Induction of apoptosis in human leukemia cells by the tyrosine kinase inhibitor adaphostin proceeds through a RAF-1/MEK/ERK- and AKT-dependent process

Potential New Therapies "ROS-Based" in CLL: An Innovative Paradigm in the Induction of Tumor Cell Apoptosis

Chronic lymphocytic leukemia, in spite of recent advancements, is still an incurable disease; the majority of patients eventually acquire resistance to treatment through relapses. In all subtypes of chronic lymphocytic leukemia, the disruption of normal B-cell homeostasis is thought to be mostly caused by the absence of apoptosis. Consequently, apoptosis induction is crucial to the management of this illness. Damaged biological components can accumulate as a result of the oxidation of intracellular lipids, proteins, and DNA by reactive oxygen species. It is possible that cancer cells are more susceptible to apoptosis because of their increased production of reactive oxygen species. An excess of reactive oxygen species can lead to oxidative stress, which can harm biological elements like DNA and trigger apoptotic pathways that cause planned cell death. In order to upset the balance of oxidative stress in cells, recent therapeutic treatments in chronic lymphocytic leukemia have focused on either producing reactive oxygen species or inhibiting it. Examples include targets created in the field of nanomedicine, natural extracts and nutraceuticals, tailored therapy using biomarkers, and metabolic targets. Current developments in the complex connection between apoptosis, particularly ferroptosis and its involvement in epigenomics and alterations, have created a new paradigm.

Transcriptional drug repositioning and cheminformatics approach for differentiation therapy of leukaemia cells

Differentiation therapy is attracting increasing interest in cancer as it can be more specific than conventional chemotherapy approaches, and it has offered new treatment options for some cancer types, such as treating acute promyelocytic leukaemia (APL) by retinoic acid. However, there is a pressing need to identify additional molecules which act in this way, both in leukaemia and other cancer types. In this work, we hence developed a novel transcriptional drug repositioning approach, based on both bioinformatics and cheminformatics components, that enables selecting such compounds in a more informed manner. We have validated the approach for leukaemia cells, and retrospectively retinoic acid was successfully identified using our method. Prospectively, the anti-parasitic compound fenbendazole was tested in leukaemia cells, and we were able to show that it can induce the differentiation of leukaemia cells to granulocytes in low concentrations of 0.1 μM and within as short a time period as 3 days. This work hence provides a systematic and validated approach for identifying small molecules for differentiation therapy in cancer.

Tg737 acts as a key driver of invasion and migration in liver cancer stem cells and correlates with poor prognosis in patients with hepatocellular carcinoma

We previously demonstrated that the Tg737 gene plays a critical role in the carcinogenesis of hepatocellular carcinoma (HCC). However, few systematic investigations have focused on the biological function of Tg737 in the invasion and migration of liver cancer stem cells (LCSCs) and on its clinical significance. In this study, Tg737 overexpression was achieved via gene transfection in MHCC97-H side population (SP) cells, which are considered a model for LCSCs in scientific studies. Tg737 overexpression significantly inhibited the invasion and migration of SP cells in an extracellular signal-regulated kinase1/2 (ERK1/2)/matrix metalloproteinase-2 (MMP-2)-dependent manner. Furthermore, Tg737 expression was frequently decreased in HCC tissues relative to that in adjacent noncancerous liver tissues. This decreased expression was significantly associated with tumor differentiation, the American Joint Committee on Cancer (AJCC) stage, metastasis, tumor size, vascular invasion, alpha-fetoprotein (AFP) levels, and tumor number. Moreover, multivariate Cox regression analyses demonstrated that Tg737 expression was an independent factor for predicting the overall survival of HCC patients. Notably, Kaplan-Meier analysis further showed that overall survival was significantly worse among patients with low Tg737 expression. Collectively, our findings demonstrated that Tg737 is a poor prognostic marker in patients with HCC, which may be due to its ability to promote LCSCs invasion and migration. These results provide a basis for investigating of Tg737 as a novel prognostic biomarker and therapeutic target.

COMMD7 functions as molecular target in pancreatic ductal adenocarcinoma

Our previous studies provided evidence that COMMD7 was associated with tumor progression in human solid cancer. Herein, we aimed to investigate its expression pattern, clinical significance, and biological function in pancreatic ductal adenocarcinoma (PDAC). We found that high COMMD7 expression was specifically detected in PDAC tissues and PDAC cell lines. In addition, COMMD7 overexpression positively correlated with histological differentiation and tumor node metastasis (TNM) stage. Patients with high COMMD7 expression had significantly poorer overall survival, and high COMMD7 expression was an independent predictor of poor prognosis. To further explore the regulatory mechanism of COMMD7, we used stable short hairpin RNA (shRNA)-mediated knockdown and divided the work into in vitro and in vivo experiments. In vitro, the anti-proliferation effects of COMMD7 inhibition were observed under long-time stress conditions, which correlated with cyclin D1 and Bcl-2 downregulation and Bax upregulation. We found that under short-time stress conditions, decreased COMMD7 expression also inhibited PDAC cell invasion in vitro which decreased the secretion of matrix metalloproteinase 2 (MMP-2). Moreover, extracellular signal-regulated kinase1/2 (ERK1/2) was identified as a direct target of COMMD7. The inhibition of ERK1/2 activity under short- or long-time stress conditions using specific inhibitors in COMMD7 inhibition cells all exhibited a strong tumorigenic role. In vivo, COMMD7 was sufficient to impair tumor growth. Our results suggest that COMMD7 plays an important role in the late progression of PDAC and is a potential novel target. © 2016 Wiley Periodicals, Inc.

Sorafenib for the treatment of multiple myeloma

INTRODUCTION

Sorafenib is an orally available compound that acts predominantly by targeting the Ras/Raf/MEK/ERK pathway and by inhibiting the vascular endothelial growth factor (VEGF). Since the Ras/Raf/MEK/ERK pathway is implicated in the proliferation of multiple myeloma (MM) cells and VEGF in bone marrow neovascularization, sorafenib is a drug offering the potential for targeting two important pathogenetic mechanisms involved in MM. Thus, sorafenib is being proposed for use in MM.

AREAS COVERED

In this review, the authors discuss the rationale for the use of sorafenib in MM. They then summarize the clinical development of sorafenib in MM, from initial Phase I to Phase II studies. A systematic literature review of the trials was performed using PubMed.

EXPERT OPINION

Preliminary data from phase I/II trials showed that sorafenib had a good safety profile but minimal anti-myeloma activity as a single agent in relapsed/refractory patients. Results of phase II trials, evaluating sorafenib combined with new drugs, such as bortezomib and lenalidomide are eagerly awaited.

Huaier aqueous extract inhibits cervical cancer cell proliferation via JNK/p38 pathway

Although the anticancer effects of Huaier extract have been widely investigated, including anti-proliferate, anti-angiogenic and anti-metastatic activities, the mechanisms are not well understood. This study aimed to elucidate the inhibitory effect of Huaier extract on tumor growth in cervical cancer cells and its molecular mechanisms. Cell viability and motility were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony assays, migration, and invasive assays, respectively. The distribution of the cell cycle was analyzed by flow cytometry. Huaier inhibited cell viability of SiHa and C33A cells in a time- and dose-dependent manner; cell migration and invasiveness were also suppressed; Huaier was able to cause G2/M cell cycle arrest in C33A cells. The western blot results confirmed Huaier dose-dependently increased expression of phosphorylated c-Jun N-terminal kinase (JNK), p-38 and downregulated the expression of phosphorylated extracellular signal-regulated kinase (ERK) in a time- and dose-dependently manner. In vivo experiments showed that Huaier significantly suppressed the tumor volume of SiHa cell xenografts. These data suggest that Huaier may inhibit tumor proliferation in cervical cancer via the JNK/p38 signaling pathway.

