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W Plunkett

Publications and source records attributed to W Plunkett.

At least 19 recordsLinked to original sources
PubMed2006

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.

Acute Disease↗
PubMed2002

Results of first salvage therapy for patients refractory to a fludarabine regimen in chronic lymphocytic leukemia.

Resistance to purine analogs is emerging as a major problem in the management of patients with chronic lymphocytic leukemia (CLL). Most of these patients have already been exposed to and have become refractory to alkylating agents. To define the natural history of fludarabine (Fludara) refractory patients with CLL, we reviewed the response to first salvage therapy of 147 patients who were refractory to Fludara or had a remission less than six months in duration after a Fludara-containing regimen. Thirty-three (22%) patients responded to their first salvage attempt. However, the median survival was only 10 months. Responders survived significantly longer than non-responders. The most effective salvage regimens were combinations of purine analogs and cyclophosphamide. Patients still possibly sensitive to alkylating agents had a superior response than alkylating agent resistant or naive patients. Subsequent salvage therapy was administered to 61 patients. The most promising results noted in the group were transplantation and the use of Campath-1H antibody. The major morbidity and cause of death were associated with infections. The probability of infection was most strongly associated with the response to salvage therapy. Gram-positive organisms were most commonly associated with infection. However, gram-negative bacilli or opportunistic infection such as fungi, Pneumocystis carinii, acid-fast bacilli and legionella were prominent causes of infection. Fludara-refractory patients are a poor prognosis group and need more effective therapeutic regimens and well-designed infection prophylactic regimens.

Adult↗
PubMed2001

Interaction of p53 and DNA-PK in response to nucleoside analogues: potential role as a sensor complex for DNA damage.

Therapeutic nucleoside analogues such as ara-C, gemcitabine, and fludarabine exert their cytotoxic activity against cancer cells mainly by incorporation into DNA and disruption of further DNA synthesis, resulting in the triggering of apoptosis. However, the molecules that recognize the incorporated analogues in DNA and subsequently initiate the downstream cellular responses remain to be identified. Here, we report that the DNA-dependent protein kinase (DNA-PK) and p53 are able to form a protein complex that interacts with the gemcitabine-containing DNA and plays a role in signaling to apoptotic pathways. DNA-PK/Ku and p53 were copurified in a protein fraction that binds to gemcitabine-containing DNA in preference to normal DNA. Immunoprecipitation experiments revealed that the two proteins physically associate in a complex. Treatment with gemcitabine resulted in an increase of DNA-PK and p53 protein and an increase in the phosphorylation of p53 at Ser15. Furthermore, confocal microscopy demonstrated a colocalization of DNA-PK and p53 to the nucleus in cells treated with gemcitabine. The nuclear localization of the DNA-PK/p53 complex was coincident with the induction of apoptosis in these cells. Although the wild-type p53 present in the protein complex exhibited 3'-5' exonuclease activity, it was incapable of excising the incorporated gemcitabine from DNA. The binding of the p53/DNA-PK complex to DNA substantially blocked further DNA synthesis by DNA polymerases alpha and epsilon in vitro, indicating a stalling of this complex at the site of drug incorporation. These data suggest that DNA-PK and p53 may form a sensor complex that detects the disruption of DNA replication caused by nucleoside analogue incorporation and may subsequently signal for apoptosis.

Antigens, Nuclear↗
PubMed2001

Phase II clinical investigation of gemcitabine in advanced soft tissue sarcomas and window evaluation of dose rate on gemcitabine triphosphate accumulation.

