Prologation of c-Jun N-terminal kinase is associated with cell death induced by tumor necrosis factor alpha in human chondrocytes

The aim of this study was to elucidate the role of JNK signaling pathway involved in tumor necrosis factor-alpha (TNF-alpha)-induced death of chondrocytes. Primary chondrocyte cultures were obtained from human knee osteoarthritis cartilages. First passage chondrocytes were treated with TNF-alpha and various potentiators, and cell death was measured with MTT assay. C-Jun N terminal kinase (JNK) activation was investigated with the solid phase kinase assay. Expression of apoptosis-related molecule was assayed with Western blot. Chondrocytes were resistant to TNF-alpha-induced cell death. In contrast, pretreatment with actinomycin D, the phosphatase inhibitor vanadate or MAP kinase phosphatase-1 (MKP-1) inhibitor Ro318220 invariably led to chondrocyte death. While TNF-alpha alone stimulated a single, brief JNK activity, a second JNK peak was observed when the cells were pretreated with actinomycin D. When the cells were pretreated with vanadate or Ro318220, TNF-alpha-induced JNK activation was greatly prolonged, which was associated with the induction of cell death. The expression of Bcl-2 and Mcl-1 decreased significantly in conditions of cell death. In conclusions, our data suggest that chondrocyte death induced by TNF-alpha is associated with sustained JNK activation. This effect may be due to downregulation of TNF-alpha induced phosphatase that inactivates JNK and of Bcl-2 family proteins.

Specific inhibition of nuclear factor-kappaB-dependent inflammatory responses by cell type-specific mechanisms upon A2A adenosine receptor gene transfer

Adenosine is a potent inhibitor of inflammatory processes, and the A(2A) adenosine receptor (A(2A)AR) plays a key nonredundant role as a suppresser of inflammatory responses in vivo. In this study, we demonstrate that increasing A(2A)AR gene expression suppressed multiple inflammatory responses in both human umbilical vein endothelial cells (HUVECs) and rat C6 glioma cells in vitro. In particular, the induction of the adhesion molecule E-selectin by either tumor necrosis factor alpha (TNFalpha) or Escherichia coli lipopolysaccharide (LPS) was reduced by more than 70% in HUVECs, whereas inducible nitric-oxide synthase (iNOS) induction was abolished in C6 cells after exposure to interferon-gamma in combination with LPS and TNFalpha, suggesting that the receptor inhibited a common step in the induction of each of these pro-inflammatory genes. Consistent with this hypothesis, A(2A)AR expression inhibited the activation of NF-kappaB, a key transcription factor whose proper function was essential for optimal iNOS and E-selectin induction. However, although NF-kappaB binding to target DNA was severely compromised in both cell types, the mechanisms by which this occurred were distinct. In C6 cells, A(2A)AR expression blocked IkappaBalpha degradation by inhibiting stimulus-induced phosphorylation, whereas in HUVECs, A(2A)AR expression inhibited NF-kappaB translocation to the nucleus independently of any effect on IkappaBalpha degradation. Together, these observations suggest that A(2A)AR-mediated inhibition NF-kappaB activation is a critical aspect of its anti-inflammatory signaling properties and that the molecular basis of this inhibition varies in a cell type-specific manner.

Contribution of disruption of the nuclear factor-kappaB pathway to induction of apoptosis in human leukemia cells by histone deacetylase inhibitors and flavopiridol

Interactions between the cyclin-dependent kinase inhibitor flavopiridol and the histone deacetylase inhibitors (HDACIs) sodium butyrate (NaB) and suberoylanilide hydroxamic acid (SAHA) have been examined in human leukemia cells in relation to effects on nuclear factor kappaB (NF-kappaB) activation. Exposure (24 h) of U937 human leukemia cells to NaB (1 mM) or SAHA (1.5 microM) resulted in a marked increase in NF-kappaB DNA binding, effects that were essentially abrogated by coadministration of flavopiridol (100 nM). These events were accompanied by a marked increase in mitochondrial injury, caspase activation, and apoptosis. Mutant cells expressing an IkappaBalpha super-repressor exhibited impairment of NF-kappaB DNA binding in response to HDACIs and a significant although modest increase in apoptosis. However, disruption of the NF-kappaB pathway also increased mitochondrial injury and caspase activation in response to flavopiridol and to an even greater extent to the combination of flavopiridol and HDACIs. Coadministration of flavopiridol with HDACIs down-regulated the X-linked inhibitor of apoptosis (XIAP), Mcl-1, and p21CIP1/WAF1 and activated c-Jun NH2-terminal kinase; moreover, these effects were considerably more pronounced in IkappaBalpha mutants. Similar responses were observed in U937 mutant cells stably expressing RelA/p65 small interfering RNA. In all cases, flavopiridol was significantly more potent than genetic interruption of the NF-kappaB cascade in promoting HDACI-mediated lethality. Together, these findings are consistent with the notion that although inhibition of NF-kappaB activation by flavopiridol contributes to antileukemic interactions with HDACIs, other NF-kappaB-independent flavopiridol actions (e.g., down-regulation of Mcl-1, XIAP, and p21CIP1/WAF1) play particularly critical roles in this phenomenon.

Chk1 is haploinsufficient for multiple functions critical to tumor suppression

The haploinsufficient tumor suppressor Chk1 is essential for embryonic cells, but the consequences of Chk1 loss in adult tissues are unknown. Using conditional Chk1 mice, we find that proliferating mammary cells lacking Chk1 undergo apoptosis leading to developmental defects. Conditional Chk1 heterozygosity increased the number of S phase cells and caused spontaneous DNA damage. Chk1+/- epithelia also exhibit a miscoordinated cell cycle in which S phase cells display an early mitotic phenotype. These cells maintain high levels of Cdc25A, which can promote inappropriate cell cycle transitions. Thus, Chk1 heterozygosity results in three distinct haploinsufficient phenotypes that can contribute to tumorigenesis: inappropriate S phase entry, accumulation of DNA damage during replication, and failure to restrain mitotic entry.

Mitogen Activated Protein kinase signal transduction pathways in the prostate

The biochemistry of the mitogen activated protein kinases ERK, JNK, and p38 have been studied in prostate physiology in an attempt to elucidate novel mechanisms and pathways for the treatment of prostatic disease. We reviewed articles examining mitogen-activated protein kinases using prostate tissue or cell lines. As with other tissue types, these signaling modules are links/transmitters for important pathways in prostate cells that can result in cellular survival or apoptosis. While the activation of the ERK pathway appears to primarily result in survival, the roles of JNK and p38 are less clear. Manipulation of these pathways could have important implications for the treatment of prostate cancer and benign prostatic hypertrophy.

The histone deacetylase inhibitor MS-275 interacts synergistically with fludarabine to induce apoptosis in human leukemia cells