Ligation of CM1 enhances apoptosis of lung cancer cells through different mechanisms in conformity with EGFR mutation

Although remarkable developments in lung cancer treatments have been made, lung cancer remains the leading cause of cancer mortality worldwide. Epidermal growth factor receptor (EGFR) is occasionally mutated in non-small cell lung cancer and heterogeneity in treatment response results from different EGFR mutations. In the present study, we found that centrocyte/centroblast marker 1 (CM1), previously reported as a possible apoptosis inducer of B lymphoma cells, is expressed on both A549 with wild-type EGFR and HCC827 with mutant EGFR lung cancer cells. Ligation of CM1 with anti-CM1 mAb enhanced apoptosis in both lung cancer cell lines through generation of reactive oxygen species (ROS) and disruption of mitochondrial membrane potential, however, the signaling mechanisms differed from each other. Further studies to investigate the signaling mechanisms identified that ligation of CM1-induced apoptosis in A549 cell involved FasL expression, caspase-8, ERK1/2 and Akt kinase, whereas apoptosis of HCC827 cells was induced through caspase-9, JNK and c-jun-dependent pathways. Taken together, we suggest that CM1 could be developed as a therapeutic target of lung cancer regardless of EGFR mutation status.

Anticancer drugs targeting the mitochondrial electron transport chain

SIGNIFICANCE

Mitochondria are emerging as highly intriguing organelles showing promise but that are yet to be fully exploited as targets for anticancer drugs.

RECENT ADVANCES

A group of compounds that induce mitochondrial destabilization, thereby affecting the physiology of cancer cells, has been defined and termed 'mitocans.' Based on their mode of action of targeting in and around mitochondria, we have placed these agents into several groups including hexokinase inhibitors, compounds targeting Bcl-2 family proteins, thiol redox inhibitors, VDAC/ANT targeting drugs, electron transport chain-targeting drugs, lipophilic cations targeting the inner membrane, agents affecting the tricarboxylic acid cycle, drugs targeting mtDNA, and agents targeting other presently unknown sites.

CRITICAL ISSUES

Mitocans have a potential to prove highly efficient in suppressing various malignant diseases in a selective manner. They include compounds that are currently in clinical trial and offer substantial promise to become clinically applied drugs. Here we update and redefine the individual classes of mitocans, providing examples of the various members of these groups with a particular focus on agents targeting the electron transport chain, and indicate their potential application in clinical practice.

FUTURE DIRECTIONS

Even though reactive oxygen species induction is important for the anticancer activity of many mitocans, the precise sequence of events preceding and following this pivotal event are not yet fully clarified, and warrant further investigation. This is imperative for effective deployment of these compounds in the clinic.

p-Aminophenol-induced cytotoxicity in Jurkat T cells: protective effect of 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid

Acetaminophen (APAP) is hepatotoxic and can cause toxicity in Jurkat T cells. p-Aminophenol (PAP), an industrial chemical and APAP metabolite, is nephrotoxic and hepatotoxic. Its potential toxicity in Jurkat T cells was investigated. PAP (10-250 µM) caused toxicity (decreased survival and increased LDH activity in incubation medium) and GSH depletion. At a concentration of 100 µM but not 250 µM, PAP increased DNA fragmentation. It decreased p-Akt levels (Elisa) and at higher concentrations decreased p-Akt expression (Western blotting). It had no effect on FasL expression. The cysteine precursor 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid (250 µM) attenuated the PAP (100 µM)-induced decrease in viability and prevented GSH depletion and increased DNA fragmentation. It attenuated the PAP-induced decrease in p-Akt levels and protected against the decrease in p-Akt expression. The results demonstrate PAP-induced toxicity and suggest that it is due at least in part to apoptosis and involves GSH depletion and p-Akt inactivation.

Icaritin causes sustained ERK1/2 activation and induces apoptosis in human endometrial cancer cells

Icaritin, a compound from Epimedium Genus, has selective estrogen receptor (ER) modulating activities, and posses anti-tumor activity. Here, we examined icaritin effect on cell growth of human endometrial cancer Hec1A cells and found that icaritin potently inhibited proliferation of Hec1A cells. Icaritin-inhibited cell growth was associated with increased levels of p21 and p27 expression and reduced cyclinD1 and cdk 4 expression. Icaritin also induced cell apoptosis accompanied by activation of caspases as evidenced by the cleavage of endogenous substrate Poly (ADP-ribose) polymerase (PARP) and cytochrome c release, which was abrogated by pretreatment with the pan-caspase inhibitor z-VAD-fmk. Icaritin treatment also induced expression of pro-apoptotic protein Bax with a concomitant decrease of Bcl-2 expression. Furthermore, icaritin induced sustained phosphorylation of extracellular signal-regulated kinase1/2 (the MAPK/ ERK1/2) in Hec1A cells and U0126, a specific MAP kinase kinase (MEK1/2) inhibitor, blocked the ERK1/2 activation by icaritin and abolished the icaritin-induced growth inhibition and apoptosis. Our results demonstrated that icaritin induced sustained ERK 1/2 activation and inhibited growth of endometrial cancer Hec1A cells, and provided a rational for preclinical and clinical evaluation of icaritin for endometrial cancer therapy.

Low-dose taxotere enhances the ability of sorafenib to induce apoptosis in gastric cancer models

Despite the low efficacy of conventional antitumour drugs, chemotherapy remains an essential tool in controlling advanced gastric and oesophageal cancers. We aimed to provide a biological rationale based on the sorafenib-taxotere interaction for the clinical treatment of gastric cancer. In vitro experiments were performed on four human gastric cancer cell lines (GK2, AKG, KKP and NCI-N87). Cytotoxicity was evaluated by sulforhodamine B (SRB) assay, cell cycle perturbations, apoptosis and mitotic catastrophe were assessed by flow cytometric and microscopic analyses, and protein expression was studied by Western blot. In the in vivo experiments, nude mice xenografted with the most resistant line were treated with sorafenib and docetaxel singly or in association. Sorafenib inhibited cell growth (IG(50) values ranged from 3.4 to 8.1 μM) and caused down-regulation of MAP-K/ERK phosphorylation and of mcl-1 and p-bad expression after a 48-hr exposure. Apoptosis induction was associated with caspase-3 and -9 activation and mitochondrial membrane depolarization. The drug combination enhanced apoptosis (up to 80%) and produced a synergistic interaction when low doses of the taxane preceded administration of the antityrosine kinase. This synergism was probably due to the induction of an anomalous multidiploid G0-G1 peak and to consequent mitotic catastrophe, which increased sensitivity to sorafenib. Consistent with in vitro results, the docetaxel-sorafenib sequence exhibited high therapeutic efficacy in NCI-N87 mouse xenografts producing tumour weight inhibition (> 65%), tumour growth delay (up to 25 days) and increased mouse survival (30%). Our findings suggest the potential clinical usefulness of treatment with sorafenib and docetaxel for advanced gastric cancer.

Adaphostin toxicity in a sensitive non-small cell lung cancer model is mediated through Nrf2 signaling and heme oxygenase 1

Background

Preclinical toxicity of adaphostin has been related to oxidative stress. This study investigated the regulatory mechanism underlying adaphostin induction of heme oxygenase 1 (HMOX1) which plays a significant role in modulation of drug-induced toxicity in the non-small cell lung cancer cell line model, NCI-H522.

Methods

The transcriptional response of NCI-H522 to adaphostin prominently involved oxidative stress genes, particularly HMOX1. Reactive oxygen species (ROS) involvement was additionally established by generation of ROS prior to modulation of adaphostin-toxicity with antioxidants. To identify up-stream regulatory elements of HMOX1, immunofluorescence was used to evaluate nuclear translocation of the transcription factor, NF-E2-related factor 2 (Nrf2), in the presence of adaphostin. The PI3-kinase inhibitor, wortmannin, was employed as a pharmacological inhibitor of this process.

