Nucleoside analogues in the treatment of haematological malignancies

Impact of genetic variants in the solute carrier (SLC) genes encoding drug uptake transporters on the response to anticancer chemotherapy

Cancer drug resistance constitutes a severe limitation for the satisfactory outcome of these patients. This is a complex problem due to the co-existence in cancer cells of multiple and synergistic mechanisms of chemoresistance (MOC). These mechanisms are accounted for by the expression of a set of genes included in the so-called resistome, whose effectiveness often leads to a lack of response to pharmacological treatment. Additionally, genetic variants affecting these genes further increase the complexity of the question. This review focuses on a set of genes encoding members of the transportome involved in drug uptake, which have been classified into the MOC-1A subgroup of the resistome. These proteins belong to the solute carrier (SLC) superfamily. More precisely, we have considered here several members of families SLC2, SLC7, SLC19, SLC22, SLCO, SLC28, SLC29, SLC31, SLC46, and SLC47 due to the impact of their expression and genetic variants in anticancer drug uptake by tumor cells or, in some cases, general bioavailability. Changes in their expression levels and the appearance of genetic variants can contribute to the Darwinian selection of more resistant clones and, hence, to the development of a more malignant phenotype. Accordingly, to address this issue in future personalized medicine, it is necessary to characterize both changes in resistome genes that can affect their function. It is also essential to consider the time-dependent dimension of these features, as the genetic expression and the appearance of genetic variants can change during tumor progression and in response to treatment.

Synthesis and Biological Profiling of Quinolino-Fused 7-Deazapurine Nucleosides

A series of quinolino-fused 7-deazapurine (pyrimido[5',4':4,5]pyrrolo[3,2-f]quinoline) ribonucleosides were designed and synthesized. The synthesis of the key 11-chloro-pyrimido[5',4':4,5]pyrrolo[3,2-f]quinoline was based on the Negishi cross-coupling of iodoquinoline with zincated 4,6-dichloropyrimidine followed by azidation and thermal or photochemical cyclization. Vorbrüggen glycosylation of the tetracyclic heterocycle followed by cross-coupling or substitution reactions at position 11 gave the desired set of final nucleosides that showed moderate to weak cytostatic activity and fluorescent properties. The corresponding fused adenosine derivative was converted to the triphosphate and successfully incorporated to RNA using in vitro transcription with T7 RNA polymerase.

Increased renal elimination of endogenous and synthetic pyrimidine nucleosides in concentrative nucleoside transporter 1 deficient mice

Concentrative nucleoside transporters (CNTs) are active nucleoside influx systems, but their in vivo roles are poorly defined. By generating CNT1 knockout (KO) mice, here we identify a role of CNT1 in the renal reabsorption of nucleosides. Deletion of CNT1 in mice increases the urinary excretion of endogenous pyrimidine nucleosides with compensatory alterations in purine nucleoside metabolism. In addition, CNT1 KO mice exhibits high urinary excretion of the nucleoside analog gemcitabine (dFdC), which results in poor tumor growth control in CNT1 KO mice harboring syngeneic pancreatic tumors. Interestingly, increasing the dFdC dose to attain an area under the concentration-time curve level equivalent to that achieved by wild-type (WT) mice rescues antitumor efficacy. The findings provide new insights into how CNT1 regulates reabsorption of endogenous and synthetic nucleosides in murine kidneys and suggest that the functional status of CNTs may account for the optimal action of pyrimidine nucleoside analog therapeutics in humans.

Geminal Diheteroatomic Motifs: Some Applications of Acetals, Ketals, and Their Sulfur and Nitrogen Homologues in Medicinal Chemistry and Drug Design

Acetals and ketals and their nitrogen and sulfur homologues are often considered to be unconventional and potentially problematic scaffolding elements or pharmacophores for the design of orally bioavailable drugs. This opinion is largely a function of the perception that such motifs might be chemically unstable under the acidic conditions of the stomach and upper gastrointestinal tract. However, even simple acetals and ketals, including acyclic molecules, can be sufficiently robust under acidic conditions to be fashioned into orally bioavailable drugs, and these structural elements are embedded in many effective therapeutic agents. The chemical stability of molecules incorporating geminal diheteroatomic motifs can be modulated by physicochemical design principles that include the judicious deployment of proximal electron-withdrawing substituents and conformational restriction. In this Perspective, we exemplify geminal diheteroatomic motifs that have been utilized in the discovery of orally bioavailable drugs or drug candidates against the backdrop of understanding their potential for chemical lability.

Parallel Solution Phase Synthesis and Preliminary Biological Activity of a 5'-Substituted Cytidine Analog Library

A 109-membered library of 5'-substituted cytidine analogs was synthesized, via funding through the NIH Roadmap Initiative and the Pilot Scale Library (PSL) Program. Reaction core compounds contained -NH₂ (2) and -COOH (44 and 93) groups that were coupled to a diversity of reactants in a parallel, solution phase format to produce the target library. The assorted reactants included -NH₂, -CHO, -SO₂Cl, and -COOH functional groups, and condensation with the intermediate core materials 2 and 44 followed by acidic hydrolysis produced 3-91 in good yields and high purity. Linkage of the amino terminus of d-phenylalanine methyl ester to the free 5'-COOH of 44 and NaOH treatment led to core library -COOH precursor 93. In a libraries from libraries approach, compound 93 served as the vital building block for our unique library of dipeptidyl cytidine analogs 94-114 through amide coupling of the -COOH group with numerous commercial amines followed by acidic deprotection. Initial screening of the complete final library through the MLPCN program revealed a modest number of hits over diverse biological processes. These hits might be considered as starting points for hit-to-lead optimization and development studies.

