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M V Relling

Publications and source records attributed to M V Relling.

At least 73 records · Page 4Linked to original sources
PubMed1998

Anti-asparaginase antibodies following E. coli asparaginase therapy in pediatric acute lymphoblastic leukemia.

Asparaginase is an effective antileukemic agent and is included in most front-line protocols for pediatric acute lymphoblastic leukemia (ALL) worldwide; however, allergic reactions to asparaginase may be dose-limiting. We evaluated plasma anti-asparaginase antibody concentrations in a cohort of children with newly diagnosed ALL, who did and who did not exhibit clinical hypersensitivity, after Escherichia coli (E. coli) asparaginase therapy. Thirty-five children who received asparaginase 10000 IU/m2 i.m. three times weekly for nine doses as part of both multiagent induction and reinduction chemotherapy, and seven monthly doses during the first 7 months of continuation treatment, were studied. Twenty-two patients experienced initial allergic reactions to asparaginase during continuation (n=20) or reinduction (n=2) phases and 13 children did not exhibit any reaction. An enzyme-linked immunosorbent assay (ELISA) was used to measure anti-asparaginase antibodies in plasma samples, diluted 1:3200, using E. coli asparaginase as the antigen. The median anti-asparaginase antibody concentration (OD at 1:3200 dilution) increased from 0.039 at induction to 0.506 at reinduction in patients who exhibited clinical hypersensitivity (P = 0.0002). By comparison, median antibody level increased from 0.011 to 0.032 OD at identical time points in patients who did not react to asparaginase (P = 0.02). Both post-induction and post-reinduction anti-asparaginase antibody levels were higher in reacting than in nonreacting patients (P = 0.004 and P = 0.01, respectively). Antibody levels were inversely related to the time elapsed between the reaction and sampling (P = 0.011). Although anti-asparaginase antibody levels increased from the post-induction plasma sample to the post-reinduction sample in 28 of 35 patients regardless of whether they exhibited clinical hypersensitivity, patients with hypersensitivity reactions had higher antibody levels than did identically treated control patients at comparable time points in therapy. Therefore, antibody analysis may be of clinical value in predicting future hypersensitivity.

Adolescent↗
PubMed1998

Reappraisal of the clinical and biologic significance of myeloid-associated antigen expression in childhood acute lymphoblastic leukemia.

PURPOSE: To reassess the clinical and biologic significance of myeloid-associated antigen expression in childhood acute lymphoblastic leukemia (ALL). PATIENTS AND METHODS: We prospectively studied 334 newly diagnosed cases of this disease, using a comprehensive panel of antibodies that represented five myeloid cluster groups (CD13, CD14, CD15, CD33, and CD65). Blast cells were tested for ETV6 and MLL rearrangement using Southern blot analysis. RESULTS: CD13 was expressed in 13.7% of cases, CD14 in 1%, CD15 in 6.6%, CD33 in 16%, and CD65 in 9.7%. Approximately one third of cases (31.4%) expressed one or more of these antigens (B-cell precursor, 31.9%; T-cell, 28.8%), while 10.5% expressed two or more (B-cell precursor, 11.3%; T-cell, 6.1%). Among the B-cell precursor leukemias, myeloid-associated antigen expression was significantly associated with a lack of hyperdiploidy and rearrangements of ETV6 or MLL gene. Most of the cases with MLL rearrangements (82%) expressed CD65, CD15, and CD33, either alone or in combination, whereas 48% of those with a rearranged ETV6 gene expressed CD13, CD33, or both. Myeloid-associated antigen expression did not correlate with event-free survival, whether the analysis was based on any of the five antigens in our panel or on the three more commonly tested antigens (CD13, CD33, and CD65). Importantly, this finding was not affected by exclusion of patients with ETV6 or MLL gene rearrangements. CONCLUSION: Even though blast cell expression of myeloid-associated antigen expression shows significant associations with specific genetic abnormalities, it lacks prognostic value in childhood ALL.

Adolescent↗
PubMed1997

Human granulocyte colony-stimulating factor after induction chemotherapy in children with acute lymphoblastic leukemia.

