Cladribine in the treatment of chronic lymphocytic leukemia

Solute Carrier Nucleoside Transporters in Hematopoiesis and Hematological Drug Toxicities: A Perspective

Simple Summary

Anticancer nucleoside analogs are promising treatments that often result in damaging toxicities and therefore ineffective treatment. Mechanisms of this are not well-researched, but cellular nucleoside transport research in mice might provide additional insight given transport’s role in mammalian hematopoiesis. Cellular nucleoside transport is a notable component of mammalian hematopoiesis due to how mutations within it relate to hematological abnormities. This review encompasses nucleoside transporters, focusing on their inherent properties, hematopoietic role, and their interplay in nucleoside drug treatment side effects. We then propose potential mechanisms to explain nucleoside transport involvement in blood disorders. Finally, we point out and advocate for future research areas that would improve therapeutic outcomes for patients taking nucleoside analog therapies.

Abstract

Anticancer nucleoside analogs produce adverse, and at times, dose-limiting hematological toxicities that can compromise treatment efficacy, yet the mechanisms of such toxicities are poorly understood. Recently, cellular nucleoside transport has been implicated in normal blood cell formation with studies from nucleoside transporter-deficient mice providing additional insights into the regulation of mammalian hematopoiesis. Furthermore, several idiopathic human genetic disorders have revealed nucleoside transport as an important component of mammalian hematopoiesis because mutations in individual nucleoside transporter genes are linked to various hematological abnormalities, including anemia. Here, we review recent developments in nucleoside transporters, including their transport characteristics, their role in the regulation of hematopoiesis, and their potential involvement in the occurrence of adverse hematological side effects due to nucleoside drug treatment. Furthermore, we discuss the putative mechanisms by which aberrant nucleoside transport may contribute to hematological abnormalities and identify the knowledge gaps where future research may positively impact treatment outcomes for patients undergoing various nucleoside analog therapies.

Pharmacophore-based screening and drug repurposing exemplified on glycogen synthase kinase-3 inhibitors

The current study was conducted to elaborate a novel pharmacophore model to accurately map selective glycogen synthase kinase-3 (GSK-3) inhibitors, and perform virtual screening and drug repurposing. Pharmacophore modeling was developed using PHASE on a data set of 203 maleimides. Two benchmarking validation data sets with focus on selectivity were assembled using ChEMBL and PubChem GSK-3 confirmatory assays. A drug repurposing experiment linking pharmacophore matching with drug information originating from multiple data sources was performed. A five-point pharmacophore model was built consisting of a hydrogen bond acceptor (A), hydrogen bond donor (D), hydrophobic (H), and two rings (RR). An atom-based 3D quantitative structure-activity relationship (QSAR) model showed good correlative and satisfactory predictive abilities (training set [Formula: see text]; test set: [Formula: see text]; whole data set: stability [Formula: see text]). Virtual screening experiments revealed that selective GSK-3 inhibitors are ranked preferentially by Hypo-1, but fail to retrieve nonselective compounds. The pharmacophore and 3D QSAR models can provide assistance to design novel, potential GSK-3 inhibitors with high potency and selectivity pattern, with potential application for the treatment of GSK-3-driven diseases. A class of purine nucleoside antileukemic drugs was identified as potential inhibitor of GSK-3, suggesting the reassessment of the target range of these drugs.

The role of transporters in the toxicity of nucleoside and nucleotide analogs

INTRODUCTION

Two families of nucleoside analogs have been developed to treat viral infections and cancer, but these compounds can cause tissue- and cell-specific toxicity related to their uptake and subcellular activity, which are dictated by host enzymes and transporters. Cellular uptake of these compounds requires nucleoside transporters that share functional similarities but differ in substrate specificity. Tissue-specific cellular expression of these transporters enables nucleoside analogs to produce their tissue-specific toxic effects, a limiting factor in the treatment of retroviruses and cancer.

AREAS COVERED

This review discusses the families of nucleoside transporters and how they mediate cellular uptake of nucleoside analogs. Specific focus is placed on examples of known cases of transporter-mediated cellular toxicity and classification of the toxicities resulting. Efflux transporters are also explored as a contributor to analog toxicity and cell-specific effects.

