1, MIM-1 and TW-37 exhibited specificity in inducing apoptosis in a Bax/Bak- and caspase-9-dependent manner, whereas the other agents showed no killing activity, or little or no specificity. Of these inhibitors, only ABT-263 and UCB-1350883 induced apoptosis in a BCL-2- or BCL-XL-dependent system. In cells that depend on MCL-1 for survival, ABT-263 and TW-37 induced extensive apoptosis, suggesting that at high concentrations these inhibitors have the propensity to inhibit MCL-1 in a cellular context. TW-37 induced apoptosis, assessed by chromatin condensation, caspase processing and phosphatidylserine externalisation, in a BAK-dependent manner and in cells that require MCL-1 for survival. TW-37-mediated apoptosis was also partly dependent on NOXA, suggesting that derivatives of TW-37, if engineered to exhibit better selectivity and efficacy at low nanomolar concentrations, may provide useful lead compounds for further synthetic programmes. Expanded medicinal chemistry iteration, as performed for the ABT series, may likewise improve the potency and specificity of the evaluated MCL-1 inhibitors.

Decoding and unlocking the BCL-2 dependency of cancer cells

Cancer cells are subject to many apoptotic stimuli that would kill them were it not for compensatory prosurvival alterations. BCL-2-like (BCL-2L) proteins contribute to such aberrant behaviour by engaging a network of interactions that is potent at promoting survival but that is also fragile: inhibition of a restricted number of interactions may suffice to trigger cancer cell death. Currently available and novel compounds that inhibit these interactions could be efficient therapeutic agents if this phenotype of BCL-2L dependence was better understood at a molecular, cellular and systems level and if it could be diagnosed by relevant biomarkers.

BAK activation is necessary and sufficient to drive ceramide synthase-dependent ceramide accumulation following inhibition of BCL2-like proteins. Biochem J. 2013;452:111-119. [PMID: 23480852 DOI: 10.1042/bj20130147]

Determining mechanistic details about how drugs kill cancer cells is critical for predicting which cancers will respond to given therapeutic regimens and for identifying effective combinations of drugs that more potently kill cancer cells while sparing normal cells. The BCL2 family of proteins and bioactive sphingolipids are intricately linked during apoptotic cell death. In fact, many chemotherapeutic drugs are known to cause accumulation of the pro-apoptotic sphingolipid ceramide; however, the mechanism by which this occurs is not completely understood. In the present study we demonstrate that direct inhibition of anti-apoptotic BCL2 proteins with ABT-263 is sufficient to induce C(16)-ceramide synthesis in multiple cell lines, including human leukaemia and myeloma cells. ABT-263 activates CerS (ceramide synthase) activity only in cells expressing BAK or in cells capable of activating BAK. Importantly, recombinant BAK is sufficient to increase in vitro CerS activity in microsomes purified from Bak-KO (knockout) cells and activated BAK more potently activates CerS than inactive BAK. Likewise, ABT-263 addition to wild-type, but not Bak-deficient, microsomes increases CerS in vitro activity. Furthermore, we present a feed-forward model by which BAK activation of CerS by chemotherapeutic drugs leads to elevated ceramide levels that result in synergistic channel formation by ceramide (or one of its metabolites) and BAX/BAK.

Targeting acute myeloid leukemia by dual inhibition of PI3K signaling and Cdk9-mediated Mcl-1 transcription

Resistance to cell death is a hallmark of cancer and renders transformed cells resistant to multiple apoptotic triggers. The Bcl-2 family member, Mcl-1, is a key driver of cell survival in diverse cancers, including acute myeloid leukemia (AML). A screen for compounds that downregulate Mcl-1 identified the kinase inhibitor, PIK-75, which demonstrates marked proapoptotic activity against a panel of cytogenetically diverse primary human AML patient samples. We show that PIK-75 transiently blocks Cdk7/9, leading to transcriptional suppression of MCL-1, rapid loss of Mcl-1 protein, and alleviation of its inhibition of proapoptotic Bak. PIK-75 also targets the p110α isoform of PI3K, which leads to a loss of association between Bcl-xL and Bak. The simultaneous loss of Mcl-1 and Bcl-xL association with Bak leads to rapid apoptosis of AML cells. Concordantly, low Bak expression in AML confers resistance to PIK-75-mediated killing. On the other hand, the induction of apoptosis by PIK-75 did not require the expression of the BH3 proteins Bim, Bid, Bad, Noxa, or Puma. PIK-75 significantly reduced leukemia burden and increased the survival of mice engrafted with human AML without inducing overt toxicity. Future efforts to cotarget PI3K and Cdk9 with drugs such as PIK-75 in AML are warranted.

MyD88 in DNA repair and cancer cell resistance to genotoxic drugs

BACKGROUND

MyD88 is an adaptor molecule in Toll-like receptor and interleukin 1 receptor signaling implicated in tumorigenesis through proinflammatory mechanisms. We have recently reported that MyD88 also directly promotes optimal activation of the Ras/Erk pathway. Here we investigate MyD88 implication in the maintenance of the transformation of Ras-dependent tumors.