BACKGROUND: Recombinant human granulocyte colony-stimulating factor PO1 CA-20180ilgrastim) hastens the recovery from neutropenia after P30 CA-21765emotherapy, but its role in the management of childhood leukemia is unclear. METHODS: We randomly assigned 164 patients with acute lymphoblastic leukemia (age range, 2 months to 17 years) to receive placebo or G-CSF (10 microg per kilogram of body weight per day subcutaneously), beginning one day after the completion of remission-induction therapy and continuing until the neutrophil count was greater than or equal to 1000 per cubic millimeter for two days. The clinical and laboratory effects of this therapy were documented for 21 days. The area under the plasma G-CSF concentration-time curve was measured on days 1 and 7 in both groups. RESULTS: Responses to the growth factor could be assessed in 148 patients (73 in the G-CSF group and 75 in the placebo group). G-CSF treatment did not significantly lower the rate of hospitalization for febrile neutropenia (58 percent in the G-CSF group vs. 68 percent in the placebo group; relative risk, 0.85; 95 percent confidence interval, 0.59 to 1.16), increase the likelihood of event-free survival at three years (83 percent in both groups), or decrease the number of severe infections (five in the G-CSF group vs. six in the placebo group). Patients treated with G-CSF had shorter median hospital stays (6 days vs. 10 days, P=0.011) and fewer documented infections (12 vs. 27, P=0.009). The median total costs of supportive care were similar in the G-CSF and placebo groups ($8,768 and $8,616, respectively). Among patients who did not have febrile neutropenia during the first week of G-CSF or placebo injections, higher systemic exposure to the growth factor on day 7 was significantly related to a lower probability of subsequent hospitalization (P=0.049). CONCLUSIONS: G-CSF treatment had some clinical benefit in children who received induction chemotherapy for acute lymphoblastic leukemia, but it did not reduce the rate of hospitalization for febrile neutropenia, prolong survival, or reduce the cost of supportive care.

Adolescent↗
PubMed1997

Molecular diagnosis of thiopurine S-methyltransferase deficiency: genetic basis for azathioprine and mercaptopurine intolerance.

BACKGROUND: Thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation (that is, inactivation) of mercaptopurine, azathioprine, and thioguanine and exhibits genetic polymorphism. About 10% of patients have intermediate TPMT activity because of heterozygosity, and about 1 in 300 inherit TPMT deficiency as an autosomal recessive trait. If they receive standard doses of thiopurine medications (for example, 75 mg/m2 body surface area per day), TPMT-deficient patients accumulate excessive thioguanine nucleotides in hematopoietic tissues, which leads to severe and possibly fatal myelosuppression. OBJECTIVE: To elucidate the genetic basis and develop molecular methods for the diagnosis of TPMT deficiency and heterozygosity. DESIGN: Diagnostic test evaluation. SETTING: Research hospital. PATIENTS: The TPMT phenotype was determined in 282 unrelated white persons, and TPMT genotype was determined in all persons who had intermediate TPMT activity (heterozygotes) and a randomly selected, equal number of persons who had high activity. In addition, genotype was determined in 6 TPMT-deficient patients. MEASUREMENTS: Polymerase chain reaction (PCR) assays were developed to detect the G238C transversion in TPMT*2 and the G460A and A719G transitions in TPMT*3 alleles. Radiochemical assay was used to measure TPMT activity. Mutations of TPMT were identified in genomic DNA, and the concordance of TPMT genotype and phenotype was determined. RESULTS: 21 patients who had a heterozygous phenotype were identified (7.4% of sample [95% CI, 4.7% to 11.2%]). TPMT*3A was the most prevalent mutant allele (18 of 21 mutant alleles in heterozygotes; 85%); TPMT*2 and TPMT*3C were more rare (about 5% each). All 6 patients who had TPMT deficiency had two mutant alleles, 20 of 21 patients (95% [CI, 76% to 99.9%]) who had intermediate TPMT activity had one mutant allele, and 21 of 21 patients (100% [CI, 83% to 100%]) who had high activity had no known TPMT mutation. Detection of TPMT mutations in genomic DNA by PCR coincided perfectly with genotypes detected by complementary DNA sequencing. CONCLUSIONS: The major inactivating mutations at the human TPMT locus have been identified and can be reliably detected by PCR-based methods, which show an excellent concordance between genotype and phenotype. The detection of TPMT mutations provides a molecular diagnostic method for prospectively identifying TPMT-deficient and heterozygous patients.

Azathioprine↗
PubMed1997

Higher frequency of glutathione S-transferase deletions in black children with acute lymphoblastic leukemia.