Safety Assessment of 4′-Thio-β-d-Arabinofuranosylcytosine in the Beagle Dog Suggests a Drug-Induced Centrally Mediated Effect on the Hypothalamic-Pituitary-Adrenal Axis

4′-Thio- β-d-arabinofuranosylcytosine (OSI-7836) is a nucleoside analogue with structural similarity to gemcitabine and cytarabine (ara-C). Myelosuppression, reversible transaminase elevations, and flu-like symptoms are common side effects associated with human use of gemcitabine and ara-C. Fatigue is also associated with the use of gemcitabine and OSI-7836 in humans. To better understand the toxicity of OSI-7836, subchronic studies were conducted in dogs. OSI-7836 was administered on days 1 and 8 or on days 1, 2, and 3 of a 21-day dose regimen. These schedules attempted to match clinical trial dosing regimens. Routine toxicity study end points demonstrated that OSI-7836 was primarily cytotoxic to the gastrointestinal tract, bone marrow, and testes; the myelotoxicity was mild and reversible. Plasma pharmacokinetics were dose-linear with an elimination half-life of 2.2 h. Follow-up single dose experiments in dogs assessed drug effects on lymphocyte subpopulations and on adrenal and thyroid function. Populations of T and B cells were equally reduced following OSI-7836 administration. There were no adverse effects on thyroid function, but there were marked reductions in circulating cortisol and adrenocorticotropic hormone concentrations suggesting a centrally mediated impairment of the hypothalamic-pituitary-adrenal axis. These findings show a toxicological profile with OSI-7836 similar to other nucleoside analogues and suggest that the beagle is a model for studying one possible cause of OSI-7836-related fatigue, impaired function of the hypothalamic-pituitary-adrenal axis.

Versatile synthesis and biological evaluation of novel 3'-fluorinated purine nucleosides

A unified synthetic strategy accessing novel 3'-fluorinated purine nucleoside derivatives and their biological evaluation were achieved. Novel 3'-fluorinated analogues were constructed from a common 3'-deoxy-3'-fluororibofuranose intermediate. Employing Suzuki and Stille cross-coupling reactions, fifteen 3'-fluororibose purine nucleosides 1-15 and eight 3'-fluororibose 2-chloro/2-aminopurine nucleosides 16-23 with various substituents at position 6 of the purine ring were efficiently synthesized. Furthermore, 3'-fluorine analogs of natural products nebularine and 6-methylpurine riboside were constructed via our convergent synthetic strategy. Synthesized nucleosides were tested against HT116 (colon cancer) and 143B (osteosarcoma cancer) tumor cell lines. We have demonstrated 3'-fluorine purine nucleoside analogues display potent tumor cell growth inhibition activity at sub- or low micromolar concentration.

Durable remission of folliculotropic mycosis fungoides achieved with a combined topical treatment with cytarabine and carmustine

Folliculotropic mycosis fungoides (MF) is an uncommon subtype of MF which has a more aggressive natural history and is more resistant to treatment than other forms of MF. In this article, an innovative method of treatment is presented. We describe a successful use of topical cytarabine combined with topical carmustine in a patient with a folliculotropic MF. Based on our patient history we suggest this method as an effective therapy option for patients with folliculotropic MF unresponsive to other forms of treatment.

N-(2-Hydroxypropyl)methacrylamide Copolymer-Drug Conjugates for Combination Chemotherapy of Acute Myeloid Leukemia

There is a need for new treatment strategies of acute myeloid leukemia (AML). In this study, four different drugs, including cytarabine, daunorubicin, GDC-0980, and JS-K, were investigated in vitro for the two-drug combinations treatment of AML. The results revealed that cytarabine and GDC-0980 had the strongest synergism. In addition, cell cycle analysis was conducted to investigate the effect of the different combinations on cell division. For future in vivo application, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-cytarabine and GDC-0980 conjugates were synthesized, respectively. In vitro studies demonstrated that both conjugates had potent cytotoxicity and their combination also showed strong synergy, suggesting a potential chemotherapeutic strategy for future AML treatment.

DNA repair mechanisms in cancer development and therapy

DNA damage has been long recognized as causal factor for cancer development. When erroneous DNA repair leads to mutations or chromosomal aberrations affecting oncogenes and tumor suppressor genes, cells undergo malignant transformation resulting in cancerous growth. Genetic defects can predispose to cancer: mutations in distinct DNA repair systems elevate the susceptibility to various cancer types. However, DNA damage not only comprises a root cause for cancer development but also continues to provide an important avenue for chemo- and radiotherapy. Since the beginning of cancer therapy, genotoxic agents that trigger DNA damage checkpoints have been applied to halt the growth and trigger the apoptotic demise of cancer cells. We provide an overview about the involvement of DNA repair systems in cancer prevention and the classes of genotoxins that are commonly used for the treatment of cancer. A better understanding of the roles and interactions of the highly complex DNA repair machineries will lead to important improvements in cancer therapy.

Synthesis, cytostatic, antimicrobial, and anti-HCV activity of 6-substituted 7-(het)aryl-7-deazapurine ribonucleosides

A series of 80 7-(het)aryl- and 7-ethynyl-7-deazapurine ribonucleosides bearing a methoxy, methylsulfanyl, methylamino, dimethylamino, methyl, or oxo group at position 6, or 2,6-disubstituted derivatives bearing a methyl or amino group at position 2, were prepared, and the biological activity of the compounds was studied and compared with that of the parent 7-(het)aryl-7-deazaadenosine series. Several of the compounds, in particular 6-substituted 7-deazapurine derivatives bearing a furyl or ethynyl group at position 7, were significantly cytotoxic at low nanomolar concentrations whereas most were much less potent or inactive. Promising activity was observed with some compounds against Mycobacterium bovis and also against hepatitis C virus in a replicon assay.

