Inhibition of Bcl-xL expression sensitizes T-cell acute lymphoblastic leukemia cells to chemotherapeutic drugs

Integration of network pharmacology and molecular docking to explore the molecular mechanism of Cordycepin in the treatment of Alzheimer's disease

Background

Cordycepin is a nucleoside adenosine analog and an active ingredient isolated from the liquid fermentation of Cordyceps. This study sought to explore the mechanism underlying the therapeutic effect of Cordycepin against Alzheimer's disease using network pharmacology and molecular docking technology.

Methods

TCMSP, SYMMAP, CTD, Super-pred, SEA, GeneCards, DisGeNET database, and STRING platform were used to screen and construct the target and protein interaction network of Cordycepin for Alzheimer's disease. The results of Gene Ontology annotation and KEGG pathway enrichment analysis were obtained based on the DAVID database. The Omicshare database was also applied in GO and KEGG pathway enrichment analysis of the key targets. The protein-protein interaction network was constructed using the STRING database, and the potential effective targets for AD were screened based on the degree values. The correlation between the potential targets of Cordycepin in the treatment of AD and APP, MAPT, and PSEN2 was analyzed using (GEPIA) databases. We obtained potential targets related to aging using the Aging Altas database. Molecular docking analysis was performed by AutoDock Vina and Pymol software. Finally, we validated the significant therapeutic targets in the Gene Expression Omnibus (GEO) database.

Results

A total of 74 potential targets of Cordycepin for treating Alzheimer's disease were identified. The potential targets of Cordycepin for the treatment of AD mainly focused on Lipid and atherosclerosis (hsa05417), Platinum drug resistance (hsa01524), Apoptosis (hsa04210), and Pathways in cancer (hsa05200). Our findings suggest that the therapeutic effect of Cordycepin on AD is primarily associated with these biological processes. We obtained 12 potential therapeutic targets for AD using the degree value in Cytoscape. Interestingly, AKT1, MAPK8, BCL2L1, FOXO3, and CTNNB1 were not only significantly associated with pathogenic genes (APP, MAPT, and PSEN2) but also with longevity in Alzheimer's Disease. Thus we speculated that the five target genes were potential core targets mediating the therapeutic effect of Cordycepin against AD. Moreover, molecular docking results analysis showed good binding affinity between Cordycepin and the five core targets. Overall, MAPK8, FOXO3 and CTNNB1 may have significant clinical and treatment implications.

Conclusion

Network pharmacology demonstrated that Cordycepin exerts a therapeutic effect against Alzheimer's disease via multiple targets and signaling pathways and has huge prospects for application in treating neurodegenerative diseases.

Inhibition of DEK Enhances Doxorubicin-Induced Apoptosis and Cell Cycle Arrest in T-Cell Acute Lymphoblastic Leukemia Cells

T-cell acute lymphoblastic leukemia (T-ALL) is a serious hematological tumor derived from early T-cell progenitors, which is extremely resistant to chemotherapy. Classically, doxorubicin (DOX) is an effective first-line drug for the treatment of T-ALL; however, DOX resistance limits its clinical effect. The DEK proto-oncogene (DEK) has been involved in neoplasms but remains unexplored in T-ALL. We silenced DEK on Jurkat cells and detected cell proliferation with cell counting and colony formation assay. Then, we detected DEK's drug sensitivity to DOX with CCK-8, cell cycle, and apoptosis with DOX treatment. Western blot analysis was performed to determine protein expression of apoptosis and cell cycle-related genes, including BCL2L1, caspase-3, and cyclin-dependent kinases (CDK). Finally, the tumorigenic ability of DEK was analyzed using a BALB/C nude mouse model. In this study, DEK was highly expressed in Jurkat cells. Inhibition of DEK can lead to decreased cell proliferation and proportion of S-phase cells in the cell cycle and more cell apoptosis, and the effect is more obvious after DOX treatment. Western blot results showed that DOX treatment leads to cell cycle arrest, reduction of cyclin-dependent kinase 6 (CDK6) protein, accumulation of CDKN1A protein, and DOX-induced apoptosis accompanied by reductions in protein levels of BCL2L1, as well as increases in protein level of caspase-3. Furthermore, DEK-silenced Jurkat cells generated a significantly smaller tumor mass in mice. Our study found that DEK is a novel, potential therapeutic target for overcoming DOX resistance in T-ALL.

