Search PubMed⌕ Search

Biomedical subjects

M V Relling

Publications and source records attributed to M V Relling.

At least 55 records · Page 3Linked to original sources
PubMed1999

High incidence of secondary brain tumours after radiotherapy and antimetabolites.

BACKGROUND: Brain tumours rarely occur in survivors of childhood acute lymphoblastic leukaemia after cranial radiotherapy. An unusually high frequency of brain tumours seen among children enrolled in one of our leukaemia treatment protocols, Total Therapy Study XII, prompted us to identify the potential causes of this complication. METHODS: We assessed clinical, biological, and pharmacokinetic features in all 52 children who received prophylactic cranial radiotherapy. We compared the cumulative incidence of brain tumours between subgroups, and with that of 421 children who received radiotherapy in previous studies. FINDINGS: The incidence of brain tumours among irradiated children (six of 52, 12.8% [SE 5.0]) was high compared with patients in the same study who did not receive radiotherapy (none of 101; p=0.0008) and with other protocols that included cranial radiotherapy (p<0.0001). Of the six children, four had erythrocyte concentrations of thioguanine nucleotide metabolites higher than the 70th percentile for the entire cohort, and three had a genetic defect in thiopurine catabolism. The 8-year cumulative incidence of brain tumour among children with defective versus wild-type thiopurine methyltransferase phenotype was 42.9% (SE 20.6) versus 8.3% (4.7; p=0.0077). This protocol differed from previous protocols, in that more intensive systemic antimetabolite therapy was given before and during radiotherapy. INTERPRETATION: These data support the elimination of prophylactic radiotherapy for acute lymphoblastic leukaemia except in patients at high risk of central-nervous-system relapse. Underlying genetic characteristics and treatment variables may be associated with an increased risk of radiation-associated brain tumours.

Adolescent↗
PubMed1999

Simultaneous quantitation of etoposide and its catechol metabolite in human plasma using high-performance liquid chromatography with electrochemical detection.

Etoposide, a highly active and widely used antineoplastic agent, is O-demethylated to its active catechol metabolite. A high-performance liquid chromatographic assay method for the simultaneous quantitation of etoposide and etoposide catechol in human plasma was established. Etoposide and etoposide catechol were extracted from plasma using chloroform and methanol followed by phase separation, evaporation of the organic phase, and reconstitution of the residue. Chromatography was accomplished using a reversed-phase phenyl analytical column (390 mm x 3.9 mm I.D.) with a mobile phase of 76.6% 25 mM citric acid-50 mM sodium phosphate (pH 2.4)-23.4% acetonitrile pumped isocratically at 1 ml/min with electrochemical detection. The limit of detection for etoposide was 1.2 nM and for etoposide catechol was 0.2 nM. The precision (CV) for etoposide ranged from 0.7 to 3% and for the catechol metabolite from 1 to 6%; accuracy of predicted values ranged from 97 to 106% and 94 to 103%, respectively. The assay was linear from 0.1 to 10 microM for etoposide and from 0.005 to 0.5 microM for etoposide catechol in plasma. Recovery of etoposide and etoposide catechol ranged from 93 to 95% and 90 to 98%, respectively. Stability of etoposide and etoposide catechol in human plasma containing ascorbic acid stored at -70 degrees C for one year was demonstrated. This assay procedure is suitable for evaluation of etoposide and etoposide catechol pharmacokinetics in plasma following etoposide administration.

Antineoplastic Agents, Phytogenic↗
PubMed1999

Prognostic importance of 6-mercaptopurine dose intensity in acute lymphoblastic leukemia.