PURPOSE: To evaluate the efficacy, toxicity, and optimal dose rate of gemcitabine in adult patients with advanced soft tissue sarcomas (STS) by comparing levels of gemcitabine triphosphate (GTP) in peripheral-blood mononuclear cells (PBMCs) of patients receiving two different dose rates. PATIENTS AND METHODS: Fifty-six assessable patients with STS (17 gastrointestinal [GI] leiomyosarcomas and 39 other histologies) were treated on a two-arm phase II study. Gemcitabine was given at 1 g/m2 as a 30-minute infusion weekly for up to 7 weeks followed by 1 week of rest and reassessment of tumor. Subsequent cycles were given at 1 g/m2 weekly for 3 weeks followed by 1 week of rest. Nine patients underwent cellular pharmacologic studies at two different dose rates (1 g/m2 over a standard 30-minute infusion on week 1 and over pharmacologically based infusion of 150 minutes on week 2) to evaluate GTP levels in PBMCs. RESULTS: Seven partial responses were noted among 39 patients, for an overall response rate of 18% (95% confidence interval, 7% to 29%). Median duration of response was 3.5 months (range, 2 to 13 months). Four of 10 patients with non-GI leiomyosarcomas achieved a partial response. No objective responses were noted in 17 patients with GI leiomyosarcomas. One patient had a mixed response. Median time to progression for all patients (both arms) was 3 months; median survival was 13.9 months. Treatment was generally well tolerated. Comparison of cellular pharmacology demonstrated a significant 1.4-fold increase in the concentration of GTP with the 150-minute infusion. CONCLUSION: Given the limited therapeutic armamentarium for STS, the activity of gemcitabine is encouraging. Its potential for combination therapy in the salvage setting should be studied with pharmacologically guided fixed dose-rate infusion.

Adult↗
PubMed2001

Cellular pharmacokinetics and pharmacodynamics of the deoxycytidine analog 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC).

The pharmacokinetics and pharmacodynamics of the novel clinical candidate 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC) were investigated in human lymphoblastoid CCRF-CEM cells and human myeloblastic leukemia ML-1 cells. Formation of CNDAC 5'-mono-, di-, and triphosphate (CNDACTP) was concentration-dependent; nucleotide accumulation was greater in the lymphoid cells than in the myeloid cells. The nucleotides were eliminated with linear kinetics from both lines, but were retained more effectively by the ML-1 cells. DNA synthesis was selectively inhibited by a 4-hr treatment with CNDAC in CCRF-CEM and ML-1 cells; the IC(50) values were 1 and 0.8 microM, respectively. Evaluation of the polymerization reaction of a primer on an M13mp19(+) template by human DNA polymerase alpha indicated that CNDACTP was incorporated effectively (K(m) = 0.22 microM) opposite a complementary dGMP in the template strand. CNDACTP competed with the normal substrate, dCTP, for incorporation, and the two nucleotides showed similar substrate efficiencies (V(max)/K(m): dCTP = 0.91; CNDACTP = 0.77). Primer extension was potently inhibited by CNDAC triphosphate (K(i) = 23 nM); once the analog had been incorporated, further extension was not observed in vitro, suggesting that primers containing a 3'-terminal nucleotide analog were high K(m) substrates for polymerase alpha. Thus, the ability of human leukemia cells to effectively accumulate and retain CNDACTP, coupled with the favorable kinetics of competition for incorporation into DNA, and the relatively strong ability of the analog to terminate further extension, are likely to contribute to the cytotoxic action of CNDAC.

Antineoplastic Agents↗
PubMed2001

Evaluation of the combination of nelarabine and fludarabine in leukemias: clinical response, pharmacokinetics, and pharmacodynamics in leukemia cells.

PURPOSE: A pilot protocol was designed to evaluate the efficacy of fludarabine with nelarabine (the prodrug of arabinosylguanine [ara-G]) in patients with hematologic malignancies. The cellular pharmacokinetics was investigated to seek a relationship between response and accumulation of ara-G triphosphate (ara-GTP) in circulating leukemia cells and to evaluate biochemical modulation of cellular ara-GTP metabolism by fludarabine triphosphate. PATIENTS AND METHODS: Nine of the 13 total patients had indolent leukemias, including six whose disease failed prior fludarabine therapy. Two patients had T-acute lymphoblastic leukemia, one had chronic myelogenous leukemia, and one had mycosis fungoides. Nelarabine (1.2 g/m(2)) was infused on days 1, 3, and 5. On days 3 and 5, fludarabine (30 mg/m(2)) was administered 4 hours before the nelarabine infusion. Plasma and cellular pharmacokinetic measurements were conducted during the first 5 days. RESULTS: Seven patients had a partial or complete response, six of whom had indolent leukemias. The disease in four responders had failed prior fludarabine therapy. The median peak intracellular concentrations of ara-GTP were significantly different (P =.001) in responders (890 micromol/L, n = 6) and nonresponders (30 micromol/L, n = 6). Also, there was a direct relationship between the peak fludarabine triphosphate and ara-GTP in each patient (r = 0.85). The cellular elimination of ara-GTP was slow (median, 35 hours; range, 18 to > 48 hours). The ratio of ara-GTP to its normal counterpart, deoxyguanosine triphosphate, was higher in each patient (median, 42; range, 14 to 1,092) than that of fludarabine triphosphate to its normal counterpart, deoxyadenosine triphosphate (median, 2.2; range, 0.2 to 27). CONCLUSION: Fludarabine plus nelarabine is an effective, well-tolerated regimen against leukemias. Clinical responses suggest the need for further exploration of nelarabine against fludarabine-refractory diseases. Determination of ara-GTP levels in the target tumor population may provide a prognostic test for the activity of nelarabine.