METHODS

RNA interference was used to inhibit MyD88 expression in the colon cancer cell lines HCT116 and LS513. Apoptosis, DNA damage, p53 function, ERCC1 levels, and Ras and inflammatory signaling pathways were analyzed. Using in vitro assays and xenotransplantation in nude mice (five per group), HCT116 tumor growth was assessed following MyD88 knockdown in presence or absence of chemotherapy.

RESULTS

MyD88 exerts antiapoptotic functions in colon cancer cells via the Ras/Erk, but not the NF-κB, pathway. MyD88 inhibition leads to defective ERCC1-dependent DNA repair and to accumulation of DNA damage, resulting in cancer cell death via p53. Furthermore, we show that knocking down MyD88 sensitizes cancer cells to genotoxic agents such as platinum salts in vitro and in vivo. Indeed, HCT116 tumor growth following treatment with a combination of suboptimal MyD88 inhibition and suboptimal doses of cisplatin (fold tumor increase = 5.4 ± 1.6) was statistically significantly reduced in comparison to treatment with doxycycline alone (12.4 ± 3.1) or with cisplatin alone (12.5 ± 2.6) (P = .005 for both, one-sided Student t test).

CONCLUSIONS

Collectively, these results indicate a novel and original link between inflammation, DNA repair, and cancer, and provide further rationale for MyD88 as a potential therapeutic target in Ras-dependent cancers, in the context of concomitant genotoxic chemotherapy.

Interdiction of sphingolipid metabolism to improve standard cancer therapies

Non-surgical therapies for human malignancies must negotiate complex cell signaling pathways to impede cancer cell growth, ideally promoting death of cancer cells while sparing healthy tissue. For most of the past half century, medical approaches for treating cancer have relied primarily on cytotoxic chemotherapeutics that interfere with DNA replication and cell division, susceptibilities of rapidly dividing cancer cells. As a consequence, these therapies exert considerable cell stress, promoting the generation of ceramide through de novo synthesis and recycling of complex glycosphingolipids and sphingomyelin into apoptotic ceramide. Radiotherapy of cancer exerts similar geno- and cytotoxic cell stresses, and generation of ceramide following ionizing radiation therapy is a well-described feature of radiation-induced cell death. Emerging evidence now describes sphingolipids as mediators of death in response to newer targeted therapies, cementing ceramide generation as a common mechanism of cell death in response to cancer therapy. Many studies have now shown that dysregulation of ceramide accumulation-whether by reduced generation or accelerated metabolism-is a common mechanism of resistance to standard cancer therapies. The aims of this chapter will be to discuss described mechanisms of cancer resistance to therapy related to dysregulation of sphingolipid metabolism and to explore clinical and preclinical approaches to interdict sphingolipid metabolism to improve outcomes of standard cancer therapies.

BCL11A overexpression predicts survival and relapse in non-small cell lung cancer and is modulated by microRNA-30a and gene amplification

Background

Aberrant activation of the proto-oncogene B-cell lymphoma/leukemia 11A (BCL11A) has been implicated in the pathogenesis of leukemia and lymphoma. However, the clinical significance of BCL11A in non-small cell lung cancer (NSCLC) remains unknown.

Results

We examined BCL11A expression at the protein and mRNA levels in a cohort (n = 114) of NSCLC patients and assessed the relationship between BCL11A expression and clinicopathological parameters. Data from array-based Comparative Genomic Hybridization (aCGH) and microRNA transfection experiments were integrated to explore the potential mechanisms of abnormal BCL11A activation in NSCLC. Compared to adjacent non-cancerous lung tissues, BCL11A expression levels were specifically upregulated in NSCLC tissues at both the mRNA (t = 9.81, P < 0.001) and protein levels. BCL11A protein levels were higher in patients with squamous histology (χ² = 15.81, P = 0.001), smokers (χ² = 8.92, P = 0.004), patients with no lymph node involvement (χ² = 5.14, P = 0.029), and patients with early stage disease (χ² = 3.91, P = 0.048). A multivariate analysis demonstrated that in early stage NSCLC (IA–IIB), BCL11A was not only an independent prognostic factor for disease-free survival (hazards ratio [HR] 0.24, 95% confidence interval [CI] 0.12-0.50, P < 0.001), but also for overall survival (HR = 0.23, 95% CI 0.09-0.61, P = 0.003). The average BCL11A expression level was much higher in SCC samples with amplifications than in those without amplifications (t = 3.30, P = 0.023). Assessing functionality via an in vitro luciferase reporter system and western blotting, we found that the BCL11A protein was a target of miR-30a.

Conclusions

Our results demonstrated that proto-oncogene BCL11A activation induced by miR-30a and gene amplification may be a potential diagnostic and prognostic biomarker for effective management of this disease.

