Chlorambucil resistance in B-cell chronic lymphocytic leukaemia is mediated through failed Bax induction and selection of high Bcl-2-expressing subclones

Chronic Lymphocytic Leukaemia in 2020: the Future Has Arrived

PURPOSE OF REVIEW

Chronic lymphocytic leukaemia is now recognised as a heterogenous disease with a variety of clinical outcomes. Here we summarise the way it is currently stratified according to genetic risk and patient characteristics and the treatment approaches used for these different subgroups.

RECENT FINDINGS

Certain patients appear to sustain MRD negativity after combination chemoimmunotherapy, leading to the suggestion that their CLL may be cured. However, 17p-deleted, p53-mutated or IGHV-UM subgroups are generally resistant to FCR, and much better responses are seen with ibrutinib and venetoclax, frequently inducing MRD negativity that hopefully will be translated into durable remissions. Small molecule inhibitors have already revolutionised CLL treatment. Going forward, we anticipate their use in the majority of patients, early after diagnosis and with curative intent.

ZGDHu-1 for cancer therapy

N,N'-di-(m-methylphenyl)-3,6-dimethyl-1,4-dihydro-1,2,4,5-tetrazine-1,4-dicarboamide (ZGDHu-1) is a novel tetrazine derivative that was initially designed and produced by Professor W.X. Hu, and which has been reported by our group to exhibit antitumor activity. Accumulating evidence suggests that the anticancer mechanisms of ZGDHu-1 may be involved indifferent biological activities, particularly in acute myeloid leukemia (AML) cells. At a high concentration, ZGDHu-1 has been demonstrated to inhibit the proliferation of the leukemia cells by arresting the cell cycle at the G₂/M phase, and by inducing cell apoptosis via inducing the accumulation of reactive oxygen species, the translocation of phosphatidylserine across the plasma membrane and the loss of mitochondrial membrane potential. Furthermore, at a low concentration, it was demonstrated to induce the differentiation and degrade the AML1-eight-twenty-one fusion protein in AML cells. Finally, results from a previous study indicate that ZGDHu-1 is a potential proteasome inhibitor. Overall, our preliminary research suggests that ZGDHu-1 may be a promising anticancer drug; however, further research is warranted to identify the exact drug target and potential clinical application in leukemia cells or solid tumors. In the present review, the application of ZGDHu-1 in cancer research, in addition to the specific underlying targets of ZGDHu-1, are discussed.

Apoptosis deregulation in CLL

The description of apoptosis and the identification of the genes that regulate it have proved pivotal to our understanding of how cancer cells accumulate and ultimately cause morbidity and mortality. It has become increasingly clear that in CLL the balance between the pro- and anti-apoptotic members of the BCL2 family of apoptotic regulatory proteins is critical in the development and clinical progression of CLL. Furthermore, the apoptotic potential of the CLL cell determines chemotherapy sensitivity and ultimately progression-free and overall survival. The unravelling of the BCL2 story in CLL has led to the development of a whole new class of therapeutic agents-the BH3 mimetics-which are significantly more targeted than conventional chemo-immunotherapy and therefore promise potent clinical activity coupled with reduced toxicity.

The role of Bcl-2 family proteins in chronic lymphocytic leukaemia

Bcl-2 family proteins have long been implicated in the pathology of chronic lymphocytic leukaemia (CLL). Indeed, a number of these proteins have been shown to have prognostic importance in this disease. The precise ways in which these proteins impact upon CLL and the ways in which they are regulated remain incompletely resolved. However, significant advances have been recently made in our understanding of how these proteins are controlled by genetic, epigenetic and microenvironmental cues. Furthermore, major progress has been made in trying to target these proteins therapeutically. Here we review the current knowledge about this family of apoptosis-regulating proteins and how they impact upon drug resistance and disease progression. We also summarise evolution in the development of Bcl-2 family inhibitors for the treatment of CLL and other cancers.

Sub-millimolar concentration of the novel phenol-based compound, 2-hydroxy benzoate zinc, induces apoptosis in human HT-1080 fibrosarcoma cells

OBJECTIVES

To examine the effect of a novel phenolic-based compound, 2-hydroxy benzoate zinc (2HBZ), and acetylsalicylic acid (ASA) on human HT-1080 fibrosarcoma cells.

MATERIALS AND METHODS

MTT assay was used to assess cell proliferation while different methods were used to detect apoptosis morphologically and immunohistochemically in Human HT-1080 fibrosarcoma cells. Apoptosis was determined by Annexine-V labelling, and caspase-3 activation. In addition, western blot was used to analyse p21, p53 and Bax and flow cytometry was to analyse the cell cycle.

RESULTS

2HBZ exhibited a more than 5-fold increase in cytotoxic potency when compared with ASA with mean LD50 values of 210 and 1100 lM respectively (P < 0.0001). The cytotoxic effects of 2HBZ were both time- and dosedependent with marked apoptosis being evident only after 24 h at concentrations as low as 200 mM. In contrast, ASA-induced apoptosis was observed only at concentrations in excess of 1000 mM at the same time point. Both 2HBZ and ASA induced caspase-3 activation in the cells, which confirmed that their cytotoxic effects were the result of apoptotic cell death. These findings were further confirmed by immunomorphological studies for the detection of apoptosis including haematoxylineosin, methyl green/pyronin Y staining and scanning electron microscopy. In addition, 2HBZ caused a marked increase in p21, p53 and Bax protein expressions and these effects were associated with an increase in G1 and G2 arrest of the cell cycle and a reduction in S-phase.