Results

Generation of ROS provided a substantial foundation for the sensitivity of NCI-H522 to adaphostin. However, in contrast to leukemia cell lines, transcriptional response to oxidative stress was associated with induction of HMOX1, which was dependent on nuclear translocation of the transcription factor, Nrf2. Pretreatment of cells with wortmannin inhibited translocation of Nrf2 and induction of HMOX1. Wortmannin pretreatment was also able to diminish adaphostin induction of HMOX1, and as a consequence, enhance the toxicity of adaphostin to NCI-H522.

Conclusions

Adaphostin-induced oxidative stress in NCI-H522 was mediated through nuclear translocation of Nrf2 leading to upregulation of HMOX1. Inhibition of Nrf2 translocation by wortmannin inhibited this cytoprotective response, and enhanced the toxicity of adaphostin, suggesting that inhibitors of the PI3K pathway, such as wortmannin, might augment the antiproliferative effects of adaphostin in solid tumors that depend on the Nrf2/ARE pathway for protection against oxidative stress.

Cigarette-smoke-induced oxidative/nitrosative stress impairs VEGF- and fluid-shear-stress-mediated signaling in endothelial cells

VEGF receptor 2 (VEGFR2), a tyrosine kinase receptor, is activated by VEGF and fluid shear stress (FSS), and its downstream signaling is important in the regulation of endothelial functions, such as cell migration, endothelium-dependent relaxation, and angiogenesis. Cigarette smoke (CS) is known to cause oxidative/nitrosative stress, leading to modifications of tyrosine kinase receptors and impaired downstream signaling. We hypothesized that CS-induced oxidative/nitrosative stress impairs VEGF- and FSS-mediated VEGFR2 activation, leading to endothelial dysfunction. Human lung microvascular endothelial cells and human umbilical vein endothelial cells were treated with different concentrations of cigarette smoke extract (CSE) to investigate the VEGF- or FSS-mediated VEGFR2 phosphorylation and its downstream signaling involved in endothelial function. CSE treatment impaired both VEGF- and FSS-mediated VEGFR2 phosphorylation, resulting in impaired endothelial nitric oxide synthase (eNOS) phosphorylation by Akt. CS-derived reactive oxygen/nitrogen species react with VEGFR2, rendering VEGFR2 inactive for its downstream signaling. Pretreatment with nitric oxide scavenger (PTIO), reactive oxygen species scavengers (combination of SOD with catalase), and N-acetyl-L-cysteine, significantly attenuated the CSE-induced impairment of VEGF-mediated Akt and eNOS phosphorylation. These findings suggest that CSE-induced oxidative/nitrosative stress impairs VEGF- and FSS-mediated endothelial cell function and has important implications in the pathogenesis of CS-induced pulmonary and cardiovascular diseases associated with endothelial dysfunction.

Heat shock proteins in glioblastomas

Glioblastoma multiforme is the most common primary central nervous system tumor. The prognosis for these malignant brain tumors is poor, with a median survival of 14 months and a 5-year survival rate below 2%. Development of novel treatments is essential to improving survival and quality of life for these patients. Endogenous heat shock proteins have been implicated in mediation of both adaptive and innate immunity, and there is a rising interest in the use of this safe and multifaceted heat shock protein vaccine therapy as a promising treatment for human cancers, including glioblastoma multiforme.

Oxidative stress by targeted agents promotes cytotoxicity in hematologic malignancies

The past decade has seen an exponential increase in the number of cancer therapies with defined molecular targets. Interestingly, many of these new agents are also documented to raise levels of intracellular reactive oxygen species (ROS) in addition to inhibiting a biochemical target. In most cases, the exact link between the primary target of the drug and effects on cellular redox status is unknown. However, it is important to understand the role of oxidative stress in promoting cytotoxicity by these agents, because the design of multiregimen strategies could conceivably build on these redox alterations. Also, drug resistance mediated by antioxidant defenses could potentially be anticipated and circumvented with improved knowledge of the redox-related effects of these targeted agents. Given the large number of targeted chemotherapies, in this review, we focus on selected agents that have shown promise in hematologic malignancies: proteasome inhibitors, histone deacetylase inhibitors, Bcl-2-targeted agents, and a kinase inhibitor called adaphostin. Despite structural differences within classes of these compounds, a commonality of causing increased oxidative stress exists, which contributes to induction of cell death.

Selected combination therapy with sorafenib: a review of clinical data and perspectives in advanced solid tumors

The development of targeted therapies has provided new options for the management of patients with advanced solid tumors. There has been particular interest in agents that target the mitogen-activated protein kinase pathway, which controls tumor growth and survival and promotes angiogenesis. Sorafenib is an oral multikinase inhibitor that has been proven effective as a single-agent therapy in renal cell carcinoma, and there is a strong rationale for investigating its use in combination with other agents. In particular, targeting multiple Raf isoforms with sorafenib may help to overcome resistance to other agents, while the ability of sorafenib to induce apoptosis may increase the cytotoxicity of chemotherapeutic agents. Based on positive results in preclinical studies, further investigation in phase I and II studies has shown potential antitumor activity when sorafenib is combined with cytotoxic agents in different solid tumors, including hepatocellular carcinoma and melanoma. Promising results have been reported in phase I and II studies of sorafenib combined with paclitaxel and carboplatin, with oxaliplatin in gastric and colorectal cancer, with docetaxel in breast cancer, with gemcitabine in ovarian cancer, and with capecitabine in different solid tumors. Phase II and III studies are currently investigating the use of sorafenib in combination with different agents in a variety of solid tumors. The primary objective of this review is to summarize the early clinical studies of sorafenib with cytotoxic agents and discuss future perspectives of these combinations in different tumor types.

The kinase inhibitor dasatinib induces apoptosis in chronic lymphocytic leukemia cells in vitro with preference for a subgroup of patients with unmutated IgVH genes

Src family kinases (SFKs) were described to be overexpressed in chronic lymphocytic leukemia (CLL). We wished to examine the effects of the Src and Abl kinase inhibitor dasatinib on the intracellular signaling and survival of CLL cells. Dasa-tinib showed a dose- and time-dependent reduction of global tyrosine phosphorylation and of activating phosphotyrosine levels of SFKs. Treatment with 100 nM dasatinib led to decreased levels of the activated, phosphorylated forms of Akt, Erk1/2, and p38, and induced PARP cleavage through caspase activity. In Mec1 and JVM-3 cell lines, dasatinib increased p53 protein levels and inhibited proliferation. In freshly isolated CLL cells, dasatinib reduced the expression of Mcl-1 and Bcl-x(L). Combination of 5 microM dasatinib and fludarabine increased the apoptosis induction of each by approximately 50%. In 15 primary CLL samples, cells with unmutated immunoglobulin variable heavy chain (IgV(H)) genes were more sensitive to dasatinib than those with mutated IgV(H) genes (P = .002). In summary, dasatinib shows potent inhibitory effects on the survival of CLL cells in vitro, most prominently in samples obtained from patients with unfavorable prognostic features.

Effects of 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid on 4-hydroxy-2-nonenal-induced apoptotic T cell death

4-Hydroxy-2-nonenal (HNE), the aldehydic product of lipid peroxidation, is associated with multiple immune dysfunctions, such as HIV and hepatitis C virus infection. HNE-induced immunosuppression could be due to a decrease in CD4+ T lymphocyte activation or proliferation. Glutathione (GSH) is the most abundant endogenous antioxidant in cells, and an adduct between HNE and GSH has been suggested to be a marker of oxidative stress. Our earlier studies showed that HNE induced cytotoxicity and Akt inactivation, which led to the enhancement of FasL expression and concomitantly decreased cellular FLICE-like inhibitory protein (c-FLIP(S)) levels. In this study, we found that HNE caused intracellular GSH depletion in Jurkat T cells, and we further investigated the role of 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA), a GSH prodrug, in attenuating HNE-induced cytotoxicity in CD4+ T lymphocytes. The results show that PTCA protected against HNE-induced apoptosis and depletion of intracellular GSH. PTCA also suppressed FasL expression through increasing levels of Akt kinase as well as antiapoptotic c-FLIP(S) and decreasing the activation of type 2 protein serine/threonine phosphatase. Taken together, these data demonstrate a novel correlation between GSH levels and Akt activation in T lymphocyte survival, which involves FasL down-regulation and c-FLIP(S) expression through increasing intracellular GSH levels. This suggests that PTCA could potentially be used in the treatment of oxidative stress-induced immunosuppressive diseases.