Pim kinases phosphorylate Chk1 and regulate its functions in acute myeloid leukemia

Phosphorylation by Akt on Ser 280 was reported to induce cytoplasmic retention and inactivation of CHK1 with consequent genetic instability in PTEN-/- cells. In acute myeloid leukemia cells carrying the FLT3-internal tandem duplication (ITD) mutation, we observed high rates of FLT3-ITD-dependent CHK1 Ser 280 phosphorylation. Pharmacological inhibition and RNA interference identified Pim1/2, not Akt, as effectors of this phosphorylation. Pim1 catalyzed Ser 280 phosphorylation in vitro and ectopic expression of Pim1/2-induced CHK1 phosphorylation. Ser 280 phosphorylation did not modify CHK1 localization, but facilitated its cell cycle and resistance functions in leukemic cells. FLT3, PIM or CHK1 inhibitors synergized with DNA-damaging agents to induce apoptosis, allowing cells to bypass the etoposide-induced G2/M arrest. Consistently, etoposide-induced CHK1-dependent phosphorylations of CDC25C on Ser 216 and histone H3 on Thr11 were decreased upon FLT3 inhibition. Accordingly, ectopic expression of CHK1 improved the resistance of FLT3-ITD cells and maintained histone H3 phosphorylation in response to DNA damage, whereas expression of unphosphorylated Ser 280Ala mutant did not. Finally, FLT3- and Pim-dependent phosphorylation of CHK1 on Ser 280 was confirmed in primary blasts from patients. These results identify a new pathway involved in the resistance of FLT3-ITD leukemic cells to genotoxic agents, and they constitute the first report of CHK1 Ser 280 regulation in myeloid malignancies.

Emerging pathways as individualized therapeutic target of multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to the growing knowledge of disease pathobiology.

AREAS COVERED

Intrinsic genetic lesions, as well as the bone marrow microenvironment, contribute to the activation of proliferation and survival pathways, impairment of cell death mechanisms and drug resistance. The phosphatidylinositol 3-kinase (PI3K) and the Ras/mitogen-activated protein kinase (MAPK) cascades are the signaling pathways mainly involved in the MM development. In the last decade, several molecules interfering with growth and survival promoting signaling have been developed.

EXPERT OPINION

Despite the availability of novel therapeutics, MM still evolves into a drug-resistant phase and most patients die of progressive disease. Therefore, there is an urgent need of novel therapeutic strategies. Among a plethora of new investigational agents, microRNA (miRNA) represents the basis for the design of novel therapeutic strategies which basically rely on miRNA inhibition or miRNA replacement approaches and take benefit respectively from the use of miRNA inhibitors or synthetic miRNAs as well as from lipid-based nanoparticles as carriers for in vivo delivery.

MutS homologue hMSH4: interaction with eIF3f and a role in NHEJ-mediated DSB repair

Background

DNA mismatch repair proteins participate in diverse cellular functions including DNA damage response and repair. As a member of this protein family, the molecular mechanisms of hMSH4 in mitotic cells are poorly defined. It is known that hMSH4 is promiscuous, and among various interactions the hMSH4-hMSH5 interaction is involved in recognizing DNA intermediate structures arising from homologous recombination (HR).

Results

We identified a new hMSH4 interacting protein eIF3f – a protein that functions not only in translation but also in the regulation of apoptosis and tumorigenesis in humans. Our studies have demonstrated that hMSH4-eIF3f interaction is mediated through the N-terminal regions of both proteins. The interaction with eIF3f fosters hMSH4 protein stabilization, which in turn sustains γ-H2AX foci and compromises cell survival in response to ionizing radiation (IR)-induced DNA damage. These effects can be, at least partially, attributed to the down-regulation of NHEJ activity by hMSH4. Furthermore, the interplay between hMSH4 and eIF3f inhibits IR-induced AKT activation, and hMSH4 promotes eIF3f-mediated bypass of S phase arrest, and ultimately enhancing an early G2/M arrest in response to IR treatment.

Conclusion

Our current study has revealed a role for hMSH4 in the maintenance of genomic stability by suppressing NHEJ-mediated DSB repair.

Vinblastine rapidly induces NOXA and acutely sensitizes primary chronic lymphocytic leukemia cells to ABT-737

Proteins of the BCL2 family provide a survival mechanism in many human malignancies, including chronic lymphocytic leukemia (CLL). The BCL2 inhibitor ABT-263 (navitoclax) is active in clinical trials for lymphoid malignancies, yet resistance is expected on the basis of preclinical models. We recently showed that vinblastine can dramatically sensitize several leukemia cell lines to ABT-737 (the experimental congener of ABT-263). The goal of these experiments was to determine the impact of vinblastine on ABT-737 sensitivity in CLL cells isolated from peripheral blood and to define the underlying mechanism. Freshly isolated CLL cells from 35 patients, as well as normal lymphocytes and platelets, were incubated with various microtubule-disrupting agents plus ABT-737 to assess sensitivity to the single agents and the combination. ABT-737 and vinblastine displayed a range of sensitivity as single agents, and vinblastine markedly sensitized all CLL samples to ABT-737 within six hours. Vinblastine potently induced the proapoptotic protein PMAIP1 (NOXA) in both time- and dose-dependent manner and this was required for the observed apoptosis. Combretastatin A4, which dissociates microtubules by binding to a different site, had the same effect, confirming that interaction of these agents with microtubules is the initial target. Similarly, vincristine and vinorelbine induced NOXA and enhanced CLL sensitivity to ABT-737. Furthermore, vinblastine plus ABT-737 overcame stroma-mediated resistance to ABT-737 alone. Apoptosis was induced with clinically achievable concentrations with no additional toxicity to normal lymphocytes or platelets. These results suggest that vinca alkaloids may improve the clinical efficacy of ABT-263 in patients with CLL.