IKAROS and CK2 regulate expression of BCL-XL and chemosensitivity in high-risk B-cell acute lymphoblastic leukemia

High-risk B-cell acute lymphoblastic leukemia (B-ALL) is an aggressive disease, often characterized by resistance to chemotherapy. A frequent feature of high-risk B-ALL is loss of function of the IKAROS (encoded by the IKZF1 gene) tumor suppressor. Here, we report that IKAROS regulates expression of the BCL2L1 gene (encodes the BCL-XL protein) in human B-ALL. Gain-of-function and loss-of-function experiments demonstrate that IKAROS binds to the BCL2L1 promoter, recruits histone deacetylase HDAC1, and represses BCL2L1 expression via chromatin remodeling. In leukemia, IKAROS' function is impaired by oncogenic casein kinase II (CK2), which is overexpressed in B-ALL. Phosphorylation by CK2 reduces IKAROS binding and recruitment of HDAC1 to the BCL2L1 promoter. This results in a loss of IKAROS-mediated repression of BCL2L1 and increased expression of BCL-XL. Increased expression of BCL-XL and/or CK2, as well as reduced IKAROS expression, are associated with resistance to doxorubicin treatment. Molecular and pharmacological inhibition of CK2 with a specific inhibitor CX-4945, increases binding of IKAROS to the BCL2L1 promoter and enhances IKAROS-mediated repression of BCL2L1 in B-ALL. Treatment with CX-4945 increases sensitivity to doxorubicin in B-ALL, and reverses resistance to doxorubicin in multidrug-resistant B-ALL. Combination treatment with CX-4945 and doxorubicin show synergistic therapeutic effects in vitro and in preclinical models of high-risk B-ALL. Results reveal a novel signaling network that regulates chemoresistance in leukemia. These data lay the groundwork for clinical testing of a rationally designed, targeted therapy that combines the CK2 inhibitor, CX-4945, with doxorubicin for the treatment of hematopoietic malignancies.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Targeting of the deubiquitinase USP9X attenuates B-cell acute lymphoblastic leukemia cell survival and overcomes glucocorticoid resistance

Although previous studies attributed a pro-survival role to USP9X in human cancer, how USP9X affects B-cell acute lymphoblastic leukemia (B-ALL) remains unclear. Here, we found that USP9X is overexpressed in B-ALL cell lines and human patients. We investigated the role of USP9X in B-ALL and found that USP9X knockdown significantly reduced leukemic cell growth and increased spontaneous apoptosis, thereby improving survival in immunodeficient mice. These effects are partially mediated by the intrinsic apoptotic pathway, as we found that USP9X-knockdown leukemic cells displayed MCL1 down-regulation, with decreased BCL-2/BCL-XL levels and increased BAX levels. In addition, we demonstrated that USP9X inhibition negatively regulates mTORC1 activity toward its substrate S6K1. Clinically, USP9X inhibition sensitized glucocorticoid-resistant ALL cells to prednisolone; this observation reveals a potential avenue for improving the treatment of drug-resistant relapses. Collectively, our findings suggest that the combination of USP9X targeting and glucocorticoids treatment has attractive utility in B-ALL. This approach represents a potential strategy for promising combination therapies for lymphoid malignancies.