The genetic polymorphisms in human glutathione S-transferases (GST) M1 and T1 have been associated with race, disease risk, and outcome of some adult cancers. Also, there are racial differences in the incidence and characteristics of childhood acute lymphoblastic leukemia (ALL). Our objectives were to compare the frequency of the null genotype for GSTM1, GSTT1, or both in children with ALL to that in healthy controls, and to determine whether GST genotype was associated with treatment outcome and prognostic factors. We studied GSTM1 and GSTT1 genotypes in somatic cell DNA from black children and white children with ALL and in 416 healthy controls, using a polymerase chain reaction technique. Ninety of 163 (55.2%) white ALL patients and 14 of 34 (41.2%) black patients were GSTM1 null, frequencies not significantly different (P = .19) than healthy controls (53.5% in whites and 27.6% in blacks), although there was a trend toward more null genotypes in black ALL patients. Twenty-three of 163 (14.1%) white ALL patients and 12 of 34 (35.3%) black ALL patients were GSTT1 null, not different (P = .34) than the frequencies in healthy controls (15.0% in whites and 24.1% in blacks). However, the frequency of the "double-null" genotype, lacking both GSTM1 and GSTT1, was higher in black patients with ALL (8 of 34 or 23.5%) than in black controls (3.9%) (P = .0005), but this was not the case in white patients with ALL (10 of 163 or 6.1%) compared to white controls (8.0%) (P = .68). In stratified analyses, the GST double-null genotype was not associated with other characteristics that might differ between whites and blacks with ALL, such as age, T-lineage immunophenotype, presenting white blood cell count, DNA index, or insurance status. The null genotype for GSTM1, GSTT1, or both was not found to be a prognostic factor for disease-free survival or probability of hematologic remission; central nervous system relapse tended to be less common in those with the GSTM1 null genotype (P = .054). The double-null genotype for GSTM1 and GSTT1 is more common among blacks but not whites with childhood ALL. These data suggest that GST genotype, coupled with unidentified additional risk factors, may play a role in risk of childhood ALL in American blacks.

Adult↗
PubMed1997

Genetic studies of childhood acute lymphoblastic leukemia with emphasis on p16, MLL, and ETV6 gene abnormalities: results of St Jude Total Therapy Study XII.

To determine the frequency and prognostic significance of recently described genetic lesions in pediatric acute lymphoblastic leukemia (ALL), all cases with available leukemic cell samples treated on St Jude Study XII were analyzed by molecular techniques for alterations of the p16, MLL and ETV6 genes. Homozygous p16 deletion was seen in 36 of 155 cases, including 14 of 23 T cell cases, but had no prognostic value. Rearrangement of MLL was seen in nine of 170 cases (5%) and conferred a poor prognosis, with a 5-year EFS estimate of only 11 +/- 7%, compared with 74 +/- 5% for the germline MLL group (P=0.0001). By contrast, rearrangement of ETV6 was found in 35 cases (21%) and was significantly associated with a better outcome (5-year EFS estimates: 87 +/- 7% vs 64 +/- 6%). In a Cox regression model adjusted for age, DNA index, race, leukocyte count, treatment group, and CNS status, ETV6 rearrangement retained independent prognostic significance (two-sided P value 0.012). Thus, in this uniformly treated group of patients, we confirmed the unfavorable prognostic significance of MLL rearrangement and demonstrated the favorable impact of ETV6 rearrangement, suggesting that these factors be added to ALL risk classification schemes.

Carrier Proteins↗
PubMed1997

Urate oxidase in prevention and treatment of hyperuricemia associated with lymphoid malignancies.

Standard prophylaxis and treatment of malignancy-associated hyperuricemia in the USA has been allopurinol with vigorous hydration, urinary alkalinization and osmotic diuresis. Urate oxidase, the enzyme that converts uric acid to allantoin (a readily excreted metabolite that has 5- to 10-fold higher solubility than uric acid), is an alternative therapy; however, few published findings support this practice. Between February 1994 and December 1996, we administered non-recombinant urate oxidase (Uricozyme) to 126 children with newly diagnosed non-B cell acute lymphoblastic leukemia (ALL) during the first 5 days of chemotherapy with methotrexate, 6-mercaptopurine or both. Their blood levels of uric acid and other indicators of tumor lysis were measured at diagnosis and during treatment and then compared with findings in 129 similarly treated historical controls who had received allopurinol to control hyperuricemia. Clinical responses to urate oxidase were also determined in eight patients with newly diagnosed B cell ALL or advanced-stage non-Hodgkin lymphoma. Patients treated with urate oxidase had rapid and significantly greater decreases in their blood uric acid levels than did the historical controls (median maximal level during treatment, 2.3 vs 3.9 mg/dl, P < 0.001). They also had lower creatinine (0.6 vs 0.7 mg/dl, P = 0.01) and blood urea nitrogen (11 vs 24 mg/dl, P < 0.001) levels. Similar findings were made in the eight cases of B cell ALL or non-Hodgkin lymphoma. None of the patients required dialysis for acute renal failure. Six (4.5%) of the 134 children given urate oxidase had allergic reactions, manifested primarily by urticaria, bronchospasm and hypoxemia. Thus, non-recombinant urate oxidase is a more effective uricolytic agent than allopurinol but is associated with acute hypersensitivity reactions, even in patients without a history of allergy.

