Pleiotropic drug resistance in B-cell chronic lymphocytic leukaemia--the role of Bcl-2 family dysregulation

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.

SG2285, a novel C2-aryl-substituted pyrrolobenzodiazepine dimer prodrug that cross-links DNA and exerts highly potent antitumor activity

The pyrrolobenzodiazepines (PBD) are naturally occurring antitumor antibiotics, and a PBD dimer (SJG-136, SG2000) is in phase II trials. Many potent PBDs contain a C2-endo-exo unsaturated motif associated with the pyrrolo C-ring. The novel compound SG2202 is a PBD dimer containing this motif. SG2285 is a water-soluble prodrug of SG2202 in which two bisulfite groups inactivate the PBD N10-C11 imines. Once the bisulfites are eliminated, the imine moieties can bind covalently in the DNA minor groove, forming an interstrand cross-link. The mean in vitro cytotoxic potency of SG2285 against human tumor cell lines is GI(50) 20 pmol/L. SG2285 is highly efficient at producing DNA interstrand cross-links in cells, but they form more slowly than those produced by SG2202. Cellular sensitivity to SG2285 was primarily dependent on ERCC1 and homologous recombination repair. In primary B-cell chronic lymphocytic leukemia samples, the mean LD(50) was significantly lower than in normal age-matched B and T lymphocytes. Antitumor activity was shown in several human tumor xenograft models, including ovarian, non-small cell lung, prostate, pancreatic, and melanoma, with cures obtained in the latter model with a single dose. Further, in an advanced-stage colon model, SG2285 administered either as a single dose, or in two repeat dose schedules, was superior to irinotecan. Our findings define SG2285 as a highly active cytotoxic compound with antitumor properties desirable for further development.

Small molecule inhibitors of Wnt/beta-catenin/lef-1 signaling induces apoptosis in chronic lymphocytic leukemia cells in vitro and in vivo

BACKGROUND

Lymphoid enhancer factor-1 (lef-1) is overexpressed in B-cell chronic lymphocytic leukemia (CLL) when compared with normal B cells and transcribes several genes implicated in the pathogenesis of CLL. We therefore hypothesize that antagonism of lef-1 might lead to killing of CLL cells. We used two small molecule inhibitors of Wnt/beta-catenin/lef-1 signaling (CGP049090 and PKF115-584) to test our hypothesis.

DESIGN AND METHODS

Enriched CLL cells and healthy B cells were used in this study. Small interfering RNA (siRNA)-mediated knockdown of lef-1 in primary CLL cells was done using nucleofection, and 50% lethal concentration (LC(50)) of two small molecules was assessed using ATP-based cell viability assay. Apoptotic response was investigated in time course experiments with different apoptotic markers. Specificity of the small molecules was demonstrated by coimmunoprecipitation experiments for the lef-1/beta-catenin interaction. In vivo studies were done in JVM-3 subcutaneous xenograft model.

RESULTS

Inhibition of lef-1 by siRNA leads to increased apoptosis of CLL cells and inhibited proliferation of JVM-3 cell lines. The two small molecule inhibitors (CGP049090 and PKF115-584) efficiently kill CLL cells (LC(50)<1 microM), whereas normal B cells were not significantly affected. Coimmunoprecipitation showed a selective disruption of beta-catenin/lef-1 interaction. In vivo studies exhibited tumor inhibition of 69% with CGP049090 and 57% with PKF115-584 when compared with vehicle-treated controls, and the intervention was well tolerated.

CONCLUSIONS

We have demonstrated that targeting lef-1 is a new and selective therapeutic approach in CLL. CGP049090 or PKF115-584 may be attractive compounds for CLL and other malignancies that deserve further (pre)clinical evaluation.

