Suppression of apoptosis: role in cell growth and neoplasia

In vitro polyphenol effects on apoptosis: An update of literature data

Polyphenols are secondary plant metabolites which have been studied extensively for their health-promoting properties, and which could also exert pharmacological activities ranging from anti-inflammatory effects, to cytotoxic activity against cancer cells. The main mechanism for programmed cell death is represented by apoptosis, and its dysregulation is involved in the etiopathology of cancer. As such, substances able to induce apoptosis in cancer cells could be used as new anticancer agents. The aim of this paper is to review literature data on the apoptotic effects of polyphenols and the molecular mechanisms through which they induce these effects in cancer cells. In addition, a brief summary of the new delivery forms used to increase the bioavailability, and clinical impact of polyphenols is provided. The studies reported show that many polyphenol rich plant extracts, originating from food and herbal medicine, as well as isolated polyphenols administered individually or in combination, can regulate cell apoptosis primarily through intrinsic and extrinsic mechanisms of action in in vitro conditions. Due to these promising results, the use of polyphenols in the treatment of cancer should therefore be deeply investigated. In particular, because of the low number of clinical trials, further studies are required to evaluate the anticancer activity of polyphenols in in vivo conditions.

AMBRA1, a Novel BH3-Like Protein: New Insights Into the AMBRA1-BCL2-Family Proteins Relationship

Cellular homeostasis swings like a pendulum backward and forward between life and death. Two of the main processes, which regulate this equilibrium, are autophagy and apoptosis. While autophagy is a highly conserved self-digestion mechanism that mediates degradation of damaged or surplus components, apoptosis is a programmed cell suicide in which typical death signals induce the elimination of undesired cells. Both these processes are highly regulated by complex molecular machineries, including some common proteins whose "dual role" favors one process or the other. Among these proteins, the well-known antiapoptotic factor BCL2 downregulates autophagy through interactions with the essential autophagic effectors, BECN1/BECLIN 1 and AMBRA1. Recently, we have demonstrated that the proautophagic protein AMBRA1 contains a BH3 domain necessary for AMBRA1 binding with the antiapoptotic factor BCL2. We found that the AMBRA1-BCL2 couple have a "dual role" in autophagy and apoptosis: the mitochondrial pool of BCL2 is able to inhibit AMBRA1-dependent autophagy, whereas in cell death conditions, the cleaved form of AMBRA1 (AMBRA1^CT), resulting from CASP/CASPASES-cleavage, abrogates the prosurvival activity of BCL2 and promotes a proapoptotic amplification loop. The CASP-cleaved form of AMBRA1 bound other antiapoptotic members of the BCL2 family proteins such as MCL1 and BCL2L1/BCL-X; by contrast, no binding could be detected with the proapoptotic-BCL2 factors such as BAK1/BAK and BAX. These findings underline an intricate interplay between autophagy and cell death in which the proautophagic protein AMBRA1 and the antiapoptotic BCL2 family members are the major players. Here, we give an overview of the AMBRA1-BCL2 family proteins interactome and its involvement in controlling life and cell death. We discuss a putative therapeutic target which offers the novel BH3 motif identified in the C-terminal part of AMBRA1.

Cell-cycle involvement in autophagy and apoptosis in yeast

Regulation of the cell cycle and apoptosis are two eukaryotic processes required to ensure maintenance of genomic integrity, especially in response to DNA damage. The ease with which yeast, amongst other eukaryotes, can switch from cellular proliferation to cell death may be the result of a common set of biochemical factors which play dual roles depending on the cell's physiological state. A wide variety of homologues are shared between different yeasts and metazoans and this conservation confirms their importance. This review gives an overview of key molecular players involved in yeast cell-cycle regulation, and those involved in mechanisms which are induced by cell-cycle dysregulation. One such mechanism is autophagy which, depending on the severity and type of DNA damage, may either contribute to the cell's survival or death. Cell-cycle dysregulation due to checkpoint deficiency leads to mitotic catastrophe which in turn leads to programmed cell death. Molecular players implicated in the yeast apoptotic pathway were shown to play important roles in the cell cycle. These include the metacaspase Yca1p, the caspase-like protein Esp1p, the cohesin subunit Mcd1p, as well as the inhibitor of apoptosis protein Bir1p. The roles of these molecular players are discussed.

Kaurene diterpene induces apoptosis in U87 human malignant glioblastoma cells by suppression of anti-apoptotic signals and activation of cysteine proteases

Gliomas are the most common and malignant primary brain tumors in humans. Studies have shown that classes of kaurene diterpene have anti-tumor activity related to their ability to induce apoptosis. We investigated the response of the human glioblastoma cell line U87 to treatment with ent-kaur-16-en-19-oic acid (kaurenoic acid, KA). We analyzed cell survival and the induction of apoptosis using flow cytometry and annexin V staining. Additionally, the expression of anti-apoptotic (c-FLIP and miR-21) and apoptotic (Fas, caspase-3 and caspase-8) genes was analyzed by relative quantification (real-time PCR) of mRNA levels in U87 cells that were either untreated or treated with KA (30, 50, or 70 µM) for 24, 48, and 72 h. U87 cells treated with KA demonstrated reduced viability, and an increase in annexin V- and annexin V/PI-positive cells was observed. The percentage of apoptotic cells was 9% for control cells, 26% for cells submitted to 48 h of treatment with 50 µM KA, and 31% for cells submitted to 48 h of treatment with 70 µM KA. Similarly, in U87 cells treated with KA for 48 h, we observed an increase in the expression of apoptotic genes (caspase-8, -3) and a decrease in the expression of anti-apoptotic genes (miR-21 and c-FLIP). KA possesses several interesting properties and induces apoptosis through a unique mechanism. Further experiments will be necessary to determine if KA may be used as a lead compound for the development of new chemotherapeutic drugs for the treatment of primary brain tumors.