CONCLUSIONS

These results demonstrate that the novel phenolic compound 2HBZ is a potent apoptosis-inducing agent in HT-1080 cells and warrants further investigation as a potential chemotherapeutic agent in primary cancer cell models.

Expression of multidrug resistance-associated ABC transporters in B-CLL is independent of ZAP70 status

PURPOSE

To assess whether the poor prognosis of ZAP70-positive B-cell chronic lymphocytic leukemia (CLL) is associated with the overexpression of ABC transporter genes that are responsible for pleiotropic drug resistance.

MATERIALS AND METHODS

The transcript level of ten drug transporters was analyzed using semiquantitative and quantitative RT-PCR in control hematopoietic cells, in 41 CLL patient samples and in 5 lymphoma cell lines. ZAP70 status was determined by immunoblotting.

RESULTS

Of all analyzed transporters, MDR1, MDR2, MRP1, MRP4, MRP5, and MRP7 were expressed at a significantly higher level in B lymphocytes when compared with other hematopoietic cells in peripheral blood. A subgroup of 41 CLL patient samples showed similar or higher expression of these genes than control B cells, and CLL cells exhibited high expression when compared with multiple lymphoma cell lines. No significant correlation between ZAP70 expression and ABC transporter expression was observed.

CONCLUSION

The ZAP70 status is independent of the multidrug resistance phenotype in CLL.

Mcl-1 expression has in vitro and in vivo significance in chronic lymphocytic leukemia and is associated with other poor prognostic markers

Bcl-2 family proteins play a critical role in the regulation of apoptosis in chronic lymphocytic leukemia (CLL). However, their association with established prognostic markers is unknown. In this study, we analyzed the expression of Bcl-2, Bax, and Mcl-1 in 185 CLL patients and evaluated their relationship with other prognostic markers, in vitro sensitivity to fludarabine, and clinical outcome. Mcl-1 expression was significantly correlated with stage of disease (P < .001), lymphocyte doubling time (P = .01), V(H) gene mutation status (P < .001), CD38 expression (P < .001), and ZAP-70 expression (P = .003). In addition, Mcl-1 and Mcl-1/Bax ratios showed strong correlations with in vitro resistance to fludarabine (P = .005 and P < .001, respectively). Furthermore, elevated Mcl-1 expression and Mcl-1/Bax ratios were predictive of time to first treatment in the whole cohort (P < .001 and P < .001, respectively) and in stage A patients only (P = .002 and P = .001, respectively). Taken together, our data show that Mcl-1 is a key controller of in vitro drug resistance and is an important regulator of disease progression and outcome in CLL. It therefore represents a promising therapeutic target in this incurable condition. The close correlation between Mcl-1 expression and V(H) gene mutation status, CD38 expression, and ZAP-70 expression offers a biologic explanation for their association with adverse prognosis.

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.

Fludarabine induces apoptosis in chronic lymphocytic leukemia--the role of P53, Bcl-2, Bax, Mcl-1, and Bag-1 proteins

The expression of P53, Bcl-2, Bax, Bag-1, and Mcl-1 proteins in CD5/CD20-positive B-chronic lymphocytic leukemia (B-CLL) cells from 30 typical CLL patients was evaluated before and after 48 h of incubation with 10(-6) M fludarabine using multiparametric flow cytometric analysis. Protein expression was correlated with annexin V expression, Rai modified clinical staging, lymphocyte doubling time, and previous treatment. Our main goal was to determine the predictive value of these proteins in CLL cells in terms of disease evolution. Bcl-2 expression decreased from a median fluorescence index (MFI) of 331.71 +/- 42.2 to 245.81 +/- 52.2 (P < 0.001) after fludarabine treatment, but there was no difference between viable cells (331.57 +/- 44.6 MFI) and apoptotic cells (331.71 +/- 42.2 MFI) before incubation (P = 0.859). Bax expression was higher in viable cells (156.24 +/- 32.2 MFI) than in apoptotic cells (133.56 +/- 35.7 MFI) before incubation, probably reflecting defective apoptosis in CLL (P = 0.001). Mcl-1 expression was increased in fludarabine-resistant cells and seemed to be a remarkable protein for the inhibition of the apoptotic process in CLL (from 233.59 +/- 29.8 to 252.04 +/- 35.5; P = 0.033). After fludarabine treatment, Bag-1 expression was increased in fludarabine-resistant cells (from 425.55 +/- 39.3 to 447.49 +/- 34.5 MFI, P = 0.012), and interestingly, this higher expression occurred in patients who had a short lymphocyte doubling time (P = 0.022). Therefore, we could assume that Bag-1 expression in such situation might identify CLL patients who will need treatment earlier.

[Bcl-2 and Bax protein interaction in B-lymphocytes of peripheral blood in patients with chronic lymphocytic leukemia]

BACKGROUND

Chronic lymphocytic leukemia (CLL) is a neoplastic disease characterized by the accumulation of morphologically mature monoclonal CD5+ B cells in the early phase (G0/G1) of the cell cycle. The accumulation of neoplastically transformed B-lymphocytes (CLL cells) is primarily the consequence of apoptosis blocking in these cells. Bcl-2 proteins are well-known modulators of this process. Some of these proteins are anti-apoptotic while the others are pro-apoptotic. All contain at least one of the four conserved regions called the Bcl-2 homologous domains (BH1-BH4). Evidence indicates that Bcl-2 and Bax form homo- and heterodimers. The anti-apoptotic effect of Bcl-2 protein is based on its ability to bind Bax protein in the heterodimer form, and thus to block the forming of Bax/Bax proapoptotic homodimers. The ratio of Bcl-2/Bax represents the cell autonomous rheostat which determinates the type of the cell reaction to an apoptotic stimulus.

