Potent antileukemic interactions between flavopiridol and TRAIL/Apo2L involve flavopiridol-mediated XIAP downregulation

Heightened JNK Activation and Reduced XIAP Levels Promote TRAIL and Sunitinib-Mediated Apoptosis in Colon Cancer Models

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis that may be a promising agent in cancer therapy due to its selectivity toward tumor cells. However, many cancer cells are resistant to TRAIL due to defects in apoptosis signaling or activation of survival pathways. We hypothesized that a disruption of pro-survival signaling cascades with the multi-tyrosine kinase inhibitor sunitinib and would be an effective strategy to enhance TRAIL-mediated apoptosis. Here we demonstrate that sunitinib significantly augments the anticancer activity of TRAIL in models of colon cancer. The therapeutic benefit of the TRAIL/sunitinib combination was associated with increased apoptosis marked by enhanced caspase-3 cleavage and DNA fragmentation. Overexpression of the anti-apoptotic factor B-cell lymphoma 2 (BCL-2) in HCT116 cells reduced TRAIL/sunitinib-mediated apoptosis, further supporting that sunitinib enhances the anticancer activity of TRAIL via augmented apoptosis. Analysis of pro-survival factors identified that the combination of TRAIL and sunitinib significantly downregulated the anti-apoptotic protein X-linked inhibitor of apoptosis protein (XIAP) through a c-Jun N-terminal kinase (JNK)-mediated mechanism. Short hairpin RNA (shRNA)-mediated knockdown of JNK confirmed its key role in the regulation of sensitivity to this combination as cells with suppressed JNK expression exhibited significantly reduced TRAIL/sunitinib-mediated apoptosis. Importantly, the therapeutic benefit of the TRAIL/sunitinib combination was validated in the HCT116-Luc and HCT15 colon cancer xenograft models, which both demonstrated significant anti-tumor activity in response to combination treatment. Collectively, our data demonstrate that sunitinib enhances TRAIL-mediated apoptosis by heightened JNK activation, diminished XIAP levels, and augmented apoptosis.

Sea Cucumber (Stichopus japonicas) F2 Enhanced TRAIL-Induced Apoptosis via XIAP Ubiquitination and ER Stress in Colorectal Cancer Cells

Natural products have shown great promise in sensitizing cells to TNF-related apoptosis-inducing ligand (TRAIL) therapy. Sea cucumber (SC) extracts possess antitumor activity, and hence their potential to sensitize colorectal cancer (CRC) cells to TRAIL therapy was evaluated. This study used Western blotting to evaluate the combination effects of SC and TRAIL in CRC, and determined the molecular mechanism underlying these effects. SC fractions and TRAIL alone did not affect apoptosis; however, combined treatment dramatically induced the apoptosis of CRC cells, but not of normal colon cells. Combined treatment induced the expression of apoptotic proteins (poly (ADP-ribose) polymerase (PARP), caspase 3, and 8), and this effect was markedly inhibited by the ubiquitination of X-linked inhibitor of apoptosis protein (XIAP). SC did not affect the mRNA levels, but it increased proteasomal degradation and ubiquitination of the XIAP protein. Furthermore, SC induced reactive oxygen species (ROS) production, thereby activating c-Jun N-terminal kinase (JNK) and endoplasmic reticulum (ER) stress-related apoptotic pathways in CRC. Altogether, our results demonstrate that the SC F2 fraction may sensitize CRC cells to TRAIL-induced apoptosis through XIAP ubiquitination and ER stress.

Myeloid cell leukemia-1 dependence in acute myeloid leukemia: a novel approach to patient therapy

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults, affecting approximately 21,000 people annually (nearly 11,000 deaths) in the United States. B-cell lymphoma 2 (BCL-2) family proteins, notably myeloid cell leukemia-1 (MCL-1), have been associated with both the development and persistence of AML. MCL-1 is one of the predominant BCL-2 family members expressed in samples from patients with untreated AML. MCL-1 is a critical cell survival factor for cancer and contributes to chemotherapy resistance by directly affecting cell death pathways. Here, we review the role of MCL-1 in AML and the mechanisms by which the potent cyclin-dependent kinase 9 inhibitor alvocidib, through regulation of MCL-1, may serve as a rational therapeutic approach against the disease.

Leukemia therapy by flavonoids: Future and involved mechanisms

Flavonoids are a varied family of phytonutrients (plant chemicals) usually are detected in fruits and vegetables. In this big family, there exist more than 10,000 members that is separated into six chief subtypes: isoflavonols, flavonoenes, flavones, flavonols, anthocyanins, and chalcones. The natural compounds, such as fruits, have visible positive effects in regulating of survival involved signaling pathways that performance as the regulator of cell survival, growth, and proliferation. Researchers have established that commonly consumption up flavonoids decreases incidence and development risk of certain cancers, especially leukemia. Flavonoids have been able to induce apoptosis and stimulate cell cycle arrest in cancer cells via different pathways. Similarly, they have antiangiogenesis and antimetastasis capability, which were shown in wide ranges of cancer cells, particularly, leukemia. It seems that flavonoid because of their widespread approval, evident safety and low rate of side effects, have hopeful anticarcinogenic potential for leukemia therapy. Based on the last decade reports, the most important acting mechanisms of these natural compounds in leukemia cells are stimulating of apoptosis pathways by upregulation of caspase 3, 8, 9 and poly ADP-ribose polymerase (PARP) and proapoptotic proteins, particularly Bax activation. As well, they can induce cell cycle arrest in target cells not only via increasing of activated levels of p21 and p53 but also by inhibition of cyclins and cyclin-dependent kinases. Furthermore, attenuation of neclear factor-κB and signal transducer and activator of transcription 3 activation, suppression of signaling pathway and downregulation of intracellular antiapoptotic proteins are other significant antileukemic function mechanism of flavonoids. Overall, it appears that flavonoids are promising and effective compounds in the field of leukemia therapy. In this review, we tried to accumulate and revise most promising flavonoids and finally declared their major working mechanisms in leukemia cells.

Ibulocydine sensitizes human hepatocellular carcinoma cells to TRAIL-induced apoptosis via calpain-mediated Bax cleavage

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells without affecting the majority of normal human cells. However, hepatocellular carcinoma (HCC) cells often display resistance to TRAIL-induced apoptosis. Ibulocydine (IB) is an isobutyrate ester pro-drug of a novel synthetic Cdk inhibitor that targets Cdk7 and Cdk9. In this study, we show that treatment with subtoxic doses of IB in combination with TRAIL displays potent cytotoxicity in TRAIL-resistant human HCC cells. Combination of IB and TRAIL was found to synergistically induce apoptosis through activation of caspases, which was blocked by a pan-caspase inhibitor (zVAD). Although the expression of Mcl-1 and survivin were reduced by IB plus TRAIL, overexpression of Mcl-1 and survivin did not block the cell death induced by co-treatment. Moreover, overexpression of Bcl-xL did not significantly interfere with the cell death induced by co-treatment of IB and TRAIL. Interestingly, the combination treatment induced cleavage of Bax, which was translocated to mitochondria upon induction of apoptosis. Furthermore, down-regulation of Bax by small interfering RNA effectively reduced the cell death and loss of mitochondrial membrane potential (MMP) caused by co-treatment with IB and TRAIL. Finally, pre-treatment of HCC cells with a calpain inhibitor effectively blocked IB plus TRAIL-induced cleavage of Bax and apoptosis. Collectively, our results demonstrate that IB increases the sensitivity of human HCC cells to TRAIL via mitochondria signaling pathway mediated by calpain-induced cleavage of Bax, suggesting that combined treatment with IB and TRAIL may offer an effective therapeutic strategy for human HCC.