Interactions between the novel benzamide histone deacetylase (HDAC) inhibitor MS-275 and fludarabine were examined in lymphoid and myeloid human leukemia cells in relation to mitochondrial injury, signal transduction events, and apoptosis. Prior exposure of Jurkat lymphoblastic leukemia cells to a marginally toxic concentration of MS-275 (e.g., 500 nM) for 24 h sharply increased mitochondrial injury, caspase activation, and apoptosis in response to a minimally toxic concentration of fludarabine (500 nM), resulting in highly synergistic antileukemic interactions and loss of clonogenic survival. Simultaneous exposure to MS-275 and fludarabine also led to synergistic effects, but these were not as pronounced as observed with sequential treatment. Similar interactions were noted in the case of (a) other human leukemia cell lines (e.g., U937, CCRF-CEM); (b) other HDAC inhibitors (e.g., sodium butyrate); and (c) other nucleoside analogues (e.g., 1-beta-D-arabinofuranosylcytosine, gemcitabine). Potentiation of fludarabine lethality by MS-275 was associated with acetylation of histones H3 and H4, down-regulation of the antiapoptotic proteins XIAP and Mcl-1, enhanced cytosolic release of proapoptotic mitochondrial proteins (e.g., cytochrome c, Smac/DIABLO, and apoptosis-inducing factor), and caspase activation. It was also accompanied by the caspase-dependent down-regulation of p27(KIP1), cyclins A, E, and D(1), and cleavage and diminished phosphorylation of retinoblastoma protein. However, increased lethality of the combination was not associated with enhanced fludarabine triphosphate formation or DNA incorporation and occurred despite a slight reduction in the S-phase fraction. Prior exposure to MS-275 attenuated fludarabine-mediated activation of MEK1/2, extracellular signal-regulated kinase, and Akt, and enhanced c-Jun NH(2)-terminal kinase phosphorylation; furthermore, inducible expression of constitutively active MEK1/2 or Akt significantly diminished MS-275/fludarabine-induced lethality. Combined exposure of cells to MS-275 and fludarabine was associated with a significant increase in generation of reactive oxygen species; moreover, both the increase in reactive oxygen species and apoptosis were largely attenuated by coadministration of the free radical scavenger L-N-acetylcysteine. Finally, prior administration of MS-275 markedly potentiated fludarabine-mediated generation of the proapoptotic lipid second messenger ceramide. Taken together, these findings indicate that the HDAC inhibitor MS-275 induces multiple perturbations in signal transduction, survival, and cell cycle regulatory pathways that lower the threshold for fludarabine-mediated mitochondrial injury and apoptosis in human leukemia cells. They also provide insights into possible mechanisms by which novel, clinically relevant HDAC inhibitors might be used to enhance the antileukemic activity of established nucleoside analogues such as fludarabine.

Flavopiridol Induces p53 via Initial Inhibition of Mdm2 and p21 and, Independently of p53, Sensitizes Apoptosis-Reluctant Cells to Tumor Necrosis Factor

Flavopiridol (FP) inhibits gene expression and causes apoptosis, and these effects cannot be explained by inhibition of cyclin-dependent kinases that govern cell cycle. The simple and established notion that FP is an inhibitor of transcription predicts its effects. Because Mdm-2 targets p53 for degradation, FP, as predicted, dramatically induced p53 by inhibiting Mdm-2. Once p53 was induced, restoration of transcription (by removal of FP) resulted in superinduction of p21 and Mdm-2. Similarly, low concentrations of FP (50 nm) induced p21 and Mdm-2 because of their initial down-regulation. A sustained decrease of Mdm-2/p21 expression and accumulation of p53 coincided with near-maximal cytotoxicity of FP at concentrations >100 nm. Induction of p53 was a marker, not a cause, of cytotoxicity. FP caused rapid apoptosis (caspase-dependent cell death) in p53-null leukemia cells. In these cells, FP-induced apoptosis was converted to growth arrest by inhibitors of caspases. In apoptosis-reluctant A549 and PC3M cancer cells, FP inhibited cell proliferation but did not cause apoptosis. Like typical inhibitors of transcription, FP sensitized cells to apoptotic stimuli, allowing tumor necrosis factor to cause rapid and massive apoptosis in otherwise apoptosis-reluctant cells. We discuss that, as a reversible inhibitor of transcription, FP can be used clinically in novel rational drug combinations.

Small molecule inhibitors targeting cyclin-dependent kinases as anticancer agents

Cyclin-dependent kinases (CDKs) and their related pathways represent some of the most attractive targets in the development of anticancer therapeutics. Among a variety of CDK inhibitors under development, flavopiridol, UCN-01, CYC202, and BMS-387032 are undergoing clinical evaluation based on evidence of preclinical antitumor activity. Flavopiridol exerts multiple effects in tumor cells, including inhibition of multiple CDKs, transcriptional inhibition secondary to disruption of P-TEFb (CDK9/cyclin T), induction of apoptosis, and antiangiogenesis. UCN-01 was initially developed as a protein kinase C (PKC) inhibitor, but its major antitumor effects appear to be related to CDK inhibition or "inappropriate" activation of cdc2/CDK1 abrogating the G2 and S checkpoints, inhibition of PDK1/Akt, and induction of apoptosis through a PKC-independent mechanism. Significantly, combining these CDK inhibitors with either conventional cytotoxic drugs or novel agents targeting signal transduction pathways can markedly enhance antitumor activity, particularly induction of apoptosis, in various preclinical models. Such findings may serve as a basis for the introduction of novel combination regimens into clinical trials.

eIF4E--from translation to transformation

Over the years, studies have focused on the transcriptional regulation of oncogenesis. More recently, a growing emphasis has been placed on translational control. The Ras and Akt signal transduction pathways play a critical role in regulating mRNA translation and cellular transformation. The question arises: How might the Ras and Akt signaling pathways affect translation and mediate transformation? These pathways converge on a crucial effector of translation, the initiation factor eIF4E, which binds the 5'cap of mRNAs. This review focuses on the role of eIF4E in oncogenesis. eIF4E controls the translation of various malignancy-associated mRNAs which are involved in polyamine synthesis, cell cycle progression, activation of proto-oncogenes, angiogenesis, autocrine growth stimulation, cell survival, invasion and communication with the extracellular environment. eIF4E-mediated translational modulation of these mRNAs plays a pivotal role in both tumor formation and metastasis. Interestingly, eIF4E activity is implicated in mitosis, embryogenesis and in apoptosis. Finally, the finding that eIF4E is overexpressed in several human cancers makes it a prime target for anticancer therapies.

Ubiquitin-proteasome system and proteasome inhibition: new strategies in stroke therapy

BACKGROUND AND PURPOSE

Proteasomes are large multicatalytic proteinase complexes that are found in the cytosol and in the nucleus of eukaryotic cells with a central role in cellular protein turnover. The ubiquitin-proteasome system (UPS) has a central role in the selective degradation of intracellular proteins. Among the key proteins whose levels are modulated by the proteasome are those involved in the control of inflammatory processes, cell cycle regulation, and gene expression. There are now overwhelming data suggesting that the UPS contributes to cerebral ischemic injury.

SUMMARY OF REVIEW

Proteasome inhibition is a potential treatment option for stroke. Thus far, proof of principle has been obtained from studies in several animal models of cerebral ischemia. Treatment with proteasome inhibitors reduces effectively neuronal and astrocytic degeneration, cortical infarct volume, infarct neutrophil infiltration, and NF-kappaB immunoreactivity with an extension of the neuroprotective effect at least 6 hours after ischemic insult. However, it is clear that the UPS represents a central pathway for the processing and metabolism of multiple proteins with critical roles in cellular function. To avoid eliciting significant side effects associated with complete inhibition of the proteasome and the possible immunosuppressive effects from persistent suppression of NF-kappaB activation, it is critical that we understand how to partially and temporally attenuate proteasome function to elicit the desired therapeutic effect before any large-scale use in humans.

CONCLUSIONS

This review highlights the most recent advances in our knowledge on UPS, as well as the early experience of using proteasome inhibition strategies to treat acute stroke.

Advances in biology of multiple myeloma: clinical applications

There appear to be 2 pathways involved in the early pathogenesis of premalignant monoclonal gammopathy of undetermined significance (MGUS) and malignant multiple myeloma (MM) tumors. Nearly half of these tumors are nonhyperdiploid and mostly have immunoglobulin H (IgH) translocations that involve 5 recurrent chromosomal loci, including 11q13 (cyclin D1), 6p21 (cyclin D3), 4p16 (fibroblast growth factor receptor 3 [FGFR3] and multiple myeloma SET domain [MMSET]), 16q23 (c-maf), and 20q11 (mafB). The remaining tumors are hyperdiploid and contain multiple trisomies involving chromosomes 3, 5, 7, 9, 11, 15, 19, and 21, but infrequently have IgH translocations involving the 5 recurrent loci. Dysregulated expression of cyclin D1, D2, or D3 appears to occur as an early event in virtually all of these tumors. This may render the cells more susceptible to proliferative stimuli, resulting in selective expansion as a result of interaction with bone marrow stromal cells that produce interleukin-6 (IL-6) and other cytokines. There are 5 proposed tumor groups, defined by IgH translocations and/or cyclin D expression, that appear to have differences in biologic properties, including interaction with stromal cells, prognosis, and response to specific therapies. Delineation of the mechanisms mediating MM cell proliferation, survival, and migration in the bone marrow (BM) microenvironment may both enhance understanding of pathogenesis and provide the framework for identification and validation of novel molecular targets.

