Proapoptotic activity of alemtuzumab alone and in combination with rituximab or purine nucleoside analogues in chronic lymphocytic leukemia cells

Proapoptotic activity of anti-CD52 monoclonal antibody, alemtuzumab (ALT) as well as ALT-affected apoptosis-regulatory mechanisms were assessed in tumor cells from 36 patients with chronic lymphocytic leukemia (CLL). Cells were treated in vitro for 24-48 h with ALT alone or in combination with rituximab (RTX), or purine nucleoside analogues (PNA), fludarabine and cladribine. Moreover, eight ALT-treated patients were examined in vivo. In 22/36 patients with the pre-treatment overexpression of Bax, Bak and Bid proteins, ALT induced a distinct (more than 50% from the baseline) increase in the incidence of apoptosis after 24 h of in vitro treatment. ALT-attributed CLL cell apoptosis was also detected after 24 h from in vivo ALT administration, with significantly downregulated Bcl-2 (P = 0.012) and Mcl-1 (P = 0.031). ALT combined with PNA or RTX exerted significantly higher proapoptotic effect in vitro than single agents, downregulating FLIP and Bcl-2 (ALT + PNA) or significantly increasing Bax expression (ALT + RTX; P = 0.007). In conclusion, the evidence of apoptotic CLL cells death in response to ALT, with deregulation of intrinsic apoptotic pathway, is presented. ALT and PNA or RTX trigger complementary changes in expression of proteins regulating cell propensity to undergo apoptosis, what provides molecular rationale for combining ALT with those agents.     

Human CD59 inhibitor sensitizes rituximab-resistant lymphoma cells to complement-mediated cytolysis

Rituximab efficacy in cancer therapy depends in part on induction of complement-dependent cytotoxicity (CDC). Human CD59 (hCD59) is a key complement regulatory protein that restricts the formation of the membrane attack complex, thereby inhibiting induction of CDC. hCD59 is highly expressed in B-cell non-Hodgkin's lymphoma (NHL), and upregulation of hCD59 is an important determinant of the sensitivity of NHL cells to rituximab treatment. Here, we report that the potent hCD59 inhibitor rILYd4 enhances CDC in vitro and in vivo, thereby sensitizing rituximab-resistant lymphoma cells and primary chronic lymphocytic leukemia cells (CLL) to rituximab treatment. By defining pharmcokinetic/pharmacodynamic profiles of rILYd4 in mice, we showed that by itself rILYd4 does not adversely mediate in vivo hemolysis of hCD59-expressing erythrocytes. Increasing expression levels of the complement regulators CD59 and CD55 in rituximab-resistant cells occur due to selection of preexisting clones rather than de novo induction of these proteins. Moreover, lymphoma cells overexpressing CD59 were directly responsible for the resistance to rituximab-mediated CDC therapy. Our results rationalize the use of rILYd4 as a therapeutic adjuvant for rituximab treatment of rituximab-resistant lymphoma and CLL. Furthermore, they suggest that preemptive elimination of CD59-overexpressing subpopulations along with rituximab treatment may be a useful approach to ablate or conquer rituximab resistance.     

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.     

Expression of apoptosis regulatory proteins of the Bcl-2 family and p53 in primary resected non-small-cell lung cancer