TRAIL-coated lipid-nanoparticles overcome resistance to soluble recombinant TRAIL in non-small cell lung cancer cells

PURPOSE

Non-small cell lung cancer (NSCLC) is one the types of cancer with higher prevalence and mortality. Apo2-Ligand/TRAIL is a TNF family member able to induce apoptosis in tumor cells but not in normal cells. It has been tested in clinical trials against different types of human cancer including NSCLC. However, results of clinical trials have shown a limited efficacy of TRAIL-based therapies. Recently we have demonstrated that artificial lipid nanoparticles coated with bioactive Apo2L/TRAIL (LUV-TRAIL) greatly improved TRAIL cytotoxic ability being capable of killing chemoresistant hematological cancer cells. In the present work we have extended the study to NSCLC.

METHODS/PATIENTS

LUV-TRAIL-induced cytotoxicity was assessed on different NSCLC cell lines with different sensitivity to soluble TRAIL and on primary human tumor cells from three patients suffering from NSCLC cancer. We also tested LUV-TRAIL-cytotoxic ability in combination with several anti-tumor agents.

RESULTS

LUV-TRAIL exhibited a greater cytotoxic effect compared to soluble TRAIL both in A549 cells and primary human NSCLC cells. LUV-TRAIL-induced cell death was dependent on caspase-8 and caspase-3 activation. Moreover, combination of LUV-TRAIL with other anti-tumor agents such as flavopiridol, and SNS-032 clearly enhanced LUV-TRAIL-induced cytotoxicity against NSCLC cancer cells.

CONCLUSION

The novel formulation of TRAIL based on displaying it on the surface of lipid nanoparticles greatly increases its anti-tumor activity and has clinical potential in cancer treatment.

Reduction of phosphorylated Thr-161 Cdk1 level participates in roscovitine-induced Fas ligand-mediated apoptosis in rat eggs cultured in vitro

The present study was aimed to find out whether roscovitine reduces phosphorylated Thr-161 of cyclin-dependent kinase 1 (Cdk1) level and induces egg apoptosis through Fas ligand (FasL)-mediated pathway. For this purpose, ovulated eggs were cultured in media 199 with or without various concentrations of roscovitine (0, 25, 50, 100, 200 μM) for 3 h in vitro. The morphological apoptotic changes, phosphorylation status of Cdk1, FasL concentration, caspase-8 and caspase-3 activities, and DNA fragmentation were analyzed. Data of the present study suggest that roscovitine significantly reduced Thr-161 phosphorylated Cdk1 level without altering the total level of Cdk1 and induced cytoplasmic fragmentation, a morphological apoptotic feature in a concentration-dependent manner. The roscovitine-induced cytoplasmic fragmentation was associated with increased FasL concentration. The increased FasL concentration induced caspase-8 followed by caspase-3 activities. The increased caspases activity finally induced DNA fragmentation in eggs that showed cytoplasmic fragmentation. Taken together, these results suggest that roscovitine reduced phosphorylated Thr-161 of Cdk1 level and induces apoptosis through FasL-mediated pathway in rat eggs cultured in vitro.

The Gβ5 protein regulates sensitivity to TRAIL-induced cell death in colon carcinoma

Aberrant signaling via G protein-coupled receptors (GPCRs) is implicated in numerous diseases including colon cancer. The heterotrimeric G proteins transduce signals from GPCRs to various effectors. So far, the G protein subunit Gβ5 has not been studied in the context of cancer. Here we demonstrate that Gβ5 protects colon carcinoma cells from apoptosis induced by the death ligand TRAIL via different routes. The Gβ5 protein (i) causes a decrease in the cell surface expression of the TRAIL-R2 death receptor, (ii) induces the expression of the anti-apoptotic protein XIAP and (iii) activates the NF-κB signaling pathway. The intrinsic resistance to TRAIL-triggered apoptosis of colon cancer cells is overcome by antagonization of Gβ5. Based on these results, targeting of G proteins emerges as a novel therapeutic approach in the experimental treatment of colon cancer.

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.

p70S6 kinase is a target of the novel proteasome inhibitor 3,3'-diamino-4'-methoxyflavone during apoptosis in human myeloid tumor cells

Acute myeloid leukemia (AML) is a deadly disease characterized by the clonal expansion and accumulation of hematopoietic stem cells arrested at various stages of development. Clinical research efforts are currently focusing on targeted therapies that induce apoptosis in AML cells. Herein, the effects and mechanisms of the novel flavone 3,3'-diamino-4'-methoxyflavone (DD1) on AML cell dysfunction were investigated in AML cells (monoblast U937, myelomonocyte OCI-AML3, promyelocyte NB4, myeloblast HL-60) and blood samples from patients with AML. The administration of DD1 inhibited proliferation and induced death of AML cell lines and reduced the clonogenic activity of AML, but not normal, blood cells. The flavone's apoptotic action in U937 cells was associated with recruitment of mitochondria, Bax activation, Bad dephosphorylation (at Ser(136)), activation of caspases -8, -9, and -3 and cleavage of the caspase substrate PARP-1. DD1 induced a marked decrease in (i) Thr(389)-phosphorylation and (ii) protein levels of the caspase-3 substrate P70 ribosomal S6 kinase (P70S6K, known for its ability to phosphorylate Bad). Caspase-dependent apoptosis and P70S6K degradation were simultaneously prevented by the caspase inhibitors. Importantly, DD1 was shown to directly inhibit the proteasome's chymotrypsin-like activity in U937 cells. Apoptotic activity of the proteasome inhibitor bortezomib was also related to Bax activation and P70S6K downregulation. Accordingly, DD1 failed to induce P70S6K cleavage, Bax stimulation and apoptosis in K562 cells resistant to bortezomib. These results indicate that DD1 has the potential to eradicate AML cells and support a critical role for Bax and P70S6K in DD1-mediated proteasome inhibition and apoptosis of leukemia cells.

Treatment of malignant melanoma by downregulation of XIAP and overexpression of TRAIL with a conditionally replicating oncolytic adenovirus

BACKGROUND AND AIM

Currently available systemic therapies for malignant melanoma produce low response rates in patients, and more effective treatment modalities are clearly needed. The tumor necrosis factor (TNF)- related apoptosis-inducing ligand has a significant impact on therapy for patients with X-linked inhibitor of apoptosis protein-downregulation malignant melanoma. The primary objective of this study was to assess its therapeutic potential.

MATERIALS AND METHODS

We employed a conditionally replicating oncolytic adenoviral vector, named CRAd5.TRAIL/siXIAP, with the characteristics of over-expression of the therapeutic gene TRAIL and downregulation of XIAP in one vector. B16F10-luc cells were employed to detect anti-tumor activity of CRAd5.TRAIL/siXIAP in vitro and in vivo.

RESULTS

CRAd5.TRAIL/siXIAP enhanced caspase-8 activation and caspase-3 maturation in B16F10 cells in vitro. Furthermore, it more effectively infected and killed melanoma cells in vitro and in vivo than other adenoviruses.

CONCLUSION

Taken together, the combination of upregulation of TRAIL and downregulation of siXIAP with one oncolytic adenoviral vector holds promise for development of an effective therapy for melanomas and other common cancers.

Vinblastine sensitizes leukemia cells to cyclin-dependent kinase inhibitors, inducing acute cell cycle phase-independent apoptosis

The efficacy of many chemotherapeutic agents can be attenuated by expression of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Mcl-1. Flavopiridol and dinaciclib are cyclin-dependent kinase 7 and 9 inhibitors that transcriptionally inhibit expression of Mcl-1. We have investigated the ability of flavopiridol and dinaciclib to sensitize a panel of leukemia cell lines to vinblastine and paclitaxel. Both drugs acutely sensitized most of the leukemia lines to vinblastine, with 100% apoptosis in 4 h. Furthermore, dinaciclib sensitized freshly isolated chronic lymphocytic leukemia cells to vinblastine. This rapid induction of apoptosis was attributed to vinblastine-mediated activation of JNK because (a) flavopiridol and dinaciclib failed to induce apoptosis when combined with non-JNK activating concentrations of vinblastine; (b) JNK inhibitors suppressed JNK activity and prevented apoptosis; (c) flavopiridol did not potentiate apoptosis induced by paclitaxel which does not activate JNK in these cells; and (d) Jurkat cells failed to activate JNK in response to vinblastine and were not sensitive to combinations of vinblastine and flavopiridol or dinaciclib. The rapid induction of apoptosis by this combination in multiple cell systems but not in normal lymphocytes provides justification for performing a clinical trial to assess the efficacy in patients.