EXPERT OPINION

Efforts to modulate transporter uptake/clearance remain long-term goals of oncologists and virologists. Accordingly, subcellular approaches that either increase or decrease intracellular nucleoside analog concentrations are eagerly sought and include transporter inhibitors and targeting transporter expression. However, additional understanding of nucleoside transporter kinetics, tissue expression and genetic polymorphisms is required to design better molecules and better therapies.

Cladribine and Fludarabine Nucleoside Change the Levels of CD Antigens on B-Lymphoproliferative Disorders

The purine analogs, fludarabine nucleoside (FdA), and cladribine (CdA) (1 μM, 24 hours), significantly changed the levels of some surface antigens on the human B-cell lines MEC2 and Raji. Changes in the surface proteins were identified using a Cluster of Differentiation (CD) antibody microarray that captures live cells and confirmed by flow cytometry. For Raji cells, CdA up-regulated CD10, CD54, CD80, and CD86, with repression of CD22, while FdA up-regulated CD20, CD54, CD80, CD86 and CD95. For MEC2 cells, CdA up-regulated CD11a, CD20, CD43, CD45, CD52, CD54, CD62L, CD80, CD86, and CD95, but FdA had no effect. Up-regulation of particular CD antigens induced on a B-cell lymphoproliferative disorder by a purine analog could provide targets for therapeutic antibodies with synergistic cell killing.

Cladribine: not just another purine analogue?

Cladribine was synthesized as a purine analogue drug that inhibited adenosine deaminase. It received FDA approval in the 1980s for treatment of hairy cell leukemia. Given its toxicity towards lymphocytes and its corresponding immunosuppressive effects, it has been studied and found efficacious in a variety of hematologic malignancies and autoimmune conditions, most recently multiple sclerosis. This review highlights pharmacological, toxicological and clinical data for the use of cladribine. It also discusses existing and new mechanisms that may contribute to its unique clinical activity. Emerging data show that in addition to its known purine nucleoside analogue activity, cladribine possesses epigenetic properties, inhibiting S-adenosylhomocysteine hydrolase and DNA methylation. This may contribute to its efficacy and highlights the importance of studying combination therapy with other epigenetic or targeted agents. Clinical trials are underway in a variety of malignant and nonmalignant conditions.

Changes in leukemic cell nuclei revealed by differential scanning calorimetry

Using differential scanning calorimetry we analyzed the thermal profiles of nuclei from normal and B-cell chronic lymphocytic leukemia mononuclear cells. Intact nuclear fraction of normal mononuclear cells is characterized by four thermal transitions, i.e., at 60, 70, 83 and 103 degrees C. Leukemic nuclear samples revealed the transitions at 67 and 83 degrees C, however, in more aggressive stage of the disease additional thermal peaks at 76 and 93 degrees C were observed. Our very preliminary results revealed that mononuclear cell nuclear fraction from blood of patients responding to the used therapy, i.e., cladribine alone or its combination with mitoxantrone and cyclophosphamide indicates decrease (or even loss) of transition at 93 degrees C concomitant with increase of transition at 76 degrees C. A complementary study showed that in mononuclear cells of patients who appeared to be sensitive to chemotherapy the decrease of antiapoptotic Bcl-2 protein expression and signs of apoptotic morphology were observed.

Characterization of the B cell epitopes associated with a truncated form of Pseudomonas exotoxin (PE38) used to make immunotoxins for the treatment of cancer patients

Recombinant immunotoxins composed of an Ab Fv fragment joined to a truncated portion of Pseudomonas exotoxin A (termed PE38) have been evaluated in clinical trials for the treatment of various human cancers. Immunotoxin therapy is very effective in hairy cell leukemia and also has activity in other hemological malignancies; however, a neutralizing Ab response to PE38 in patients with solid tumors prevents repeated treatments to maximize the benefit. In this study, we analyze the murine Ab response as a model to study the B cell epitopes associated with PE38. Sixty distinct mAbs to PE38 were characterized. Mutual competitive binding of the mAbs indicated the presence of 7 major epitope groups and 13 subgroups. The competition pattern indicated that the epitopes are discrete and could not be reproduced using a computer simulation program that created epitopes out of random surface residues on PE38. Using sera from immunotoxin-treated patients, the formation of human Abs to each of the topographical epitopes was demonstrated. One epitope subgroup, E1a, was identified as the principal neutralizing epitope. The location of each epitope on PE38 was determined by preparing 41 mutants of PE38 in which bulky surface residues were mutated to either alanine or glycine. All 7 major epitope groups and 9 of 13 epitope subgroups were identified by 14 different mutants and these retained high cytotoxic activity. Our results indicate that a relatively small number of discrete immunogenic sites are associated with PE38, most of which can be eliminated by point mutations.