Clinical practice guidelines for diagnosis, treatment, and follow-up of patients with mantle cell lymphoma. Recommendations from the GEL/TAMO Spanish Cooperative Group

Mantle cell lymphoma (MCL) is considered a distinct type of B-cell lymphoma genetically characterized by the t(11;14) translocation and cyclin D1 overexpression. There is also a small subset of tumors negative for cyclin D1 expression that are morphologically and immunophenotypically indistinguishable from conventional MCL. Although in the last decades, the median overall survival of patients with MCL has improved significantly, it is still considered as one of the poorest prognoses diseases among B-cell lymphomas. Election of treatment for patients with MCL is complex due to the scarcity of solid evidence. Current available data shows that conventional chemotherapy does not yield satisfactory results as in other types of B-cell lymphomas. However, the role of other approaches such as autologous or allogenic stem cell transplantation, immunotherapy, the administration of consolidation or maintenance schedules, or the use of targeted therapies still lack clear indications. In view of this situation, the Spanish Group of Lymphomas/Autologous Bone Marrow Transplantation has conducted a series of reviews on different aspects of MCL, namely its diagnosis, prognosis, first-line and salvage treatment (both in young and elderly patients), new targeted therapies, and detection of minimal residual disease. On the basis of the available evidence, a series of recommendations have been issued with the intention of providing guidance to clinicians on the diagnosis, treatment, and monitoring of patients with MCL.

Sugar-modified derivatives of cytostatic 7-(het)aryl-7-deazaadenosines: 2'-C-methylribonucleosides, 2'-deoxy-2'-fluoroarabinonucleosides, arabinonucleosides and 2'-deoxyribonucleosides

A series of novel sugar-modified derivatives of cytostatic 7-hetaryl-7-deazaadenosines (2'-C-methylribonucleosides, 2'-deoxy-2'-fluoroarabinonucleosides, arabinonucleosides and 2'-deoxyribonucleosides) was prepared and screened for biological activity. The synthesis consisted of preparation of the corresponding sugar-modified 7-iodo-7-deazaadenine nucleosides and their aqueous-phase Suzuki-Miyaura cross-coupling reactions with (het)arylboronic acids or Stille couplings with hetarylstannanes in DMF. The synthesis of 7-iodo-7-deazaadenine nucleosides was based on a glycosidation of 6-chloro-7-iodo-7-deazapurine with a suitable sugar synthon or on an interconversion of 2'-OH stereocenter (for arabinonucleosides). Several examples of 2'-C-Me-ribonucleosides showed moderate anti-HCV activities in a replicon assay accompanied by cytotoxicity. Several 7-hetaryl-7-deazaadenine fluoroarabino- and arabinonucleosides exerted moderate micromolar cytostatic effects. The most active was 7-ethynyl-7-deazaadenine fluoroarabinonucleoside which showed submicromolar antiproliferative activity. However, all the sugar-modified derivatives were less active than the parent ribonucleosides.

Phosphoramidate pronucleotides of cytostatic 6-aryl-7-deazapurine ribonucleosides

A series of O-phenyl methyl-, ethyl- and benzylalanyl phosphoramidate pronucleotides derived from cytostatic 6-aryl-7-deazapurine ribonucleosides were prepared by the cross-coupling reactions of the 2',3'-isopropylidene protected 6-chloro-7-deazapurine ribonucleoside phosphoramidates with (het)arylboronic acids or -stannanes followed by deprotection. Most of the prepared prodrugs exerted in vitro cytostatic effects against both solid tumor and lymphoid cancer cells within low micromolar range of concentrations. These activities were in general weaker or comparable to the activities of the parent nucleosides. Additional testing of selected prodrugs suggests that the lack of activity improvement over parent nucleosides is not due to the lack of permeability or inefficient catabolism of alanyl-ester by intracellular hydrolases. More likely, active efflux of prodrugs may play a role in their weak cytotoxic activity.

CycloSal-phosphate pronucleotides of cytostatic 6-(Het)aryl-7-deazapurine ribonucleosides: Synthesis, cytostatic activity, and inhibition of adenosine kinases

A series of cycloSal-phosphate prodrugs of a recently described new class of nucleoside cytostatics (6-hetaryl-7-deazapurine ribonucleosides) was prepared. The corresponding 2',3'-isopropylidene 6-chloro-7-deazapurine nucleosides were converted into 5-O'-cycloSal-phosphates. These underwent a series of Stille or Suzuki cross-couplings with diverse (het)arylstannanes or -boronic acids to yield the protected 6-(het)aryl-7-deazapurine pronucleotides that were subsequently deprotected to give 12 derivatives of free pronucleotides. The in vitro cytostatic effect of the pronucleotides was compared with parent nucleoside analogues. In most cases, the activity of the pronucleotide was similar to or somewhat lower than that of the corresponding parent nucleosides, with the exception of 7-fluoro pronucleotides 13 a, 13 b, and 13 d, which had exhibited GIC(50) values that were improved by one order of magnitude (to the low nanomolar range). The presence of a cycloSal-phosphate group also influenced selectivity toward various cell lines. Several pronucleotides were found which strongly inhibit human adenosine kinase but only weakly inhibit the MTB adenosine kinase.

