The role of fludarabine in hematological malignancies

Fludarabine-induced bradycardia in allogeneic hematopoietic stem cell transplantation: A retrospective study

INTRODUCTION

Fludarabine, a purine analog, is getting more attention with the increasing use of reduced intensive conditioning regimens in allogeneic hematopoietic stem cell transplantation (allo-HSCT). The side effect of bradycardia was observed in only a few cases reported in the literature. In clinical practice, bradycardia can be asymptomatic or cause syncope and cardiac arrest. This study aimed to evaluate the bradycardia side effect of fludarabine used in the conditioning regimen in allo-HSCT recipients and to increase awareness of this issue.

METHODS

This retrospective study included 73 patients who received fludarabine in the allo-HSCT conditioning regimen between January 2015 and January 2021. Patients with and without bradycardia were compared regarding demographic data, allo-HSCT characteristics, electrolyte values, fludarabine administration dose and duration, and survival. Univariate and multivariate analyzes were performed to evaluate independent predictors for fludarabine-induced bradycardia.

RESULTS

Fludarabine administration doses and days were higher in the bradycardia group, but no statistically significant difference was observed. In the multivariate analysis, age was the only independent predictor of fludarabine-induced bradycardia (odds ratio (OR) 0.93, 95% confidence interval (CI): 0.89-0.98, p = 0.007). The median age in the group with bradycardia was 19 years younger than those without bradycardia (34 (19-49) vs 53 (19-69), p = 0.005). In 11 (84.6%) of the patients who had bradycardia, bradycardia improved with the discontinuation of fludarabine alone, but atropine was administered in 2 (15.4%) patients.

CONCLUSION

Age was the only independent predictor of fludarabine-induced bradycardia; therefore, close heart rate monitoring is recommended during fludarabine administration, especially in younger patients.

Inhibitors of the Cancer Target Ribonucleotide Reductase, Past and Present

Ribonucleotide reductase (RR) is an essential multi-subunit enzyme found in all living organisms; it catalyzes the rate-limiting step in dNTP synthesis, namely, the conversion of ribonucleoside diphosphates to deoxyribonucleoside diphosphates. As expression levels of human RR (hRR) are high during cell replication, hRR has long been considered an attractive drug target for a range of proliferative diseases, including cancer. While there are many excellent reviews regarding the structure, function, and clinical importance of hRR, recent years have seen an increase in novel approaches to inhibiting hRR that merit an updated discussion of the existing inhibitors and strategies to target this enzyme. In this review, we discuss the mechanisms and clinical applications of classic nucleoside analog inhibitors of hRRM1 (large catalytic subunit), including gemcitabine and clofarabine, as well as inhibitors of the hRRM2 (free radical housing small subunit), including triapine and hydroxyurea. Additionally, we discuss novel approaches to targeting RR and the discovery of new classes of hRR inhibitors.

Clinical pharmacology and clinical trials of ribonucleotide reductase inhibitors: is it a viable cancer therapy?

PURPOSE

Ribonucleotide reductase (RR) enzymes (RR1 and RR2) play an important role in the reduction of ribonucleotides to deoxyribonucleotides which is involved in DNA replication and repair. Augmented RR activity has been ascribed to uncontrolled cell growth and tumorigenic transformation.

METHODS

This review mainly focuses on several biological and chemical RR inhibitors (e.g., siRNA, GTI-2040, GTI-2501, triapine, gemcitabine, and clofarabine) that have been evaluated in clinical trials with promising anticancer activity from 1960's till 2016. A summary on whether their monotherapy or combination is still effective for further use is discussed.

RESULTS

Among the RR2 inhibitors evaluated, GTI-2040, siRNA, gallium nitrate and didox were more efficacious as a monotherapy, whereas triapine was found to be more efficacious as combination agent. Hydroxyurea is currently used more in combination therapy, even though it is efficacious as a monotherapy. Gallium nitrate showed mixed results in combination therapy, while the combination activity of didox is yet to be evaluated. RR1 inhibitors that have long been used in chemotherapy such as gemcitabine, cladribine, fludarabine and clofarabine are currently used mostly as a combination therapy, but are equally efficacious as a monotherapy, except tezacitabine which did not progress beyond phase I trials.

CONCLUSIONS

Based on the results of clinical trials, we conclude that RR inhibitors are viable treatment options, either as a monotherapy or as a combination in cancer chemotherapy. With the recent advances made in cancer biology, further development of RR inhibitors with improved efficacy and reduced toxicity is possible for treatment of variety of cancers.

