Flavopiridol circumvents Bcl-2 family mediated inhibition of apoptosis and drug resistance in B-cell chronic lymphocytic leukaemia

Cyclin-dependent kinase (CDK) 9 and 4/6 inhibitors in acute myeloid leukemia (AML): a promising therapeutic approach

Introduction: Despite advancements over the last 2 years, outcomes for acute myeloid leukemia (AML) are poor; however, a greater comprehension of disease mechanisms has driven the investigation of new targeted treatments. Cyclin-dependent kinases (CDKs) regulate cell cycle progression, transcription and DNA repair, and are aberrantly expressed in AML. Targeting the CDK pathway is an emerging promising therapeutic strategy in AML.Areas covered: We describe the rationale for targeting CDK9 and CDK4/6, the ongoing preclinical and clinical trials and the potential of these inhibitors in AML. Our analysis included an extensive literature search via the Pubmed database and clinicaltrials.gov (March to August, 2019).Expert opinion: While CDK4/6 inhibitors are early in development for AML, CDK9 inhibition with alvocidib has encouraging clinical activity in newly diagnosed and relapsed/refractory AML. Preclinical data suggests that leukemic MCL-1 dependence may predict response to alvocidib. Moreover, MCL-1 plays a key role in resistance to BCL-2 inhibition with venetoclax. Investigational strategies of concomitant BCL-2 and CDK9 inhibition represent a promising therapeutic platform for AML. Furthermore, preclinical data suggests that CDK4/6 inhibition has selective activity in patients with KMT2A-rearrangements and FLT3 mutations. Incorporation of CDK9 and 4/6 inhibitors into the existing therapeutic armamentarium may improve outcomes in AML.

Protective Effects of Baicalin on Experimental Myocardial Infarction in Rats

Objective

This study aimed to investigate the protective effects of baicalin on myocardial infarction in rats and explore the related mechanisms.

Methods

Fifty Sprague Dawley rats were randomly divided into the control, model, and low-, medium- and high-dose baicalin groups. The latter 3 groups were intraperitoneally injected with baicalin, with a dose of 12.5, 25 and 50 mg/kg, respectively. Then, the myocardial infarction model was established. The hemodynamic of rats was tested, the serum lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB), prostacyclin (PGI₂) and thromboxane A₂ (TXA₂) were determined, the myocardial superoxide dismutase (SOD) and malondialdehyde (MDA) levels were detected, and the myocardial B-cell lymphoma-2 (Bcl-2) and Bcl-2 associated X (Bax) protein expressions were determined.

Results

Compared with the model group, in the high-dose baicalin group the ST segment height and LVEDP were significantly decreased (P<0.05), the LVSP was significantly increased (P<0.05), the serum LDH, CK-MB and TXA2 levels were significantly decreased (P<0.05), the PGI₂ level was significantly increased (P<0.05), the myocardial SOD level was significantly increased (P<0.05), and the myocardial MDA level was significantly decreased (P<0.05); the myocardial Bcl-2 protein level was significantly increased, and the Bax protein level was significantly decreased (P<0.05).

Conclusion

Baicalin has protective effects on myocardial infarction in rats. The possible mechanisms may be related to its resistance to oxidative stress, and up-regulation of Bcl-2 protein expression and down-regulation of Bax protein expression in myocardial tissue.

Alvocidib (flavopiridol) for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Alvocidib, which has orphan drug designation in chronic lymphocytic leukemia (CLL) from the FDA and the EMA, is a plant-derived semisynthetic flavone that acts as a cyclin-dependent kinase inhibitor. It induces apoptosis in CLL cells in vitro and was introduced into clinical trials in CLL as an intravenous infusion in 1997, which proved disappointing. Since the drug avidly binds to plasma proteins, higher serum concentrations were required for clinical antileukemia activity than those suggested by in vitro studies. Subsequent studies utilizing bolus plus infusional doses revealed significant activity against CLL, even in patients with unfavorable characteristics. However, significant toxicity including high rates of major tumor lysis syndrome, cytokine release syndrome and secretory diarrhea were also observed.

AREAS COVERED

The chemistry, pharmacodynamics, pharmacokinetics and metabolism of alvocidib are briefly discussed and phase I-II studies in CLL are discussed in detail. To date, no phase III studies in CLL have been reported.

EXPERT OPINION

A number of much less toxic drugs with similar efficacy against CLL both with and without unfavorable cytogenetics have come to market. Furthermore, enthusiasm for the development of alvocidib as a single agent for the treatment of CLL has waned, primarily due to its toxicity.

Spontaneous regression of chronic lymphocytic leukemia to a monoclonal B-lymphocytosis or to a normal phenotype

Spontaneous remission of chronic lymphocytic leukemia (CLL) is an unusual and poorly characterized event. We performed a search for spontaneous remission in patients with CLL. Cases must have had a pathological diagnosis of CLL with disease duration > 6 months. Spontaneous remission was defined as absence of lymphadenopathy or splenomegaly with lymphocyte counts < 5 × 10(9)/L for > 9 months without therapy. We identified 20 cases and included one additional case from our institution. Fourteen cases (67%) showed remission into monoclonal B lymphocytosis (MBL) and seven (33%) into a normal phenotype. There was no difference in age distribution, lymphocyte count or stage between groups. There was a significant difference in the median duration of CLL prior to remission, 13 years in the MBL versus 3 years in the normal phenotype group (p = 0.03). This difference in the duration of CLL prior to remission could be due to a possible distinct pathophysiology for these events.

The impact of CDK inhibition in human malignancies associated with pronounced defects in apoptosis: advantages of multi-targeting small molecules

Malignant cells in chronic lymphocytic leukemia (CLL) and related diseases are heterogeneous and consist primarily of long-lived resting cells in the periphery and a minor subset of dividing cells in proliferating centers. Both cell populations have different molecular signatures that play a major role in determining their sensitivity to therapy. Contemporary approaches to treating CLL are heavily reliant on cytotoxic chemotherapeutics. However, none of the current treatment regimens can be considered curative. Pharmacological CDK inhibitors have extended the repertoire of potential drugs for CLL. Multi-targeted CDK inhibitors affect CDKs involved in regulating both cell cycle progression and transcription. Their interference with transcriptional elongation represses anti-apoptotic proteins and, thus, promotes the induction of apoptosis. Importantly, there is evidence that treatment with CDK inhibitors can overcome resistance to therapy. The pharmacological CDK inhibitors have great potential for use in combination with other therapeutics and represent promising tools for the development of new curative treatments for CLL.

Stromal control of cystine metabolism promotes cancer cell survival in chronic lymphocytic leukaemia

Tissue stromal cells interact with leukemia cells and profoundly affect their viability and drug sensitivity. Here we show a biochemical mechanism by which bone marrow stromal cells modulate the redox status of chronic lymphocytic leukemia (CLL) cells and promote cellular survival and drug resistance. Primary CLL cells from patients exhibit limited ability to transport cystine for glutathione (GSH) synthesis due to a low expression of Xc- transporter, while bone marrow stromal cells effectively import cystine and convert it to cysteine, which is then released into the microenvironment for uptake by CLL cells to promote GSH synthesis. The elevated GSH enhances leukemia cell survival and protects them from drug-induced cytotoxicity. Furthermore, disabling this protective mechanism significantly sensitizes CLL cells to drug treatment in stromal environment. This stromal-leukemia interaction is critical for CLL cell survival and represents a key biochemical pathway for effectively targeting leukemia cells to overcome drug resistance in vivo.