GCS induces multidrug resistance by regulating apoptosis-related genes in K562/AO2 cell line

We have previously shown that the expression of glucosylceramide synthase (GCS) gene in drug-resistant K562/AO2 human leukemia cell was higher than that in drug-sensitive K562 cell, and the sensitivity to adriamycin of K562/AO2 cell was enhanced by inhibiting GCS. It is concluded that the overexpression of GCS gene is one of the reasons which lead to multidrug resistance (MDR) of leukemia cell. Meanwhile, we also found that higher expression of Bcl-2 gene and protein were exhibited in K562/AO2 cell compared with K562 cell. Basing on this, we hypothesized that the high expression of GCS gene which results in MDR of leukemia cell is correlated with Bcl-2 signal transduction. In order to validate the hypothesis, the inhibition of GCS gene in K562/AO2 cell was observed by using chemical suppressor PPMP and siRNA targeted at GCS, and applying RT-PCR and flow cytometry, the expression levels of apoptosis-related gene Bcl-2 and Bax were analyzed before and after inhibiting GCS gene in K562/AO2 cell. The results demonstrated that the gene and protein of Bcl-2 in K562/AO2 cell were both down-regulated significantly after GCS gene being inhibited; however, the Bax mRNA expression had no apparent change in different groups. This suggested that GCS gene may contributed to MDR of human leukemia cell K562/AO2 by Bcl-2 signal transduction.

The novel nuclear factor-kappaB inhibitor LC-1 is equipotent in poor prognostic subsets of chronic lymphocytic leukemia and shows strong synergy with fludarabine

PURPOSE

We have recently shown that the novel nuclear factor-kappaB (NF-kappaB) inhibitor LC-1 is effective in primary chronic lymphocytic leukemia (CLL) cells. Here we elucidated the mechanism of action of LC-1, evaluated its relative cytotoxicity in prognostic subsets, and investigated its potential synergistic interaction with fludarabine.

EXPERIMENTAL DESIGN

Ninety-six fully characterized CLL cases were assessed for in vitro sensitivity to LC-1 and fludarabine. In selected cases, caspase activation, inhibition of Rel A DNA binding, and the transcription of CFLAR, BIRC5, and BCL2 were measured before and after exposure to LC-1. In addition, the efficacy of LC-1 was assessed in the presence of the survival factors CD154 and interleukin-4, and the potential synergistic interaction between LC-1 and fludarabine was evaluated.

RESULTS

Cell death was associated with caspase-3 activation mediated via activation of both caspase-8 and caspase-9. Apoptosis was preceded by a reduction of nuclear Rel A DNA binding and inhibition of CFLAR, BIRC5, and BCL2 transcription. Importantly, LC-1 overcame the cytoprotective effects by interleukin-4 and CD40 ligand and was equipotent in CLL cells derived from good and bad prognostic subsets. LC-1 exhibited strong synergy with fludarabine, and the combination produced a highly significant mean dose reduction index for fludarabine of > 1,000.

CONCLUSIONS

In view of imminent first-in-man study of LC-1 in Cardiff, these data show an important mechanistic rationale for the use of LC-1 in this disease. Furthermore, it validates the concept of targeting nuclear factor-kappaB in CLL and identifies the therapeutic potential of LC-1 in combination with fludarabine even in patients with fludarabine resistance.

Targeting the apoptotic pathway with BCL-2 inhibitors sensitizes primary chronic lymphocytic leukemia cells to vesicular stomatitis virus-induced oncolysis