Altered mitochondrial apoptotic pathway in placentas from undernourished rat gestations

Maternal undernutrition (MUN) during pregnancy results in intrauterine growth-restricted (IUGR) fetuses and small placentas. Although reduced fetal nutrient supply has been presumed to be etiologic in IUGR, MUN-induced placental dysfunction may occur prior to detectable fetal growth restriction. Placental growth impairment may result from apoptosis signaled by mitochondria in response to reduced energy substrate. Therefore, we sought to determine the presence of mitochondrial-induced apoptosis under MUN and ad libitum diet (AdLib) pregnancies. Pregnant rats were fed an AdLib or a 50% MUN diet from embryonic day 10 (E10) to E20. At E20, fetuses and placentas from proximal- and mid-horns (extremes of nutrient/oxygen supply) were collected. Right-horn placentas were used to quantify apoptosis. Corresponding left-horn placentas were separated into basal (hormone production) and labyrinth (feto-maternal exchange) zones, and protein expression of the mitochondrial pathway was determined. Our results show that the MUN placentas had significantly increased apoptosis, with lower expression of cytosolic and mitochondrial anti-apoptotic Bcl2 and Bcl-X(L), and significantly higher expression of pro-apoptotic Bax and Bak especially in the labyrinth zone. This was paralleled by higher coimmunostaining with the mitochondrial marker manganese superoxide dismutase (MnSOD), indicating transition of pro-apoptotic factors to the mitochondrial membrane. Also, cytosolic cytochrome c and activated caspases-9 and -3 were significantly higher in all MUN. Conversely, peroxisome proliferator-activator receptor-γ (PPARγ), a member of the nuclear receptor family with anti-apoptotic properties, was significantly downregulated in both zones and horns. Our results suggest that MUN during rat pregnancy enhances mitochondria-dependent apoptosis in the placenta, probably due to the downregulation of PPARγ expression.

Flavone induces changes in intermediary metabolism that prevent microadenoma formation in colonic tissue of carcinogen-treated mice

SCOPE

Colorectal cancer is a major cause of cancer deaths worldwide with the need for improved therapeutics and adjuvants.

METHODS AND RESULTS

We here tested whether the secondary plant compound flavone affects the development of aberrant crypt foci and microadenomas triggered in C57BL/6J mice by 1,2-dimethylhydrazine. Ten weeks after the last 1,2-dimethylhydrazine injection, flavone was applied at 400 mg/kg body weight over 4 wk by gavage. Flavone was found to increase apoptosis and to reduce the rate of proliferation and aberrant crypt formation. More importantly, development of microadenomas was completely suppressed by flavone. Proteome analysis by 2-DE with mass spectrometric identification of regulated proteins suggests a downregulation of tricarboxylic acid cycle activity in colonocytes with compensation by increased FADH(2) production via a partial beta-oxidation of long-chain fatty acids to meet energy demands. Transcriptome analysis, using a Gene Chip expression array with 24,000 gene probes confirmed the proteome data and moreover revealed the increased expression of various solute transporters, suggesting increased substrate supply to be used for tricarboxylic acid cycle-independent energy production.

CONCLUSION

In conclusion, changes in the levels of proteins from intermediary metabolism or their encoding mRNAs are linked to flavone-induced apoptosis and the prevention of microadenoma formation in transformed colonocytes of mice.

Increased death receptor pathway of apoptotic signaling in septic mouse aorta: effect of systemic delivery of FADD siRNA

Recent evidence suggests that apoptotic cell death plays an important role in the pathophysiology of sepsis. Because there is extensive apoptosis of vascular endothelial cells in sepsis, we examined whether the death receptor pathway of apoptotic signaling is altered in thoracic aortas from mice with polymicrobial sepsis, as produced by cecal ligation and puncture (CLP). In septic aorta, total and surface expression levels of the two death receptors tumor necrosis factor receptor 1 and Fas were highly upregulated. Furthermore, marked increases in the mRNA and protein levels of Fas-associated death domain (FADD), an adaptor molecule to recruit procaspase-8 into the death-inducing signal complex, were observed in septic aorta, which were strongly suppressed by systemic delivery of small interfering RNA (siRNA) against FADD. No increase in expression of death receptors and FADD was observed in endothelium-denuded aortic tissues from septic animals. Systemic administration of FADD siRNA also resulted in great attenuation of sepsis-induced increases in expression and activation of caspase-3, an effector protease in the apoptosis cascade. Terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling (TUNEL) revealed that the significant appearance of cell apoptosis in aortic endothelium after CLP-induced sepsis was eliminated when FADD siRNA was systemically applied. Light and electron microscopic examinations of septic aorta showed cell swelling, nuclear fragmentation, and partial detachment of endothelial cells from the basal membrane, which were prevented by systemic treatment with FADD siRNA. Finally, FADD siRNA administration dramatically improved survival of CLP mice, supporting the feasibility of this gene-based approach for treating septic shock.