METHODS

The aim of this study was to determine the level of interaction between these two proteins in CLL cells using the co-immunoprecipition method. The study included the analysis of 20 peripheral blood specimens from 20 patients with CLL, and 20 peripheral blood specimens from healthy persons, who were in the control group. Specimens were precipitated with the monoclonal antibody for Bcl-2 protein, and immunoblotted with the palyclonal antibady for Bax protein (IP: Bcl-2/WB:Bax). At the same time, specimens were precipitated with the polyclonal antibody for Bax protein, and immunoblotted with the monoclonal antibody for Bcl-2 protein (IP: Bax/WB:Bcl-2). The intensity of Bcl-2 and Bax protein's binding compared to the control samples of the peripheral blood from healthy persons, was increased in CLL cells.

RESULTS

IP: Bax/WB: Bcl-2 showed a high level of "free" Bcl-2 protein which was not bound in the heterodimer form to Bax protein. Simultaneously IP: Bcl-2/WB: Bax showed that a higher quantity of Bax protein was bound in the heterodimer form to Bcl-2 protein as opposed to the quantity of pro-apoptotic Bax protein potentialy bound in the homodimer form.

CONCLUSION

Further studies involving larger groups of patients are necessary to explore the potential significance of the Bcl-2/Bax protein ratio as a prognositc parameter in the CLL treatment.

Autocrine/paracrine involvement of insulin-like growth factor-I and its receptor in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is characterized by the accumulation of long-lived B lymphocytes blocked in G(0/1) by impaired apoptosis. As insulin-like growth factor-I (IGF-I) is known for its antiapoptotic effects in different cell types, we investigated whether IGF-I and its receptor (IGF-IR) participate in autocrine/paracrine loops affecting the survival of CLL cells. IGF-IR protein and mRNA was present in CLL cells in 44% and 59% of patients respectively. IGF-IR expression in CLL patients was positively correlated with the expression of the antiapoptotic protein Bcl-2 and was involved in CLL cell survival in vitro. Serum IGF-I was elevated in CLL patients, but growth hormone (GH) was normal. CLL cells expressed IGF-I mRNA and secreted the growth factor in vitro. Therefore, local production of IGF-I can account for the increased levels of serum IGF-I, independently of GH, and may be related to autocrine/paracrine control of lymphocyte survival acting at IGF-IR. This is the first demonstration of IGF-IR expression in a subgroup of CLL patients and of its antiapoptotic effects in vitro, highlighting the importance of this growth factor receptor as a possible therapeutic target in CLL.

Common Polymorphism G(-248)A in the Promoter Region of the bax Gene Results in Significantly Shorter Survival in Patients With Chronic Lymphocytic Leukemia Once Treatment Is Initiated

Purpose

Chronic lymphocytic leukemia (CLL) is characterized by the development of drug resistance. The underlying biologic and genetic reasons for this resistance are complex, but the bcl-2 gene family seems to play a critical role. This retrospective study assessed the clinical impact of a common single nucleotide polymorphism of the pro-apoptotic bax gene in patients with chronic lymphocytic leukemia.

Patients and Methods

The frequency of the novel polymorphism, G(−248)A, in the promoter region of the bax gene and bax protein expression was assessed in 203 CLL patients. The results were correlated with clinical outcome.

Results

The polymorphism was found in 23% of the CLL cohort and 15% of normal controls with no significant difference in allele frequency between the two groups (P = .15). It was associated with lower Bax protein expression and a shorter overall survival, especially in the treated patient group (P = .03). Furthermore, the adverse impact of the polymorphism was accentuated when comparing survival from the date of first treatment rather than diagnosis (P = .012). No significant difference in age at diagnosis, stage of disease at presentation, lymphocyte doubling time, time to first treatment, or progression-free survival were observed.

Conclusion

The presence of this single nucleotide polymorphism in CLL critically influences the response to treatment and overall survival. Given the relatively high prevalence of this polymorphism in the normal population, further prospective studies in CLL and other human malignancies are indicated.

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.

G125A single-nucleotide polymorphism in the human BAX promoter affects gene expression

Earlier we had reported a guanine to adenosine substitution at position 125 (G125A) in the BAX promoter, and its association with higher stage of the disease and failure to achieve complete response to treatment in chronic lymphocytic leukemia (CLL) patients. The aim of this study was to test the hypothesis that G125A leads to a reduction in the transcription of the BAX gene and that this is a direct cause of altered BAX mRNA and protein expression. In lymphocytes of CLL patients, BAX mRNA expression was determined by RNase protection assay and Bax protein was detected by immunoblotting. The presence of G125A in the BAX promoter was associated with lower BAX mRNA (P=0.004) and protein (P=0.024) levels. In transient expression assays using wild-type and mutant BAX promoter sequences linked to Luciferase as a reporter, the G125A polymorphism reduced expression of the BAX promoter by 2.6-fold. These studies suggest a mechanism for the biological effect of the G125A.