6-Mercaptopurine (6MP) and methotrexate are the backbone of continuation therapy for childhood acute lymphoblastic leukemia (ALL). In studies of oral 6MP and methotrexate, indices of chronic systemic exposure to active metabolites of these agents, namely, red blood cell (RBC) concentrations of methotrexate polyglutamates (MTXPGs) and thioguanine nucleotides (TGNs) have positively correlated with event-free survival (EFS). Our objective was to evaluate whether MTXPGs, TGNs, and the dose intensity of administered methotrexate and 6MP were prognostic in the setting of a treatment protocol in which all treatment was coordinated through a single center, and the weekly doses of methotrexate were given parenterally. On protocol Total XII, 182 children achieved remission and received weekly methotrexate 40 mg/m2 parenterally and daily oral 6MP, interrupted every 6 weeks during the first year by pulse chemotherapy. A total of 709 TGN, 418 MTX-PG, and 267 thiopurine methyltransferase (TPMT) measurements, along with complete dose intensity information (dose received divided by protocol dose per week) for 19,046 weeks of 6MP and methotrexate, were analyzed. In univariate analyses, only higher dose intensity of 6MP and of weekly methotrexate were significant predictors of overall EFS (P =.006 and. 039, respectively). The occurrence of neutropenia was associated with worse outcome (P =.040). In a multivariate analysis, only higher dose intensity of 6MP (P =.020) was a significant predictor of EFS, with lower TPMT activity (P =.096) tending to associate with better outcome. 6MP dose intensity was also associated (P =.007) with EFS among patients with homozygous wild-type TPMT phenotype. Lower 6MP dose intensity was primarily due to missed weeks of therapy and not to reductions in daily dose. We conclude that increased dose-intensity of oral 6MP is an important determinant of EFS in ALL, particularly among those children with a homozygous wild-type TPMT phenotype. However, increasing intensity of therapy such that neutropenia precludes chemotherapy administration may be counterproductive.

Administration, Oral↗
PubMed1999

Reduced folate carrier expression in acute lymphoblastic leukemia: a mechanism for ploidy but not lineage differences in methotrexate accumulation.

Methotrexate (MTX) is one of the most active and widely used agents for the treatment of acute lymphoblastic leukemia (ALL). To elucidate the mechanism for higher accumulation of MTX polyglutamates (MTX-PG) in hyperdiploid ALL and lower accumulation in T-lineage ALL, expression of the reduced folate carrier (RFC) was assessed by reverse transcription-polymerase chain reaction in ALL blasts isolated from newly diagnosed patients. RFC expression exhibited a 60-fold range among 29 children, with significantly higher expression in hyperdiploid B-lineage ALL (median, 11.3) compared with nonhyperdiploid ALL (median, 2.1; P <.0006), but no significant difference between nonhyperdiploid B-lineage and T-lineage ALL. Furthermore, mRNA levels of RFC (mapped by FISH to chromosome 21) were significantly related to chromosome 21 copy number (P =.0013), with the highest expression in hyperdiploid ALL blasts with 4 copies of chromosome 21. To assess the functional significance of gene copy number, MTX-PG accumulation was compared in ALL blasts isolated from 121 patients treated with either low-dose MTX (LDMTX; n = 60) or high-dose MTX (HDMTX; n = 61). After LDMTX, MTX-PG accumulation was highest in hyperdiploid B-lineage ALL with 4 copies of chromosome 21 (P =.011), but MTX-PG accumulation was not significantly related to chromosome 21 copy number after HDMTX (P =.24). These data show higher RFC expression as a mechanism for greater MTX accumulation in hyperdiploid B-lineage ALL and indicate that lineage differences in MTX-PG accumulation are not due to lower RFC expression in T-lineage ALL.

Carrier Proteins↗
PubMed1999

Pharmacokinetics of paclitaxel in an anephric patient.

PURPOSE: To assess the pharmacokinetics of paclitaxel for recurrent Wilms' tumor in an anephric pediatric patient receiving hemodialysis. METHODS: Paclitaxel was administered at a dose of 250 mg/m2 and 350 mg/m2 by 24-h continuous intravenous (IV) infusion as two consecutive courses, respectively, separated by approximately 3 weeks. Paclitaxel plasma concentrations were measured by high-performance liquid chromatography (HPLC). RESULTS: Paclitaxel disposition was comparable to that reported in similarly treated children with normal renal function. For the first course (250 mg/ m2), paclitaxel concentrations were best fit by a two-compartment, first-order model. The calculated pharmacokinetic parameters were 0.312 h(-1) for the first-order rate constant of elimination (Ke), 52.4 l/m2 for the apparent volume of distribution (Vc), 0.170 h(-1) and 0.105 h(-1) for the first-order rate constants for transit from central to peripheral compartments (Kcp) and peripheral to central compartments (Kpc), respectively, 16.9 microM x h for the area under the plasma concentration-versus-time curve (AUC), and 273 ml/min per m2 for average clearance (Cl). The concentration-versus-time data with the second course (at the higher dosage of 350 mg/m2) were better described by a two-compartment model with saturable elimination. The calculated pharmacokinetic parameters were 12.0 micromol x h(-1) for the maximal rate of elimination (Vm1-0), 0.158 microM for the concentration at which the rate of elimination is 50% of maximal (Km1-0), 0.809 h(-1) for Kcp, 0.0792 h(-1) for Kpc, 23.5 l/m2 for Vc, 20.9 microM x h for AUC, and 327 ml/min per m2 for Cl. Paclitaxel was undetectable in the dialysate. CONCLUSIONS: The level of systemic exposure in our anephric patient was comparable to or lower than that achieved in patients with normal renal function at similar dosages. The patient tolerated therapy without problems. It appears that pediatric patients in renal failure can be treated with paclitaxel as a 24-h continuous infusion at doses similar to those used in patients with normal renal function.