Combined modality therapy with TRAIL or agonistic death receptor antibodies

Molecularly targeted therapies, such as antibodies and small molecule inhibitors have emerged as an important breakthrough in the treatment of many human cancers. One targeted therapy under development is tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) due to its ability to induce apoptosis in a variety of human cancer cell lines and xenografts, while lacking toxicity in most normal cells. TRAIL and apoptosis-inducing agonistic antibodies to the TRAIL death receptors have been the subject of many preclinical and clinical studies in the past decade. However, the sensitivity of individual cancer cell lines of a particular tumor type to these agents varies from highly sensitive to resistant. Various chemotherapy agents have been shown to enhance the apoptosis-inducing capacity of TRAIL receptor-targeted therapies and induce sensitization of TRAIL-resistant cells. This review provides an overview of the mechanisms associated with chemotherapy enhancement of TRAIL receptor-targeted therapies including modulation of the apoptotic (death receptor expression, FLIP, and Bcl-2 or inhibitors of apoptosis (IAP) families) as well as cell signaling (NFκB, Akt, p53) pathways. These mechanisms will be important in establishing effective combinations to pursue clinically and in determining relevant targets for future cancer therapies.

Combining naturally occurring polyphenols with TNF-related apoptosis-inducing ligand: a promising approach to kill resistant cancer cells?

TNF-related apoptosis-inducing ligand (TRAIL) and its receptors are attractive targets for anticancer therapy owing to their ability to trigger apoptosis selectively in cancer cells but not in normal cells. To date, many combinatorial strategies, such as chemotherapy or radiotherapy, have given encouraging results for overcoming TRAIL resistance in preclinical models. In this review, we provide an overview of the molecular mechanisms underlying sensitization to TRAIL-induced apoptosis by polyphenols. These naturally occurring compounds can restore tumor cell sensitivity to TRAIL-induced cell death with no apparent toxicity towards normal cells. Both extrinsic and intrinsic pathways can be modulated by polyphenols, the activation of which largely depends on the cell type, the particular polyphenolic compound, and the conditions of treatment. The large variety of polyphenol cellular targets could prove useful in circumventing TRAIL resistance. The relevance of these combined treatments for cancer therapy is discussed in the light of recent preclinical studies.

Fragment-based design of small molecule X-linked inhibitor of apoptosis protein inhibitors

We report on a general structure- and NMR-based approach to derive druglike small molecule inhibitors of protein-protein interactions in a rapid and efficient manner. We demonstrate the utility of the approach by deriving novel and effective SMAC mimetics targeting the antiapoptotic protein X-linked inhibitor of apoptosis protein (XIAP). The XIAP baculovirus IAP repeat 3 (Bir3) domain binds directly to the N-terminal of caspase-9, thus inhibiting programmed cell death. It has been shown that in the cell this interaction can be displaced by the protein second mitochondrial activator of caspases (SMAC) and that its N-terminal tetrapeptide region (NH2-AVPI, Ala-Val-Pro-Ile) is responsible for this activity. However, because of their limited cell permeability, synthetic SMAC peptides are inefficient when tested in cultured cells, limiting their use as potential chemical tools or drug candidates against cancer cells. Hence, as an application, we report on the derivation of novel, selective, druglike, cell permeable SMAC mimics with cellular activity.

New therapeutic strategies in acute lymphoblastic leukemia

While cure rates of over 80% are achieved in contemporary pediatric acute lymphoblastic leukemia (ALL) protocols, most adults with ALL succumb to their disease, and little progress has been made in the treatment of refractory and relapsed ALL. Moreover, the burden of therapy is high in a significant number of newly diagnosed patients, and in all those with relapse. Early response to therapy measured by minimal residual disease evaluation has proven the single most important prognostic factor and is increasingly used in risk stratification. However, as the benefit from intensification of frontline therapy becomes limiting, it becomes increasingly challenging to rescue patients who fail on contemporary risk-adapted protocols. New therapeutic strategies are needed, not only in salvage regimens but also in frontline protocols for patients who are at high risk of relapse. Current novel approaches include new formulations of existing chemotherapeutic agents, new antimetabolites and nucleoside analogs, monoclonal antibodies against leukemic-associated antigens, cellular immunotherapy, and molecular therapeutics. Some have already been adopted into standard regimens, while others remain in early stages of development. This review summarizes the current status of these novel therapies as they get integrated into ALL regimens.

The TRAIL apoptotic pathway in cancer onset, progression and therapy

Triggering of tumour cell apoptosis is the foundation of many cancer therapies. Death receptors of the tumour necrosis factor (TNF) superfamily have been largely characterized, as have the signals that are generated when these receptors are activated. TNF-related apoptosis-inducing ligand (TRAIL) receptors (TRAILR1 and TRAILR2) are promising targets for cancer therapy. Herein we review what is known about the molecular control of TRAIL-mediated apoptosis, the role of TRAIL in carcinogenesis and the potential therapeutic utility of recombinant TRAIL and agonistic antibodies against TRAILR1 and TRAILR2.

Roscovitine sensitizes breast cancer cells to TRAIL-induced apoptosis through a pleiotropic mechanism

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/APO2L) is a member of the TNF gene superfamily that induces apoptosis upon engagement of cognate death receptors. While TRAIL is relatively non-toxic to normal cells, it selectively induces apoptosis in many transformed cells. Nevertheless, breast tumor cells are particularly resistant to the effects of TRAIL. Here we report that, in combination with the cyclin-dependent kinase inhibitor roscovitine, exposure to TRAIL induced marked apoptosis in the majority of TRAIL-resistant breast cancer cell lines examined. Roscovitine facilitated TRAIL death-inducing signaling complex formation and the activation of caspase-8. The cFLIP(L) and cFLIP(S) FLICE-inhibitory proteins were significantly down-regulated following exposure to roscovitine and, indeed, the knockdown of cFLIP isoforms by siRNA sensitized breast tumor cells to TRAIL-induced apoptosis. In addition, we demonstrate that roscovitine strongly suppressed Mcl-1 expression and up-regulated E2F1 protein levels in breast tumor cells. Significantly, the silencing of Mcl-1 by siRNA sensitized breast tumor cells to TRAIL-induced apoptosis. Furthermore, the knockdown of E2F1 protein by siRNA reduced the sensitizing effect of roscovitine in TRAIL-induced apoptosis. In summary, our results reveal a pleitropic mechanism for the pro-apoptotic influence of roscovitine, highlighting its potential as an antitumor agent in breast cancer in combination with TRAIL.

Targeting MET transcription as a therapeutic strategy in multiple myeloma

Multiple myeloma (MM) is an incurable indolent malignancy with an average lifespan of 3 years, underscoring the need for new therapies. Studies have shown that the receptor MET and its ligand hepatocyte growth factor play an important role in proliferation, migration, adhesion, and survival of MM cells. Hence, an effective way to decrease MET receptor may act as a viable therapeutic option. Since MET mRNA and protein have short half-lives, we hypothesized that transcription inhibitor will reduce MET transcript and protein levels and this will lead to cell death. Pharmacological (flavopiridol) and molecular (shRNA) transcription inhibitor were used to impede formation of MET transcripts. The diminution of global RNA synthesis with flavopiridol was related to phosphorylation status of Ser residues (r (2) = 0.90 and 0.92 for Ser2 and Ser5) on the C-terminal-domain of RNA polymerase II. This was accompanied with a time-dependent decrease in MET transcript, which reached to less than 30% (1 microM) and 10% (3 microM) by 24 h. This decline in transcript level was directly associated with a reduction in MET protein level (r (2) = 0.82) and resulted in cell death. Assessment of MET in MM survival was done by using shRNA targeted towards MET. When cells were infected with shRNA viral construct, there was increased cell death with a decline in MET transcript and protein. Taken together, our study demonstrates that MET plays a critical role in the survival and removal or lowering of MET by flavopiridol or shRNA results in the demise of MM cells.

