BCL-2 expression in childhood leukemia versus spontaneous apoptosis, drug induced apoptosis, and in vitro drug resistance

Evaluation of BAX and BCL-2 Gene Expression and Apoptosis Induction in Acute Lymphoblastic Leukemia Cell Line CCRFCEM after High- Dose Prednisolone Treatment

Objective: Glucocorticoids are one of the most important drugs in the treatment of acute lymphoblastic leukemia for children. It is very important to response to glucocorticoid in the prognosis of these patients. Therefore, resistance to treatment is a major problem in lymphoid leukemia cases. In, this study, CCRF-CEM cell line was selected as a chemotherapy-resistant model. The aim of this study was to evaluate the effect of high dose prednisolone on induction of apoptosis and changes in BAX and BCL-2 gene expression at different times. Methods: CCRF-CEM cell lines were grown in standard conditions. Based on previous studies, a dose of 700 μM as subtoxic dose was selected. Changes in gene expression of BAX and BCL-2 were evaluated by using real time PCR techniques. Also stained with annexin V and the induction of apoptosis was assessed by FACS machine. Results: In this study it was found that prednisolone in high doses at different times significantly increased the gene expression of BAX and on the other hand the amount of BCL-2 expression was reduced. Cells that treated for 48 hours had more significant changes in gene expression. Based on flowcytometry data, prednisolone can induce apoptosis in a time dependent manner on this cancerous resistant cell line. Conclusions: Apoptosis induced by high-dose prednisolone in the CCRF-CEM cells, which is almost resistant, and possibly mediated by reducing the expression of BCL-2 and BAX up-regulation.

miR-34a is an intracellular and exosomal predictive biomarker for response to docetaxel with clinical relevance to prostate cancer progression

BACKGROUND

Docetaxel-resistance limits successful treatment of castration resistant prostate cancer. We previously demonstrated that extracellular vesicles (exosomes) may play a role in regulating docetaxel resistance. Here, we investigated intracellular and extracellular (exosomal) miRNAs related to docetaxel resistance.

METHODS

Following global miRNA profiling of cell line models of docetaxel-resistance and their corresponding exosomes, we investigated the clinical relevance of four selected miRNAs (miR-598, miR-34a, miR-146a, miR-148a) in four publically available clinical cohorts representing both primary and advanced disease in tissue and urine specimens. One of these miRNAs, miR-34a was selected for functional evaluation by miRNA inhibition and over-expression in vitro. We further assessed the panel of miRNAs for their combined clinical relevance as a biomarker signature by examining their common predicted targets.

RESULTS

A strong correlation was found between the detection of miRNAs in exosomes and their corresponding cells of origin. Of the miRNAs chosen for further validation and clinical assessment, decreased miR-34a levels showed substantial clinical relevance and so was chosen for further analysis. Manipulating miR-34a in prostate cancer cells confirms that this miRNA regulates BCL-2 and may, in part, regulate response to docetaxel. When combined, these miRNAs are predicted to regulate a range of common mRNA targets, two of which (e.g., SNCA, SCL7A5) demonstrate a strong relationship with prostate cancer progression and poor prognosis.

CONCLUSIONS

This study supports the extracellular environment as an important source of minimally invasive predictive biomarkers representing their cellular origin. Using miR-34a as example, we showed that biomarkers identified in this manner may also hold functional relevance.

Glucocorticoid sensitisation in Mixed Lineage Leukaemia-rearranged acute lymphoblastic leukaemia by the pan-BCL-2 family inhibitors gossypol and AT-101

AIM OF THE STUDY

Resistance to glucocorticoids (GCs) remains a major problem in the treatment of infants with acute lymphoblastic leukaemia (ALL) carrying Mixed Lineage Leukaemia (MLL) translocations. Despite intensive research, the mechanism(s) underlying GC resistance remain poorly understood. Recent studies suggested an important role for the pro-survival BCL-2 family member MCL1 in GC resistance in MLL-rearranged ALL.

METHODS

We exposed GC-resistant MLL-rearranged SEMK2 cells to potent MCL1-inhibiting agents, including gossypol, AT-101, rapamycin, SU9516 and obatoclax (GX15-070) and determined GC sensitisation using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assays. Using Western blotting we analysed the protein expression of most BCL-2 family members in MLL-rearranged SEMK2 cells after treatment with potent MCL-1 inhibiting agents.