Quantitation of synergism of arabinosylcytosine and cladribine against the growth of arabinosylcytosine-resistant human lymphoid cells

This report presents a quantitative analysis of the synergistic interaction of arabinosylcytosine (araC) and cladribine (CdA) in human H9-lymphoid cell lines sensitive and resistant to araC (H9-araC cells). H9-araC cells obtained by cultivation of H9 cells in the presence of 0.5 microM arabinosylcytosine (araC) had lower deoxycytidine kinase (dCK) than the parental cell line. The IC50 values of araC and CdA calculated by using median-effect analysis and CalcuSyn software were: 0.55 microM and 1.16 microM for CdA and 0.0058 microM and 3.5 microM for araC in H9 and H9-araC cells, respectively. These values were reduced to 0.10 microM and 0.38 microM for CdA and to 0.004 microM and to 0.77 microM for araC when the drugs were used in combination. Computerized simulation of dose reduction index (DRI) indicated that at 50-99% growth inhibition levels, the doses of araC could be reduced by 2.0 to 11.9-fold and 2.9 to 5.3-fold and the doses of CdA by 5.9 and 183.7-fold and 3.1 to 164.8-fold in H9 and H9-araC cells, respectively, when the drugs are used in combination. Assessment by combination index (CI) analysis showed that the combination exhibited moderate to strong synergistic lympho-cytotoxic effects. CdA metabolic studies (influx and activation) in the presence of deoxyadenosine, deoxycytidine, or araC suggested that CdA enters cells by a deoxyadenosine-inhibitable transport system, which is different than that of araC and deoxycytidine transport system. Thus, in addition to the known mechanisms, other mechanisms might be involved in the metabolism of CdA. The demonstration that araC and CdA combinations exert synergistic cytotoxicity even in the resistant cells raises hope that such a combination may be useful in tumors that were found resistant to these drugs.

Therapy of Chronic Lymphocytic Leukaemia with Purine Nucleoside Analogues

Chronic lymphocytic leukaemia (CLL) is a neoplastic disease of unknown aetiology characterised by an absolute lymphocytosis in peripheral blood and bone marrow. The disease is diagnosed most commonly in the elderly with the median age at diagnosis being about 65 years. The purine nucleoside analogues (PNAs) fludarabine, cladribine (2-chlorodeoxyadenosine) and pentostatin (2'-deoxycoformycin) are highly active in CLL, both in previously treated and in refractory or relapsed patients. These three agents share similar chemical structures and mechanisms of action such as induction of apoptosis. However, they also exhibit significant differences, especially in their interactions with enzymes involved in adenosine and deoxyadenosine metabolism. Recent randomised studies suggest that fludarabine and cladribine have similar activity in CLL. However, clinical observations indicate the existence of cross-resistance between fludarabine and cladribine. Patients who received PNAs as their initial therapy and achieved long-lasting response can be successfully retreated with the same agent. PNAs administered in combination with other chemotherapeutic agents and/or monoclonal antibodies may produce higher response rates, including complete response (CR) or molecular CR, compared with PNAs alone or other treatment regimens. Management decisions are more difficult in elderly patients because of the apparent increase in toxicity of PNAs in this population. In elderly patients, we recommend chlorambucil as the first-line treatment, with PNAs in lower doses in refractory or relapsed patients. Myelosuppression and infections, including opportunistic varieties, are the most frequent adverse effects in patients with CLL treated with PNAs. Therefore, some investigators recommend routine antibacterial and antiviral prophylaxis during and after PNA treatment. This review presents current results and treatment strategies with the use of PNAs in CLL, especially in elderly patients.