Proteins of the Bcl-2 family as well as p53 are important regulators of apoptosis. Alterations in the expression of these proteins can contribute to the formation of cancer, as well as influence tumour response to chemo- and radiotherapy. We used antibodies specific for the human Bcl-2, Mcl-1, Bax, Bak and p53 proteins to examine the expression of these apoptosis-regulating genes in 49 archival specimens of patients with radically resected non-small-cell lung cancer (NSCLC). Tumour cells containing immunostaining for the antiapoptotic proteins Bcl-2 and Mcl-1 were present in 31% and 58% of the cases evaluated, respectively, whereas immunopositivity for the proapoptotic proteins Bax and Bak was found in 47% and 58% of the samples. p53 immunopositivity was detected in 61% of the samples. The expression of Bcl-2 and p53 and the expression of Mcl-1 and Bax showed a positive association (P = 0.02 and P = 0.06 respectively), whereas the expression of Bax was inversely related to p53 (P = 0.008). The expression of Bcl-2 had a negative influence on relapse-free survival in this population of primary resected NSCLC patients (P = 0.02). The expression of p53 and Bcl-2 was significantly associated with metastasis-free survival (P < 0.01). Only patients with p53-positive tumours developed metastases during the follow-up period. Our results establish the frequent expression of the Bcl-2 family proteins Bcl-2, Mcl-1, Bax and Bak in NSCLC. It can be expected that Bcl-2 family members have no straightforward impact on clinical outcome in this disease because their interactions in the regulation of apoptosis are complex.     

Ofatumumab: a new CD20 monoclonal antibody therapy for B-cell chronic lymphocytic leukemia

Though most patients with chronic lymphocytic leukemia (CLL) respond to first-line therapy, all patients eventually relapse, after which therapeutic options are limited. Fludarabine-refractory patients have a particularly poor prognosis. The addition of the CD20 monoclonal antibody (MoAb) rituximab to chemotherapy in CLL has improved outcomes, particularly in early lines of therapy; however, the efficacy of rituximab monotherapy in CLL is limited, potentially in part because of reduced cell lysis via complement-dependent cytotoxicity (CDC) in this setting. Rituximab CDC is dependent on CD20 expression; CLL cells underexpress CD20. Ofatumumab is a human MoAb that targets an epitope encompassing the membrane-proximal small-loop on the CD20 molecule, which differs from the binding location of rituximab. In vitro studies with ofatumumab have demonstrated that it is significantly more effective than rituximab at corresponding dose levels at lysing CLL cells and B-cell lines, especially those with low CD20 copy numbers. In patients with CLL refractory to both fludarabine and alemtuzumab or refractory to fludarabine with bulky lymphadenopathy and, therefore, less suitable for treatment with the CD52 MoAb alemtuzumab, results from the planned interim analysis showed an encouraging response rate with ofatumumab (Independent Endpoint Review Committee evaluated) and survival parameters, which seemed to be higher than those reported from a historical assessment of other salvage therapies in a corresponding group of patients. Ofatumumab was also well tolerated; the most common adverse events were transient grade 1 or 2 infusion reactions and infections. Ongoing trials will help confirm the role of ofatumumab in CLL, in addition to the effect of this agent in combination with chemotherapies and other MoAbs.     

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.     

Drug-induced apoptosis in chronic lymphocytic leukemia.

Glucocorticoids and fludarabine are able to induce typical features of apoptosis in CLL lymphocytes.Cysteinyl aspartate specific proteases (caspases) play a key biochemical role in the apoptotic pathway. Caspase activation following cytotoxic stimuli leads to highly specific proteolytic cleavage of functionally important cellular enzymes. One of them is poly ADP-ribose) polymerase (PARP). To some extent caspase activation seems to be under the control of the Bcl-2 family of interacting proteins. We determined the role of Bcl-2-family proteins Bcl-2 (anti-apoptotic) and Bax (pro-apoptotic), activation of caspase-3 (CPP32/Yama) and activation of PARP in CLL apoptosis. All 21 analyzed CLL samples expressed Bcl-2 and Bax. Four of 13 (31%) samples with a low Bcl-2/Bax ratio exhibited in vitro prednisolone resistance, whereas eight of nine (88%) samples with a high Bcl-2/Bax ratio were in vitro resistant (相似文献   

Histological and immunophenotypic changes in 59 cases of B-cell non-Hodgkin's lymphoma after rituximab therapy