Evidence for modulation of BAG3 by polyomavirus JC early protein

Polyomavirus JC (JCV) infects oligodendrocytes and astrocytes in the brain and is the cause of the demyelinating disease progressive multifocal leukoencephalopathy (PML). In cell culture, JCV infection is characterized by severe damage to cellular DNA, which begins early in infection, and a viral cytopathic effect, which is observed late in infection. Nevertheless, these JCV-infected cells show a low level of apoptosis, at both the early and late stages of infection. This suggests that there is conflicting interplay between viral anti-apoptotic pathways that seek to optimize virus production, e.g. through T antigen (T-Ag)-p53 interaction, and cellular pro-apoptotic pathways that seek to eliminate virally infected cells. The apoptosis regulatory protein BAG3 is a member of the human Bcl-2-associated athanogene (BAG) family of proteins, which function as molecular co-chaperones through their interaction with Hsc70/Hsp70 and function in the regulation of the cellular stress response, proliferation and apoptosis. This study showed that BAG3 protein is downregulated upon JCV infection and that this effect is mediated by JCV T-Ag via repression of the BAG3 promoter. The site of action of T-Ag was mapped to an AP2 site in the BAG3 promoter, and gel shift and chromatin immunoprecipitation assays showed that T-Ag inhibited AP2 binding to this site, resulting in downregulation of BAG3 promoter expression. Using BAG3 and T-Ag expression and BAG3 siRNA, it was found that BAG3 and T-Ag had antagonistic effects on the induction of apoptosis, being anti-apoptotic and pro-apoptotic, respectively. The significance of these interactions to the JCV life cycle is discussed.

Expression of PTEN and SHP1, investigated from tissue microarrays in pediatric acute lymphoblastic, leukemia

PTEN and SHP1 are tumor suppressor genes involved in the regulation of cell cycle control and apoptosis. The authors investigated the protein expression of PTEN and SHP1, by immunohistochemistry in tissue microarrays from bone marrow samples in children, diagnosed with acute lymphoblastic leukaemia and nonmalignant controls. PTEN was overexpressed in diagnostic ALL samples, while SHP1 showed a low expression. Both proteins showed a significant difference in expression compared to nonmalignant controls. The roles of PTEN and SHP1 are not well investigated in pediatric leukemia and could in the future play a role as prognostic factors.

Caspase 8L, a novel inhibitory isoform of caspase 8, is associated with undifferentiated neuroblastoma

Caspase 8 is a key apoptotic factor in the receptor/ligand apoptosis-signaling cascade. Absent caspase 8 expression is shown to correlate with poor prognosis in neuroblastoma. Paradoxically, the caspase 8 gene can produce as plice variant and novel inhibitor of itself-caspase 8l. The presence of caspase 8 alone in tumors may not necessarily portend a good prognosis. We sought to determine whether caspase 8l is present in neuroblastoma and whether over-expression of this protein could inhibit caspase 8-dependent apoptosis. Six of 6 histologically undifferentiated and 2 of 5 differentiated neuroblastoma tumors expressed the caspase 8l isoform, whereas caspase 8l was absent in 3 of 3 ganglioneuromas. Seven human neuroblastoma cell lines were surveyed. Two of the 5 cell lines that expressed caspase 8 also expressed the caspase 8l isoform and both were of a less differentiated neuronal phenotype. Over-expression of caspase 8l in cell lines afforded protection against TRAIL, but not against etoposide induced apoptosis. Conversely, blockade of Caspase 8l in cells that express this splice variant made them more sensitive to apoptosis induced cell death. We demonstrate the caspase 8l isoform is present in neuroblastoma and appears to be associated with undifferentiated cell lines and tumors. Furthermore, it suppresses caspase 8-dependent apoptosis.

Effects of JC virus infection on anti-apoptotic protein survivin in progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease of the central nervous system resulting from the productive infection of oligodendrocytes by the opportunistic polyomavirus JC virus (JCV). Apoptosis is a host defense mechanism to dispose of damaged cells; however, certain viruses have the ability to deregulate apoptotic pathways to complete their life cycles. One such pathway involves survivin, a member of the inhibitor of apoptosis family, which is abundantly expressed during development in proliferating tissues but should be absent in normal, terminally differentiated cells. Immunohistochemistry performed in 20 cases of PML revealed the presence of survivin in JCV-infected oligodendrocytes and bizarre astrocytes within demyelinated plaques. Survivin up-regulation was also found in oligodendroglial and astrocytic cultures infected with JCV. Cell cycle analysis and DNA laddering demonstrated a significantly lower number of cells undergoing apoptosis on JCV infection compared with noninfected cultures; small interfering RNA inhibition of survivin resulted in a dramatic increase in apoptotic cells in JCV-infected cultures. This is the first report describing the activation of survivin by JCV infection in vitro and in PML clinical cases. These observations provide new insights into the anti-apoptotic mechanisms used by JCV to complete its lytic cycle and may suggest new therapeutic targets for PML.

The suppression of aberrant crypt multiplicity in colonic tissue of 1,2-dimethylhydrazine-treated C57BL/6J mice by dietary flavone is associated with an increased expression of Krebs cycle enzymes

Colorectal cancer is the second leading cause of cancer deaths worldwide with diet playing a prominent role in disease initiation and progression. Flavonoids are secondary plant compounds that are suggested as protective ingredients of a diet rich in fruits and vegetables. We here tested whether flavone, a flavonoid that proved to be an effective apoptosis inducer in colon cancer cells in culture, can affect the development of aberrant crypt foci (ACFs) in C57BL/6J mice in vivo when preneoplastic lesions were induced by the carcinogen 1,2-dimethylhydrazine (DMH). Flavone applied at either a low dose (15 mg/kg body wt per day) or a high dose (400 mg/kg body wt per day) reduced the numbers of ACFs significantly, independent of whether it was supplied simultaneously with the carcinogen (blocking group) or subsequent to the tumor induction phase (suppressing group). Proteome analysis performed in colonic tissue samples revealed that flavone treatment increased the expression of a number of Krebs cycle enzymes in the suppressing group and this was associated with reduced crypt multiplicity. It suggests that mitochondrial substrate oxidation is increased by flavone in colonic cells in vivo as already observed in HT-29 cells in vitro as the prime mechanism underlying tumor cell apoptosis induction by flavone. In conclusion, flavone reduces the number of ACFs in DMH-treated mice at doses that can be achieved for flavonoids by a diet rich in fruits and vegetables. Moreover, reduction in crypt multiplicity by flavone is most probably due to the preservation of a normal oxidative metabolism.

