Pharmacokinetic and pharmacodynamic comparison of fluoropyrimidine derivatives, capecitabine and 5′-deoxy-5-fluorouridine (5′-DFUR)

Purpose Capecitabine is a three-step prodrug that was rationally designed to be a more effective and safer alternative to its intermediate metabolite, 5-deoxy-5-fluorouridine (5-DFUR). We compared the pharmacokinetics/pharmacodynamics of these drugs in metastatic breast cancer patients.Methods Six patients received oral capecitabine at 1657 mg/m² twice daily and 17 received 5-DFUR at 400 mg three times daily. Both drugs were administered for 21 days followed by a 7-day rest.Results Median daily 5-DFUR AUC was significantly higher for capecitabine than for 5-DFUR (81.1 vs 32.6 mmol h/l; P=0.01). Following treatment with 5-DFUR, the median AUC and C_max of 5-DFUR tended to be higher in patients with a partial response (3.83 g h/ml and 4.88 g/ml) and stable disease (6.46 g h/ml and 4.96 g/ml) than in those with disease progression (2.53 g h/ml and 1.36 g/ml). The AUC and C_max of 5-DFUR was significantly related to overall survival.Conclusions These results support the superiority of capecitabine over 5-DFUR.     

Protection against fludarabine neurotoxicity in leukemic mice by the nucleoside transport inhibitor nitrobenzylthioinosine

Summary Fludarabine phosphate (F-ara-AMP, Fludara) is rapidly converted in the circulation to fludarabine (F-ara-A) and is among the most effective single agents in the treatment of chronic lymphocytic leukemia. Although current treatment protocols are well tolerated, severe neurotoxicity was a consequence of high-dose F-ara-AMP regimens used in early phase I trials against adult acute leukemia. The present study showed that in mice implanted with leukemia L1210, fatal neurotoxicity, which initially manifested as hind-limb paralysis, was a consequence of high-dose-F-ara-AMP treatment. However, the incidence of neurotoxicity was reduced by the coadministration of NBMPR-P, the 5-phosphate of nitrobenzylthioinosine, a potent inhibitor of thees equilibrative nucleoside transport (NT) system. NBTGR-P, the 5-phosphate of nitrobenzylthioguanosine (also a potent NT inhibitor) similarly prevented F-ara-AMP neurotoxicity in this experimental system. Treatment with F-ara-AMP/NBMPR-P combinations was more effective with respect to the fractional yield of cured mice than were the same treatment regimens without NBMPR-P.Abbreviations ara-A 9--d-arabinofuranosyladenine - F-ara-A 9--d-arabinofuranosyl-2-fluoroadenine (fludarabine) - F-ara-AMP fludarabine 5-monophosphate (Fludara) - NBMPR 6-[(4-nitrobenzyl)thio]-9--d-ribofuranosylpurine - NBMPR-P NBMPR 5-monophosphate - NBTGR 2-amino-6[(4-nitrobenzyl)thio]-9--d-ribofuranosylpurine - NBTGR-P NBMPR 5-monophosphate - NBdAdo-P N⁶-(4-nitrobenzyl)-9--d-2-deoxyribofuranosyladenine 5-monophosphate This study was supported by the National Cancer Institute of Canada     

Antitumor activity of 3′, 5′-diesters of 5-fluoro-2′-deoxyuridine against murine leukemia L1210 cells