The place of cladribine in the treatment of chronic lymphocytic leukemia: a 10-year experience in Poland

Cladribine (2-CdA) is structurally similar to another purine analog, fludarabine (FA), recently accepted in several centers as the first-line treatment in chronic lymphocytic leukemia (CLL). Unfortunately, there is less experience with the use of 2-CdA than with FA in patients with CLL in the majority of Western countries. In the last decade we performed several phase II studies and two phase III randomized trials to evaluate the activity and toxicity of 2-CdA in previously treated and untreated patients with CLL. We have also compared the results of Polish studies with the data presented by other investigators. Similarly to FA this agent has been found to be more effective in previously untreated CLL than in patients refractory to or relapsed after conventional therapy with alkylating agents. In different studies the overall response (OR) rate ranged from 70 to 85% and complete response (CR) from 10 to 47%. Higher CR and OR rates in CLL patients treated with 2-CdA and prednisone than with chlorambucil and prednisone were confirmed in our multicenter, randomized study. Subsequently, we performed a multicenter, randomized study comparing 2-CdA alone with a combination of 2-CdA and cyclophosphamide (CC) or cyclophosphamide and mitoxantrone (CMC). Our updated results seem to indicate that the CC program used as a first-line therapy in CLL gives higher CR and OR and better elimination of minimal residual disease (MRD) than 2-CdA alone. CC is also less myelotoxic than CMC. More recently, we have undertaken a phase II study to determine the efficacy and toxicity of 2-CdA combined with the anti-CD20 monoclonal antibody rituximab in CLL and other refractory or relapsed indolent lymphoproliferative disorders. The preliminary results seem to be better than in similar patients previously treated in our institution with 2-CdA alone. In conclusion, the studies performed in the last decade in Poland and other countries have shown that 2-CdA used alone or in combination with other agents is, similarly to FA, a highly active and relatively safe agent in previously treated and untreated patients with CLL.

Transport of physiological nucleosides and anti-viral and anti-neoplastic nucleoside drugs by recombinant Escherichia coli nucleoside-H(+) cotransporter (NupC) produced in Xenopus laevis oocytes

The recently identified human and rodent plasma membrane proteins CNT1, CNT2 and CNT3 belong to a gene family (CNT) that also includes the bacterial nucleoside transport protein NupC. Heterologous expression in Xenopus oocytes has established that CNT1-3 correspond functionally to the three major concentrative nucleoside transport processes found in human and other mammalian cells (systems cit, cif and cib, respectively) and mediate Na(+) - linked uptake of both physiological nucleosides and anti-viral and anti-neoplastic nucleoside drugs. Here, one describes a complementary Xenopus oocyte transport study of Escherichia coli NupC using the plasmid vector pGEM-HE in which the coding region of NupC was flanked by 5'- and 3'-untranslated sequences from a Xenopus beta-globin gene. Recombinant NupC resembled human (h) and rat (r) CNT1 in nucleoside selectivity, including an ability to transport adenosine and the chemotherapeutic drugs 3'-azido-3'-deoxythymidine (AZT), 2',3'- dideoxycytidine (ddC) and 2'-deoxy-2',2'-difluorocytidine (gemcitabine), but also interacted with inosine and 2',3'- dideoxyinosine (ddl). Apparent affinities were higher than for hCNT1, with apparent K(m) values of 1.5-6.3 microM for adenosine, uridine and gemcitabine, and 112 and 130 microM, respectively, for AZT and ddC. Unlike the relatively low translocation capacity of hCNT1 and rCNT1 for adenosine, NupC exhibited broadly similar apparent V(max) values for adenosine, uridine and nucleoside drugs. NupC did not require Na(+) for activity and was H(+) - dependent. The kinetics of uridine transport measured as a function of external pH were consistent with an ordered transport model in which H(+) binds to the transporter first followed by the nucleoside. These experiments establish the NupC-pGEM-HE/oocyte system as a useful tool for characterization of NupC-mediated transport of physiological nucleosides and clinically relevant nucleoside therapeutic drugs.

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.

Metabolic response patterns of nucleotides in B-cell chronic lymphocytic leukaemias to cladribine, fludarabine and deoxycoformycin

Nucleotides (NTPs and dNTPs) have been measured in patient-derived chronic lymphocytic leukaemia (CLL) cells stimulated with TPA plus ionomycin and then exposed to cladribine, fludarabine or deoxycoformycin (1 microM, 16 h). dNTPs were not measurable in 10(8) unstimulated CLL cells which are quiescent. Time-dependent changes in nucleotides in CLL cells showed that the mechanism of action changed as the drug triphosphate accumulated. dCf induced substantial accumulation of dATP in CLL cells in culture, and similar levels of dATP in the same patient during subsequent treatment with dCf. Determination of "metabolic response patterns" of nucleotides in CLL cells treated with drugs might distinguish patients with susceptible and refractory CLL prior to chemotherapy.