Rituximab is a chimeric monoclonal antibody that recognizes the CD20 antigen. It has been used to treat B-cell non-Hodgkin lymphoma (B-NHL), but recently rituximab resistance has been a cause for concern. We examined histological and immunohistochemical changes in 59 patients with B-NHL after rituximab therapy. The patients comprised 32 men and 27 women with a median age of 59 years. Pre-rituximab specimens comprised 34 follicular lymphomas (FL), 11 diffuse large B-cell lymphomas (DLBCL), 10 mantle cell lymphomas, two marginal zone B-cell lymphomas (MZBCL), and two chronic lymphocytic leukemias (CLL). CD20 expression in lymphoma cells was evaluated by immunohistochemistry or flow cytometry. Post-rituximab materials were taken a median of 6 months (4 days to 59 months) after rituximab therapy. Sixteen cases (27%) showed loss of CD20 expression with four histological patterns: pattern 1, no remarkable histological change (FL, 5; DLBCL, 3; and CLL, 2); pattern 2, proliferation of plasmacytoid cells (FL, 2; DLBCL, 1; and MZBCL, 1); pattern 3, transformation to classical Hodgkin's lymphoma (FL, 1); and pattern 4, transformation to anaplastic large cell lymphoma-like undifferentiated lymphoma (FL, 1). Loss of CD20 was unrelated to the interval of biopsies, treatment regimen, clinical response, and frequency of rituximab administration. Loss of CD20 within 1 month of rituximab therapy (3/14, 21%) and regain of CD20 (2/7, 29%) were not frequent. CD20-positive relapse with transformation occurred most frequently in cases of early relapse. In conclusion, B-NHL showed various histological and immunophenotypic changes after rituximab therapy, including not only CD20 loss but also proliferation of plasmacytoid cells or transformation to special subtypes of lymphoma. ( Cancer Sci 2009; 100: 54–61)     

Quercetin downregulates Mcl-1 by acting on mRNA stability and protein degradation

Background:

We recently demonstrated that quercetin, a flavonoid naturally present in food and beverages belonging to the large class of phytochemicals, was able to sensitise leukaemic cells isolated from patients with chronic lymphocytic leukaemia (CLL) when associated with recombinant tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) or anti-CD95. We also showed that quercetin potentiated the effect of fludarabine on resistant B cells from CLL patients. Resistance to therapy in CLL depends on the expression and activity of anti-apoptotic proteins of the Bcl-2 family. Among these, myeloid cell leukaemia-1 (Mcl-1) has been associated with apoptotic resistance in CLL. Therefore, we investigate here whether the sensitising activity of this flavonoid, which leads to increased apoptosis in both cell lines and CLL, could be related to Mcl-1 expression and stability.

Results:

B cells isolated from CLL patients showed different levels of Mcl-1 protein expression, resulting, in several cases, in increased sensitivity to fludarabine. Quercetin significantly enhanced the downregulation of Mcl-1 in B cells isolated from selected patients expressing detectable levels of Mcl-1. In U-937 cells, quercetin increased Mcl-1 mRNA instability in the presence of actinomycin D. When cells were treated with MG-132, a proteasome inhibitor, Mcl-1 protein level increased. However, quercetin, in the presence of Z-Vad-FMK, continued to lower Mcl-1 protein expression, indicating its independence from caspase-mediated degradation. In contrast, co-treatment of quercetin and MG-132 did not revert the effect of MG-132 mono-treatment, thus suggesting a possible interference of quercetin in regulating the proteasome-dependent degradation of Mcl-1. Gossypol, a small-molecule inhibitor of Bcl-2 family members, mimics the activity of quercetin by lowering Mcl-1 expression and sensitising U-937 cells to apoptosis induced by recombinant TRAIL and the Fas-ligand.

Conclusion:

This study demonstrates that in U-937 cells, quercetin downregulates Mcl-1 acting directly or indirectly on its mRNA stability and protein degradation, suggesting that the same mechanism may bypass resistance to apoptosis in leukaemic cells isolated from CLL patients and sensitise B cells to apoptosis induced by drugs and death receptor inducers.     