Summary Antitumor activity of several 3,5-diesters of 5-fluoro-2-deoxyuridine (FUdR) against L1210 leukemia cells following intraperitoneal administration was examined. Esters of FUdR with aromatic acid or aliphatic acid of longer chain length were markedly active. Their activities, with respect to ILS₃₀, were as much as 100 times that of unesterified FUdR. 3,5-ditoluoyl FUdR also had an improved therapeutic effect: its therapeutic ratio was increased to 8.1, as against 2.0 for FUdR. On the other hand, 3,5-diesters of FUdR with aliphatic acid of shorter chain length do not appear to be as active as FUdR. The relationship between the antitumor activity and plasma levels has also been examined. After 3,5-diacetyl FUdR, which is one of the drug group showing low cytotoxicity, the plasma concentration rapidly decreased to unmeasurable level 3 h after dosing. This tendency is similar to that shown in FUdR. On the other hand, with 3,5-dipalmitoyl FUdR and 3,5-dibenzoyl FUdR, each of which has a marked antitumor effect, plasma concentrations decreased slowly and were maintained for as long as 48 h after dosing. The results show that the cytotoxicity of diesters of FUdR is correlated with the duration of a high plasma level of FUdR.     

Potentiation of the chemotherapeutic action of 5′-deoxy-5-fluorouridine in combination with guanosine and related compounds

Summary The effect of inosine, guanosine, and guanosine 5-monophosphate (GMP) on the antitumor activity of 5-deoxy-5-fluorouridine (5-DFUR) was investigated using P388 leukemia and P815 mastocytoma.The antitumor activity of 5-DFUR was markedly enhanced by coadministration of inosine or guanosine. The increase in lifespan (ILS) of mice treated with 5-DFUR was augmented by the combination with guanosine or inosine in a dose-dependent fashion, and the maximum ILS was about 160% with the combination, while that in the case of 5-DFUR alone was only 48% in the P388 leukemia system. The therapeutic ratio (dose at ILS_max/dose at ILS₃₀) of the combination with guanosine or inosine was 333 and 136, respectively, whereas that of 5-DFUR alone was 3.6. GMP also markedly potentiated the antitumor activity of 5-DFUR in both P388 leukemia and P815 mastocytoma systems, just as it potentiated the activity of 5-fluorouracil in the latter system.The uric acid level in the serum was elevated after IP injection of guanosine or inosine but the value was much lower in the case of guanosine than in inosine.     

Toxicity and metabolism of 3′-deoxyadenosine N1-oxide in mice and Ehrlich ascites tumor cells

Summary The toxic effect of 3-deoxyadenosine N¹-oxide (3-dANO) on mice, on their different organs, and on Ehrlich ascites tumor cells was studied. In both healthy and tumour-bearing animals, the lethal dose for 10% of the mice receiving i. p. injections (LD₁₀) of 3-dANO was estimated to be about 300 mg/kg×4 days in one mouse strain (Theiller). In another mouse strain (NMRI), we obtained a markedly higher LD₁₀ value (675 mg/kg×5 days). At nonlethal doses (250 mg/kg×4 days), we observed reversible neurological symptoms on days 4–12 after treatment, but no macroscopical or microscopical changes was detected in the brain, heart, thymus, lung, lymph node, spleen, liver, kidney, bone marrow, or gastrointestinal tract. At doses of 450 mg/kg×4 days, severe neurological symptoms were observed, and atony of the gastrointestinal canal and damage to the kidney and liver were registered. Even at doses that were lethal to the mice, no histopathological change was observed in the bone marrow or in the gastrointestinal canal. Pharmacokinetics studies showed that after the i.p. injection of 3-dANO, the maximal plasma concentration was reached after 10 min, after which it declined showing a half-life of about 40 min. A transient accumulation of 3-deoxyadenosine triphosphate (3-dATP) was observed within 24 h in the liver and kidney, with the maximal concentration being reached after about 2–3 h. 3-dANO was excreted partly as the unchanged substance and partly as the metabolite 3-deoxyinosine within 24 h. Flow-cytometric DNA analysis of Ehrlich tumor cells treated either in vitro or in vivo with 3-dANO revealed no therapy-induced change in the cell-cycle perturbations, which indicates that cells were randomly killed during all phases of the cycle.Abbreviations 3-dANO 3-deoxyadenosine N¹-oxide - 3-dA 3-deoxyadenosine - 3-dI 3-deoxyinosine - 3-dATP 3-deoxyadenosine triphosphate This work was supported by grants from the Director Ib Hendriksens Foundation and the P. Carl Petersens Foundation     

