The role of nucleoside analogues in the treatment of chronic lymphocytic leukemia-lessons learned from prospective randomized trials

Humanized mouse G6 anti-idiotypic monoclonal antibody has therapeutic potential against IGHV1-69 germline gene-based B-CLL

In 10-20% of the cases of chronic lymphocytic leukemia of B-cell phenotype (B-CLL), the IGHV1-69 germline is utilized as VH gene of the B cell receptor (BCR). Mouse G6 (MuG6) is an anti-idiotypic monoclonal antibody discovered in a screen against rheumatoid factors (RFs) that binds with high affinity to an idiotope expressed on the 51p1 alleles of IGHV1-69 germline gene encoded antibodies (G6-id(+)). The finding that unmutated IGHV1-69 encoded BCRs are frequently expressed on B-CLL cells provides an opportunity for anti-idiotype monoclonal antibody immunotherapy. In this study, we first showed that MuG6 can deplete B cells encoding IGHV1-69 BCRs using a novel humanized GTL mouse model. Next, we humanized MuG6 and demonstrated that the humanized antibodies (HuG6s), especially HuG6.3, displayed ∼2-fold higher binding affinity for G6-id(+) antibody compared to the parental MuG6. Additional studies showed that HuG6.3 was able to kill G6-id(+) BCR expressing cells and patient B-CLL cells through antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Finally, both MuG6 and HuG6.3 mediate in vivo depletion of B-CLL cells in NSG mice. These data suggest that HuG6.3 may provide a new precision medicine to selectively kill IGHV1-69-encoding G6-id(+) B-CLL cells.

2-Chlorodeoxyadenosine treatment for cutaneous T-cell lymphoma

The primary cutaneous lymphomas are often indolent but difficult to treat. In the early stages psoralen and ultraviolet-A therapy is the standard treatment whereas at the tumor stage chemotherapy (e.g. pegylated doxorubicin) is often used for debulking. The purine analog 2-chlorodeoxyadenosine (2CdA) acts in non-Hodgkin’s lymphoma and has been used in our center for the treatment of advanced primary cutaneous T-cell lyphomas (CTCL). Here, we report on the efficacy and side effects of 2CdA in six patients with CTCL. One patient died owing to myelosuppression. Partial responses were seen in four cases but full remission was observed in only one case. We concluded that 2CdA has a limited usefulness in the management of advanced CTCL.

Chronic Myelomonocytic Leukemia Coexisting with B-cell Chronic Lymphocytic Leukemia

Coexistence of B-cell chronic lymphocytic leukemia (B-CLL) and chronic myelomonocytic leukemia (CMML) is an unusal event, and to our knowledge, only four such cases have been reported in the literature. We report a 68-year-old white woman in whom these two diseases were diagnosed concomitantly. The diagnosis was made on the basis of peripheral blood count, morphology and immunophenotyping, and bone marrow cytology and histology. Interphase FISH analysis detected a 13q14.3 deletion in lymphocytes nuclei and no such abnormality in monocytes nuclei. The PCR analysis of IgH gene rearrangement in the bone marrow, as well as the peripheral blood lymphocytes, showed two different monoclonal IgH configurations as the result of biallelic clonal rearrangement of IgH genes suggesting an origin of lymphocytes from B-cell progenitors. The patient was originally treated with prednisone 1 mg/kg/day because of progressive significant thrombocytopenia, without improvement. Subsequently, she received one course of cladribine (2-CdA). Significant reduction of lymphocytes in the peripheral blood was observed. However, rapid increase of monocytes was seen shortly after the 2-CdA treatment. Subsequently, she received hydroxyurea (1.5 g/day) without hematological improvement. The patient died in January 2003, three months after diagnosis because of progression of both leukemias and associated pneumonia. Possible etiopathogenic relationship between both disorders is discussed.