Adult↗
PubMed2001

S-Phase arrest by nucleoside analogues and abrogation of survival without cell cycle progression by 7-hydroxystaurosporine.

The mechanisms of resistance to nucleoside analogues established in preclinical models are rarely found in primary tumors resistant to therapy with these agents. We tested the hypothesis that cells sense sublethal incorporation of analogues into DNA during replication and react by arresting further DNA synthesis and cell cycle progression. After removal of drug, cells may be able to repair damaged DNA and continue proliferation, thus escaping nucleoside analogue toxicity. As a corollary, we evaluated whether dysregulation of this mechanism causes cell death. Using gemcitabine as a model of S-phase-specific nucleoside analogues in human acute myelogenous leukemia ML-1 cells, we found that DNA synthesis decreased, cells arrested in S-phase transit, and 60-70% of the population accumulated in S-phase in response to cytostatic conditions. Proliferation continued after washing the cells into drug-free medium. S-phase-arrested cells were then treated with otherwise nontoxic concentrations of UCN-01, which caused rapid onset of apoptosis without cell cycle progression specifically in cells with an S-phase DNA content. Thus, S-phase arrest by nucleoside analogues sensitizes cells to UCN-01, which appears to activate signaling for death mechanisms and/or inhibit survival pathways. These results differ from those in cells arrested at the G2 checkpoint, in which UCN-01 abrogates cell cycle arrest, permitting cells to progress in the cell cycle before apoptosis.

Alkaloids↗
PubMed2001

Design of new anticancer therapies targeting cell cycle checkpoint pathways.

The mammalian cell cycle is exquisitely controlled by the cyclin-dependent kinases, which regulate cell cycle progression. Cell cycle transitions are, in turn, controlled by checkpoints that monitor the integrity and replication status of the genetic material before cells commit to either replicate or segregate their DNA. On activation, checkpoints interface with cyclin-Cdk complexes to block the cell cycle. Pharmacologic compounds that exploit our current knowledge of cell cycle and checkpoint pathway regulation offer insights into the development of novel therapeutic strategies.

Animals↗
PubMed2001

2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine: a novel anticancer nucleoside analog that causes both DNA strand breaks and G(2) arrest.

The mechanism of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC) action was investigated in human lymphoblastoid CEM cells and myeloblastic leukemia ML-1 cells. CNDAC was metabolized to its 5'-triphosphate and incorporated into DNA, which was associated with inhibition of DNA synthesis. After incubation of cells with [(3)H]CNDAC, metabolites were detected in 3'-->5' phosphodiester linkage and at the 3' terminus of cellular DNA. Specific enzymatic hydrolysis of DNA demonstrated that the parent nucleoside and its 2'-epimer 2'-C-cyano-2'-deoxy-2-ribo-pentofuranosylcytosine accounted for approximately 65% of the total analogs incorporated into DNA and essentially all of the drug in the 3'-->5' phosphodiester linkage. In contrast, all detectable radioactivity at 3' termini was associated with 2'-C-cyano-2',3'-didehydro-2',3'-dideoxycytidine. This de facto DNA chain-terminating nucleotide arises from an electronic characteristic and cleavage of the 3'-phosphodiester bond subsequent to the addition of a nucleotide to the incorporated CNDAC moiety by beta-elimination, a process that generates a single strand break in DNA. Investigation of the biological consequences of these actions indicated that, after incubation with cytostatic concentrations of CNDAC, cell cycle progression was delayed during S phase, but that cells arrested predominantly in the G(2) phase. This differed from the S phase-arresting actions of ara-C and gemcitabine, other deoxycytidine analogs that inhibit DNA replication but do not cause strand breaks. Thus, once incorporated into DNA, the CNDAC molecule appears to act by a dual mechanism that 1) delays the progress of further DNA replication, but 2) upon addition of a deoxynucleotide results in the conversion of the incorporated analog to a de facto DNA chain terminator at the 3' terminus of a single strand break. It is likely that DNA strand breaks trigger cell cycle arrest in G(2).