Synergistic effect of 3′-deoxyadenosine N 1-oxide and adenosine deaminase inhibitors on growth of Ehrlich ascites tumor cells in vivo

Summary The simultaneous administration of 3-deoxyadenosine N ^l-oxide (3-dANO) and the adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) or 2-deoxycoformycin (2-dCF) to mice bearing Ehrlich ascites tumor cells resistant to 3-dANO resulted in 80%–90% inhibition of tumor growth in vivo. 3-dANO and 2-dCF increased the survival time of tumor-bearing mice by a factor of 2. In vitro studies showed that the 3-dANO resistant Ehrlich cells initiate the metabolism of 3-dANO by a reduction to 3-deoxyadenosine, which is converted primarily to 3-deoxyinosine by adenosine deaminase and, to a small extent, phosphorylated to the cell toxic agent 3-dATP. By the addition of EHNA or 2-dCF it was possible to block the formation of 3-deoxyinosine, resulting in a profound stimulation in the accumulation of 3-dAtP. The development of resistance to 3-dANO was studied in cell cultures and found to be accompanied by changes in the enzyme activities of the reductase, the adenosine kinase, and the adenosine deaminase.Abbreviations 3-dANO 3-deoxyadenosine N ^l-oxide - 3-dA 3-deoxyadenosine - 3-dI 3-deoxyinosine - 3-dATP 3-deoxyadenosine triphosphate - EHNA erythro-9-(2-hydroxy-3-nonyl) adenine - 2-dCF 2-deoxycoformycin This work was supported by the Danish Medical Research Council, Gerda and Åge Haensch Foundation, Dirktør Åge Henriksens Foundation, P. Carl Petersens Foundation and the Danish Cancer Society     

Studies on the mechanism of cytotoxicity of 3′-deoxyadenosine N1-oxide in different strains of Ehrlich ascites tumor cells

Summary The correlation between the metabolic processing of 3-deoxyadenosine N ¹-oxide (3-dANO) in vitro and its effect on tumor growth in vivo has been investigated in seven different strains of Ehrlich ascites tumor cells.The metabolism of 3-dANO is initiated by reduction to 3-deoxyadenosine (3-dA). This process is the rate-limiting process. The 3-dA does not accumulate, but is converted to 3-deoxyadenosine triphosphate (3-dATP) or 3-deoxyinosine (3-dI). The ratio between 3-dATP and 3-dI inosine corresponds to the ratio between the activities of adenosine kinase and adenosine deaminase in the cell.Two of the cell lines were markedly inhibited by 3-dANO in vivo. In these cells the accumulation of 3-dATP was 1.4–2.2 nmol/h per mg cells, which accounts for the major part of the metabolized 3-dANO. Five of the cell lines were not inhibited by 3-dANO and the formation of 3-dATP was 5–10 times less in these than in the sensitive strains. The low level of 3-dATP is caused primarily by a low ratio between the activities of adenosine kinase and adenosine deaminase, which is 15 time less than in the sensitive cell lines. The rate of reduction of 3-dANO seems to be of minor importance.These results indicate a correlation between the inhibition of tumor growth by 3-dATP and the ability of the cell to accumulate 3-dATP from 3-dANO and show that this conversion is determined solely by the rate of reduction of 3-dANO (3-dANO reductase activity) and the ratio between the activities of adenosine kinase and adenosine deaminase in the cell. Consequently, the estimation of these enzyme activities in cell lysate of a given tumor can be used to predict whether the tumor is susceptible to inhibition by 3-dANO.Abbreviation 3-dANO 3-deoxyadenosine N ¹-oxide - 3-dA 3-deoxyadenosine - 3-dI 3-deoxyinosine - 3-dATP 3-deoxyadenosine triphosphate This work was supported by The Danish Medical Research Council, Gerda and Åge Haensch Fond, Direktor Åge Henriksens Fond, P. Carl Petersens Fond and the Danish Cancer Society     