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

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

Treatment options for high-risk chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common form of leukaemia in the Western world. The natural history of CLL is extremely variable with a survival time from initial diagnosis that ranges from 2 to more than 20 years. Understanding the clinical diversity and allowing the subclassification of CLL into various prognostic groups not only assists in predicting future outcome for patients, but also helps to direct treatment decisions. Chlorambucil and fludarabine were the standard therapy for CLL for decades. Randomized studies have reported superior overall response and progression-free survival (PFS) for fludarabine compared with alkylator-based therapy and for the fludarabine-cyclophospamide (FC) combination over fludarabine alone. More recently the addition of rituximab to the FC regimen (R-FC) has shown significant improvement in overall response, PFS and overall survival compared with FC alone. However, there are patients for whom this regimen still provides less satisfactory results. Within the above studies CLL patients who have some of the poorer prognostic markers, such as unmutated IgVH genes and/or high beta-2 microglobulin (B2M), and those who fail to achieve a minimal residual disease (MRD) negative remission are likely to have a shorter PFS compared with those without these features. Various strategies have been explored to improve the outcome for such patients. These include the addition of agents to a frontline R-FC regimen, use of consolidation and consideration of maintenance. The only group that can be clearly identified pretreatment for whom conventional fludarabine-based therapies produce significantly inferior response rates, PFS and overall survival are the patients who harbour a genetic fault; deletion or mutation or a combination of deletion and mutation of tumour protein p53 (TP53). TP53 inactivation is a less common finding at first treatment but becomes much more common in fludarabine-refractory patients. Alemtuzumab and high-dose corticosteroids have been shown to be effective in this group of CLL patients. Trials combining these two agents have shown improved responses, particularly for those patients with bulky nodal disease for whom alemtuzumab alone may be insufficient. Since the duration of responses remains relatively short, suitable patients should be considered for allogeneic stem cell transplantation according to the European Group for Blood and Marrow Transplantation (EBMT) guidelines. Furthermore, there are a number of other new treatments on the horizon, including humanized antibodies directed against novel targets and small-molecule inhibitors.

Aberrantly activated anti-apoptotic signalling mechanisms in chronic lymphocytic leukaemia cells: clues to the identification of novel therapeutic targets

Chronic lymphocytic leukaemia (CLL) is the commonest haematological malignancy in the western world and is incurable by cytotoxic therapy. Considerable research effort has identified the signal transduction pathways in CLL cells that contribute to anti-apoptotic signalling. Some pathways are constitutively activated in CLL cells but upregulated in normal cells only when protein tyrosine kinases (PTKs) are activated by ligands. This review describes which PTKs are aberrantly activated in CLL cells and are potential targets for inhibition. Additional potential targets within pathways downstream of these PTKs include Mek/Erk, mTorc1, protein kinase C, PI-3 kinase/Akt, nuclear factor-κB and cyclin-dependent protein kinase. Numerous studies have identified chemical agents and antibodies that selectively kill CLL cells, irrespective of their genetic resistance to conventional chemotherapeutic agents, and which can overcome cytoprotective microenvironmental signalling. These studies have resulted in identification of novel therapies, some of which are currently undergoing clinical trials. In vitro and animal model studies and clinical trials could determine which inhibitors of which targets are the likely to be most effective and least toxic either singly or in combination.

Mcl1 haploinsufficiency protects mice from Myc-induced acute myeloid leukemia

Antiapoptotic BCL2 family members have been implicated in the pathogenesis of acute myelogenous leukemia (AML), but the functional significance and relative importance of individual proteins (e.g., BCL2, BCL-XL, and myeloid cell leukemia 1 [MCL1]) remain poorly understood. Here, we examined the expression of BCL2, BCL-XL, and MCL1 in primary human hematopoietic subsets and leukemic blasts from AML patients and found that MCL1 transcripts were consistently expressed at high levels in all samples tested. Consistent with this, Mcl1 protein was also highly expressed in myeloid leukemic blasts in a mouse Myc-induced model of AML. We used this model to test the hypothesis that Mcl1 facilitates AML development by allowing myeloid progenitor cells to evade Myc-induced cell death. Indeed, activation of Myc for 7 days in vivo substantially increased myeloid lineage cell numbers, whereas hematopoietic stem, progenitor, and B-lineage cells were depleted. Furthermore, Mcl1 haploinsufficiency abrogated AML development. In addition, deletion of a single allele of Mcl1 from fully transformed AML cells substantially prolonged the survival of transplanted mice. Conversely, the rapid lethality of disease was restored by coexpression of Bcl2 and Myc in Mcl1-haploinsufficient cells. Together, these data demonstrate a critical and dose-dependent role for Mcl1 in AML pathogenesis in mice and suggest that MCL1 may be a promising therapeutic target in patients with de novo AML.

A unique RNA-directed nucleoside analog is cytotoxic to breast cancer cells and depletes cyclin E levels

In contrast to deoxyribose or arabinose containing nucleoside analogs that are currently established for cancer therapeutics, 8-chloro-adenosine (8-Cl-Ado) possesses a ribose sugar. This unique nucleoside analog is RNA-directed and is in a phase I clinical trial for hematological malignancies. RNA-directed therapies are effective for the treatment of many malignancies as their activities are primarily aimed at short-lived transcripts, which are typically encoded by genes that promote the growth and survival of tumor cells such as cyclin E in breast cancer. Based on this, we hypothesized that 8-Cl-Ado, a transcription inhibitor, will be effective for the treatment of breast cancer cells. The metabolism of 8-Cl-Ado and the effect on ATP in the breast cancer cell lines MCF-7 and BT-474 were measured using HPLC analysis. In these cells, 8-Cl-Ado was effectively taken up, converted to its cytotoxic metabolite, 8-Cl-ATP, and depleted the endogenous ATP levels. This in turn led to an inhibition of RNA synthesis. The RNA synthesis inhibition was associated with a depletion of cyclin E expression, which is indicative of a diminished tumorigenic phenotype. The final outcome of 8-Cl-Ado treatment of the breast cancer cells was growth inhibition due to an induction of apoptosis and a loss of clonogenic survival. These results indicate that 8-Cl-Ado, which is currently in clinic for hematological malignancies, may be an effective agent for the treatment of breast cancer.

BAX and BAK proteins are required for cyclin-dependent kinase inhibitory drugs to cause apoptosis

In previous reports, we have shown in SH-SY5 cells that olomoucine and roscovitine, two inhibitory drugs of cyclin-dependent kinases, caused apoptosis independent of the extrinsic pathway. In this experimental paradigm, apoptosis was refractory to the protective effects of either Bcl-2 or Bcl-XL overexpression. We are now reporting that the failure of Bcl-XL to prevent dell death was consistent with no effect on the kinetics of caspase activation and cytochrome c release. To further characterize this issue, we have discarded a direct effect of either olomoucine or roscovitine on mitochondrial permeability transition. Moreover, we have evidence that an intrinsic pathway took place in SH-SY5Y cells by showing the mitochondrial translocation of a GFP-Bax construct on transfection and treatment with cyclin-dependent kinase inhibitory drugs. Finally, we tested the effect of olomoucine and roscovitine on wild-type, bax-/-, bak-/-, and double bax-/-bak-/- mouse embryonic fibroblasts (MEF). In wild-type MEFs, both drugs induced cell death by apoptosis in a dose-dependent manner. In bax-/-, bak-/-, and, particularly, double bax-/-bak-/- MEFs, we observed the inhibition of apoptosis. In conclusion, olomoucine and roscovitine caused apoptosis through an intrinsic pathway, with Bax and Bak proteins being involved.