Antineoplastic Agents↗
PubMed2001

DNA repair initiated in chronic lymphocytic leukemia lymphocytes by 4-hydroperoxycyclophosphamide is inhibited by fludarabine and clofarabine.

PURPOSE: Chronic lymphocytic leukemia (CLL) lymphocytes respond to DNA alkylation by excision repair, with the extent of repair increasing as the cells acquire resistance to alkylating agents. Because incorporation of nucleotide analogues into the repair patches elicits death signals in quiescent cells, the increased capacity for excision repair in alkylator-resistant cells could facilitate incorporation of nucleotide analogues. We hypothesized that the mechanism-based interaction of nucleoside analogues with alkylating agents could elicit greater than additive killing of CLL cells. EXPERIMENTAL DESIGN: Lymphocytes from 50 patients with CLL that were not refractory to alkylators were treated in vitro with 4-hydroperoxycyclophosphamide (4-HC) with or without prior incubation with fludarabine nucleoside (F-ara-A) or with clofarabine (Cl-F-ara-A). DNA damage repair kinetics were determined by the single-cell gel electrophoresis (comet) assay. Cytotoxicity was assessed by staining with annexin V. RESULTS: CLL lymphocytes promptly initiated and completed excision repair in response to 4-HC. A 2-h preincubation with 10 microM F-ara-A or 10 microM Cl-F-ara-A inhibited the repair initiated by 4-HC, with inhibition peaking at the intracellular concentrations of 50 microM F-ara-ATP or 5 microM Cl-F-ara-ATP. Combining 4-HC with either F-ara-A or Cl-F-ara-A produced more than additive apoptotic cell death than the sum of each alone. The increase in cytotoxicity was proportional to the initial magnitude of the DNA incision and to the extent of repair inhibition by the nucleoside analogues, suggesting close correlation between the repair inhibition and induction of cell death. CONCLUSIONS: DNA repair, which is active in CLL lymphocytes, may be a biological target for facilitating the incorporation of nucleoside analogues and increasing their cytotoxicity. Thus, the increased repair capacity associated with resistant disease may be manipulated to therapeutic advantage.

Adenine Nucleotides↗
PubMed2000

The role of c-Jun kinase in the apoptotic response to nucleoside analogue-induced DNA damage.

Activation of the c-Jun NH2-terminal kinase type 1 (JNK1) signaling pathway is often associated with apoptosis. In this report, we elucidated the role of this kinase in the programmed cell death induced by the nucleoside analogue 9-beta-D-arabinosyl-2-fluoroadenine (F-ara-A). Treatment of ML-1 cells with 3 or 10 microM F-ara-A specifically killed cells in the S-phase of the population. Incorporation of F-ara-ATP, the nucleoside triphosphate of F-ara-A, into DNA resulted in the activation of JNK1 in a time- and dose-dependent fashion. Activation of JNK1 temporally preceded DNA fragmentation. When incorporation of F-ara-A into DNA was blocked by pretreatment of the cells with aphidicolin to inhibit DNA synthesis, neither JNK1 signaling nor apoptosis was evident. Furthermore, inhibition of JNK1 by treatment of the cells with forskolin or by pretreatment with an antisense oligonucleotide directed against JNK1 mRNA resulted in a decrease in F-ara-A-induced apoptosis. Finally, the JNK1 signaling pathway appeared to be upstream to that of the effector caspases in nucleoside analogue-induced apoptosis. Thus, our data strongly suggest that JNK1 is involved in transduction of F-ara-A-induced distress signals into an apoptotic response.

Antineoplastic Agents↗
PubMed2000

Superoxide dismutase as a target for the selective killing of cancer cells.

Superoxide dismutases (SOD) are essential enzymes that eliminate superoxide radical (O2-) and thus protect cells from damage induced by free radicals. The active O2- production and low SOD activity in cancer cells may render the malignant cells highly dependent on SOD for survival and sensitive to inhibition of SOD. Here we report that certain oestrogen derivatives selectively kill human leukaemia cells but not normal lymphocytes. Using complementary DNA microarray and biochemical approaches, we identify SOD as a target of this drug action and show that chemical modifications at the 2-carbon (2-OH, 2-OCH3) of the derivatives are essential for SOD inhibition and for apoptosis induction. Inhibition of SOD causes accumulation of cellular O2- and leads to free-radical-mediated damage to mitochondrial membranes, the release of cytochrome c from mitochondria and apoptosis of the cancer cells. Our results indicate that targeting SOD may be a promising approach to the selective killing of cancer cells, and that mechanism-based combinations of SOD inhibitors with free-radical-producing agents may have clinical applications.