Proteomic Analysis Identifies Oxidative Stress Induction by Adaphostin

PURPOSE

Activities distinct from inhibition of Bcr/abl have led to adaphostin (NSC 680410) being described as "a drug in search of a mechanism." In this study, proteomic analysis of adaphostin-treated myeloid leukemia cell lines was used to further elucidate a mechanism of action.

EXPERIMENTAL DESIGN

HL60 and K562 cells treated with adaphostin for 6, 12, or 24 h were analyzed using two-dimensional PAGE. Differentially expressed spots were excised, digested with trypsin, and analyzed by liquid chromatography-tandem mass spectrometry. The contribution of the redox-active hydroquinone group in adaphostin was also examined by carrying out proteomic analysis of HL60 cells treated with a simple hydroquinone (1,4-dihydroxybenzene) or H(2)O(2).

RESULTS

Analysis of adaphostin-treated cells identified 49 differentially expressed proteins, the majority being implicated in the response to oxidative stress (e.g., CALM, ERP29, GSTP1, PDIA1) or induction of apoptosis (e.g., LAMA, FLNA, TPR, GDIS). Interestingly, modulation of these proteins was almost fully prevented by inclusion of an antioxidant, N-acetylcysteine. Validation of the proteomic data confirmed GSTP1 as an adaphostin resistance gene. Subsequent analysis of HL60 cells treated with 1,4-dihydroxybenzene or H(2)O(2) showed similar increases in intracellular peroxides and an almost identical proteomic profiles to that of adaphostin treatment. Western blotting of a panel of cell lines identified Cu/Zn superoxide dismutase (SOD) as correlating with adaphostin resistance. The role of SOD as a second adaphostin resistance gene was confirmed by demonstrating that inhibition of SOD using diethyldithiocarbamate increased adaphostin sensitivity, whereas transfection of SOD I attenuated toxicity. Importantly, treatment with 1,4-dihydroxybenzene or H(2)O(2) replicated adaphostin-induced Bcr/abl polypeptide degradation, suggesting that kinase inhibition is a ROS-dependent phenomenon.

CONCLUSION

Adaphostin should be classified as a redox-active-substituted dihydroquinone.

The kinase inhibitor sorafenib induces cell death through a process involving induction of endoplasmic reticulum stress

Sorafenib is a multikinase inhibitor that induces apoptosis in human leukemia and other malignant cells. Recently, we demonstrated that sorafenib diminishes Mcl-1 protein expression by inhibiting translation through a MEK1/2-ERK1/2 signaling-independent mechanism and that this phenomenon plays a key functional role in sorafenib-mediated lethality. Here, we report that inducible expression of constitutively active MEK1 fails to protect cells from sorafenib-mediated lethality, indicating that sorafenib-induced cell death is unrelated to MEK1/2-ERK1/2 pathway inactivation. Notably, treatment with sorafenib induced endoplasmic reticulum (ER) stress in human leukemia cells (U937) manifested by immediate cytosolic-calcium mobilization, GADD153 and GADD34 protein induction, PKR-like ER kinase (PERK) and eukaryotic initiation factor 2alpha (eIF2alpha) phosphorylation, XBP1 splicing, and a general reduction in protein synthesis as assessed by [35S]methionine incorporation. These events were accompanied by pronounced generation of reactive oxygen species through a mechanism dependent upon cytosolic-calcium mobilization and a significant decline in GRP78/Bip protein levels. Interestingly, enforced expression of IRE1alpha markedly reduced sorafenib-mediated apoptosis, whereas knockdown of IRE1alpha or XBP1, disruption of PERK activity, or inhibition of eIF2alpha phosphorylation enhanced sorafenib-mediated lethality. Finally, downregulation of caspase-2 or caspase-4 by small interfering RNA significantly diminished apoptosis induced by sorafenib. Together, these findings demonstrate that ER stress represents a central component of a MEK1/2-ERK1/2-independent cell death program triggered by sorafenib.

Pretreatment with low nitric oxide protects osteoblasts from high nitric oxide-induced apoptotic insults through regulation of c-Jun N-terminal kinase/c-Jun-mediated Bcl-2 gene expression and protein translocation

Nitric oxide (NO) can regulate osteoblast activity. In this study, we evaluated the effects of pretreatment with a low concentration of NO on osteoblast injuries induced by a high level of NO and its possible molecular mechanisms. Exposure of osteoblasts to 0.3 mM sodium nitroprusside (SNP), an NO donor, slightly increased cellular NO levels without affecting cell viability. SNP at 2 mM greatly increased the levels of cellular NO and reactive oxygen species, and induced osteoblast death. Thus, osteoblasts were treated with 0.3 and 2 mM SNP as the sources of low and high NO, respectively. Exposure of osteoblasts to high NO decreased alkaline phosphatase (ALP) activity and cell viability, and induced cell apoptosis. With low-NO pretreatment, the high NO-induced cell insults were significantly ameliorated. When the culture medium was totally replaced after pretreatment with low NO, the protective effects obviously decreased. Administration of high NO significantly decreased c-Jun N-terminal kinase (JNK) phosphorylation and nuclear c-Jun levels. Meanwhile, pretreatment with low NO significantly alleviated the high NO-induced reduction in activation of JNK and c-Jun. Sequentially, high NO inhibited Bcl-2 mRNA and protein synthesis. After pretreatment with low NO, the high NO-induced inhibition of the production of Bcl-2 mRNA and protein significantly decreased. Imaging analysis from confocal microscopy further revealed that high NO decreased translocation of the Bcl-2 protein from the cytoplasm to mitochondria. However, pretreatment with low NO significantly ameliorated the high NO-induced suppression of Bcl-2's translocation. Exposure of human osteoblasts to high NO significantly decreased ALP activity and cell viability, and induced cell apoptosis. Pretreatment with low NO significantly lowered the high NO-induced alterations in ALP activity, cell viability, and cell apoptosis. This study shows that pretreatment with low NO can protect osteoblasts from high NO-induced cell insults via JNK/c-Jun-mediated regulation of Bcl-2 gene expression and protein translocation.

Up-regulation of c-Jun inhibits proliferation and induces apoptosis via caspase-triggered c-Abl cleavage in human multiple myeloma

Here we show the antimyeloma cytotoxicity of adaphostin and carried out expression profiling of adaphostin-treated multiple myeloma (MM) cells to identify its molecular targets. Surprisingly, c-Jun was the most up-regulated gene even at the earliest point of analysis (2 h). We also observed adaphostin-induced c-Abl cleavage in immunoblot analysis. Proteasome inhibitor bortezomib, but not melphalan or dexamethasone, induced similar effects, indicating unique agent-dependent mechanisms. Using caspase inhibitors, as well as caspase-resistant mutants of c-Abl (TM-c-Abl and D565A-Abl), we then showed that c-Abl cleavage in MM cells requires caspase activity. Importantly, both overexpression of the c-Abl fragment or c-Jun and knockdown of c-Abl and c-Jun expression by small interfering RNA confirmed that adaphostin-induced c-Jun up-regulation triggers downstream caspase-mediated c-Abl cleavage, inhibition of MM cell growth, and induction of apoptosis. Finally, our data suggest that this mechanism may not only be restricted to MM but may also be important in a broad range of malignancies including erythroleukemia and solid tumors.