RESULTS

Only gossypol and its synthetic analogue AT-101 induced GC sensitivity in MLL-rearranged ALL cells. Remarkably, the GC-sensitising effects of gossypol and AT-101 appeared not to be mediated by down-regulation MCL1 or other anti-apoptotic BCL-2 family members, but rather involved up-regulation of multiple pro-apoptotic BCL-2 family members, in particular that of BIM and BID.

CONCLUDING REMARKS

In conclusion, gossypol and AT-101 induce GC sensitivity in MLL-rearranged ALL cells, most likely mediated by the activation of BID and BIM without the necessity to down-regulate anti-apoptotic BCL-2 family members like MCL1. Hence, co-administration of either gossypol or AT-101 during GC treatment of GC-resistant MLL-rearranged ALL patients may overcome GC resistance and improve prognosis in this high-risk childhood leukaemia.

The BCL-2 protein in precursor B acute lymphoblastic leukemia in children

The BCL-2 protein plays an important role in controlling apoptosis. Disorders of this process can lead to the emergence and development of acute lymphoblastic leukemia (ALL) and can determine the resistance of leukemic cells to chemotherapy. The levels of BCL-2 mRNA were determined in 20 children with pre-B ALL using RT-polymerase chain reaction and the percentage of BCL-2+ cells in 51 patients using flow cytofluorometry. Similar levels of BCL-2 mRNA (P=0.18) with a higher percentage of cells BCL-2+ (P=0.04) were shown in the bone marrow of patients with pre-B ALL compared to normal peripheral blood mononuclear cells. We could not find any connection between the level of BCL-2 mRNA or the percentage of BCL-2+ cells and selected clinical features. A high percentage of BCL-2+ cells and high levels of BCL-2 mRNA did not affect the 5-year overall survival probability nor the 5-year relapse-free survival probability. These results may indicate a high activity of mechanisms promoting the development of the final form of the BCL-2 protein from mRNA in leukemic cells. A high BCL-2 level does not affect the clinical course or worsen the prognosis in children with ALL.

Targeting paediatric acute lymphoblastic leukaemia: novel therapies currently in development

Modifications to the treatment of acute lymphoblastic leukaemia (ALL) in children have led to a dramatic increase in survival in the past 40 years. Despite this success, a significant subset of paediatric leukaemia patients either relapse or fail to ever achieve a complete remission. Additionally, some patients necessitate treatment with intensified chemotherapy regimens due to clinical or laboratory findings which identify them as high risk. These patients are unlikely to respond to further minor adjustments to the dosing or timing of administration of the same chemotherapy medications. Many novel targeted therapies for the treatment of childhood ALL provide potential mechanisms to further improve cure rates, and provide the possibility of minimizing toxicity to non-malignant cells, given their specificity to malignant cell phenotypes. This article explores many of the potential targeted therapies in varying stages of development, from those currently in clinical trials to those still being refined in the research laboratory.

Apoptosis inhibition by Bcl-2 gives way to autophagy in glucocorticoid-treated lymphocytes

Glucocorticosteroid hormones, including prednisone and dexamethasone (Dex), have been used to treat lymphoid malignancies for many years because they readily induce apoptosis in immature lymphocytes lacking Bcl-2. However, elevated expression of the anti-apoptotic protein Bcl-2 inhibits apoptosis and contributes to glucocorticoid resistance. Using the Bcl-2-negative WEHI7.2 lymphoma line as an experimental model, we found that Dex not only induces apoptosis but also induces autophagy. The caspase inhibitor Z-VAD-fmk inhibited apoptosis but not autophagy in Dex-treated cells. Bcl-2 overexpression inhibited Dex-induced apoptosis even more potently than Z-VAD-fmk and, contrary to previous reports, Bcl-2 neither interacted with Beclin-1 nor inhibited autophagy. Rather, Bcl-2 overexpression facilitated detection of Dex-induced autophagy by both steady state methods and flux measurements, ostensibly due to apoptosis inhibition. Autophagy contributed to prolonged survival of Bcl-2-positive lymphoma cells following Dex treatment, as survival was reduced when autophagy was inhibited by 3-methyladenine. These findings emphasize the important interplay between apoptosis and autophagy and suggest a novel mechanism by which Bcl-2, which is frequently elevated in lymphoid malignancies, contributes to glucocorticoid resistance and survival of lymphoma cells.