Assessment of expression of selected Bcl-2 family proteins in lymphoid infiltration in patients with B-cell chronic lymphocytic leukaemia treated with nucleoside analogues

B-cell chronic lymphocytic leukaemia (B-CLL) is characterized by clonal growth and accumulation of mature lymphoid cells due to disturbance in genetically regulated form of cell death called apoptosis. The intrinsic mechanism of apoptosis is controlled by Bcl-2 family proteins. Purine nucleoside analogues induce the apoptosis in cells in a state of quiescence. The aim of the study was to assess expression of selected Bcl-2 family proteins in neoplastic infiltration in bone marrow in patients with B-CLL treated with nucleoside analogues. The study comprised examination of bone marrow obtained routinely by trephine biopsy from 18 patients with B-CLL diagnosed before administration of purine nucleoside analogues treatment and after its completion. Expression of Bcl-2, Bcl-x and Bax proteins was examined. Lymphoid cells in bone marrow were present in all patients before administration of treatment. After treatment in two patients bone marrow was infiltrated in diffuse pattern, whereas other patients presented nodular pattern of infiltration. The difference between stage of infiltration before and after treatment was statistically significant (p<0.002). High percentage of infiltration cells with positive anti Bcl-2 reaction from 42.0% in one patient to 85.33+/-3.06% in four patients before treatment was observed. After treatment percentage of infiltration cells with positive anti Bcl-2 antibody reaction was from 33.0+/-18.38% in two patients to 99.0% in one patient. Positive correlation between stage of infiltration and expression of Bcl-2 protein was confirmed before and after treatment. Such correlations were not observed in case of Bax and Bcl-x. Strong staining of immunohistochemical reaction of cells in lymphoid infiltration with Bcl-2 antibody was confirmed. There was a difference between Bcl-/Bax ratio before and after treatment. Immunohistochemical assessment of expression of Bcl-2 family proteins in cells of lymphoid infiltration in bone marrow of patients with CLL is an important method in detection of minimal residual disease (MRD) after treatment.

Recent progress in the management of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a clonal disease characterized by proliferation and accumulation of small CD5-positive B cells. More than 50% of patients are asymptomatic at diagnosis and usually require no treatment. However, treatment is needed in the advanced and progressive disease. Chlorambucil with or without steroids has been the drug of choice for many years in previously untreated patients with CLL. The purine nucleoside analogs (PNAs), fludarabine (FA), cladribine (2-CdA-chlorodeoxyadenosine) and pentostatin (DCF, 2'-deoxycoformycin) also have been introduced for treatment of CLL. Significantly higher overall response (OR) and complete response (CR) and longer progression free survival (PFS) in patients with CLL treated with FA or 2-CdA have been confirmed in randomized, multicenter trials and more recently in meta-analysis. However, the median survival time did not differ between patients treated with PNA and alkylating agents. Combination therapies with PNAs and cyclophosphamide and especially with cyclophosphamide and rituximab are more active than monotherapy in terms of OR, CR and PFS. Several reports have shown significant activity of alemtuzumab in previously untreated and pretreated patients even when refractory to FA. Alemtuzumab also can be used in CLL as a preparative regimen before stem cell transplantation (SCT) and to eliminate minimal residual disease (MRD). Recently, several new agents have shown promise in treating CLL, including new monoclonal antibodies, agents targeting bcl-2 family of proteins, antisense oligonucleotides and other agents. Moreover, autologous and allogenic hematopoietic cell transplantations are increasingly considered for treatment of patients with CLL. In this review current therapeutic strategies in CLL are presented.

Purine Analogue-Based Chemotherapy Regimens for Second-Line Therapy in Patients With Chronic Lymphocytic Leukemia

A dramatic change has occurred in the management of chronic lymphocytic leukemia (CLL) over the past 20 years. The use of newer therapies, including the purine analogues, has resulted in higher frequencies of response. Combination therapy with purine analogues, alkylators, and/or monoclonal antibodies represents a promising new approach to the treatment of patients with CLL. The most commonly studied regimens have utilized fludarabine, but severe myelosuppression and immunosuppression of these combinations require close attention to dosing and schedule. Of the purine analogues that show activity in CLL, pentostatin appears to be the least myelosuppressive. These combination strategies are associated with high-quality responses in the majority of patients and may one day lead to improved survival or possibly even a cure for patients with CLL.