Triptolide sensitizes AML cells to TRAIL-induced apoptosis via decrease of XIAP and p53-mediated increase of DR5

Acute myeloid leukemia (AML) cells are relatively resistant to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL). We previously reported that triptolide, a potent anticancer agent from a Chinese herb, decreases XIAP in leukemic cells. We evaluated the combination of triptolide and TRAIL and found synergistic promotion of apoptosis in AML cells. XIAP-overexpressing U937 cells (U937XIAP) were more resistant to TRAIL than U937neo cells, and inhibition of XIAP with the small-molecule inhibitor 1396-11 enhanced TRAIL-induced apoptosis, implying XIAP as a resistance factor in AML. Furthermore, triptolide increased DR5 levels in OCI-AML3, while the DR5 increase was blunted in p53-knockdown OCI-AML3 and p53-mutated U937 cells, confirming a role for p53 in the regulation of DR5. In support of this finding, disruption of MDM2-p53 binding with subsequent increase in p53 levels by nutlin3a increased DR5 levels and sensitized OCI-AML3 cells to TRAIL. The combination of 1396-11 plus nutlin3a plus TRAIL was more effective than either the 1396-11 and TRAIL or nutlin3a and TRAIL combinations in OCI-AML3 cells, further supporting the role of triptolide as a sensitizer to TRAIL-induced apoptosis in part by independent modulation of XIAP expression and p53 signaling. Thus, the combination of triptolide and TRAIL may provide a novel strategy for treating AML by overcoming critical mechanisms of apoptosis resistance.

Flavopiridol induces cellular FLICE-inhibitory protein degradation by the proteasome and promotes TRAIL-induced early signaling and apoptosis in breast tumor cells

The cyclin-dependent kinase inhibitor flavopiridol is undergoing clinical trials as an antitumor drug. We show here that pretreatment of different human breast cancer cell lines with flavopiridol facilitates tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. In breast tumor cells, apoptosis induction by TRAIL is blocked at the level of apical caspase-8 activation. Flavopiridol treatment enhances TRAIL-induced formation of death-inducing signaling complex and early processing of procaspase-8. Subsequently, a TRAIL-induced, mitochondria-operated pathway of apoptosis is activated in cells treated with flavopiridol. Down-regulation of cellular FLICE-inhibitory proteins (c-FLIP; c-FLIP(L) and c-FLIP(S)) is observed on flavopiridol treatment. c-FLIP loss and apoptosis sensitization by flavopiridol are both prevented in cells treated with an inhibitor of the ubiquitin-proteasome system. Furthermore, targeting c-FLIP directly with small interfering RNA oligonucleotides also sensitizes various human breast tumor cell lines to TRAIL-induced apoptosis. Our results indicate that flavopiridol sensitizes breast cancer cells to TRAIL-induced apoptosis by facilitating early events in the apoptotic pathway, and this combination treatment could be regarded as a potential therapeutic tool against breast tumors.

Mechanism and functional role of XIAP and Mcl-1 down-regulation in flavopiridol/vorinostat antileukemic interactions

The mechanism and functional significance of XIAP and Mcl-1 down-regulation in human leukemia cells exposed to the histone deacetylase inhibitor vorinostat and the cyclin-dependent kinase inhibitor flavopiridol was investigated. Combined exposure of U937 leukemia cells to marginally toxic concentrations of vorinostat and flavopiridol resulted in a marked increase in mitochondrial damage and apoptosis accompanied by pronounced reductions in XIAP and Mcl-1 mRNA and protein. Down-regulation of Mcl-1 and XIAP expression by vorinostat/flavopiridol was associated with enhanced inhibition of phosphorylation of RNA polymerase II and was amplified by caspase-mediated protein degradation. Chromatin immunoprecipitation analysis revealed that XIAP and Mcl-1 down-regulation were also accompanied by both decreased association of nuclear factor-kappaB (XIAP) and increased E2F1 association (Mcl-1) with their promoter regions, respectively. Ectopic expression of Mcl-1 but not XIAP partially protected cells from flavopiridol/vorinostat-mediated mitochondrial injury at 48 h, but both did not significantly restored clonogenic potential. Flavopiridol/vorinostat-mediated transcriptional repression of XIAP, Mcl-1-enhanced apoptosis, and loss of clonogenic potential also occurred in primary acute myelogenous leukemia (AML) blasts. Together, these findings indicate that transcriptional repression of XIAP and Mcl-1 by flavopiridol/vorinostat contributes functionally to apoptosis induction at early exposure intervals and raise the possibility that expression levels may be a useful surrogate marker for activity in current trials.

Arsenic trioxide sensitizes promonocytic leukemia cells to TNFα-induced apoptosis via p38-MAPK-regulated activation of both receptor-mediated and mitochondrial pathways

Treatment with the anti-leukemic drug arsenic trioxide (As(2)O(3), 1-4 microM) sensitizes U937 promonocytes and other human myeloid leukemia cell lines (HL60, NB4) to apoptosis induction by TNFalpha. As(2)O(3) plus TNFalpha increases TNF receptor type 1 (TNF-R1) expression, decreases c-FLIP(L) expression, and causes caspase-8 and Bid activation, and apoptosis is reduced by anti-TNF-R1 neutralizing antibody and caspase-8 inhibitor. The treatment also causes Bax translocation to mitochondria, cytochrome c and Omi/HtrA2 release from mitochondria, XIAP down-regulation, and caspase-9 and caspase-3 activation. Bcl-2 over-expression inhibits cytochrome c release and apoptosis, and also prevents c-FLIP(L) down-regulation and caspase-8 activation, but not TNF-R1 over-expression. As(2)O(3) does not affect Akt phosphorylation/activation or intracellular GSH content, nor prevents the TNFalpha-provoked stimulation of p65-NF-kappaB translocation to the nucleus and the increase in NF-kappaB binding activity. Treatments with TNFalpha alone or with As(2)O(3) plus TNFalpha cause TNF-R1-mediated p38-MAPK phosphorylation/activation. P38-MAPK-specific inhibitors attenuate the As(2)O(3) plus TNFalpha-provoked activation of caspase-8/Bid, Bax translocation, cytochrome c release, and apoptosis induction. In conclusion, the sensitization by As(2)O(3) to TNFalpha-induced apoptosis in promonocytic leukemia cells is an Akt/NF-kappaB-independent, p38-MAPK-regulated process, which involves the interplay of both the receptor-mediated and mitochondrial executioner pathways.

Sphingolipids and the sphingosine kinase inhibitor, SKI II, induce BCL-2-independent apoptosis in human prostatic adenocarcinoma cells

BACKGROUND

Elevated BCL-2 is one mechanism of therapeutic resistance in prostate cancer (PC), and new approaches are needed to overcome such resistance.

METHODS

We evaluated the effects of BCL-2 over-expression in human prostatic adenocarcinoma cells on their susceptibility to sphingolipids (SLs) and to the sphingosine kinase (SpK) inhibitor, SKI II.

RESULTS

In survival assays, no significant differences were observed in the responses to sphingosine or ceramide among parental PC-3 cells lacking detectable BCL-2 and BCL-2 over-expressing PC-3 transfectants; similarly, the responses to dimethyl-sphingosine (DMSP) of parental LNCaP cells and a BCL-2 over-expressing LNCaP transfectant were equivalent. SKI II induced protracted, BCL-2-independent survival loss in both PC-3 and LNCaP parental/transfectant pairs; in contrast, DMSP induced rapid cell shrinkage, caspase activation and caspase-dependent DNA fragmentation. DMSP-induced DNA fragmentation and loss of mitochondrial membrane potential were equivalent in BCL-2 transfectants and parental PC-3 cells and were not associated with BCL-2 downregulation. DMSP-mediated cytotoxicity was not associated with the enhanced production of reactive oxygen intermediates. SL analyses of parental and transfectant PC-3 cells did not reveal increased levels of sphingosine-1-phosphate in the BCL-2 transfectants; further, there only a modest early shift, corresponding to apoptotic onset, in pro- versus anti-apoptotic SLs in response to DMSP treatment.