High concentrations of L-ascorbic acid specifically inhibit the growth of human leukemic cells via downregulation of HIF-1α transcription

We examined the antileukemic effects of high concentrations of L-ascorbic acid (high AA) on human leukemic cells. In vitro, high AA markedly induced apoptosis in various leukemic cell lines by generating hydrogen peroxide (H₂O₂) but not in normal hematopoietic stem/progenitor cells. High AA significantly repressed leukemic cell proliferation as well as neoangiogenesis in immunodeficient mice. We then noted that in leukemic cells, HIF-1α transcription was strongly suppressed by high AA and correlated with the transcription of VEGF. Our data indicate that exposure to high AA markedly increased the intracellular AA content of leukemic cells and inhibited the nuclear translocation of NF-κB, which mediates expression of HIF-1α. We next generated K562 cells that overexpressed HIF-1α (K562-HIF1α cells) and assessed the mechanistic relationship between inhibition of HIF-1α transcription and the antileukemic effect of high AA. The ability of high AA to induce apoptosis was significantly lower in K562-HIF1α cells than in K562 cells in vitro. We found that expression of HIF-1α-regulated antiapoptotic proteins of the Bcl-2 family, such as Mcl-1, Bcl-x_L, and Bcl-2, was significantly suppressed by high AA in K562 cells, but was sustained at higher levels in K562-HIF1α cells, regardless of high AA exposure. Moreover, repression of cell proliferation and neoangiogenesis by high AA was completely abrogated in mice receiving transplants of K562-HIF1α cells. These results indicate that, along with H₂O₂ generation, downregulation of HIF-1α transcription plays a crucial role in growth inhibition of human leukemic cells by high AA.

Let-7c governs the acquisition of chemo- or radioresistance and epithelial-to-mesenchymal transition phenotypes in docetaxel-resistant lung adenocarcinoma

MicroRNA (miRNA) expression and functions have been reported to contribute to phenotypic features of tumor cells. Although targets and functional roles for many miRNAs have been described in lung adenocarcinoma (LAD), their pathophysiologic roles in phenotypes of chemoresistant LAD cells are still largely unclear. Previously, docetaxel (DTX)-resistant LAD cell lines (SPC-A1/DTX and H1299/DTX) were established by our laboratory and displayed chemo- or radioresistance and mesenchymal features with enhanced invasiveness and motility. Unbiased miRNA profiling indicated that let-7c (MIRLET7C) was significantly downregulated in SPC-A1/DTX cells. Ectopic let-7c expression increased the in vitro and in vivo chemo- or radiosensitivity of DTX-resistant LAD cells through enhanced apoptosis, reversal of epithelial-to-mesenchymal phenotypes, and inhibition of in vivo metastatic potential via inactivation of Akt phosphorylation, whereas a let-7c inhibitor decreased the chemo- or radiosensitivity of parental cells. Further investigation suggested that let-7c significantly reduced the luciferase activity of a Bcl-xL 3'-UTR-based reporter, concordant with reduced Bcl-xL protein levels. Additionally, siRNA-mediated Bcl-xL knockdown mimicked the same effects of let-7c precursor, and enforced Bcl-xL expression partially rescued the effects of let-7c precursor in DTX-resistant LAD cells. Furthermore, we found that Bcl-xL was significantly upregulated in DTX-nonresponding LAD tissues, and its expression was inversely correlated with let-7c expression. This study suggests an important role for let-7c in the molecular etiology of chemoresistant lung adenocarcinoma.

Selective glucocorticoid receptor translational isoforms reveal glucocorticoid-induced apoptotic transcriptomes