Interruption of the NF-κB pathway by Bay 11-7082 promotes UCN-01-mediated mitochondrial dysfunction and apoptosis in human multiple myeloma cells

Interactions between pharmacologic NF-κB inhibitors (eg, Bay 11-7082, SN-50) and the checkpoint abrogator UCN-01 have been examined in human multiple myeloma (MM) cells. Exposure of U266 cells to Bay 11-7082 (Bay) in combination with UCN-01 resulted in the abrogation of NF-κB/DNA binding activity and the synergistic induction of apoptosis. Comparable synergism was observed in other MM cell lines and patient-derived CD138+ cells and between an inhibitory peptide of NF-κB (SN50) and UCN-01. Bay/UCN-01-mediated lethality involved mitochondrial dysfunction, caspase cleavage, and poly adenosine diphosphate-ribose polymerase (PARP) degradation. Although Bay modestly blocked UCN-01-induced extracellular signal-regulated kinase (ERK) phosphorylation, coadministration activated c-Jun N-terminal kinase (JNK) and cdc2/cdk1 and down-regulated Mcl-1, XIAP, and Bcl-xL. Transfection with a constitutively activated mitogen-activated protein kinase kinase (MEK1)/green fluorescent protein (GFP) construct failed to block apoptosis induced by Bay/UCN-01 but significantly attenuated MEK inhibitor (U0126)/UCN-01-induced lethality. Inhibiting JNK activation with SP600125 or D-JNKI1 peptide markedly reduced Bay/UCN-01-mediated mitochondrial dysfunction and apoptosis and the down-regulation of Mcl-1, XIAP, and Bcl-xL but not of cdc2/cdk1 activation. Stable transfection of cells with dominant-negative caspase-9 dramatically diminished Bay/UCN-01 lethality without altering JNK or cdc2/cdk1 activation. Neither interleukin-6 (IL-6)- nor fibronectin-mediated adherence conferred resistance to Bay/UCN-01-induced apoptosis. Together, these findings suggest that a strategy combining UCN-01 with disruption of the IκB kinase (IKK)/IκB/NF-κB pathway warrants attention in MM. (Blood. 2004;103:2761-2770)

Cyr61 expression confers resistance to apoptosis in breast cancer MCF-7 cells by a mechanism of NF-kappaB-dependent XIAP up-regulation

The aggressiveness of a tumor is partly attributed to its resistance to chemotherapeutic agent-induced apoptosis. Cysteine-rich 61 (Cyr61), from the CCN gene family, is a secreted and matrix-associated protein, which is involved in many cellular activities such as growth and differentiation. Here we established a cell model system to examine whether stable expression of Cyr61 in MCF-7 cells can confer resistance to apoptosis and identify possible participating mechanisms. We showed that stable cell lines overexpressing Cyr61 had acquired a remarkable resistance to apoptosis induced by paclitaxel, adriamycin, and beta-lapachone. Most interesting, gel shift and reporter assays showed that the Cyr61-overexpressing cells had significantly increased NF-kappaB activity compared with neo control cells. Blockage of NF-kappaB activity in Cyr61-expressing cells by transfecting with a dominant negative (DN)-IkappaB or with an NF-kappaB decoy rendered them more susceptible to anti-cancer drugs-induced apoptosis. In addition, several NF-kappaB-regulated anti-apoptotic genes were examined, and we found that only XIAP showed a significant 3-4-fold increase in mRNA and protein in Cyr61-overexpressing cells but not in neo control cells. Treatment with inhibitor of apoptosis protein (XIAP)-specific antisense, but not sense, oligonucleotides abolished the apoptosis resistance of the Cyr61-overexpressing cells. At the same time, transfection of these stable cells with DN-IkappaB to block NF-kappaB activity also effectively reduced the elevated XIAP level. Function-neutralizing antibodies to alpha(v)beta(3) and alpha(v)beta(5) could inhibit Cyr61-mediated NF-kappaB activation as well as XIAP expression. Taken together, our data suggested that Cyr61 plays an important role in resistance to chemotherapeutic agent-induced apoptosis in human breast cancer MCF-7 cells by a mechanism involving the activation of the integrins/NF-kappaB/XIAP signaling pathway.

Downmodulation of ERK protein kinase activity inhibits VEGF secretion by human myeloma cells and myeloma-induced angiogenesis

The mitogen-activated protein (MAP) cascade leading to the activation of extracellular signal-regulated kinases 1/2 (ERK1/2) is critical for regulating myeloma cell growth; however, the relationship of ERK1/2 activity with vascular endothelial growth factor (VEGF) production and the effects of its downmodulation in myeloma cells are not elucidated. We found that the treatment with MAP/ERK kinase 1 (MEK1) inhibitors PD98059 or PD184352 produced a reduction of phosphorylated ERK1/2 (p-ERK1/2) levels in myeloma cells of more than 80% and prevented the increase of p-ERK1/2 induced by interleukin-6 (IL-6). MEK1 inhibitors also induced a significant inhibition of myeloma cell proliferation and blunted the stimulatory effect induced by IL-6. A significant inhibition of basal VEGF secretion by myeloma cells as well as a suppression of the stimulatory effect of IL-6 on VEGF was observed by either PD98059 or PD184352. Moreover, we also found that the PI3K kinase inhibitors, but not p38 MAPK inhibitors, reduced VEGF secretion by myeloma cells and increase the inhibitory effect of MEK1 inhibitors. In an 'in vitro' model of angiogenesis, we found that MEK1 inhibitors impair vessel formation induced by myeloma cells and restored by VEGF treatment, suggesting that the downmodulation of ERK1/2 activity reduces myeloma-induced angiogenesis by inhibiting VEGF secretion.

Bortezomib and flavopiridol interact synergistically to induce apoptosis in chronic myeloid leukemia cells resistant to imatinib mesylate through both Bcr/Abl-dependent and -independent mechanisms

Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and the proteasome inhibitor bortezomib were examined in Bcr/Abl(+) human leukemia cells. Coexposure of K562 or LAMA84 cells to subtoxic concentration of flavopiridol (150-200 nM) and bortezomib (5-8 nM) resulted in a synergistic increase in mitochondrial dysfunction and apoptosis. These events were associated with a marked diminution in nuclear factor kappaB (NF-kappaB)/DNA binding activity; enhanced phosphorylation of SEK1/MKK4 (stress-activated protein kinase/extracellular signal-related kinase 1/mitogen-activated protein kinase kinase 4), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK); down-regulation of Bcr/Abl; and a marked reduction in signal transducer and activator of transcription 3 (STAT3) and STAT5 activity. In imatinib mesylate-resistant K562 cells displaying increased Bcr/Abl expression, bortezomib/flavopiridol treatment markedly increased apoptosis in association with down-regulation of Bcr/Abl and BclxL, and diminished phosphorylation of Lyn, Hck, CrkL, and Akt. Parallel studies were performed in imatinib mesylate-resistant LAMA84 cells exhibiting reduced expression of Bcr/Abl but a marked increase in expression/activation of Lyn and Hck. Flavopiridol/bortezomib effectively induced apoptosis in these cells in association with Lyn and Hck inactivation. The capacity of flavopiridol to promote bortezomib-mediated Bcr/Abl down-regulation and apoptosis was mimicked by the positive transcription elongation factor-b (P-TEFb) inhibitor DRB (5,6-dichloro 1-beta-d-ribofuranosylbenzinida-sole). Finally, the bortezomib/flavopiridol regimen also potently induced apoptosis in Bcr/Abl(-) human leukemia cells. Collectively, these findings suggest that a strategy combining flavopiridol and bortezomib warrants further examination in chronic myelogenous leukemia and related hematologic malignancies.