MiRNA-Mediated Knock-Down of Bcl-2 and Mcl-1 Increases Fludarabine-Sensitivity in CLL-CII Cells

Background: Over-expression of anti-apoptotic proteins such as Bcl-2 and Mcl-1 is associated with resistance to chemotherapeutic agents such as fludarabine. Moreover, an inverse relationship between miRNA-15a levels with Bcl-2 and Mcl-1 expression has been observed in CLL patients. In this study, the effect of miRNA-15a on apoptosis and sensitivity of the CLL cells to fludarabine was investigated. Methods: After treatments, the Mcl-1 and Bcl-2 expression levels were quantified by RT-qPCR. Trypan blue assay was used to explore the effects of miRNA-15a and fludarabine on cell proliferation. The cytotoxicity was measured using MTT assay and combination index analysis. Cell death was determined using cell death detection ELISA assay and caspase-3 activity assay Kits. Results: Results showed that miRNA-15a clearly decreased the mRNA levels of Bcl-2 and Mcl-1 in a time dependent manner, which led to CLL-II cell proliferation inhibition and enhancement of apoptosis (p < 0.05, relative to control). Transfection of the miRNA-15a synergistically reduced the cell survival rate and lowered the IC50 value of fludarabine. Furthermore, miRNA-15a significantly enhanced the apoptotic effect of fludarabine. Conclusions: Our data propose that suppression of Bcl-2 and Mcl-1 by miRNA-15a can effectively inhibit the cell proliferation and sensitize CLL cells to fludarabine. Therefore, miRNA-15a can be considered as a potential therapeutic target in CLL resistant patients.     

Combined Treatment with Stattic and Docetaxel Alters the Bax/Bcl-2 Gene Expression Ratio in Human Prostate Cancer Cells

Docetaxel, recognized as a stabilizing microtubule agent, is frequently administrated as a first line treatment for prostate cancers. Due to high side effects of monotherapy, however, combinations with novel adjuvants have emerged as an alternative strategy in cancer therapy protocols. Here, we investigated the combined effects of stattic and docetaxel on the DU145 prostate cancer cell line. Cytotoxicity was evaluated by MTT assay. To understand molecular mechanisms of stattic action, apoptotic related genes including Bcl-2, Mcl-1, Survivin and Bax were evaluated by real-time RT-PCR. Alteration in the expression of pro-apoptotic Bax and anti-apoptotic Bcl-2 genes and Bax/Bcl-2 ratio were investigated via the 2ΔΔCTmethod. The IC50 values for docetaxel and stattic were 3.7 ± 0.9 nM and 4.6±0.8 μM, respectively. Evaluation of key gene expression levels revealed a noticeable decrease in antiapoptotic Bcl-2 and Mcl-1 along with an increase in pro-apoptotic Bax mRNA levels (p<0.05). Our results suggest that combination of a STAT3 inhibitor with doctaxel can be considered as a potent strategy for induction of apoptosis via increasing Bax mRNA expression.     

Bisindolylmaleimide IX is a potent inducer of apoptosis in chronic lymphocytic leukaemic cells and activates cleavage of Mcl-1.

New agents are required for the treatment of chronic lymphocytic leukaemia (CLL). We show here that a protein kinase C inhibitor, bisindolylmaleimide IX, is a potent inducer of apoptosis in CLL cells, and investigate the mechanisms by which this is induced. Bisindolylmaleimide IX induced a conformational change and subcellular redistribution of Bax from the cytosol to the mitochondria, resulting in the release of the proapoptotic mediators cytochrome c, Smac and Omi/HtrA2 from the mitochondrial inner membrane space. This was followed by the activation of caspase-9 as the apical caspase and subsequent activation of effector caspases. CLL cells undergoing apoptosis showed a rapid caspase-mediated cleavage of Mcl-1, an antiapoptotic member of the Bcl-2 family implicated in CLL survival and poor prognosis. This cleavage was mediated primarily by caspase-3. Cleavage of Mcl-1 may provide a feed-forward amplification loop, resulting in the rapid induction of apoptosis. Bisindolylmaleimide IX or a related derivative may be of clinical use in the treatment of CLL.     