Janus kinase 2 (V617F) mutation status, signal transducer and activator of transcription-3 phosphorylation and impaired neutrophil apoptosis in myelofibrosis with myeloid metaplasia

An activating point mutation in Janus kinase 2 (JAK2 V617F) was recently identified in myelofibrosis with myeloid metaplasia (MMM). To further elucidate the pathogenic significance, we examined the JAK2 mutation burden, phosphorylation of JAK2 substrates and neutrophil apoptotic resistance. Immunoblotting revealed phosphorylation of signal transducer and activator of transcription-3 (STAT3) in all four JAK2 with high V617F mutant allele burden and seven of eight with intermediate mutant allele burden, but only one of eight with wild-type JAK2 (P<0.001). In contrast, STAT5 phosphorylation was undetectable in patient MMM neutrophils; and phosphorylation of Akt and extracellular signal-regulated kinases (ERKs) failed to correlate with JAK2 mutation status. Apoptosis was lower in MMM neutrophils (median 41% apoptotic cells, n=50) compared to controls (median 66%, n=9) or other myeloproliferative disorder patients (median 53%, n=11; P=0.002). Apoptotic resistance in MMM correlated with anemia (P=0.01) and the JAK2-V617F (P=0.01). Indeed, apoptotic resistance was greatest in MMM neutrophils with high mutant allele burden (median 22% apoptosis, n=5) than with intermediate burden (median 39%, n=23) or wild-type JAK2 (median 47%, n=22; P=0.008). These results suggest that mutant JAK2 contributes to MMM pathogenesis by constitutively phosphorylating STAT3 and diminishing myeloid cell apoptosis.

Expression of JC virus regulatory proteins in human cancer: potential mechanisms for tumourigenesis

JC virus (JCV) is a human polyomavirus that is the etiologic agent of the fatal demyelinating disease of the central nervous system known as progressive multifocal leukoencephalopathy (PML). JCV is also linked to some tumours of the brain and other organs as evidenced by the presence of JCV DNA sequences and the expression of viral proteins in clinical samples. Since JCV is highly oncogenic in experimental animals and transforms cells in culture, it is possible that JCV contributes to the malignant phenotype of human tumours with which it is associated. JCV encodes three non-capsid regulatory proteins: large T-antigen, small t-antigen and agnoprotein that interact with a number of cellular target proteins and interfere with certain normal cellular functions. In this review, we discuss how JCV proteins deregulate signalling pathways especially ones pertaining to transcriptional regulation and cell cycle control. These effects may be involved in the progression of JCV-associated tumours and may represent potential therapeutic targets.

Raf kinase as a target for anticancer therapeutics

The Ras-Raf-MEK-ERK (ERK) pathway is a logical therapeutic target because it represents a common downstream pathway for several key growth factor tyrosine kinase receptors which are often mutated or overexpressed in human cancers. Although considered mainly growth-promoting, in certain contexts, this pathway also seems to be apoptosis-suppressing. Several novel agents targeting this pathway have now been developed and are in clinical trials. One of the most interesting new agents is BAY 43-9006. Although initially developed as a Raf kinase inhibitor, it can also target several other important tyrosine kinases including VEGFR-2, Flt-3, and c-Kit, which contributes to its antiproliferative and antiangiogenic properties. To date, encouraging results have been seen with BAY 43-9006, particularly in renal cell cancers which are highly vascular tumors. This review will provide an overview of the ERK signaling pathway in normal and neoplastic tissue, with a specific focus on novel therapies targeting the ERK pathway at the level of Raf kinase.

Immunogenicity of Bcl-2 in patients with cancer

B-cell lymphoma 2 (Bcl-2) is a pivotal regulator of apoptotic cell death and it is overexpressed in many cancers. Consequently, the Bcl-2 protein is an attractive target for drug design, and Bcl-2–specific antisense oligonucleotides or small-molecule Bcl-2 inhibitors have shown broad anticancer activities in preclinical models and are currently in several clinical trials. The clinical application of immunotherapy against cancer is rapidly moving forward in multiple areas, including the adoptive transfer of anti–tumor-reactive T cells and the use of “therapeutic” vaccines. The overexpression of Bcl-2 in cancer and the fact that immune escape by down-regulation or loss of expression of this protein would impair sustained tumor growth makes Bcl-2 a very attractive target for anticancer immunotherapy. Herein, we describe spontaneous T-cell reactivity against Bcl-2 in peripheral blood from patients suffering from unrelated tumor types (ie, pancreatic cancer, breast cancer, acute myeloid leukemia [AML], and chronic lymphocytic leukemia [CLL]). Additionally, we show that these Bcl-2–reactive T cells are indeed peptide-specific, cytotoxic effector cells. Thus, Bcl-2 may serve as an important and widely applicable target for anticancer immunotherapeutic strategies (eg, in the combination with conventional radiotherapy and chemotherapy).

Prognostic value of quantifying apoptosis factor expression in favorable histology wilms tumors

Important in the homeostasis of normal tissues, apoptosis can be altered to favor cell survival within tumors. High expression of survivin, an inhibitor of apoptosis, and absence of caspase 8, a pro-apoptotic enzyme, independently correlate with poor outcomes in several tumor types. Favorable histology Wilms tumor has a remarkably high cure rate; as a result, the focus of therapy is now aimed at reducing treatment-related morbidity. With the goal of safely reducing therapy in select subgroups of patients, the authors investigated whether the levels of apoptotic factors in tumors could predict the risk for recurrence. Tumor apoptotic factor levels were surveyed in a case-control study from the National Wilms Tumor Study 5 (NWTS-5) and measured via quantitative real-time RT-PCR. Survivin and caspase 8 levels were surveyed in 92 primary tumor specimens and SMAC, Bid, and CD95 were surveyed in 24 specimens. All four pro-apoptotic factors studied (caspase 8, SMAC, Bid, and CD95) were analyzed individually and in relation to survivin expression. Although survivin mRNA was present at markedly greater levels than in normal kidney, none of the factors assayed independently or as a ratio was associated with stage of disease or risk for tumor recurrence in this group of tumors.

