Genetic polymorphism in MDR1 C3435T is a determinant of methotrexate cerebrospinal fluid concentrations in Chinese children with acute lymphoblastic leukemia
.

AIM: This study aimed to investigate the influence of single-nucleotide polymorphism in exon 26 (C3435T) of multidrug resistance 1 (MDR1) transporter gene on the concentration of methotrexate (MTX) in Chinese childhood patients with acute lymphoblastic leukemia (ALL) receiving intravenous (IV) and intrathecal (IT) high-dose methotrexate (HDMTX) chemotherapy. MATERIALS AND METHODS: MDR1 C3435T polymorphism was investigated in 60 patients with Chinese childhood ALL. The study also compared the MDR1; polymorphism between the patients with Chinese childhood ALL and the published data on Americans, Mexicans, Caucasians, and Thais. The C3435T polymorphism was identified using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and direct sequence analysis. Cerebrospinal fluid (CSF) and plasma concentrations of MTX were measured using high-performance liquid chromatography (HPLC). MTX concentrations were compared according to MDR1 C3435T genotypes. RESULTS: The frequencies of MDR1 C3435T genotype in male and female patients with Chinese childhood ALL were significantly different (p = 0.001). For the frequencies of MDR1 C3435T genotype in Hui and Han patients with Chinese childhood ALL there was no difference (p = 0.188). The distribution of allele frequencies in patients with Chinese childhood ALL was similar to the published data on Americans, Mexican, Caucasians, and Thais (p > 0.05). The CSF concentrations of MTX were found to be significantly different between the C allele (CC + CT) carriers and TT homozygous group (p = 0.04). The plasma concentrations of MTX had no significant difference between the C allele (CC + CT) carriers and TT homozygous group (p > 0.1). CONCLUSION: This study showed that the polymorphism of MDR1 C3435T influenced the CSF concentration of MTX in patients with Chinese childhood ALL receiving IV and IT HDMTX treatment.

Comparison of pharmacokinetics and toxicity after high-dose methotrexate treatments in children with acute lymphoblastic leukemia.

We carried out a detailed comparative study of the pharmacokinetics and toxicity of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) after high-dose intravenous methotrexate (HD-MTX) in children with acute lymphoblastic leukemia (ALL). Overall, 65 children were treated with 5 g/m2/24 h MTX and 88 children were treated with 2 g/m2/24 h MTX according to ALL-BFM 95 and ALL IC-BFM 2002 protocols (mean age: 6.4 years, range 1.0-17.9 years). A total of 583 HD-MTX courses were analyzed. Serum MTX and 7-OH-MTX levels were measured at 24, 36, and 48 h, and cerebrospinal fluid (CSF) MTX levels were determined 24 h after the initiation of the infusion. The area under the concentration-time curve was calculated. Hepatotoxicity, nephrotoxicity, and bone marrow toxicity were estimated by routine laboratory tests. We investigated pharmacokinetics and toxicity in distinct age groups (< 6 and > 14 years). 5 g/m2/24 h treatments resulted in higher serum and CSF MTX and 7-OH-MTX levels (P < 0.05). The CSF penetration rate of MTX was independent of the MTX dose [2.3% (95% confidence interval: 1.7-2.5%) vs. 2.8% (95% confidence interval: 2.4-3%)]. The CSF MTX concentration was correlated with the 24 h MTX serum level (r = 0.38, P < 0.0001). Repeated treatments did not alter MTX or 7-OH-MTX levels. 7-OH-MTX levels were correlated with nephrotoxicity (r = 0.36, P < 0.0001). Higher MTX levels and toxicity occurred more frequently in children aged older than 14 years (P < 0.05). Therapeutic serum and CSF MTX concentrations can be achieved more reliably with 5 g/m2/24 h treatments. To predict the development of toxicity, monitoring of the level of the 7-OH-MTX is useful. Monitoring of pharmacokinetics is essential to prevent the development of severe adverse events in adolescents.