Arsenite sensitizes human melanomas to apoptosis via tumor necrosis factor alpha-mediated pathway

Arsenic is a well established human carcinogen and is associated with a variety of cancers including those of the skin. Paradoxically, arsenic has also been used, amid at low doses, in the treatment of leukemia for over a century. Here we demonstrate that low to moderate concentrations of arsenite (2-10 microm) that has little or no effect on normal melanocytes may induce apoptosis of human melanomas including highly metastatic ones despite their low surface Fas levels. The two prerequisites that dictate apoptotic response of melanomas upon arsenite treatment are low nuclear NF-kappaB activity and an endogenous expression of tumor necrosis factor alpha. Under these conditions, melanoma cells acquired sensitivity to tumor necrosis factor alpha-mediated killing. On the other hand, signaling pathways including those of phosphatidylinositol 3-kinase-AKT, MEK-ERK, and JNK play a protective role against arsenite-induced oxidative stress and apoptosis in melanoma cells. Suppression of these pathways dramatically accelerates arsenite-induced apoptosis. Taken together, these data could provide potential approaches to sensitize melanomas to the cytotoxic effects of arsenite through modulating the signaling pathways.

Abrogation of p21 Expression by Flavopiridol Enhances Depsipeptide-Mediated Apoptosis in Malignant Pleural Mesothelioma Cells

PURPOSE

Recent insights regarding the pathogenesis of malignant pleural mesothelioma (MPM) provide new opportunities for targeted molecular therapies for this highly lethal disease. The present study was undertaken to examine the effects of the histone deacetylase inhibitor, Depsipeptide (DP) FK228, in conjunction with the cyclin-dependent kinase inhibitor, Flavopiridol (FLA), in cultured MPM cells.

EXPERIMENTAL DESIGN

Proliferation and apoptosis in drug-treated, virally transduced, or control cells were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Apo-bromodeoxyuridine techniques. Western blot and ELISA techniques were used to examine signal transduction and cell cycle-related protein levels in MPM cells exposed to DP and/or FLA in the presence or absence of calphostin, phorbol-12,13-dibutyrate, 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole, or adenoviral p21 transduction.

RESULTS

DP (1-50 ng/ml x 6 h) or FLA (100-200 nM x 72 h) alone, mediated low-level, dose-dependent growth inhibition in MPM cells. In contrast, sequential DP/FLA treatment mediated marked growth inhibition and apoptosis in these cell lines. The cytotoxic effects of DP/FLA were considerably less pronounced in cultured normal cells. The proapoptotic effects of DP/FLA treatment coincided with inhibition of DP-mediated induction of p21 by FLA. Overexpression of p21 by adenoviral gene transfer techniques rendered MPM cells refractory to the cytotoxic effects of this treatment regimen. In p21 reporter assays, promoter activation by DP was antagonized by FLA. The magnitude of inhibition of DP-mediated p21 induction by FLA exceeded that observed with the pTEFb antagonist 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole. Calphostin C abrogated p21 induction mediated by DP and enhanced DP-mediated apoptosis in a manner comparable with FLA in MPM cells; in contrast, phorbol-12,13-dibutyrate blocked FLA-mediated inhibition of p21 induction by DP and markedly protected these cells from the apoptotic effects of sequential DP/FLA.

CONCLUSIONS

FLA abrogates DP-mediated induction of p21 expression, in part, via inhibition of protein kinase C signaling and markedly potentiates the cytotoxic effects of DP in MPM cells.

Sodium butyrate and tributyrin induce in vivo growth inhibition and apoptosis in human prostate cancer

Histone deacetylase inhibitors (HDACs) are known to exhibit antiproliferative effects on various carcinoma cells. In this study, the in vivo efficiency of two HDACs, sodium butyrate and tributyrin, on prostate cancer growth inhibition were investigated. To gain an insight into the possible underlying pathways, cell culture experiments were performed focusing on the expression of p21, Rb and c-myc. For in vivo testing, prostate cancer cell lines (PC3 and TSU-Pr1) were seeded on the chorioallantois membrane (CAM) and implanted in a xenograft model using nude mice. Standard Western blot analysis was performed for protein expression of p21, Rb and c-myc in HDAC-treated vs untreated prostate cancer cells. Both sodium butyrate and tributyrin had a considerable treatment effect on microtumours on the chicken egg at already very low concentrations of 0.1 mM. Tributyrin-treated tumours showed the strongest effect with 38% apoptotic nuclei in the prostate cancer cell line PC3. In the mouse model, there was almost no difference between sodium butyrate and tributyrin. In untreated animals the tumours were almost double the size 4 weeks after implantation. Tumours of the treatment groups had a significantly lower percentage of Ki-67-positive-stained nuclei. As demonstrated by Western blot analysis, these effects seem to be independent of p53 status and a pathway via p21–Rb–c-myc is possibly involved. In this study we have demonstrated a substantial in vivo treatment effect, which can be induced by the application of sodium butyrate or the orally applicable tributyrin in human prostate cancer. The given results may provide the rationale to apply these drugs in well-controlled clinical trials in patients being at high risk of recurrence after specific therapy or in patients with locally or distant advanced prostate cancer.

Update on the Proteasome Inhibitor Bortezomibin Hematologic Malignancies

The ubiquitin-proteasome system plays a crucial role in eukaryotic cells in maintaining protein homeostasis. Through the disruption of a variety of pathways and cell cycle checkpoints, proteasome inhibition leads to apoptosis and in experimental models can overcome chemoresistance. Bortezomib is the first of its class of proteasome inhibitors tested in humans that showed promising activity in several tumor types, and especially in hematologic malignancies, in phase I studies. The remarkable results obtained in phase II studies in multiple myeloma (MM) led to its fast-track approval by the US Food and Drug Administration in May 2003 for relapsed MM. More recent observation also revealed promising activity in non-Hodgkin's lymphoma. This review will explore the rationale for the use of bortezomib in hematologic malignancies as well as provide an update on the results of ongoing studies and future directions for the use of this new agent in hematologic malignancies. The mechanism of action of bortezomib and its nonoverlapping toxicity profile make it a very appealing drug for combination with other chemotherapeutic or biologic agents. Bortezomib represents an excellent example of how progress in understanding the biology of cancer cells can impact clinical practice and lead toward a new era of rational therapeutics.

Comparison of tumor marker CA 242 with CA 19-9 and carcinoembryonic antigen (CEA) in pancreatic cancer

BACKGROUND/AIMS

Although there are a variety of tumor markers used for diagnosis of pancreatic carcinoma, the sensitivity and specificity of those markers have not yet reached an ideal level. The aim of this study was to compare the diagnostic value of CA 242 with CA 19-9 and CEA in the patients with pancreatic cancer.

METHODOLOGY

Serum CA 242, CA 19-9 and CEA levels were determined in 135 subjects in the following groups: Pancreatic cancer (n = 40), cholangiocellular carcinoma (n = 15), hepatocellular carcinoma (n = 10), cirrhosis (n = 7), chronic active hepatitis (n = 7), choledochal stone (n = 12), chronic pancreatitis (n = 9), acute pancreatitis (n = 6), and healthy controls (n = 29).

RESULTS

An elevated serum CA 242 concentration (> 20 U/mL) was found in 30 out of 40 (70%) (mean; 2163 +/- 838 U/mL) patients with pancreas cancer, in 11 out of 15 patients with cholangiocellular carcinoma (93.3%) (mean 916 +/- 529 U/mL), in none of patients with hepatocellular carcinoma and healthy controls. Slightly elevated CA 242 concentration was found in 6 out of 41 patients with benign hepatobiliary and pancreatic disease (range 0.4-97.8 U/mL) (1 acute pancreatitis, 2 chronic pancreatitis, 1 cirrhosis, 2 choledochal stone). Mean serum CA 242, CA 19-9 and CEA levels of the pancreas cancer group were significantly higher than those of the other groups except the cholangiocellular carcinoma group. There was no significant difference between the stage of pancreas cancer regarding mean serum CA 242, CA 19-9 and CEA level. There was positive correlation between serum CA 242 and CA 19-9 level. In the pancreas cancer, the sensitivity of CA 242, CA 19-9 and CEA was 75%, 80%, 40%, respectively and the specificity of those markers was 85.5%, 67.5% and 73%, respectively.