A cell culture system that mimics chronic lymphocytic leukemia cells microenvironment for drug screening and characterization

Chronic Lymphocytic Leukaemia (CLL) is an incurable disease that warrants new therapeutic treatments. CLL cells accumulate in the peripheral blood, in the bone marrow and in secondary lymphoid organs. Unlike circulating CLL cells, CLL cells resident in these last two compartments display high chemoresistance and proliferative capacity. Given the importance of the microenvironment in this disease, strategies that aim to develop new therapeutic agents need to consider this critical factor. Various cell culture conditions have been described that attempt to emulate either the different types of microenvironments in which CLL cells are found or an individual component of a particular microenvironment. Here, a methodology that partially mimics the interaction between CLL cells and the CD3+ CD4+ CD154+ T cells is described. Moreover, within this method, two protocols are presented and compared that may partially recapitulate different physiological states. The methodology can be exploited for target validation and drug development in CLL.

In SituEvaluation of Fludarabine-DNA Interaction Using a DNA-Electrochemical Biosensor

Fludarabine, 9-β-D-arabinosyl-2-fluoroadenine, the nucleoside analog, represents a highly effective treatment for hairy cell leukemia. The electrochemical behaviour of fludarabine is an irreversible diffusion controlled oxidation mechanism and was investigated at a glassy carbon electrode in different supporting electrolytes using cyclic, differential pulse, and square wave voltammetry. The diffusion coefficient of fludarabine was calculated to beDFLU=1.71×10−6 cm2s-1in pH 7.0 0.1 M phosphate buffer. The oxidation mechanism of fludarabine occurs with the transfer of one proton and one electron and the formation of a hydroxylated species. The interaction of fludarabine with DNA was investigated, by differential pulse voltammetry, in incubated solutions and using dsDNA- and polyhomonucleotides-, poly[G] and poly[A], electrochemical biosensors. The results showed that fludarabine interacts with DNA causing changes in the DNA structure.

Treatment of patients with fludarabine-refractory chronic lymphocytic leukemia: need for new treatment options

Fludarabine-refractory chronic lymphocytic leukemia is associated with poor survival rates. Chemoimmunotherapy combinations that include purine analogs, alkylating agents, and monoclonal antibodies have shown the highest response rates to date. Intensive treatment approaches can be associated with poor tolerability that is often characterized by deteriorating immune functions and high infection rates. Treatment with some monoclonal antibodies is often complicated by infusion-related adverse events and increased risk of infections. Several novel agents are currently being investigated for this difficult-to-treat patient population. Ofatumumab is an anti-CD20 monoclonal antibody that targets a different epitope from the one targeted by rituximab and, it has shown promising antileukemia activity. Lenalidomide is an immunomodulatory agent that has shown promising activity in patients with fludarabine-refractory chronic lymphocytic leukemia, many of whom had poor prognostic features and bulky disease. Encouraging results have been observed with each of these agents individually. However, given the diverse mechanisms governing CLL pathogenesis and disease progression, ongoing clinical trials combinations of these agents may improve clinical outcomes for this patient population.

Chemotherapeutic agents and the skin: An update

Chemotherapeutic agents give rise to numerous well described adverse effects that may affect the skin, hair, mucous membranes, or nails. The mucocutaneous effects of longstanding agents have been extensively studied and reviewed. Over the last 2 decades, a number of new molecular entities for the treatment of cancer have been approved by the United States Food and Drug Administration (FDA). This article reviews the cutaneous toxicity patterns of these agents. It also reviews one drug that has not received FDA approval but is in use outside the United States and is important dermatologically. Particular emphasis is placed on the novel signal transduction inhibitors as well as on newer literature pertaining to previously described reactions.

LEARNING OBJECTIVES

At the completion of this learning activity, participants should able to list the newer chemotherapeutic agents that possess significant mucocutaneous side effects and describe the range of reactions that are seen with each drug. In addition, they should be able to formulate appropriate management strategies for these reactions.