4-arylcoumarin analogues of combretastatins stimulate apoptosis of leukemic cells from chronic lymphocytic leukemia patients

OBJECTIVE

To investigate the proapoptotic capacities of four arylcoumarin analogues of combretastatins on leukemic cells from B-cell chronic lymphocytic leukemia (CLL), a malignancy characterized by apoptosis deficiency.

MATERIALS AND METHODS

The effects of the four compounds on several nuclear, membrane, and mitochondrial events of apoptosis and on expression of proteins controlling the apoptosis were analyzed after treatment of cultured CLL patients' cells.

RESULTS

Treatment with all four compounds resulted in a dose-dependent internucleosomal DNA fragmentation, in stimulation of phosphatidylserine externalization, disruption of the mitochondrial transmembrane potential and caspase-3 activation. DNA fragmentation was prevented in the presence of the pan-caspase inhibitor z-VAD-fmk. Two of the compounds downregulated the expression of Mcl-1, a protein thought to be crucial for the antiapoptotic state in CLL, while Bcl-2 expression was unaffected. No effects were observed on the expression of p27kip1 or the inducible nitric oxide synthase, two proteins, which are constitutively overexpressed by CLL cells and downregulated during the apoptosis induced by other plant-derived molecules (flavopiridol, polyphenols, or hyperforin). This suggests different mechanisms of action for the compounds studied here. Furthermore, normal B lymphocytes from healthy donors appeared less sensitive than CLL cells to the proapoptotic activity of the four compounds.

CONCLUSION

The four arylcoumarin analogues were able to promote the apoptosis of CLL cells ex vivo through the caspase-dependent mitochondrial pathway. Therefore, these compounds may be of interest to develop new therapies of CLL based on apoptosis restoration.

The NF-κB subunit Rel A is associated with in vitro survival and clinical disease progression in chronic lymphocytic leukemia and represents a promising therapeutic target

In this study, we characterized nuclear factor κB (NF-κB) subunit DNA binding in chronic lymphocytic leukemia (CLL) samples and demonstrated heterogeneity in basal and inducible NF-κB. However, all cases showed higher basal NF-κB than normal B cells. Subunit analysis revealed DNA binding of p50, Rel A, and c-Rel in primary CLL cells, and Rel A DNA binding was associated with in vitro survival (P = .01) with high white cell count (P = .01) and shorter lymphocyte doubling time (P = .01). NF-κB induction after in vitro stimulation with anti-IgM was associated with increased in vitro survival (P < .001) and expression of the signaling molecule ZAP-70 (P = .003). Prompted by these data, we evaluated the novel parthenolide analog, LC-1, in 54 CLL patient samples. LC-1 induced apoptosis in all the samples tested with a mean LD50 of 2.8 μM after 24 hours; normal B and T cells were significantly more resistant to its apoptotic effects (P < .001). Apoptosis was preceded by a marked loss of NF-κB DNA binding and sensitivity to LC-1 correlated with basal Rel A DNA binding (P = .03, r2 = 0.15). Furthermore, Rel A DNA binding was inversely correlated with sensitivity to fludarabine (P = .001, r2 = 0.3), implicating Rel A in fludarabine resistance. Taken together, these data indicate that Rel A represents an excellent therapeutic target for this incurable disease.

Flavopiridol displays preclinical activity in acute lymphoblastic leukemia

BACKGROUND

New agents are needed for treatment of children with relapsed acute lymphoblastic leukemia (ALL). Based on altered expression of cell cycle regulatory proteins, including frequent p16 (INK4A) and p15 (INK4B) deletions, flavopiridol (FP; Alvocidib) is an attractive agent for relapsed ALL.

PROCEDURE

We evaluated the efficacy of FP in ALL cell lines using cell proliferation assays, determined the effects of FP treatment on cell growth and viability in cell lines and patient samples, examined cell cycle kinetics, and evaluated the effect of FP on endogenous cyclin-dependent kinase (CDK) activity, Mcl-1 expression, and RNA polymerase II expression and phosphorylation.

RESULTS

ALL cell lines are sensitive to FP. At lower concentrations, FP induces transient G(1)-S cell cycle arrest and modest levels of apoptosis in cell lines. In contrast, a sustained G(1)-S and G(2)-M arrest and substantial apoptosis are observed following exposure to higher FP concentrations. After treatment with FP, ALL cell lines have decreased expression of retinoblastoma protein phosphorylated at serines 795 and 807/811, indicating reduced CDK activity. We also show that ALL cell lines are sensitive to clinically achievable concentrations of FP in medium supplemented with human serum and that FP reduces the expression of Mcl-1 and phosphorylated forms of the C-terminal domain of RNA polymerase II. FP also increases cell death by approximately twofold over baseline in primary ALL blasts.

CONCLUSIONS

These data provide a biological rationale for testing FP in relapsed ALL.

Tumor suppressor pRb2/p130 gene and its derived product Spa310 spacer domain as perspective candidates for cancer therapy

Tumor suppressor pRb2/p130 gene belongs to the retinoblastoma (Rb) gene family, which also includes pRb/p105 and pRb/p107. The members of the Rb gene family have attracted a great deal of interest because of their essential role in regulating cell cycle and, consequently, cell proliferation. This mini review discusses the potential therapeutic applications both of pRb2/p130 and its derived product Spa310 spacer domain in cancer treatment.

Flavopiridol causes early mitochondrial damage in chronic lymphocytic leukemia cells with impaired oxygen consumption and mobilization of intracellular calcium

Effective administration of flavopiridol in advanced-stage chronic lymphocytic leukemia (CLL) is often associated with early biochemical evidence of tumor cell lysis. Previous work using other cell types showed that flavopiridol impacts mitochondria, and in CLL cells flavopiridol down-regulates the mitochondrial protein Mcl-1. We therefore investigated mitochondrial structure and function in flavopiridol-treated CLL patient cells and in the lymphoblastic cell line 697 using concentrations and times at which tumor lysis is observed in treated patients. Mitochondrial membrane depolarization was detected in flavopiridol-treated CLL cells by 6 hours, well before the onset of cell death. Flavopiridol-induced mitochondrial depolarization was not blocked by caspase inhibitors or by the calcium chelator EGTA, but was reduced by Bcl-2 overexpression. Intracellular calcium mobilization was noted at early time points using fluorescence microscopy. Furthermore, electron paramagnetic resonance oximetry showed a gradual but significant reduction in cellular oxygen consumption rate by 6 hours, corresponding with ultrastructural mitochondrial damage detected by electron microscopy. These observations suggest that in CLL and 697 cells, flavopiridol mediates its cytotoxic effects via induction of the mitochondrial permeability transition and changes in intracellular calcium.