BCL-2 dependence and ABT-737 sensitivity in acute lymphoblastic leukemia

Cancer cells acquire disruptions in normal signal transduction pathways and homeostatic mechanisms that would trigger apoptosis in normal cells. These abnormalities include genomic instability, oncogene activation, and growth factor independent proliferation. Therefore, cancer cells likely require a block in apoptosis in order to survive. Overexpression of the antiapoptotic protein BCL-2 provides a block in apoptosis that is frequently observed in cancer cells. We have developed methods for the detection and analysis of BCL-2 dependence and here apply them to acute lymphoblastic leukemia (ALL). BH3 profiling, a mitochondrial assay that classifies blocks in the intrinsic apoptotic pathway, indicated a dependence on BCL-2 of both ALL cell lines and primary samples. This dependence predicted that BCL-2 would be complexed with select pro-death BH3 family proteins, a prediction confirmed by the isolation of BCL-2 complexes with BIM. Furthermore, the BH3 profiling and protein analysis predicted that ALL cell lines and primary cells would be sensitive to ABT-737 as a single agent. Finally, BH3 profiling and protein studies accurately predicted a relative degree of sensitivity to BCL-2 antagonism in cell lines. The ALL cells studied exhibit BCL-2 dependence, supporting clinical trials of BCL-2 antagonists in ALL as single agents or combination therapies.

A novel Bcl-2 small molecule inhibitor 4-(3-methoxy-phenylsulfannyl)-7-nitro-benzofurazan-3-oxide (MNB)-induced apoptosis in leukemia cells

A novel small molecule inhibitor, 4-(3-methoxy-phenylsulfannyl)-7-nitro-benzofurazan-3-oxide (MNB), competes with the Bak BH3 peptide to bind Bcl-2 protein with a binding affinity of IC(50) = 0.70 microM, as assessed by a fluorescence polarization based binding assay. HL-60 cells express the highest levels of Bcl-2 among the cell lines examined. Treated with 5 microM of MNB only for 6 h, 85% of HL-60 cells were detected to undergo apoptosis. Pan-caspase inhibitor, Z-VAD-FMK, blocks MNB-induced apoptosis in HL-60 cells. Caspase-2, caspase-3, caspase-7, caspase-8, caspase-9, and PARP activation were observed at as early as 4 to 6 h of MNB treatment. In addition, it has been confirmed that the caspase-3 specific inhibitor, Z-DEVD-FMK, blocks the activation of caspase-8 in MNB-treated HL-60 cells. MNB treatment does not change Bcl-2 or Bax expression level in HL-60 cells, but causes Bid cleavage. Further experiments have illustrated that MNB inhibits the heterodimerization of Bcl-2 with Bax or Bid, reduces the mitochondrial membrane potential (DeltaPsimt), and induces cytochrome c release from mitochondria in HL-60 cells. These results suggest that MNB induces apoptosis in HL-60 by inhibiting the heterodimerization of Bcl-2 with pro-apoptosis Bcl-2 members, resulting in a decrease in the mitochondrial membrane potential and cytochrome c release, activation of caspases and PARP; it is a caspase-dependent process in which the activation of caspase-8 is dependent on the mitochondrial apoptosis signal transduction pathway. MNB prolongs the life spans of HL-60 bearing mice, potently kills fresh AML and ALL cells, indicating that it has the potential to be developed to treat leukemia.

Lack of mitochondrial depolarization by oxidative stress is associated with resistance to buthionine sulfoximine in acute lymphoblastic leukemia cells

Raised intracellular glutathione is one characteristics of high-risk childhood acute lymphoblastic leukemia (ALL). Depletion of glutathione by buthionine sulfoximine (BSO) has been reported to be toxic against some cancer cells. To assess the role of glutathione in ALL, the toxicity of BSO was studied in B-precursor ALL cell lines. BSO increased oxidative stress equally in all cell lines; however mitochondrial depolarization was observed only in BSO-sensitive cells. BSO up-regulated Bcl-2 protein, and antagonized the anti-ALL effect of prednisolone in BSO-resistant cells. A lack of mitochondrial death-signal activation by oxidative stress seemed to be associated with BSO-resistance in ALL.