The Antileukemia Drug 2-Chloro-2′-deoxyadenosine: An Intrinsic Transcriptional Antagonist

The nucleoside analog 2-chloro-2'-deoxyadenosine (CldAdo; cladribine) is effective in the treatment of hairy cell leukemia and chronic lymphocytic leukemia. CldAdo is phosphorylated and incorporated into cellular DNA but is not an absolute chain terminator. We demonstrated by in vitro gel-shift assays that binding interactions of the human TATA box-binding protein (TBP) were disrupted on 2-chlorodeoxyadenosine monophosphate (CldAMP)-substituted TATA box consensus sequences. We hypothesized that human RNA polymerase II (pol II) transcriptional processes would therefore be affected by 2-chlorodeoxyadenosine triphosphate (CldATP) incorporation into a promoter TATA element. Double-stranded DNA templates containing the adenovirus major late promoter and coding sequences were enzymatically synthesized as control or with site-specific CldAMP residues, incubated with HeLa extract, and the synthesis of radiolabeled 44-base transcripts was assessed. With increasing amounts of HeLa extract, CldAMP substitution for dAMP within the TATA box decreased in vitro pol II transcription by approximately 35% compared with control substrates. Time-course studies showed that transcript production increased in a linear fashion on control substrates. In contrast, transcription on CldAMP-substituted TATA sequences reached a plateau after 20 min. Furthermore, CldAMP-substituted promoter sequences trapped or sequestered TBP, preventing its dissociation from DNA and subsequent binding to additional TATA elements to reinitiate transcription. CldAdo thus represents the first example of a nucleoside analog that acts as a transcriptional antagonist. CldATP incorporation into gene regulatory sequences may provide a novel strategy to modulate specific protein/DNA interactions.

2-Chlorodeoxyadenosine alone and in combination with cyclophosphamide and mitoxantrone induce apoptosis in B chronic lymphocytic leukemia cells in vivo

The purpose of the study was to determine some apoptotic events in mononuclear cells obtained from peripheral blood of patients with B-cell chronic lymphocytic leukemia (B-CLL) during and after therapy with 2-chlorodeoxyadenosine (2-CdA; C), and the combination of 2-CdA with cyclophosphamide (CC), or 2-CdA with mitoxantrone and cyclophosphamide (CMC). Western blot technique was performed to estimate expression/proteolytic degradation of generally accepted apoptotic markers, i.e., Bcl-2 protein, lamin B, PARP-1, and caspase-3 in leukemic cells isolated from blood samples of patients before treatment and subjected to drug(s) administration. The decrease of antiapoptotic protein Bcl-2 expression and proteolytic cleavage of nuclear proteins--lamin B and PARP-1 were observed in leukemic cells of patients treated according to the above therapy protocols, however, each to a different level among the studied groups. The obtained results indicated also that procaspase-3 was cleaved and activated in leukemic cells of three drug(s) treated groups. However, the cleavage of procaspase-3 and the generation of fragments with mol. mass of 17/20 kDa occurred especially effectively among patients treated according to CMC regimen. The changes in expression/proteolytic degradation of the above selected apoptotic markers, are accompanied by the appearance of apoptotic morphology in leukemic cells originated from blood of patients treated with the above drug(s) in comparison to untreated ones.