CONCLUSIONS

Thus, in contrast to the inhibitory effects of BCL-2 on apoptosis induced by various agents in tumor cells, SKI II and selected pro-apoptotic SLs appear atypical in their independence from such inhibition, and may have merits as new candidates for treatment of AI PC.

The multikinase inhibitor sorafenib potentiates TRAIL lethality in human leukemia cells in association with Mcl-1 and cFLIPL down-regulation

Interactions between the multikinase inhibitor sorafenib and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were examined in malignant hematopoietic cells. Pretreatment (24 h) of U937 leukemia cells with 7.5 micromol/L sorafenib dramatically increased apoptosis induced by sublethal concentrations of TRAIL/Apo2L (75 ng/mL). Similar interactions were observed in Raji, Jurkat, Karpas, K562, U266 cells, primary acute myelogenous leukemia blasts, but not in normal CD34+ bone marrow cells. Sorafenib/TRAIL-induced cell death was accompanied by mitochondrial injury and release of cytochrome c, Smac, and AIF into the cytosol and caspase-9, caspase-3, caspase-7, and caspase-8 activation. Sorafenib pretreatment down-regulated Bcl-xL and abrogated Mcl-1 expression, whereas addition of TRAIL sharply increased Bid activation, conformational change of Bak (ccBak) and Bax (ccBax), and Bax translocation. Ectopic Mcl-1 expression significantly attenuated sorafenib/TRAIL-mediated lethality and dramatically reduced ccBak while minimally affecting levels of ccBax. Similarly, inhibition of the receptor-mediated apoptotic cascade with a caspase-8 dominant-negative mutant significantly blocked sorafenib/TRAIL-induced lethality but not Mcl-1 down-regulation or Bak/Bax conformational change, indicating that TRAIL-mediated receptor pathway activation is required for maximal lethality. Sorafenib/TRAIL did not increase expression of DR4/DR5, or recruitment of procaspase-8 or FADD to the death-inducing signaling complex (DISC), but strikingly increased DISC-associated procaspase-8 activation. Sorafenib also down-regulated cFLIP(L), most likely through a translational mechanism, in association with diminished eIF4E phosphorylation, whereas ectopic expression of cFLIP(L) significantly reduced sorafenib/TRAIL lethality. Together, these results suggest that in human leukemia cells, sorafenib potentiates TRAIL-induced lethality by down-regulating Mcl-1 and cFLIP(L), events that cooperate to engage the intrinsic and extrinsic apoptotic cascades, culminating in pronounced mitochondrial injury and apoptosis.

Immunohistochemical detection of the X-linked inhibitor of apoptosis protein (XIAP) in cervical squamous intraepithelial neoplasia and squamous carcinoma

Premalignant and invasive squamous lesions of the uterine cervix were surveyed for the immunohistochemical detectability of the X-linked inhibitor of apoptosis protein (XIAP), believed to be the most potent of a novel group of proteins designated inhibitor of apoptosis proteins (IAPs). IAPs bind and prevent the activation of apoptosis-mediating caspases. Recent cancer biologic studies have implicated IAPs in therapeutic resistance and tumor aggressiveness. XIAP in particular is considered a highly promising target for drug discovery. Forty-four formalin-fixed and paraffin-embedded archival tissue sections were deparaffinized; subjected to citrate-based antigen retrieval; and immunostained with anti-XIAP monoclonal antibody (clone 48, BD Biosciences, San Jose, Calif) diluted 1:250, 4 degrees C x 72 hours; and developed using EnVision-Plus (Dako, Carpinteria, Calif) and diaminobenzidine as chromagen. Particulate or heterogeneous cytoplasmic staining was considered positive. Normal squamous epithelium was XIAP-positive in 7 of 34 cases (20.6%). Preinvasive intraepithelial lesions were positively stained in 54.5% of cases. Nineteen of 22 invasive squamous carcinomas were positive (86.4%). The intensity and extensiveness of XIAP immunostaining varied among individual cases, but trended upward with loss of tumor differentiation: 8 of 9 cases with strong staining were poorly differentiated carcinomas. The present study suggests the characteristic link between poor tumor differentiation and more aggressive clinical behavior could in some malignancies be based upon the concomitant induction of XIAP. Induction of XIAP appears to occur in a subset of intraepithelial lesions; in others, XIAP is detected only upon progression to invasive carcinoma. Detection of enhanced XIAP expression may also pinpoint those lesions that might benefit from pharmacologic disruption of XIAP's actions.

Histone deacetylase inhibitors enhance lexatumumab-induced apoptosis via a p21Cip1-dependent decrease in survivin levels

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in malignant cells by binding to the death receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). Several agents that therapeutically exploit this phenomenon are being developed. We investigated the anticancer activity of two novel, highly specific agonistic monoclonal antibodies to TRAIL-R1 (mapatumumab, HGS-ETR1) and TRAIL-R2 (lexatumumab, HGS-ETR2) in colon cancer cell lines. Our analyses revealed that colon cancer cells display significantly higher surface expressions of TRAIL-R2 than TRAIL-R1, and are more sensitive to lexatumumab-induced apoptosis. The proapoptotic effects of lexatumumab in TRAIL-resistant HCT8 and HT29 cells were dramatically augmented by the histone deacetylase inhibitors trichostatin A or suberoylanilide hydroxamic acid. The presence of p21, but not p53, was critical for the synergy between lexatumumab and histone deacetylase inhibitors. The absence of p21 did not interfere with the formation of the death-inducing signaling complex by lexatumumab, suggesting the involvement of other apoptotic and/or cell cycle regulators. Indeed, treatment with suberoylanilide hydroxamic acid greatly reduced the expression of the inhibitor of apoptosis protein survivin and cdc2 activity in HCT116 p21(+/+) cells but not in the HCT116 p21(-/-) cells. Inhibition of cdc2 activity with flavopiridol decreased survivin expression and sensitized the p21-deficient cells to lexatumumab-induced apoptosis. Similarly, small interfering RNA-mediated knockdown of survivin also enhanced lexatumumab-mediated cell death. Therefore, survivin expression plays a key role in lexatumumab resistance, and reducing survivin expression by inhibiting cdc2 activity is a promising strategy to enhance the anticancer activity of lexatumumab.

New therapeutic strategies for the treatment of acute lymphoblastic leukaemia

Although contemporary treatments cure more than 80% of children with acute lymphoblastic leukaemia (ALL), some patients require intensive treatment and many patients still develop serious acute and late complications owing to the side effects of the treatments. Furthermore, the survival rate for adults with ALL remains below 40%. Therefore, new treatment strategies are needed to improve not only the cure rate but also the quality of life of these patients. Here, we discuss emerging new treatments that might improve the clinical outcome of patients with ALL. These include new formulations of existing chemotherapeutic agents, new antimetabolites and nucleoside analogues, monoclonal antibodies against leukaemia-associated antigens, and molecular therapies that target genetic abnormalities of the leukaemic cells and their affected signalling pathways.

Constitutively activated nuclear factor-kappaB, but not induced NF-kappaB, leads to TRAIL resistance by up-regulation of X-linked inhibitor of apoptosis protein in human cancer cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in most, but not all, cancer cells. The molecular factors regulating the sensitivity to TRAIL are still incompletely understood. The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated, but its exact role is controversial. We studied different cell lines displaying varying responses to TRAIL and found that TRAIL can activate NF-kappaB in all our cancer cell lines regardless of their TRAIL sensitivity. Inhibition of NF-kappaB via adenoviral expression of the IkappaB-alpha super-repressor only sensitized the TRAIL-resistant pancreatic cancer cell line Panc-1. Panc-1 cells harbor constitutively activated NF-kappaB, pointing to a possible role of preactivated NF-kappaB in protection from TRAIL. Furthermore, we could reduce X-linked inhibitor of apoptosis protein (XIAP) levels in Panc-1 cells by inhibition of constitutively activated NF-kappaB and sensitize Panc-1 cells to TRAIL by RNA interference against XIAP. These results implicate elevated XIAP levels caused by high basal NF-kappaB activity in TRAIL resistance and suggest that therapeutic strategies involving TRAIL can be abetted by inhibition of NF-kappaB and/or XIAP only in tumor cells with constitutively activated NF-kappaB.