Induction of T-cell apoptosis contributes to the anti-inflammatory and antineoplastic benefits of glucocorticoids. The glucocorticoid receptor (GR) translational isoforms have distinct proapoptotic activities in osteosarcoma cells. Here we determined whether GR isoforms selectively induce apoptosis in Jurkat T lymphoblastic leukemia cells. Jurkat cells stably expressing individual GR isoforms were generated and treated with vehicle or dexamethasone (DEX). DEX induced apoptosis in cells expressing the GR-A, -B, or -C, but not the GR-D, isoform. cDNA microarray analyses of cells sensitive (GR-C3) and insensitive (GR-D3) to DEX revealed glucocorticoid-induced proapoptotic transcriptomes. Genes that were regulated by the proapoptotic GR-C3, but not by the GR-D3, isoform likely contributed to glucocorticoid-induced apoptosis. The identified genes include those that are directly involved in apoptosis and those that facilitate cell killing. Chromatin immunoprecipitation assays demonstrated that distinct chromatin modification abilities may underlie the distinct functions of GR isoforms. Interestingly, all GR isoforms, including the GR-D3 isoform, suppressed mitogen-stimulated cytokines. Furthermore, the GR-C isoforms were selectively upregulated in mitogen-activated primary T cells and DEX treatment induced GR-C target genes in activated T cells. Cell-specific expressions and functions of GR isoforms may help to explain the tissue- and individual-selective actions of glucocorticoids and may provide a basis for developing improved glucocorticoids.

STAT5 mediates antiapoptotic effects of methylprednisolone on oligodendrocytes

Methylprednisolone (MP), a synthetic glucocorticoid agonist, is widely used for the clinical therapy of white matter diseases in the nervous system, such as spinal cord injury and multiple sclerosis. In addition to its potent anti-inflammatory and antioxidant properties, we recently discovered a selective antiapoptotic effect of MP on oligodendrocytes via the activation of the glucocorticoid receptor (GR) and the upregulation of bcl-X(L), a splicing isoform of the bcl-x gene. Based on published findings of the functional interactions between GR and STAT5, a transcription factor from the family of signal transducers and activators of transcription (STAT), we examined whether the glucocorticoid signaling pathway interacts with STAT5 to upregulate bcl-X(L) and protect oligodendrocytes. We show herein that (1) the GR and STAT5 complex is present on the STAT5-binding site of the bcl-x promoter region in oligodendrocytes; (2) the overexpression of an activated form of STAT5 prevents alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced oligodendrocyte cell death; and (3) this prevention is lost when the STAT5 gene is knocked down. Thus, our results provide one molecular mechanism underlying the postinjury protective effects of oligodendrocytes by stress hormones.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

Mechanisms involved in tissue-specific apopotosis regulated by glucocorticoids

Physiological cell turnover is under the control of a sharp and dynamic balance of different homeostatic mechanisms such as the equilibrium between cell proliferation and cell death. These mechanisms play an important role in maintaining normal tissue function and architecture. It is well known that apoptosis is the prevalent mode of physiological cell loss in most tissues. Steroid hormones like glucocorticoids have been identified as key signals controlling cell turnover by modulating programmed cell death in a tissue- and cell-specific manner. In this sense, several reports have demonstrated that glucocorticoids are able to induce apoptosis in cells of the hematopoietic system such as monocytes, macrophages, and T lymphocytes. In contrast, they protect against apoptotic signals evoked by cytokines, cAMP, tumor suppressors, in glandular cells such as the mammary gland epithelia, endometrium, hepatocytes, ovarian follicular cells, and fibroblasts. Although several studies have provided significant information on hormone-dependent apoptosis in an specific tissue, a clearly defined pathway that mediates cell death in response to glucocorticoids in different cell types is still misunderstood. The scope of this review is held to those mechanisms by which glucocorticoids control apoptosis, emphasizing tissue-specific expression of genes that are involved in the apoptotic pathway.

Inhibition of BCL11B expression leads to apoptosis of malignant but not normal mature T cells

The B-cell chronic lymphocytic leukemia (CLL)/lymphoma 11B gene (BCL11B) encodes a Krüppel-like zinc-finger protein, which plays a crucial role in thymopoiesis and has been associated with hematopoietic malignancies. It was hypothesized that BCL11B may act as a tumor-suppressor gene, but its precise function has not yet been elucidated. Here, we demonstrate that the survival of human T-cell leukemia and lymphoma cell lines is critically dependent on Bcl11b. Suppression of Bcl11b by RNA interference selectively induced apoptosis in transformed T cells whereas normal mature T cells remained unaffected. The apoptosis was effected by simultaneous activation of death receptor-mediated and intrinsic apoptotic pathways, most likely as a result of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) upregulation and suppression of the Bcl-xL antiapoptotic protein. Our data indicate an antiapoptotic function of Bcl11b. The resistance of normal mature T lymphocytes to Bcl11b suppression-induced apoptosis and restricted expression pattern make it an attractive therapeutic target in T-cell malignancies.