Pharmacokinetics and efficacy of pemetrexed in patients with brain or leptomeningeal metastases.

Brain metastases (BM) and leptomeningeal metastases (LM) are devastating neurologic complications. Pemetrexed is a multi-targeted anti-folate agent approved for treatment of nonsquamous non-small cell lung cancer but has anti-tumor activity in other solid tumors. We performed two trials using pemetrexed in patients with BM and LM to assess CSF penetration and anti-tumor activity. Patients were treated with intravenous pemetrexed at doses of 500 (n = 3), 750 (n = 3), 900 (n = 12) or 1,050 mg/m(2) (n = 3) every 3 weeks. Neuro-imaging was done every 6 weeks. Matched CSF and plasma samples were obtained serially from three patients with Ommaya reservoirs; the remaining patients had a single paired collection. Twenty-one patients (15 women and six men) with median age of 50 years and median KPS of 90 were treated. Primary tumors included breast (13), lung (4), colorectal (1), endometrial (1), esophageal (1) and pinealoblastoma (1). Nine patients had prior whole brain RT and median number of prior chemotherapies was two including prior methotrexate in four patients. Median pemetrexed doses administered was three (range 1-14). Responses included one partial response, ten stable disease and ten progressive disease. Median time to progression and survival was 2.7 and 7.3 months; PFS six was 22 %. No major toxicities were seen. Pemetrexed distributed from the plasma to the CSF within 1-4 h with the resulting CSF concentrations < 5 % of plasma. Pemetrexed was tolerated in solid tumor patients with CNS metastases. Limited anti-tumor activity was seen, which might have been due to low CSF concentrations, although some patients displayed prolonged benefit.

Accidental overdose of intrathecal cytarabine in children.

OBJECTIVE: To report 2 cases of intrathecal cytarabine overdose in children with cancer, neither of whom underwent cerebrospinal fluid (CSF) exchange per current recommendations or developed apparent toxicity related to the event. CASE SUMMARY: A 17-year-old female with newly diagnosed acute myeloid leukemia received 177 mg of intrathecal cytarabine rather than the appropriate dose of 70 mg. She was monitored closely with no apparent toxicity from the event. A 4-year-old boy with newly diagnosed precursor B-cell acute lymphoblastic leukemia received 175 mg of intrathecal cytarabine rather than the appropriate dose of 70 mg. CSF was immediately withdrawn and intrathecal hydrocortisone was instilled for possible antiinflammatory effect. He developed no apparent toxicity from the event. DISCUSSION: Cytarabine is an important chemotherapeutic agent in the treatment of leukemia. One case report of intrathecal cytarabine overdose was identified in the literature, which recommended CSF exchange as management. Neither child in our report underwent CSF exchange or developed apparent toxicity related to the event. Institutional changes were made in both cases to prevent similar events. CONCLUSIONS: These cases demonstrate that measures such as CSF exchange are not uniformly required for cytarabine overdose.

Sequential arabinosylcytosin with or without fludarabine in paracmastic patients with acute myeloid leukemia.

The purpose of this study is to assess how fludarabine (Fa) influences arabinosylcytosin's (Ara-C) mode of action. Plasma, cerebrospinal and urine samples were withdrawn from two study groups at specific time points and analyzed by HPLC. Group A was treated with Ara-C only whereas Group B was treated with Fa+Ara-C. The two study groups are all undergoing complete remission (CR). The Ara-C dose for Group A was 3g/m2 x 2, and the AUC(0-4) was 5.131 +/- 0.936. The Ara-C dose for Group B was 2g/m2 x 2, and the AUC(0-4) was 12.245 +/- 3.863. The AUC(0-4) for Group B is more than twice the AUC(0-4) for Group A, and these results indicate that Fa conduces a synergistic increase in the concentration and AUC of Ara-C in plasma and in cerebrospinal fluid. The pharmacokinetics between the different dose treatments was statistically different (P = 0.016). The differences in the ratios of C(Ara-u) to C(Ara-C), and in the Tmax between Groups A and B could indicate whether or not Ara-C combined with Fa. Although Group B demonstrates a higher AUC(0-4) with lower doses of Ara-C (2 g/m2 x 2), the adverse drug reaction (ADR) and bone inhibition were not more pronounced in Group B compared to Group A. These results are based on a limited number of case studies, hence, additional studies are necessary to support and prove this hypothesis.