Antineoplastic Agents, Phytogenic↗
PubMed1999

Low frequency of TEL-AML1 in relapsed acute lymphoblastic leukemia supports a favorable prognosis for this genetic subgroup.

The long-term outcome of children with TEL-AML1-positive acute lymphoblastic leukemia (ALL) is uncertain. Although studies of newly diagnosed cases have indicated that the TEL-AML1 fusion confers a favorable prognosis, analyses of relapsed cases have suggested that this may not be true. Because of treatment implications for this subgroup of patients, we have now analyzed 49 cases of relapsed ALL for the presence of TEL-AML1. Only 10% of these cases expressed the fusion, compared to 20-25% of newly diagnosed ALL cases. Additional follow-up of the cohort of 48 newly diagnosed patients with the TEL-AML1 fusion previously reported showed that the 10-year cumulative risk of relapse was 9 +/- 5% (s.e.). Together, these results suggest an excellent outcome for TEL-AML1-positive ALL.

Child↗
PubMed1999

Polymorphism of the thiopurine S-methyltransferase gene in African-Americans.

The molecular basis for the genetic polymorphism of thiopurine S -methyltransferase (TPMT) has been estab-lished for Caucasians, but it remains to be elucidated in African populations. In the current study, we determined TPMT genotypes in a population of 248 African-Americans and compared it with allele frequencies in 282 Caucasian Americans. TPMT genotype was determined in all individuals with TPMT activity indicative of a heterozygous genotype (</=10.1 U/ml pRBC, n = 23African-Americans, n = 21 Caucasians) and a control group with TPMT activity indicative of a homozygous wild-type genotype (>10.2 U/ml pRBC, n = 23 African-Americans, n = 21 Caucasians). No mutant alleles were found in the high activity control groups. The overall mutant allele frequencies were similar in African-Americans and Caucasians (4.6 and 3.7% of alleles, respectively). However, while TPMT*3C was the most prevalent mutant allele in African-Americans (52.2% of mutant alleles), it represented only 4.8% of mutant alleles in Caucasians ( P < 0.001). In contrast, TPMT*3A and TPMT*2 were less common in African-Americans (17.4 and 8.7% of mutant alleles), whereas TPMT*3A was the most prevalent mutant allele in Caucasians (85.7% of mutant alleles). A novel allele ( TPMT*8 ), containing a single nucleotide transition (G644A), leading to an amino acid change at codon 215 (Arg-->His), was found in one African-American with intermediate activity. These data indicate that the same TPMT mutant alleles are found in American black and white populations, but that the predominant mutant alleles differ in these two ethnic groups.

Alleles↗
PubMed1999

Sex differences in prognosis for children with acute lymphoblastic leukemia.