2-Chloro-2'-deoxyadenosine: alteration of DNA:TATA element binding protein (TBP) interactions

2-Chloro-2'-deoxyadenosine (CldAdo, cladribine) is used therapeutically for hairy cell and other leukemias. The nucleoside is converted in leukemia cells to the 2-Cl-analog of dATP and incorporated into DNA, where it may alter binding of transcription factors to gene regulatory AT-rich sequences. Here we model the effects of CldATP incorporation into the adenovirus major late promoter TATA element recognized by TATA binding protein (TBP). The modeling results are consistent with experimental studies of DNA:TBP binding and indicate which positions in the canonical TATA sequence are most severely affected by CldATP incorporation.FIGURE Structure of the DNA:TBP complex. The protein is shown as a ribbon structure, and the DNA as a stick model

Caspase-mediated cell death in hematological malignancies: theoretical considerations, methods of assessment, and clinical implications

Apoptosis, the caspase-mediated cell death, plays an important role in the etiology, pathogenesis and therapy of a variety of diseases. Abnormalities of apoptosis regulation, resulting in either its inhibition or enhancement, play a key role in the development of various malignant hematological disorders. Several routine and new therapeutic strategies in Oncohematology are based on apoptosis modulation. Cytotoxic effects of most antineoplastic drugs are based on induction of apoptosis. The accurate estimate of incidence of apoptosis, therefore, is of importance in Oncohematology. In this review we provide an overview of the methods designed to measure the incidence of apoptosis, including the recently developed assays that are based on detection of caspases activation. We also review recent findings on the role of caspase-mediated cell death in hematological malignancies and discuss their clinical implications, including new therapeutical strategies that evolve from these findings.

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

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

Treatment of pure red cell aplasia and autoimmune haemolytic anaemia in chronic lymphocytic leukaemia with Campath-1H

A patient with chronic lymphocytic leukaemia (CLL) progressive on fludarabine therapy and life-threatening anaemia related to immune haemolysis and pure red cell aplasia was treated with Campath-1H. The patient had sustained complete remission of both CLL and anaemia, but died of recurrent sepsis and cachexia 10 months after completion of the treatment. Campath-1H (alemtuzumab), a humanised anti-CD52 monoclonal antibody, is a potent therapeutic agent against advanced CLL and immune cytopenias. It could be indicated in the treatment of severe immune complications of CLL unresponsive to corticosteroids. Prolonged immunosuppression is a serious side-effect leading to severe infectious complication.

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.

Successful treatment of leukaemia cutis with cladribine in a patient with B-cell chronic lymphocytic leukaemia

Cutaneous presentation of B-cell chronic lymphocytic leukaemia (B-CLL) is uncommon, and the influence of skin changes on B-CLL prognosis is unclear. We report a patient with B-CLL Rai II, with multiple nodular skin infiltrations on the trunk, upper arms and thighs as well as constitutional symptoms, who was successfully treated with cladribine. The peripheral blood (PB) lymphocytes were CD19, CD20, CD23 and CD5 positive, which confirmed the diagnosis of B-CLL. Skin biopsy of one of the lesions showed an intense infiltrate composed of small lymphocytes with no epidermotropism. These cells also showed the expression of CD19, CD20, CD23 and CD5 antigens similar to those presented on PB lymphocytes. Polymerase chain reaction performed on bone marrow lymphocytes and a lesional skin biopsy using consensus primers for immunoglobulin heavy-chain genes also showed the same monoclonal population of B lymphocytes both in the bone marrow and in the skin. The patient received four courses of cladribine 0.12 mg kg-1 daily as a 2-h infusion for five consecutive days. The courses were repeated at monthly intervals. The lymphocytosis gradually decreased and the PB count normalized after three courses. At the same time, a significant decrease in the cutaneous symptoms was observed. The patient became free of skin tumours after the fourth course of cladribine; only slight discoloration at the previous sites of cutaneous infiltration remained. There was no relapse of leukaemia cutis during a further 7 months of observation.

Anthracyclines potentiate activity against murine leukemias L1210 and P388 in vivo and in vitro