Flavopiridol administered using a pharmacologically derived schedule is associated with marked clinical efficacy in refractory, genetically high-risk chronic lymphocytic leukemia

Despite promising preclinical studies with the cyclin-dependent kinase inhibitor flavopiridol in chronic lymphocytic leukemia (CLL) and other diseases, previous clinical trials with this agent have been disappointing. The discovery of differential protein binding of flavopiridol in human and bovine serum contributed to an effective pharmacokinetic-derived schedule of administration of this agent. On the basis of pharmacokinetic modeling using our in vitro results and data from a previous trial, we initiated a phase 1 study using a 30-minute loading dose followed by 4 hours of infusion administered weekly for 4 of 6 weeks in patients with refractory CLL. A group of 42 patients were enrolled on 3 cohorts (cohort 1, 30 mg/m2 loading dose followed by 30 mg/m2 4-hour infusion; cohort 2, 40 mg/m2 loading dose followed by 40 mg/m2 4-hour infusion; and cohort 3, cohort 1 dose for treatments 1 to 4, then a 30 mg/m2 loading dose followed by a 50 mg/m2 4-hour infusion). The dose-limiting toxicity using this novel schedule was hyperacute tumor lysis syndrome. Aggressive prophylaxis and exclusion of patients with leukocyte counts greater than 200x10(9)/L have made this drug safe to administer at the cohort 3 dose. Of the 42 patients treated, 19 (45%) achieved a partial response with a median response duration that exceeds 12 months. Responses were noted in patients with genetically high-risk disease, including 5 (42%) of 12 patients with del(17p13.1) and 13 (72%) of 18 patients with del(11q22.3). Flavopiridol administered using this novel schedule has significant clinical activity in refractory CLL. Patients with bulky disease and high-risk genetic features have achieved durable responses, thereby justifying further study of flavopiridol in CLL and other diseases.

Short nucleotide polymorphic insertions in the MCL-1 promoter affect gene expression

We have recently reported novel short nucleotide (six and eighteen) polymorphic insertions, in the MCL-1 promoter and their association with higher mRNA and protein levels. The aim of the present study was to test the hypothesis that these insertions directly affect MCL-1 gene expression. Haematopoietic and epithelial human cell lines were transfected with +0, +6, or +18 MCL-1 promoter fragments positioned upstream of the Firefly luciferase reporter gene. The cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and granulocyte macrophage colony-stimulating factor (GM-CSF). Compared to +0, both polymorphic insertions (+6 and +18) were associated with increased promoter activity. Although chromatin immunoprecipitation assay showed that there are Sp1/Sp3 binding sites in the MCL-1 promoter, electrophoretic mobility shift assay showed that it is unlikely that these sites are in the region harboring these insertions. These results provide further evidence for the biological effect of MCL-1 promoter polymorphisms on gene expression.

A small molecule based on the pRb2/p130 spacer domain leads to inhibition of cdk2 activity, cell cycle arrest and tumor growth reduction in vivo

One strategy in the development of anticancer therapeutics has been to arrest malignant proliferation through inhibition of the enzymatic activity of cyclin-dependent kinases (cdks), which are key regulatory molecules of the cell cycle. Over the past few years, numerous compounds with remarkable cdk inhibitory activity have been studied in cancer therapy, although it is very difficult to point out the best cdk to target. An excellent candidate appears to be cdk2, whose alteration is a pathogenic hallmark of tumorigenesis. The small molecule described in our study showed an inhibitory effect on the kinase activity of cdk2, a significant growth arrest observed in a colony formation assay and a reduction in the size of the tumor in nude mice, thus suggesting its potential role as a promising new type of mechanism-based antitumor drug, also for the treatment of hyperproliferative disorders.

Role of angiogenesis in chronic lymphocytic leukemia

Angiogenesis is a physiologic process of new blood vessels formation mediated by various cytokines called angiogenic and angiostatic factors. Although its potential pathophysiologic role in solid tumors has been extensively studied for more than 3 decades, enhancement of angiogenesis in chronic lymphocytic leukemia (CLL) and other malignant hematological disorders has been recognized more recently. An increased level of angiogenesis has been documented by various experimental methods both in bone marrow and lymph nodes of patients with CLL. Although the role of angiogenesis in the pathophysiology of this disease remains to be fully elucidated, experimental data suggest that several angiogenic factors play a role in the disease progression. Biologic markers of angiogenesis were also shown to be of prognostic relevance in CLL. The current findings provide the rationale for investigating antiangiogenic agents in CLL. In the current review angiogenesis in CLL is discussed and its potential diagnostic and therapeutic applications.

Mechanisms of cell death of chronic lymphocytic leukemia lymphocytes by RNA-directed agent, 8-NH2-adenosine

PURPOSE

To determine if RNA-directed nucleoside analogue, 8-NH(2)-adenosine, induces cell death and if that is accompanied with transcription inhibition of the key survival factors of chronic lymphocytic leukemia (CLL) cells.

EXPERIMENTAL DESIGN

Primary lymphocytes from CLL patients were incubated with 10 micromol/L 8-NH(2)-adenosine for 2, 4, and 6 or 8 hours. The accumulation of analogue triphosphate and the decline in endogenous ATP pool were analyzed by high-performance liquid chromatography. Inhibition of global RNA and protein synthesis was measured and correlated with specific decline in transcript and protein levels of MCL-1, XIAP, and BCL-2, the key survival factors of CLL. These biochemical and molecular end points were related to cell death of these quiescent lymphocytes.

RESULTS

In vitro incubations of CLL lymphocytes with 8-NH(2)-adenosine resulted in rapid but heterogeneous accumulation of 8-NH(2)-ATP (390-680 micromol/L), with a concomitant decline in endogenous ATP (median, >50% by 4 hour). Global RNA synthesis was decreased in all samples and was associated with a decline in MCL-1, XIAP, and BCL-2 transcripts. There was a parallel decrease in the protein level of MCL-1 and XIAP but not BCL-2. These biochemical changes were accompanied by apoptosis.

CONCLUSION

The evidence of CLL cell death with complementary changes in the expression of survival proteins provides a molecular rationale for using 8-NH(2)-adenosine as a therapeutic agent for this indolent leukemia.

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

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

Transactivation of cyclin E gene by EWS-Fli1 and antitumor effects of cyclin dependent kinase inhibitor on Ewing's family tumor cells

Chromosomal translocation t(11; 22)(q24; q12) is detected in approximately 90% of Ewing's family tumors (EFTs) including Ewing's sarcoma and primitive neuroectodermal tumor. This results in the formation of the EWS-Fli1 fusion gene, which produces EWS-Fli1 fusion protein. This chimerical gene product acts as an aberrant transcriptional activator, which may be responsible for the tumorigenesis of EFTs. We have previously reported that cyclin E expression was upregulated in EFT cells and in EWS-Fli1 transformed fibroblastic cells. However, the mechanism of the overexpression of cyclin E by EWS-Fli1 is still unknown. In our study, we investigated the mechanism of transactivation of the cyclin E gene in EFT cells. We found that EWS-Fli1 enhanced the activity of the cyclin E gene promoter partially through E2F binding sites in the promoter. In addition, the basic transcriptional factor, Sp1, might also be involved in the transactivation of the cyclin E gene by EWS-Fli1. To study the biological significance of cyclin E overexpression in EFT cells, we used flavopiridol, a pan-cyclin-dependent kinase (CDK) inhibitor and found that flavopiridol efficiently suppressed the growth of EFT cells in vitro and in vivo by the inhibition of cyclinE/CDK2 kinase activity and the induction of apoptosis. These results suggest that targeting of the cyclin/CDK complex may provide new insight into treatment of EFTs.

