The primacy of NF1 loss as the driver of tumorigenesis in neurofibromatosis type 1-associated plexiform neurofibromas.

Neurofibromatosis type 1 (NF1) is a common tumor-predisposition disorder due to germline mutations in the tumor suppressor gene NF1. A virtually pathognomonic finding of NF1 is the plexiform neurofibroma (PN), a benign, likely congenital tumor that arises from bi-allelic inactivation of NF1. PN can undergo transformation to a malignant peripheral nerve sheath tumor, an aggressive soft-tissue sarcoma. To better understand the non-NF1 genetic contributions to PN pathogenesis, we performed whole-exome sequencing, RNASeq profiling and genome-wide copy-number determination for 23 low-passage Schwann cell cultures established from surgical PN material with matching germline DNA. All resected tumors were derived from routine debulking surgeries. None of the tumors were considered at risk for malignant transformation at the time; for example, there was no pain or rapid growth. Deep (~500X) NF1 exon sequencing was also conducted on tumor DNA. Non-NF1 somatic mutation verification was performed using the Ampliseq/IonTorrent platform. We identified 100% of the germline NF1 mutations and found somatic NF1 inactivation in 74% of the PN. One individual with three PNs had different NF1 somatic mutations in each tumor. The median number of somatic mutations per sample, including NF1, was one (range 0-8). NF1 was the only gene that was recurrently somatically inactivated in multiple tumors. Gene Set Enrichment Analysis of transcriptome-wide tumor RNA sequencing identified five significant (FDR<0.01) and seven trending (0.01⩽FDR<0.02) gene sets related to DNA replication, telomere maintenance and elongation, cell cycle progression, signal transduction and cell proliferation. We found no recurrent non-NF1 locus copy-number variation in PN. This is the first multi-sample whole-exome and whole-transcriptome sequencing study of NF1-associated PN. Taken together with concurrent copy-number data, our comprehensive genetic analysis reveals the primacy of NF1 loss as the driver of PN tumorigenesis.

Vandetanib successfully controls medullary thyroid cancer-related Cushing syndrome in an adolescent patient.

CONTEXT: Ectopic Cushing syndrome due to ACTH secretion from metastatic medullary thyroid cancer (MTC) is associated with significant morbidity and mortality. OBJECTIVE: The aim of the study was to describe the first case of Cushing syndrome associated with MTC in a pediatric patient and the successful reversal of Cushing syndrome with tyrosine kinase inhibitor (vandetanib) therapy. PATIENT AND METHODS: A 17-year-old Brazilian adolescent presented with metastatic MTC and associated ACTH-dependent ectopic Cushing syndrome in the context of multiple endocrine neoplasia type 2B. When the patient was treated with the tyrosine kinase inhibitor vandetanib, rapid decrease in serum cortisol and improvement of clinical symptoms were observed. CONCLUSION: We describe the first pediatric case of clinical and biochemical improvement of paraneoplastic MTC-related Cushing syndrome after treatment with vandetanib. Vandetanib and possibly other tyrosine kinase inhibitors may be a novel beneficial option in patients with neuroendocrine tumor-related ectopic Cushing syndrome.

Phase I trial of pegylated interferon-alpha-2b in young patients with plexiform neurofibromas.

OBJECTIVE: Interferon has antiproliferative and antiangiogenic properties. We sought to evaluate preliminary efficacy and determine the recommended phase II dose (RP2D) for pegylated interferon-α-2b (PI) in patients with unresectable progressive or symptomatic plexiform neurofibromas (PN). METHODS: PI was administered weekly in cohorts of 3-6 patients during the dose-finding phase and continued for up to 2 years. Twelve patients were treated at the RP2D to further evaluate toxicity and activity. RESULTS: Thirty patients (median age 9.3 years, range 1.9-34.7 years) were enrolled. No dose-limiting toxicity (DLT) was seen in patients treated at the 3 µg/kg dose level (DL) during the first 4 weeks. All 5 patients treated at the 4.5 µg/kg DL came off study or required dose reductions for behavioral toxicity or fatigue. Similar DLT on the 3 µg/kg DL became apparent over time. There was 1 DLT (myoclonus) in 12 patients enrolled at the 1.0 µg/kg DL. Eleven of 16 patients with pain showed improvement and 13 of 14 patients with a palpable mass had a decrease in size. Five of 17 patients (29%) who underwent volumetric analysis had a 15%-22% decrease in volume. Three of 4 patients with documented radiographic progression prior to enrollment showed stabilization or shrinkage. CONCLUSIONS: The RP2D of PI for pediatric patients with PN is 1 µg/kg/wk. Clinical and radiographic improvement and cessation of growth can occur. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that pegylated interferon-α-2b in patients with unresectable, progressive, symptomatic, or life-threatening PNs results in radiographic reduction or stabilization of PN size.