Bryostatin induces protein kinase C modulation, Mcl-1 up-regulation and phosphorylation of Bcl-2 resulting in cellular differentiation and resistance to drug-induced apoptosis in B-cell chronic lymphocytic leukemia cells

Bryostatin, a macrocyclic lactone and protein kinase C (PKC) modulator, has been shown to have differentiation and anti-tumor activity against several leukemia cell lines in vitro. In this study, we demonstrated Bryostatin-induced differentiation in B-cell chronic lymphocytic leukemia (B-CLL) cells, characterized by an increase in cell size and a marked up-regulation of CD11c expression. The specific inhibitors of the extracellular signal-regulated kinase (ERK) and protein kinase C pathways, PD98059 and GF 109203X respectively, each completely blocked Bryostatin-induced differentiation of B-CLL cells, suggesting that activation of the ERK pathway plays a direct role in this process in a PKC-dependent manner. Furthermore, Bryostatin reduced both spontaneous and drug-induced apoptosis with chlorambucil, fludarabine and 2-chloro-2'-deoxyadenosine (2-Cda) in B-CLL cells. This resistance was associated with an early up-regulation of the anti-apoptotic protein Mcl-1 and post-translational phosphorylation of Bcl-2 at serine 70. The anti-apoptotic effects of Bryostatin were abrogated by GF 109203X, and to a lesser extent by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, LY294002. Interestingly, the ERK inhibitor, PD98059 inhibited Mcl-1 expression but had little effect on Bryostatin-induced survival suggesting that the ERK pathway predominantly affects differentiation. Taken together these results present an explanation for Bryostatin-induced B-CLL cell survival in which modulation of the PKC pathway couples differentiation with an increase in antiapoptotic protein expression and calls into question the rationale for its use in the treatment of B-CLL.

The novel sequence-specific DNA cross-linking agent SJG-136 (NSC 694501) has potent and selective in vitro cytotoxicity in human B-cell chronic lymphocytic leukemia cells with evidence of a p53-independent mechanism of cell kill

SJG-136 (NSC 694501) is a novel DNA cross-linking agent that binds in a sequence-selective manner in the minor groove of the DNA helix. It is structurally novel compared with other clinically used DNA cross-linking agents and has exhibited a unique multilog differential pattern of activity in the NCI 60-cell line screen (i.e., is COMPARE negative to other cross-linking agents). Given this profile, we undertook a preclinical evaluation of SJG-136 in primary tumor cells derived from 34 B-cell chronic lymphocytic leukemia (B-CLL) patients. SJG-136 induced apoptosis in all of the B-CLL samples tested with a mean LD50 value (the concentration of drug required to kill 50% of the cells) of 9.06 nmol/L. Its cytotoxicity was undiminished in B-CLL cells derived from patients treated previously, those with unmutated VH genes, and those with p53 mutations (P=0.17; P=0.63; P=0.42, respectively). SJG-136-induced apoptosis was associated with the activation of caspase-3 that could be partially abrogated by the caspase-9 inhibitor Z-LEHD-FMK. Furthermore, SJG-136 did not trigger the phosphorylation of p53 or the up-regulation of GADD45 expression in B-CLL cells whereas the cross-linking agent chlorambucil elicited both of these effects. This suggests that SJG-136 cross-linking adducts are not subject to p53-mediated DNA excision repair mechanisms in B-CLL cells. Taken together, these data demonstrate a novel mechanism of action for SJG-136 that appears to circumvent the effects of poor prognostic markers. This unique cytotoxicity profile warrants further investigation and supports the evaluation of this agent in Phase I clinical trials for patients with B-CLL.

The role of Bcl-2 family members in tumorigenesis

The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor 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.

The P2X7 receptor gene polymorphism 1513 A→C has no effect on clinical prognostic markers, in vitro sensitivity to fludarabine, Bcl-2 family protein expression or survival in B-cell chronic lymphocytic leukaemia

A cohort of 121 patients with B-cell chronic lymphocytic leukaemia (B-CLL) was investigated for a single nucleotide polymorphism in the P2X7 receptor gene (1513 A-->C), and the findings were correlated with clinical prognostic markers, in vitro sensitivity to fludarabine, expression of Bcl-2 family proteins and overall survival. The frequency of the polymorphism in B-CLL samples was not significantly different from that found in normal healthy controls (P = 0.27; Fisher's exact test). Furthermore, when the B-CLL patients were analysed according to P2X7 genotype (1513 A/A versus 1513 A/C), there was no significant difference in age at diagnosis, stage at diagnosis, lymphocyte doubling time, time to first treatment, progression-free survival and overall survival, and neither was there any evidence of bias in terms of VH gene mutational status, CD38 expression, in vitro sensitivity to fludarabine or expression of Bcl-2, Bax or Mcl-1 between the two groups. These results indicate that the 1513 A-->C polymorphism of the P2X7 gene is unlikely to play a significant role in the pathogenesis or disease progression of B-CLL.

Conformational change and mitochondrial translocation of Bax accompany proteasome inhibitor-induced apoptosis of chronic lymphocytic leukemic cells

Chemotherapy resistance remains a major clinical problem in patients with B-cell chronic lymphocytic leukemia (B-CLL). Proteasome inhibitors are able to induce apoptosis in chemotherapy-resistant B-CLL cells in vitro. Exposure of B-CLL cells to the proteasome inhibitors, MG132 and lactacystin, resulted in inhibition of proteasomal activity within 30 min of treatment and was accompanied by an increase in the level of ubiquitinated proteins. Proteasome inhibitors did not alter the levels of expression of the proapoptotic Bcl-2 family proteins, Bax and Bid, prior to the onset of apoptosis. Instead, proteasome inhibitors induced a caspase-independent conformational change in Bax (as shown by a conformation-specific Bax antibody) and its translocation to mitochondria, resulting in mitochondrial perturbation, as evidenced by loss of the mitochondrial membrane potential and cytochrome c release. Similar conformational change and subcellular localization of Bax were observed during apoptosis induced with fludarabine, chlorambucil and prednisolone. These data suggest that alteration of Bax conformation and its redistribution to mitochondria are common and early features of B-CLL apoptosis in response to proteasome inhibitors and other chemotherapeutic agents.