6-(Het)aryl-7-deazapurine ribonucleosides as novel potent cytostatic agents

A series of novel 7-deazapurine ribonucleosides bearing an alkyl, aryl, or hetaryl group in position 6 and H, F, or Cl atom in position 7 has been prepared either by Pd-catalyzed cross-coupling reactions of the corresponding protected 6-chloro-(7-halogenated-)7-deazapurine ribonucleosides with alkyl- or (het)arylorganometallics followed by deprotection, or by single-step aqueous phase cross-coupling reactions of unprotected 6-chloro-(7-halogenated-)7-deazapurine ribonucleosides with (het)arylboronic acids. Significant cytostatic effect was detected with a substantial proportion of the prepared compounds. The most potent were 7-H or 7-F derivatives of 6-furyl- or 6-thienyl-7-deazapurines displaying cytostatic activity in multiple cancer cell lines with a geometric mean of 50% growth inhibition concentration ranging from 16 to 96 nM, a potency comparable to or better than that of the nucleoside analogue clofarabine. Intracellular phosphorylation to mono- and triphosphates and the inhibition of total RNA synthesis was demonstrated in preliminary study of metabolism and mechanism of action studies.

Differences in cytosolic and mitochondrial 5'-nucleotidase and deoxynucleoside kinase activities in Sprague-Dawley rat and CD-1 mouse tissues: implication for the toxicity of nucleoside analogs in animal models

Cytosolic and mitochondrial deoxynucleoside kinases (dNKs), as well as 5'deoxynucleotidases (5'-dNTs), control intracellular and intramitochondrial phosphorylation of natural nucleotides and nucleoside analogs used in antiviral and cancer chemotherapy. The balance in the activities of these two groups of enzymes to a large extent determines both the efficacy and side effects of these drugs. Because of the broad and overlapping substrate specificities of the nucleoside kinases and 5'-NTs, their tissue distribution and roles in the metabolism of both natural nucleosides and their analogs are still not fully elucidated. Here, the activity of dNKs: dCK and TK (TK1 and TK2) as well as 5'-dNTs: CN1, CN2 and dNT (dNT1 and dNT2) were determined in 14 different adult mouse and rat tissues. In most cases tissue activities of TK1, TK2 and dCK were 2-3-fold higher in the mouse, a similar pattern was found with CN1 and dNTs although with several exceptions, e.g., TK2 activities in muscle extracts from rats were 2-10-fold higher than in the mouse. Furthermore CN1 activities in hepatic, renal and adipose extracts were 2-3-fold higher in the rat. CN2 had higher levels in the testis, spleen, pancreas and diaphragm and lower level in the lung of mouse compared to rat tissues. The result suggests that a major difference in these activity profiles between mouse and rat may account for discrepancies in pharmacological response of the two animals to certain nucleoside compounds, and may help to improve the usefulness of animal models in future efforts of drug discovery.

Current status of older and new purine nucleoside analogues in the treatment of lymphoproliferative diseases

For the past few years more and more new cytotoxic agents active in the treatment of hematological malignancies have been synthesized and become available for either in vitro studies or clinical trials. Among them the class of antineoplastic drugs belonging to the purine nucleoside analogues group (PNAs) plays an important role. Three of them: pentostatin (DCF), cladribine (2-CdA) and fludarabine (FA) were approved by Food and Drug Administration (FDA) for the treatment of hematological malignancies. Recently three novel PNAs: clofarabine (CAFdA), nelarabine (ara-G) and forodesine (immucillin H, BCX-1777) have been synthesized and introduced into preclinical studies and clinical trials. These agents seem to be useful mainly for the treatment of human T-cell proliferative disorders and they are currently undergoing clinical trials in lymphoid malignancies. However, there are also several studies suggesting the role of these drugs in B-cell malignancies. This review will summarize current knowledge concerning the mechanism of action, pharmacologic properties, clinical activity and toxicity of PNAs accepted for use in clinical practice, as well as new agents available for clinical trials.

Nucleoside analogs: molecular mechanisms signaling cell death

Nucleoside analogs are structurally similar antimetabolites that have a broad range of action and are clinically active in both solid tumors and hematological malignancies. Many of these agents are incorporated into DNA by polymerases during normal DNA synthesis, an action that blocks further extension of the nascent strand and causes stalling of replication forks. The molecular mechanisms that sense stalled replication forks activate cell cycle checkpoints and DNA repair processes, which may contribute to drug resistance. When replication forks are not stabilized by these molecules or when subsequent DNA repair processes are overwhelmed, apoptosis is initiated either by these same DNA damage sensors or by alternative mechanisms. Recently, strategies aimed at targeting DNA damage checkpoints or DNA repair processes have demonstrated effectiveness in sensitizing cells to nucleoside analogs, thus offering a means to elude drug resistance. In addition to their DNA synthesis-directed actions many nucleoside analogs trigger apoptosis by unique mechanisms, such as causing epigenetic modifications or by direct activation of the apoptosome. A review of the cellular and molecular responses to clinically relevant agents provides an understanding of the mechanisms that cause apoptosis and may provide rationale for the development of novel therapeutic strategies.

Treatment of lymphomatous and leukemic meningitis with liposomal encapsulated cytarabine

Liposomal encapsulated cytarabine (DepoCyte, Mundipharma GmbH, Limburg/Lahn, Germany) is a slow-release formulation of conventional cytarabine. It is licensed for intrathecal use in patients with lymphomatous and leukemic meningitis. DepoCyte obtained superior response rates, improved patient quality of life and improved the time to neurological progression in a randomized albeit small clinical trial. In this review we briefly summarize the clinical data and discuss them in light of clinical problems and possible treatment scenarios.

Effect of cytarabine and decitabine in combination in human leukemic cell lines

PURPOSE

1-beta-D-Arabinofuranosylcytosine (cytarabine; ara-C) is the most active agent in myeloid leukemia. 5-Aza-2'-deoxycytidine (DAC) is a cytosine analogue that inhibits DNA methylation and also has activity in myeloid leukemia. Therefore, we investigated combining these two drugs in human leukemia cell lines in vitro.