Chronic lymphocytic leukemia (CLL) is characterized by clonal accumulation of CD5(+) CD19(+) B lymphocytes that are arrested in the G(0)/G(1) phase of the cell cycle and fail to undergo apoptosis because of overexpression of the antiapoptotic B-cell CLL/lymphoma 2 (BCL-2) protein. Oncolytic viruses, such as vesicular stomatitis virus (VSV), have emerged as potential anticancer agents that selectively target and kill malignant cells via the intrinsic mitochondrial pathway. Although primary CLL cells are largely resistant to VSV oncolysis, we postulated that targeting the apoptotic pathway via inhibition of BCL-2 may sensitize CLL cells to VSV oncolysis. In the present study, we examined the capacity of EM20-25--a small-molecule antagonist of the BCL-2 protein--to overcome CLL resistance to VSV oncolysis. We demonstrate a synergistic effect of the two agents in primary ex vivo CLL cells (combination index of 0.5; P < 0.0001). In a direct comparison of peripheral blood mononuclear cells from healthy volunteers with primary CLL, the two agents combined showed a therapeutic index of 19-fold; furthermore, the combination of VSV and EM20-25 increased apoptotic cell death in Karpas-422 and Granta-519 B-lymphoma cell lines (P < 0.005) via the intrinsic mitochondrial pathway. Mechanistically, EM20-25 blocked the ability of the BCL-2 protein to dimerize with proapoptotic BAX protein, thus sensitizing CLL to VSV oncolytic stress. Together, these data indicate that the use of BCL-2 inhibitors may improve VSV oncolysis in treatment-resistant hematological malignancies, such as CLL, with characterized defects in the apoptotic response.

Flavopiridol in the treatment of chronic lymphocytic leukemia

PURPOSE OF REVIEW

The synthetic flavone flavopiridol induces apoptosis of chronic lymphocytic leukemia cells in vitro; however, initial studies administering flavopiridol by a 24- to 72-h continuous intravenous infusion demonstrated no clinical activity. This review focuses on a novel dosing regimen that has achieved significant clinical activity in relapsed, poor-risk chronic lymphocytic leukemia.

RECENT FINDINGS

Binding to human plasma proteins reduces free flavopiridol concentration and makes continuous intravenous infusion dosing ineffective. Pharmacokinetic modeling indicated that administering flavopiridol by a 30-min intravenous bolus followed by a 4-h continuous intravenous infusion would achieve serum concentrations necessary to induce in-vivo apoptosis. Our institution conducted a phase I study in relapsed chronic lymphocytic leukemia. Dose-limiting toxicity was acute tumor lysis syndrome resulting in fatal hyperkalemia. Careful monitoring and aggressive intervention for hyperkalemia, including hemodialysis if necessary, allowed flavopiridol to be given safely. Nineteen of 42 patients responded (45%), including five of 12 patients (42%) with del(17p13) and 13 of 18 patients (72%) with del(11q22).

SUMMARY

Flavopiridol, when administered by a 30-min intravenous bolus followed by a 4-h continuous intravenous infusion, is active in high-risk, refractory chronic lymphocytic leukemia. Careful monitoring and aggressive intervention for tumor lysis syndrome and hyperkalemia is necessary for safe drug administration. Further studies to optimize the dose and schedule of administration, and to study this drug in other hematologic malignancies, are ongoing.

Emerging drugs for chronic lymphocytic leukaemia

Although the philosophy of management of patients with chronic lymphocytic leukaemia (CLL) has been altered with the advent of fludarabine-based therapies, impact on long-term survival is unclear and a significant proportion of patients will develop resistance to fludarabine. Similar to other haematological malignancies, a potential for 'cure' is likely to be achieved only if 'high-quality' complete remissions (CRs) are achieved. Treatment options for patients who develop resistance to fludarabine continue to be limited, with only a proportion obtaining a response (usually not CRs) with salvage therapies. This review summarises novel therapies that are being evaluated in patients with CLL, specifically those targeting the antiapoptotic Bcl-2 family of proteins and receptors (e.g., CD40, CD80, HLA-DR) involved in mediating survival signals from the microenvironment.