Inhibition of Mitochondrial Respiration as a Source of Adaphostin-induced Reactive Oxygen Species and Cytotoxicity

Adaphostin is a dihydroquinone derivative that is undergoing extensive preclinical testing as a potential anticancer drug. Previous studies have suggested that the generation of reactive oxygen species (ROS) plays a critical role in the cytotoxicity of this agent. In this study, we investigated the source of these ROS. Consistent with the known chemical properties of dihydroquinones, adaphostin simultaneously underwent oxidation to the corresponding quinone and generated ROS under aqueous conditions. Interestingly, however, this quinone was not detected in intact cells. Instead, high performance liquid chromatography demonstrated that adaphostin was concentrated by up to 300-fold in cells relative to the extracellular medium and that the highest concentration of adaphostin (3000-fold over extracellular concentrations) was detected in mitochondria. Consistent with a mitochondrial site for adaphostin action, adaphostin-induced ROS production was diminished by >75% in MOLT-4 rho(0) cells, which lack mitochondrial electron transport, relative to parental MOLT-4 cells. In addition, inhibition of oxygen consumption was observed when intact cells were treated with adaphostin. Loading of isolated mitochondria to equivalent adaphostin concentrations caused inhibition of uncoupled oxygen consumption in mitochondria incubated with the complex I substrates pyruvate and malate or the complex II substrate succinate. Further analysis demonstrated that adaphostin had no effect on pyruvate or succinate dehydrogenase activity. Instead, adaphostin inhibited reduced decylubiquinone-induced cytochrome c reduction, identifying complex III as the site of inhibition by this agent. Moreover, adaphostin enhanced the production of ROS by succinate-charged mitochondria. Collectively, these observations demonstrate that mitochondrial respiration rather than direct redox cycling of the hydroquinone moiety is a source of adaphostin-induced ROS and identify complex III as a potential target for antineoplastic agents.

Different target range and cytotoxic specificity of adaphostin and 17-allylamino-17-demethoxygeldanamycin in imatinib-resistant and sensitive cell lines

Imatinib mesylate is a selective inhibitor of the oncogenic tyrosine kinase, Bcr-Abl, and is widely used as a first-line treatment for chronic myeloid leukaemia (CML). Prolonged monotherapy is frequently associated with patients becoming refractory to imatinib. Therefore, there is considerable interest in small molecule inhibitors which may be used either as replacements or as adjuncts to existing imatinib therapy. For this purpose, it is most likely that drugs which do not share imatinib's mechanism of action will be most valuable. We compared two such compounds with different modes of action, adaphostin and 17-allylamino-17-demethoxygeldanamycin (17-AAG), for their cytotoxic effect and ability to induce the downregulation of cellular proteins in a murine haemopoietic cell line transformed with human p210(Bcr-Abl), and two subclones resistant to imatinib owing to an Abl-kinase domain mutation (E255K) or amplification of the BCR-ABL gene, respectively. We found that, whereas 17-AAG selectively killed Bcr-Abl-positive cells and inhibited proteins dependent on heat-shock protein 90 for their stability (p210(Bcr-Abl) and Akt), adaphostin induced the downregulation of multiple cell-signalling proteins (p210(Bcr-Abl), Akt, Bcr, Abl and STAT5a) and was cytotoxic to both Bcr-Abl-positive and -negative cells. We suggest that both compounds may prove useful in the treatment of CML but caution that undesirable side-effects may result from the inhibition of multiple cell signalling proteins.

Genetic and cellular toxicology of dental resin monomers

Monomers are released from dental resin materials, and thus cause adverse biological effects in mammalian cells. Cytotoxicity and genotoxicity of some of these methacrylates have been identified in a vast number of investigations during the last decade. It has been well-established that the co-monomer triethylene glycol dimethacrylate (TEGDMA) causes gene mutations in vitro. The formation of micronuclei is indicative of chromosomal damage and the induction of DNA strand breaks detected with monomers like TEGDMA and 2-hydroxyethyl methacrylate (HEMA). As a consequence of DNA damage, the mammalian cell cycle was delayed in both G1 and G2/M phases, depending on the concentrations of the monomers. Yet, the mechanisms underlying the genetic and cellular toxicology of resin monomers have remained obscure until recently. New findings indicate that increased oxidative stress results in an impairment of the cellular pro- and anti-oxidant redox balance caused by monomers. It has been demonstrated that monomers reduced the levels of the natural radical scavenger glutathione (GSH), which protects cell structures from damage caused by reactive oxygen species (ROS). Depletion of the intracellular GSH pool may then significantly contribute to cytotoxicity, because a related increase in ROS levels can activate pathways leading to apoptosis. Complementary, cytotoxic, and genotoxic effects of TEGDMA and HEMA are inhibited in the presence of ROS scavengers like N-acetylcysteine (NAC), ascorbate, and Trolox (vitamin E). Elevated intracellular levels of ROS can also activate a complex network of redox-responsive macromolecules, including redox-sensitive transcription factors like nuclear factor kappaB (NF-kappaB). It has been shown that NF-kappaB is activated probably to counteract HEMA-induced apoptosis. The induction of apoptosis by TEGDMA in human pulp cells has been associated with an inhibition of the phosphatidylinositol 3-kinase (PI3-K) cell-survival signaling pathway. Although the details of the mechanisms leading to cell death, genotoxicity, and cell-cycle delay are not completely understood, resin monomers may be able to alter the functions of the cells of the oral cavity. Pathways regulating cellular homeostasis, dentinogenesis, or tissue repair may be modified by monomers at concentrations well below those which cause acute cytotoxicity.

Adaphostin and bortezomib induce oxidative injury and apoptosis in imatinib mesylate-resistant hematopoietic cells expressing mutant forms of Bcr/Abl

Effects of the tyrphostin adaphostin and bortezomib were examined in Bcr/Abl+ leukemia cell resistant to imatinib mesylate secondary to Bcr/Abl point mutations. Adaphostin was equally effective in inducing mitochondrial damage, caspase activation, JNK activation, and Raf-1, phospho-Stat3 and -Stat5 inactivation in mutant and wild-type cells, but differentially down-regulated phospho-Bcr/Abl. Adaphostin and bortezomib synergistically induced apoptosis in wild-type and mutant cells, including T315I mutants. Notably, adaphostin+/-bortezomib potently induced ROS and lethality in mutant cells, effects attenuated by the antioxidant NAC. These findings indicate that adaphostin+/-bortezomib circumvent imatinib resistance due to Bcr/Abl point mutations most likely through ROS generation.

Molecular mechanism of adaphostin-mediated G1 arrest in prostate cancer (PC-3) cells: signaling events mediated by hepatocyte growth factor receptor, c-Met, and p38 MAPK pathways

Adaphostin (NSC680410), a small molecule congener of tyrphostin AG957, has been demonstrated previously to have significant anti-proliferative effects in several leukemia models. However, this effect of adaphostin in adherent cells/solid tumor models has not been examined. In this study, we investigated the anti-proliferative effects of adaphostin in the human prostate cancer cell line PC-3. Specifically, we explored the potential molecular mechanism(s) by which adaphostin elicits its anti-proliferative effect(s). We demonstrate that adaphostin inhibits the proliferation of PC-3 cells by inducing a G(1) phase cell cycle arrest. This adaphostin-induced G(1) arrest was associated with an increase in the expression of p21 and p27 and a decrease in the expression of G(1)-specific cyclins (cyclin A, D1, and D3) and cyclin-dependent kinases 4 and 6. Consequently, a dramatic decrease in the phosphorylation of retinoblastoma protein was also observed. Additionally, we found that adaphostin treatment induced a decrease in the phosphorylation of nucleophosmin, a major nuclear phosphoprotein, and that this decreased phosphorylation was a result of the p21- and p27-mediated inactivation of cyclin E-cyclin-dependent kinase 2 complex kinase activity. Furthermore, we have determined that the adaphostin-mediated cell cycle arrest of PC-3 cells is dependent upon activation of the p38 MAPK. We also demonstrate that the hepatocyte growth factor receptor-c-Met is involved in the adaphostin-mediated signaling events that regulate p38 MAPK. Taken together, these results identify for the first time a signaling cascade of adaphostin-mediated G(1) phase-specific cell cycle arrest in PC-3 cells. These findings suggest that the tyrphostin member has a broader spectrum of activity than originally predicted.