Nitric oxide levels in human preneoplastic colonocytes determine their susceptibility toward antineoplastic agents

The efficacy of antineoplastic compounds can depend heavily on the genetic background of the cells exposed to the drugs. This becomes evident by the fact that HT-29 human colon cancer cells but not primary murine nontransformed colonocytes are efficiently submitted to apoptosis by the flavonoid flavone. By determining caspase-3 activation, plasma membrane disintegration, and nuclear fragmentation, we show here that flavone also does not promote apoptosis in preneoplastic NCOL-1 colonocytes derived from a nontransformed human biopsy specimen. In clear contrast, the antitumor drug camptothecin potently induces apoptosis in NCOL-1 cells associated with a specific down-regulation of the antiapoptotic factor bcl-XL at the mRNA and protein levels and with the activation of the mitochondrial apoptosis pathway. Confocal microscopy revealed an increased production of superoxide anion radicals in the mitochondria of NCOL-1 cells that preceded the apoptotic events. However, in the case of flavone, the mitochondrial oxygen radicals were effectively scavenged by physiological concentrations of nitric oxide (NO), whereas in the case of camptothecin, the available nitric oxide was rapidly scavenged by the production of large quantities of cytosolic superoxide anions. Increasing the levels of nitric oxide inside NCOL-1 cells by sodium nitroprusside prevented the apoptosis induction by camptothecin. Reducing the levels of nitric oxide by using the NO synthase inhibitor, Nomega-nitro-l-arginine methyl ester in NCOL-1 cells or using HT-29 cells that intrinsically have low NO levels enabled flavone to trigger the apoptosis pathway. In conclusion, our studies demonstrate that the intracellular levels of nitric oxide significantly change the apoptotic response to antineoplastic agents in colonic cells.

NF-κB/Rel-mediated regulation of apoptosis in hematologic malignancies and normal hematopoietic progenitors

The activity of NF-kappaB/Rel transcription factors can downmodulate apoptosis in normal and neoplastic cells of the hematologic and other compartments, contributing in maintaining neoplastic clone survival and impairing response to therapy. Alterations in nfkappab or ikappaB genes are documented in some hematologic neoplasias, while in others dysfunction in NF-kappaB/Rel-activating signaling pathways can be recognized. The prosurvival properties of NF-kappaB/Rel appear to rely on the induced expression of molecules (caspase inhibitors, Bcl2 protein family members, etc.), which interfere with the apoptosis pathway. Constitutive NF-kappaB/Rel activity in some hematologic malignancies could be advantageous for neoplastic clone expansion by counteracting stress stimuli (consumption of growth factors and metabolites) and immune system-triggered apoptosis; it is furthermore likely to play a central role in determining resistance to therapy. Based on this evidence, NF-kappaB/Rel-blocking approaches have been introduced in antineoplastic strategies. The identification of NF-kappaB/Rel target genes relevant for survival in specific neoplasias is required in order to address tailored therapies and avoid possible detrimental effects due to widespread NF-kappaB/Rel inhibition. Moreover, comparative analyses of normal hematopoietic progenitors and neoplastic cell sensitivities to inhibitors of NF-kappaB/Rel and their target genes will allow to evaluate the impact of these tools on normal bone marrow.

Differential effects of kinase cascade inhibitors on neoplastic and cytokine-mediated cell proliferation

The Raf/MEK/ERK and PI3K/Akt pathways regulate proliferation and prevent apoptosis, and their altered expression is commonly observed in human cancer due to the high mutation frequency of upstream regulators. In this study, the effects of Raf, MEK, and PI3K inhibitors on conditionally transformed hematopoietic cells were examined to determine if they would display cytotoxic differences between cytokine- and oncogene-mediated proliferation, and whether inhibition of both pathways was a more effective means to induce apoptosis. In the hematopoietic model system employed, proliferation was conditional and occurred when either interleukin-3 (IL-3) or the estrogen receptor antagonist 4-hydroxytamoxifen (4HT), which activates the conditional oncoprotein (DeltaRaf:ER), were provided. Thus, upon the addition of the signal transduction inhibitors and either IL-3 or 4HT, the effects of these drugs were examined in the same cell under 'cytokine-' and 'oncoprotein' -mediated growth conditions avoiding genetic and differentiation stage heterogeneity. At drug concentrations around the reported IC(50) for the Raf inhibitor L-779,450, it suppressed DNA synthesis and induced apoptosis in hematopoietic FDC-P1 cells transformed to grow in response to either Raf-1 or A-Raf (FD/DeltaRaf-1:ER and FD/DeltaA-Raf:ER), but it displayed less effects on DNA synthesis and apoptosis when the cells were cultured in IL-3. This Raf inhibitor was less effective on B-Raf- or MEK1-responsive cells, demonstrating the specificity of this drug. MEK inhibitors also suppressed DNA synthesis and induced apoptosis in Raf-responsive cells and the effects were more significant on Raf-responsive compared to cytokine-mediated growth. The PI3K inhibitor LY294002 suppressed Raf-mediated growth, indicating that part of the long-term proliferative effects mediated by Raf are PI3K dependent. Simultaneous inhibition of both Raf/MEK/ERK and PI3K/Akt pathways proved a more efficient means to suppress DNA synthesis and induce apoptosis at lower drug concentrations.