In vitro drug resistance in B cell chronic lymphocytic leukemia: a comparison with acute myelocytic and acute lymphocytic leukemia

The aim of the study was to evaluate cellular drug resistance in B cell chronic lymphocytic leukemia (B-CLL) in vitro, and compare it with that in acute myelocytic leukemia (AML) and acute lymphocytic leukemia (ALL). In vitro drug resistance was analyzed by the fluorometric microculture cytotoxicity assay (FMCA) in all samples from patients with leukemia sent to our laboratory between 1992 and 2001. Up to 14 standard drugs were evaluated in samples from 66 patients with B-CLL, 212 patients with AML and 80 patients with ALL. B-CLL cells were found to be more sensitive than cells from both AML and ALL to cytarabine, cladribine, fludarabine, doxorubicin, idarubicin, vincristine and cyclophosphamide (p<0.05). No difference in cellular drug resistance was found between B-CLL and ALL cells for prednisolone, whereas AML cells were more resistant (p<0.0001). In B-CLL, cells from patients who had received previous chemotherapy were more resistant to almost all tested drugs as compared to cells from treatment-naive patients. In AML and ALL, in vitro drug resistance was not related to previous chemotherapy. For all drugs, there was a good agreement between the activity in vitro and the known clinical disease-specific activity. The study also demonstrated an acquired cellular drug resistance in B-CLL, but not in the acute leukemias.

Phase II study of theophylline in chronic lymphocytic leukemia: a study of the Eastern Cooperative Oncology Group (E4998)

The Eastern Cooperative Oncology Group (ECOG) performed a phase 2 study in B-cell chronic lymphocytic leukemia (CLL) of oral theophylline, a methylxanthine that inhibits cyclic nucleotide phosphodiesterases, thereby inducing the intracellular accumulation of cyclic adenosine monophosphate (cAMP). In 25 patients with Rai stages 0-I, theophylline, 200 mg given orally every 12 h was well tolerated. There was one complete response after 22.5 months of treatment, which continues at 27+ months, and 18 other patients had stable disease. In vitro exposure of patients' lymphocytes to aminophylline (75-250 microg/ml), the soluble form of theophylline, resulted in dose- and time-dependent induction of apoptosis in 9/20 patients studied. Apoptosis was documented flow-cytometrically by monitoring the expression of bcl-2 and bax, forward light scatter, fluorescence intensity of binding of CD45 antibody, and the binding of annexin. Patients whose leukemic lymphocytes were susceptible to apoptosis induction by aminophylline in vitro experienced a significantly longer progression-free survival than patients whose cells were resistant to the drug in culture (P=0.025). This suggests that in a CLL population treated with theophylline, induction of an apoptotic response to the drug in vitro is prognostic for absence of clinical progression.

Pharmacogenetics and proteomics of anticancer drugs in non-Hodgkin's lymphoma

The variability of tumor responses to chemotherapeutic agents is a topic of major interest in current cancer research. Advances in the knowledge of dysregulation of key molecular pathways in cancer cells have enabled techniques to be developed that can profile tumor cells for their genetic background, allowing selection of anticancer agents on an individual basis. The next generation of anticancer treatments might therefore be tailored according to the molecular alterations identified in tumor cells of individual patients. However, before these alterations can be exploited from a therapeutic point of view, it is necessary to understand how such alterations influence the cellular pathways that control sensitivity to chemotherapeutic agents. Pharmacogenetics and pharmacoproteomics, novel disciplines that investigate the relationship between gene and protein expression in tumor cells and the response to anticancer agents, will be instrumental in developing optimal chemotherapeutic regimens for patients with non-Hodgkin's lymphoma.