Acquired resistance to rituximab is associated with chemotherapy resistance resulting from decreased Bax and Bak expression.

PURPOSE: Targeting malignant B cells using rituximab (anti-CD20) has improved the efficacy of chemotherapy regimens used to treat patients with non-Hodgkin's lymphoma. Despite the promising clinical results obtained using rituximab, many patients relapse with therapy-resistant disease following rituximab-based treatments. We have created a cell line model of rituximab resistance using three B-cell non-Hodgkin's lymphoma-derived cell lines (Raji, RL, and SUDHL-4). In an attempt to define strategies to overcome rituximab resistance, we sought to determine the chemotherapy sensitivity of our rituximab-resistant cell lines (RRCL). EXPERIMENTAL DESIGN: Parental, rituximab-sensitive cell lines (RSCL) Raji, RL, and SUDHL-4, along with RRCLs derived from them, were exposed to several chemotherapeutic agents with different mechanisms of action and the ability of these agents to induce apoptotic cell death was measured. Expression of multidomain Bcl-2 family proteins was studied as potential mediators of chemotherapy/rituximab resistance. RESULTS: We found that RRCLs are resistant to multiple chemotherapeutic agents and have significantly decreased expression of the Bcl-2 family proteins Bax, Bak, and Bcl-2. RRCLs do not undergo rituximab- or chemotherapy-induced apoptosis but die in a caspase-dependent manner when either wild-type Bax or Bak is exogenously expressed. Furthermore, forced expression of Bak sensitized RRCL to chemotherapy-induced apoptosis. CONCLUSIONS: Whereas a single or limited exposure of lymphoma cells to rituximab may lead to a favorable ratio of proapoptotic to antiapoptotic Bcl-2 family proteins, repeated exposure to rituximab is associated with a therapy-resistant phenotype via modulation of Bax and Bak expression.     

The role of complement in the mechanism of action of rituximab for B-cell lymphoma: implications for therapy

Rituximab, a genetically engineered chimeric monoclonal antibody specifically binding to CD20, was the first antibody approved by the U.S. Food and Drug Administration for the treatment of cancer. Rituximab significantly improves treatment outcome in relapsed or refractory, low-grade or follicular B-cell non-Hodgkin's lymphoma (NHL). However, there are also some challenges for us to overcome: why approximately 50% of patients are unresponsive to rituximab in spite of the expression of CD20, and why some responsive patients develop resistance to further treatment. Although the antitumor mechanisms of rituximab are not completely understood, several distinct antitumor activities of rituximab have been suspected, including complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), apoptosis, and direct growth arrest. To counteract resistance to rituximab therapy, several strategies have been developed to: (a) augment the CDC effect by increasing CD20 expression, heteroconjugating rituximab to cobra venom factor and C3b, and inhibiting membrane complement regulatory protein, especially CD59, function; (b) enhance the ADCC effect through some immunomodulatory cytokines and CR3-binding beta-glucan; and (c) reduce the apoptotic threshold or induce apoptotic signaling on the tumor. Extensive studies indicate that rituximab combined with these approaches is more effective than a single rituximab approach. Herein, the mechanism of action of and resistance to rituximab therapy in B-cell NHL, in particular, the involvement of the complement system, are extensively reviewed.     

Apoptosis induced by histone deacetylase inhibitors in leukemic cells is mediated by Bim and Noxa.