Adaphostin has significant and selective activity against chronic and acute myeloid leukemia cells

Adaphostin is a tyrphostin that was designed to inhibit Bcr/Abl tyrosine kinase by altering the binding site of peptide substrates rather than that of adenosine triphosphate, a known mechanism of imatinib mesylate (IM). However, it has been shown that adaphostin-mediated cytotoxicity is dependent on oxidant production and does not require Bcr/Abl. We have tested adaphostin against both Philadelphia chromosome (Ph)-positive (K562, KBM5, KBM5-R [IM resistant KBM5], KBM7, and KBM7-R [IM-resistant KBM7]) and Ph-negative (OCI/AML2 and OCI/AML3) cells, and against cells from patients with chronic myeloid leukemia (CML) and acute myeloid leukemia (AML). Adaphostin significantly inhibited growth of all cell lines (50% inhibition of cell proliferation [IC50] 0.5-1 microM) except K562 (IC50 13 microM). Ph-positive IM-resistant cell lines showed significant cross resistance to adaphostin. Simultaneous or sequential treatment with adaphostin and IM did not exert a synergistic effect in any KBM line. Adaphostin induced superoxide and apoptosis in a dose-dependent and time-dependent fashion in both Ph-positive and Ph-negative cells. Adaphostin selectively inhibited colony growth of cells from CML (IM-sensitive and IM-resistant) and AML patients. Analysis of tyrosine phosphorylated proteins after treatment with adaphostin revealed alternate effects in different cells consistent with the modulation of multiple targets. In conclusion, adaphostin showed significant and selective activity against CML and AML cells and its development for clinical testing is warranted.

Adaphostin cytoxicity in glioblastoma cells is ROS-dependent and is accompanied by upregulation of heme oxygenase-1

PURPOSE

To delineate a role for reactive oxygen species (ROS) induction in adaphostin-induced apoptosis in glioblastoma cells.

METHODS

Three glioblastoma cell lines with different sensitivities to adaphostin were characterized for sensitivity to an oxidant, tert-butyl hydroperoxide. The degree and duration of the ROS levels was assessed in the three cell lines after adaphostin exposure. Antioxidant protein levels were evaluated by Western blotting.

RESULTS

Of the three glioblastoma cell lines, the U87 cells were least sensitive to adaphostin. These cells were also least sensitive to tert-butyl hydroperoxide, indicating that sensitivity to a direct oxidant stress mirrors the cells' adaphostin sensitivities. In addition, the antioxidant N-acetylcysteine, (NAC) was protective against adaphostin-induced apoptosis. Direct measurement of intracellular peroxides showed a transient increase in the two less sensitive cell lines (U87 and LN18) which diminishes by 24 h. In contrast, U251 cells, which are most sensitive to adaphostin, display a sustained increase in the ROS levels. After the initial increase in intracellular peroxides, the heat shock protein and antioxidant heme oxygenase-1 (HO-1) was upregulated. Levels of other antioxidant proteins, such as catalase and thioredoxin, however, were not altered by adaphostin in glioblastoma cell lines. NAC attenuated HO-1 upregulation, confirming the time course analysis.

CONCLUSIONS

These results suggest a primary role for ROS in adaphostin-induced apoptosis in glioblastoma. Our data indicate that the duration of intracellular ROS levels is a key factor in mediating sensitivity to adaphostin. Furthermore, upregulation of HO-1 is a novel molecular marker of adaphostin's action. The kinetics with which adaphostin upregulates HO-1 correlates with sensitivity to the drug. Taken together, our data indicate that a cell's ability to cope with ROS dictates sensitivity to adaphostin and conceivably other chemotherapies that cause redox perturbations.

Requirement for Map2k1 (Mek1) in extra-embryonic ectoderm during placentogenesis

Map2k1(-/-) embryos die at mid-gestation from abnormal development and hypovascularization of the placenta. We now show that this phenotype is associated with a decreased labyrinth cell proliferation and an augmented cell apoptosis. Although the activation of MAP2K1 and MAP2K2 is widespread in the labyrinthine region, MAPK1 and MAPK3 activation is restricted to the cells lining the maternal sinuses, suggesting an important role for the ERK/MAPK cascade in these cells. In Map2k1(-/-) placenta, ERK/MAPK cascade activation is perturbed. Abnormal localization of the syncytiotrophoblasts is also observed in Map2k1(-/-) placenta, even though this cell lineage is specified at the correct time during placentogenesis. The placental phenotype can be rescued in tetraploid experiments. In addition, Map2k1-specific deletion in the embryo leads to normal embryo development and to the birth of viable Map2k1(-/-) mice. Altogether, these data enlighten the essential role of Map2k1 in extra-embryonic ectoderm during placentogenesis. In the embryo, the Map2k1 gene function appears dispensable.

Cigarette smoke exposure impairs VEGF-induced endothelial cell migration: role of NO and reactive oxygen species

Endothelial dysfunction is one of the earliest pathological effects of cigarette smoking. Vascular endothelial growth factor (VEGF) has been shown to be an important regulator of endothelial healing and growth. Accordingly, we tested the hypothesis that cigarette smoke exposure impairs VEGF actions in endothelial cells. In human umbilical vein endothelial cells (HUVECs), cigarette smoke extracts (CSE) inhibited VEGF-induced tube formation in the matrigel assay. CSE did not affect HUVECs proliferation, but significantly reduced cellular migration in response to VEGF. This impaired migratory activity was associated with a reduced expression of alpha(v)beta(3), alpha(v)beta(5), alpha(5)beta(1) and alpha(2)beta(1) integrins. The Akt/eNOS/NO pathway has been shown to be important for VEGF-induced endothelial cell migration. We found that CSE inhibited Akt/eNOS phosphorylation and NO release in VEGF-stimulated HUVECs. This was associated with an increased generation of reactive oxygen species (ROS). Importantly, in HUVECs exposed to CSE, treatment with antioxidants (NAC, vitamin C) reduced ROS formation and rescued VEGF-induced NO release, cellular migration and tube formation. Moreover, treatment with NO donors (SNAP, SNP) or a cGMP analog (8-Br-cGMP) rescued integrin expression, cellular migration and tube formation in endothelial cells exposed to CSE. (1) Cigarette smoke exposure impairs VEGF-induced endothelial cell migration and tube formation. (2) The mechanism involves increased generation of ROS, decreased expression of surface integrins together with a blockade of the Akt/eNOS/NO pathway. (3) These findings could contribute to explain the negative effect of cigarette smoking on endothelial function and vessel growth.

Cannabidiol-Induced Apoptosis in Human Leukemia Cells: A Novel Role of Cannabidiol in the Regulation of p22phox and Nox4 Expression

In the current study, we examined the effects of the nonpsychoactive cannabinoid, cannabidiol, on the induction of apoptosis in leukemia cells. Exposure of leukemia cells to cannabidiol led to cannabinoid receptor 2 (CB2)-mediated reduction in cell viability and induction in apoptosis. Furthermore, cannabidiol treatment led to a significant decrease in tumor burden and an increase in apoptotic tumors in vivo. From a mechanistic standpoint, cannabidiol exposure resulted in activation of caspase-8, caspase-9, and caspase-3, cleavage of poly(ADP-ribose) polymerase, and a decrease in full-length Bid, suggesting possible cross-talk between the intrinsic and extrinsic apoptotic pathways. The role of the mitochondria was further suggested as exposure to cannabidiol led to loss of mitochondrial membrane potential and release of cytochrome c. It is noteworthy that cannabidiol exposure led to an increase in reactive oxygen species (ROS) production as well as an increase in the expression of the NAD(P)H oxidases Nox4 and p22(phox). Furthermore, cannabidiol-induced apoptosis and reactive oxygen species (ROS) levels could be blocked by treatment with the ROS scavengers or the NAD(P)H oxidase inhibitors. Finally, cannabidiol exposure led to a decrease in the levels of p-p38 mitogen-activated protein kinase, which could be blocked by treatment with a CB2-selective antagonist or ROS scavenger. Together, the results from this study reveal that cannabidiol, acting through CB2 and regulation of Nox4 and p22(phox) expression, may be a novel and highly selective treatment for leukemia.