Roles of Chk1 in cell biology and cancer therapy

The evolutionally conserved DNA damage response (DDR) and cell cycle checkpoints preserve genome integrity. Central to these genome surveillance pathways is a protein kinase, Chk1. DNA damage induces activation of Chk1, which then transduces the checkpoint signal and facilitates cell cycle arrest and DNA damage repair. Significant progress has been made recently toward our understanding of Chk1 regulation and its implications in cancer etiology and therapy. Specifically, a model that involves both spatiotemporal and conformational changes of proteins has been proposed for Chk1 activation. Further, emerging evidence suggests that Chk1 does not appear to be a tumor suppressor; instead, it promotes tumor growth and may contribute to anticancer therapy resistance. Recent data from our laboratory suggest that activating, but not inhibiting, Chk1 in the absence of chemotherapy might represent an innovative approach to suppress tumor growth. These findings suggest unique regulation of Chk1 in cell biology and cancer etiology, pointing to novel strategies for targeting Chk1 in cancer therapy.

Brd4 maintains constitutively active NF-κB in cancer cells by binding to acetylated RelA

Acetylation of the RelA subunit of NF-κB at lysine-310 regulates the transcriptional activation of NF-κB target genes and contributes to maintaining constitutively active NF-κB in tumors. Bromodomain-containing factor Brd4 has been shown to bind to acetylated lysine-310 (AcLys310) and to regulate the transcriptional activity of NF-κB, but the role of this binding in maintaining constitutively active NF-κB in tumors remains elusive. In this study, we demonstrate the structural basis for the binding of bromodomains (BDs) of bromodomain-containing protein 4 (Brd4) to AcLys310 and identify the BD inhibitor JQ1 as an effective small molecule to block this interaction. JQ1 suppresses TNF-α-mediated NF-κB activation and NF-κB-dependent target gene expression. In addition, JQ1 inhibits the proliferation and transformation potential of A549 lung cancer cells and suppresses the tumorigenicity of A549 cells in severe combined immunodeficiency mice. Furthermore, we demonstrate that depletion of Brd4 or treatment of cells with JQ1 induces the ubiquitination and degradation of the constitutively active nuclear form of RelA. Our results identify a novel function of Brd4 in maintaining the persistently active form of NF-κB found in tumors, and they suggest that interference with the interaction between acetylated RelA and Brd4 could be a potential therapeutic approach for the treatment of NF-κB-driven cancer.

Chemical perturbation of Mcl-1 pre-mRNA splicing to induce apoptosis in cancer cells

The myeloid cell leukemia-1 (MCL1) gene encodes antiapoptotic Mcl-1(L) and proapoptotic Mcl-1(S) proteins. In cancer, the Mcl-1(L)/Mcl-1(S) ratio is very high, accounting for the antiapoptotic nature of cancer cells. As such, reducing this ratio can render the cancer cells prone to apoptosis. The Mcl-1(L)/Mcl-1(S) ratio is determined in the alternative pre-mRNA splicing step that is regulated by splicing factor 3B1 (SF3B1). Here, we report that meayamycin B, a potent inhibitor of SF3B1, reversed the dominant isoform from Mcl-1(L) to Mcl-1(S) at the mRNA and protein levels. The resulting proapoptotic cellular environment was further exploited; when meayamycin B was combined with Bcl-x(L) inhibitor ABT-737, the combination treatment triggered apoptosis in nonsmall cell lung cancer A549 and H1299 cells that were otherwise resistant to ABT-737. These results demonstrate that perturbation of the MCL1 splicing with small molecule inhibitors of SF3B1 provides a means to sensitize cancer cells toward Bcl-x(L) inhibitors.

Novel agents for chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a heterogeneous group of B-cell neoplasm. CLL is typically sensitive to a variety of cytotoxic agents, but relapse frequently occurs with conventional approaches. The treatment of CLL is evolving rapidly with the introduction of novel drugs, such as bendamustine, ofatumumab, lenalidomide, ibrutinib, idelalisib, veltuzumab, XmAb5574, navitoclax, dasatinib, alvespimycin, and TRU-016. This review summarizes the most current clinical experiences with these agents in the treatment of CLL.

Therapeutic enhancement of ER stress by insulin-like growth factor I sensitizes myeloma cells to proteasomal inhibitors

PURPOSE

Multiple myeloma is a clonal plasma cell disorder in which growth and proliferation are linked to a variety of growth factors, including insulin-like growth factor type I (IGF-I). Bortezomib, the first-in-class proteasome inhibitor, has displayed significant antitumor activity in multiple myeloma.

EXPERIMENTAL DESIGN

We analyzed the impact of IGF-I combined with proteasome inhibitors on multiple myeloma cell lines in vivo and in vitro as well as on fresh human myeloma cells.

RESULTS

Our study shows that IGF-I enhances the cytotoxic effect of proteasome inhibitors against myeloma cells. The effect of bortezomib on the content of proapoptotic proteins such as Bax, Bad, Bak, and BimS and antiapoptotic proteins such as Bcl-2, Bcl-XL, XIAP, Bfl-1, and survivin was enhanced by IGF-I. The addition of IGF-I to bortezomib had a minor effect on NF-κB signaling in MM.1S cells while strongly enhancing reticulum stress. This resulted in an unfolded protein response (UPR), which was required for the potentiating effect of IGF-I on bortezomib cytotoxicity as shown by siRNA-mediated inhibition of GADD153 expression.