2-Methoxyestradiol↗
PubMed2000

High-performance liquid chromatography method for the determination and quantitation of arabinosylguanine triphosphate and fludarabine triphosphate in human cells.

A gradient anion-exchange high-performance liquid chromatographic assay was developed for the simultaneous determination and quantitation of the cytotoxic triphosphates of arabinosylguanine (ara-GTP) and fludarabine (F-ara-ATP). The method was validated with respect to selectivity, recovery, linearity, precision, and accuracy using authentic standards. To test this assay in a more complex biological matrix, perchloric acid extracts of circulating human leukemia cells spiked with known concentrations of ara-GTP and F-ara-ATP were examined. Finally, to assess the clinical utility of our method, perchloric acid extracts of circulating human leukemia cells isolated from patients treated with fludarabine and nelarabine were analyzed. The range of quantitation was 0.0125-10 nmol for the ara- and native NTPs in cellular extracts. This assay should be helpful in establishing the mechanistic rationales for drug scheduling and combinations of nelarabine and fludarabine, and for correlating the therapeutic efficacy and levels of the cytotoxic triphosphates in target cells.

Arabinonucleotides↗
PubMed2000

Nucleotide requirements for the in vitro activation of the apoptosis protein-activating factor-1-mediated caspase pathway.

Adenine deoxynucleosides, such as 2-chlorodeoxyadenosine (2CdA) and fludarabine, induce apoptosis in quiescent lymphocytes, and are thus useful drugs for the treatment of indolent lymphoproliferative diseases. We previously demonstrated that that the 5'-triphosphate metabolite of 2CdA (2CdATP), similar to dATP, can cooperate with cytochrome c and apoptosis protein-activating factor-1 (APAF-1) to trigger a caspase pathway in a HeLa cell-free system. We used a fluorometry-based assay of caspase activation to extend the analysis to several other clinically relevant adenine deoxynucleotides in B-chronic lymphocytic leukemia extracts. The nucleotide-induced caspase activation displayed typical Michaelis-Menten kinetics. As estimated by the V(max)/K(m) ratios, the relative efficiencies of different nucleotides were Ara-ATP > 9-fluoro-9-beta-D-arabinofuranosyladenine 5'-triphosphate > dATP > 2CdATP > 9-beta-D-arabinofuranosylguanine 5'-triphosphate > dADP > ATP. In contrast to dADP, both ADP and its nonhydrolyzable alpha, beta-methylphosphonate analog were strong inhibitors of APAF-1-dependent caspase activation. The hierarchy of nucleotide activation was confirmed in a fully reconstituted system using recombinant APAF-1 and recombinant procaspase-9. These results suggest that the potency of adenine deoxynucleotides as co-factors for APAF-1-dependent caspase activation is due both to stimulation by the 5'-triphosphates and lack of inhibition by the 5'-diphosphates. The capacity of adenine deoxynucleoside metabolites to activate the apoptosome pathway may be an additional biochemical mechanism that plays a role in the chemotherapy of indolent lymphoproliferative diseases.

Apoptosis↗
PubMed2000

Phase II trial and pharmacokinetic evaluation of cytosine arabinoside for leptomeningeal metastases from breast cancer.

PURPOSE: To determine the efficacy and pharmacokinetics of intraventricular cytosine arabinoside (Ara-C) as front-line treatment for leptomeningeal metastases from breast cancer. METHODS: Ten patients newly diagnosed with leptomeningeal metastases (LMM) from breast cancer were treated with 100 mg intraventricular cytosine arabinoside (IVT Ara-C) via an Ommaya reservoir. Treatment was administered three times a week for 2 weeks, then once a week for 4 weeks, and then once every 6 weeks for four cycles to responding patients. Nine patients were evaluable clinically, and seven patients underwent testing to determine the pharmacokinetic profile of Ara-C in the cerebrospinal fluid (CSF). RESULTS: Two patients had partial responses lasting 9 and 40 weeks, respectively. Two other patients had stable disease. The median survival duration was 30 weeks (range: 5-58 weeks). Seven patients died from LMM. Acute toxic effects associated with IVT Ara-C included meningismus, nausea, vomiting, and myelosuppression. The median peak Ara-C level in CSF was 16.69+/-6.30 mM (SD). The half life for elimination was 1.45+/-0.61 h (SD) There was no drug accumulation between courses. Neuropsychological evaluations were completed in eight patients, six (75%) of whom had preexisting cognitive deficits. Their condition generally improved over the course of treatment until the LMM progressed. No neurotoxic side effects of IVT Ara-C were observed in the two patients who had normal baseline cognitive assessments. CONCLUSIONS: IVT Ara-C at this dose and schedule has minimal activity as initial treatment for LMM from breast cancer despite achievement of high peak levels of the drug in the cerebrospinal fluid. A liposomal Ara-C formulation is currently under investigation.