Liposomal cytarabine for central nervous system embryonal tumors in children and young adults.

To assess the tolerability and efficacy of liposomal cytarabine (LC), an encapsulated, sustained-release, intrathecal (IT) formulation of cytosine arabinoside, in de novo and relapsed central nervous system (CNS) embryonal tumors in children and young adults. We studied retrospectively all patients less than age 30 at our institution treated consecutively with LC for medulloblastoma (MB), primitive neuroectodermal tumor (PNET), and atypical teratoid rhabdoid tumor (ATRT). Seventeen patients received LC (2 mg/kg up to 50 mg, every 2 weeks to monthly) at diagnosis of high-risk CNS embryonal tumor (2 PNET, 3 ATRT) or relapse of MB (12 MB; 9 had leptomeningeal metastases). Sixteen patients received concurrent systemic chemotherapy. A total of 108 doses were administered (IT 82, intraventricular 26) with a mean of six (range 1-16) treatments per patient. Only three administrations were associated with adverse effects of arachnoiditis or headache. None developed malignant cerebrospinal fluid (CSF) cytology while receiving LC. All the six evaluable patients with malignant CSF cytology and treated with at least two doses cleared their CSF (mean 3 doses, range 1-5). Median overall survival in relapse patients was 9.1 months. Five patients (4 de novo and 1 relapsed) remain alive in complete remission for a median 26.8 months from first LC. Liposomal cytarabine is an easily administered, well-tolerated, and active drug in patients with high-risk embryonal neoplasms. One-third of our cohort remains in remission from otherwise fatal diagnoses. Our findings warrant a phase II trial of LC in newly diagnosed or recurrent CNS embryonal tumors.

Therapeutic drug monitoring of methotrexate in cerebrospinal fluid after systemic high-dose infusion in children: can the burden of intrathecal methotrexate be reduced?

The use of intrathecal (IT) methotrexate (MTX) in combination with systemic high-dose (HD) MTX is an established procedure for central nervous system prophylaxis in patients with acute lymphoblastic leukemia, but the evidence for the necessity of this combination is not convincing. The MTX concentration in the cerebrospinal fluid (CSF) was evaluated in 138 samples from children with acute lymphoblastic leukemia and non-Hodgkin lymphoma. CSF samples were obtained by lumbar puncture 12-24 hours after starting the HD MTX infusion (5 g/m2 over 24 hours) and immediately before the IT administration of MTX. Serum MTX concentrations at the end of infusion were assessed by routine therapeutic drug monitoring. Cytotoxic MTX concentrations of 1 microM or greater were detected in 81.2% of CSF samples. CSF MTX concentrations were significantly lower in samples from patients younger than 7 years. The correlation between MTX concentrations in the serum and the CSF was moderate (r = 0.451) and became stronger with increasing age. The median CSF MTX concentrations per cycle were comparable (1.40, 1.25, 1.39, 1.38 microM for cycles 1-4, respectively). The predictive value and the accuracy of the CSF MTX concentration measured during the first cycle of HD MTX in respect to concentrations in the following cycles were high (94.4% and 85.7%, respectively) suggesting that the CSF MTX concentration during the first HD MTX infusion is a useful predictor for sufficient CSF MTX concentrations in the following HD MTX cycles. Our results confirm previously published data on MTX accumulation in the CSF after 5 g/m2 MTX over 24 hours in an independent cohort monitored in a real-life setting. Based on the common opinion that 1 microM represents the minimal antileukemic MTX concentration, current data warrant reevaluation of the necessity of routine IT MTX following HD MTX. Our findings offer a perspective on reducing the burden of IT MTX in children on consolidation therapy by CSF MTX drug monitoring.