EXPERIMENTAL DESIGN

We initially examined the effects of ara-C and DAC on human leukemia cell lines HL60, ML-1, RAji, and Jurkat. We measured IC(50) of DAC and ara-C in these cell lines and calculated a combination index of these two drugs given either simultaneously or sequentially. In searching for mechanisms relative to epigenetic regulation for this effect, we examined DNA methylation of LINE and Alu repetitive elements as a surrogate for global genomic DNA methylation. In addition, we sorted Annexin V positive and negative cells and measured differences in LINE methylation between them.

RESULTS

The combination of DAC and ara-C showed additive induction of cell death in ML-1 and synergistic induction in HL60, Raji, and Jurkat. Sequentially, DAC followed by ara-C was a synergistic combination in all cell lines. Low-dose DAC induced more hypomethylation than high doses of the drug, whereas ara-C had no effects on methylation. The combination of ara-C with DAC either together or DAC followed by ara-C resulted in inhibition of LINE demethylation in HL60. The RIL gene, which is silenced by DNA hypermethylation, was activated by DAC, but the addition of ara-C to DAC reduced RIL gene activation. DAC treatment increased H3 Lys(9) acetylation of Alu elements, whereas ara-C had no effect, and the addition of ara-C to DAC inhibited this effect. Finally, we showed that after DAC exposure, Annexin V positive cells were more hypomethylated than Annexin V negative cells.

CONCLUSION

The combination of DAC and ara-C showed additive or synergistic effects on cell death in four human leukemia cell lines in vitro, but antagonism in terms of epigenetic effects. One possible explanation for these paradoxical observations is that hypomethylated cells are sensitized to cell killing by ara-C. These data suggest that DAC used in combination with ara-C has clinical potential in the treatment of acute myeloid leukemia.

Central nervous system involvement of previously undiagnosed chronic lymphocytic leukemia in a patient with neuroborreliosis

Leukemic involvement of the central nervous system (CNS) in previously undiagnosed chronic lymphocytic leukemia (CLL) is very rare. We report the case of a 62-year-old man with neuroborreliosis in which cytologic, immunocytochemical, and flow cytometry analyses revealed the presence of clonal B-lymphocytes in the cerebrospinal fluid (CSF). After the patient received antimicrobial therapy, his meningeal symptoms cleared up, and the number of cells in the CSF decreased. Monoclonal lymphocytes were still detectable at the same percentage, however, despite systemic chlorambucil therapy. The application of intrathecal dexamethasone therapy led to the disappearance of B-cell CLL (B-CLL) cells in the CSF. We presumed that the neuroborreliosis enabled the transmigration of leukocytes, including B-CLL cells, across the blood-brain barrier via activation of matrix metalloproteinase 9, an enzyme known to open the blood-brain barrier.

Cytotoxic activity of gemcitabine and correlation with expression profile of drug-related genes in human lymphoid cells

Gemcitabine is an inhibitor of ribonucleotide reductase (RR) and DNA polymerization with promising activity in hematologic malignancies. Gemcitabine enters the cell mostly via the human equilibrative nucleoside transporter-1 (hENT1), while drug metabolism occurs by phosphorylation by deoxycytidine kinase (dCK), 5'-nucleotidase (cN-II) and cytidine deaminase (CDA) are the main inactivating enzymes. The aim of this study was to investigate the role of these determinants in gemcitabine cytotoxicity and analyze their expression in lymphoid cells. Cytotoxicity was assessed by MTT, and modulated by simultaneous addition of 2'-deoxycytidine (dCK natural substrate), tetrahydrouridine (CDA competitive inhibitor) and diethylpyrocarbonate (cN-II non-competitive inhibitor), while the expression of hENT1, dCK, cN-II, CDA and RR in WIL2-S, Jurkat and CCRF-CEM cells as well as in lymphoid cells from 25 chronic lymphocytic B-leukemia (B-CLL) patients was studied with quantitative-PCR. Cell cycle modulation and induction of apoptosis were analyzed by cytofluorimetry and bisbenzimide staining. Gemcitabine was highly cytotoxic, increased the cells in S-phase and significantly enhanced apoptosis. The crucial role of metabolism in gemcitabine activity was confirmed by the significant modulation of cytotoxicity by inhibitors of dCK, CDA and cN-II. Furthermore, PCR demonstrated a correlation between gemcitabine sensitivity and expression of its determinants, and that their values were within those observed in patients. These data indicate that gemcitabine is cytotoxic against lymphoid cells, affecting cell cycle and apoptosis. Furthermore, chemosensitivity may be predicted on the basis of gene expression profile of critical determinants involved in gemcitabine mechanism of action, suggesting the use of pharmacogenetic profiling for treatment optimization.

High-throughput five minute microwave accelerated glycosylation approach to the synthesis of nucleoside libraries

The Vorbrüggen glycosylation reaction was adapted into a one-step 5 min/130 degrees C microwave assisted reaction. Triethanolamine in acetontrile containing 2% water was determined to be optimal for the neutralization of trimethylsilyl triflate allowing for direct MPLC purification of the reaction mixture. When coupled with a NH3/methanol deprotection reaction, a high-throughput method of nucleoside library synthesis was enabled. The method was demonstrated by examining the ribosylation of 48 nitrogen containing heteroaromatic bases that included 25 purines, four pyrazolopyrimidines, two 8-azapurines, one 2-azapurine, two imidazopyridines, two benzimidazoles, three imidazoles, three 1,2,4-triazoles, two pyrimidines, two 3-deazapyrimidines, one quinazolinedione, and one alloxazine. Of these, 32 yielded single regioisomer products, and six resulted in separable mixtures. Seven examples provided inseparable regioisomer mixtures of -two to three compounds (16 nucleosides), and three examples failed to yield isolable products. For the 45 single isomers isolated, the average two-step overall yield +/- SD was 26 +/- 16%, and the average purity +/- SD was 95 +/- 6%. A total of 58 different nucleosides were prepared of which 15 had not previously been accessed directly from glycosylation/deprotection of a readily available base.