The vitamin D3 analog EB1089 induces apoptosis via a p53-independent mechanism involving p38 MAP kinase activation and suppression of ERK activity in B-cell chronic lymphocytic leukemia cells in vitro

EB1089, a novel vitamin D3 analog, has been shown to have cytotoxic and antiproliferative properties in a variety of malignant cells. However, its potential as a treatment for B-cell chronic lymphocytic leukemia (B-CLL) has not been evaluated. EB1089 induced apoptosis in all of the 102 B-CLL samples tested with a mean LD(50) (the concentration of EB1089 required to kill 50% of cells) value (+/- SD) of 2.1 x 10(-8) M (+/- 1.4 x 10(-8) M). Furthermore, no significant difference was found in the cytotoxicity of EB1089 in B-CLL samples from previously treated and untreated patients (P =.1637). Induction of apoptosis was associated with a reduction in Bcl-2 and Mcl-1 protein expression, but this was evident only in the apoptotic cells. In contrast, the expression of Bax, p21, and p53 was not altered in the viable or apoptotic cells from either B- or T-lymphocyte lineages. EB1089-induced apoptosis was preceded by activation of p38 mitogen-activated protein (MAP) kinase and suppression of extracellular signal-regulated kinase (ERK) activity, and this was associated with downstream activation of caspase-3. The pancaspase inhibitor (Z-VAD-FMK) and the caspase-9 inhibitor (Z-LEHD-FMK) were able to partially abrogate the apoptotic effects of EB1089 but did not affect the phosphorylation of p38 MAP kinase or the suppression of ERK. The B-CLL cells in the study were shown to highly express vitamin D receptor, but an additional receptor-independent mechanism of cell killing cannot be ruled out at this stage. These findings show that EB1089 is a potent apoptosis-inducing agent in B-CLL cells and may be useful in the treatment of B-CLL patients, particularly those with p53 mutations or drug-resistant disease.

Prodigiosin induces apoptosis of B and T cells from B-cell chronic lymphocytic leukemia

We have previously reported that prodigiosin (2-methyl-3-pentyl-6-methoxyprodigiosene) induces apoptosis in human hematopoietic cancer cell lines with no marked toxicity in nonmalignant cell lines. In this study, we demonstrate that prodigiosin induces apoptosis of B-cell chronic lymphocytic leukemia (B-CLL) cells (n=32 patients). The dose-response for the cytotoxic effect of prodigiosin was analyzed in cells from 12 patients showing an IC(50) of 116+/-25 nM. Prodigiosin induced apoptosis of B-CLL cells through caspase activation. We also analyzed the cytotoxic effect of prodigiosin in T cells from B-CLL samples and no differences were observed with respect to leukemia cells. This is the first report showing that prodigiosin induces apoptosis in human primary cancer cells.

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.

Retinoid-induced apoptosis in B-cell chronic lymphocytic leukaemia cells is mediated through caspase-3 activation and is independent of p53, the retinoic acid receptor, and differentiation

The aim of this study was to investigate the effects of all-trans retinoic acid (ATRA) on apoptosis induction, Bcl-2 family protein expression, and differentiation in B-cell chronic lymphocytic leukaemia (B-CLL) cells. ATRA induced apoptosis in all the B-CLL samples tested, and this was accompanied by a specific reduction in Bcl-2 and Mcl-1 protein expression in the apoptotic cells. In contrast, Bax, p21, and p53 expression was not altered in either the viable or apoptotic B-CLL cells, inferring that ATRA utilises a p53-independent cell death pathway. Caspase-3 activation was shown to be a prerequisite for ATRA-induced apoptosis, which was inhibited by the pan-caspase inhibitor Z-VAD-FMK and the caspase-9 inhibitor Z-LEHD-FMK. In addition, the retinoic acid receptor (RAR) antagonist AGN194310 failed to abrogate the apoptotic effects of ATRA, indicating that RAR binding was not necessary for ATRA-induced apoptosis. Furthermore, there was no evidence of ATRA-induced differentiation of the B-CLL cells in this study either in terms of altered morphology or immunophenotype. In summary these data indicate that ATRA induces apoptosis via the intrinsic apoptotic pathway, and this is independent of RAR binding, p53 activation, and cellular differentiation in B-CLL cells.

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.

Bax expression correlates with cellular drug sensitivity to doxorubicin, cyclophosphamide and chlorambucil but not fludarabine, cladribine or corticosteroids in B cell chronic lymphocytic leukemia

In B-CLL, non-proliferating B cells accumulate due to defective apoptosis. Cytotoxic therapies trigger apoptosis and deregulation of apoptotic pathways contributes to chemoresistance. Loss of the apoptosis-promoting Bax has been implicated in resistance to cytotoxic therapy. We therefore evaluated ex vivo drug sensitivity of CLL, producing chemoresponse data which are prognostic indicators for B-CLL, in particular in the case of purine nucleoside analogs. To analyze the underlying mechanisms of drug resistance, we compared endogenous Bax and Bcl-2 expression to ex vivo response to eight drugs, and to survival in 39 B-CLL patients. We found that reduced Bax levels correlated well with ex vivo resistance to traditional B-CLL therapies - anthracyclines, alkylating agents and vincristine (all P < 0.04). Surprisingly, no such relationship was observed for the purine nucleoside analogs or corticosteroids (all P > 0.5). Mutational analysis of p53 could not explain the loss of Bax protein expression. Levels of Bcl-2 were not associated with sensitivity to any drug. In contrast to the ex vivo data, neither Bax or Bcl-2 expression nor doxorubicin sensitivity were associated with increased survival whereas sensitivity to fludarabine correlated with better overall survival (P = 0.031). These findings suggest that the resistance to purine nucleoside analogs and corticosteroids in B-CLL is due to inactivation of pathways different from those activated by anthracyclines, vinca alkaloids and alkylating agents and may be the molecular rationale for the efficacy of purine analogs in this disease.