CONCLUSIONS

These results suggest that the high baseline level of protein synthesis in myeloma can be exploited therapeutically by combining proteasome inhibitors with IGF-I, which possesses a "priming" effect on myeloma cells for this family of compounds.

Histone deacetylase inhibitors interact with melanoma differentiation associated-7/interleukin-24 to kill primary human glioblastoma cells

We presently demonstrate that histone deacetylase inhibitors (HDACIs) enhance toxicity of melanoma differentiation-associated gene-7/interleukin 24 (mda-7/IL-24) in invasive primary human glioblastoma multiforme (GBM) cells. Additionally, a method is described to augment the efficacy of adenoviral delivery of mda-7/IL-24 in these cells. HDACIs synergized with melanoma differentiation-associated (MDA)-7/IL-24 killing GBM cells. Enhanced lethality correlated with increased autophagy that was dependent on the expression of ceramide synthase 6. HDACIs interacted with MDA-7/IL-24 prolonging generation of reactive oxygen species and Ca(2+). Quenching of reactive oxygen species and Ca(2+) blocked HDACI and MDA-7/IL-24 killing. In vivo MDA-7/IL-24 prolonged the survival of animals carrying orthotopic tumors, and HDACIs enhanced survival further. A serotype 5/3 adenovirus more effectively delivers mda-7/IL-24 to GBM tumors than a serotype 5 virus. Hence, we constructed a serotype 5/3 adenovirus that conditionally replicates in tumor cells expressing MDA-7/IL-24, in which the adenoviral early region 1A (E1A) gene was driven by the cancer-specific promoter progression elevated gene-3 [Ad.5/3 (INGN 241)-PEG-E1A-mda-7; also called Ad.5/3-CTV (cancer terminator virus)]. Ad.5/3-CTV increased the survival of mice carrying GBM tumors to a significantly greater extent than did a nonreplicative virus Ad.5/3-mda-7. Ad.5/3-CTV exhibited no toxicity in the brains of Syrian hamsters. Collectively our data demonstrate that HDACIs enhance MDA-7/IL-24 lethality, and adenoviral delivery of mda-7/IL-24 combined with tumor-specific viral replication is an effective preclinical GBM therapeutic.

Effect of bortezomib in combination with cisplatin and 5‑fluorouracil on 4T1 breast cancer cells

Bortezomib is a highly selective and reversible inhibitor of the 26S proteasome. It has been approved for the treatment of patients with relapsed and refractory multiple myeloma. A number of studies have been conducted to evaluate the activity and safety of bortezomib either alone or in combination with several cytotoxic agents and radiation. In the current study, the efficacy of bortezomib alone or in combination with cisplatin and 5‑fluorouracil was evaluated in 4T1 breast cancer cells, a highly metastatic murine cancer cell line. Using MTT assay, IC50 values of cisplatin and 5‑fluorouracil were determined to be 14.2 and 8.9 µM for cisplatin and 5‑fluorouracil, respectively. The effects of different concentrations of cisplatin and 5‑fluorouracil in combination with two different concentrations of bortezomib were examined in the 4T1 cells. Statistically significant differences were found when 1 or 5 µM cisplatin was combined with 10 or 50 nM bortezomib. Similarly, 1 µM 5‑fluorouracil or 5 µM 5‑fluorouracil in combination with 10 nM bortezomib caused significant cell death as compared to treatment with single agents. However, 1 or 5 µM 5‑fluorouracil did not potentiate the effects of higher concentrations of bortezomib (50 nM). The effect of the combination of cisplatin, 5‑fluorouracil and bortezomib was determined by soft agar assay. It was confirmed that a combination of cisplatin and bortezomib was more effective than each drug as a monotherapy. Therefore, the combination of cisplatin and bortezomib should be tested further in clinical settings.

The sensitivity of diffuse large B-cell lymphoma cell lines to histone deacetylase inhibitor-induced apoptosis is modulated by BCL-2 family protein activity

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is a genetically heterogeneous disease and this variation can often be used to explain the response of individual patients to chemotherapy. One cancer therapeutic approach currently in clinical trials uses histone deacetylase inhibitors (HDACi's) as monotherapy or in combination with other agents.

METHODOLOGY/PRINCIPAL FINDINGS

We have used a variety of cell-based and molecular/biochemical assays to show that two pan-HDAC inhibitors, trichostatin A and vorinostat, induce apoptosis in seven of eight human DLBCL cell lines. Consistent with previous reports implicating the BCL-2 family in regulating HDACi-induced apoptosis, ectopic over-expression of anti-apoptotic proteins BCL-2 and BCL-XL or pro-apoptotic protein BIM in these cell lines conferred further resistance or sensitivity, respectively, to HDACi treatment. Additionally, BCL-2 family antgonist ABT-737 increased the sensitivity of several DLBCL cell lines to vorinostat-induced apoptosis, including one cell line (SUDHL6) that is resistant to vorinostat alone. Moreover, two variants of the HDACi-sensitive SUDHL4 cell line that have decreased sensitivity to vorinostat showed up-regulation of BCL-2 family anti-apoptotic proteins such as BCL-XL and MCL-1, as well as decreased sensitivity to ABT-737. These results suggest that the regulation and overall balance of anti- to pro-apoptotic BCL-2 family protein expression is important in defining the sensitivity of DLBCL to HDACi-induced apoptosis. However, the sensitivity of DLBCL cell lines to HDACi treatment does not correlate with expression of any individual BCL-2 family member.