Phase II study of gemcitabine–dexamethasone with or without cisplatin in relapsed or refractory mantle cell lymphoma

Single-agent gemcitabine has shown encouraging results in patients with mantle cell lymphoma (MCL). This phase II study further explored the potential of a gemcitabine-based regimen in patients with relapsed or refractory MCL. Patients <70 years old received the PDG regimen: gemcitabine (1000 mg/m(2), days 1 and 8), dexamethasone (40 mg/m(2), days 1-4), and cisplatin (100 mg/m(2), day 1). Patients >/=70 years of age received dexamethasone and gemcitabine only (DG regimen). Thirty patients (12 in the DG group, 18 in the PDG group) with a median age 66.5 years (range, 47-81) received a median of six cycles in both groups. The overall response rate was 36.4% [95% confidence interval (CI), 15.2% to 64.6%] with the DG regimen and 44.4% (95% CI 24.6% to 66.3%) with the PDG regimen. The median progression-free survival was 3 months (95% CI 0.0-7.9) in the DG group and 8.5 months (95% CI 4.8-12.2) in the PDG group. With a median follow-up of 38.8 months, 13 patients (including 11 given PDG) are still alive. DG was well tolerated, and thrombocytopenia was the most prevalent toxicity in patients receiving PDG. Both regimens deserve to be further investigated as a backbone for combination chemotherapy in patients with MCL.

Management of infections by the human polyomavirus JC: past, present and future

Progressive multifocal leukoencephalopathy is a fatal demyelinating disease caused by infection of oligodendrocytes by the human polyomavirus known as JC virus. Over the past 10 years, the disease has been documented almost exclusively in AIDS patients, who constitute a rapidly growing population of immunosuppressed individuals. More recently, progressive multifocal leukoencephalopathy has also been described in patients undergoing solid organ or cell transplant, as a result of immunosuppressive therapy to avoid graft rejection. Although there are several reports of successful treatment of progressive multifocal leukoencephalopathy, large-scale prospective trials have been few, and with mixed results. As more is discovered about the biology of JC virus infection and advances are made in targeted parenchymal delivery of therapeutic agents, there is hope for the development of an effective therapy for progressive multifocal leukoencephalopathy.

Targeting Hsp90 by 17-AAG in leukemia cells: mechanisms for synergistic and antagonistic drug combinations with arsenic trioxide and Ara-C

17-Allylamino-17-demethoxygeldanamycin (17-AAG) is a new anticancer agent currently in clinical trials. The ability of 17-AAG to abrogate the function of heat-shock protein Hsp90 and modulate cellular sensitivity to anticancer agents has prompted recent research to use this compound in drug combination therapy. Here we report that 17-AAG has striking opposite effects on the activity of arsenic trioxide (ATO) and ara-C. Combination of 17-AAG with ATO exhibited a synergistic effect in leukemia cells, whereas coincubation of 17-AAG and ara-C showed antagonistic activity. Mechanistic studies revealed that ATO exerted cytotoxic action by reactive oxygen species generation, and activated Akt survival pathway. 17-AAG abrogated Akt activation and enhanced the activity of ATO. In contrast, treatment of leukemia cells with 17-AAG caused a G1 arrest, a decrease in DNA synthesis and reduced ara-C incorporation into DNA, leading to antagonism. The ability of 17-AAG to enhance the antileukemia activity of ATO was further demonstrated in primary leukemia cells isolated from patients with acute myeloid leukemia and chronic lymphocytic leukemia, including cells from refractory patients. Our data suggest that combination of 17-AAG and ATO may be an effective therapeutic regimen. Caution should be exercised in using 17-AAG together with ara-C, as their combination effects are schedule dependent.

Enforced expression of cytosolic 5'-nucleotidase I confers resistance to nucleoside analogues in vitro but systemic chemotherapy toxicity precludes in vivo selection

PURPOSE

Retroviral transfer of cDNA sequences that confer drug resistance can be used to protect against chemotherapy-induced hematopoietic toxicity and for the selective expansion of gene-modified cells. To successfully expand genetically engineered cells in vivo, an appropriate balance must be achieved between systemic toxicity induced by the selecting agent and the expansion of modified cells.

METHOD

In this study, we investigate retroviral transfer of cytosolic 5'-nucleotidase I (cN-I) for protection and selection of gene-modified cells when treated with 2-chloro-2'-deoxyadenosine (2-CdA) and 5-fluorouracil (5-FU) alone and in combination. We also attempt to design a treatment strategy for the potential in vivo selection of cN-I-modified cells by administering 5-FU to mice prior to 2-CdA treatment.

RESULTS

Our results show that cN-I can be transferred by recombinant retroviruses, and that enforced expression of cN-I protects murine fibroblast and hematopoietic progenitor cells from the cytotoxic effects of 2-CdA and/or 5-FU. Furthermore, we show that the combined administration of 5-FU and 2-CdA potentiates hematopoietic stem cell toxicity. However, the treatment also results in severe myelosuppression.

CONCLUSION

These results show that while cN-I provides both protective and selective benefits to gene-modified cells in vitro, selection requires a treatment strategy that is likely too toxic to consider cN-I as an in vivo selectable marker.

Economic assessment on the management of chronic lymphocytic leukaemia

In the last decade, several new promising treatments for chronic lymphocytic leukaemia (CLL) have been developed. Healthcare costs are increasing and new treatments tend to be very expensive; therefore, information about the cost effectiveness in treatments for CLL is urgently needed. The authors performed a literature review on the currently available economic evaluations on CLL treatments. A total of 65 articles were found, of which 11 could be included. These articles were evaluated on the basis of six methodological requirements for economic evaluations, enabling readers to judge the value of the studies. Only a small amount of information was available on the costs of CLL treatments. Future economic evaluations should be performed according to the methodological requirements for these studies, which should also be properly documented.

