Pharmacokinetics of clofarabine in patients with high-risk inherited metabolic disorders undergoing brain-sparing hematopoietic cell transplantation

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.

Quantification of clofarabine in urine and plasma by LC-MS/MS: suitable for PK study and TDM in pediatric patients with relapsed or refractory ALL

Clofarabine is approved for the treatment of relapsed or refractory acute lymphoblastic leukemia (ALL) in pediatric patients aged 1 to 21 years.

Population Pharmacokinetics of Clofarabine as Part of Pretransplantation Conditioning in Pediatric Subjects before Hematopoietic Cell Transplantation

The primary objective of this work was to characterize the pharmacokinetics (PK) of systemic clofarabine (clo-fara) in pediatric allogeneic hematopoietic cell transplantation (HCT) recipients receiving either nucleoside monotherapy or a dual nucleoside analog preparative regimen. Fifty-one children (median age, 4.9 years; range, .25 to 14.9 years) undergoing allogeneic HCT for a variety of malignant and nonmalignant disorders underwent PK assessment. Plasma samples were collected over the 4 to 5 days of clo-fara treatment and quantified for clo-fara, using a validated liquid chromatography/tandem mass spectrometry assay. Nonlinear mixed-effects modeling was used to develop the population PK model, including identification of covariates that influenced drug disposition. In agreement with previously published models, a 2-compartment PK model with first-order elimination best described the PK of clo-fara. Final parameter estimates for clo-fara were consistent with previous reports and were as follows: clearance (CL), 23 L/h/15 kg; volume of the central compartment, 42 L/15 kg; volume of peripheral compartment, 47 L/15 kg; and intercompartmental CL, 9.8 L/h/15 kg. Unexplained variability was acceptable at 33%, and the additive residual error (reflective of the assay) was estimated to be 0.36 ng/mL. Patient-specific factors significantly impacting clo-fara CL included actual body weight and age. The covariate model was able to estimate clo-fara CL with good precision in children spanning a wide age range from infancy to early adulthood and demonstrates the need for variable dosing in children of different ages. For example, the dose required for a 6-month and 1-year old was approximately 43% and 17% lower, respectively, than the typical 40 mg/m²dose to achieve the median AUC_0-24of 1.04 mg·h/L in the study population. Despite the known renal elimination of clo-fara, no significant clinical parameters for renal function were retained in the final model (P> .05). Coadministration of fludarabine with clo-fara did not alter the CL of clo-fara (P> .05). These results will help inform individualized dosing strategies for clo-fara to improve clinical outcomes and limit drug-related adverse events in children undergoing HCT.

Genotypes Affecting the Pharmacokinetics of Anticancer Drugs

Cancer treatment is becoming more and more individually based as a result of the large inter-individual differences that exist in treatment outcome and toxicity when patients are treated using population-based drug doses. Polymorphisms in genes encoding drug-metabolizing enzymes and transporters can significantly influence uptake, metabolism, and elimination of anticancer drugs. As a result, the altered pharmacokinetics can greatly influence drug efficacy and toxicity. Pharmacogenetic screening and/or drug-specific phenotyping of cancer patients eligible for treatment with chemotherapeutic drugs, prior to the start of anticancer treatment, can identify patients with tumors that are likely to be responsive or resistant to the proposed drugs. Similarly, the identification of patients with an increased risk of developing toxicity would allow either dose adaptation or the application of other targeted therapies. This review focuses on the role of genetic polymorphisms significantly altering the pharmacokinetics of anticancer drugs. Polymorphisms in DPYD, TPMT, and UGT1A1 have been described that have a major impact on the pharmacokinetics of 5-fluorouracil, mercaptopurine, and irinotecan, respectively. For other drugs, however, the association of polymorphisms with pharmacokinetics is less clear. To date, the influence of genetic variations on the pharmacokinetics of the increasingly used monoclonal antibodies has hardly been investigated. Some studies indicate that genes encoding the Fcγ-receptor family are of interest, but more research is needed to establish if screening before the start of therapy is beneficial. Considering the profound impact of polymorphisms in drug transporters and drug-metabolizing enzymes on the pharmacokinetics of chemotherapeutic drugs and hence, their toxicity and efficacy, pharmacogenetic and pharmacokinetic profiling should become the standard of care.

Simultaneous determination of fludarabine and clofarabine in human plasma by LC-MS/MS

A method for quantification of fludarabine (FDB) and clofarabine (CFB) in human plasma was developed with an API5000 LC-MS/MS system. FDB and CFB were extracted from EDTA plasma samples by protein precipitation with trichloroacetic acid. Briefly, 50 μL plasma sample was mixed with 25 μL internal standard (50 ng/mL aqueous 2-Cl-adensosine) and 25 μL 20% trichloroacetic acid, centrifuged at 25,000 × g (20,000 rpm) for 3 min, and then transfered to an autosampler vial. The extracted sample was injected onto an Eclipse extend C18 column (2.1 mm×150 mm, 5 μm) and eluted with 1mM NH4OH (pH 9.6) - acetonitrile in a gradient mode. Electrospray ionization in positive mode (ESI(+)) and multiple reaction monitoring (MRM) were used, and ion pairs 286/134 for FDB, 304/170 for CFB and 302/134 for the internal standard were selected for quantification. The retention times were typically 3.72 min for FDB, 4.34 min for the internal standard, 4.79 min for CFB. Total run time was 10 min per sample. Calibration range was 0.5-80 ng/mL for CFB and 2-800 ng/mL for FDB. The method was applied to a clinical pharmacokinetic study in pediatric patients.