Delayed recognition of intrathecal methotrexate overdose.

A 10-year-old girl who presented to our hospital was diagnosed as having B-precursor cell acute lymphoblastic leukemia. St Jude's Total XIII protocol was started. In the second block of the consolidation phase, 10 hours after triple intrathecal treatment, we realized that instead of 12 mg, 120 mg of methotrexate had accidentally been given. Although the patient had no symptoms 10 hours after intrathecal treatment, to prevent the possible neurotoxic effects of methotrexate, a cerebrospinal fluid exchange was performed. Simultaneously, systemic dexamethasone and calcium folinic acid were given. At the time of this writing (2 y), the patient has had no symptoms and has continued on the chemotherapy protocol as planned. Administration of high-dose intrathecal methotrexate may not lead to symptoms, as was the case in our patient. This may be related to individual variations in cerebrospinal fluid dynamics and drug metabolism.

Pharmacodynamic properties of methotrexate and Aminotrexate during weekly therapy.

4-Amino-pteroyl-glutamic acid (Aminotrexate; AMT) has several advantages over the related antifolate methotrexate (MTX), including greater potency, complete oral bioavailability, and greater accumulation by leukemic blasts in vitro. We compared the pharmacodynamic properties of AMT (given orally at 4 mg/m2 in two divided doses per week) and MTX (100 mg/m2 in four divided doses per week) among children with acute lymphoblastic leukemia. We find AMT and MTX to have equivalent penetration into the bone marrow compartment of these patients, as indicated by the steady-state concentrations within mature red blood cells (RBCs). However, MTX concentrations in the cerebrospinal fluid after oral dosage are significantly greater than AMT. To confirm these clinical observations, mice were treated four weekly injections of AMT or MTX, at a 1:20 dosage ratio, and tissue antifolate content was then determined over the subsequent 22 days. We confirm the selective exclusion of AMT from the CNS compartment, while showing equivalent accumulation of AMT and MTX in the RBCs, liver, spleen, kidneys and testes. Finally, we demonstrate that AMT, MTX, and their predominant polyglutamate species are equipotent inhibitors of their target intracellular enzyme dihydrofolate reductase, emphasizing the critical nature of steady-state tissue accumulation in determining the relative cytotoxic potency of these two antifolates.

Influence of particle size on transport of methotrexate across blood brain barrier by polysorbate 80-coated polybutylcyanoacrylate nanoparticles.

Transports of methotrexate-loaded polybutylcyanoacrylate nanoparticles with different sizes across blood brain barrier were investigated in this experiment. The drug-loaded nanoparticles were prepared by emulsion polymerization method. After coating with polysorbate 80, nanoparticles with the size 70, 170, 220, 345 nm were, respectively, i.v. injected into rats at the dose of 3.2 mg/kg. Uncoated nanoparticles and methotrexate solution were also i.v. injected at the same dosage as controls. 0.5, 1, 1.5, 2, 3, 4 h after injection, cerebrospinal fluids and brain tissues were collected for tests. Drug level in all biological samples was determined by HPLC. It was found out that nanoparticles overcoated by polysorbate 80 could significantly improve the drug level in both brain tissues and cerebrospinal fluids compared with uncoated ones and simple solution. Seventy-nanometer nanoparticles could deliver more drugs into brain while no significant difference was observed among the other three size ranges. In conclusion, polysorbate 80-coated polybutylcyanoacrylate nanoparticles could be used to overcome blood brain barrier especially those whose diameter was below 100 nm.