The pattern of deoxycytidine- and deoxyguanosine kinase activity in relation to messenger RNA expression in blood cells from untreated patients with B-cell chronic lymphocytic leukemia

Deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK) catalyze the first step in the intracellular cascade of fludarabine (2-fluoroadenine-beta-D-arabinofuranoside) and cladribine (2-chlorodeoxyadenosine) phosphorylation, which leads to activation of these prodrugs, commonly used for treatment of chronic lymphocytic leukemia (CLL). Thus, resistance to nucleoside analogues may primarily be due to low levels of deoxynucleoside kinase activity. The purpose of this study was to investigate the activity profiles of dCK and dGK and characterize the possible relationship between the levels of dCK enzymatic activities and mRNA levels in B-CLL cells from untreated patient samples in an attempt to determine the best approach for predicting sensitivity to nucleoside analogues and thereby optimizing treatment of CLL. For this purpose, dCK and dGK analyses were done in blood cells from 59 untreated symptomatic patients with CLL. The dGK activity towards 2-chlorodeoxyadenosine was significantly lower than of dCK (median 73 pmol/mg protein/min (85-121, 95% CI) versus 353 pmol/mg protein/min (331-421)). The median dCK mRNA level was 0.107 (0.096-0.120, 95% CI). There was a lack of correlation between the activities of dCK and dGK, which indicates that these proteins are regulated independently. We also found that the dCK and dGK activity measurement towards their endogenous substrates were comparable to the nucleoside analogues tested. Such variations in enzyme activities and mRNA levels may well explain differences in clinical responses to treatment. There was no correlation between the levels of dCK mRNAs and enzymatic activities using a quantitative real-time PCR procedure. Sequencing of dCK mRNA did not reveal alternate splicing or mutations in the coding region. The relation between activity and mRNA levels was studied by short interfering RNA (siRNA) method, which showed that in the siRNA treated cells the down-regulation of dCK expression, and activity followed each other. However, in control cells the mRNA levels remained stable but the protein activity markedly decreased. These data demonstrate that the dCK activity is not reflected by dCK mRNA expression that indicates a post-translational mechanism(s).

Therapy of chronic lymphocytic leukemia with purine analogs and monoclonal antibodies

B-cell chronic lymphocytic leukemia (CLL) is a clonal hematopoietic disorder characterized by proliferation and accumulation of small lymphocytes. It is the most common form of leukemia in North America and Europe. The management of CLL is determined by the stage and activity of the disease. Several randomized studies indicate that cytotoxic therapy based on alkylating agents in the indolent phase of disease, does not prolong the survival time of CLL patients. Chlorambucil, with or without steroids, has been for many years the drug of choice in previously untreated patients with this leukemia. Alternative treatment approaches, including new purine nucleoside analogs (PNA), such as fludarabine and 2-chlorodeoxyadenosine (cladribine) have also shown activity in CLL. The randomized studies have indicated a higher overall response, complete remission rates and longer response duration in patients treated initially with PNA than with chlorambucil or cyclophosphamide based combination regimens. These agents alone or in combinations, seem to be the treatment of choice for patients failing standard therapies. The monoclonal antibodies directed against CD52 antigen (alemtuzumab, Campath-1H) and CD20 antigen (rituximab) demonstrate also significant activity in CLL patients. These agents have significant single-agent activity, distinct mechanism of action and generally, favorable toxicity profiles. Both antibodies achieved the most promising results in the treatment of patients with relapsed or refractory CLL. More recently the effect of alemtuzumab in previously untreated patients has been also investigated and results are very encouraging. A multicenter prospective randomized study comparing alemtuzumab and chlorambucil as first line therapies are ongoing and preliminary results show acceptable toxicity profile of monoclonal antibody.