Low glucocorticoid receptor (GR), high Dig2 and low Bcl-2 expression in double positive thymocytes of BALB/c mice indicates their endogenous glucocorticoid hormone exposure

Several studies have shown that of the four major thymocyte subsets, the CD4/CD8 double positive (DP) thymocytes are the most sensitive to in vivo glucocorticoid hormone (GC)-induced apoptosis. Our aim was to analyse fine molecular differences among thymocyte subgroups that could underlie this phenomenon. Therefore, we characterised the glucocorticoid hormone receptor (GR) expression of thymocyte subgroups both at the mRNA and protein levels by real-time PCR and flow cytometry, and correlated these features to their apoptotic sensitivity. We also investigated the time-dependent effects of the GC agonist dexamethasone (DX) with or without GC antagonist (RU486) treatments on GR mRNA/protein expression. We also analysed the expression of two apoptosis-related gene products: dexamethasone-induced gene 2 (Dig2) mRNA and Bcl-2 protein. We found that DN thymocytes had the highest GR expression, followed by CD8 single positive (SP), CD4 SP and DP thymocytes in 4-week-old BALB/c mice, both at the mRNA and protein levels, respectively. In DP cells, the Dig2 expression was significantly higher, while the Bcl-2 expression was significantly lower than in DN, CD4 SP and CD8 SP thymocytes. Single high dose DX treatment caused time-dependent depletion of DP thymocytes due to their higher apoptosis rate, which could not be abolished with RU486 pretreatment. After a single high dose DX treatment, there was a transient, significant increase of the GR mRNA and protein level of unsorted thymocytes after 8 and 16 h, followed by a significant decrease at 24 h, respectively. The time-dependent GR expression changes after DX administration could not be inhibited by the GC antagonist RU486. Twenty-four hours after exposure to high dose DX the DN, CD4 SP and CD8 SP cells showed a significant decrease of GR mRNA and protein expression, whereas the DP thymocytes, showed no significant alteration of GR mRNA or protein expression. The kinetical analysis of GR expression and apoptotic marker changes upon single high dose GC analogue administration revealed a two-phase process in thymocytes: early events, within 4-8 h, include GR upregulation and early apoptosis induction, while the late events appear most prominently at 16-20 h, when the GR is already downregulated and apoptotic cell ratio reaches its peak, with marked DP cell depletion. The low GR, high Dig2 and low Bcl-2 expression, coupled with the absence of homologous downregulation of GR after exogenous GC analogue treatment, could contribute to the high GC sensitivity of DP thymocytes. The downregulated GR and Bcl-2 together with the upregulated Dig2 level in DP cells indicates the significance of intrathymic GC effects at this differentiation stage. Since GR expression changes and apoptotic events could not be completely inhibited by GC antagonist, we propose the involvement of non-genomic GR mechanisms in these processes.

Glucocorticoids repress bcl-X expression in lymphoid cells by recruiting STAT5B to the P4 promoter

The bcl-X gene plays a critical role in apoptosis. Six different isoforms generated by tissue-specific promoter usage and alternative splicing were described. Some of them exert opposite effects on cell death. In mammary epithelial cells glucocorticoids induce bcl-X expression and increase the ratio bcl-X(L) (antiapoptotic)/bcl-X(S) (apoptotic) by activating P4 promoter, which contains two hormone response elements. Here we show that, on mouse thymocytes and T lymphocyte derivative S49 cells, glucocorticoids inhibited transcription from P4 and decreased the ratio bcl-X(L)/bcl-X(S) favoring apoptosis. Upon hormonal treatment, glucocorticoid receptor (GR), steroid receptor coactivator-1, and RNA polymerase II were transiently recruited to P4 promoter, whereas STAT5B was also recruited but remained bound. Concomitant with the release of GR, silencing mediator for retinoic acid receptor and thyroid hormone receptor and histone deacetylase 3 were recruited, histone H3 was deacetylated, and RNA polymerase II left the promoter. Inhibition of STAT5 activity reverted glucocorticoid repression to activation of transcription and was accompanied by stable recruitment of GR and RNA polymerase II to P4.