CONCLUSIONS

In conclusion, the advantage of CA 242 compared to CA 19-9 is that its specificity is higher than that of CA 19-9 in the diagnosis of pancreas cancer.

Critical upstream signals of cytochrome C release induced by a novel Bcl-2 inhibitor

Cytochrome c release is a central step in the apoptosis induced by many death stimuli. Bcl-2 plays a critical role in controlling this step. In this study, we investigated the upstream mechanism of cytochrome c release induced by ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate (HA14-1), a recently discovered small molecule inhibitor of Bcl-2. HA14-1 was found to induce cytochrome c release from the mitochondria of intact cells but not from isolated mitochondria. Cytochrome c release from isolated mitochondria requires the presence of both HA14-1 and exogenous Ca(2+). This suggests that both mitochondrial and extramitochondrial signals are important. In intact cells, treatment with HA14-1 caused Ca(2+) spike, change in mitochondrial membrane potential (Delta psi(m)) transition, Bax translocation, and reactive oxygen species (ROS) generation prior to cytochrome c release. Pretreatment with either EGTA acetoxymethyl ester or vitamin E resulted in a significant decrease in cytochrome c release and cell death induced by HA14-1. Furthermore pretreatment with RU-360, an inhibitor of the mitochondrial Ca(2+) uniporter, or with EGTA acetoxymethyl ester, but not with vitamin E, prevented the HA14-1-induced Delta psi(m) transition and Bax translocation. This suggests that ROS generation is an event that occurs after the Delta psi(m) transition and Bax translocation. Together these data demonstrate that the Ca(2+) spike, mitochondrial Bcl-2 presensitization, and subsequent Delta psi(m) transition, Bax translocation, and ROS generation are important upstream signals for cytochrome c release upon HA14-1 stimulation. The involvement of endoplasmic reticulum and mitochondrial signals suggests both organelles are crucial for HA14-1-induced apoptosis.

12-O-Tetradecanoylphorbol-13-acetate May Both Potentiate and Decrease the Generation of Apoptosis by the Antileukemic Agent Arsenic Trioxide in Human Promonocytic Cells

Arsenic trioxide (As(2)O(3)) caused apoptosis in U-937 human promonocytic cells. This effect was potentiated by the simultaneous addition of the glutathione (GSH) synthesis inhibitor DL-buthionine-(R,S)-sulfoximine or the protein kinase C activators 12-O-tetradecanoylphorbol-13-acetate (TPA) and bryostatin 1. In addition TPA decreased the intracellular GSH content, caused ERK activation, and potentiated the As(2)O(3)-provoked activation of p38 and JNK. The addition of N-acetyl-L-cysteine, the PKC inhibitor GF109203X, and the MEK/ERK inhibitors PD98059 and U0126 attenuated both apoptosis induction and GSH decrease, whereas the p38 inhibitor SB203580 and the JNK inhibitor SP600125 were ineffective. TPA also potentiated ERK activation and GSH depletion when added simultaneously to cadmium chloride (CdCl(2)) and doxorubicin. However, TPA only enhanced apoptosis in the case of CdCl(2), which is a GSH-sensitive agent, whereas it reduced the toxicity of doxorubicin and other DNA-specific drugs. Finally, preincubation for 14-24 h with TPA did not potentiate but, instead, attenuated the As(2)O(3)- and CdCl(2)-provoked apoptosis. The same result was obtained by preincubation with bryostatin 1 and other differentiation inducers. It is concluded that TPA increases the apoptotic action of As(2)O(3), an effect mediated by ERK activation and GSH depletion. However, the increase in apoptosis is only effective in non-differentiated cells.

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) Promotes Mitochondrial Dysfunction and Apoptosis Induced by 7-Hydroxystaurosporine and Mitogen-Activated Protein Kinase Kinase Inhibitors in Human Leukemia Cells That Ectopically Express Bcl-2 and Bcl-xL

Previous studies have demonstrated that cotreatment with mitogen activated-protein kinase kinase (MEK) 1/2 inhibitors (e.g., PD184352) and the checkpoint abrogator 7-hydroxystaurosporine (UCN-01) dramatically induces apoptosis in a variety of human leukemia and multiple myeloma cell types. The purpose of this study was to evaluate the roles of Bcl-2 family members and the relative contribution of the intrinsic mitochondrial versus the extrinsic receptor-related apoptotic pathways to MEK inhibitors/UCN-01-induced leukemic cell death. Cotreatment of U937 cells with PD184352 and UCN-01 resulted in the activation of procaspase-3, -9, and -8 as well as Bid cleavage. PD184352/UCN-01-induced mitochondrial dysfunction and apoptosis were both substantially attenuated in cells ectopically expressing Bcl-2, an N-terminal phosphorylation loop-deleted mutant Bcl-2, or Bcl-xL, but not in cells expressing dominant-negative (DN) caspase-8, cytokine response modifier A (cowpox virus-encoded antiapoptotic protein), or DN Fas-associated death domain. Coadministration of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) or TNF-alpha substantially increased MEK inhibitors (e.g., PD184352 or U0126)/UCN-01-induced mitochondrial dysfunction, activation of procaspase-8 and Bid, and apoptosis in Bcl-2- and Bcl-xL-overexpressing cells but not in those in which the extrinsic pathway was interrupted. Together, these findings suggest that the MEK inhibitors/UCN-01 regimen primarily induces leukemic cell apoptosis by engaging the intrinsic, mitochondrial apoptotic pathway and that resistance to these events conferred by increased expression of certain antiapoptotic Bcl-2 family members can be overcome, at least in part, by coadministration of TRAIL and other agents that activate the extrinsic apoptotic cascade.

The proteasome inhibitor bortezomib promotes mitochondrial injury and apoptosis induced by the small molecule Bcl-2 inhibitor HA14-1 in multiple myeloma cells

Interactions between the small molecule Bcl-2 inhibitor HA14-1 and proteasome inhibitors, including bortezomib (Velcade; formerly known as PS-341) and MG-132, have been examined in human multiple myeloma cells. Sequential (but not simultaneous) exposure of MM.1S cells to bortezomib or MG-132 (10 h) followed by HA14-1 (8 h) resulted in a marked increase in mitochondrial injury (loss of DeltaPsim, cytochrome c, Smac/DIABLO, and apoptosis-inducing factor release), activation of procaspases-3, -8, and -9, and Bid, induction of apoptosis, and loss of clonogenicity. Similar interactions were observed in U266 and MM.1R dexamethasone-resistant myeloma cells. These events were associated with Bcl-2 cleavage, Bax, Bak, and Bad accumulation, mitochondrial translocation of Bax, abrogation of Mcl-1, Bcl-xL, and XIAP upregulation, and a marked induction of JNK and p53. Bortezomib/HA14-1 treatment triggered an increase in reactive oxygen species (ROS), which, along with apoptosis, was blocked by the free radical scavenger N-acetyl-L-cysteine (L-NAC). L-NAC also opposed bortezomib/HA14-1-mediated JNK activation, upregulation of p53 and Bax, and release of cytochrome c and Smac/DIABLO. Finally, bortezomib/HA14-1-mediated apoptosis was unaffected by exogenous IL-6. Together, these findings indicate that sequential exposure of myeloma cells to proteasome and small molecule Bcl-2 inhibitors such as HA14-1 may represent a novel therapeutic strategy in myeloma.