Phase I/II tolerability/pharmacokinetic study with one-hour intravenous infusion of doxifluiridine (5′-dFUrd) 3 g/m2 VS 5 g/m2 QD x 5 per month

Summary Eighteen patients with advanced solid cancer were treated with daily 5-dFUrd infusions given over 1 h on days 1–5 of a 4-week cycle. Nine patients received 3 g/m² 5-dFUrd daily and another nine patients 5 g/m². One patient on 5 g/m² 5-dFUrd was not fully evaluable for tolerability due to early death (progressive disease) 4 weeks after the first cycle. A total of 48 cycles was given. The gastrointestinal and hematological toxicity was generally mild (grade 1–2). Central neurotoxicity (ataxia, unsteadiness, diplopia, dysarthria, sometimes confusion) was observed in 7 of 8 patients on 5 g/m² 5-dFUrd leading to premature discontinuation of treatment in 3 patients (after 2 cycles). Only 3 of the 9 patients in the 3 g/m² group had slight signs of cerebellopathy. Typically, the reversible neurological side effects started at the end of the 2nd week of a cycle. The serum elimination kinetics of 5-dEUrd and its metabolites 5-FU and 5-dFUH₂ have been investigated in the serum and showed very low intra- and interindividual variations. Peak concentrations of the 5-dFUrd at the end of the infusion approximated 500 mol/l and 1000 mol/l for the 3 g/m² and 5 g/m² group, respectively. The peak of the serum 5-FU was reached at the same time, the ratio 5-FU/5-dFUrd being around 10%. The elimination half-life time for 5-FU was protracted by a factor of 2–3 compared with the direct injection of 5-FU.Monthly infusion of 5-dFUrd 5 mg/m² per day on days 1–5 lead to an unacceptable frequency and degree of neurological toxicity. Similar infusions of 5-dFUrd 3 g/m² per day on days 1–5 were well tolerated.     

Elevation of plasma levels of fluorinated pyrimidines by guanosine 5′-monophosphate

Summary The plasma concentration of 5-fluorouracil (FUra) following the i.v. administration of FUra and guanosine 5-monophosphate (GMP) or guanosine 5-triphosphate (GTP) was markedly elevated. These values were more than 5-fold higher than those obtained with FUra alone over 60 min after administration. The elevation of plasma levels corresponded to the dose of GMP. Higher levels of FUra were maintained in the plasma after injection of inosine or inosine 5-monophosphate in combination with FUra than after FUra alone, but they were lower than those induced by GMP or GTP.Moreover, plasma levels of two other fluorinated pyrimidines, 5-deoxy-5-fluorouridine (DFUR) and 5-fluoro-2-deoxycytidine (FdCyd), were also elevated by GMP. The combination of DFUR and GMP resulted in higher plasma levels of DFUR itself and FUra (12- and 10-fold, respectively, 30 min after treatment). After administration of FdCyd plus GMP, the plasma levels of FdCyd, 5-fluoro-2-deoxyuridine, which is converted from FdCyd by cytidine deaminase, and FUra were 2-, 6-, and 7-fold higher, respectively, than those after FdCyd alone 30 min after treatment. Thus, GMP is the most effective compound for the maintenance of high plasma levels of fluorinated pyrimidines.This study was supported by a Grant-in-Aid from the Ministry of Health and Welfare for a Comprehensive 10-Year Strategy for Cancer Control, Japan     

Modulation of drug cytotoxicity in wild-type and multidrug-resistant tumor cells by stereoisomeric series of C-20′-vinblastine congeners that lack antimicrotubule activity