In vitro susceptibility of CD4+ and CD8+ T cell subsets to fludarabine

Administration of the adenosine analogue fludarabine (FLU) in vivo induces a profound and prolonged T lymphopenia which mainly affects CD4(+) cells. To better understand the mechanistic basis underlying this preferential depletion, we analyzed the in vitro susceptibility of T cell subsets to FLU-induced apoptosis. Contrasting with observations in vivo, our results showed that treatment of peripheral blood mononuclear cells with FLU induced a higher level of apoptosis in CD8(+) than in CD4(+) T lymphocytes. This increased sensitivity of CD8(+) T cells to FLU was observed in samples from both, healthy donors and B cell chronic lymphocytic leukemia patients, and resulted in higher CD4:CD8 ratios in FLU-treated than in untreated cultures (P<0.01). Expression of factors involved in FLU transport and metabolism was then evaluated by quantitative real time-PCR in normal T cell subsets. It was found that mRNA levels of human equilibrative nucleoside transporter-1 nucleoside transporter were higher whereas deoxycytidine kinase and IMP/GMP selective 5'-nucleotidase mRNA levels were lower in CD4(+) cells. However the dCK/cN-II ratio was 2-fold greater in CD8(+) than in CD4(+) T lymphocytes, which could account for the higher apoptosis levels observed in the CD8(+) subset. These results favor the view that decreased CD4:CD8 ratios in FLU-treated patients should be attributed to differences in cell recovery and/or homing between T cell subsets.

Correlation between chromosome damage and apoptosis induced by fludarabine and idarubicin in normal human lymphocytes

Fludarabine (FLU, a fluorinated purine analog) and idarubicin (IDA, a DNA-topoisomerase II poison) are frequently used in cancer chemotherapy. The effects of these drugs on cultured normal human lymphocytes were studied to establish the possible involvement of chromosome damage in the apoptotic program. Chromosome aberrations (CA) were evaluated in first division metaphases and the apoptotic process was measured by morphological and electrophoretical techniques. The percentage of abnormal cells was increased from the doses of FLU 1.0 microg/ml and IDA 0.005 microg/ml (P<0.0001) with an important decrease in the mitotic index (MI) for the highest doses assayed. A significant dose-dependent induction of abnormal cells was observed for both drugs. An increase of apoptotic cells was found at 5.0 and 10.0 microg/ml of FLU (P<0.001) while IDA activated apoptosis at 0.05 microg/ml (P<0.01) and markedly from 0.1 microg/ml (P<0.001). These increments were dose dependent. Apoptotic cell morphology was associated with DNA fragmentation at the highest doses. The increased induction of abnormal cells and the decreased MI were in correlation with the apoptotic index for FLU and IDA, suggesting the role of CA in drug-induced cell death.

Therapy-related refractory anemia with ringed sideroblasts in chronic lymphocytic leukemia. involvement of 3q21 region

Therapy-related myelodysplastic syndrome/acute myelogenous leukemia (t-MDS/AML) is extremely rare in chronic lymphocytic leukemia (CLL) despite extensive use of alkylating agents. We present a case of heavily treated CLL with resultant therapy-related refractory anemia with ringed sideroblasts (RARS). A complex cytogenetic abnormality including involvement of 3q21 was detected and to our knowledge, is the first report of a RARS case with a 3q21 abnormality.

Distinct inhibitory effects of 2-chloro-2'-deoxyadenosine and 9-beta-D-arabinosyl-2-fluoroadenine on DNA methyltransferase in human T-lymphocytes

The effect of 2-chloro-2'-deoxyadenosine and 9-beta-D-arabinosyl-2-fluoroadenine on DNA methyltransferase activity in stimulated human T-lymphocytes was estimated. In comparative studies 5-aza-deoxycytidine and deoxyadenosine plus deoxycoformycin were used. These antileukemic compounds demonstrated different effects; both 2CdA and dAdo plus dCF, like 5-aza-dCyt, inhibited the enzyme activity by 85-90% after 72 hours activation of lymphocytes, while the effect of F-ara-A, under the same conditions, was insignificant.

Synthesis and biological activity of certain 4'-thio-D-arabinofuranosylpurine nucleosides

A series of 4'-thio-D-arabinofuranosylpurine nucleosides was prepared and evaluated as potential anticancer agents. The details of a convenient and high-yielding synthesis of the carbohydrate precursor 1-O-acetyl-2,3,5-tri-O-benzyl-4-thio-D-arabinofuranose (6) are presented. Proof of structure and configuration at all chiral centers of the nucleosides was obtained through an X-ray crystal structure of 9alpha as well as through NOE experiments on 9beta and 9alpha. All six target compounds were evaluated in a series of human cancer cell lines in culture. Two target compounds, beta anomers with diaminopurine (12) and guanine (16) as the bases, had significant cytotoxicity. One of these compounds (12) was selected for animal studies but was found to have no selectivity at the maximum tolerated dose in the murine colon 36 tumor model.