Proteasome inhibitors potentiate leukemic cell apoptosis induced by the cyclin-dependent kinase inhibitor flavopiridol through a SAPK/JNK- and NF-κB-dependent process

Interactions between proteasome and cyclin-dependent kinase inhibitors have been examined in human leukemia cells in relation to induction of apoptosis. Simultaneous exposure (24 h) of U937 myelomonocytic leukemia cells to 100 nM flavopiridol and 300 nM MG-132 resulted in a marked increase in mitochondrial injury (cytochrome c, Smac/DIABLO release, loss of deltaPsi(m)), caspase activation, and synergistic induction of cell death, accompanied by a marked decrease in clonogenic potential. Similar effects were observed with other proteasome inhibitors (e.g., Bortezomib (VELCADE trade mark bortezomib or injection), lactacystin, LLnL) and cyclin-dependent kinase inhibitors (e.g., roscovitine), as well as other leukemia cell types (e.g., HL-60, Jurkat, Raji). In U937 cells, synergistic interactions between MG-132 and flavopiridol were associated with multiple perturbations in expression/activation of signaling- and survival-related proteins, including downregulation of XIAP and Mcl-1, activation of JNK and p34(cdc2), and diminished expression of p21(CIP1). The lethal effects of MG-132/flavopiridol were not reduced in leukemic cells ectopically expressing Bcl-2, but were partially attenuated in cells ectopically expressing dominant-negative caspase-8 or CrmA. Flavopiridol/proteasome inhibitor-mediated lethality was also significantly diminished by agents and siRNA blocking JNK activation. Lastly, coadministration of MG-132 with flavopiridol resulted in diminished DNA binding of NF-kappaB. Notably, pharmacologic interruption of the NF-kappaB pathway (e.g., by BAY 11-7082, PDTC, or SN-50) or molecular dysregulation of NF-kappaB (i.e., in cells ectopically expressing an IkappaBalpha super-repressor) mimicked the actions of proteasome inhibitors in promoting flavopiridol-induced mitochondrial injury, JNK activation, and apoptosis. Together, these findings indicate that proteasome inhibitors strikingly lower the apoptotic threshold of leukemic cells exposed to pharmacologic CDK inhibitors, and suggest that interruption of the NF-kappaB cytoprotective pathway and JNK activation both play key roles in this phenomenon. They also raise the possibility that combining proteasome and CDK inhibitors could represent a novel antileukemic strategy.

Inhibition of PI-3 kinase sensitizes human leukemic cells to histone deacetylase inhibitor-mediated apoptosis through p44/42 MAP kinase inactivation and abrogation of p21CIP1/WAF1 induction rather than AKT inhibition

Effects of the PI-3 kinase inhibitor LY294002 (LY) have been examined in relation to responses of human leukemia cells to histone deacetylase inhibitors (HDIs). Coexposure of U937 cells for 24 h to marginally toxic concentrations of LY294002 (e.g., 30 microM) and sodium butyrate (SB; 1 mM) resulted in a marked increase in mitochondrial damage (e.g., cytochrome c and Smac/DIABLO release, loss of DeltaPsi(m)), caspase activation, and apoptosis. Similar results were observed in Jurkat, HL-60, and K562 leukemic cells and with other HDIs (e.g., SAHA, MS-275). Exposure of cells to SB/LY was associated with Bcl-2 and Bid cleavage, XIAP and Mcl-1 downregulation, and diminished CD11b expression. While LY blocked SB-mediated Akt activation, enforced expression of a constitutively active (myristolated) Akt failed to attenuate SB/LY-mediated lethality. Unexpectedly, treatment of cells with SB+/-LY resulted in a marked reduction in phosphorylation (activation) of p44/42 mitogen-activated protein (MAP) kinase. Moreover, enforced expression of a constitutively active MEK1 construct partially but significantly attenuated SB/LY-induced apoptosis. Lastly, cotreatment with LY blocked SB-mediated induction of p21(CIP1/WAF1); moreover, enforced expression of p21(CIP1/WAF1) significantly reduced SB/LY-mediated apoptosis. Together, these findings indicate that LY promotes SB-mediated apoptosis through an AKT-independent process that involves MEK/MAP kinase inactivation and interference with p21(CIP1/WAF1) induction.

Downmodulation of ERK activity inhibits the proliferation and induces the apoptosis of primary acute myelogenous leukemia blasts

MAP kinase/ERK kinase (MEK)-extracellular signal-regulated kinase (ERK) kinases are frequently activated in acute myelogenous leukemia (AML), and can have prosurvival function. The purpose of this study was to induce downmodulation of MEK-ERK activation in AML primary blasts in order to detect the effect on cell cycle progression and on the apoptosis of leukemic cells. We investigated 14 cases of AML with high ERK 1/2 activity and four cases with undetectable or very low activity. After 24 h incubation of the AML blasts with high ERK activity using PD98059 (New England BioLabs, Beverly, MA, USA), a selective inhibitor of MEK1 phosphorylation, at concentrations of 20 and 40 microM, we observed a strong decrease in the levels of ERK1/2 activity. A significant decrease of blast cell proliferation compared with untreated controls was found. In contrast, the proliferation of blast cells that expressed low or undetectable levels of ERK activity was not inhibited. Time-course analysis demonstrated that the downmodulation of MEK1/2, ERK1 and ERK2 dual-phosphorylation was evident even after 3 h of treatment with 20 and 40 microM. The cleavage of poly(ADP-ribose) polymerase (PARP), an early sign of apoptosis, appeared after 18 h of PD98059 treatment at concentrations of 20 and 40 microM in eight of the 14 cases. After 24 h of treatment, cleaved PARP appeared in all 14 cases. Time-course analysis of cell cycle progression and apoptosis showed that PD98059 induced a G1-phase accumulation with low or undetectable levels of apoptosis after 24 h incubation; after 48 and 72 h incubation, a significant increase of apoptosis was observed. Thus, the primary effect of ERK downmodulation was a cell cycle arrest followed by the apoptosis of a significant percentage of the leukemic blasts. The preclinical model of leukemia treatment reported in this paper makes further comment with regard to MEK1 inhibition as a useful antileukemic target, and encourages the conducting of in vivo studies and clinical investigations.

Synergistic antileukemic interactions between 17-AAG and UCN-01 involve interruption of RAF/MEK- and AKT-related pathways

Interactions between the protein kinase C (PKC) and Chk1 inhibitor UCN-01 and the heat shock protein 90 (Hsp90) antagonist 17-AAG have been examined in human leukemia cells in relation to effects on signal transduction pathways and apoptosis. Simultaneous exposure (30 hours) of U937 monocytic leukemia cells to minimally toxic concentrations of 17-AAG (eg, 400 nM) and UCN-01 (eg, 75 nM) triggered a pronounced increase in mitochondrial injury (ie, loss of mitochondrial membrane potential [Deltapsim]; cytosolic release of cytochrome c), caspase activation, and apoptosis. Synergistic induction of apoptosis was also observed in other human leukemia cell types (eg, Jurkat, NB4). Coexposure of human leukemia cells to 17-AAG and the PKC inhibitor bisindolylmaleimide (GFX) did not result in enhanced lethality, arguing against the possibility that the PKC inhibitory actions of UCN-01 are responsible for synergistic interactions. The enhanced cytotoxicity of this combination was associated with diminished Akt activation and marked down-regulation of Raf-1, MEK1/2, and mitogen-activated protein kinase (MAPK). Coadministration of 17-AAG and UCN-01 did not modify expression of Hsp90, Hsp27, phospho-JNK, or phospho-p38 MAPK, but was associated with further p34cdc2 dephosphorylation and diminished expression of Bcl-2, Mcl-1, and XIAP. In addition, inducible expression of both a constitutively active MEK1/2 or myristolated Akt construct, which overcame inhibition of ERK and Akt activation, respectively, significantly attenuated 17-AAG/UCN-01-mediated lethality. Together, these findings indicate that the Hsp90 antagonist 17-AAG potentiates UCN-01 cytotoxicity in a variety of human leukemia cell types and suggest that interference with both the Akt and Raf-1/MEK/MAP kinase cytoprotective signaling pathways contribute to this phenomenon.

Apoptotic signaling in multiple myeloma: therapeutic implications

Fifteen thousand new cases of multiple myeloma (MM) will occur in the United States in 2003, and the disease remains incurable. Diverse classes of chemotherapeutic agents induce cell death or apoptosis in MM cells; however, prolonged drug exposures ultimately induce chemoresistance. The mechanisms whereby MM cells resist drugs include alterations in intracellular signaling as well as adherence and cytokines in the bone marrow (BM) microenvironment. Novel agents that target the MM cell in its BM microenvironment are needed to both enhance anti-MM activity and prevent development of drug resistance. Delineation of cellular growth and apoptotic signaling pathways in MM cells may identify molecules that serve as novel therapeutic targets on the basis of interruption of MM cell growth or triggering of MM cell death.