Characteristics of children enrolled in treatment trials for NF1-related plexiform neurofibromas.

OBJECTIVE: To describe the characteristics of children enrolled in treatment trials for neurofibromatosis type 1 (NF1)-related plexiform neurofibroma (PN), PN tumor burden, PN-related complications, and treatment outcomes and to highlight the differences between characteristics of children with NF1 vs children with cancers entered on early phase drug trials. METHODS: Pre-enrollment characteristics and complications of PN were retrospectively analyzed in a cohort of 59 children with NF1-related PN treated on 1 of 7 clinical trials at the NIH between 1996 and 2007. Outcome was analyzed in a subset of 19 patients enrolled in phase I trials. Comparisons to children with cancer were made from a similar analysis performed recently. RESULTS: The median age at enrollment was 8 years. The median PN volume was 555 mL. Most patients had no prior chemotherapy or radiation, but nearly half had previous surgery for PN. PN-associated complications and NF1 manifestations were common, including pain (53%), other tumors (18%), and hypertension (8%). Investigational drug therapy was well tolerated. A median of 10 treatment cycles was administered. Patients with NF1-related PN were younger, had better performance score, had less prior therapy, and remained on study longer than cancer patients. CONCLUSIONS: Children with NF1-related plexiform neurofibroma (PN) enrolled in clinical trials had large tumors with substantial morbidity. Clinical trials in these children provide information about drug tolerance, cumulative toxicity, and pharmacokinetics in a younger population than early phase pediatric cancer trials. This report may aid in the evaluation of the applicability of traditional pediatric cancer trial designs and endpoints for NF1-related PN.

NF1 plexiform neurofibroma growth rate by volumetric MRI: relationship to age and body weight.

OBJECTIVE: To longitudinally analyze changes in plexiform neurofibroma (PN) volume in relation to age and body growth in children and young adults with neurofibromatosis type 1 and inoperable, symptomatic, or progressive PNs, using a sensitive, automated method of volumetric MRI analysis. METHODS: We included patients 25 years of age and younger with PNs entered in a natural history study or in treatment trials who had volumetric MRI over > or =16 months. RESULTS: We studied 49 patients (median age 8.3 years) with 61 PNs and a median evaluation period of 34 months (range 18 to 70). The PN growth rates varied among patients, but were constant within patients. Thirty-four patients (69%) experienced > or =20% increase in PN volume during the observation period. PN volume increased more rapidly than body weight over time (p = 0.026). Younger patients had the most rapid PN growth rate. CONCLUSIONS: Volume increase of plexiform neurofibromas is a realistic and meaningful trial endpoint. In most patients plexiform neurofibroma growth rate exceeded body growth rate. The youngest patients had the fastest plexiform neurofibroma growth rate, and clinical drug development should be directed toward this population. Age stratification for clinical trials for plexiform neurofibromas should be considered.

Phase II trial of intravenous lobradimil and carboplatin in childhood brain tumors: a report from the Children's Oncology Group.

BACKGROUND: [corrected] Lobradimil is a synthetic bradykinin analog that rapidly and transiently increases the permeability of the blood-brain barrier (BBB). The combination of lobradimil and carboplatin was studied in pediatric patients with primary brain tumors in a phase II trial, the primary endpoints of which were to estimate the response rate and time to disease progression. PATIENTS AND METHODS: Patients were stratified by histology into five cohorts: brainstem glioma, high-grade glioma, low-grade glioma, medullobastoma/primitive neuroectodermal tumor (PNET), and ependymoma. Patients received carboplatin adaptively dosed to achieve a target AUC of 3.5 mg min/ml per day (7 mg.min/ml/cycle) intravenously over 15 min on 2 consecutive days and lobradimil 600 ng/kg ideal body weight/day on 2 consecutive days each 28 day cycle. RESULTS: Forty-one patients, age 2-19 years, were enrolled; 38 patients, including 1 patient ultimately determined to have atypical neurocytoma, were evaluable for response. No objective responses were observed in the brainstem glioma (n=12) and high-grade glioma (n = 9) cohorts, although two patients with high-grade glioma had prolonged disease stabilization (>6 months). The study was closed for commercial reasons prior to achieving the accrual goals for the ependymoma (n = 8), medulloblastoma/PNET (n = 6) and low-grade glioma (n = 2) cohorts, although responses were observed in 1 patient with PNET and 2 patients with ependymoma. CONCLUSION: The combination of lobradimil and carboplatin was inactive in childhood high-grade gliomas and brainstem gliomas.