Therapeutic efficacy of prenylation inhibitors in the treatment of myeloid leukemia

Farnesyltransferase inhibitors (FTIs) represent a new class of anticancer agents that specifically target post-translational farnesylation of various proteins that mediate several cellular processes such as signal transduction, growth, differentiation, angiogenesis and apoptosis. These compounds were originally designed to block oncogenic RAS-induced tumor growth by impeding RAS localization to the membrane, but it is now evident that FTIs also affect processing of several other proteins. The need for novel therapies in myeloid leukemia is underscored by the high rate of treatment failure due to high incidences of relapse- and treatment-related toxicities. As RAS deregulation is important in the pathogenesis of myeloid leukemias, targeting of RAS signaling may provide a new therapeutic strategy. Several FTIs (eg BMS-214662, L-778,123, R-115777 and SCH66336) have entered phase I and phase II clinical trials in myeloid leukemias. This review discusses recent clinical results, potential combination therapies, mechanisms of resistance and the clinical challenges of toxicities associated with prenylation inhibitors.

Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention

The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.

Interferons and apoptosis

The interferons (IFNs), in addition to their well-known antiviral activities, have important roles in the control of cell proliferation and are effective agents for the treatment of a limited number of malignant diseases. IFNs not only regulate cell growth and division but also influence cell survival through their effects on apoptosis. This review describes the current state of knowledge about the mechanisms of action of these cytokines on the apoptotic machinery, with particular emphasis on the synergism that exists between the IFNs and other proapoptotic agents, such as members of the tumor necrosis factor (TNF) family. The review also discusses the physiologic and clinical implications of the effects of the IFNs on apoptosis for regulation of viral infection and tumor growth.

Requirement for the PI3K/Akt pathway in MEK1-mediated growth and prevention of apoptosis: identification of an Achilles heel in leukemia

The Raf/MEK/ERK kinase cascade plays a critical role in transducing growth signals from activated cell surface receptors. Using DeltaMEK1:ER, a conditionally active form of MEK1 which responds to either beta-estradiol or the estrogen receptor antagonist 4 hydroxy-tamoxifen (4HT), we previously documented the ability of this dual specificity protein kinase to abrogate the cytokine-dependency of human (TF-1) and murine (FDC-P1 and FL5.12) hematopoietic cells lines. Here we demonstrate the ability of DeltaMEK1:ER to activate the phosphatidylinositol 3-kinase (PI3K)/Akt/p70 ribosomal S6 kinase (p70(S6K)) pathway and the importance of this pathway in MEK1-mediated prevention of apoptosis. MEK1-responsive cells can be maintained long term in the presence of beta-estradiol, 4HT or IL-3. Removal of hormone led to the rapid cessation of cell proliferation and the induction of apoptosis in a manner similar to cytokine deprivation of the parental cells. Stimulation of DeltaMEK1:ER by 4HT resulted in ERK, PI3K, Akt and p70(S6K) activation. Treatment with PI3K, Akt and p70(S6K) inhibitors prevented MEK-responsive growth. Furthermore, the apoptotic effects of PI3K/Akt/p70(S6K) inhibitors could be enhanced by cotreatment with MEK inhibitors. Use of a PI3K inhibitor and a constitutively active form of Akt, [DeltaAkt(Myr(+))], indicated that activation of PI3K was necessary for MEK1-responsive growth and survival as activation of Akt alone was unable to compensate for the loss of PI3K activity. Cells transduced by MEK or MEK+Akt displayed different sensitivities to signal transduction inhibitors, which targeted these pathways. These results indicate a requirement for the activation of the PI3K pathway during MEK-mediated transformation of certain hematopoietic cells. These experiments provide important clues as to why the identification of mutant signaling pathways may be the Achilles heel of leukemic cell growth. Leukemia treatment targeting multiple signal transduction pathways may be more efficacious than therapy aimed at inhibiting a single pathway.

Clinical relevance of increased retinoid and cAMP transcriptional programs in tumor cells rendered non-malignant by dominant negative inhibition of NFkappaB

We previously reported reciprocal regulation of extracellular matrix degrading enzymes and their endogenous inhibitors by NFkappaB. As such, dominant negative inhibition of NFkappaB in a murine lung alveolar carcinoma cell, Line 1, afforded a decrease in malignant proclivity [Cancer Res. 60(23) (2000) 6557-6562]. Contrasting the gene expression profile of malignant Line 1 tumor cells (WT-Line 1) and their non-malignant counterparts transduced with a dominant negative inhibitor of NFkappaB (mIkappaB-Line 1), we observed upregulated retinoic acid receptors (RARs) and the cAMP response element modulator (CREM), in mIkappaB-Line 1 tumor cells, and utilized heterologous promoter-reporter constructs to confirm enhanced responsiveness. We translate these findings by inducing retinoid and cAMP transcriptional programs in WT-Line 1 tumor cells with pharmacologic doses of all-trans retinoic acid (at-RA) and pentoxyfilline (PTX), respectively, and demonstrate suppression of NFkappaB activity, tumor cell derived matrix metalloprotease 9 activity, tumor cell invasiveness in vitro and spontaneous metastasis in vivo. Our results are consistent with the putative role of retinoids and cAMP in the malignant reversion of tumor cells and illustrative of the binary nature of transcriptional programs that modulate malignant progression.