Baicalin-induced apoptosis is mediated by Bcl-2-dependent, but not p53-dependent, pathway in human leukemia cell lines

Acute lymphoblastic leukemia (ALL), especially T-acute lymphoblastic leukemia (T-ALL), is a common childhood malignant neoplastic disorder. Chemotherapy agents, particularly those that can induce apoptosis, are the major intervening strategy in the treatment of ALL. In this study, we investigated in T-ALL cell line, CCRF-CEM, the in vitro cytotoxic effect and the mechanism of action of baicalin, a compound extracted from Scutellaria baicalensis Georgi and S. rivularis Benth (Labiateae). Results demonstrated that baicalin displayed a remarkable cytotoxic effect in CCRF-CEM, with an IC(50) value of 10.6 microg/ml. It triggered apoptotic effect by fragmentizing cellular DNA and arrested the cell cycle at G(0)/G(1) phase. Baicalin (37.5 microg/ml) had not effected the expression of p53 and Fas protein. It was shown to decline the expression of Bcl-2 (22.0 pg/ml), which consequently caused the loss (52.7%) of transmembrane potential (Delta Psi m) in the mitochondria after 72 hours of treatment. Baicalin (37.5 microg/ml) also elevated the amount of cytosolic cytochrome c (19.2 microg/ml), which finally triggered the activation of caspase-3 (50.1 pmol/min). In conclusion, baicalin was found to induce apoptosis in T-ALL cell lines through multiple pathways. This finding encourages further investigation of baicalin in its role as a potential candidate for chemotherapeutic agents in T-ALL.

RNA interference: a potential therapeutic tool for silencing splice isoforms linked to human diseases

Alternative splicing of precursor messenger RNAs (pre-mRNAs) is one of the most important sources of protein diversity in vertebrates. An estimated 35%-70% of human genes generate transcripts that are alternatively spliced, and defects in this process are linked to numerous human genetic diseases and various forms of cancer. The discovery that 21-23 nucleotide RNA duplexes, known as small interfering RNAs (siRNAs), can knockdown the homologous mRNAs in mammalian cells has revolutionized many aspects of drug discovery including down-regulation of disease-associated splicing isoforms. In addition, RNA interference (RNAi)-mediated silencing of splicing regulators has the potential to define the complex network of alternative splicing regulation and to analyze gene function. In this review, I first provide a brief introduction to mRNA splicing and its relationship to human diseases. This is followed by a brief overview of RNAi. Finally I discuss the therapeutic potential of RNAi in targeting disease-linked splicing isoforms.

HA14-1, a small molecule Bcl-2 antagonist, induces apoptosis and modulates action of selected anticancer drugs in follicular lymphoma B cells

The BCL-2 overexpression is a hallmark of follicular lymphoma (FL). Since patients with FL often suffer from resistant to chemotherapy refractory disease, the development of new regimens is required. Herein, we analyze for the first time the effects of a B-cell lymphoma 2 (Bcl-2) antagonist, HA14-1, alone and in combination with antineoplastic agents commonly used against follicular lymphoma, in human FL cell lines with t(14;18). All cell lines tested were sensitive to HA14-1-induced cytotoxicity and apoptosis, as depicted by morphological changes, SYTO16/PI staining, oligonucleosomal DNA fragmentation and loss of Deltapsi(m). Moreover, HA14-1 significantly enhanced dexamethasone- and doxorubicin-mediated (in schedule independent and dependent manner, respectively), but not vincristine-mediated cytotoxicity and apoptosis.