Induction of Apoptosis in Renal Cell Carcinoma by Reactive Oxygen Species: Involvement of Extracellular Signal-Regulated Kinase 1/2, p38δ/γ, Cyclooxygenase-2 Down-Regulation, and Translocation of Apoptosis-Inducing Factor

Renal cell carcinoma (RCC) is the most common malignancy of the kidney. Unfortunately, RCCs are highly refractory to conventional chemotherapy, radiation therapy, and even immunotherapy. Thus, novel therapeutic targets need to be sought for the successful treatment of RCCs. We now report that 6-anilino-5,8-quinolinequinone (LY83583), an inhibitor of cyclic GMP production, induced growth arrest and apoptosis of the RCC cell line 786-0. It did not prove deleterious to normal renal epithelial cells, an important aspect of chemotherapy. To address the cellular mechanism(s), we used both genetic and pharmacological approaches. LY83583 induced a time- and dose-dependent increase in RCC apoptosis through dephosphorylation of mitogen-activated protein kinase kinase 1/2 and its downstream extracellular signal-regulated kinases (ERK) 1 and -2. In addition, we observed a decrease in Elk-1 phosphorylation and cyclooxygenase-2 (COX-2) down-regulation. We were surprised that we failed to observe an increase in either c-Jun NH(2)-terminal kinase or p38alpha and -beta mitogen-activated protein kinase activation. In contradiction, reintroduction of p38delta by stable transfection or overexpression of p38gamma dominant negative abrogated the apoptotic effect. Cell death was associated with a decrease and increase in Bcl-x(L) and Bax expression, respectively, as well as release of cytochrome c and translocation of apoptosis-inducing factor. These events were associated with an increase in reactive oxygen species formation. The antioxidant N-acetyl l-cysteine, however, opposed LY83583-mediated mitochondrial dysfunction, ERK1/2 inactivation, COX-2 down-regulation, and apoptosis. In conclusion, our results suggest that LY83583 may represent a novel therapeutic agent for the treatment of RCC, which remains highly refractory to antineoplastic agents. Our data provide a molecular basis for the anticancer activity of LY83583.

Guggulsterones induce apoptosis and differentiation in acute myeloid leukemia: identification of isomer-specific antileukemic activities of the pregnadienedione structure

In this study, the antileukemic effects of three isomeric pregnadienedione steroids [i.e., cis-guggulsterone, trans-guggulsterone, and 16-dehydroprogesterone] were investigated in HL60 and U937 cells as well as in primary leukemic blasts in culture. Our results show that all three compounds inhibited the proliferation of HL60 and U937 cells, with IC50s ranging from 3.6 to 10.9 micromol/L after treatment for 6 days. These growth inhibitory effects correlated with externalization of phosphatidylserine and loss of mitochondrial membrane potential, suggesting that these isomeric steroids induce apoptosis in leukemia cells. z-VAD-fmk prevented phosphatidylserine externalization but not mitochondrial membrane potential loss, indicating that mitochondrial dysfunction occurred in the absence of caspase activation. Interestingly, although all three compounds increased the generation of reactive oxygen species and decreased phosphorylation of extracellular signal-regulated kinase, only cis-guggulsterone induced a rapid depletion of reduced glutathione levels and oxidation of the mitochondrial phospholipid cardiolipin. 16-Dehydroprogesterone and trans-guggulsterone induced differentiation of HL60 and NB4 cells as evidenced by increased surface expression of CD11b and/or CD14, and all three steroids rapidly induced mitochondrial dysfunction and phosphatidylserine externalization of CD34-positive blasts from primary leukemic samples. This study is the first to show that guggulsterones and 16-dehydroprogesterone exert antileukemic effects via the induction of apoptosis and differentiation and, more importantly, identifies the pregnadienedione structure as a potential chemotherapeutic scaffold.

The role of Mcl-1 downregulation in the proapoptotic activity of the multikinase inhibitor BAY 43-9006

BAY 43-9006, a multikinase inhibitor that targets Raf, prevents tumor cell proliferation in vitro and inhibits diverse human tumor xenografts in vivo. The mechanism of action of BAY 43-9006 remains incompletely defined. In the present study, the effects of BAY 43-9006 on the antiapoptotic Bcl-2 family member Mcl-1 were examined. Treatment of A549 lung cancer cells with BAY 43-9006 diminished Mcl-1 levels in a time- and dose-dependent manner without affecting other Bcl-2 family members. Similar BAY 43-9006-induced Mcl-1 downregulation was observed in ACHN (renal cell), HT-29 (colon), MDA-MB-231 (breast), KMCH (cholangiocarcinoma), Jurkat (acute T-cell leukemia), K562 (chronic myelogenous leukemia) and MEC-2 (chronic lymphocytic leukemia) cells. Mcl-1 mRNA levels did not change in BAY 43-9006-treated cells. Instead, BAY 43-9006 enhanced proteasome-mediated Mcl-1 degradation. This Mcl-1 downregulation was followed by mitochondrial cytochrome c release and caspase activation as well as enhanced sensitivity to other proapoptotic agents. The caspase inhibitor Boc-D-fmk inhibited BAY 43-9006-induced caspase activation but not cytochrome c release. In contrast, Mcl-1 overexpression inhibited cytochrome c release and other features of BAY 43-9006-induced apoptosis. Conversely, Mcl-1 downregulation by short hairpin RNA enhanced BAY 43-9006-induced apoptosis. Collectively, these findings demonstrate that drug-induced Mcl-1 downregulation contributes to the proapoptotic effects of BAY 43-9006.

Preclinical pharmacology of the novel antitumor agent adaphostin, a tyrphostin analog that inhibits bcr/abl

PURPOSE

To define several pharmacological properties for the potential anticancer agent, adaphostin, in order to determine whether the compound is appropriate for clinical evaluation as an anticancer agent.

METHODS

The analytical procedure involved high-performance liquid chromatography and utilized an analytical J'Sphere ODS H-80 column.

RESULTS

The stability of adaphostin at two different concentrations was determined at temperatures of 37 degrees C, 4 degrees C, and -80 degrees C, in the plasma of mice, rats, dogs, and humans. The compound was most stable at the lower temperatures. At all temperatures, adaphostin was generally most stable in human plasma and least stable in dog plasma. Adaphostin bound strongly (>93%) to proteins in plasma from all four species. Following intravenous (i.v.) administration to mice (50 mg/kg; 150 mg/m(2)), plasma concentrations declined rapidly from 50 microM at 2 min to 1 microM at 2 h. Elimination was triexponential, with t (1/2) values of 1.1, 9.1, and 41.2 min. The Cl(tb) was 0.411 L/(min.m(2)), the V (dss) was 24.6 L/m(2), and the AUC was 927 microM.min. In a comparison of vehicles for intraperitoneal (i.p.) dosing, PEG 300 allowed the highest plasma concentrations of adaphostin. Bioavailability following an i.p. dose was greater than that following a subcutaneous dose, or that for a dose administered by oral gavage. For rats dosed i.v. with adaphostin (50 mg/kg; 300 mg/m(2)), plasma concentrations also decreased triexponentially, with t (1/2) values of 1.8, 10.6, and 136 min. Other pharmacokinetic values were Cl(tb) = 0.466 L/(min.m(2)), AUC = 1,161 microM.min, and V (dss)=8.0 L/m(2). Analysis of samples collected from two dogs dosed i.v. with adaphostin (7.5 mg/kg; 150 mg/m(2)) showed that plasma concentrations decreased in a biphasic manner, with individual values for t (1/2alpha) of 6.0 and 9.8 min for the distribution phase and t (1/2beta) of 40.6 and 66.2 min for the elimination phase. Other pharmacokinetic values were Cl(tb) = 0.565 and 0.852 L/(min.m(2)), AUC = 673 and 446 microM min, and V (dss) = 29.6 and 56.8 L/m(2).