Identifying the membrane proteome of HIV-1 latently infected cells

Profiling integral plasma membrane proteins is of particular importance for the identification of new biomarkers for diagnosis and for drug development. We report in this study the identification of surface markers by performing comparative proteomics of established human immunodeficiency virus-1 (HIV-1) latent cell models and parental cell lines. To this end we isolated integral membrane proteins using a biotin-directed affinity purification method. Isolated proteins were separated by two-dimensional gel electrophoresis and identified by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) after in gel digestion. Seventeen different proteins were found to vary on the surface of T-cells due to HIV-1 infection. Of these proteins, 47% were integral membrane proteins, and 18% were membrane-associated. Through the use of complementary techniques such as Western blotting and fluorescent staining, we confirmed the differential expression of some of the proteins identified by MALDI-TOF including Bruton's tyrosine kinase and X-linked inhibitor of apoptosis. Finally, using phosphatidylinositol 3-kinase inhibitors and flavopiridol to inhibit Bruton's tyrosine kinase localization at the membrane and X-linked inhibitor of apoptosis protein expression, respectively, we showed that HIV-1 latently infected cells are more sensitive to these drugs than uninfected cells. This suggests that HIV-1 latently infected cells may be targeted with drugs that alter several pathways that are essential for the establishment and maintenance of latency.

Flavopiridol synergizes TRAIL cytotoxicity by downregulation of FLIPL

PURPOSE

Flavopiridol is known to modulate the transcription of genes. We investigated the effect of flavopiridol pretreatment on TRAIL cytotoxicity and on the expression of FLIP(L) in different TRAIL-resistant cell lines, because FLIP expression is known to confer TRAIL-resistance.

METHODS

Apoptosis was assessed by PI staining and protein expression by Western blotting. RT-PCR was used for mRNA quantitation. siRNA gene silencing was used to knock down FLIP(L).

RESULTS

Flavopiridol pretreatment synergized TRAIL-induced apoptosis in human myeloma and breast cancer cells. Flavopiridol treatment repressed the transcription of FLIP(L) and downregulated its expression in both myeloma and breast cancer cells. Silencing of FLIP(L) gene by siRNA sensitized myeloma cells to TRAIL. Flavopiridol treatment downregulated the expression of the proapoptotic members of the Bcl-2 family proteins (Bak, Bax and PUMA-alpha). The expression of the antiapoptotic Bcl-2 members (Bcl-2 and Bcl-X(L)) was not altered by flavopiridol treatment in myeloma cells.

CONCLUSION

Our data indicate that flavopiridol synergizes TRAIL cytotoxicity by downregulation of FLIP(L) and this synergistic effect is Bcl-2 family independent.

IAP family protein expression correlates with poor outcome of multiple myeloma patients in association with chemotherapy-induced overexpression of multidrug resistance genes

Multidrug-resistant (MDR) multiple myeloma (MM) patients who fail chemotherapy frequently express MDR1 protein, which serves as an efflux pump that protects neoplastic cells. The expression of lung resistance protein (LRP), which mediates intercellular and nucleocytoplasmic transport, is also correlated with chemotherapy resistance and shorter survival of MM patients. Here, we investigated the chemotherapy-induced change of MDR expression in MM patients using quantitative RT-PCR. Overall expression levels of MDR1 and LRP in MM patients were significantly higher than those in control subjects and increased after chemotherapy. More than half of the patients exhibited increased expression of MDR1 (14/26) or LRP (17/26) after chemotherapy. Also, the expression of inhibitor of apoptosis proteins (IAP) was determined in association with the prognosis of the patients. Among patients with increased MDR1-expression after chemotherapy, those with a poor outcome exhibited significant increases in survivin, cIAP1, cIAP2, and XIAP expression by chemotherapy compared with those with a good prognosis. Similarly, in the LRP expression-increased group, patients with a poor outcome showed significant increases of cIAP1 and cIAP2 expression compared with those with longer survival. In patients with reduced-MDR1 or LRP expression after chemotherapy, changes in the expression of IAPs induced by chemotherapy did not correlate with their prognosis. These findings indicate that IAP family proteins might play a role in worsening the prognosis of MM patients in association with chemotherapy-induced overexpression of MDR1 or LRP.

Cyclin-dependent kinase pathways as targets for cancer treatment

Cyclin-dependent kinases (cdks) are critical regulators of cell cycle progression and RNA transcription. A variety of genetic and epigenetic events cause universal overactivity of the cell cycle cdks in human cancer, and their inhibition can lead to both cell cycle arrest and apoptosis. However, built-in redundancy may limit the effects of highly selective cdk inhibition. Cdk4/6 inhibition has been shown to induce potent G1 arrest in vitro and tumor regression in vivo; cdk2/1 inhibition has the most potent effects during the S and G2 phases and induces E2F transcription factor-dependent cell death. Modulation of cdk2 and cdk1 activities also affects survival checkpoint responses after exposure to DNA-damaging and microtubule-stabilizing agents. The transcriptional cdks phosphorylate the carboxy-terminal domain of RNA polymerase II, facilitating efficient transcriptional initiation and elongation. Inhibition of these cdks primarily affects the accumulation of transcripts with short half-lives, including those encoding antiapoptosis family members, cell cycle regulators, as well as p53 and nuclear factor-kappa B-responsive gene targets. These effects may account for apoptosis induced by cdk9 inhibitors, especially in malignant hematopoietic cells, and may also potentiate cytotoxicity mediated by disruption of a variety of pathways in many transformed cell types. Current work is focusing on overcoming pharmacokinetic barriers that hindered development of flavopiridol, a pan-cdk inhibitor, as well as assessing novel classes of compounds potently targeting groups of cell cycle cdks (cdk4/6 or cdk2/1) with variable effects on the transcriptional cdks 7 and 9. These efforts will establish whether the strategy of cdk inhibition is able to produce therapeutic benefit in the majority of human tumors.

TRAIL sensitisation by arsenic trioxide is caspase-8 dependent and involves modulation of death receptor components and Akt

The majority of leukaemic cells are resistant to apoptosis induced by tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Here, we show that sublethal concentrations of arsenic trioxide (ATO) specifically enhanced TRAIL-induced apoptosis in leukaemic but not in other tumour cell lines. The combination of ATO and TRAIL synergistically enhanced cleavage of caspase-8, which was blocked by the caspase inhibitor IETD.fmk as well as in cells deficient for caspase-8, suggesting a requirement for the death-inducing signalling complex. Arsenic trioxide led to increased cell surface expression of DR5 (death receptor 5), inhibition of the serine/threonine kinase Akt and downregulation of the short isoform of FLIP (FLICE-inhibitory protein, FLIP_S). Inhibition of the phosphatidylinositol 3 kinase (PI3K) was equally efficient in sensitising leukaemic cells to TRAIL with similar effects on DR5 and FLIP_S expression, suggesting that ATO may in part act through inhibition of the PI3K/Akt signalling pathway. These results indicate that the enhancement in TRAIL-mediated apoptosis induced by ATO is due to alteration in the levels of multiple components and regulators of the death receptor-mediated pathway. These findings offer a promising and novel strategy involving a combination of TRAIL and ATO, or more specific Akt inhibitors in the treatment of various haematopoietic malignancies.