Pediatric phase I trial and pharmacokinetic study of the platelet-derived growth factor (PDGF) receptor pathway inhibitor SU101.

PURPOSE: To determine the maximum tolerated dose and the toxicity profile of the PDGF receptor pathway inhibitor SU101 in pediatric patients with refractory solid tumors, and to define the plasma pharmacokinetics of SU101 and its active metabolite SU0020 in children. EXPERIMENTAL DESIGN: Patients between 3 and 21 years of age with CNS malignancy, neuroblastoma, or sarcoma refractory to standard therapy were eligible. The starting dose of SU101 was 230 mg/m(2) per day administered as a 96-h continuous infusion every 21 days. Blood for pharmacokinetic analysis was obtained during the first cycle. RESULTS: Entered into the trial were 27 patients, and 24 were fully evaluable for toxicity. Dose-limiting central nervous system toxicity was observed in two patients at the 440 mg/m(2) per day dose level. Non-dose-limiting toxicities included nausea, vomiting, headache, fatigue, abdominal discomfort, diarrhea, pruritus, anorexia, constipation, and paresthesias. There were no complete or partial responses. One patient with rapidly progressive desmoplastic small round-cell tumor experienced symptomatic improvement and prolonged stable disease. Steady-state concentrations of SU101 were rapidly achieved and proportional to dose. The concentration of SU0020 was 100- to 1000-fold greater than that of SU101. The median clearance of SU0020 was 0.19 l/day per m(2) and its terminal elimination half-life was 14 days. CONCLUSIONS: SU101 administered on this schedule was generally well tolerated. The maximum tolerated dose of SU101 is 390 mg/m(2) per day for 4 days repeated every 3 weeks. The neurotoxicity observed at the 440 mg/m(2) per day dose level suggests that patients receiving repetitive cycles must be monitored closely, as SU0020 may accumulate over time.

Meeting report: pharmacology in pediatric oncology. Summary of the 10th international expert meeting of the Kind Philipp Foundation for leukemia research, June 10 - 13, 2001 at the Schloss Reisensburg, Günzburg an der donau.

The Kind-Philipp foundation invited a group of international experts from academia, industry, and regulatory institutions to discuss aspects of new drug development in pediatric oncology. The current design, conduct and infrastructure of clinical trials in Europe and the United States, recent regulatory changes of drug development, and the impact of the likely availability of more targeted anti-cancer agents on drug development for pediatric cancers were discussed. This included a review of risk factors, surrogate markers, novel targets, and new anti-cancer agents for pediatric cancers. A special effort was made to define the requirements of well performed clinical trials, including target evaluation, trial design, use of pharmacokinetic (PK) studies, surrogate markers, ethical, and statistical aspects. The greater need for collaboration beyond the National level was recognized.

Phase I trial of lobradimil (RMP-7) and carboplatin in children with brain tumors.