Depsipeptide (FR901228) induces histone acetylation and inhibition of histone deacetylase in chronic lymphocytic leukemia cells concurrent with activation of caspase 8-mediated apoptosis and down-regulation of c-FLIP protein

Depsipeptide is in clinical trials for chronic lymphocytic leukemia (CLL) on the basis of earlier observations demonstrating selective in vitro activity in CLL. We sought to determine the relationship of histone H3 and H4 acetylation, inhibition of histone deacetylase, and apoptosis observed in CLL cells to justify a pharmacodynamic end point in these clinical trials. We demonstrate that in vitro depsipeptide induces histone H3 and H4 acetylation and histone deacetylase enzyme inhibition at concentrations corresponding to the LC50 (concentration producing 50% cell death) for cultured CLL cells (0.038 microM depsipeptide). The changes in histone acetylation are lysine specific, involving H4 K5, H4 K12, and H3 K9, and to a lesser extent H4 K8, but not H4 K16 or H3 K14. Depsipeptide-induced apoptosis is caspase dependent, selectively involving the tumor necrosis factor (TNF) receptor (extrinsic pathway) initiating caspase 8 and effector caspase 3. Activation of caspase 8 was accompanied by the down-regulation of cellular FLICE-inhibitory protein (c-FLIP, I-FLICE) without evidence of Fas (CD95) up-regulation. Changes in other apoptotic proteins, including Bcl-2, Bax, Mcl-1, and X-linked inhibitor of apoptosis (XIAP), were not observed. Our results demonstrate a relationship between target enzyme inhibition of histone deacetylase, histone H3 and H4 acetylation, and apoptosis involving the TNF-receptor pathway of apoptosis that is not used by other therapeutic agents in CLL. These data suggest use of histone H3 and H4 acetylation, inhibition of histone deacetylase, and down-regulation of FLIP as pharmacodynamic end points for further evaluation of this drug in patients.

Map kinase signaling pathways and hematologic malignancies

Mitogen-activated protein (Map) kinases are widely expressed serine-threonine kinases that mediate important regulatory signals in the cell. Three major groups of Map kinases exist: the p38 Map kinase family, the extracellular signal-regulated kinase (Erk) family, and the c-Jun NH2-terminal kinase (JNK) family. The members of the different Map kinase groups participate in the generation of various cellular responses, including gene transcription, induction of cell death or maintenance of cell survival, malignant transformation, and regulation of cell-cycle progression. Depending on the specific family isoform involved and the cellular context, Map kinase pathways can mediate signals that either promote or suppress the growth of malignant hematopoietic cells. Over the last few years, extensive work by several groups has established that Map kinase pathways play critical roles in the pathogenesis of various hematologic malignancies, providing new molecular targets for future therapeutic approaches. In this review, the involvement of various Map kinase pathways in the pathophysiology of hematologic malignances is summarized and the clinical implications of the recent advances in the field are discussed.

The effect of flavopiridol on the growth of p16+ and p16- melanoma cell lines

Flavopiridol is the first cyclin-dependent kinase inhibitor to enter clinical trials. Flavopiridol has been shown to mimic, in part, the effect of the cell cycle control gene p16, which is frequently lost or mutated in malignant melanoma, making it an ideal candidate for targeted therapy in this disease. In these studies we investigated the effect of flavopiridol, at various concentrations, on the growth and gene expression of nine human melanoma cell lines with intact, absent or mutated p16. A cytostatic effect of flavopiridol on the growth of six melanoma cell lines with a mutated or non-expressed p16 (p16-) was seen at low concentrations of flavopiridol (mean 50% inhibitory concentration [IC(50)] = 12.5 nM), while the three melanoma cell lines with intact p16 (p16+) required higher concentrations (mean IC(50) = 25 nM) to produce this effect. Apoptotic cell death increased with increasing concentrations of flavopiridol in both p16- and p16+ cells. Exposure of cells to high flavopiridol concentrations (>100 nM) resulted in decreased expression of genes downstream in the normal p16 cell cycle control pathway (Rb and E2F) and the anti-apoptotic gene BCL2. No change in BCL2 expression was found after exposure to IC(50) concentrations of flavopiridol. These data indicate that flavopiridol in low, clinically achievable concentrations may have significant cytostatic effects, particularly in p16- melanoma cells, and may provide new molecular-based therapies for melanoma, particularly when combined with agents that target anti-apoptotic mechanisms.

Designing anticancer drugs via the achilles heel: ceramide, allylic ketones, and mitochondria

Published reports are reviewed as the basis of a proposal that an effective antineoplastic drug should contain several features: (a) resemblance to the natural lipid, ceramide; (b) an allylic alcohol and/or allylic ketone moiety; (c) a hydroxyl and/or a nitrogen atom near the allylic group; (d) conjugated double bonds as part of the allylic region. The drug should produce reactive oxygen species in tumor mitochondria, stimulate the generation of ceramide in the tumor, and condense with mitochondrial glutathione. It is pointed out that some antibiotics with these features are also active against cancer cells; perhaps anticancer drugs with these features will prove useful as antibiotics. Common problems in working with lipoidal substances are discussed.

Targeting oncogene dependence and resistance

Our expanding experience with imatinib mesylate provides instructive lessons on the power and pitfalls of targeted therapy. The often impressive initial clinical responses seen with imatinib in a variety of malignancies inevitably give way to the emergence of resistant disease. Recent findings reveal several mechanisms of resistance and suggest ways to overcome them.

Issues and progress with protein kinase inhibitors for cancer treatment

Identification of the key roles of protein kinases in cancer has led to extensive efforts to develop kinase inhibitors for the treatment of a wide range of cancers, and more than 30 such agents are now in clinical trials. Here, we consider the crucial issues in the development of kinase inhibitors for cancer, and discuss strategies to address the challenges raised by these issues in the light of preclinical and clinical experiences so far.

The use of cyclin-dependent kinase inhibitors alone or in combination with established cytotoxic drugs in cancer chemotherapy

Cyclin-dependent kinase (CDK) inhibitors are small molecule inhibitors of the kinases required for the orderly progression of cells, both normal and neoplastic, through the cell cycle. Because cell cycle dysregulation is such a common occurrence in neoplasia, the search for agents that might block cell cycle traverse has been the focus of intense interest. These efforts have led to the identification of a broad array of compounds that interfere directly with the function of CDKs. Two of these agents (flavopiridol and UCN-01) have now entered the clinical arena, and others are scheduled to do so in the near future. In preclinical studies, CDK inhibitors have shown the ability not only to block neoplastic cell proliferation, but also to induce, through a variety of mechanisms, programmed cell death. The latter capacity may stem from the diverse effects that CDK inhibitors exert on multiple kinases and apoptotic regulatory molecules. In addition, there is abundant preclinical evidence that CDK inhibitors can potentiate, generally in a dose- and sequence-dependent manner, the anti-tumor effects of many established cytotoxic agents. In clinical studies in humans, flavopiridol and UCN-01 have been shown to be tolerable, although clear evidence of single agent activity or enhancement of the efficacy of established agents has not yet emerged. This may reflect a failure to optimize drug schedules/pharmacokinetics, or to identify the critical molecular targets of these agents. Finally, in recent years, a rationale has emerged for combining CDK inhibitors with other molecularly targeted agents (i.e. differentiation-inducers and signal transduction modulators). Current research has basically two goals: (a). to identify CDK inhibitor concentrations and schedules that inhibit the growth of and induce apoptosis in specific tumor cell types; and (b). to establish a rational basis for combining CDK inhibitors with more conventional cytotoxic agents to enhance antitumor efficacy. This review gives a brief summary of such efforts, with an emphasis on agents and combinations that are in or near clinical development.