Involvement of PI3K/Akt pathway in cell cycle progression, apoptosis, and neoplastic transformation: a target for cancer chemotherapy

The PI3K/Akt signal transduction cascade has been investigated extensively for its roles in oncogenic transformation. Initial studies implicated both PI3K and Akt in prevention of apoptosis. However, more recent evidence has also associated this pathway with regulation of cell cycle progression. Uncovering the signaling network spanning from extracellular environment to the nucleus should illuminate biochemical events contributing to malignant transformation. Here, we discuss PI3K/Akt-mediated signal transduction including its mechanisms of activation, signal transducing molecules, and effects on gene expression that contribute to tumorigenesis. Effects of PI3K/Akt signaling on important proteins controlling cellular proliferation are emphasized. These targets include cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors. Furthermore, strategies used to inhibit the PI3K/Akt pathway are presented. The potential for cancer treatment with agents inhibiting this pathway is also addressed.

Phosphatidylcholine and cell death

Phosphatidylcholine (PC) constitutes a major portion of cellular phospholipids and displays unique molecular species in different cell types and tissues. Inhibition of the CDP-choline pathway in most mammalian cells or overexpression of the hepatic phosphatidylethanolamine methylation pathway in hepatocytes leads to perturbation of PC homeostasis, growth arrest or even cell death. Although many agents that perturb PC homeostasis and induce cell death have been identified, the signaling pathways that mediate this cell death have not been well defined. This review summarizes recent progress in understanding the relationship between PC homeostasis and cell death.

Targeting the Raf kinase cascade in cancer therapy--novel molecular targets and therapeutic strategies

The mitogen-activated protein kinases (MAPKs) are a group of signal transducers with oncogenic potential in an assortment of cell types. Dysregulated signalling from any of the members of this family has been shown to result in development of human malignancies. Consequently, the collective goal of the scientific community is to inhibit aberrant signalling initiated from these molecules whilst minimising toxicity associated with such inhibition. This review covers events responsible for MAPK activation in detail, with an emphasis placed upon possible points of pharmacological intervention. A discussion addressing numerous chemotherapeutic approaches that have been developed over the previous decade for MAPK inhibition is also included. In addition, emphasis is placed upon the various arrays of kinase inhibitors, small molecule inhibitors, competitive inhibitors, nucleic acid aptamers and other molecules which have been proven effective in prevention of MAPK signalling. Finally, the potential therapeutic promise of many of these compounds is addressed in a manner that encompasses the complexities of MAPK signal transduction, in addition to concerns surrounding the development of drug resistance.

Novel gene therapy approach for nasopharyngeal carcinoma

This article will provide an overview on the status of cancer gene therapy, focussed specifically on its potential application in nasopharyngeal carcinoma (NPC). The concepts and strategies behind the design of therapeutic targets such as p53, p16, and death genes will be described. One of the major challenges in cancer gene therapy is tumor-specific expression of therapeutic genes, and a transcriptional targeting approach will be reviewed, in reference to NPC. Specifically, the ability to exploit the presence of Epstein-Barr virus (EBV) will be emphasized. The currently available preclinical data on genetic therapeutic approaches for NPC will be reviewed, and an outline for its future role in management of NPC, in conjunction with existing cytotoxic modalities of ionizing radiation and chemotherapy will be provided.

Enhanced microtubule-dependent trafficking and p53 nuclear accumulation by suppression of microtubule dynamics

The tumor suppressor protein p53 localizes to microtubules (MT) and, in response to DNA damage, is transported to the nucleus via the MT minus-end-directed motor protein dynein. Dynein is also responsible for MT-mediated nuclear targeting of adenovirus type 2 (Ad2). Here we show that treatment with low concentrations of MT-targeting compounds (MTCs) that do not disrupt the MT network but are known to suppress MT dynamics enhanced p53 nuclear accumulation, and the activation of the p53-downstream target genes. p53 nuclear accumulation required binding of MTCs to MTs and enhanced the induction of p53-up-regulated modulator of apoptosis (PUMA) mRNA and apoptosis on challenging cells with the DNA-damaging drug adriamycin. Low concentrations of MTCs enhanced the rate of movement of fluorescent Ad2 to the nucleus and increased the nuclear targeting efficiency of Ad2. We propose that suppression of MT dynamics by low concentrations of MTCs enhances MT-dependent trafficking toward the minus ends of MTs and facilitates nuclear targeting.

Functional analysis of zinc finger proteins that bind to the silencer element in the glutathione transferase P gene

Glutathione transferase P (GST-P) gene expression is repressed in normal rats but markedly promoted during the early stage of chemical hepatocarcinogenesis. We have previously identified a silencer region in this gene promoter. The silencer is composed of several cis-elements to which at least three proteins (Silencer factor-A, -B, and -C: SF-A, SF-B, and SF-C) are known to bind. We cloned and characterized the nuclear factor 1 family and the CCAAT/enhancer-binding protein family as SF-A and SF-B, respectively. Recently, zinc finger proteins as candidates for SF-C, which binds to GST-P silencer 2 (GPS2), were isolated. These proteins include four Krüppel-like proteins (BTEB2, EZF, LKLF, and TIEG1) and other factors containing multiple zinc finger motifs (TFIIIA and MZFP). In the present study, we found that the zinc finger proteins showed the same DNA-binding affinities to GPS2. Moreover, transfection analyses revealed that BTEB2, EZF, and TIEGI repressed the GST-P promoter activity. Therefore, these three factors might contribute to the repression of the GST-P gene expression in normal rat liver.