Summary Seven binary vinca alkaloid congeners were newly synthesized as the C14 or C16(20) or C1416(20) stereoisomers of C20-modified VBL. These congeners lacked detectable antimicrotubule activity in assays of polymerization of purified microtubule protein and of mitotic arrest induction. The compounds modulated the cytotoxicity of VBL, VCR, and DOX in sarcoma and colontumor cell lines. In wild-type cell lines, each congener elicited a concentration-dependent enhancement of cytotoxicity that was drug-and cell-type-selective. For example, C20-deoxy C141620-epi VBL sensitized sarcoma S180 cells 19-fold to DOX and 11-fold to VCR but had no effect on VBL cytotoxicity. In the rat colon-cancer cell lines there was preferential enhancement of VCR cytotoxicity by most congeners. In two MDR cell strains of S180, the modulation potency of each congener was independent of specific drug or of resistance level. As a result, the amount of modulator (concentration) required for reversal was proportional to the drug-resistance level. Such properties were not displayed by the monomeric vinca alkaloid modulator vindoline. The potency of drug modulation in both wild-type and MDR cell strains was dependent on the stereoisomeric form of the congener and its C20-substituents.Abbreviations MDR multidrug resistance - VBL vinblastine - VCR vincristine - DOX doxorubicin - MTP purified microtubule protein - MTX methotrexate - 5-FU 5-fluorouracil This work was supported by grants CH-424 from the American Cancer Institute (to L.S.B.), RO1 12010 from the NCI (to M.E.K.), and P30 CA 22435 from the NCI (to the Vermont Regional Cancer Center). The contents are the responsibility of the authors and do not necessarily represent the views of the NCI     

Noninvasive fluorine-19 NMR study of fluoropyrimidine metabolism in cell cultures of human pancreatic and colon adenocarcinoma

Summary Fluorine-19 NMR spectrometry was used to monitor the metabolism of two antineoplastic fluoropyrimidines, 5-fluorouracil (5FU) and 5-deoxy-5-fluorouridine (5dFUrd), in cell cultures of human pancreatic (Capan-1) and colon (HT-29) adenocarcinoma. The preliminary results showed, for the two tumor cell lines treated with 5FU, the presence in nonperfused cells of three signals corresponding to intracellular metabolites: 5FU, F-nucleotides and F-nucleosides. When the cells were perfused only the signals of F-nucleotides and 5FU were present. The F-nucleosides observed during the analysis of the nonperfused cells came from the conversion of F-nucleotides. During the NMR recording of Capan-1 cells at 37 °C the first metabolite of the catabolic pathway of 5FU, 5,6-dihydro-5-fluorouracil, occurred. At the beginning of the NMR recording of Capan-1 cells treated with 5dFUrd, two signals corresponding to F-nucleotides and F-nucleosides (consistent with 5dFUrd) were observed; during the analysis, a supplementary signal corresponding to 5FU appeared. Even after pretreatment with methotrexate the signal of 5FU incorporated into RNA was not detected. Our experiments, performed in attempts to observe the signal of the ternary complex between thymidylate synthetase (TS), 5-fluoro-2-deoxyuridine-5-monophosphate (FdUMP) and 5,10-methylene-tetrahydrofolate (5,10-CH₂FH₄), allowed detection in some cases of a broad signal, whose chemical shift was similar to that reported in the literature following incubation of TS with FdUMP and 5,10-CH₂FH₄, but our results were not always reproducible.This study was supported by grants from Université Paul Sabatier, Conseil Régional Midi-Pyrénées-CNRS and Caisse Nationale de l'Assurance Maladie des Travailleurs Salariés (INSERM)     

The clinical pharmacology of the adenosine deaminase inhibitor 2′-deoxycoformycin

Summary 2-deoxycoformycin (2-dCF; Pentostatin), a stoichiometric inhibitor of mammalian adenosine deaminase (ado deaminase), exhibits immunosuppressive and antilymphocytic activity in animal test systems. A clinical pharmacology/phase I study of 2-dCF administered as a single agent has been completed (18 patients). Dose levels ranged from 0.1 mg/kgx1 to 0.25 mg/kg/dayx5; ado deaminase and 2-dCF were measured spectrophotometrically. Plasma decay curves were bi-exponential ( and t_1/2 values about 1 and 10 h respectively). Recovery of unchanged 2-dCF from urine (48 h) was 32%–48% of the administered drug. Major toxic manifestations were lymphocytopenia (all patients) and urate nephropathy (1 patient, with subsequent patients in the series receiving allopurinol, 300 mg/day). Three partial responses were seen in seven patients with acute lymphocytic leukaemia receiving 0.25 mg 2-dCF/kg/dayx5.     