PURPOSE: Whether recent improvements in the treatment of childhood acute lymphoblastic leukemia (ALL) have nullified the adverse prognosis associated with male sex remains unclear. Therefore, we analyzed the survival experience and presenting clinical and laboratory features of boys and girls with newly diagnosed ALL who were treated at our institution over the past three decades. PATIENTS AND METHODS: One thousand one hundred fifty-one boys and 904 girls were treated in 13 consecutive Total Therapy studies between 1962 and 1994. An overview analysis was used to investigate the impact of sex on overall and event-free survival, both for the entire cohort and for subgroups defined by treatment era and blast-cell immunophenotype. Stratified analyses were performed to adjust for treatment protocol and known risk factors, and in the modern treatment era, for protocol, immunophenotype, and the DNA content of leukemic cells (ie, DNA index). The pharmacokinetics of methotrexate, teniposide, and cytarabine, as well as the thiopurine methyltransferase activity of erythrocytes, were compared between boys and girls treated on a single protocol. RESULTS: Compared with girls, boys were more likely to have T-cell ALL (20.9% v 10.7%, P < .001) and seemed less likely to have a favorable DNA index (17.8% v 25.1%, P = .072). There were no other statistically significant differences between the two sexes with respect to presenting features, including leukemic-cell genetic abnormalities, nor were there significant sex differences in the pharmacokinetics of methotrexate, teniposide, or cytarabine or in erythrocyte thiopurine methyltransferase activity. Girls clearly fared better than boys (P < .001) on protocols used during the early era of treatment (10-year event-free survival +/- 1 SE, 43.1%+/-2.1% v 31.5%+/-1.7%). Although prognosis improved for both sexes in the modern era, the difference in outcome between girls and boys persisted (P = .025) (10-year event-free survival, 73.4%+/-3.7% v 63.5%+/-4.0%). However, stratification of modern-era patients by protocol, immunophenotype, and DNA index mitigated statistical evidence of a sex difference in overall survival (P = .263) and event-free survival (P = .124). CONCLUSION: Although boys and girls alike have benefited from improvements in ALL therapy, these gains have not completely eliminated the sex difference in prognosis that has persisted since the early 1960s. The apparent difference in outcome is partially explained by differences between boys and girls in the distributions of ALL immunophenotype and DNA index.

Adolescent↗
PubMed1999

Cerebrospinal fluid asparagine concentrations after Escherichia coli asparaginase in children with acute lymphoblastic leukemia.

PURPOSE: The CNS is an important sanctuary site in childhood acute lymphoblastic leukemia (ALL). CSF asparagine concentration reflects asparaginase systemic pharmacodynamics. We evaluated the time course of CSF asparagine depletion in children with ALL during and after a course of Escherichia coli asparaginase. PATIENTS AND METHODS: Thirty-one children (24 newly diagnosed and seven at relapse) received E coli asparaginase 10,000 IU/m2 intramuscularly three times weekly for six and nine doses, respectively, as part of multiagent induction chemotherapy. CSF asparagine levels were measured before, during, and after asparaginase dosing. RESULTS: The percentage of patients with undetectable (< 0.04 micromol/L) CSF asparagine was 3.2% (one of 31 patients) at baseline, 73.9% (17 of 23) during asparaginase therapy, and 56.3% (nine of 16) 1 to 5 days, 43.8% (seven of 16) 6 to 10 days, 20.0% (two of 10) 11 to 30 days and 0% (zero of 21) more than 30 days after asparaginase therapy. The proportion of patients with depleted CSF asparagine was higher during asparaginase therapy than at baseline (P < .001), 11 to 30 days (P = .003), and more than 30 days after asparaginase therapy (P < .001). Median CSF asparagine concentrations were 4.42 micromol/L before, less than 0.04 micromol/L during, and less than 0.04 micromol/L at 1 to 5 days, 1.63 micromol/L at 6 to 10 days, 1.70 micromol/L at 11 to 30 days, and 5.70 micromol/L at more than 30 days after asparaginase therapy, respectively. CSF depletion was more common in patients with low baseline CSF asparagine concentrations (P = .003). CONCLUSION: CSF asparagine concentrations are depleted by conventional doses of E coli asparaginase in the majority of patients, but they rebound once asparaginase therapy is completed.

Adolescent↗
PubMed1999

Phase I targeted systemic exposure study of paclitaxel in children with refractory acute leukemias.