Glucocorticoid-induced apoptosis and glucocorticoid resistance: molecular mechanisms and clinical relevance

The ability of glucocorticoids (GC) to efficiently kill lymphoid cells has led to their inclusion in essentially all chemotherapy protocols for lymphoid malignancies. This review summarizes recent findings related to the molecular basis of GC-induced apoptosis and GC resistance, and discusses their potential clinical implications. Accumulating evidence suggests that GC may induce cell death via different pathways resulting in apoptotic or necrotic morphologies, depending on the availability/responsiveness of the apoptotic machinery. The former might result from regulation of typical apoptosis genes such as members of the Bcl-2 family, the latter from detrimental GC effects on essential cellular functions possibly perpetuated by GC receptor (GR) autoinduction. Although other possibilities exist, GC resistance might frequently result from defective GR expression, perhaps the most efficient means to target multiple antileukemic GC effects. Numerous novel drug combinations are currently being tested to prevent resistance and improve GC efficacy in the therapy of lymphoid malignancies.

Mechanisms of glucocorticoid-induced apoptosis in hematologic malignancies: updates

PURPOSE OF REVIEW

Glucocorticoids remain a central component of the therapeutic armamentarium for a broad spectrum of hematologic malignancies. There is an extensive body of evidence suggesting that the efficacy of glucocorticoids stems from their ability to mediate apoptosis in leukemia, lymphoma, and myeloma cells.

RECENT FINDINGS

Traditionally, glucocorticoid-induced apoptosis is divided into three stages: an initiation stage, which involves glucocorticoid receptor activation and glucocorticoid receptor-mediated gene regulation; a decision stage, which engages the prosurvival and proapoptotic factors at the mitochondrial level; and an execution stage, which implicates caspases and endonuclease activation. Recent discoveries have clarified many aspects of the apoptotic pathway, including activation of the caspases cascade and multicatalytic proteasome, suppression of prosurvival transcription factors such as AP-1, c-myc, nuclear factor-kappaB, as well as cross-talk between the T-cell receptor and cytokine signaling pathways.

SUMMARY

This review focuses primarily on insights gained during recent years into the mechanism of the signaling pathways responsible for mediating glucocorticoid-induced apoptosis in hematologic malignancies. This information provides a scientific basis to explore synergistic approaches that may enhance glucocorticoid-induced apoptosis and may bypass mechanism of resistance.

On the link between Bcl-2 family proteins and glucocorticoid-induced apoptosis

As immunosuppressive agents, glucocorticoids (GCs) act by inhibiting the expression of cytokines and adhesion molecules at the transcriptional and post-transcriptional levels. In addition, GCs exerted their effects by modulating apoptosis. In view of the central role of the Bcl-2 family protein in regulating apoptosis, it was tempting to speculate that GCs modulated apoptosis through modulation of the expression of proapoptotic (Bax, Bcl-X(S), Bak) and prosurvival (Bcl-2, Bcl-X(L), Bcl-w) Bcl-2 family members. Prosurvival Bcl-2 family members in various cell types antagonized GC-induced apoptosis, thereby suggesting a causal relationship between GC-induced apoptosis and Bcl-2 proteins. The antagonism of apoptosis afforded by prosurvival Bcl-2 proteins appeared to be specific for the GCs, as Bcl-2 and Bcl-x(L) blocked GC-induced apoptosis in T cell hybridomas but did not affect Fas or activation-induced apoptosis. Although it is speculated that GC-induced apoptosis may be mediated through the activation of proapoptotic Bcl-2 proteins, recent findings suggest that this may vary depending on the conditions and the cell types used. The mechanism by which Bcl-2 inhibited GC-induced apoptosis remains uncertain. It was suggested that Bcl-2 acted on outer mitochondrial membranes to preserve their function. Bcl-2 overexpression also inhibited GC-induced apoptotic events, including caspase activation and mitochondrial dysfunction. The cross-talk of the GC receptors with other secondary messengers could lead to modulation of the activity of Bcl-2 proteins through modification of their phosphorylation status, without ruling out the possibility of a physical interaction between activated GR with Bcl-2 proteins.