New approach to metabolism of 5′-deoxy-5-fluorouridine in humans with fluorine-19 NMR

Summary The metabolism of 5-deoxy-5-fluorouridine (5dFUrd), an antitumor fluoropyrimidine, has been investigated in human biofluids (blood, plasma, urine) using a new method: fluorine-19 NMR spectrometry. This method allows direct study of the biological sample and simultaneous identification of all the fluorinated metabolites. In the blood of a patient treated with 5dFUrd during a 6-h continuous perfusion, we observed unmetabolized 5dFUrd, 5-fluorouracil, 5,6-dihydrofluorouracil, and another metabolite which has not previously been reported -fluoro--alanine. The two major metabolites in urine are unmetabolized 5dFUrd and -fluoro-alanine.     

Reduced cardiotoxicity and increased cytotoxicity in a novel anthracycline analogue, 4′-amino-3′-hydroxy-doxorubicin

Summary The acute and chronic cardiotoxicity and cytotoxicity of the novel doxorubicin (DXR) derivative 4-amino-3-hydroxy-DXR were compared with those of 4-deoxy-DXR and DXR. In the acute cardiotoxicity study, the ECG and hemodynamic changes recorded in anesthetized rats that had been treated i.v. with 10 mg/kg 4-amino-3-hydroxy-DXR or 8.6 mg/kg 4-deoxy-DXR were significantly less severe than those caused by 13 mg/kg DXR. In the chronic cardiotoxicity study, rats received 3 weekly i.v. injections of 3 mg/kg DXR, 3 mg/kg 4-amino-3-hydroxy-DXR, or 2 mg/kg 4-deoxy-DXR during the first 14 days of the study and were observed for an additional 35-day period. DXR induced severe cardiomyopathy that was characterized by ECG changes in vivo (ST-segment widening and T-wave flattening) and by impairment of the contractile responses (F _max,±dF/dt _max) to adrenaline of hearts isolated from treated animals. 4-Deoxy-DXR caused a progressive enlargement of the ST segment in vivo and a significant impairment of the-dF/dt _max value in vitro, which were less severe than those produced by DXR. The least cardiotoxic drug was 4-amino-3-hydroxy-DXR, which induced minor ECG changes without causing significant alterations in the contractile responses of isolated hearts to adrenaline. On the basis of the drug concentration required to inhibit 50% of the colony formation (IC₅₀) of cell lines in vitro, 4-amino-3-hydroxy-DXR was less active than 4-deoxy-DXR but at least twice as active as DXR against human cancer and murine transformed cell lines. These data indicate that 4-amino-3-hydroxy-DXR is significantly less cardiotoxic and more cytotoxic than DXR.     

Occurrence of circulating 7-deoxyaglycone metabolites of 4′-deoxydoxorubicin in man

Summary In five cancer patients we have determined the pharmacokinetics of 4-deoxydoxorubicin (4-DOX), its alcoholic metabolite 4-deoxydoxorubicinol and the occurrence of circulating 7-deoxyaglycone metabolites. The 7-deoxyaglycone of the alcohol metabolite, the major aglycone of Adriamycin (ADR) present in man, was not detected in any serum sample. The 7-deoxyaglycone of the parent drug, which appears in concentrations in excess of 30ng/ml after ADR administration, was detected in only 2/5 patients in trace amounts. These preliminary data indicate a difference in biotransformation between ADR and 4-DOX despite their close structural similarities.     