Several histone deacetylase inhibitors (HDACi), which have recently entered early clinical trials, exert their anticancer activity in part through the induction of apoptosis although the precise mechanism of this induction is not known. Induction of apoptosis by structurally diverse HDACi in primary cells from patients with chronic lymphocytic leukemia (CLL) and different leukemic cell lines was mediated by the Bcl-2 regulated intrinsic pathway and demonstrated a requirement for de novo protein synthesis. A marked time-dependent induction of the pro-apoptotic BH3-only proteins, Bim, Noxa and Bmf was observed, which preceded the induction of apoptosis. A key role for both Bim and Noxa was proposed in HDACi-mediated apoptosis based on our findings that siRNA for Bim and Noxa but not Bmf largely prevented the HDACi-induced loss in mitochondrial membrane potential, caspase processing and phosphatidylserine externalization. Noxa, induced by HDACi, in CLL cells and tumor cell lines, bound extensively to Mcl-1, a major anti-apoptotic Bcl-2 family member present in CLL cells. Our data strongly suggests that HDACi induce apoptosis primarily through inactivation of anti-apoptotic Bcl-2 family members by increases in Bim and Noxa and highlights these increases as a potential clinical target for CLL/lymphoma therapy.     

Mcl-1 down-regulation potentiates ABT-737 lethality by cooperatively inducing Bak activation and Bax translocation

The Bcl-2 antagonist ABT-737 targets Bcl-2/Bcl-xL but not Mcl-1, which may confer resistance to this novel agent. Here, we show that Mcl-1 down-regulation by the cyclin-dependent kinase (CDK) inhibitor roscovitine or Mcl-1-shRNA dramatically increases ABT-737 lethality in human leukemia cells. ABT-737 induces Bax conformational change but fails to activate Bak or trigger Bax translocation. Coadministration of roscovitine and ABT-737 untethers Bak from Mcl-1 and Bcl-xL, respectively, triggering Bak activation and Bax translocation. Studies employing Bax and/or Bak knockout mouse embryonic fibroblasts (MEFs) confirm that Bax is required for ABT-737+/-roscovitine lethality, whereas Bak is primarily involved in potentiation of ABT-737-induced apoptosis by Mcl-1 down-regulation. Ectopic Mcl-1 expression attenuates Bak activation and apoptosis by ABT-737+roscovitine, whereas cells overexpressing Bcl-2 or Bcl-xL remain fully sensitive. Finally, Mcl-1 knockout MEFs are extremely sensitive to Bak conformational change and apoptosis induced by ABT-737, effects that are not potentiated by roscovitine. Collectively, these findings suggest down-regulation of Mcl-1 by either CDK inhibitors or genetic approaches dramatically potentiate ABT-737 lethality through cooperative interactions at two distinct levels: unleashing of Bak from both Bcl-xL and Mcl-1 and simultaneous induction of Bak activation and Bax translocation. These findings provide a mechanistic basis for simultaneously targeting Mcl-1 and Bcl-2/Bcl-xL in leukemia.     

Bax to Bcl-2 ratio and Ki-67 index are useful predictors of neoadjuvant chemoradiation therapy in bladder cancer

OBJECTIVE: In this study, locally advanced bladder cancer was treated by radiation combined with cisplatin therapy and a retrospective analysis was conducted to predict the clinical response to chemoradiotherapy (CRT) based on the immunohistochemistry of apoptosis-related proteins. METHODS: Sixty-two patients (median age, 68 years; range, 45-89 years) with transitional cell carcinoma of the bladder (pT1G3-pT4M0) treated with CRT (median dose: 40.5 Gy of radiation and 230 mg of cisplatin) were studied. Mucosal biopsy was performed before and after CRT. Paraffin-embedded tumor specimens were examined with TUNEL and were immunostained for Ki-67, p53, Bcl-2 and Bax; the Bax/Bcl-2 ratio and apoptosis index (AI) were calculated. Clinical features of the patients and response to CRT were compared with data obtained from examination of the tumors. RESULTS: The 62 patients had a median follow-up period of 34 months (range, 3-84 months). Responses to CRT were as follows: CR, 34%; PR, 45%; NC, 21%. The survival rate of patients with Ki-67-positive tumors was significantly lower than those of patients with Ki-67-negative tumors (P < 0.05). No significant correlation was observed between the expression of any protein, the AI and the clinical response. However, the Bax/Bcl-2 ratio showed a significant association with the CR rate (P = 0.0289). CONCLUSIONS: The results of this study suggest that the combined assessment of Bcl-2 and Bax protein expression may be used to predict a clinical response to CRT based on the Bax/Bcl-2 ratio determined before therapy. The Ki-67 index may be a useful predictor of prognosis in patients treated by CRT.     