In vitro cytotoxic effect of proteasome inhibitor bortezomib in combination with purine nucleoside analogues on chronic lymphocytic leukaemia cells

OBJECTIVE

The anti-tumour in vitro activity of proteasome inhibitor bortezomib (PS-341, VELCADE) in combination with purine nucleoside analogues, cladribine (2-CdA) and fludarabine (FA) was tested in lymphocytes derived from 26 patients with B-cell chronic lymphocytic leukaemia (B-CLL).

METHODS

Cell viability was assessed by propidium iodide staining, and apoptosis by annexin-V and caspase activation flow cytometry assays. Additionally, expression of the apoptosis-regulating proteins Bax, Bak, Bid, Bcl-w, Bcl-2, XIAP and Mcl-1 was evaluated in B-CLL lymphocytes.

RESULTS

Bortezomib alone induced significant, dose-dependent cytotoxicity starting from the low concentration 2.5 nm, inducing apoptosis of B-CLL cells. Combination of this agent with 2-CdA or FA resulted in an increase of cytotoxicity when compared with that mediated by single drugs. The observed increase was especially evident when 5 nm of bortezomib were combined with suboptimal doses of 2-CdA or FA. The combination index (CI) was 0.87 for bortezomib + 2-CdA and 0.82 for bortezomib + FA, indicating an evident additive effect of these combinations. Moreover, B-CLL cells were more sensitive to proteasome inhibitor used alone or combined with 2-CdA or FA comparing to CD3+ lymphocytes. Corresponding to enhanced apoptosis, the expression levels of several apoptosis-regulating proteins were altered. The most pronounced changes were down-regulation of XIAP and up-regulation of Bid proteins by the combination of bortezomib with either 2-CdA or FA.

CONCLUSIONS

This study suggest that the in vitro cytotoxic effect through proteasome inhibition by bortezomib can be increased substantially with low doses of the purine nucleoside analogues, 2-CdA and FA, and that this effect on B-CLL cell is selectively higher than on normal, CD3-positive lymphocytes.

Nurselike cells express BAFF and APRIL, which can promote survival of chronic lymphocytic leukemia cells via a paracrine pathway distinct from that of SDF-1alpha

We examined expression of B cell-activating factor of the tumor necrosis factor (TNF) family (BAFF) and a proliferation-inducing ligand (APRIL) on chronic lymphocytic leukemia (CLL) B cells and nurselike cells (NLCs), which differentiate from CD14+ cells when cultured with CLL B cells. NLCs expressed significantly higher levels of APRIL than monocytes and significantly higher levels of BAFF and APRIL than CLL B cells. Also, the viability of CLL B cells cultured with NLCs was significantly reduced when CLL B cells were cultured with decoy receptor of B-cell maturation antigen (BCMA), which can bind both BAFF and APRIL, but not with BAFF receptor:Fc (BAFF-R:Fc), which binds only to BAFF. The effect(s) of BAFF or APRIL on leukemia cell survival appeared additive and distinct from that of stromal cell-derived factor-1alpha (SDF-1alpha), which in contrast to BAFF or APRIL induced leukemia cell phosphorylation of p44/42 mitogen-activated protein kinase (extracellular signal-regulated kinase-1/2 [ERK1/2]) and AKT. Conversely, BAFF and APRIL, but not SDF-1alpha, induced CLL-cell activation of the nuclear factor-kappaB1 (NF-kappaB1) and enhanced CLL-cell expression of the antiapoptotic protein Mcl-1. However, BAFF, but not APRIL, also induced CLL-cell activation of NF-kappaB2. We conclude that BAFF and APRIL from NLCs can function in a paracrine manner to support leukemia cell survival via mechanisms that are distinct from those of SDF-1alpha, indicating that NLCs use multiple distinct pathways to support CLL-cell survival.

Bodyguards and assassins: Bcl-2 family proteins and apoptosis control in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy in the Western world and exists as subtypes with very different clinical courses. CLL is generally described as a disease of failed apoptosis. Apoptosis resistance may stem from a combination of microenvironmental survival signals as well as from intrinsic alterations in the apoptotic machinery within the CLL cell. The molecular mechanism involved in controlling apoptosis in CLL is complex and is influenced by many factors, including Bcl-2 family proteins, which are critical regulators of cell death. Here we review the significance of apoptosis dysregulation in CLL, focusing on the role of Bcl-2 and related Bcl-2 family proteins, such as Bax and Mcl-1. The differential properties of the newly described subsets of CLL are also highlighted.

Role of myeloid cell factor-1 (Mcl-1) in chronic lymphocytic leukemia

The primary abnormality in chronic lymphocytic leukemia (CLL) is a defect in apoptosis, probably related to alterations in the expressions of Bcl-2 family members. In transgenic mice over expressing the anti-apoptotic Bcl-2 family member, myeloid cell factor-1 (Mcl-1), B cell lymphomas occur. Moreover, mice conditional for the loss of Mcl-1 display a profound reduction in B and T lymphocytes. This suggests that Mcl-1 is an essential survival factor in lymphocytes. In the present study, we have evaluated the role of Mcl-1 in CLL. Mcl-1 protein expression was measured by Western blot analysis in the CLL cells of 45 patients and correlated with clinical variables and survival. Mcl-1 levels were similar in 29 patients to normal B and T lymphocytes, were decreased in 8 patients and increased in 12 patients. An inverse correlation was found between Mcl-1 expression and Rai stage (P = 0.001). When assessed by flow cytometry, Mcl-1 expressions were normally distributed among CLL cells in individual patients and the mean levels correlated with those obtained by Western blotting. To evaluate the role of Mcl-1 in drug resistance, Mcl-1 levels were sequentially measured in the leukemic cells of 4 CLL patients during therapy with fludarabine (Flu). The Mcl-1 levels were found to increase in 2 patients while the peripheral blood lymphocyte counts dropped, suggesting that the residual drug-resistant cells had the highest Mcl-1 levels. Primary CLL cells were also treated with chlorambucil (CLB) or Flu in vitro and the Mcl-1 levels decreased correlating with the sensitivity of these cells to undergo apoptosis. Drug sensitivities of the CLL cells to CLB and Flu were also measured by MTT assay and the concentrations of drug required to decrease cell viability by 50% (IC50) varied from 1.9 to 9.27 microM for Flu (median, 9.4 microM) and 10 to 32.5 microM (median, 5.5 microM) for CLB. The sensitivities of the leukemic cells to CLB correlated inversely with Mcl-1 levels (P < 0.05). These results suggest that Mcl-1 may contribute to cell survival in CLL.