PURPOSE: To determine the maximum tolerated dose (MTD), the incidence and severity of toxicities, and the pharmacokinetics of lobradimil administered intravenously over 10 min in combination with carboplatin in children with refractory brain tumors. METHODS: A group of 25 children with primary brain tumors received carboplatin and lobradimil on two consecutive days every 28 days. The 10-min lobradimil infusion began 5 min before the end of the carboplatin infusion. Four lobradimil dose levels (100, 300, 450 and 600 ng/kg ideal body weight, IBW) were studied in cohorts of 4 to 13 patients. Carboplatin was adaptively dosed based on the glomerular filtration rate to achieve a target plasma area under the concentration-time curve (AUC) of 7.0 mg min/ml per course (5.0 mg min/ml for patients who had previously received craniospinal radiation or myeloablative chemotherapy). RESULTS: Lobradimil toxicity was immediate, tolerable and rapidly reversible. The most frequent toxicities were hypotension, flushing, headache and gastrointestinal complaints. One patient on the 600 ng/kg dose level had a seizure during the lobradimil infusion. The incidence and severity of lobradimil toxicities were not dose-related and the lobradimil dose was not escalated beyond the 600 ng/kg IBW dose level. Two patients had partial responses and ten patients had stable disease. Myelosuppression (thrombocytopenia more prominent than neutropenia) was the primary toxicity attributed to carboplatin. Lobradimil pharmacokinetics were characterized by rapid clearance from the plasma compartment and substantial interpatient variability. CONCLUSIONS: The combination of carboplatin and lobradimil is safe and tolerable. An MTD for lobradimil was not defined because toxicity was not dose-related. The recommended pediatric phase II dose of lobradimil is 600 ng/kg IBW.

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.

A phase I trial and pharmacokinetic study of 9-cis-retinoic acid (ALRT1057) in pediatric patients with refractory cancer: a joint Pediatric Oncology Branch, National Cancer Institute, and Children's Cancer Group study.

PURPOSE: To determine the maximum tolerated dose and describe the toxicities of 9-cis-retinoic acid (9cRA, ALRT1057) administered p.o. tid in pediatric patients with refractory cancer and to study the pharmacokinetics of 9cRA and determine whether systemic drug exposure changes with chronic dosing. PATIENTS AND METHODS: Children with refractory cancer (stratified by age, < or =12 and >12 years) were treated with p.o. 9cRA for 28 consecutive days. The starting dose was 50 mg/m(2)/day divided into 3 doses with planned escalations to 65, 85, and 110 mg/m(2)/day. Pharmacokinetic sampling was performed on days 1 and 29 of the first cycle. RESULTS: Of the 37 patients entered, 18 patients < or =12 years of age and 11 patients >12 years of age were evaluable for toxicity. In patients >12 years of age, dose-limiting headache occurred in 2/2 patients at the 110 mg/m(2)/day dose level; 1/8 patients at 85 mg/m(2)/day developed dose-limiting pseudotumor cerebri. In patients < or =12 years of age, 3/5 patients at the starting dose level of 50 mg/m(2)/day developed dose-limiting pseudotumor cerebri; and 0/6 patients experienced dose-limiting toxicity at 35 mg/m(2)/day. Reversible non-dose-limiting hepatotoxicity was observed in 15 patients across all of the dose levels. There was considerable interpatient variability in 9cRA plasma concentrations. Peak plasma concentrations of 9cRA occurred at a median of 1.5 h after a p.o. dose, and the harmonic-mean terminal half-life was 43 min. By day 29 of 9cRA administration, the plasma 9cRA area under the curve declined by an average of 65% from day 1 values. CONCLUSIONS: The dose-limiting toxicity of 9cRA in pediatric patients was neurotoxicity, primarily pseudotumor cerebri. Younger children tolerate significantly lower doses of 9cRA than older children. Similar to all-trans-retinoic acid, the pharmacokinetics of 9cRA demonstrated a wide degree of interpatient variability and decreased over time when administered on a daily basis. The recommended Phase II dose of 9cRA in patients < or =12 and >12 years of age is 35 and 85 mg/m(2)/day, respectively.

Plasma pharmacokinetics and cerebrospinal fluid penetration of thioguanine in children with acute lymphoblastic leukemia: a collaborative Pediatric Oncology Branch, NCI, and Children's Cancer Group study.