Richterʼs Syndrome

Richter's syndrome, that is, transformation of chronic lymphocytic leukemia to a large cell or immunoblastic lymphoma, occurs in up to 10% of patients with chronic lymphocytic leukemia. The onset of Richter's syndrome is characterized by worsening systemic symptoms, rapid tumor growth, and/or extranodal involvement. Median survival with conventional chemotherapy is less than 6 months. Therapy with more recent therapeutic regimens, such as hyperCVXD (fractionated cyclophosphamide, vincristine, liposomal daunorubicin, and dexamethasone), augmented hyperCVXD, and yttrium-90 ibritumomab tiuxetan, has not produced major improvements in response rates or overall survival. Improvement in the outcome of patients with Richter's syndrome may be aided by a more comprehensive understanding of the pathogenesis of Richter's syndrome; therapy could then be targeted against specific abnormalities. Current data indicate that the transformation of chronic lymphocytic leukemia to a large-cell or immunoblastic lymphoma is associated with abnormalities in cell cycle regulation (e.g., loss of the cell cycle inhibitors p16(INK4a) and p27(KIP1) ) and DNA repair (e.g., mutations and/or deletions of the p53, ATM, and p14(ARF) genes and epigenetic silencing of the MLH1 gene). However, the critical event leading to transformation is unclear. Given the poor prognosis of patients with Richter's syndrome, every effort should be made to enroll these patients into clinical trials evaluating novel agents with the appropriate correlative studies.

Functional analysis of genetic variants in the human concentrative nucleoside transporter 3 (CNT3; SLC28A3)

The human concentrative nucleoside transporter, CNT3 (SLC28A3), plays an important role in mediating the cellular entry of a broad array of physiological nucleosides and synthetic anticancer nucleoside analog drugs. As a first step toward understanding the genetic basis for interindividual differences in the disposition and response to antileukemic nucleoside analogs, we examined the genetic and functional diversity of CNT3. In all, 56 variable sites in the exons and flanking intronic region of SLC28A3 were identified in a collection of 270 DNA samples from US populations (80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). Of the 16 coding region variants, 12 had not been previously reported. Also, 10 resulted in amino-acid changes and three of these had total allele frequencies of >/=1%. Nucleotide diversity (pi) at nonsynonymous and synonymous sites was estimated to be 1.81 x 10(4) and 18.13 x 10(4), respectively, suggesting that SLC28A3 is under negative selection. All nonsynonymous variants, constructed by site-directed mutagenesis and expressed in Xenopus laevis oocytes, transported purine and pyrimidine model substrates, except for c. 1099G>A (p. Gly367Arg). This rare variant alters an evolutionarily conserved site in the putative substrate recognition domain of CNT3. The presence of three additional evolutionarily conserved glycine residues in the vicinity of p. Gly367Arg that are also conserved in human paralogs suggest that these glycine residues are critical in the function of the concentrative nucleoside transporter family. The genetic analysis and functional characterization of CNT3 variants suggest that this transporter does not tolerate nonsynonymous changes and is important for human fitness.

Influence of 2-chlorodeoxyadenosine (cladribine) on human erythrocytes

2-Chlorodeoxyadenosine (2-CdA, cladribine) is one of the newest chemotherapy drugs which has been around and in use for a few years. Drug in tumour cells causes the inhibition of DNA synthesis and repair processes in replication cells, and the accumulation of DNA strand breaks in nonproliferating cells. The present study was undertaken to characterize the influence of cladribine on the fluidity of the lipid bilayer and protein conformation in human erythrocytes. The effect of cladribine on the erythrocyte membrane structure was examined by electron spin resonance (ESR) spectroscopy and fluorescence measurements. It was observed that under the studied conditions (c: 0.1-5 microg/ml, t = 1 h, 37 degrees C), cladribine localised mainly in the erythrocyte membrane and affected its organization. The alterations in the fluidity were observed mainly in the deeper regions of the cell membrane. The incorporation of drug into human erythrocytes also caused negligible conformational alterations of membrane cytoskeletal proteins and did not change the internal viscosity of the cells. We can conclude from these data that 2-CdA in vitro is significantly much less toxic to erythrocytes than anthracycline drugs, which are used in treatment of leukemias. However, the higher concentrations of 2-CdA (about 5 microg/ml) can be also toxic to erythrocytes.

Fludarabine and mitoxantrone for patients with chronic lymphocytic leukemia

BACKGROUND

The objective of the current study was to assess the efficacy of combination therapy with fludarabine and mitoxantrone in patients with B-cell chronic lymphocytic leukemia (CLL).

METHODS

Eighty-eight patients were treated with fludarabine 30 mg/m(2) intravenously daily for 3 days and mitoxantrone 10 mg/m(2) on Day 1 (FN). Patients were divided into four groups based on expected response to single-agent fludarabine. These four groups included previously untreated patients, patients who previously were treated with alkylating agents, patients who were successfully treated with alkylating agents and fludarabine but who developed recurrent disease, and patients whose disease was refractory to fludarabine with or without alkylating agents.