CD26 expression correlates with a reduced sensitivity to 2'-deoxycoformycin-induced growth inhibition and apoptosis in T-cell leukemia/lymphomas

PURPOSE AND EXPERIMENTAL DESIGN

dCF (2'-deoxycoformycin) is a potent inhibitor of ADA (adenosine deaminase), an enzyme regulating intra- and extracellular concentrations of purine metabolites. ADA exists as cytosolic and extracellular forms, the latter colocalized on the cell surface with CD26. Once the surface expression of CD26 and ADA in a panel of cell lines and primary samples of T-cell leukemia/lymphoma was defined, we correlated this expression with the antiproliferative and apoptotic effect of dCF.

RESULTS

Surface expression of CD26 inversely correlated with the capability of dCF to inhibit cell growth and induce apoptosis both in T-cell lines and primary samples of T-cell malignancies. This conclusion was sustained by a decreased sensitivity to dCF-mediated proapoptotic and/or antiproliferative in vitro effects of: (a) leukemia/lymphoma T-cell lines expressing surface CD26/ADA complex; (b) primary CD26(+) T cell malignancies; and (c) normal T cells (CD26(+)) as compared with tumor T cells (CD26(-)) in unpurified samples from three cases of T-cell receptor gammadelta(+) T-cell malignancies characterized by a mixture of normal and neoplastic cells. This latter point was confirmed in vivo, in a patient affected by CD26(-) T-cell receptor gammadelta(+) hepatosplenic gammadelta(+) T-cell lymphomas treated on a compassionate basis with dCF. The inverse correlation between CD26 expression and sensitivity to dCF was also demonstrated in a lymphoblastic lymphoma case in which CD26 was expressed on circulating blasts at relapse but not at diagnosis, as well as in two H9 T-cell clones expressing or not expressing CD26 mRNA and protein.

CONCLUSIONS

This study corroborates the notion of CD26 as a marker of poor prognosis for T-cell malignancies and delineates a role for CD26 as a predictor of poor response to dCF.

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.

The conjugate Rituximab/saporin-S6 completely inhibits clonogenic growth of CD20-expressing cells and produces a synergistic toxic effect with Fludarabine

Immunotoxins are chimeric proteins consisting of a toxin coupled to an antibody. To date, several clinical trials have been conducted, and some are still ongoing, to evaluate their anti-tumor efficacy. In this view, we chemically constructed an anti-CD20 immunotoxin with the mAb Rituximab and the type 1 ribosome-inactivating protein (RIP) saporin-S6, designed for B cells non-Hodgkin's lymphoma (NHL) therapy. This immunotoxin showed a specific cytotoxicity for the CD20+ cell lines Raji and D430B, evidenced by inhibition of protein synthesis, evaluation of apoptosis and clonogenic assay. Upon conjugation, saporin-S6 increased its toxicity on target cells by at least 2 logs, with IC(50) values of 0.1-0.3 nM. The percentage of AnnexinV+ cells was over 95% in both cell lines treated with 10 nM immunotoxin. A complete elimination of Raji clones was reached with the 10 nM immunotoxin, whereas a mixture of free RIP and mAb gave about 90% of clonogenic growth. Rituximab/saporin-S6, at 10 nM concentration, also induced apoptosis in 80% of lymphoma cells from NHL patients. Moreover, sensitivity of Raji to Rituximab/saporin-S6 was augmented when cells were coincubated with Fludarabine. The synergistic toxic effect of the two drugs led to a total elimination of the neoplastic population.

The role of surrogate markers in the clinical development of antiretroviral therapy: a model for early evaluation of targeted cancer drugs

Both CD4 cell counts and measurements of plasma HIV-1 RNA (i.e. viral load) have become established surrogate markers for predicting treatment and disease outcome in HIV infection, and are instrumental for the evaluation of new antiretroviral drugs in clinical trials. Recently, HIV drug-resistance testing has also become available and has been shown to have prognostic value in providing guidance with antiretroviral therapy. The identification of robust surrogate markers is also an essential requirement for the clinical development of targeted anticancer agents, which unlike their cytotoxic counterparts, are often devoid of the toxicities that have been traditionally used to monitor the efficacy of chemotherapy. In particular, biological or molecular markers that are predictive of a drug effect need to be integrated into early efficacy trials of targeted therapies in order to confirm that the drug is in fact "hitting" the intended target. The full clinical significance of many of the altered cell types or polymorphisms, which are selected by cytostatic agents, remains to be elucidated. However, molecular genotyping of these targets, akin to drug resistance testing for HIV infection, may constitute an important strategy to assist with the selection and monitoring of targeted chemotherapy in cancer patients. Thus, lessons from HIV/AIDS on the value of surrogate makers may assist with the development and optimization of targeted cancer therapy.

Nucleoside transporters in chronic lymphocytic leukaemia

Nucleoside derivatives have important therapeutic activity in chronic lymphocytic leukaemia (CLL). Experimental evidence indicates that in CLL cells most of these drugs induce apoptosis ex vivo, suggesting that programmed cell death is the mechanism of their therapeutic action, relying upon previous uptake and metabolic activation. Although defective apoptosis and poor metabolism often cause resistance to treatment, differential uptake and/or export of nucleosides and nucleotides may significantly modulate intracellular drug bioavailability and, consequently, responsiveness to therapy. Two gene families, SLC28 and SLC29, encode transporter proteins responsible for concentrative and equilibrative nucleoside uptake (CNT and ENT, respectively). Furthermore, selected members of the expanding ATP-binding cassette (ABC) protein family have recently been identified as putative efflux pumps for the phosphorylated forms of these nucleoside-derived drugs, ABCC11 (MRP8) being a good candidate to modulate cell sensitivity to fluoropyrimidines. Sensitivity of CLL cells to fludarabine has also been recently correlated with ENT-type transport function, suggesting that, besides the integrity of apoptotic pathways and appropriate intracellular metabolism, transport across the plasma membrane is also a relevant event during CLL treatment. As long as nucleoside transporter expression in leukaemia cells is not constitutive, the possibility of regulating nucleoside transporter function by pharmacological means may also contribute to improve therapy.