The interactions of 2-chlorodeoxyadenosine (2-CdA, cladribine) and three anthracyclines: doxorubicin (DOX), idarubicin (IDA) and mitoxantrone (MIT) were evaluated on murine leukemias P388 and L1210. Prolongation of survival time of animals receiving drugs in combination compared to mice treated with drugs in monotherapy was tested. We have also evaluated interactions of the cytostatics on murine leukemias in vitro by measuring their inhibitory effects on P388 and L1210 cell proliferation. We have observed a synergistic effect of MIT and IDA in combination with 2-CdA on P388 leukemia resulting in an increase of life span (ILS)=226% in case of MIT+2-CdA and ILS=126% in the case of IDA+2-CdA, whereas 2-CdA used as a sole drug resulted in an ILS=47%. The survival time of animals inoculated with P388 leukemic cells and treated with DOX+ 2-CdA was similar to ILS gained by DOX monotherapy (178% and 200% respectively). The mice bearing L1210 leukemia receiving combined chemotherapy lived significantly longer than the animals on single agent regimens. The animals treated with schedule 2-CdA+MIT lived significantly longer (P=0.004) as compared to the groups receiving drugs in monotherapy (ILS of 2-CdA+MIT group=60%, ILS of MIT group 33%, and 2-CdA group 33%). Finally, combination of DOX or IDA with 2-CdA resulted in ILS =73% (2-CdA+DOX regimen), and ILS=60% in case of 2-CdA+IDA regimen, which is significantly higher than ILS gained on monotherapy schedules. In vitro tests revealed that all tested anthracyclines enhance the antiproliferative activity of 2-CdA against L1210 and P388 leukemic cells (P<0.05). Our study has shown that all anthracyclines potentiate 2-CdA antileukemic activity, both in vivo and in vitro. It failed however to point the best one to be combined with cladribine. We suggests that further clinical trials with such combinations are needed.

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

The newer purine nucleoside analogues (PNA), fludarabine (FAMP) and cladribine (2-chlorodeoxyadenosine, 2-CdA) have been synthesized recently and introduced into the treatment of chronic lymphocytic leukemia (CLL). The results of large phase II studies indicate that FAMP and 2-CdA are similarly active in CLL. Unfortunately, no prospective randomized study comparing the results of the treatment of CLL patients with FAMP and 2-CdA has been published so far. Significantly higher overall response (OR) and complete remission (CR) in patients treated initially with PNA than with chlorambucil or cyclophosphamide based combination regimens has been recently confirmed in five prospective multicentre randomized trials. These studies have also shown longer response duration in patients treated with PNA than with conventional chemotherapy. Overall survival progression free and events free survival were similar in patients treated with PNA and with chlorambucil or other alkylating agent based regimens. However, the majority of randomized trials were designed as cross over studies and most patients, treated with conventional chemotherapy were given PNA when refractory or in early relapse, which may influence the survival time. The results of a randomized study have shown a higher incidence of neutropenia and infections in patients treated with PNA than with chlorambucil. However. the frequency of autoimmune hemolytic anemia, pure red cell aplasia, secondary neoplasms and Richter's syndrome seems to be similar in patients treated with PNA and standard alkylating agents based chemotherapy. In conclusion, alkylating agents still have an important place in the routine management of the majority of CLL patients. They are in general safe, given on an out patients basis and significantly cheaper than PNA. PNA should be routinely used as second line treatment, and possibly as first line therapy in younger patients, who are candidates for potentially curative treatment such as stem cell transplantation and/or monoclonal antibodies.

Chronic lymphocytic leukemia

This update of early stage B-cell chronic lymphocytic leukemia (B-CLL) embraces current information on the diagnosis, biology, and intervention required to more fully develop algorithms for management of this disease. Emphasis on early stage is based on the rapid advancement in our understanding of the disease parameters and our increasing ability to predict for a given early stage patient whether there is a need for more aggressive management. In Section I, Dr. Terry Hamblin addresses the nature of the disease, accurate diagnostic procedures, evidence for an early "preclinical" phase, the use of newer prognostic features to distinguish who will be likely to progress or not, and whether it is best to watch or treat early stage disease. In Section II, Dr. Neil Kay and colleagues address the biologic aspects of the disease and how they may relate to disease progression. Review of the newer insights into gene expression, recurring genetic defects, role of cytokines/autocrine pathways, and the interaction of the CLL B cell with the microenvironment are emphasized. The relationship of these events to both trigger disease progression and as opportunities for future therapeutic intervention even in early stage disease is also considered. In Section III, Dr. John Byrd and colleagues review the historical and now current approaches to management of the previously untreated progressive B-CLL patient. They discuss what decision tree could be used in the initial decision to treat a given patient. The use of single agents versus newer combination approaches such as chemoimmunotherapy are discussed here. In addition, the place of marrow transplant and some of the newer antibodies available for treatment of B-CLL are considered. Finally, a challenge to utilize our growing knowledge of the biology of B-CLL in the early stage B-CLL is proffered.