RESULTS

The overall response rate was 66%. The response rates were 83% in previously untreated patients, 87% in patients previously treated with alkylating agents, 50% in patients whose disease was not refractory to fludarabine at the start of therapy, and 25% in patients whose disease was refractory to fludarabine. The complete remission (CR) rate was 20% for previously untreated patients, which was not significantly different from the CR rate for a group of historical control patients who were treated with single-agent fludarabine. The median follow-up was 8 years for surviving patients. The median progression free survival was 24 months for all patients and 34 months for previously untreated patients. The median overall survival was 40 months, and the median survival of previously untreated patients was 88 months. The most common toxicities were myelosuppression and infection. Eleven patients (12.5%) developed a second malignancy after a median of 62 months.

CONCLUSIONS

The FN regimen did not have a significant advantage over fludarabine alone in the treatment of patients with CLL.

Fludarabine plus cyclophosphamide for the treatment of advanced chronic lymphocytic leukemia

OBJECTIVES

Therapeutic results in advanced chronic lymphocytic leukemia (CLL) are still unsatisfactory in terms of complete remission achievement and duration, in spite of the extensive use of purine analogs. The objective of this study was to describe the clinical characteristics and treatment results from a series of 32 patients managed with a therapeutic program based on the combination of fludarabine and cyclophosphamide (CTX).

METHODS

Thirty-two patients (median age 63 yr, range 42-75 yr) with newly diagnosed (47%) or refractory-relapsed (53%) CLL were programmed to receive six courses of a 3-d combination of fludarabine at 30 mg/m2/d plus CTX at 300 mg/m2/d. Refractory-relapsed patients had previously received different chemotherapy lines from 1 to 5.

RESULTS

Fourteen of 32 (44%) patients achieved a complete remission, 16 (50%) obtained partial remission and two (6%) failed to respond. The CR rate was higher in untreated patients; in particular, CR was achieved in nine of 15 (60%) newly diagnosed cases as opposed to five of 17 (29%) among pretreated patients. Toxicity was caused by myelosuppression and/or infections in most cases. After a median follow-up of 24 months (range 8-48 months), 20 of 32 patients (62%) are alive, and 14 of 32 (44%) are free from progression. Median overall survival and median time to progression were 35 and 25 months, respectively.

CONCLUSION

The combination of fludarabine with CTX is effective in advanced CLL with acceptable toxicity, either as first-line therapy or in refractory-relapsed patients. In particular, a considerable rate of complete remission can be achieved in untreated patients. Myelosuppression represents the major side-effect.

Purine nucleoside analogues in the treatment of myleoid leukemias

The purine nucleoside analogues (PNA), fludarabine (FA), cladribine (2-chlorodeoxyadenosine, 2-CdA) and 2'-deoxycoformycin (DCF), represent a novel group of cytotoxic agents with high activity in low-grade lymphoid malignancies. However, several investigations have revealed that these agents are active also in acute myeloid leukemia (AML) and chronic myelogenous leukemia (CML). Synergistic interaction between FA or 2-CdA with cytarabine (Ara-C) have been demonstrated in both preclinical and clinical studies. PNA enhance the cell concentration of Ara-CTP, which is active metabolite of Ara-C. It is likely that the addition of granulocyte colony stimulating factor (G-CSF) may further improve the effects of FA (FLAG) or 2-CdA (CLAG). The addition of anthracyclines to induction therapy does not appear to result in a substantial advantage in terms of CR achievement and duration. An alternative approach to increase FLAG activity might be the addition of investigational drugs with novel mechanism of action, such as topoiromerase I inhibitors. The addition of anthracyclines to induction therapy does not appear to result in a substantial advantage in terms of CR achievement and duration. Clinical studies have confirmed the efficacy of PNA alone or in combination protocols in the treatment of AML. These regimens seem to produce superior results with acceptable toxicities in previously treated and relapsed, poor risk AML. However, early relapses remain a significant problem in a majority of refractory or relapsed patients in CR after treatment with PNA based regimens. To prolong remission duration or even cure AML, auto--or allo stem cell transplantation should be considered. However, FAMP or 2-CdA containing regimens may impair mobilization and collection of stem cells from peripheral blood for autotransplantation. Few studies have analyzed the role of PNA in CML. 2-CdA, FAMP and DCF can induce hematologic response in chronic phase of CML but cytogenetic responses have not been observed. Preliminary results suggest, that PNA used alone or in combination may be used as palliation in blast phase of the disease. However, currently, the role of these agents in CML is insignificant because of the high activity of Glivec in this disease. Finally, PNA, especially FA play an important role in non-myeloablative conditioning regimens for allogenic stem cell transplantation in high-risk patients, possibly also with myeloid malignancies.