Potentiation of the lethality of the histone deacetylase inhibitor LAQ824 by the cyclin-dependent kinase inhibitor roscovitine in human leukemia cells

Interactions between the novel histone deacetylase inhibitor LAQ824 and the cyclin-dependent kinase inhibitor roscovitine were examined in human leukemia cells. Pretreatment (24 hours) with a subtoxic concentration of LAQ824 (30 nmol/L) followed by a minimally toxic concentration of roscovitine (10 micromol/L; 24 hours) resulted in greater than additive effects on apoptosis in U937, Jurkat, and HL-60 human leukemia cells and blasts from three patients with acute myelogenous leukemia. These events were associated with enhanced conformational changes in Bax; mitochondrial release of cytochrome c, Smac/DIABLO, and apoptosis-inducing factor; and a marked increase in caspase activation. LAQ824/roscovitine-treated cells displayed caspase-dependent down-regulation of p21(CIP1) and Mcl-1 and a pronounced caspase-independent reduction in X-linked inhibitor of apoptosis (XIAP) expression. The lethality of this regimen was significantly attenuated by ectopic expression of XIAP, a nuclear localization signal-defective p21(CIP1) mutant, Mcl-1, and Bcl-2. Combined exposure to LAQ824 and roscovitine resulted in a significant reduction in XIAP mRNA levels and diminished phosphorylation of the carboxyl-terminal domain of RNA polymerase II. Notably, roscovitine blocked LAQ824-mediated differentiation. Finally, LAQ824 and roscovitine individually and in combination triggered an increase in generation of reactive oxygen species; moreover, coadministration of the free radical scavenger N-acetylcysteine prevented LAQ824/roscovitine-mediated mitochondrial injury and apoptosis. Collectively, these findings suggest that combined treatment of human leukemia cells with LAQ824 and roscovitine disrupts maturation and synergistically induces apoptosis, lending further support for an antileukemic strategy combining novel histone deacetylase and cyclin-dependent kinase inhibitors.

Phase I and pharmacokinetic study of flavopiridol followed by 1-beta-D-arabinofuranosylcytosine and mitoxantrone in relapsed and refractory adult acute leukemias

PURPOSE

The serine/threonine kinase inhibitor flavopiridol targets multiple cyclin-dependent kinases, induces checkpoint arrest, and interrupts transcriptional elongation. We designed a phase I clinical trial using a timed sequential therapy approach where flavopiridol was given for the dual purpose of initial cytoreduction and enhancing cell cycle progression of the remaining leukemia cell cohort followed by cycle-dependent drugs 1-beta-D-arabinofuranosylcytosine (ara-C) and mitoxantrone.

EXPERIMENTAL DESIGN

Flavopiridol was given by 1-hour infusion daily for 3 days beginning day 1 followed by 2 g/m2/72 h ara-C beginning day 6 and 40 mg/m2 mitoxantrone beginning day 9. In vivo correlates included pharmacokinetics, modulation of blast cycle regulators, and serum and marrow supernatant vascular endothelial growth factor levels.

RESULTS

Of 34 adults receiving induction therapy, 16 (47%) evinced direct leukemia cytotoxicity with > or =50% drop in peripheral blast counts and tumor lysis in 9 (26%). Four (12%) died during therapy (two fungal infections and two sudden death). Dose-limiting toxicity occurred at 60 mg/m2/d with profound neutropenia >40 days duration, and maximal tolerated dose was 50 mg/m2/d. Overall response rate was 31% in 26 acute myelogenous leukemia and 12.5% in acute lymphoblastic leukemia. Pharmacokinetics showed that a linear two-compartment model with first-order elimination provided the best fit of the observed concentration versus time data. Flavopiridol down-regulated one or more target proteins in marrow blasts in vivo. Vascular endothelial growth factor was detected in sera and marrow supernatant pretreatment, and sera obtained on day 3 inhibited bovine aortic endothelial cell proliferation by a mean of 32% (range, 10-80%).

CONCLUSIONS

Our data suggest that flavopiridol is cytotoxic to leukemic cells and, when followed by ara-C and mitoxantrone, exerts biological and clinical effects in patients with relapsed and refractory acute leukemias. These findings warrant continuing development of flavopiridol at 50 mg/m2/d x 3 days in combination with cytotoxic and biological agents for acute leukemias.

Synergistic enhancement of TRAIL- and tumor necrosis factor alpha-induced cell death by a phenoxazine derivative

2-Amino-4,4alpha-dihydro-4alpha,7-dimethyl-3H-phenoxazine-3-one (Phx-1) has been developed as a novel phenoxazine derivative having an anticancer activity on a variety of cancer cell lines as well as transplanted tumors in mice with minimal toxicity to normal cells. We examined the effects of Phx-1 on Jurkat cells, a human T cell line. Phx-1 inhibited proliferation of the cells in a dose-dependent manner but hardly induced cell death, suggesting that Phx-1 acts primarily as an antiproliferative reagent but not as a cytocidal drug. Phx-1 enhanced tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptotic cell death about 100-fold. Tumor necrosis factor alpha, which alone does not induce cell death of Jurkat cells, caused apoptosis in combination with Phx-1. These enhancements of cell death were not due to up-regulation of the death receptors. Phx-1 decreased serum-induced phosphorylation of Akt, a kinase involved in cell proliferation and survival, and inhibited complex III of mitochondrial respiratory chain. Considering that both TRAIL and Phx-1 have only marginal cytotoxicity to most normal cells, Phx-1 may provide an ideal combination for cancer therapy with TRAIL.

Immunocytochemical detection of XIAP in body cavity effusions and washes

Body cavity effusions may be the first manifestation of malignancy or of recurrence or relapse. We surveyed effusions and washes for expression of X-linked inhibitor of apoptosis (XIAP), a potent constituent of the inhibitor of apoptosis (IAP) family of proteins. IAPs prevent apoptosis by blocking the activation of caspases, thereby preventing caspase-mediated cell degradation. Elevated expression of XIAP could be an underpinning of relapse and/or resistance to apoptosis-inducing cancer therapy. We performed an immunocytochemical survey of XIAP expression in cell blocks from benign and malignant body cavity effusions and washes. In all, 116 alcohol-fixed, formalin postfixed paraffin-embedded cell block specimens from 82 pleural effusions, 22 ascites, 11 pelvic/peritoneal washes and one pericardial effusion were evaluated immunocytochemically with monoclonal anti-XIAP (#610763, BD Biosciences, San Jose, USA) 1:250, 4 degrees C x 72 h, and developed using EnVision-Plus reagents (Dako) and diaminobenzidine as chromagen. Particulate cytoplasmic staining was considered positive. The prevalence of staining for specific malignancies varied with the tissue of origin as follows: ovarian (13/13, 100%); lung (9/11, 82%), breast (6/13, 46%); gastric (4/7, 57%), colon (0/4, 0%), pancreas (2/3, 67%), gallbladder (1/1, 100%), fallopian tube (1/3, 33%), endometrial (6/7, 86%), mesothelioma (4/5, 80%), carcinoma of unknown primary (5/5, 100%) and hematopoietic malignancies (3/9, 33%). Overall, 54 out of 81 (67%) malignant effusions displayed XIAP positivity. Benign effusions (n = 35) were virtually XIAP-negative except for two cases (6%) in which histiocytes showed moderate staining. Weak nonspecific staining was sometimes noted in inflammatory cells or histiocytes. XIAP immunostaining, when strong, allows for ready distinction of malignant from benign and reactive cell populations. Strong XIAP staining was most prevalent in ovarian carcinomas and less prevalent in mammary carcinomas. The degree of XIAP staining of tumor cells may be a means of identifying the most therapy-resistant cases (ie, those with strong XIAP expression), and allow additional triaging to XIAP-blocking drugs presently being developed and clinically tested.