CONCLUSIONS/SIGNIFICANCE

These studies indicate that the sensitivity of DLBCL to treatment with HDACi's is dependent on the complex regulation of BCL-2 family members and that BCL-2 antagonists may enhance the response of a subset of DLBCL patients to HDACi treatment.

Early Chk1 phosphorylation is driven by temozolomide-induced, DNA double strand break- and mismatch repair-independent DNA damage

Temozolomide (TMZ) is a DNA methylating agent used to treat brain cancer. TMZ-induced O6-methylguanine adducts, in the absence of repair by O6-methylguanine DNA methyltransferase (MGMT), mispair during DNA replication and trigger cycles of futile mismatch repair (MMR). Futile MMR in turn leads to the formation of DNA single and double strand breaks, Chk1 and Chk2 phosphorylation/activation, cell cycle arrest, and ultimately cell death. Although both pChk1 and pChk2 are considered to be biomarkers of TMZ-induced DNA damage, cell-cycle arrest, and TMZ induced cytotoxicity, we found that levels of pChk1 (ser345), its downstream target pCdc25C (ser216), and the activity of its upstream activator ATR, were elevated within 3 hours of TMZ exposure, long before the onset of TMZ-induced DNA double strand breaks, Chk2 phosphorylation/activation, and cell cycle arrest. Furthermore, TMZ-induced early phosphorylation of Chk1 was noted in glioma cells regardless of whether they were MGMT-proficient or MGMT-deficient, and regardless of their MMR status. Early Chk1 phosphorylation was not associated with TMZ-induced reactive oxygen species, but was temporally associated with TMZ-induced alkalai-labile DNA damage produced by the non-O6-methylguanine DNA adducts and which, like Chk1 phosphorylation, was transient in MGMT-proficient cells but persistent in MGMT-deficient cells. These results re-define the TMZ-induced DNA damage response, and show that Chk1 phosphorylation is driven by TMZ-induced mismatch repair-independent DNA damage independently of DNA double strand breaks, Chk2 activation, and cell cycle arrest, and as such is a suboptimal biomarker of TMZ-induced drug action.

Cyclin-dependent kinase inhibitor therapy for hematologic malignancies

INTRODUCTION

Cyclin-dependent kinases (CDKs) regulate cell cycle progression. Certain CDKs (e.g., CDK7, CDK9) also control cellular transcription. Consequently, CDKs represent attractive targets for anticancer drug development, as their aberrant expression is common in diverse malignancies, and CDK inhibition can trigger apoptosis. CDK inhibition may be particularly successful in hematologic malignancies, which are more sensitive to inhibition of cell cycling and apoptosis induction.

AREAS COVERED

A number of CDK inhibitors, ranging from pan-CDK inhibitors such as flavopiridol (alvocidib) to highly selective inhibitors of specific CDKs (e.g., CDK4/6), such as PD0332991, that are currently in various phases of development, are profiled in this review. Flavopiridol induces cell cycle arrest, and globally represses transcription via CDK9 inhibition. The latter may represent its major mechanism of action via down-regulation of multiple short-lived proteins. In early phase trials, flavopiridol has shown encouraging efficacy across a wide spectrum of hematologic malignancies. Early results with dinaciclib and PD0332991 also appear promising.

EXPERT OPINION

In general, the antitumor efficacy of CDK inhibitor monotherapy is modest, and rational combinations are being explored, including those involving other targeted agents. While selective CDK4/6 inhibition might be effective against certain malignancies, broad-spectrum CDK inhibition will likely be required for most cancers.

Activation of Triggering Receptor Expressed on Myeloid Cells-1 Protects Monocyte from Apoptosis through Regulation of Myeloid Cell Leukemia-1

Background:

Triggering receptor expressed on myeloid cells-1 (TREM-1) can amplify the proinflammatory response and may contribute to the pathogenesis of inflammatory disease such as sepsis. However, the role of TREM-1 in monocyte fate and the detailed molecular mechanisms evoked by TREM-1 are unknown.

Methods:

Adenoviruses overexpressing TREM-1 were constructed and transfected into a monocytic cell line. After activation of TREM-1 by agonist antibody with or without lipopolysaccharide, apoptosis was induced and assayed using flow cytometry. The signaling pathways downstream of TREM-1 were illustrated by inhibitory experiments. Proapoptotic/antiapoptotic protein levels were measured using immunoblot. In addition, the relationship between the expression levels of TREM-1 in monocytes and the magnitude of monocyte apoptosis were analyzed in septic patients.