Expression of Bcl-2-family proteins in peripheral blood B-lymphocytes in patients with cronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a neoplastic disease characterized by the accumulation of morphologically mature monoclonal CD 5+ B cells in the early phase (G0/G1) of the cell cycle. It is considered that the accumulation of neoplastically transformed lymphocytes B (CLL cells) is primarily the consequence of the disturbance, i.e., blockade of these cells' apoptosis process. Apoptosis is the specific process of programmed cell death regulated by numerous extracellular and intracellular mechanisms. The Bcl-2 proteins are well-known modulators of this process. Some of these proteins (such as Bcl-2, and Bcl-Xl) are anti-apoptotic, while others (such as Bad or Bax) are pro-apoptotic. Our study included the analysis of 20 peripheral blood specimens from 20 patients with CLL, and 20 peripheral blood specimens of healthy persons who represented the control group. Using Western blotting analysis, we quantitatively examined the protein expression of Bcl-2 family (Bcl-2, Bax, Bad, and Bcl-Xl). The level of Bcl-2 (p=3,68?10-10), Bax (p=0,019), and Bad (p=0,073) proteins expression was significantly increased in all the analyzed peripheral blood samples of patients, while the level of Bcl-Xl protein (p=0,75) did not significantly differ in peripheral blood samples of patients, compared to the controls. The results of this study showed that the increased level of expression of Bcl-2, Bax, and Bad protein represented the most striking feature of CLL cells. Moreover, the variations in the expression of only one protein of the Bcl-2 family could not represent the prognostic parameter in the treatment of this disease.

Hematopoietic stem cells and other hematopoietic cells show broad resistance to chemotherapeutic agents in vivo when overexpressing bcl-2

Objective. Chemotherapeutic agents function by inducing apoptosis and their effectiveness depends on the balance of pro- and anti-apoptotic proteins in cells. Due to the complicated interactions of the many proteins involved, it has been difficult to determine in tumors whether overexpression of single genes is prognostic for increased resistance. Therefore, we studied the influence of bcl-2 overexpression on resistance to chemotherapeutics in a transgenic mouse system. This allowed us to study a wide variety of cells, including important but rare populations such as hematopoietic stem cells (HSC).Methods. H2K-bcl-2 transgenic and wild-type (WT) mice were treated with several agents(5-fluoruracil, cyclophosphamide, and busulfan) to determine the contribution of increased amounts of bcl-2 to the response to these chemotherapeutics in vivo. Populations were enumerated using flow cytometry. HSC were studied by FACS purification and long-term reconstitution assays in vivo and resistance was confirmed by short-term proliferation assays with different amounts of chemotherapeutics in vitro.Results. bcl-2 overexpression alone protects many cell types, though protection levels differ between populations and agents. However, even sensitive populations return to pretreatment levels faster in transgenic mice. bcl-2 overexpression also prevents the dramatic changes in HSC following 5-FU treatment (downregulation of c-kit, upregulation of Lin, less efficient long-term reconstitution). In vitro studies directly demonstrate increased resistance of bcl-2 overexpressing HSC to chemotherapeutic agents.Conclusions. Increased expression of bcl-2 in HSC and their progeny endows these cells with broad resistance to chemotherapeutic agents. The ability to (differentially) regulate sensitivity to apoptosis of bystander and tumor cells is clinically important.

Stressful death of T-ALL tumor cells after treatment with the anti-tumor agent Tetrocarcin-A

The T-ALL cell lines CCRF-CEM and Jurkat were studied for their sensitivity toward apoptosis induced by tetrocarcin-A (TC-A), an antibacterial and antitumor agent isolated from the actinomycete Micromonospora. This substance promoted cell death via a mitochondrial signaling pathway, that is, by activation of Bid and Bax, loss of the mitochondrial transmembrane potential, release of cytochrome c, and activation of effector caspases, even under conditions of Bcl-2 overexpression. Furthermore, sensitivity to TC-A was not dependent on expression of wild-type caspase-8. In contrast, this apoptotic pathway was inhibited markedly by pretreatment of cells with cycloheximide, an inhibitor of de novo protein synthesis. cDNA microarray chip analysis revealed that TC-A induced a significant up-regulation of members of the heat shock protein family known to be involved in the endoplasmic reticulum (ER)-stress-induced apoptotic program. The activation of caspase-12, the central inducer caspase involved in ER-stress by TC-A treatment, is in concordance with this result. These results show that, in T-ALL cells, TC-A induces an apoptotic machinery via mitochondrial and ER signaling, which is not inhibited by aberrant expression/function of important regulators of death receptor- and drug-induced apoptosis.