Antiapoptotic signaling pathways in non-small-cell lung cancer: biology and therapeutic strategies

One of the hallmarks of lung cancer is the deregulation of apoptotic or programmed cell death mechanisms usually found in normal cells that allow for corrupted cells to undergo cellular suicide. This includes mechanisms that attenuate proapoptotic pathways and/or amplify antiapoptotic pathways. Increasing evidence suggests that lung cancer cells use multiple and perhaps redundant pathways to maintain survival. Increasing knowledge of these pathways offers a better understanding of the biology of lung cancer as well as novel therapeutic strategies that can enhance lung cancer cell death. This review discusses the apoptotic machinery and signal transduction pathways that regulate apoptosis, methods of identifying the presence of activated survival signaling pathways in human lung cancers, and the clinical significance and relevance for therapy for patients with lung cancer.

Flavones and polyphenols inhibit the NO pathway during apoptosis of leukemia B-cells

We recently reported that resveratrol, a grape-derived polyphenol, in vitro induces the apoptosis of leukemic B-cells and simultaneously inhibits the production of endogenous nitric oxide (NO) through inducible NO synthase (iNOS) down-regulation. The same results were observed in the present study with not only acetate derivatives of polyphenols, particularly the pentaacetate of -viniferin (resveratrol dimer), but also with a synthetic flavone (a diaminomethoxyflavone) in both leukemia B-cell lines and B-cell chronic lymphocytic leukemia (B-CLL) patients' cells. Moreover, flavopiridol, another flavone already known for its pro-apoptotic properties in B-CLL cells, was also found to down-regulate both iNOS expression and NO production. Thus, inhibition of the NO pathway during apoptosis of leukemia B-cells appears a common mechanism for several compounds belonging to two distinct families of phytoalexins, the flavones and grape-derived polyphenols.

Prognostic significance of a short sequence insertion in the MCL-1 promoter in chronic lymphocytic leukemia

BACKGROUND

Mcl-1 protein contributes to the longevity of chronic lymphocytic leukemia (CLL) B cells, and its higher expression has been associated with resistance to chemotherapy. We sought structural changes in the MCL-1 gene in CLL patients and associated these with clinical parameters of the disease.

METHODS

The MCL-1 gene from peripheral blood lymphocytes from 58 CLL patients and 18 control subjects and from the RL and BC-3 lymphoma cell lines was sequenced. Mcl-1 mRNA expression (in 20 consecutive patients and four control subjects) was analyzed by RNase protection assay, and Mcl-1 protein expression (in 18 consecutive patients and four controls) was analyzed by western blotting. Genetic changes in MCL-1 were associated with biochemical and clinical characteristics, including expression of CD38, a negative prognostic factor. Cox proportional hazards modeling was used to determine the prognostic importance of changes in the MCL-1 gene, and the Kaplan-Meier method was used to analyze patient survival. All statistical tests were two sided.

RESULTS

A 6- or 18-nucleotide sequence insertion was found in the same site in the MCL-1 promoter in 17 of 58 patients and in BC-3 cells; it was absent in all control subjects and in RL cells. Of 21 CD38-negative patients, 10 had a promoter insertion; of 17 CD38-positive patients, one had a promoter insertion (P =.0099). Patients with a promoter insertion had higher mRNA (median = 26.8 relative units, interquartile range [IQR] = 14.9 to 35.2, versus median = 8.8 relative units, IQR = 3.9 to 15.7, P =.030, U-test) and protein (median = 0.84 relative units, IQR = 0.81 to 1.0 versus median = 0.47, IQR = 0.32 to 0.70, P =.021, U-test) expression, more rapid disease progression (P =.012), poorer response to chemotherapy (P =.001), and shorter overall (P =.0088) and disease-specific (P <.001) survival than patients with a normal promoter. The presence of an MCL-1 promoter insertion had prognostic significance in a Cox model (P =.001).

CONCLUSIONS

The MCL-1 promoter insertion may identify a high-risk group of CD38-negative CLL patients.

Small molecule inhibitors targeting cyclin-dependent kinases as anticancer agents

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

Protein kinases in the regulation of apoptosis in B-cell chronic lymphocytic leukemia

The involvement of several protein kinase pathways in the regulation of apoptosis and cell survival has been analyzed in a wide range of models. This article reviews current understanding of the protein kinases involved in the control of apoptosis in B-cell chronic lymphocytic leukemia (B-CLL) cells. Protein kinase C (PKC), phosphatidylinositol 3-kinase (P13K) and nuclear factor-kappa B (NF-kappaB) play important roles in the survival of these leukemic cells. These survival pathways affect proteins involved in the control of apoptosis by altering their expression or function. The elucidation of the signal transduction network involved in the survival of B-CLL cells could provide novel pharmacological targets for the therapy of B-CLL.

Flavopiridol downregulates the expression of both the inducible NO synthase and p27(kip1) in malignant cells from B-cell chronic lymphocytic leukemia

Flavopiridol, an inhibitor of cyclin-dependent kinases and other protein kinases, induces in vitro apoptosis of malignant cells from B-cell chronic lymphocytic leukemia (B-CLL). Previously, we reported that nitric oxide (NO), produced by an inducible NO synthase (iNOS), spontaneously expressed by the B-CLL cells, contributed to their deficiency in apoptosis. In the present work, we show that ex vivo treatment of leukemic cells from B-CLL patients with flavopiridol results in the inhibition of iNOS expression, as determined by immunofluorescence and Western blotting, and in a marked inhibition of NO production measured in situ with a specific fluorescent probe (DAF-2 DA). These effects are accompanied by membrane, mitochondrial and nuclear events of apoptosis. Flavopiridol exposure also results in the stimulation of caspase 3 activity and in caspase-dependent cleavage of p27(kip1), a negative regulator of the cell cycle, which is overexpressed in B-CLL. Thus, flavopiridol is capable of downregulating both iNOS and p27(kip1) expression in B-CLL cells. Furthermore, flavopiridol-promoted apoptosis is partly reverted by an NO donor, suggesting that inhibition of the NO pathway could participate in the apoptotic effects of flavopiridol on the leukemic cells.

Mcl-1 and Bcl-2/Bax ratio are associated with treatment response but not with Rai stage in B-cell chronic lymphocytic leukemia

Although both Bcl-2/Bax ratio and Mcl-1 have been identified to be of clinical relevance in B-cell chronic lymphocytic leukemia (CLL), there is controversy regarding their role; further, their relative importance is not well delineated. Expression of Bcl-2, Bax, the Bcl-2/Bax ratio, and Mcl-1 in 51 consecutive previously untreated CLL patients and 16 controls was determined by Western blotting. Only 37 patients were treated, all with chlorambucil and prednisone initially. Six patients achieved complete response (CR), 14 were non-responders (NR), and 17 had a partial response (PR), as defined by NCI criteria. There was considerable inter-patient variability in protein expression and overlap with healthy volunteers (P > 0.05). All patients with CR had low Mcl-1 levels compared to the PR + NR group (0.07 +/- 0.02 vs. 0.14 +/- 0.07, P = 0.043). Higher Mcl-1 expression as determined by dichotomizing the data was associated with a failure to achieve CR (P = 0.021). The Bcl-2/Bax ratio was significantly associated with treatment response only when CR and PR were considered together (0.89 +/- 0.53 [CR + PR] vs. 3.38 +/- 4.47 [NR], P = 0.0118). There was no association with Rai stage. Low Mcl-1 appears to be a requirement for CR, while low Bcl-2/Bax ratio is indicative of some response to conventional treatment.