The distribution ofo,p′-DDD (Mitotane) among serum lipoproteins in normo- and hypertriglyceridemia

Summary We found that the distribution of the lipophilic chemotherapeutic agento,p-DDD (mitotane) among serum (lipo)proteins was altered in hypertriglyceridemia, with relatively moreo,p-DDD accumulating in the chylomicron and very-low-density lipoprotein (VLDL) fraction. Intralipid, an artificial chylomicron emulsion, or isolated VLDL could extracto,p-DDD from the other serum (lipo)proteins. There was an inverse relationship between the relative amount ofo,p-DDD found in the fraction exhibiting a density of <1.006 g/ml (chylomicrons plus VLDL) and the relative amount observed in the LDL or HDL fractions of serum. Our results indicate that hypertriglyceridemia may impede the entry ofo,p-DDD into the brain or the adrenals. For therapeutic monitoring ofo,p-DDD levels in severe hypertriglyceridemia, we recommend that the chylomicron and VLDL fraction first be removed from the serum by ultracentrifugation.     

Fluorescence assays and pharmacokinetic studies of 4′-deoxydoxorubicin and doxorubicin in organs of mice bearing solid tumors

Summary The pharmacokinetic of 4-deoxydoxorubicin, a new analog of doxorubicin, was compared with that of its parent compound in mice treated with equal and equiactive doses. The levels of total fluorescence due to the initial drugs and to metabolites were determined in tissue extracts by fluorometry. 4-Deoxydoxorubicin reached the same tissue levels as doxorubicin in all the organs tested except in spleen and lung, where a higher peak was found in the animals treated with the new analog. The rate of elimination of 4-deoxydoxorubicin from the organs tested was higher than that of doxorubicin.     

Inhibition of fludarabine metabolism by arabinosylcytosine during therapy

Summary The active 5-triphosphate of arabinosyl-2-fluoroadenine (F-ara-ATP) increases the anabolism of arabinosylcytosine (ara-C), whereas ara-C 5-triphosphate inhibits the phosphorylation of arabinosyl-2-fluoroadenine (F-ara-A) in human leukemia cells in vitro. These interactions have a potential impact on drug scheduling. Clinical trials of relapsed leukemia in which fludarabine (F-ara-A 5-monophosphate) and ara-C were given in sequence provided the opportunity to evaluate the effects of ara-C infusion on two sequelae: the pharmacokinetics of F-ara-A in plasma and that of F-ara-ATP in leukemia cells. First, F-ara-A pharmacokinetics were altered by ara-C infusion. This was visualized as a transient increase in F-ara-A plasma levels during the ara-C infusion that was given 4 h after fludarabine. The perturbation in F-ara-A plasma levels was dependent on the dose of ara-C. Second, peak F-ara-ATP concentrations were lower in leukemia cells of patients who received ara-C in addition to fludarabine as compared with those who received fludarabine alone. The terminal half-life of F-ara-A in plasma and the half-life of intracellular F-ara-ATP were reduced after the ara-C infusion in a concentration-dependent manner. Studies using purified deoxycytidine kinase support the conclusion that the increase in plasma levels of F-ara-A is in part the result of an effective competition by ara-C for phosphorylation by this enzyme, leading to a perturbation of the pharmacokinetics of intracellular F-ara-ATP.Abbreviations ara-C 9--d-arabinofuranosylcytosine - ara-CTP 9--d-arabinofuranosylcytosine 5-triphosphate - AUC area under the concentration-time curve - AUC_p inerease in the AUC caused by perturbation - CLL chronic lymphocytic leukemia - dCyd kinase deoxycytidine kinase - F-ara-A 9--d-arabinofuranosyl-2-fluoroadenine 5 - fludarabine F-ara-AMP, 9--d-arabinofuranosyl-2-fluoroadenine 5-monophosphate - F-ara-ATP 9--d-arabinofuranosyl-2-fluoroadenine 5-triphosphate - t _1/2 half-life of elimination This work was supported in part by grants CA32839, CA46452, CA53311, and CA57629 from the National Cancer Institute, Department of Health and Human Services, by the German Research Association (DFG), and by a contract from Berlex Laboratories, Inc.     