Feasibility of clofarabine cytoreduction followed by haploidentical hematopoietic stem cell transplantation in patients with relapsed or refractory advanced acute leukemia

Clofarabine is a novel purine nucleoside analogue with immunosuppressive and anti-leukemic activity in acute lymphoblastic and myeloid leukemia (AML, ALL). This retrospective study was performed to evaluate the feasibility and anti-leukemic activity of a sequential therapy using clofarabine for cytoreduction followed by conditioning for haploidentical hematopoietic stem cell transplantation (HSCT) in patients with non-remission acute leukemia. Patients received clofarabine (5 × 30 mg/m² IV) followed by a T cell replete haploidentical transplantation for AML (n = 15) or ALL (n = 3). Conditioning consisted of fludarabine, cyclophosphamide plus either melphalan, total body irradiation or treosulfan/etoposide. High-dose cyclophosphamide was administered for post-grafting immunosuppression. Neutrophil engraftment was achieved in 83 % and complete remission in 78% at day +30. The rate of acute graft versus host disease (GvHD) grade II-IV was 22%, while chronic GvHD occured in five patients (28%). Non-relapse mortality (NRM) after 1 year was 23%. At a median follow-up of 19 months, estimated overall survival and relapse-free survival at 1 year from haploidentical HSCT were 56 and 39%, respectively. Non-hematological regimen-related grade III-IV toxicity was observed in ten patients (56%) and included most commonly transient elevation of liver enzymes (44%), mucositis (40%), and skin reactions including hand-foot syndrome (17%), creatinine elevation (17%), and nausea/vomiting (17%). The concept of a sequential therapy using clofarabine for cytoreduction followed by haploidentical HSCT proved to be feasible and allows successful engraftment, while providing an acceptable toxicity profile and anti-leukemic efficacy in patients with advanced acute leukemia. NRM and rate of GvHD were comparable to results after HSCT from HLA-matched donors.

Fifty years of melphalan use in hematopoietic stem cell transplantation

Melphalan remains the most widely used agent in preparative regimens for hematopoietic stem cell transplantation (SCT). From its initial discovery more than 50 years ago, it has been gradually incorporated in the conditioning regimens for both autologous and allogeneic transplantations because of its myeloablative properties and broad antitumor effects as a DNA alkylating agent. Melphalan remains the mainstay conditioning for multiple myeloma and lymphomas, and it has been used successfully in preparative regimens of a variety of other hematological and nonhematological malignancies. The addition of newer agents to conditioning, such as bortezomib or lenalidomide for myeloma or clofarabine for myeloid malignancies, may improve antitumor effects for transplantation, whereas melphalan in combination with alemtuzumab may represent a backbone for future cellular therapy because of reliable engraftment and low toxicity profile. This review summarizes the development and the current use of this remarkable drug in hematopoietic SCT.

Cytotoxic purine nucleoside analogues bind to A1, A2A, and A3 adenosine receptors

Fludarabine, clofarabine, and cladribine are anticancer agents which are analogues of the purine nucleoside adenosine. These agents have been associated with cardiac and neurological toxicities. Because these agents are analogues of adenosine, they may act through adenosine receptors to elicit their toxic effects. The objective of this study was to evaluate the ability of cytotoxic nucleoside analogues to bind and activate adenosine receptor subtypes (A(1), A(2A), A(2B), and A(3)). Radioligand binding studies utilizing Chinese hamster ovary cells, stably transfected with adenosine A(1), A(2A), or A(3) receptor subtype, were used to assess the binding affinities of these compounds, whereas adenylyl cyclase activity was used to assess the binding to A(2B) receptors. Clofarabine and cladribine both bound to the A(2A) receptor with a K (i) of 17 and 15 μM, respectively. Clofarabine was the only adenosine analogue to bind to the A(3) receptor with a K (i) of 10 μM, and none of these compounds bound to the A(2B) receptor. Results show that clofarabine, cladribine, and fludarabine bind to the A(1) receptor. In addition, clofarabine, cladribine, and fludarabine were A(1) agonists (IC(50) 3.1, 30, and 30 μM, respectively). Neither pyrimidine nucleoside analogues gemcitabine nor cytarabine associated with any of the adenosine receptor subtypes (K (i) > 100μM). This is the first report of an interaction between all adenosine receptor subtypes and chemotherapeutic nucleoside analogues commonly used in the treatment of cancer. Therefore, activation of these receptors may be at least one mechanism through which fludarabine-associated toxicity occurs.