Discovery of 6-Diazo-5-oxo-l-norleucine (DON) Prodrugs with Enhanced CSF Delivery in Monkeys: A Potential Treatment for Glioblastoma.

The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON, 1) has shown robust anticancer efficacy in preclinical and clinical studies, but its development was halted due to marked systemic toxicities. Herein we demonstrate that DON inhibits glutamine metabolism and provides antitumor efficacy in a murine model of glioblastoma, although toxicity was observed. To enhance DON's therapeutic index, we utilized a prodrug strategy to increase its brain delivery and limit systemic exposure. Unexpectedly, simple alkyl ester-based prodrugs were ineffective due to chemical instability cyclizing to form a unique diazo-imine. However, masking both DON's amine and carboxylate functionalities imparted sufficient chemical stability for biological testing. While these dual moiety prodrugs exhibited rapid metabolism in mouse plasma, several provided excellent stability in monkey and human plasma. The most stable compound (5c, methyl-POM-DON-isopropyl-ester) was evaluated in monkeys, where it achieved 10-fold enhanced cerebrospinal fluid to plasma ratio versus DON. This strategy may provide a path to DON utilization in glioblastoma multiforme patients.

Evaluation of Biomarkers of Oxidative Stress and Apoptosis in Patients With Severe Methotrexate Neurotoxicity: A Case Series.

Central nervous system (CNS) treatment is an essential part of acute lymphocytic leukemia (ALL) therapy, and the most common CNS treatment is intrathecal (IT) and high-dose intravenous (IV) methotrexate (MTX). Treatment with MTX may cause neurotoxicity, which is often accompanied by neurologic changes, delays in treatment, and prolonged hospital stays. This article reports clinical presentations of 3 patients with severe MTX toxicity as well as levels of oxidative stress and apoptosis biomarkers in cerebrospinal fluid (CSF). Oxidative stress was measured by oxidized phosphatidylcholine (PC), oxidized phosphatidylinositol (PI), and F2 isoprostanes; apoptosis was measured by caspase 3/7 activity. Most consistent biomarker changes in all 3 cases were increases in caspase 3/7 and F2 isoprostanes prior to acute toxicity while increases in oxidized phospholipids occurred slightly later. Progressive increases in F2 isoprostanes and caspase 3/7 activity prior to and/or during acute toxicity suggests MTX induces oxidative stress and an associated increase in apoptosis. These findings support the role of oxidative stress in MTX-related neurotoxicity.

Pharmacokinetics of methotrexate in cerebrospinal fluid and serum after osmotic blood-brain barrier disruption in patients with brain lymphoma.

OBJECTIVE: To evaluate the pharmacokinetics of methotrexate in ventricular cerebrospinal fluid and serum after osmotic blood-brain barrier disruption and intra-arterial administration compared with intravenous or simple intra-arterial infusion in patients with primary central nervous system lymphoma. METHODS: Serum and ventricular cerebrospinal fluid were sampled after methotrexate administration in 12 patients. Blood-brain barrier disruption was induced on 2 sequential days by mannitol (25%) infusion delivered to the vertebral or internal carotid artery territories followed by intra-arterial methotrexate (dose, 1.4 g/m2; 47 treatments). Sixteen treatments were given without barrier disruption by intravenous (3.5 g/m2; nine treatments) or intra-arterial (2.8 g/m2; seven treatments) infusion. RESULTS: Ventricular cerebrospinal fluid-methotrexate peak levels after blood-brain barrier disruption of the vertebral and the internal carotid arteries territories were 19.3 +/- 2.9 and 8.5 +/- 0.7 micromol/L (P < .001), and the area under the curve from time 0 to infinity was 178.0 +/- 21.3 and 110.0 +/- 12.4 [micromol/L x h, respectively (P < .01). No significant differences were observed in serum levels. After intra-arterial infusion was performed without disruption, the serum peak level was higher than that achieved by intravenous treatment (518.2 +/- 67.7 versus 180.6 +/- 31.8 micromol/L; P < .001). No differences were observed in cerebrospinal fluid concentrations, which dropped below 1 micromol/L at 6 hours. The cerebrospinal fluid/serum ratio [AUC(%)] of methotrexate after blood-brain barrier disruption was three to four times greater than that by systemic administration. CONCLUSION: Enhanced methotrexate delivery to the central nervous system can be attained by intra-arterial administration combined with osmotic disruption of the blood-brain barrier compared with simple intra-arterial or intravenous administration.