Results:

Activation of TREM-1 protected monocytes from staurosporine-induced apoptosis. This characteristic was also obtained under lipopolysaccharide stimulation. The protection of TREM-1 against monocyte apoptosis was abrogated after inhibition of extracellular signal–regulated kinase or v-akt murine thymoma viral oncogene homologue signaling. Cross-linking of TREM-1 remarkably up-regulated myeloid cell leukemia-1 protein level, and inhibition of extracellular signal–regulated kinase or v-akt murine thymoma viral oncogene homologue resulted in the reduction of myeloid cell leukemia-1 expression. Inhibition of myeloid cell leukemia-1 abolished the antiapoptotic effect of TREM-1. Furthermore, in septic patients, TREM-1 levels were inversely correlated to the magnitude of apoptosis in monocyte.

Conclusions:

TREM-1 played an important role in apoptosis in monocytes. Activation of TREM-1 protected monocytic cells from apoptosis through activation of both extracellular signal–regulated kinase and v-akt murine thymoma viral oncogene homologue pathways and increased expression of myeloid cell leukemia-1 protein. These findings provide a novel additional mechanism for TREM-1–mediated hyperinflammatory response in monocytes.

Alterations of Gab2 signalling complexes in imatinib and dasatinib treated chronic myeloid leukaemia cells

BACKGROUND

The Gab2 docking protein acts as an important signal amplifier downstream of various growth factor receptors and Bcr-Abl, the driver of chronic myeloid leukaemia (CML). Despite the success of Bcr-Abl tyrosine kinase inhibitors (TKI) in the therapy of CML, TKI-resistance remains an unsolved problem in the clinic. We have recently shown that Gab2 signalling counteracts the efficacy of four distinct Bcr-Abl inhibitors. In the course of that project, we noticed that two clinically relevant drugs, imatinib and dasatinib, provoke distinct alterations in the electrophoretic mobility of Gab2, its signalling output and protein interactions. As the signalling potential of the docking protein is highly modulated by its phosphorylation status, we set out to obtain more insights into the impact of TKIs on Gab2 phosphorylation.

FINDINGS

Using stable isotope labelling by amino acids in cell culture (SILAC)-based quantitative mass spectrometry (MS), we show now that imatinib and dasatinib provoke distinct effects on the phosphorylation status and interactome of Gab2. This study identifies several new phosphorylation sites on Gab2 and confirms many sites previously known from other experimental systems. At equimolar concentrations, dasatinib is more effective in preventing Gab2 tyrosine and serine/threonine phosphorylation than imatinib. It also affects the phosphorylation status of more residues than imatinib. In addition, we also identify novel components of the Gab2 signalling complex, such as casein kinases, stathmins and PIP1 as well as known interaction partners whose association with Gab2 is disrupted by imatinib and/or dasatinib.

CONCLUSIONS

By using MS-based proteomics, we have identified new and confirmed known phosphorylation sites and interaction partners of Gab2, which may play an important role in the regulation of this docking protein. Given the growing importance of Gab2 in several tumour entities we expect that our results will help to understand the complex regulation of Gab2 and how this docking protein can contribute to malignancy.

Structure-based design, discovery and development of checkpoint kinase inhibitors as potential anticancer therapies

INTRODUCTION

Checkpoint kinase (CHK) inhibitors offer the promise of enhancing the effectiveness of widely prescribed cancer chemotherapies and radiotherapy by inhibiting the DNA damage response, as well as the potential for single agent efficacy.

AREAS COVERED

This article surveys structural insights into the checkpoint kinases CHK1 and CHK2 that have been exploited to enhance the selectivity and potency of small molecule inhibitors. Furthermore, the authors review the use of mechanistic cellular assays to guide the optimisation of inhibitors. Finally, the authors discuss the status of the current clinical candidates and emerging new clinical contexts for CHK1 and CHK2 inhibitors, including the prospects for single agent efficacy.

EXPERT OPINION

Protein-bound water molecules play key roles in structural features that can be targeted to gain high selectivity for either enzyme. The results of early phase clinical trials of checkpoint inhibitors have been mixed, but significant progress has been made in testing the combination of CHK1 inhibitors with genotoxic chemotherapy. Second-generation CHK1 inhibitors are likely to benefit from increased selectivity and oral bioavailability. While the optimum therapeutic context for CHK2 inhibition remains unclear, the emergence of single agent preclinical efficacy for CHK1 inhibitors in specific tumour types exhibiting constitutive replication stress represents exciting progress in exploring the therapeutic potential of these agents.

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.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

MEK inhibitors selectively suppress alloreactivity and graft-versus-host disease in a memory stage-dependent manner

Immunosuppressive strategies currently used in hematopoietic stem cell transplantation reliably decrease graft-versus-host disease (GVHD) rates, but also impair pathogen-specific immunity. Experimental transplant studies indicate that GVHD-initiating alloreactive T cells reside primarily in naive and central memory T-cell compartments. In contrast, virus-specific T cells comprise a more differentiated memory population. After finding that the rat sarcoma/mitogen-activated protein kinase kinase/extracellular receptor kinase (RAS/MEK/ERK) pathway is preferentially activated in naive and central memory human T cells, we hypothesized that MEK inhibitors would preferentially inhibit alloreactive T cells, while sparing more differentiated virus-specific T cells. Confirming our hypothesis, we found that MEK inhibitors including selumetinib preferentially inhibited cytokine production and alloreactivity mediated by naive and central memory human CD4(+) and CD8(+) T cells while sparing more differentiated T cells specific for the human herpesviruses cytomegalovirus and Epstein-Barr virus. We then demonstrated that short-term posttransplant administration of selumetinib in a major histocompatibility complex major- and minor-mismatched murine model significantly delayed the onset of GVHD-associated mortality without compromising myeloid engraftment, demonstrating the in vivo potential of MEK inhibitors in the setting of hematopoietic stem cell transplantation. These findings demonstrate that targeting memory-dependent differences in T-cell signaling is a potent and selective approach to inhibition of alloreactivity.