Clearance of anticancer drugs in children is highly variable, leading to wide variability in the systemic exposure associated with each dosage escalation in Phase I studies. The purpose of this Phase I study was to escalate targeted systemic exposure to paclitaxel, rather than dose, to attenuate the impact of pharmacokinetic variability at each escalation level. Children with recurrent acute leukemias received paclitaxel as 24-h infusions at escalating levels of paclitaxel systemic exposure [i.e., area under the concentration-versus-time curve (AUC)]. Plasma paclitaxel concentrations were measured by high-performance liquid chromatography-UV detection. A Bayesian algorithm using a two-compartment model with saturable distribution and saturable elimination was used to estimate clearance during the first 8 h of infusion; the infusion rate was adjusted 12 h after the start of infusion to achieve the target AUC. Toxicity and evidence of activity were assessed after each course. Six boys and one girl received eight courses of paclitaxel. The target AUC ranged from 31.5 to 45 microM x h. Five of the seven evaluable courses had AUCs between 75% and 125% of the target after adjustment (median, 100.2%; range, 51-151%), whereas none of the seven courses was projected to be in the target range had no change in dose been made (P = 0.021). The ratio of the achieved AUC to the target AUC was inversely related to clearance (r = -0.857; P = 0.014). Mucositis was the exposure-limiting toxicity, at AUCs lower than were expected based on Phase I studies in children with solid tumors. Pharmacokinetically-guided dosing strategies reduced variability in systemic exposure. Alternatives to traditional Phase I studies may be important in the setting of childhood leukemias because these patients show poor tolerance to Phase I therapy.

Acute Disease↗
PubMed1998

The frequency of illegitimate V(D)J recombinase-mediated mutations in children treated with etoposide-containing antileukemic therapy.

Etoposide is among the most widely used anti-cancer drugs. Its use, however, has been associated with increased risk of secondary acute myeloid leukemia (AML) which is characterized by chromosomal translocations suggesting involvement of recombination-associated motifs at the breakpoints. A PCR-based assay was developed to quantitate the frequency of two illegitimate V(D)J recombinase-mediated genomic rearrangements-a 20-kb deletion in the hprt gene and the bcl2/IgH translocation (t(14;18)) found in non-Hodgkin's lymphoma. We examined both lymphocyte and non-lymphocyte blood cell DNA of children with acute lymphoblastic leukemia (ALL) for changes in the frequencies of these biomarkers during etoposide therapy to determine the level of illegitimate V(D)J recombination changes during therapy. A low level of t(14;18) was found in the lymphocytes before etoposide treatment, which was significantly reduced during etoposide therapy. In before-etoposide samples, no t(14;18) were found among 7.72x107 non-lymphocytes; during treatment none were found among 1.87x108 non-lymphocytes. Deletions were not found before etoposide treatment in either the lymphocytes (6.67x107) or non-lymphocytes (5.43x107) and were non-significantly elevated during etoposide therapy (1 in 1.4x108 lymphocytes and 1 in 1.39x108 non-lymphocytes). It is interesting to note the one patient with an hprt deletion mutation in non-lymphocytes; V(D)J recombination is not normally found in this cell type, but is the cell type from which AML derives. Several patients had clones of t(14;18)-bearing cells as determined by DNA sequence analysis. These results suggest that this etoposide-based chemotherapy was ineffective in producing genomic rearrangements mediated by illegitimate V(D)J recombination in these patients.

Base Sequence↗
PubMed1998

A human lymphoid leukemia cell line with a V(D)J recombinase-mediated deletion of hprt.

Large deletions of exons 2 and 3 of the hprt gene are the most common type of hprt mutation in lymphocytes of newborn infants, and their frequency increases in cultured human T-lymphoid cells as a result of exposure to etoposide. Sequenced PCR products for these deletions are consistent with a V(D)J recombinase-mediated mechanism underlying their genesis. Herein, we describe the isolation and characterization of an etoposide-induced mutant CEM cell line that is clonal for a V(D)J recombinase-mediated exon 2 + 3 deletion. Human CCRF-CEM cells were exposed to 5 muM etoposide for 4 h, selected in 6-thioguanine, and an exon 2 + 3 deletion mutant was isolated through serial limiting dilution, using a PCR-based assay for detection of the exon 2 + 3 deletion. Untreated CEM cells and cells treated with 6-thioguanine alone were similarly subcultured. The exon 2 + 3 deletion-containing line was termed SJCEM808 and had a slightly longer doubling time than the control lines, tended to clump in suspension, and was characterized by cell membrane blebbing. Compared to the parent line, SJCEM808 had similar cytogenetic abnormalities, lower CD2, CD1, and CD10 expression, and negligible RAG-1 expression. However, RAG-1 expression was down-regulated in some untreated parental subclones following similar subculturing. The sequence of the exon 2 + 3 deletion mutation exhibited nucleotide insertions, and the breakpoints were adjacent to heptamer signal recognition sequences in intact hprt, consistent with a V(D)J recombinase-mediated mechanism underlying its genesis. There were no MLL gene or interlocus T-cell receptor (TCR) rearrangements. These results indicate that non-homologous recombination following etoposide treatment is neither necessarily accompanied by other large DNA rearrangements nor simply a pre-lethal event, and this cell line may serve as a useful tool for studying illegitimate V(D)J recombinase-mediated deletions.