Successful treatment of intrathecal methotrexate overdose by using ventriculolumbar perfusion and intrathecal instillation of carboxypeptidase G2.

Prompt and appropriate management measures are critical in order to achieve a favorable outcome after a major overdose of intrathecally (IT) administered methotrexate (MTX). Published information available to guide clinicians in the immediate management of this medical emergency is scant. Herein we describe a 6-year-old boy with acute lymphoblastic leukemia who received an inadvertent overdose of 600 mg of IT administered MTX instead of the intended dose of 12 mg. Severe acute neurotoxicity developed rapidly. Lumbar puncture and drainage of 15 mL of cerebrospinal fluid 2 hours after administration resulted in removal of 32% of the administered drug. Ventriculolumbar perfusion with 240 mL of warmed isotonic saline through ventricular and lumbar catheters for 3 hours resulted in removal of a total of 90% of the drug within 8 1/2 hours after administration. IT administration of 2,000 U of carboxypeptidase G2 (CPDG2), an enzyme that inactivates MTX, resulted in a further 150-fold reduction in cerebrospinal fluid MTX concentration. The patient experienced complete recovery. To our knowledge, this is the first reported case of the use of IT instillation of CPDG2 for the treatment of an overdose of IT administered MTX in a human, and it is only the second reported favorable outcome after an IT overdose of more than 500 mg of MTX. Minor IT overdoses of MTX can be managed by immediate lumbar drainage alone. Major overdoses may also necessitate prompt ventriculolumbar perfusion, IT instillation of CPDG2, and further supportive measures for a successful outcome after this infrequent but potentially catastrophic event.

Variability in methotrexate serum and cerebrospinal fluid pharmacokinetics in children with acute lymphocytic leukemia: relation to assay methodology and physiological variables.

Methotrexate (MTX) steady state concentrations were evaluated in 42 children who had received high-dose infusions (6-8 g/m2) for acute lymphocytic leukemia. Concentrations in serum and cerebrospinal fluid (CSF) measured by immunoassay were found to be highly variable. Reanalysis by a reference high-pressure liquid chromatography method ruled out analytical factors as a source of this variability. The correlation coefficient between the analytical methods was 0.77 for the serum data and 0.88 for the CSF data. The variability of serum and CSF concentrations was higher in younger patients (serum; P = 0.05 and CSF; P = 0.18), and the CSF concentration decreased with decreasing age and in later courses. Body surface area, body mass index, weight, and gender were not significantly related to MTX variability. We conclude that the pronounced pharmacokinetic variability seen during MTX infusions remains largely unexplained.

Plasma and cerebrospinal fluid pharmacokinetics of gemcitabine after intravenous administration in nonhuman primates.