Diverse pathways mediate chemotherapy-induced cell death in acute lymphoblastic leukemia cell lines

Cancer cell resistance to chemotherapy may be mediated by defects in apoptotic pathways. A prior study showed that in vivo apoptosis of Acute Lymphoblastic Leukemia (ALL) blasts in response to chemotherapy could occur through diverse pathways including both p53-dependent and -independent mechanisms. In this study we investigated the apoptotic response in more detail by using a panel of ALL cell lines that differed in respect to p53 status. Upon exposure to a uniform stimulus, expression of apoptotic proteins, including the effector caspase-3, varied among ALL cell lines partly depending on p53 transcriptional activity and caspase-8 activation. Although the expression and contribution to apoptosis differed among known members of the apoptotic pathway, apoptosis was universally mediated by mitochondrial depolarization. The NFkappaB pathway was activated in response to chemotherapy but NFkappaB inhibition appeared to not influence chemosensitivity. This study further documents the highly variable nature of cell death programs in ALL and provides the foundation for cell death pathway modulation to improve ALL cure rates without increasing chemotherapy-related toxicity.

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.

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.

Molecular determinants of glucocorticoid sensitivity and resistance in acute lymphoblastic leukemia

Glucocorticoids (GC) are probably the most important drugs in the treatment of ALL. Despite the extensive use of GC for many years, little is known about the molecular mechanisms of sensitivity and resistance. This review summarizes the knowledge on GC cytotoxicity in leukemia. The relevance of polymorphisms, splice variants and the number and regulation of the GC receptor are discussed. The role of multidrug resistance proteins, glutathione and glutathione S-transferase is evaluated, as well as the influence of the different heat-shock chaperone (hsp 90 and 70) and co-chaperone proteins (BAG-1 and others) which form a complex together with the GC receptor. Finally, the transactivation and transrepression (via NF-kappa B and AP-1 binding) of a wide range of genes (like c-myc) which initiates the final apoptosis pathway are discussed and suggestions for future directions of research in ALL patients are given.

Antisense Bcl2 oligonucleotide in cisplatin-resistant bladder cancer cell lines

OBJECTIVE

To determine the change of expression of Bcl2 in cisplatin-resistant bladder cancer cell lines and the reversibility of chemoresistance to cisplatin with antisense oligonucleotide against Bcl2, as higher expression of Bcl2 is associated with drug resistance in many different cancer cell lines.

MATERIALS AND METHODS

In the cisplatin-resistant bladder tumour cell lines T24R1 and T24R2, the expression of Bcl2 was determined by reverse transcription-polymerase chain reaction and Western blot assay, and antisense oligonucleotide targeting of the Bcl2 coding sequence was administered with lipofectin.

RESULTS

The expression of Bcl2 mRNA and protein was greater in T24R1 and T24R2 cells than in the parent T24 cells. Short-term exposure to cisplatin up-regulated Bcl2 mRNA and protein expression in parent T24 cells. Treatment with antisense oligonucleotide down-regulated Bcl2 protein expression and significantly enhanced the cytotoxicity of cisplatin.

CONCLUSIONS

Up-regulation of Bcl2 protein expression might be one of the mechanisms of cisplatin resistance in bladder cancer cells, and antisense Bcl2 oligonucleotide may be helpful in chemotherapy for bladder cancer by reversing cisplatin resistance.

Recent insights into the mechanism of glucocorticosteroid-induced apoptosis

Glucocorticosteroid hormones induce apoptosis in lymphocytes. Therefore, glucocorticoids are commonly used as immunosuppressive and chemotherapeutic agents. This review examines many facets of the process by which glucocorticoids induce apoptosis. This process is divided into three stages, an initiation stage that involves glucocorticoid receptor-mediated gene regulation, a decision stage that involves the counterbalancing influence of prosurvival and proapoptotic factors, and the execution stage which involves caspase and endonuclease activation. Many aspects of glucocorticoid-induced apoptosis, such as mitochondrial dysfunction and caspase activation, are important steps in virtually all forms of apoptosis. But the process glucocorticoid-induced apoptosis differs from other forms of apoptosis in terms of initiation at the transcriptional level and involvement of the multicatalytic proteasome and calcium. Moreover, the abundant opportunity for crosstalk between the glucocorticoid receptor and other signaling pathways increases the complexity of glucocorticoid-induced apoptosis and its regulation.

Salvage therapy for refractory or relapsed acute lymphocytic leukemia

The overall prognosis for patients with relapsed or refractory adult ALL remains poor. Further insight into the biology of ALL is required, and novel therapeutic agents are needed to counter mechanisms of resistance. A palliative approach to the management of multiply relapsed or refractory ALL should be supplanted by enrollment into clinic trials to promote drug discovery. Monitoring of minimal residual disease may allow an earlier intervention before overt clinical relapse and improve outcome; prospective studies are needed. Attainment of a second or later CR should be followed by allogeneic BMT when feasible owing to the paucity of long-term survivors with salvage chemotherapy alone.