Mechanisms of apoptosis induction by nucleoside analogs

Nucleoside analogs are structurally, metabolically, and pharmacodynamically related agents that nevertheless have diverse biological actions and therapeutic consequences. This class of agents affects the structural integrity of DNA, generally after incorporation during replication or DNA excision repair synthesis, leading to stalled replication forks and chain termination. The DNA damage sensors ATM, ATR and DNA-PK recognize these events. These and other protein kinases activate checkpoint pathways that arrest cell cycle progression, and also signal for DNA repair. In addition, if these survival mechanisms are overwhelmed by the damage caused, a third function of these sensors is to activate signaling pathways that initiate apoptotic processes. A review of the spectrum of responses that are activated by clinically relevant nucleoside analogs begins to provide a mechanistic basis for diverse outcomes in cell viability. Such information, when coupled with an understanding of the intrinsic apoptotic potential of a tumor cell type may provide a rational basis for the design of therapeutic strategies.

Acute myeloid leukemia

In this chapter, Drs. Keating and Willman review recent advances in our understanding of the pathophysiology of acute myeloid leukemia (AML) and allied conditions, including the advanced myelodysplastic syndromes (MDS), while Drs. Goldstone, Avivi, Giles, and Kantarjian focus on therapeutic data with an emphasis on current patient care and future research studies. In Section I, Dr. Armand Keating reviews the role of the hematopoietic microenvironment in the initiation and progression of leukemia. He also discusses recent data on the stromal, or nonhematopoietic, marrow mesenchymal cell population and its possible role in AML. In Section II, Drs. Anthony Goldstone and Irit Avivi review the current role of stem cell transplantation as therapy for AML and MDS. They focus on data generated on recent Medical Research Council studies and promising investigation approaches. In Section III, Dr. Cheryl Willman reviews the current role of molecular genetics and gene expression analysis as tools to assist in AML disease classification systems, modeling of gene expression profiles associated with response or resistance to various interventions, and identifying novel therapeutic targets. In Section IV, Drs. Hagop Kantarjian and Francis Giles review some promising agents and strategies under investigation in the therapy of AML and MDS with an emphasis on novel delivery systems for cytotoxic therapy and on targeted biologic agents.

Induction of apoptosis in the human mast cell leukemia cell line HMC-1 by various antineoplastic drugs

Mast cell leukemia (MCL) is a rare disorder characterized by rapid disease progression, resistance against conventional cytoreductive drugs, and short survival. In an attempt to identify drugs that show significant antiproliferative effects on neoplastic mast cells (MC), we exposed the MCL-derived cell line HMC-1 to various cytotoxic drugs including 2-chlorodeoxyadenosine [2CdA], fludarabine and cytosine arabinoside [ARA-C]. The effects of these drugs on 3H-thymidine incorporation, electron microscopic signs of apoptosis, and DNA fragmentation in HMC-1 cells, were analyzed. As assessed by 3H-thymidine incorporation, all drugs produced inhibition of proliferation in HMC-1 cells with the following rank order of potency: ARA-C > doxorubicine > 2-CdA > etoposide > vincristine > fludarabine > cisplatin. Fludarabin, cisplatin, etoposide and 2-CdA also induced ladder-type fragmentation of DNA, endonuclease activity in a Tunel assay, and electron microscopic signs of apoptosis in HMC-1 cells. Together, our data show that various cytostatic drugs can induce apoptosis and inhibition of proliferation in the human MCL cell line HMC-1. Whether these drugs, alone or in combination, are also effective in patients with MCL, remains to be determined.

Induction of DNA ligase I by 1-beta-D-arabinosylcytosine and aphidicolin in MiaPaCa human pancreatic cancer cells

Exposure of MiaPaCa cells to 1-beta-D-arabinosylcytosine (ara-C) resulted in an increase in DNA ligase levels up to threefold compared to that in the untreated control cells, despite significant growth inhibition. Increased levels of DNA ligase I protein appear to correlate with the appearance of increased mRNA levels. The [(3)H]thymidine incorporation experiment and the biochemical assay of total polymerase activity revealed that an increase in DNA ligase I levels after treatment with ara-C was not accompanied by an increase of DNA synthesis or an increased presence of DNA polymerase activity inside cells. When cells resumed DNA synthesis after drug treatment, DNA ligase I levels began to drop, indicating that increased DNA ligase I is not required for DNA synthesis. An increase in DNA ligase I was also observed in cells treated with aphidicolin, another inhibitor of DNA synthesis that inhibits DNA polymerases without incorporating itself into DNA, indicating that an increase in DNA ligase I levels could be caused by the arrest of DNA replication by these agents. Interestingly, caffeine, which is a well-known inhibitor of DNA damage checkpoint kinases, abrogated the increase in DNA ligase I in MiaPaCa cells treated with ara-C and aphidicolin, suggesting that caffeine-sensitive kinases might be important mediators in the pathway leading to the increase in DNA ligase I levels in response to anticancer drugs, including ara-C and aphidicolin. We propose that ara-C and aphidicolin induce damage to the DNA strand by arresting DNA replication forks and subsequently increase DNA ligase I levels to facilitate repair of DNA damage.