New directions in the diagnosis and treatment of chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common leukaemia of adults in Western countries. It is a systemic haematological malignancy that originates from B cells (B-CLL) in 95% of patients, while only a minority are derived through malignant transformation of T cells (T-CLL). Although B-CLL is classified as a non-Hodgkin's lymphoma, several issues make this leukaemia a unique entity among malignant lymphoma. Inhibition of the programmed cell death (apoptosis) and upregulation of the anti-apoptotic protein Bcl-2 are key elements of the pathophysiology of B-CLL cells and define clinical prognosis. Furthermore, B-CLL cells are arrested in G0/G1 phase of the cell cycle. Dysfunctional apoptosis and cell cycle are the main reasons for the clinical enigma, that CLL can not yet be cured with conventional chemotherapy. However, the molecular pathways that are responsible for this characteristic feature of the B-CLL cells still need further definition.Recently, considerable progress has been made in defining the molecular basis for the pathogenesis of CLL and in finding new therapeutic options. Recent studies indicate that B-CLL cells may be delineated from two main groups of normal B cells, i.e. pre- and postgerminal B cells, and can be distinguished through lack of or existence of mutations of the V heavy chain gene. This differential mutational status of the Ig V gene has significant impact on patient survival. Modern cytogenetic methods such as fluorescence in situ hybridisation (FISH) have opened a new era in the molecular analysis of CLL cells. Determining the chromosomal aberration of the leukaemic cells has become a standard scientific programme for each clinical trial. The cytogenetic profile may soon help to define a clinical risk profile and guide the various treatment strategies. Further progress has been made in the therapy of CLL. Purine analogues such as fludarabine were able to induce significant improvement in remission rates; however, they did not lead to improved survival. Chimera of murine or rat monoclonal antibodies and human antibodies were designed to treat CLL. Antibodies such as rituximab and alemtuzumab (Campath-1H), directed against CD20 and CD52, respectively, appear as attractive alternatives to conventional chemotherapy because of their lack of significant myelotoxicity. Studies using myeloablative chemotherapy followed by autologous or allogeneic stem cell transplantation were initiated with the hope of finding a cure for CLL. In contrast to autologous stem cell transplantation, allogeneic transplants appear to display a plateau of relapse rates. In conclusion, for many years CLL was considered as a chronic haematological malignancy that required only few diagnostic tools and for whom no hope of cure could be offered. The current review focuses on recent improvements in diagnosis and treatment of CLL that have opened a new era in the management of patients with this systemic malignancy.

Tetrocarcin-A--induced ER stress mediates apoptosis in B-CLL cells via a Bcl-2--independent pathway

Tetrocarcin-A (TC-A), an antibiotic agent isolated from actinomycetes, has recently been described to antagonize Bcl-2 functions, thereby sensitizing tumor cells to cell death signals under control of Bcl-2. In this study, we analyzed the direct proapoptotic effect of TC-A in the B-chronic lymphocytic leukemia (B-CLL) model. We focused on the signal cascade triggered by TC-A in B-CLL cells and identified activated mitochondrial as well as endoplasmatic reticulum (ER) stress signals. The expression levels of known effector molecules mediating mitochondrial signaling, such as Bax and Bid, and the antagonistic molecule Bcl-2 did not influence sensitivity of B-CLL cells to TC-A. Furthermore, the molecular chaperone and sensor of ER stress, HSP70, though significantly up-regulated in B-CLL cells undergoing TC-A-triggered apoptosis, was ineffective to exert its anti-apoptotic function described in multiple cell death pathways. Autologous T cells of B-CLL patients were significantly less sensitive to TC-A as were also T cells from healthy donors when compared with their normal B-cell fraction. Furthermore, sensitivity of B-CLL cells to TC-A treatment in vitro was dependent neither on the expression levels of CD38-a prognostic factor for survival of B-CLL patients as well as for their response to therapy-nor on the clinical stage or pretreatment status of patients. From our data showing that TC-A induced a cell death pathway via ER stress preferentially in B cells and that it acted independently of important markers of drug sensitivity and of clinical markers, we conclude that TC-A might represent an attractive candidate drug for further evaluation in preclinical trials.

Flavopiridol induces apoptosis in B-cell chronic lymphocytic leukaemia cells through a p38 and ERK MAP kinase-dependent mechanism

Flavopiridol, a synthetic flavone, has been previously shown to induce apoptosis in B-cell chronic lymphocytic leukaemia (B-CLL) cells in vitro. The apoptosis was associated with a concomitant activation of caspase-3 without evidence of dependence on functional p53 or Bcl-2 family modulation. In this study, we examined flavopiridol-induced apoptosis in terms of upstream caspase activity, cell cycle distribution and signal transduction, in order to elucidate the mechanism of action of this potent cytotoxic agent. Flavopiridol-induced apoptosis was significantly abrogated by the caspase-9 inhibitor Z-LEHD-FMK (p = 0.002; paired t-test) but was not altered by the caspase-8 inhibitor Z-IETD-FMK (p = 0.37; paired t-test). There was a concentration-dependent increase in a sub G0/G1 peak indicative of apoptotic cells but if these cells were excluded by gating no other cell cycle perturbations were observed suggesting that flavopiridol is capable of inducing apoptosis in cells in all phases of the cell cycle. Significantly, apoptosis was associated with activation of p38 MAP kinase and suppression of ERK activity (p = 0.0036 and p = 0.0048, respectively; paired t-test). These results show for the first time that flavopiridol modulates specific cellular signal transduction pathways in B-CLL cells thereby altering the balance between survival and cell death signals and providing a rationale for the p53-independent nature of flavopiridol-induced apoptosis. Further work is required to identify whether combinations of conventional chemotherapeutic drugs and novel agents like flavopiridol can be used to improve patient outcomes in the treatment of B-CLL.

Sildenafil and vardenafil, types 5 and 6 phosphodiesterase inhibitors, induce caspase-dependent apoptosis of B-chronic lymphocytic leukemia cells

Type 4 phosphodiesterase (PDE4) inhibitors reportedly induce apoptosis in chronic lymphocytic leukemia (CLL) cells. Following clinical improvement of one previously untreated CLL patient with sildenafil therapy, we evaluated the in vitro induction of apoptosis in CLL cells by 4 PDE5/6 inhibitors, including sildenafil, vardenafil, zaprinast, and methoxyquinazoline (MQZ). After 24 hours of culture, the various PDE inhibitors differed in their ability to induce apoptosis, with zaprinast displaying no killing effect. Normal B cells isolated from control donors were totally resistant to PDE-induced apoptosis. Vardenafil was 3 and 30 times more potent an inducer of apoptosis than sildenafil and MQZ, respectively. Both vardenafil and sildenafil failed to elevate adenosine 3'5' cyclic monophosphate (cAMP) levels, largely excluding an inhibitory effect on cAMP-PDE3, -PDE4, and -PDE7. Vardenafil- or sildenafil-treated B-CLL cells displayed up to 30% intracellular active caspase 3. Drug-induced apoptosis was inhibited by the caspase inhibitor z-VAD.fmk, prevented by interleukin-4 (IL-4), and significantly reduced by stromal-derived factor1-alpha (SDF-1alpha). We conclude that vardenafil and sildenafil induce caspase-dependent apoptosis of B-CLL cells in vitro and thus might be considered in the treatment of CLL patients. However, further in vivo investigations should be warranted.