CONCLUSIONS

The stability of adaphostin in plasma varies with species. In mice and dogs dosed with adaphostin, plasma concentrations of the compound decreased rapidly. The clearance of adaphostin from plasma, on an m(2) basis, was equivalent for mice and rats but more rapid in dogs. These results are relevant for assessing the pharmacologic and toxicologic profiles and the antitumor activity of adaphostin in humans.

Adaphostin-induced oxidative stress overcomes BCR/ABL mutation-dependent and -independent imatinib resistance

The BCR/ABL kinase has been targeted for the treatment of chronic myelogenous leukemia (CML) by imatinib mesylate. While imatinib has been extremely effective for chronic phase CML, blast crisis CML and Ph+ acute lymphoblastic leukemia (ALL) are often resistant. In particular, mutation of the T315 residue in the bcr/abl activation loop renders cells highly resistant to imatinib and to second-generation kinase inhibitors such as BMS-354825 or AMN107. Adaphostin is a tyrphostin that was originally intended to inhibit the BCR/ABL kinase by competing with its peptide substrates. Recent findings have in addition implicated reactive oxygen species (ROS) in the cytotoxic mechanism of adaphostin. In view of this unique mode of action, we examined the effects of adaphostin on numerous imatinib-resistant leukemia models, including imatinib-resistant CML and Ph+ ALL cell lines, cells harboring point mutations in BCR/ABL, and specimens from imatinib-resistant CML patients, using assays for intracellular ROS, apoptosis, and clonogenicity. Every model of imatinib resistance examined remained fully sensitive to adaphostin-induced cell death. Collectively, these data suggest that ROS generation by adaphostin overcomes even the most potent imatinib resistance in CML and Ph+ ALL.

Inhibition of insulin/IGF-1 receptor signaling enhances bile acid toxicity in primary hepatocytes

Modulation of ERBB and insulin-like growth factor 1 (IGF-1) receptor function is recognized as a potential mechanism to inhibit tumor growth. We and others have shown that inhibition of ERBB1 can enhance bile acid toxicity. Herein, we extend our analyses to examine the impact of insulin/IGF-1 receptor inhibition on primary hepatocyte survival when exposed to the secondary bile acid deoxycholic acid (DCA) and compare the impact inhibition of this receptor has on bile acid toxicity effects to that of ERBB1/MEK1/2 inhibition. The insulin/IGF-1 receptor inhibitor NVP-ADW742 at concentrations which inhibit both the insulin and IGF-1 receptors had a modest negative impact on hepatocyte viability, and strongly potentiated DCA-induced apoptotic cell death. Identical data were obtained expressing a dominant negative IGF-1 receptor in hepatocytes; a receptor which acts to inhibit both the IGF-1 receptor and the insulin receptor in trans. Inhibition of ERBB1 function using Iressa (gefitinib) or the tyrphostin AG1478 had more modest effects at enhancing DCA lethality than inhibition of the insulin/IGF-1 receptor function. In contrast, over-expression of a dominant negative ERBB1 protein had pleiotropic effects on multiple signaling pathways in an apparently non-specific manner. These findings suggest that novel therapeutic kinase inhibitors, targeted against growth factor receptors, have the potential to promote bile acid toxicity in hepatocyte when bile flow may be impaired.

Oncogenes as novel targets for cancer therapy (part II): Intermediate signaling molecules

This is the second part of a four-part review on potential therapeutic targeting of oncogenes. The previous part introduced the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes, which we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part I included a discussion of growth factors and tyrosine kinases. This portion of the review covers intermediate signaling molecules and the various strategies used to inhibit their expression or decrease their activities.

The tyrphostin adaphostin interacts synergistically with proteasome inhibitors to induce apoptosis in human leukemia cells through a reactive oxygen species (ROS)-dependent mechanism

Interactions between the tyrphostin adaphostin and proteasome inhibitors (eg, MG-132 and bortezomib) were examined in multiple human leukemia cell lines and primary acute myeloid leukemia (AML) specimens. Cotreatment of Jurkat cells with marginally toxic concentrations of adaphostin and proteasome inhibitors synergistically potentiated mitochondrial damage (eg, cytochrome c release), caspase activation, and apoptosis. Similar interactions occurred in other human leukemia cell types (eg, U937, HL-60, Raji). These interactions were associated with a marked increase in oxidative damage (eg, ROS generation), down-regulation of the Raf/MEK/ERK pathway, and JNK activation. Adaphostin/MG-132 lethality as well as mitochondrial damage, down-regulation of Raf/MEK/ERK, and activation of JNK were attenuated by the free-radical scavenger NAC, suggesting that oxidative damage plays a functional role in antileukemic effects. Ectopic expression of Raf-1 or constitutively active MEK/ERK or genetic interruption of the JNK pathway significantly diminished adaphostin/MG-132-mediated lethality. Interestingly, enforced Raf or MEK/ERK activation partially diminished adaphostin/MG-132-mediated ROS generation, suggesting the existence of an amplification loop. Finally, the adaphostin/MG-132 regimen displayed similar toxicity toward 5 primary AML samples but not normal hematopoietic progenitors (eg, bone marrow CD34+ cells). Collectively, these findings suggest that potentiating oxidative damage by combining adaphostin with proteasome inhibitors warrants attention as an antileukemic strategy.

Transcriptional Profiling Identifies Altered Intracellular Labile Iron Homeostasis as a Contributing Factor to the Toxicity of Adaphostin: Decreased Vascular Endothelial Growth Factor Secretion Is Independent of Hypoxia-Inducible Factor-1 Regulation

PURPOSE

Adaphostin was developed as an inhibitor of the p210(bcr-abl) tyrosine kinase, but as its activity is not limited to tumor cell lines containing this translocation, transcriptional profiling was used as a tool to elucidate additional mechanisms responsible for adaphostin cytotoxicity.

EXPERIMENTAL DESIGN

Profiles of drug-induced transcriptional changes were measured in three hematopoietic cell lines following 1 and 10 micromol/L adaphostin for 2 to 6 hours and then confirmed with real-time reverse transcription-PCR (2-24 hours). These data indicated altered iron homeostasis, and this was confirmed experimentally. Alteration of vascular endothelial growth factor (VEGF) secretion through hypoxia-inducible factor-1 (HIF-1) regulation was also investigated.

RESULTS

Drug-induced genes included heat shock proteins and ubiquitins, but an intriguing response was the induction of ferritins. Measurement of the labile iron pool showed release of chelatable iron immediately after treatment with adaphostin and was quenched with the addition of an iron chelator. Pretreatment of cells with desferrioxamine and N-acetyl-cysteine reduced but did not ablate the sensitivity of the cells to adaphostin, and desferrioxamine was able to modulate adaphostin-induced activation of p38 and inactivation of AKT. VEGF secretion was shown to be reduced in cell lines after the addition of adaphostin but was not dependent on HIF-1.

CONCLUSIONS

Adaphostin-induced cytotoxicity is caused in part by a rapid release of free iron, leading to redox perturbations and cell death. Despite this, reduced VEGF secretion was found to be independent of regulation by the redox responsive transcription factor HIF-1. Thus, adaphostin remains an interesting agent with the ability to kill tumor cells directly and modulate angiogenesis.