In vivo monitoring of therapy-induced apoptotic process in patients with chronic lymphocytic leukemia and acute non-lymphoblastic leukemia

BACKGROUND: The level of spontaneous apoptosis, the maximal response by apoptosis and the time when maximal apoptotic response is established are significant prognostic parameters that correlate with the therapeutic response of patients with malignant diseases. METHODS: Our study included 12 patients with B-CLL (I group of 7 patients) and ANLL (II group of 5 patients). Detection of apoptotic parameters on semifine section of peripheral blood was performed. Bcl 2 and mutated p53 expression were analyzed using the monoclonal antibodies by APAAP techniques. RESULTS: In our work, the established levels of spontaneous and therapy induced apoptosis correlate with clinical response of patients. All patients were bcl 2 strongly positive. Expression of p53 protein was not detected in these patients. The ultra structural analysis of the malignant cells has shown that a great number of cells react to antineoplastic agents? effect either by activating the cell response to stress or by apoptosis. CONCLUSION: The results of our pilot study have shown that the established levels of spontaneous and therapy induced apoptosis are in correlation with the clinical response of the patients to the applied therapy and that the measurable apoptotic parameters can represent prognostic parameters in treatment of hematologic neoplasms.

Spontaneous apoptosis in chronic lymphocytic leukemia and its relationship to clinical and cell kinetic parameters

Chronic lymphocytic leukemia (CLL) presents considerable variability in clinical presentation as well as in its evolution. In contrast to the inhibition of apoptosis in vivo, spontaneous apoptosis after short-term culture occurs. We studied the degree of this apoptosis in vitro, and its interactions with several clinical and laboratory parameters. Apoptosis was measured by the annexin V technique. Proliferation rate was evaluated by the AgNOR (nucleolar organizer regions) technique. There were inverse correlations between the percentage of annexin V-positive cells and peripheral lymphocyte count (r = - 0.49), Rai stage (r = - 0.40), Binet stage (r = - 0.50), TTM (total tumor mass score; r = - 0.51), and percentage of cells with one AgNOR cluster (r = - 0.45). Direct correlations were found with hemoglobin values ( r = 0.34) and platelet counts (r = 0.52). The number of CD8-positive cells showed a correlation with peripheral lymphocyte count (r = 0.49). When this variable was held constant, a correlation was detected between CD8-positive cells and staging (r = -0.47), TTM (r = - 0.42), and platelet count (r = 0.67). CD4-positive lymphocytes presented a correlation only with CD8-positive lymphocytes. In a cluster analysis, it was possible to create three groups of patients with different apoptosis rates using the TTM and AgNOR values. We conclude that, with the progression of the disease, together with the increase of tumor mass and proliferation rate, there is a decrease in the susceptibility to apoptosis.

Upstream mediators of the Fas apoptotic transduction pathway are defective in B-chronic lymphocytic leukemia

Data concerning the presence and the functionality of Fas receptor in malignant B-cells are controversial. We have analyzed Fas molecules on B-cells from patients with B-chronic lymphocytic leukemia (B-CLL) cells. We observed a large variability, both of percentage of Fas-positive cells and of intensity of Fas level. Fas triggering was inefficient in inducing apoptosis whatever the number of Fas-positive B-cells, the amount of Fas receptors. B-cells were also resistant to etoposide treatment, but able to undergo apoptosis after dexamethasone treatment. We suggest that the Fas apoptotic pathway is altered in B-CLL patients at the initial step(s) of apoptotic machinery.

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

Flavopiridol, a synthetic flavone, is currently under clinical investigation for the treatment of B-cell chronic lymphocytic leukaemia (B-CLL). In this study, we examined the in vitro effects of flavopiridol and fludarabine on B-CLL cells from 64 patients (36 treated and 28 untreated) in terms of apoptosis induction and Bcl-2 family expression. Both flavopiridol and fludarabine induced apoptosis in all the samples tested with mean LD(50) values (+/- SD) of 59.7 nmol/l (+/- 36.5) and 6.2 micromol/l (+/- 7.5) respectively. Mean flavopiridol LD(50) values were not significantly different between the treated and untreated patient groups (P = 0.35), whereas the fludarabine LD(50) values were significantly higher in the previously treated patient group (P = 0.01). Bcl-2 and Mcl-1 expression were downregulated in both flavopiridol and fludarabine-induced apoptotic cells, but the increase in Bax expression that accompanied fludarabine-induced apoptosis was not evident in flavopiridol-treated cells. In addition, Bcl-2:Bax ratios were not predictive of flavopiridol cytotoxicity (P = 0.82), whereas they were highly predictive of in vitro responsiveness to fludarabine (P = 0.001). Overall, these findings suggest that flavopiridol exerts its cytotoxic effect through a novel cell-death pathway that is not subject to the Bcl-2 family mediated resistance mechanisms that reduce the efficacy of many conventional chemotherapeutic drugs.

Bcl-2 antisense oligonucleotides enhance the cytotoxicity of chlorambucil in B-cell chronic lymphocytic leukaemia cells

We have previously shown that the Bcl-2 antisense oligonucleotide ODN 2009 can induce apoptosis in B-cell chronic lymphocytic leukaemia (B-CLL) cells. In this study we evaluated whether ODN 2009 could increase the sensitivity of B-CLL cells to Chlorambucil-induced cell death in vitro in order to establish whether the notion of antisense-mediated chemosensitisation could be applied to B-CLL. Bcl-2 antisense in combination with Chlorambucil resulted in a more marked reduction in Bcl-2 protein expression (p = 0.003), enhanced Bax expression (p < 0.0001) and increased apoptosis when compared to cells incubated with Chlorambucil alone (p = 0.03). This increased in vitro cytotoxicity demonstrates a proof of the concept that a combination of Bcl-2 antisense oligonucleotides with conventional chemotherapeutic drugs may elicit an enhanced therapeutic effect in B-CLL and should therefore be considered for further investigation in the form of a clinical trial.