PURPOSE: Gemcitabine (dFdC) is a difluorine-substituted deoxycytidine analogue that has demonstrated antitumor activity against both leukemias and solid tumors. Pharmacokinetic studies of gemcitabine have been performed in both adults and children but to date there have been no detailed studies of its penetration into cerebrospinal fluid (CSF). The current study was performed in nonhuman primates to determine the plasma and CSF pharmacokinetics of gemcitabine and its inactive metabolite, difluorodeoxyuridine (dFdU) following i.v. administration. METHODS: Gemcitabine, 200 mg/kg, was administered i.v. over 45 min to four nonhuman primates. Serial plasma and CSF samples were obtained prior to, during, and after completion of the infusion for determination of gemcitabine and dFdU concentrations. Gemcitabine and dFdU concentrations were measured using high-performance liquid chromatography (HPLC) and modeled with model-dependent and model-independent methods. RESULTS: Plasma elimination was rapid with a mean t1/2 of 8 +/- 4 min (mean +/- SD) for gemcitabine and 83 +/- 8 min for dFdU. Gemcitabine total body clearance (ClTB) was 177 +/- 40 ml/min per kg and the Vdss was 5.5 +/- 1.0 l/kg. The maximum concentrations (Cmax) and areas under the time concentration curves (AUC) for gemcitabine and dFdU in plasma were 194 +/- 64 microM and 63.8 +/- 14.6 microM.h, and 783 +/- 99 microM and 1725 +/- 186 microM.h, respectively. The peak CSF concentrations of gemcitabine and dFdU were 2.5 +/- 1.4 microM and 32 +/- 41 microM, respectively. The mean CSF:plasma ratio was 6.7% for gemcitabine and 23.8% for dFdU. CONCLUSIONS: There is only modest penetration of gemcitabine into the CSF after i.v. administration. The relatively low CSF exposure to gemcitabine after i.v. administration suggests that systemic administration of this agent is not optimal for the treatment of overt leptomeningeal disease. However, the clinical spectrum of antitumor activity and lack of neurotoxicity after systemic administration of gemcitabine make this agent an excellent candidate for further studies to assess the safety and feasibility of intrathecal administration.

Effect of probenecid on ventricular cerebrospinal fluid methotrexate pharmacokinetics after intralumbar administration in nonhuman primates.

PURPOSE: Intrathecal methotrexate (MTX) achieves high concentrations in the cerebrospinal fluid (CSF) following intralumbar administration. However, peak ventricular CSF MTX concentrations are highly variable and are < 10% of those achieved with intraventricular dosing. The objectives of this study were to evaluate the effect of intralumbar and intravenous probenecid on ventricular CSF MTX concentrations after intralumbar administration of MTX, and to compare the pharmacokinetics of MTX after intralumbar and intraventricular administration. METHODS: Nonhuman primates (Macaca mulatta) with permanently implanted catheters in the lateral and fourth ventricles received 0.5 mg intraventricular (lateral ventricle) MTX, or 0.5 mg intralumbar MTX with and without intralumbar or intravenous probenecid. Animals were kept prone for 1 h after MTX administration, and ventricular CSF was sampled up to 48 h from a fourth ventricular Ommaya reservoir. MTX concentrations were measured using the dihydrofolate reductase enzyme inhibition assay. Area under the ventricular CSF MTX concentration-time curve (AUC) was used as a measure of MTX exposure. RESULTS: Peak ventricular CSF MTX concentrations and AUCs were highly variable after intralumbar MTX administration. Ventricular CSF MTX AUCs increased by a mean of 3.2-fold after the addition of intralumbar probenecid. Intravenous administration of probenecid did not result in an increase in ventricular CSF MTX AUCs. Asymptomatic pleocytosis was observed in all animals after intralumbar probenecid administration. Ventricular CSF MTX concentrations and AUCs were less variable after intraventricular administration of MTX. CONCLUSION: The administration of intralumbar but not intravenous probenecid increases the ventricular CSF MTX exposure after intralumbar MTX administration.

The plasma pharmacokinetics and cerebrospinal fluid penetration of the thymidylate synthase inhibitor raltitrexed (Tomudex) in a nonhuman primate model.