Antigens, Surface↗
PubMed1998

Early intensification of intrathecal chemotherapy virtually eliminates central nervous system relapse in children with acute lymphoblastic leukemia.

Central nervous system (CNS) relapse has been an obstacle to uniformly successful treatment of childhood acute lymphoblastic leukemia (ALL) for many years. We therefore intensified intrathecal chemotherapy (simultaneously administered methotrexate, hydrocortisone, and cytarabine) for 165 consecutive children with newly diagnosed ALL enrolled in Total Therapy Study XIIIA from December 1991 to August 1994. The 64 patients (39%) who had 1 or more blast cells in cytocentrifuged preparations of cerebrospinal fluid at diagnosis, with or without associated higher-risk features, received additional doses of intrathecal chemotherapy during remission induction and the first year of continuation treatment. Patients with higher-risk leukemia, regardless of cerebrospinal fluid findings, also received additional doses of intrathecal chemotherapy during the first year of continuation treatment. Cranial irradiation was reserved for patients with higher-risk leukemia (22% of the total). The 5-year cumulative risk of an isolated CNS relapse among all 165 patients was 1.2% (95% confidence interval, 0% to 2.9%), whereas that of any CNS relapse was 3.2% (0. 4% to 6.0%). The probability of surviving for 5 years without an adverse event of any type was 80.2% +/- 9.2% (SE). Our results suggest that early intensification of intrathecal chemotherapy will reduce the risk of CNS relapse to a very low level in children with ALL, securing a higher event-free survival rate overall.

Adolescent↗
PubMed1998

Conventional compared with individualized chemotherapy for childhood acute lymphoblastic leukemia.

BACKGROUND: The rate of clearance of antileukemic agents differs by a factor of 3 to 10 among children with acute lymphoblastic leukemia. We hypothesized that the outcome of treatment would be improved if doses were individualized to prevent low systemic exposure to the drugs in patients with fast drug clearance. METHODS: We stratified and randomly assigned 182 children with newly diagnosed acute lymphoblastic leukemia to postremission regimens that included high-dose methotrexate and teniposide plus cytarabine. The doses of these drugs were based on body-surface area (in the conventional-therapy group) or the rates of clearance of the three medications in each patient (in the individualized-treatment group). In the individualized-treatment group, doses were increased in patients with rapid clearance and decreased in patients with very slow clearance. RESULTS: Patients who received individualized doses had significantly fewer courses of treatment with systemic exposures below the target range than did patients who received conventional doses (P<0.001 for each medication). Among the patients with B-lineage leukemia, those who received individualized therapy had a significantly better outcome than those given conventional therapy (P=0.02); the mean (+/-SE) rates of continuous complete remission at five years were 76+/-6 percent and 66+/-7 percent, respectively. There was no significant difference between treatments for patients with T-lineage leukemia (P=0.54). In a proportional-hazards model, the time-dependent systemic exposure to methotrexate, but not to teniposide or cytarabine, was significantly related to the risk of early relapse in children with B-lineage leukemia. CONCLUSIONS: Adjusting the dose of methotrexate to account for the patient's ability to clear the drug can improve the outcome in children with B-lineage acute lymphoblastic leukemia.

Adolescent↗
PubMed1998

Isolation of a human thiopurine S-methyltransferase (TPMT) complementary DNA with a single nucleotide transition A719G (TPMT*3C) and its association with loss of TPMT protein and catalytic activity in humans.