Adult↗
PubMed2000

Inhibition of RNA transcription: a biochemical mechanism of action against chronic lymphocytic leukemia cells by fludarabine.

Fludarabine is a nucleotide analog effective in the clinical treatment of chronic lymphocytic leukemia (CLL) and other indolent lymphocytic malignancies. Although the incorporation of fludarabine into DNA is a key event in causing cytotoxicity in proliferating leukemia cells, the precise mechanisms by which fludarabine kills CLL cells remain unclear because of the quiescent nature of this malignancy. The present study demonstrated that inhibition of RNA transcription correlated significantly with the cytotoxic action of fludarabine in CLL cells. In contrast, suppression of the low level of DNA synthesis did not affect the survival of the leukemia cells. In addition, inhibition of fludarabine incorporation into cellular DNA through repair synthesis in CLL cells did not alter the cytotoxicity of this drug. Rather, inhibition of RNA synthesis by fludarabine led to a specific diminishment of certain cellular proteins from CLL cells. The combination of fludarabine with another RNA synthesis inhibitor, actinomycin D, or with the protein synthesis inhibitor, puromycin, substantially enhanced the cytotoxic activity against CLL cells. These results suggest that termination of mRNA transcription and the consequent depletion of proteins required for cell survival may be a novel biochemical mechanism of action of fludarabine in CLL cells. Thus, inhibition of RNA/protein synthesis may provide a new therapeutic strategy for the treatment of CLL patients.

Antineoplastic Agents↗
PubMed2000

Pharmacokinetics of nelarabine and 9-beta-D-arabinofuranosyl guanine in pediatric and adult patients during a phase I study of nelarabine for the treatment of refractory hematologic malignancies.

PURPOSE: To characterize the pharmacokinetics of nelarabine (506U78), the water-soluble prodrug of 9-beta-D-arabinofuranosyl guanine (ara-G), and ara-G in pediatric and adult patients with refractory hematologic malignancies. Ara-G is phosphorylated within leukemic cells to form ara-G triphosphate (ara-GTP), which acts to terminate DNA chain elongation, resulting in cell death. PATIENTS AND METHODS: The pharmacokinetics of nelarabine and/or ara-G were evaluated in 71 patients (25 pediatric and 46 adult patients) on the first day of therapy. Blood was collected at specified times for the determination of plasma nelarabine and ara-G concentrations. RESULTS: There were no statistically significant differences in the pharmacokinetics of nelarabine between any of the groups of patients. The harmonic mean half-life (t1/2) of nelarabine in pediatric and adult patients was 14.1 minutes and 16.5 minutes, respectively. The maximum concentrations (C(max)) of ara-G occurred at or near the end of the nelarabine infusion. The C(max) of ara-G ranged from 11.6 micromol/L to 308.7 micromol/L at nelarabine doses of 5 to 75 mg/kg and was linearly related to the nelarabine dose. No statistically significant differences were noted for the pharmacokinetic parameter estimates of ara-G between adult male and female patients. In children versus adults, the dose-normalized C(max), time of the C(max), and the steady-state volume of distribution of ara-G were similar. However, the clearance of ara-G was higher in pediatric patients (0.312 L.h(-1).kg(-1)) as compared with adult patients (0. 213 L.h(-1).kg(-1)) (P <.001). The t1/2 of ara-G was shorter in pediatric patients as compared with adult patients (2.1 hours v 3.0 hours; P <.01). CONCLUSION: Nelarabine is an effective prodrug of ara-G, allowing systemic concentrations of ara-G that result in clinical activity.

Adolescent↗