Bcl-2 has differing effects on the sensitivity of breast cancer cells depending on the antineoplastic drug used

The aim of this paper was to evaluate the role of bcl-2 in the susceptibility of the MCF7 ADR human breast carcinoma line overexpressing the P-170 glycoprotein (P-170) to various drugs. The sensitivity to four multidrug resistance (MDR)-related drugs (doxorubicin (ADR), vincristine (VCR), vinblastine (VBL), actinomycin D (ACTD)) and three MDR-non-related drugs (cisplatin (DDP), bischloroethylnitrosourea (BCNU), 5-fluorouracil (5-FU)) was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay in three bcl-2-overexpressing clones obtained from the MCF7 ADR line. We found that the bcl-2-overexpressing clones show increased resistance to DDP and BCNU, while no difference to 5-FU were observed between the control cells and bcl-2 transfectants. Surprisingly, bcl-2-overexpressing clones displayed an increased sensitivity compared with the control cells to the MDR-related drugs ADR, VCR, VBL and ACTD. Focusing on DDP and ADR, we found that the increased resistance of the bcl-2 transfectants to DDP was correlated to their ability to prevent apoptosis, while the enhanced sensitivity to ADR was associated with an increased ADR accumulation and a decreased ADR efflux. Moreover, while bcl-2 overexpression does not induce changes in P-170 glycoprotein expression, it did induce a reduction of the adenosine triphosphate (ATP) levels and basal protein kinase C (PKC) activity, both of which have a crucial role in the regulation of the MDR phenotype. In conclusion, the effect of bcl-2 on antineoplastic sensitivity observed in this study underscores the idea that bcl-2 may have distinct biological effects depending on the anticancer drug used.

Phase I clinical and pharmacokinetic study of flavopiridol administered as a daily 1-hour infusion in patients with advanced neoplasms

PURPOSE

To define the maximum-tolerated dose (MTD), dose-limiting toxicity, and pharmacokinetics of the cyclin-dependent kinase inhibitor flavopiridol administered as a daily 1-hour infusion every 3 weeks.

PATIENTS AND METHODS

Fifty-five patients with advanced neoplasms were treated with flavopiridol at doses of 12, 17, 24, 30, 37.5, and 52.5 mg/m(2)/d for 5 days; doses of 50 and 62.5 mg/m(2)/d for 3 days; and doses of 62.5 and 78 mg/m(2)/d for 1 day. Plasma sampling was performed to characterize the pharmacokinetics of flavopiridol with these schedules.

RESULTS

Dose-limiting neutropenia developed at doses >/= 52.5 mg/m(2)/d. Nonhematologic toxicities included nausea, vomiting, diarrhea, hypotension, and a proinflammatory syndrome characterized by anorexia, fatigue, fever, and tumor pain. The median peak concentrations of flavopiridol achieved at the MTDs on the 5-day, 3-day, and 1-day schedule were 1.7 micro mol/L (range, 1.3 to 4.2 micro mol/L), 3.2 micro mol/L (range, 1.7 to 4.8 micro mol/L), and 3.9 micro mol/L (1.8 to 5.1 micro mol/L), respectively. Twelve patients had stable disease for >/= 3 months, with a median duration of 6 months (range, 3 to 11 months).

CONCLUSION

The recommended phase II doses of flavopiridol as a 1-hour infusion are 37.5 mg/m(2)/d for 5 days, 50 mg/m(2)/d for 3 days, and 62.5 mg/m(2)/d for 1 day. Flavopiridol as a daily 1-hour infusion can be safely administered and can achieve concentrations in the micromolar range, sufficient to inhibit cyclin-dependent kinases in preclinical models. Further studies to determine the optimal schedule of flavopiridol as a single agent and in combination with chemotherapeutic agents are underway.

Role of caspases and apoptosis-inducing factor (AIF) in cladribine-induced apoptosis of B cell chronic lymphocytic leukemia

We have evaluated the role of caspases and the mitochondrial apoptosis inducing-factor (AIF) in apoptosis induced by cladribine (2CdA), in vitro, in cells from patients of B-CLL and in peripheral blood lymphocytes from normal donors. In sensitive B-CLL cells, apoptosis was characterized by cell shrinking, loss of mitochondrial membrane potential (DeltaPsi(m)), phosphatidylserine exposure, activation of caspases 3, 7, 8 and 9, reduction of Mcl-1 levels, translocation of AIF from mitochondria to nucleus and chromatin condensation. No significant variations in the levels of Bcl-2, Bax and Bak proteins were noticed upon treatment with 2CdA. Co-treatment of cells with the pan-caspase inhibitor Z-VAD-fmk attenuated some morphological and biochemical characteristics of apoptosis and delayed 2CdA-induced DeltaPsi(m) loss, but did not prevent cell death. Z-VAD-fmk did not prevent 2CdA-induced AIF translocation but in this case apoptotic cells displayed only peripheral chromatin condensation, characteristic of AIF action. Reduced or negligible caspase 3 expression did not prevent 2CdA toxicity in cells from four patients. Cells from three patients that responded poorly to 2CdA lacked expression of caspases 9 or 3. Cells from another patient resistant to 2CdA expressed caspases 3, 7, 8 and 9 but they were not activated by treatment. These results indicate that execution of apoptosis is carried out independently by AIF and caspases, which are responsible for the development of apoptotic phenotype in response to 2CdA. Although caspases can also collaborate in DeltaPsi(m) loss, proapoptotic proteins from the Bcl-2 superfamily may be the key inducers of DeltaPsi(m) loss and apoptosis in B-CLL cells sensitive to 2CdA.

Spontaneous and drug-induced apoptosis is mediated by conformational changes of Bax and Bak in B-cell chronic lymphocytic leukemia

The role of Bax and Bak, 2 proapoptotic proteins of the Bcl-2 family, was analyzed in primary B-cell chronic lymphocytic leukemia (CLL) cells following in vitro treatment with fludarabine, dexamethasone, or the combination of fludarabine with cyclophosphamide and mitoxantrone (FCM). A strong correlation was found between the number of apoptotic cells and the percentage of cells stained with antibodies recognizing conformational changes of Bax (n = 33; r = 0.836; P <.001) or Bak (n = 10; r = 0.948; P <.001). Preincubation of CLL cells with Z-VAD.fmk (N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone), a broad caspase inhibitor, abolished caspase-3 activation, exposure of phosphatidylserine residues, and reactive oxygen species generation; partially reversed the loss of transmembrane mitochondrial potential (DeltaPsim); but did not affect Bax or Bak conformational changes. These results indicate that the conformational changes of Bax and Bak occur upstream of caspase activation or are caspase independent. Following drug-induced apoptosis, Bax integrates into mitochondria, as demonstrated by fluorescence microscopy and Western blot, without changes in the total amount of Bax or Bak protein. Fludarabine and FCM induce p53 stabilization, but do not seem to be essential in inducing Bax and Bak conformational changes, as they are also observed in dexamethasone-treated CLL cells. These results demonstrate that, in CLL cells, the change in the intracellular localization of Bax from cytosol to mitochondria and the conformational changes of Bax and Bak are among the early steps in the induction of cell death.