Molecular abnormalities in B-cell chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia is the commonest adult leukaemia, however the pathogenesis is largely unknown. Since the 1980s specific chromosomal abnormalities have been identified, of which the commonest are deletions of chromosomes 6q, 11q23, 13q14 and 17q13 and trisomy 12. The search for the responsible oncogenes at these sites has proved to be extremely frustrating. There are many oncogenes at 11q23 but the exact gene(s) responsible have yet to be identified. Germline abnormalities of the ATM gene occur in about 18% of patients compared to a normal population carriage of 0.5% but not all studies agree that ATM is the gene responsible. Unfortunately, despite the identification of various minimally deleted regions and the full sequencing of 13q14 no oncogenes have been identified. All original studies suggested the presence of a autosomally recessive tumour suppressor gene at this site but more recent studies suggest this may not be the case and the pathogenesis is more complex than first thought. Similarly, no genes have been identified at 6q or on chromosome 12. We know that the p53 tumour suppressor gene at 17p13 is an important prognostic indicator but it occurs in a minority of patients (about 15%), usually in patients with advanced disease, and therefore probably is not of aetiological importance.

Doxorubicin and a butyric acid derivative effectively reduce levels of BCL-2 protein in the cells of chronic lymphocytic leukemia patient

B-chronic lymphocytic leukemia (B-CLL) is a disease caused primarily by defects in the apoptosis mechanism. AN-9, a butyric acid (BA) derivative, is a potent differentiating and an anti-cancer drug that induces apoptosis in HL-60 cells. Herein we show the affect of AN-9, alone and in combination with doxorubicin, on cell cultures from B-CLL patients. Cells from 17 patients were cultured and tested for viability, apoptosis, bcl-2 and bax protein expression. Exposure of B-CLL cell cultures to AN-9 was accompanied by apoptosis and a marked viability loss (up to 46%, p=0.0017). AN-9 reduced up to 51% (p=0.0017) the levels of bcl-2 in 57% of the cultures that express bcl-2. The combination of low concentrations of AN-9 and doxorubicin more than additively enhanced apoptosis and reduced bcl-2 levels in B-CLL cultures which were resistant to AN-9. AN-9 enhanced bax expression up to 58%(p=0.008) in cultures from 53% of the patients, but had no effect on bax levels when combined with doxorubicin. In conclusion, AN-9 alone reduced bcl-2 and enhanced bax expression in cultures from B-CLL patients, and the reduction of bcl-2 levels in combination with doxorubicin was greater than additive. These results may be beneficial in possible future combination therapy with AN-9 in B-CLL.

Interleukin 4 content in chronic lymphocytic leukaemia (CLL) B cells and blood CD8+ T cells from B-CLL patients: impact on clonal B-cell apoptosis

B-chronic lymphocytic leukaemia (CLL) clonal B cells are characterized by resistance to apoptosis. We evaluated clonal B cells and blood T cells for interleukin 4 (IL-4) content as IL-4 is able to increase CLL cell resistance to apoptosis. The content of IL-4 in CD8+ T cells of CLL patients (n = 9) ranged from 37% to 63% of the total CD8+ T cells (mean level of 49% +/- 3.4) compared with a range of 5-10% for control CD8+ T cells. Clonal B cells positive for cytoplasmic IL-4 ranged from 1% to 97% (mean value 57.8 +/- 6.9%). CD8+ T cells and clonal B cells secreted detectable levels of IL-4, but only clonal CLL B cells (n = 4) secreted IL-4 in association with increasing cell numbers. Fludarabine (F-ara-AMP, 0.1-100 micromol/ml) was able to downregulate the IL-4 content of CD8+ T cells, but not clonal B-cell IL-4. Culture supernatant from CLL CD8+ T cells decreased the spontaneous apoptotic rate of clonal B cells that was reversed with anti-IL-4 and soluble IL-4 receptor. These findings show that IL-4 is present in the microenvironment of B-CLL. In addition, use of agents that can interfere with IL-4 presentation to clonal B cells can be effective in increasing clonal B-cell apoptosis.

Bcl-2 and bax expression and chlorambucil-induced apoptosis in the T-cells and leukaemic B-cells of untreated B-cell chronic lymphocytic leukaemia patients

Chlorambucil and other cytotoxic drugs kill cells, non-selectively, by inducing apoptosis. In this study, we measured the apoptotic response to chlorambucil in T- and B-cells from untreated B-CLL patients and T-cells, from normal control subjects. We found increased chemosensitivity in the T-cells of B-CLL patients compared to the controls (P=0.0002). The chlorambucil ID(50) values for T-cells from B-CLL patients showed a direct correlation with Bcl-2 expression (P=0.002) and an inverse correlation with CD3 cell count (P<0.0001), suggesting a trend of increasing chemosensitivity and decreasing Bcl-2 expression with an elevated T-cell count. There was no differential expression of Bcl-2 or Bax between the CD4(+) and CD8(+) cells of B-CLL patients, isolated by immunomagnetic separation. We found correlations in the leukaemic B-cells between chlorambucil ID(50) values and both Bcl-2 expression (P=0.006), and Bcl-2/Bax ratios (P=0.002), suggesting a role for the Bcl-2/Bax ratio in predicting the response of untreated CLL patients to cytotoxic treatment. Chlorambucil produced almost identical changes in Bcl-2 and Bax expression in normal T-cells and leukaemic B-cells triggered to die by apoptosis, which together with the correlation between Bcl-2 and chemosensitivity confirms a pivotal role for Bcl-2 in regulating a distal step in the apoptotic pathway following cytotoxic cellular damage.