In vivo effects in mice produced by a 3′-branched homologue of α-2′-deoxythioguanosine

Summary Studies with a 3-branched chain homolog (-3-BCTGdR) of 2-deoxythioguanosine (-TGdR) showed that it did not prolong the survival of mice bearing the Mecca lymphosarcoma. Host toxicity was quite profound and resembled that seen with 6-thioguanine (6-TG). Evidence was obtained that this nucleoside derivative was not appreciably converted to 6-TG in the mouse. Mice treated with toxic doses of 6-TG or -3-BCTGdR were found to have very similar pathological changes. The granulocytes were eliminated from the peripheral blood, bone marrow was acellular, and some more limited damage was seen in the intestinal crypts. Experiments with radiosulfur-labeled drugs demonstrated that -3-BCTGdR was incorporated into the DNA of mouse bone marrow, predominantly in the chain-terminating position, with the result that shorter chains of DNA accumulated. The new homolog, unlike -TGdR, was phosphorylated in bone marrow as well as in tumor, and incorporated well into the DNA both of bone marrow and of the neoplastic cells. In devising other homologs attention must be given to the specificity of the kinases, i.e., to whether phosphorylation is superior in tumor cells or in the growing normal cells.Abbreviations used are 6-TG 6-thioguanine - ,-TGdR ,-2-deoxythioguanosine - -3-BCTGdR 6-thioguanine--2,3-dideoxy-3-(hydroxymethyl)-d-erythro-pentofuranose - ³H-TdR Tritium-labeled (methyl) thymidine     

Pharmacokinetic study of doxifluridine given by 5-day stepped-dose infusion

Summary Doxifluridine (5-deoxy-5-fluorouridine, 5-dFUR) metabolism has been reported to be saturable and associated with a fall in clearance of the drug as the dose is increased. The aim of the present study was to determine the disposition of 5-dFUR and 5-fluorouracil (5-FU) when 5-dFUR was given as a 5-day infusion, with the infusion rate increased stepwise every 24 h. Measurement of plasma and urinary levels of 5-dFUR and 5-FU at steadystate for each infusion rate enabled the estimation of 5-dFUR renal (Cl_R) and nonrenal (Cl_NR) clearance and 5-FU renal clearance. A total of 28 patients with histologically proven malignancy received 5-day courses of 5-dFUR ranging in dose from 3.75 to 20 g/m² per 120 h. The lowest dose given over 24 h was 0.25 g/m², and the highest was 5 g/m². Steady-state plasma levels of 5-dFUR ranged from 167 to 6.519 ng/ml. At these plasma levels there was no evidence of significant saturation of 5-dFUR metabolism; steady-state plasma levels of 5-dFUR increased approximately linearly with dose, and nonrenal clearance did not change significantly with dose. There was also no evidence of nonlinearity in 5-dFUR renal clearance. The mean (±SD) Cl_R of 5-dFUR was 108.9±53.6 ml/min per m² (range, 45.7–210 ml/min per m²), and the Cl_NR was 728±181 ml/min per m² (range, 444–1,119 ml/min per m²). Renal clearance comprised 13% of the total 5-dFUR clearance. The mean renal clearance of 5-FU was 100.8±48.6 ml/min per m² (range, 23.5–198 ml/min per m²). There was considerable interpatient variability in 5-dFUR renal and nonrenal clearance, event at the same dose level. We concluded that the administration of 5-dFUR by the infusion method described avoided the saturation of nonrenal elimination processes reported to occur with shorter infusion schedules.This study was supported by a grant from F. Hoffmann-La Roche, Basel, Switzerland