Bryostatin 1 and UCN-01 potentiate 1-beta-D-arabinofuranosylcytosine-induced apoptosis in human myeloid leukemia cells through disparate mechanisms

The effects of the PKC activator and down-regulator bryostatin 1 and the PKC and Chk1 inhibitor 7-hydroxystaurosporine (UCN-01) were compared with respect to potentiation of 1-beta-D-arabinofuranosylcytosine (ara-C)-induced apoptosis in human myelomonocytic leukemia cells (U937). Whereas bryostatin 1 and UCN-01 both markedly enhanced ara-C-induced mitochondrial injury (e.g., cytochrome c and Smac/DIABLO release, loss of mitochondrial membrane potential), caspase activation, and apoptosis, ectopic expression of an N-terminal loop-deleted Bcl-2 mutant protein protected cells from ara-C/UCN-01- but not ara-C/bryostatin 1-mediated lethality. Conversely, ectopic expression of CrmA or dominant-negative caspase-8 abrogated potentiation of ara-C-mediated apoptosis by bryostatin 1 but not by UCN-01. Exposure of cells to ara-C and bryostatin 1 (but not UCN-01) resulted in sustained release of tumor necrosis factor (TNF) alpha; moreover, potentiation of ara-C lethality by bryostatin 1 (but not by UCN-01) was reversed by coadministration of TNF soluble receptors or the selective PKC inhibitor bisindolylmaleimide (1 microM). Finally, similar events were observed in the human promyelocytic leukemia cell line HL-60. Together, these findings suggest that potentiation of ara-C lethality in human myeloid leukemia cells by bryostatin 1 but not UCN-01 involves activation of the extrinsic, receptor-mediated apoptotic pathway, and represents a consequence of bryostatin 1-mediated release of TNF-alpha. They also argue that the mechanism by which bryostatin 1 promotes ara-C-induced mitochondrial injury, caspase activation, and apoptosis involves factors other than or in addition to PKC down-regulation or modulation of Bcl-2 phosphorylation status.

Combined treatment with the checkpoint abrogator UCN-01 and MEK1/2 inhibitors potently induces apoptosis in drug-sensitive and -resistant myeloma cells through an IL-6-independent mechanism

The effects of combined exposure to the checkpoint abrogator UCN-01 and pharmacologic MEK1/2 inhibitors were examined in human multiple myeloma (MM) cell lines. Treatment of RPMI8226, NCI-H929, and U266 MM cells with a minimally toxic concentration of UCN-01 (150 nM) for 24 hours resulted in mitogen-activated protein (MAP) kinase activation, an effect that was blocked by coadministration of the MEK1/2 inhibitor PD184352. These events were accompanied by enhanced activation of p34(cdc2) and a marked increase in mitochondrial damage (loss of DeltaPsim; cytochrome c and Smac/DIABLO (direct IAP binding protein with low pI) release), poly(ADP-ribose) polymerase (PARP) cleavage, and apoptosis. PD184352/UCN-01 also dramatically reduced clonogenic survival in each of the MM cell lines. In contrast to As(2)0(3), apoptosis induced by PD184352/UCN-01 was not blocked by the free-radical scavenger N-acetyl-L-cysteine. Whereas exogenous interleukin 6 substantially prevented dexamethasone-induced lethality in MM cells, it was unable to protect them from PD184352/UCN-01-induced apoptosis despite enhancing Akt activation. Insulinlike growth factor 1 (IGF-1) also failed to diminish apoptosis induced by this drug regimen. MM cell lines selected for a high degree of resistance to doxorubicin, melphalan, or dexamethasone, or displaying resistance secondary to fibronectin-mediated adherence, remained fully sensitive to PD184352/UCN-01-induced cell death. Finally, primary CD138(+) MM cells were also susceptible to UCN-01/MEK inhibitor-mediated apoptosis. Together, these findings suggest that simultaneous disruption of cell cycle and MEK/MAP kinase signaling pathways provides a potent stimulus for mitochondrial damage and apoptosis in MM cells, and also indicate that this strategy bypasses the block to cell death conferred by several other well-described resistance mechanisms.

Synergistic induction of mitochondrial damage and apoptosis in human leukemia cells by flavopiridol and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)

Interactions between the histone deacetylase inhibitor SAHA (suberoylanilide hydroxamic acid) and the cyclin-dependent kinase (CDK) inhibitor flavopiridol (FP) were examined in human leukemia cells. Simultaneous exposure (24 h) of myelomonocytic leukemia cells (U937) to SAHA (1 microM) and FP (100 nM), which were minimally toxic alone (1.5 +/- 0.5% and 16.3 +/- 0.5% apoptosis respectively), produced a dramatic increase in cell death (ie 63.2 +/- 1.9% apoptotic), reflected by morphology, procaspase-3 and -8 cleavage, Bid activation, diminished DeltaPsi(m), and enhanced cytochrome c release. FP blocked SAHA-mediated up-regulation of p21(CIP1) and CD11b expression, while inducing caspase-dependent Bcl-2 and pRb cleavage. Similar interactions were observed in HL-60 and Jurkat leukemic cells. Enhanced apoptosis in SAHA/FP-treated cells was accompanied by a marked reduction in clonogenic surivival. Ectopic expression of either dominant-negative caspase-8 (C8-DN) or CrmA partially attenuated SAHA/FP-mediated apoptosis (eg 45 +/- 1.5% and 38.2 +/- 2.0% apoptotic vs 78 +/- 1.5% in controls) and Bid cleavage. SAHA/FP induced-apoptosis was unaffected by the free radical scavenger L-N-acetyl cysteine or the PKC inhibitor GFX. Finally, ectopic Bcl-2 expression marginally attenuated SAHA/FP-related apoptosis/cytochrome c release, and failed to restore clonogenicity in cells exposed to these agents. Together, these findings indicate that SAHA and FP interact synergistically to induce mitochondrial damage and apoptosis in human leukemia cells, and suggest that this process may also involve engagement of the caspase-8-dependent apoptotic cascade.

Synergistic induction of apoptosis in human myeloid leukemia cells by phorbol 12-myristate 13-acetate and flavopiridol proceeds via activation of both the intrinsic and tumor necrosis factor-mediated extrinsic cell death pathways

Previous studies have shown that coexposure to marginally toxic concentrations of phorbol 12-myristate 13-acetate (PMA; 10 nM) and the cyclin-dependent kinase inhibitor flavopiridol (FP; 100-200 nM) synergistically induces apoptosis in human myeloid leukemia cells U937 and HL-60 (i.e., >50% apoptotic at 24 h). Attempts have now been made to characterize the cell death pathway(s) involved in this phenomenon. In contrast to cytochrome c release and caspase-3 activation, which occur within 2.5 h of PMA/FP coexposure, caspase-8 activation and Bid cleavage appeared as later events. Such findings implicate the mitochondria-dependent pathway in the initial induction of apoptosis by PMA/FP. However, U937 cells ectopically expressing CrmA, dominant-negative caspase-8, or dominant-negative Fas-associated death domain that were highly resistant to tumor necrosis factor (TNF)/cycloheximide-induced lethality displayed significant, albeit incomplete, resistance to PMA/FP-induced apoptosis after 24 h. Furthermore, coadministration of TNF soluble receptor significantly attenuated PMA/FP-induced apoptosis in U937 (p < 0.02) and HL-60 (p < 0.03) cells at 24 h. PMA/FP coadministration also triggered substantial increases in TNFalpha mRNA and protein secretion compared with the effects of PMA administered alone. The protein kinase C (PKC) inhibitor bisindolylmaleimide (1 microM) completely blocked PMA/FP-induced TNFalpha secretion in U937 cells and attenuated apoptosis. Taken together, these results suggest that coadministration of PMA with FP in myeloid leukemia cells initially triggers mitochondrial damage, an event followed by the PKC-dependent induction and release of TNFalpha, supporting a model in which the synergistic induction of leukemic cell apoptosis by this drug combination proceeds via both mitochondrial- and TNF receptor-related apoptotic pathways.