Heterotopic implantation alters the regulation of apoptosis and the cell cycle and generates a new metastatic site in a human pancreatic tumor xenograft model

Differences in growth and in response to antineoplastic drugs between s.c. and orthotopically implanted tumors in nude mice and between the primary tumor and the metastases in human tumors suggest that implantation site may alter the molecular regulation of tumor cells. We assessed the influence of implantation site on cell cycle and apoptotic regulation and the possible contribution of the implantation site in directing the choice of metastatic site by comparing the behavior of tumor aliquots of two human pancreatic xenografts (NP18 and NP9) implanted in the organ where the tumor grows (orthotopically), in heterotopic sites (the site of metastases (liver), and in nonmetastatic sites (subcutis and colon). We observed that implantation site changes tumor growth by altering apoptotic or cell cycle regulation in a tumor-specific manner. In the NP18 tumor it occurs by altering apoptotic induction and activation of the Bad/Bcl-XL/caspase-3 pathway through AKT and Erk regulation, but in the NP9 tumor by changing the activation and/or expression of the proteins that regulate the cell cycle (Erk, PCNA, and cyclin B1). We also observed that implantation site alters the metastatic pattern of the NP9 tumor, originating a new metastatic site.

CD4+CD7- leukemic T cells from patients with Sézary syndrome are protected from galectin-1-triggered T cell death

In early stages of cutaneous T cell lymphoma (Sézary syndrome) both CD4+CD7- and CD4+CD7+ T cells clonally expand whereas in late stages of the disease CD7- cells are predominant in number, giving rise to the question whether CD7- T cells have a survival advantage in the skin. Galectin-1, a cell-bound lectin, was recently reported to trigger apoptosis in activated CD7+ T cells. Here, we demonstrate that in contrast to activated CD7(+) T cells, quiescent and activated CD69+ CD7- T cells from healthy donors and from Sézary patients are resistant to galectin-1-mediated cell death. CD7- T cells are apoptosis-resistant even during coculture with IFN-gamma-stimulated endothelial cells that constitutively express galectin-1 in high amounts. These data imply that resistance of CD7- T cells to galectin-1-induced apoptosis may contribute to the accumulation of CD7- Sézary T cells during progression of the disease.

The Raf/MEK/ERK signal transduction cascade as a target for chemotherapeutic intervention in leukemia

The Raf/MEK/ERK (MAPK) signal transduction cascade is a vital mediator of a number of cellular fates including growth, proliferation and survival, among others. The focus of this review centers on the MAPK signal transduction pathway, its mechanisms of activation, downstream mediators of signaling, and the transcription factors that ultimately alter gene expression. Furthermore, negative regulators of this cascade, including phosphatases, are discussed with an emphasis placed upon chemotherapeutic intervention at various points along the pathway. In addition, mounting evidence suggests that the PI3K/Akt pathway may play a role in the effects elicited via MAPK signaling; as such, potential interactions and their possible cellular ramifications are discussed.

The enhanced in vitro hematopoietic activity of leridistim, a chimeric dual G-CSF and IL-3 receptor agonist

The in vitro activity of leridistim was characterized for cell proliferation, generation of colony-forming units (CFU) and differentiation of CD34+ cells. In AML-193.1.3 cells, leridistim exhibited a significant increase in potency compared to rhG-CSF, SC-65303 (an IL-3 receptor agonist) or an equimolar combination of rhG-CSF and SC-65303. CFU-GM assays demonstrated that at 50% of the maximum response, the relative potency of leridistim was 12-fold greater than the combination of rhG-CSF and rhIL-3 and 44-fold more potent than rhG-CSF alone. In multi-lineage CFU assays, a combination of erythropoietin (rhEPO) and leridistim resulted in greater numbers of BFU-E, CFU-GEMM and CFU-Mk than rhEPO alone. Ex vivo culture of peripheral blood or bone marrow CD34+ cells with leridistim substantially increased total viable cells over cultures stimulated with rhG-CSF, SC-65303, or a combination of rhG-CSF and SC-65303. Culture with leridistim, resulted in a greater increase in myeloid (CD15+/CD11b+), monocytic (CD41-/CD14+) and megakaryocytic (CD41+/CD14-) precursor cells without depleting the progenitor pool (CD34+/CD15-/CD11b-). These results demonstrate that leridistim is a more potent stimulator of hematopoietic proliferation and differentiation than the single receptor agonists (rhG-CSF and SC-65303) either alone or combined. These unique attributes suggest that leridistim may enhance hematopoietic reconstitution following myelosuppressive chemotherapy.

Enhanced ability of daniplestim and myelopoietin-1 to suppress apoptosis in human hematopoietic cells

Modified and chimeric cytokines have been developed to aid in the recovery of hematopoietic precursor cells after myeloablative chemotherapy. The interleukin-3 (IL-3) receptor agonist, daniplestim, binds to the IL-3 receptor-alpha subunit with 60-fold greater affinity and induces cell proliferation and colony-forming unit formation 10- to 22-fold better than native IL-3. A chimeric cytokine, myelopoietin-1, composed of daniplestim and a G-CSF receptor agonist binds both the IL-3 and G-CSF receptors. While the in vivo effects of daniplestim and myelopoietin-1 are well described, the mechanisms by which they stimulate growth are not well understood. We have investigated the effects of daniplestim and myelopoietin-1 on the prevention of apoptosis in two human hematopoietic cell lines, OCI-AML.5 and AML 193. Daniplestim and myelopoietin-1 prevented apoptosis to a greater degree than native recombinant IL-3 or G-CSF as determined by annexin V/propidium iodide binding and TUNEL assays. Daniplestim and myelopoietin-1 promoted the maintenance of the mitochondrial membrane potential better than native IL-3 or G-CSF. These cytokines promoted a lower redox potential as higher levels of free radicals were detected after cytokine treatment than in cytokine-deprived cells implying increased respiration. These results indicate that daniplestim and myelopoietin-1 are able to prevent apoptosis in hematopoietic cells more effectively than native IL-3 and G-CSF. These effects of daniplestim and myelopoietin-1 may contribute to their effective ability to repopulate hematopoietic precursor cells after chemotherapy.