Flavopiridol and histone deacetylase inhibitors promote mitochondrial injury and cell death in human leukemia cells that overexpress Bcl-2

Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and histone deacetylase (HDAC) inhibitors (suberoylanilide hydroxamide and sodium butyrate) were examined in human leukemia cells (U937 and HL-60) ectopically expressing Bcl-2/Bcl-x(L) and in primary AML cells. Coadministration of flavopiridol with HDAC inhibitors synergistically potentiated mitochondrial damage (cytochrome c, second mitochondria-derived activator of caspases/direct IAP binding protein with low pI, and apoptosis-inducing factor release), caspase activation, poly(ADP-ribose) polymerase degradation, and cell death in both wild type and Bcl-2- or Bcl-x(L)-overexpressing cells and induced a pronounced loss of clonogenicity. In contrast, Bcl-2 and Bcl-x(L) largely blocked these events in cells exposed to the cytotoxic agent 1-beta-d-arabinofuranosylcytosine (ara-C). Enforced expression of dominant-negative Fas-associated death domain failed to protect cells from the flavopiridol/histone deacetylase inhibitor (HDACI) regimen, arguing against the involvement of the receptor pathway in lethality. Ectopic expression of a phosphorylation loop-deleted Bcl-2 or Bcl-2 lacking the serine(70) phosphorylation site, which dramatically protected cells from ara-C lethality, delayed but did not prevent flavopiridol/HDAC inhibitor-induced mitochondrial injury, cell death, or loss of clonogenicity. Ectopic expression of Bcl-2 or Bcl-x(L) was also unable to prevent the flavopiridol/HDACI regimen from inducing a conformational change in and mitochondrial translocation of Bax, and it did not attenuate Bax dimerization. As a whole, these findings indicate that in contrast to certain conventional cytotoxic agents such as ara-C, overexpression of Bcl-2 or Bcl-x(L) are largely ineffective in preventing perturbations in Bax, mitochondrial injury, and cell death in human leukemia cells subjected to simultaneous CDK and HDAC inhibition. They also raise the possibility that a strategy combining CDK and HDAC inhibitors may be effective against drug-resistant leukemia cells overexpressing Bcl-2 or Bcl-x(L).

Transcription inhibition by flavopiridol: mechanism of chronic lymphocytic leukemia cell death

Flavopiridol is active against chronic lymphocytic leukemia (CLL) cells in vitro and in the treatment of advanced stage disease, but the mechanisms of these actions remain unclear. Originally developed as a general cyclin-dependent kinase inhibitor, flavopiridol is a potent transcriptional suppressor through the inhibition of positive transcription elongation factor b (P-TEFb; CDK9/cyclin T). P-TEFb phosphorylates the C-terminal domain (CTD) of RNA polymerase II to promote transcriptional elongation. Because most CLL cells are not actively cycling, and their viability is dependent upon the continuous expression of antiapoptotic proteins, we hypothesized that flavopiridol induces apoptosis in CLL cells through the transcriptional down-regulation of such proteins. This study demonstrated that flavopiridol inhibited the phosphorylation of the CTD of RNA polymerase II in primary CLL cells and reduced RNA synthesis. This was associated with a decline of the transcripts and the levels of short-lived antiapoptotic proteins such as myeloid cell leukemia 1 (Mcl-1), and resulted in the induction of apoptosis. The B-cell lymphoma 2 (Bcl-2) protein level remained stable, although its mRNA was consistently reduced, suggesting that the outcome of transcriptional inhibition by flavopiridol is governed by the intrinsic stability of the individual transcripts and proteins. The dependence of CLL-cell survival on short-lived oncoproteins may provide the biochemical basis for the therapeutic index in response to flavopiridol.

The histone deacetylase inhibitor LAQ824 induces human leukemia cell death through a process involving XIAP down-regulation, oxidative injury, and the acid sphingomyelinase-dependent generation of ceramide

Determinants of differentiation and apoptosis induction by the novel histone deacetylase inhibitor (HDACI) LAQ824 were examined in human leukemia cells (U937 and Jurkat). Exposure of U937 cells to a low concentration of LAQ824 (30 nM) resulted in a delayed (2 h) increase in reactive oxygen species (ROS), induction of p21(WAF1/CIP1), pRb dephosphorylation, growth arrest of cells in G(0)/G(1) phase, and differentiation. On the other hand, exposure of cells to a higher concentration of LAQ824 (75 nM) resulted in the early (30 min) generation of ROS, arrest of cells in G(2)/M phase, down-regulation of XIAP (at the transcriptional level) and Mcl-1 (through a caspase-mediated process), the acid sphingomyelinase-dependent generation of ceramide, and profound mitochondrial injury, caspase activation, and apoptosis. LAQ824-induced lethality in U937 cells did not involve the extrinsic apoptotic pathway, nor was it associated with death receptor up-regulation; instead, it was markedly inhibited by ectopic expression of Bcl-2, Bcl-x(L), XIAP, and Mcl-1. The free radical scavenger N-acetyl cysteine blocked LAQ824-mediated ROS generation, mitochondrial injury, Mcl-1 down-regulation, ceramide generation, and apoptosis, suggesting a primary role for oxidative injury in LAQ824 lethality. Together, these findings indicate that LAQ824-induced lethality represents a multifactorial process in which LAQ824-mediated ROS generation is necessary but not sufficient to induce apoptosis, and that the degree of XIAP and Mcl-1 down-regulation and ceramide generation determines whether this agent engages a maturation rather than an apoptotic program.

Protein Kinase C Inhibition and X-Linked Inhibitor of Apoptosis Protein Degradation Contribute to the Sensitization Effect of Luteolin on Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand–Induced Apoptosis in Cancer Cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is an important member of the TNF superfamily with great potential in cancer therapy. Luteolin is a dietary flavonoid commonly found in some medicinal plants. Here we found that pretreatment with a noncytotoxic concentration of luteolin significantly sensitized TRAIL-induced apoptosis in both TRAIL-sensitive (HeLa) and TRAIL-resistant cancer cells (CNE1, HT29, and HepG2). Such sensitization is achieved through enhanced caspase-8 activation and caspase-3 maturation. Further, the protein level of X-linked inhibitor of apoptosis protein (XIAP) was markedly reduced in cells treated with luteolin and TRAIL, and ectopic expression of XIAP protected against cell death induced by luteolin and TRAIL, showing that luteolin sensitizes TRAIL-induced apoptosis through down-regulation of XIAP. In search of the molecular mechanism responsible for XIAP down-regulation, we found that luteolin and TRAIL promoted XIAP ubiquitination and proteasomal degradation. Next, we showed that protein kinase C (PKC) activation prevented cell death induced by luteolin and TRAIL via suppression of XIAP down-regulation. Moreover, luteolin inhibited PKC activity, and bisindolylmaleimide I, a general PKC inhibitor, simulated luteolin in sensitizing TRAIL-induced apoptosis. Taken together, these results present a novel anticancer effect of luteolin and support its potential application in cancer therapy in combination with TRAIL. In addition, our data reveal a new function of PKC in cell death: PKC activation stabilizes XIAP and thus suppresses TRAIL-induced apoptosis.

Bortezomib abolishes tumor necrosis factor-related apoptosis-inducing ligand resistance via a p21-dependent mechanism in human bladder and prostate cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor family of cytokines that induces apoptosis in some tumor cells but not in normal cells. Unfortunately, many human cancer cell lines are refractory to TRAIL-induced cell death, and the molecular mechanisms underlying resistance are unclear. Here we report that TRAIL resistance was reversed in human bladder and prostate cancer cell lines by the proteasome inhibitor bortezomib (PS-341, Velcade). Synergistic induction of apoptosis occurred within 4 to 6 hours in cells treated with TRAIL plus bortezomib and was associated with accumulation of p21(WAF-1/Cip-1) (p21) and inhibition of cyclin-dependent kinase (cdk) activity. Roscovitine, a specific cdk1/2 inhibitor, also sensitized cells to TRAIL. Silencing p21 expression reduced levels of DNA fragmentation by 50% in cells treated with bortezomib and TRAIL, confirming that p21 was required for the response. Analysis of the TRAIL pathway revealed that caspase-8 processing was enhanced in a p21-dependent fashion in cells exposed to TRAIL and bortezomib as compared with cells treated with TRAIL alone. Thus, all downstream components of the pathway (Bid cleavage, cytochrome c release, and caspase-3 activation) were amplified. These data strongly suggest that p21-mediated cdk inhibition promotes TRAIL sensitivity via caspase-8 activation and that TRAIL and bortezomib should be combined in appropriate in vivo models as a possible approach to solid tumor therapy.