PURPOSE: In preclinical studies, thioguanine (TG) has been shown to be more potent than the standard acute lymphoblastic leukemia (ALL) maintenance agent, mercaptopurine (MP), suggesting that TG may be more efficacious than MP in the treatment of childhood ALL. As part of a pilot trial in which TG was used in place of MP, we studied the plasma pharmacokinetics of oral TG and measured steady-state plasma and CSF TG concentrations during a continuous intravenous infusion (CIVI) in children with newly diagnosed standard-risk ALL. METHODS: Nine plasma samples were collected after each patient's first 60 mg/m2 oral TG dose during maintenance. CIVI TG (20 mg/m2/h over 24 h) was administered during the consolidation phase of therapy, and simultaneous plasma and CSF samples were collected near the end of the infusion. TG was measured by reverse-phase HPLC with ultraviolet detection. Erythrocyte TG nucleotide (TGN) concentrations were measured 7 days after a course of CIVI TG and prior to the start of each maintenance cycle. RESULTS: After oral TG (n = 35), the mean (+/- SD) peak plasma concentration was 0.46 +/- 0.68 microM and the AUC ranged from 0.18 to 9.5 microM.h (mean 1.5 microM.h). Mean steady-state plasma and CSF TG concentrations during CIVI (n = 33) were 2.7 and 0.5 microM, respectively. The mean (+/- SD) TG clearance was 935 +/- 463 ml/min per m2. Plasma TG concentrations did not correlate with erythrocyte TGN concentrations after oral or CIVI TG. The 8-OH-TG metabolite was detected in plasma and CSF. CONCLUSIONS: TG concentrations that are cytotoxic to human leukemia cell lines can be achieved in plasma after a 60 mg/m2 oral dose of TG and in plasma and CSF during CIVI of TG.

Pharmacokinetics and metabolism of the methotrexate metabolite 2, 4-diamino-N(10)-methylpteroic acid.

The novel methotrexate (MTX) rescue agent carboxypeptidase-G(2) (CPDG(2)) converts >98% of plasma MTX to 2, 4-diamino-N(10)-methylpteroic acid (DAMPA) and glutamate in patients with MTX-induced renal failure and delayed MTX excretion. DAMPA is eliminated more rapidly than MTX in these patients, suggesting nonrenal elimination. The pharmacokinetics and metabolism of DAMPA were studied in four nonhuman primates with reverse-phase HPLC with UV, photodiode array detection, and mass spectroscopy. The mean peak plasma DAMPA concentration was 51 microM and the plasma disposition was described by a three-compartment open model with first order elimination. The mean clearance of DAMPA was 1.9 l/kg/h and the mean terminal half-life was 51 min. Forty-six percent of the dose was excreted in the urine as parent compound. Three DAMPA metabolites, hydroxy-DAMPA, DAMPA-glucuronide, and hydroxy-DAMPA-glucuronide, were identified in plasma and urine. These metabolites also were identified in plasma from patients who received CPDG(2) as an MTX rescue agent. The cytotoxicity of DAMPA and its effect on MTX cytotoxicity were assessed in the Molt-4 human leukemic cell line. DAMPA was not cytotoxic and did not significantly alter the cytotoxicity of MTX. In nonhuman primates metabolism of DAMPA is a major route of DAMPA elimination, and metabolism underlies the more rapid elimination of DAMPA versus MTX in patients with MTX-induced renal dysfunction after administration of CPDG(2).

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.

Thioguanine administered as a continuous intravenous infusion to pediatric patients is metabolized to the novel metabolite 8-hydroxy-thioguanine.

Thiopurine antimetabolites have been in clinical use for more than 40 years, yet the metabolism of thiopurines remains only partially understood. Data from our previous pediatric phase 1 trial of continuous i.v. infusion of thioguanine (CIVI-TG) suggested that TG was eliminated by saturable mechanism, with conversion of the drug to an unknown metabolite. In this study we have identified this metabolite as 8-hydroxy-thioguanine (8-OH-TG). The metabolite coeluted with the 8-OH-TG standard on HPLC and had an identical UV spectrum, with a lambda(max) of 350 nm. On mass spectroscopy, the positive ion, single quad scan of 8-OH-TG yielded a protonated molecular ion at 184 Da and contained diagnostic ions at m/z 167, 156, 142, and 125 Da. Incubation of TG in vitro with partially purified aldehyde oxidase resulted in 8-OH-TG formation. 8-OH-TG is the predominant circulating metabolite found in patients receiving CIVI-TG and is likely generated by the action of aldehyde oxidase.

Dihydrofolate reductase enzyme inhibition assay for plasma methotrexate determination using a 96-well microplate reader.

Microplate reader assays offer several advantages over conventional spectrophotometric assays. We adapted the dihydrofolate reductase (DHFR) enzyme inhibition assay for use in a 96-well microplate reader to measure plasma methotrexate (MTX) concentrations. The assay is linear from 0.01 to 0.1 micromol/L. The within-run CVs at 0.03 micromol/L and 0.08 micromol/L MTX were 4.0% and 2.7%, respectively, and the interday (total) CVs were 7.6% and 1.8%. Cross-reactivity with the inactive MTX metabolite 2, 4-diamino-N10-methylpteroic acid (DAMPA) was 3.9%, significantly less than that described with commercial immunoassays; with 7-hydroxymethotrexate cross-reactivity was 1.7%. In addition to sensitivity and specificity, the advantages of this assay are small sample volumes, simultaneous analysis of multiple samples, and rapid turnaround. Because of its greater specificity, the DHFR enzyme inhibition assay may be useful when DAMPA is present in plasma samples and HPLC is not available.