Are activation markers (CD25, CD38 and CD103) predictive of sensitivity to purine analogues in patients with T-cell prolymphocytic leukemia and other lymphoproliferative disorders?

T-cell prolymphocytic leukemia (T-PLL) is a rare lymphoproliferative disorder with distinctive clinical and laboratory features. It is often resistant to conventional chemotherapy, but complete or partial responses have been documented with the use of purine analogues. We report on two cases of T-PLL with a slightly different immunophenotype but a remarkably different response to pentostatin. We discuss the possible therapeutic implications of this finding and establish a comparison between immunophenotype and sensitivity to purine analogues in patients with T-PLL and other chronic lymphoproliferative disorders.

Re-treatment with cladribine-based regimens in relapsed patients with B-cell chronic lymphocytic leukemia. Efficacy and toxicity in comparison with previous treatment

The aim of the study was to determine the effectiveness and toxicity of cladribine (2-CdA) used alone or in combination with prednisone (P) or cyclophosphamide and mitoxantrone in re-treatment of patients with progressive B-cell chronic lymphocytic leukemia (B-CLL). We analyzed treatment outcome in 40 patients who had responded to previous treatment with 2-CdA-based regimens. Criteria for re-treatment were the same as for the first treatment. The patients were retreated with the same agents if they responded to the first treatment and then relapsed with progressive disease not earlier than 3 months after achieving the first response. Eight patients received 2-CdA alone (0.12 mg kg(-1) d(-1)) i.v. for 5 d, and 21 patients additionally were given P (30 mg m(-2) d(-1)) orally, also for 5 d. Eleven patients received 2-CdA for 3 d combined with cyclophosphamide (650 mg m(-2)) i.v. and mitoxantrone (10 mg m(-2)) i.v. on day 1 (CMC regimen). The cycles were repeated usually at 4 wk intervals or longer if severe myelosuppression or infections occurred. The therapy was finished if complete remission (CR) was achieved or until maximum of six courses. Overall response (OR) in re-treatment was obtained in 16 out of 40 (40%) patients (95% CI 16-64), including 62% after 2-CdA, 33% after 2-CdA +P and 36% after CMC. CR was obtained in four (10%) patients. Residual disease evaluated in the patients with CR by surface immunophenotyping had been demonstrated in 5 out of 16 (31%) patients after the first treatment and in one out of four (25%) patients after re-treatment. The median progression-free survival (PFS) was 16 months (range 3-39) for the first treatment and 9.5 months (range 3-18) for re-treatment (P=0.34). Grade III or IV neutropenia was observed in 20% patients during the first treatment and in 35% patients during re-treatment (P=0.1). 2-CdA-induced thrombocytopenia occurred in 20% and 42% of the patients, respectively (P=0.05). Anemia was also more frequent during re-treatment (35%) than during the first treatment (7%) (P=0.007). Autoimmune hemolytic anemia developed in four (10%) of the patients during or after re-treatment. Severe infections, including pneumonia and herpes reactivation, occurred in 11 patients during the first treatment and in 10 patients during re-treatment. Twelve (30%) patients died during the study. Infections were the cause of death in six and AIHA in two patients. In conclusion, 2-CdA applied in monotherapy or in combination with prednisone or cyclophosphamide and mitoxantrone has therapeutic activity in some B-CLL patients in whom these drugs induced earlier complete or partial remission. However, since the second response is usually shorter and myelotoxicity more pronounced than during the first therapy, more clinical trials to find other therapeutical approaches are necessary.