Modification of Alternative Splicing by Antisense Therapeutics

Alternative splicing allows the production of several different proteins from a single pre-mRNA, resulting in an increased diversity of proteins derived from a relatively limited number of transcribed genes. Although it is necessary for normal development, alternative splicing and its aberrations are also implicated in disease states from thalassemia and cancer to neurodegenerative disorders. Techniques that trick the splicing machinery to alter the splicing pathways can be of high therapeutic value. Antisense technology, used mostly for RNA downregulation, recently has been adapted to alter the splicing process. The promise of this approach is now being realized as a result of chemical modification of oligonucleotides and improvements in their delivery in vivo.

A small inhibitor of the interaction between Bax and Bcl-X(L) can synergize with methylprednisolone to induce apoptosis in Bcl-X(L)-overexpressing breast-cancer cells

PURPOSE

To identify inhibitors of the interaction between Bax and Bcl-X(L).

METHODS

Using an assay based on biosensor technology, we screened a chemical library of 10,000 compounds for inhibitors of the interaction between Bax and Bcl-X(L). Using cell-culture systems we tested active compounds for their ability to induce apoptosis in Bcl-X(L)-overexpressing MCF7 cells and increase the sensitivities of the cells to apoptosis-inducing drugs [vincristine sulphate, dexamethasone, cycloheximide and 6alpha-methylprednisolone (MP)].

RESULTS

A single compound, 2',4',5',7'-tetrabromofluorescein (A5), from the library was found to inhibit this interaction efficiently. Several structural analogues of A5 were tested and two of these [4',5'-dibromofluorescein (A9) and 3,4,5,6-tetrabromofluorescein (A11)] were found to be active, and their activities were confirmed by an independent in vitro pull-down assay. These active compounds were observed to induce apoptosis in Bcl-X(L)-overexpressing MCF7 cells. Moreover, two of the compounds (A5 and A11) appeared to increase the sensitivities of the cells to MP. A more rigorous test using the isobologram technique showed that there is a synergistic cytotoxic effect between A11 and MP.

CONCLUSIONS

We have identified a small inhibitor of the interaction between Bax and Bcl-X(L) that can synergize with methylprednisolone to induce apoptosis in Bcl-X(L)-overexpressing breast-cancer cells.

Cellular response to an antisense-mediated shift of Bcl-x pre-mRNA splicing and antineoplastic agents

Overexpression of Bcl-xL, an anti-apoptotic member of the Bcl-2 family, negatively correlates with the sensitivity of various cancers to chemotherapeutic agents. We show here that high levels of expression of Bcl-xL promoted apoptosis of cells treated with an antisense oligonucleotide (5'Bcl-x AS) that shifts the splicing pattern of Bcl-x pre-mRNA from the anti-apoptotic variant, Bcl-xL, to the pro-apoptotic variant, Bcl-xS. This surprising finding illustrates the advantage of antisense-induced modulation of alternative splicing versus down-regulation of targeted genes. It also suggests a specificity of the oligonucleotide effects since non-cancerous cells with low levels of Bcl-xL should resist the treatment. 5'Bcl-x AS sensitized cells to several antineoplastic agents and radiation and was effective in promoting apoptosis of MCF-7/ADR cells, a breast cancer cell line resistant to doxorubicin via overexpression of the mdr1 gene. Efficacy of 5'Bcl-x AS combined with chemotherapeutic agents in the PC3 prostate cancer cell line may be translated to clinical prostate cancer since recurrent prostate cancer tissue samples expressed higher levels of Bcl-xL than benign prostate tissue. Treatment with 5'Bcl-x AS may enhance the efficacy of standard anti-cancer regimens and should be explored, especially in recurrent prostate cancer.