PURPOSE: Raltitrexed (Tomudex), ZD1694) is a novel quinazoline folate analog that selectively inhibits thymidylate synthase. Intracellularly, raltitrexed is polyglutamated to its active form which can be retained in cells for prolonged periods. The pharmacokinetics of raltitrexed in plasma and cerebrospinal fluid (CSF) were studied in a nonhuman primate model. METHODS: Animals received 3 mg/m(2) (n = 1), 6 mg/m(2) (n = 3), or 10 mg/m(2) (n = 3) i.v. over 15 min, and frequent plasma samples were obtained over 48 h. CSF samples were drawn from an indwelling 4th ventricular Ommaya reservoir over 48 h. Plasma and CSF raltitrexed concentrations were measured with a novel, sensitive enzyme inhibition assay with a lower limit of quantification of 0.005 microM. A three-compartment pharmacokinetic model was fitted to the raltitrexed plasma concentration-time data. RESULTS: The plasma concentration-time profile of raltitrexed was triexponential with a rapid initial decline and a prolonged terminal elimination phase (t(1/2) > 24 h), which was related to retention of raltitrexed in a deep tissue compartment. At the peak approximately 30% of the administered dose was in the deep tissue compartment, and 24 h after the dosing >20% of the administered dose remained in the body with >99% in the deep tissue compartment. The mean peak (end of infusion) plasma concentrations after the 3, 6, and 10 mg/m(2) doses were 1.5, 2.4 and 4.8 microM, respectively. The clearance of raltitrexed ranged from 110 to 165 ml/min per m(2), and the steady-state volume of distribution exceeded 200 l/m(2). The CSF penetration of raltitrexed was limited (0.6 to 2.0%) and drug could only be detected in the CSF following a 10 mg/m(2 )dose. CONCLUSIONS: The elimination of raltitrexed is triexponential with a prolonged terminal elimination phase. The pharmacokinetic profile is consistent with extensive polyglutamation and intracellular retention of ralitrexed. The three-compartment model presented here may be useful for the analysis of the pharmacokinetics of raltitrexed in humans.

Pharmacokinetics and cerebrospinal fluid penetration of phenylacetate and phenylbutyrate in the nonhuman primate.

INTRODUCTION: Phenylbutyrate (PB) and its metabolite phenylacetate (PA) demonstrate anticancer activity in vitro through promotion of cell differentiation, induction of apoptosis through the p21 pathway, inhibition of histone deacetylase, and in the case of PB, direct cytotoxicity. We studied the pharmacokinetics, metabolism, and cerebrospinal fluid (CSF) penetration of PA and PB after intravenous (i.v.) administration in the nonhuman primate. METHODS: Three animals received 85 mg/kg PA and 130 mg/kg PB as a 30-min infusion. Blood and CSF samples were obtained at 15, 30, 35, 45, 60 or 75 min, and at 1.5, 2.5, 3.5, 5.5, 6.5, 8.5, 10.5 and 24.5 h after the start of the infusion. Plasma was separated immediately, and plasma and CSF were frozen until HPLC analysis was performed. RESULTS: After i.v. PA administration, the plasma area under the concentration-time curve (AUC) of PA (median +/- SD) was 82 +/- 16 mg/ml.min, the CSF AUC was 24 +/- 7 mg/ml.min, clearance (Cl) was 1 +/- 0.3 ml/min per kg, and the AUCCSF:AUCplasma ratio was 28 +/- 19%. After i.v. PB administration, the plasma PB AUC was 19 +/- 3 mg/ml.min, the CSF PB AUC was 8 +/- 11 mg/ml.min, the PB Cl was 7 +/- 1 ml/min per kg, and the AUCCSF:AUCplasma ratio was 41 +/- 47%. The PA plasma AUC after i.v. PB administration was 50 +/- 9 mg/ml.min, the CSF AUC was 31 +/- 24 mg/ml.min, and the AUCCSF:AUCplasma ratio was 53 +/- 46%. CONCLUSIONS: These data indicate that PA and PB penetrate well into the CSF after i.v. administration. There may be an advantage to administration of PB over PA, since the administration of PB results in significant exposure to both active compounds. Clinical trials to evaluate the activity of PA and PB in pediatric central nervous system tumors are in progress.