Using flow cytometry to follow the apoptotic cascade

Flow cytometry has been extensively used to follow the apoptotic cascade and to enumerate apoptotic cells, both in cell cultures and, to a lesser extent, in tissue biopsies. An overview of the apoptotic cascade and how flow cytometric measurements can be used to observe the different elements of this process is presented.

Role of Bcl-2 family of proteins in malignancy

B cell lymphoma gene-2 (Bcl-2) is the prototypic member of a growing family of proteins that play evolutionarily conserved, key regulatory roles in apoptosis. The Bcl-2 family members are characterized by the presence of one or more Bcl-2 homology domains and are comprised of both the prosurvival and proapoptotic proteins. Bcl-2 itself is a prosurvival member of the family and its aberrant expression has been linked to a variety of different cancers, including several hematological malignancies. Although the exact mechanism of action of Bcl-2 family of proteins in regulating apoptosis is still a matter of some debate, these proteins appear to act upstream of caspase activation. Many recent studies have shown the therapeutic potential of targeting Bcl-2 family members for the treatment of cancer. This article summarizes what is currently known about Bcl-2-like proteins and how the evolving understanding of the biology of these proteins is paving way for the development of novel cancer therapeutics.

Pharmacogenetics of anticancer drugs in non-Hodgkin lymphomas

The variability of tumour responses to chemotherapeutic agents is a topic of major interest in current oncology research. Advances in the knowledge of molecular pathology of cancer make available strategies by which tumour cells can be profiled for their genetic background in order to select anticancer agents that might selectively kill cells in a molecular context that matches the mechanism of action of drugs. The next generation of anticancer treatments might thus be tailored on the basis of the numerous molecular alterations identified in tumour cells of a particular patient. However, to exploit these alterations, it is necessary to understand how they influence the cellular pathways that control the sensitivity or, conversely, resistance to chemotherapeutic agents. The aim of this article is to outline major genetic abnormalities in non-Hodgkin lymphomas that can be used to streamline anticancer drug selection and to underscore the major role of pharmacogenetics, which studies the interactions between genetic background and drug activity, to the prediction of likelihood of response and identification of potential new targets for pharmacological intervention.

Phosphodiesterase type 4 inhibitor suppresses expression of anti-apoptotic members of the Bcl-2 family in B-CLL cells and induces caspase-dependent apoptosis

B cell chronic lymphocytic leukemia (B-CLL) is an incurable clonal disease which shows initial responsiveness to a number of chemotherapeutic drugs. However, in most patients the disease becomes resistant to treatment. Rolipram, a specific inhibitor of phosphodiesterase (PDE) type 4, the PDE predominantly expressed in B-CLL cells, has been shown to induce cAMP-dependent apoptosis in these cells. In the present study, we demonstrate that the extent of rolipram-induced apoptosis is similar to fludarabine-induced apoptosis in vitro. The combination of rolipram and fludarabine results in an enhancement in the number of apoptotic cells compared to apoptosis induced by either agent alone. Second, rolipram suppresses the expression of anti-apoptotic members of the Bcl-2 family and induces the pro-apoptotic protein Bax, thereby shifting the balance between pro- and anti-apoptotic members of the Bcl-2 family towards a pro-apoptotic direction. Finally rolipram-induced apoptosis is caspase-dependent. PDE 4 inhibitors are currently under investigation for chronic obstructive pulmonary disease and asthma in phase III clinical trials showing promising results with tolerable side-effects. In conclusion, by inducing apoptosis, by enhancing apoptosis induced by fludarabine, by suppressing Bcl-2, Bcl-X and by inducing Bax expression, PDE 4 inhibitors may add a new therapeutic option for patients with B-CLL.