Carboxypeptidase-G2, thymidine, and leucovorin rescue in cancer patients with methotrexate-induced renal dysfunction.

PURPOSE: Methotrexate nephrotoxicity can lead to delayed methotrexate elimination and the development of life-threatening toxicity, which may not be preventable with the standard rescue agent leucovorin. In preclinical studies, we previously demonstrated that carboxypetidase-G2 (CPDG2) rapidly hydrolyzes methotrexate to nontoxic metabolites. A protocol for the compassionate use of CPDG2 in patients who develop nephrotoxicity while receiving high-dose methotrexate was therefore developed. The pharmacologic and clinical outcome of CPDG2 rescue administered with thymidine and leucovorin in 20 patients is presented here. METHODS: Patients with high-dose methotrexate-induced renal dysfunction received one to three doses of CPDG2, 50 U/kg body weight intravenously (i.v.), thymidine 8 g/m2/d by continuous i.v. infusion, and standard pharmacokinetically guided leucovorin rescue. Plasma concentrations of methotrexate and its inactive metabolite 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA) were measured before and after CPDG2 using high-pressure liquid chromatography (HPLC). Tolerance of CPDG2 and thymidine, development of methotrexate toxicities, and recovery of renal function were monitored. RESULTS: Twenty patients who received high-dose methotrexate for osteosarcoma (n = 11), lymphoid cancers (n = 8), and gastric cancer (n = 1) developed nephrotoxicity (median serum creatinine, 3.2 mg/dL) and elevated plasma methotrexate concentrations (median, 201 mumol/L at hour 46). CPDG2 and thymidine rescue was well tolerated and resulted in a rapid 95.6% to 99.6% reduction in the plasma methotrexate concentration. Methotrexate-related toxicity was mild to moderate. Serum creatinine returned to normal values at a median of 22 days. CONCLUSION: CPDG2, thymidine, and leucovorin rescue was highly effective in 20 patients at high risk for developing life-threatening methotrexate toxicity after the onset of methotrexate-induced nephrotoxicity and delayed methotrexate excretion.

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.

Carboxypeptidase-G2 rescue in a patient with high dose methotrexate-induced nephrotoxicity.

BACKGROUND: High dose methotrexate (HDMTX) induced renal failure is a medical emergency, as methotrexate (MTX) is primarily eliminated by renal excretion. High doses of leucovorin (LV) do not necessarily prevent toxicity in the presence of sustained elevated plasma MTX concentrations. The bacterial enzyme carboxypeptidase-G2 (CPDG2) hydrolyzes MTX into inactive metabolites and has been demonstrated to lower plasma MTX concentrations to nontoxic levels rapidly in the nonhuman primate after HDMTX infusion. Therefore, CPDG2 was evaluated as a rescue agent in a patient with acute renal dysfunction secondary to HDMTX: METHODS: A 16 year old patient with osteosarcoma experienced acute renal dysfunction after HDMTX administration, which resulted in markedly elevated and sustained plasma MTX concentrations. She received three doses of CPDG2 on the fifth day after HDMTX: Plasma MTX concentrations were determined before and after CPDG2 administration. RESULTS: The plasma MTX concentrations decreased from 60 to 1.2 microM within 15 minutes after the first dose of CPDG2. No rebound increase in plasma MTX concentrations or adverse reactions to the enzyme were observed. The patient developed only mild mucositis. Serum creatinine at the time of CPDG2 administration was 5 mg/dl and returned to normal within 7 weeks of enzyme administration. CONCLUSIONS: Carboxypeptidase-G2 rapidly, markedly, and persistently lowered plasma MTX concentrations to a level that could be rescued safely with LV. Based on the experience with this patient and on preclinical studies in nonhuman primates, CPDG2 appears to be more effective than hemodialysis or hemoperfusion, and may prove beneficial for patients at risk for life-threatening toxicity secondary to delayed excretion of MTX.