Potency switch between CHK1 and MK2: discovery of imidazo[1,2-a]pyrazine- and imidazo[1,2-c]pyrimidine-based kinase inhibitors

Chemistry has been developed to access both imidazo[1,2-a]pyrazines and imidazo[1,2-c]pyrimidines. Small structural modifications in both series led to a switch of potency between two kinases involved in mediating cell cycle checkpoint control, CHK1 and MK2.

A focus on the preclinical development and clinical status of the histone deacetylase inhibitor, romidepsin (depsipeptide, Istodax(®))

Romidepsin (Istodax(®), depsipeptide, FR901228, FK228, NSC 630176) is a cyclic peptide, broad-spectrum, potent histone deacetylase inhibitor, with activity mainly against class I histone deacetylase enzymes. In this article, we give an overview of the putative modes of action, such as effects on gene expression, cell cycle regulation, apoptosis induction, DNA repair, protein acetylation and induction of autophagy. Romidepsin has mainly been developed as a therapy for hematologic malignancies and is approved by the US FDA for the treatment of cutaneous T-cell lymphomas. This report outlines the laboratory and clinical development of the compound as a single agent that has more recently been evaluated in combination with other anticancer therapeutics, such as proteasome inhibitors.

ATR inhibition broadly sensitizes ovarian cancer cells to chemotherapy independent of BRCA status

Replication stress and DNA damage activate the ATR-Chk1 checkpoint signaling pathway that licenses repair and cell survival processes. In this study, we examined the respective roles of the ATR and Chk1 kinases in ovarian cancer cells using genetic and pharmacologic inhibitors in combination with cisplatin, topotecan, gemcitabine, and the PARP inhibitor veliparib (ABT-888), four agents with clinical activity in ovarian cancer. RNA interference (RNAi)-mediated depletion or inhibition of ATR sensitized ovarian cancer cells to all four agents. In contrast, while cisplatin, topotecan, and gemcitabine each activated Chk1, RNAi-mediated depletion or inhibition of this kinase in cells sensitized them only to gemcitabine. Unexpectedly, we found that neither the ATR kinase inhibitor VE-821 nor the Chk1 inhibitor MK-8776 blocked ATR-mediated Chk1 phosphorylation or autophosphorylation, two commonly used readouts for inhibition of the ATR-Chk1 pathway. Instead, their ability to sensitize cells correlated with enhanced CDC25A levels. In addition, we also found that VE-821 could further sensitize BRCA1-depleted cells to cisplatin, topotecan, and veliparib beyond the potent sensitization already caused by their deficiency in homologous recombination. Taken together, our results established that ATR and Chk1 inhibitors differentially sensitize ovarian cancer cells to commonly used chemotherapy agents and that Chk1 phosphorylation status may not offer a reliable marker for inhibition of the ATR-Chk1 pathway. A key implication of our work is the clinical rationale it provides to evaluate ATR inhibitors in combination with PARP inhibitors in BRCA1/2-deficient cells.

Inhibition of Wee1, AKT, and CDK4 underlies the efficacy of the HSP90 inhibitor XL888 in an in vivo model of NRAS-mutant melanoma

The HSP90 inhibitor XL888 is effective at reversing BRAF inhibitor resistance in melanoma, including that mediated through acquired NRAS mutations. The present study has investigated the mechanism of action of XL888 in NRAS-mutant melanoma. Treatment of NRAS-mutant melanoma cell lines with XL888 led to an inhibition of growth, G2-M phase cell-cycle arrest, and the inhibition of cell survival in three-dimensional spheroid and colony formation assays. In vitro, HSP90 inhibition led to the degradation of ARAF, CRAF, Wee1, Chk1, and cdc2 and was associated with decreased mitogen-activated protein kinase (MAPK), AKT, mTOR, and c-jun NH2 kinase (JNK) signaling. Apoptosis induction was associated with increased BIM expression and a decrease in the expression of the prosurvival protein Mcl-1. The critical role of increased BIM and decreased Mcl-1 expression in the survival of NRAS-mutant melanoma cell lines was shown through siRNA knockdown and overexpression studies. In an animal xenograft model of NRAS-mutant melanoma, XL888 treatment led to reduced tumor growth and apoptosis induction. Important differences in the pattern of client degradation were noted between the in vivo and in vitro studies. In vivo, XL888 treatment led to degradation of CDK4 and Wee1 and the inhibition of AKT/S6 signaling with little or no effect observed upon ARAF, CRAF, or MAPK. Blockade of Wee1, using either siRNA knockdown or the inhibitor MK1775, was associated with significant levels of growth inhibition and apoptosis induction. Together, these studies have identified Wee1 as a key target of XL888, suggesting novel therapeutic strategies for NRAS-mutant melanoma.