OBJECTIVE: Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme that catalyzes the S-methylation of mercaptopurine, azathioprine, thioguanine and most of their nucleotide metabolites. TPMT exhibits genetic polymorphism, with about 10% of individuals having intermediate TPMT activity because of heterozygosity at the TPMT locus and about 1 in 300 inheriting TPMT deficiency as an autosomal recessive trait. Although several mutant alleles have now been associated with inheritance of TPMT deficiency in humans, the expression of only TPMT*2 and TPMT*3A has been established by isolation and characterization of complementary DNA (cDNA) from individuals with low TPMT activity. METHODS: Radiochemical assay, Western blot analysis, polymerase chain reaction (PCR) genotyping, and cDNA sequencing were used to analyze TPMT activity and protein levels in erythrocytes and to determine TPMT genotype. RESULTS: We established expression of another common mutant allele, TPMT*3C (containing only the A719G mutation), by sequence analysis of cDNA isolated from an individual with a heterozygous TPMT phenotype (7 units/ml packed erythrocytes). The TPMT*3C allele was also confirmed in an unrelated individual by sequencing TPMT coding exons after PCR amplification of genomic DNA. Moreover, Western blot analysis of erythrocytes obtained from five heterozygous individuals with the TPMT*3C allele (i.e., TPMT*1/TPMT*3C) exhibited about 50% less immunodetectable TPMT protein compared with homozygous wild-type individuals, and a TPMT-deficient individual with a TPMT*3A/TPMT*3C genotype had no immunodetectable TPMT protein. CONCLUSION: These data establish that the TPMT*3C allele is expressed in humans and is associated with lower immunodetectable TPMT protein and catalytic activity.

Adult↗
PubMed1998

Etoposide and antimetabolite pharmacology in patients who develop secondary acute myeloid leukemia.

Etoposide, an effective agent for acute lymphoblastic leukemia (ALL), can cause secondary acute myeloid leukemia (AML) in a subset of patients. Our objectives were to determine whether patients who develop secondary AML displayed altered etoposide pharmacokinetics or other pharmacologic characteristics compared to identically treated patients who did not develop AML. Children with newly diagnosed ALL were treated according to a protocol which included etoposide 300 mg/m2 given three times over 8 days during remission induction and once every 2-4 weeks during 120 weeks of continuation therapy. Characteristic 11q23 rearrangements were documented in seven of the eight patients with AML. Etoposide clearance, time that etoposide concentrations exceeded 10 microM, etoposide or etoposide catechol area-under-the-plasma-concentration vs time curve (AUC), serum albumin, and average methotrexate concentration did not differ significantly between the two groups; thiopurine methyltransferase (TPMT) activity tended to be lower in the eight children who did vs the 23 matched control children who did not develop AML (P=0.16). Further regression analyses likewise indicated that lower TPMT activity tended to be associated with shorter onset of secondary AML (P=0.11); it also tended to be lower among the eight index cases compared to the entire unmatched cohort of 105 identically treated children with ALL (P=0.10). We observed no statistically significant differences in etoposide disposition and antimetabolite pharmacology between patients who did and did not develop secondary AML.

Adolescent↗
PubMed1998

Transient encephalopathy following high-dose methotrexate treatment in childhood acute lymphoblastic leukemia.

The purpose of this study was to determine the incidence of and pharmacokinetic parameters associated with the development of transient encephalopathy following the administration of high-dose methotrexate and intrathecal chemotherapy in children with acute lymphoblastic leukemia (ALL). Two hundred and fifty-nine children with newly diagnosed ALL treated on one of two consecutive trials were analyzed. Presenting features in patients who developed transient encephalopathy were compared with those of patients who did not experience this event. For each patient who developed transient encephalopathy, methotrexate pharmacokinetic parameters were compared with those of matched controls. The cumulative incidence of acute encephalopathy was 3% (SE 1%) at 1 year and was associated with age greater than or equal to 10 years at diagnosis. Pharmacokinetic data did not differ between patients who developed transient encephalopathy and those who did not. The majority of patients had no long-term sequelae and were able to receive further courses of methotrexate without modification. Transient focal neurologic deficits occur in about 3% of children with ALL following the administration of intravenous and intrathecal methotrexate. These events cannot be predicted by pharmacokinetic parameters Of methotrexate disposition. However, these events are generally benign, suggesting that patients who experience acute encephalopathy should continue to receive this important chemotherapeutic agent.

Adolescent↗