Chlorambucil in Chronic Lymphocytic Leukemia: Mechanism of Action

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries but the clinical presentation and rate of disease progression are highly variable. When treatment is required the most commonly used therapy is the nitrogen mustard alkylating agent, chlorambucil (CLB), with or without prednisone. Although CLB has been used in the treatment of CLL for forty years the exact mechanism of action of this agent in CLL is still unclear. Studies in proliferating model tumor systems have demonstrated that CLB can bind to a variety of cellular structures such as membranes, RNA, proteins and DNA; however, DNA crosslinking appears to be most important for antitumor activity in these systems. In addition, a number of different mechanisms can contribute to CLB resistance in these tumor models including increased drug metabolism, DNA repair and CLB detoxification resulting from elevated levels of glutathione (GSH) and glutathione S-transferase (GST) activity. However, unlike tumor models in vitro, CLL cells are generally not proliferating and studies in CLL cells have raised questions about the hypothesis that DNA crosslinking is the major mechanism of antitumor action for CLB in this disease. CLB induces apoptosis in CLL cells and this appears to correlate with the clinical effects of this agent. Thus, alkylation of cellular targets other than DNA, which can also induce apoptosis, may contribute to the activity of CLB. Alterations in genes such as p53, mdm-2, bcl-2 and bax which control entry into apoptosis may cause drug resistance. Loss of wild-type p53 by mutation or deletion occurs in 10 to 15% of CLL patients and appears to correlate strongly with poor clinical response to CLB. The induction of apoptosis by CLB is paralleled by an increase in P53 and Mdm-2 but this increase is not observed in patients with p53 mutations indicating that with high drug concentrations CLB can produce cell death through P53 independent pathways. The level of Mdm-2 mRNA in the CLL cells is not a useful predictor of drug sensitivity. In addition, although Bax and Bcl-2 are important regulators of apoptosis and the levels of these proteins are elevated in CLL cells compared with normal B cells, the levels of Bax and Bcl-2, ortheBax:Bcl-2 ratio, are not important determinants of drug sensitivity in this leukemia. Finally, whereas CLB and nucleoside analogs may produce cell death in CLL by a P53 dependent pathway other agents, such as dexamethasone or vincristine, may act through P53-independent pathways.     

Expression of complement regulatory proteins: CD46, CD55, and CD59 and response to rituximab in patients with CD20(+) non-Hodgkin’s lymphoma

Rituximab is an anti-CD20 humanized monoclonal antibody widely used in the treatment of B-cell non-Hodgkin’s lymphomas (NHLs). Its mechanism of action is related with complement function—complement mediated cytotoxicity. CD46, CD55, and CD59 are complement regulatory proteins. The aim of this study was to analyze expression of complement inhibitors CD46, CD55, and CD59 in patients with CD20(+) NHLs treated with rituximab combined with chemotherapy. A total of 27 patients with CD20(+) NHLs were evaluated (13 females and 14 males). The median age of patients was 56 years. All patients were examined before treatment with rituximab. Expression of CD46, CD55, and CD59 was determined by two-color flow cytometry. A total of 15 patients achieved complete response (CR), 5 patients achieved partial response, and 7 patients had no or minimal response (NR) after rituximab therapy. We observed that expression of CD46 and CD59 were higher in patients with CR than in group with NR. Expression of CD55 and CD59 were higher in patients with bulky disease. In conclusion level of expression of CD46, CD55, and CD59 could be clinically helpful to predict the response to rituximab therapy.