The apoptotic pathway: a target for therapy in chronic lymphocytic leukemia

Cell division and apoptosis (programmed cell death) are the two major physiological processes which control the size of cell populations. Chronic lymphocytic leukaemia arises as a result of the clonal expansion of, usually B-, lymphocytes in which a dysregulation of apoptosis leads to prolonged cell survival. The same process becomes exaggerated with increasing drug resistance, the usual cause of treatment failure in this condition. The identification of points in the apoptotic pathway at which dysregulation occurs is beginning to open up new therapeutic opportunities where the conventional cytotoxic chemotherapy approach is found to fail. Although these strategies are still in their infancy they may increase understanding of the pathogenesis of the disorder and overcome the problem of drug resistance.

Chronic lymphocytic leukemia

Chronic lymphocytic leukemia continues to attract much basic and clinical research interest. Despite recent advances, the disease still has no established cure. Nonetheless, significant strides have been made in our understanding of the genetics, biology, and clinical staging of this disease. This understanding may improve our ability to segregate patients into subtypes that differ in their cytogenesis, propensity toward disease progression, or response to standard or innovative forms of therapy. Finally, several promising new modalities of treatment are being evaluated in clinical trials, involving novel drugs or drug-combinations, monoclonal antibodies, stem cell transplantation, or gene therapy.

Cell-surface exposure of phosphatidylserine correlates with the stage of fludarabine-induced apoptosis in chronic lymphocytic leukemia and expression of apoptosis-regulating genes

BACKGROUND

Programmed cell death (PCD) is characterized by a sequence of tightly regulated events that result in the activation of caspases and in internucleosomal DNA cleavage. Late apoptotic events such as DNA-strand breaks can be assayed by in situ end labeling (ISEL) and DNA measurement (sub G1) using flow cytometry. Phosphatidylserine (PS) redistribution from the inner plasma membrane leaflet to the outer leaflet, an early event in PCD, can be detected by annexin V (AxV) binding to PS. AxV-fluorescein isothiocyanate (FITC) fluorescence intensity is variable and characterizes different cell populations, denoted here as AxV-negative (AxV(neg)), AxV-low-positive (AxV(lo)), and AxV-high-positive (AxV(hi)).

METHODS

We investigate the correlation of three methods (ISEL, sub G1 DNA content, and AxV assay) for detecting apoptosis with focus on differences between populations with different levels of PS. We also examined the expression of PCD-regulating Bcl-2 family members in these cell populations by reverse transcription-polymerase chain reaction (RT-PCR). Chronic lymphocytic leukemia (CLL) cells exposed to fludarabine (FAMP) were used as an in vitro model. Cells with different PS/AxV levels were separated using fluorescence-activated cell sorting (FACS).

RESULTS

Only purified AxV(hi) cells had high positivity in the ISEL and sub G1 assays (94 +/- 0.6%, 88.6 +/- 6.6%, and 98.6 +/- 0.6%, respectively), indicating that late apoptotic cells are detected equally by all three methods. In the AxV(lo) population, ISEL was positive in 21% +/- 13% and DNA sub G1 in 20% +/- 6.6% of cells, suggesting that AxV identifies early apoptotic cells better than the other assays. Anti-apoptotic Bcl-2 and Bcl-X(L) were upregulated by FAMP when cells entered apoptosis (AxV(lo)), as was pro-apo- ptotic Bcl-X(S), which was undetectable in nonapoptotic AxV(neg) cells. Pro-apoptotic Bax was only expressed in AxV(neg) and AxV(lo) cells. Late apoptotic AxV(hi) cells did not express Bcl-X(S) or Bax.

RESULTS

(1) AxV staining is more sensitive than sub G1 or ISEL in detecting early apoptotic cells; (2) only late apoptotic cells are equally detected by all assays; (3) AxV is a valuable tool in the detection and isolation of apoptotic cells at different stages of PCD; and (4) pro-apoptotic Bcl-X(S) and Bax are expressed at early, not late, stages of apoptosis.

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

B-cell chronic lymphocytic leukaemia (B-CLL) is an incurable clonal disease which shows initial responsiveness to a number of chemotherapeutic drugs. However, most treated patients become resistant to treatment and this represents a major problem in the successful management of the condition. Experimental evidence points to the fact that most chemotherapeutic drugs ultimately exert their cell killing effect through the process of apoptosis. In this study we compared the apoptotic responses of B-CLL cells in vitro following exposure to several chemotherapeutic drugs. We found that there was a correlation between ID50 values for all the drugs under investigation; particularly between Chlorambucil and Fludarabine (P = 0.0002). In addition, we analysed the expression of Bcl-2 and Bax, two proteins pivotal to the regulation of apoptosis, both immediately ex vivo and in viable and apoptotic sub-populations following exposure to drug. Our data suggest that high Bcl-2/Bax ratios may be predictive of a drug resistant phenotype in B-CLL cells and that modulation of these proteins is essential for the induction of cell death. Furthermore, it seems likely that the superior potency that has been ascribed to Fludarabine is due to it being administered in a more optimised dose. A recently reported clinical trial of Fludarabine against high-dose Chlorambucil supports this view since it showed that both treatment modalities were comparable in terms of response rate and survival times.