Allopurinol↗
PubMed1997

Cytochrome P450 2D6 and glutathione S-transferase genotype in sudden infant death syndrome.

OBJECTIVES: The risk of sudden infant death syndrome (SIDS) has been linked with xenobiotic exposures, race and inheritance. Because cytochrome P450 2D6 (CYP2D6) and glutathione S-transferases (GSTM1 and GSTT1) are genetically regulated, polymorphically distributed, and responsible for detoxification of many centrally acting exogenous and endogenous bioactive compounds, our objective was to determine whether the prevalences of deficiencies in CYP2D6, GSTM1, and GSTT1 differ in SIDS victims compared to healthy controls. METHODS: CYP2D6 mutations (deletion, A, B, and T alleles) and GSTM1 and GSTT1 null genotypes were assessed in DNA from 50 SIDS victims. CYP2D6 phenotype, assigned using dextromethorphan urinary ratios, was assessed in 25 unrelated parents of SIDS victims. RESULTS: The CYP2D6B mutation was the only mutant CYP2D6 allele found in SIDS victims, present in 26.2% of patients (11/42) and 13.1% (11/84) of alleles. Adjusting for race, the prevalence of wild-type CYP2D6 alleles and of homozygous wild-type CYP2D6 phenotype was not different in SIDS victims compared to controls (P = 0.585 and 0.224, respectively). Among the 25 parents of SIDS victims, all subjects were extensive metabolizers, a prevalence not different from controls (P = 0.243). The prevalence of the null genotype for GSTM1, GSTT1 and double-null for GSTM1 and GSTT1 was 33.3%, 21.4% and 9.5%, respectively, among SIDS victims, and was not different than controls (P = 0.61, 0.1, 0.28, respectively). The combination of CYP2D6 homozygous wild-type genotype and the null genotype for GSTM1, GSTT1, or both GSTM1 + GSTT1 also did not differ in SIDS victims and controls. CONCLUSIONS: The frequencies of CYP2D6 mutant genotypes and the null genotypes for GSTM1 and GSTT1 were not different among SIDS victims compared to normal controls, and thus these polymorphisms are unlikely to identify families with a high risk of SIDS.

Cytochrome P-450 CYP2D6↗
PubMed1997

Differences in folylpolyglutamate synthetase and dihydrofolate reductase expression in human B-lineage versus T-lineage leukemic lymphoblasts: mechanisms for lineage differences in methotrexate polyglutamylation and cytotoxicity.

Cellular accumulation of methotrexate polyglutamates (MTXPGs) is recognized as an important determinant of the cytotoxicity and selectivity of methotrexate in acute lymphoblastic leukemia (ALL). We identified a significantly lower cellular accumulation of MTXPGs in T-lineage versus B-lineage lymphoblasts in children with ALL, which is consistent with the worse prognosis of T-lineage ALL when treated with conventional antimetabolite-based therapy. Maximum MTXPG accumulation in leukemic blasts in vivo was 3-fold greater in lymphoblasts of children with B-lineage ALL (129 children) compared with those with T-lineage ALL (20 children) (p < 0.01) and was characterized by a saturable (Emax) model in both groups. The human leukemia cell lines NALM6 (B-lineage) and CCRF/CEM (T-lineage) were used to assess potential mechanisms for these lineage differences in MTX accumulation, revealing i) greater total and long-chain MTXPG accumulation in NALM6 over a wide range of methotrexate concentrations (0.2-100 microM), ii) saturation of MTXPG accumulation in both cell lines, with a higher maximum (Emax in NALM6, iii) 3-fold higher constitutive FPGS mRNA expression and enzyme activity in NALM6 cells, iv) 2-fold lower levels of DHFR mRNA and protein in NALM6 cells, and v) 4-6 fold lower extracellular MTX concentration and 2-fold lower intracellular MTXPG concentration to produce equivalent cytotoxicity (LC50) in NALM6 versus CEM. There was a significant relationship between FPGS mRNA and enzyme activity in lymphoblasts from children with newly diagnosed ALL, and blast FPGS mRNA and activity increased after methotrexate treatment. These data indicate higher FPGS and lower DHFR levels as potential mechanisms contributing to greater MTXPG accumulation and cytotoxicity in B-lineage lymphoblasts.

Antimetabolites, Antineoplastic↗
PubMed1996

Relationship between cytotoxicity and site-specific DNA recombination after in vitro exposure of leukemia cells to etoposide.

BACKGROUND: Etoposide, an inhibitor of the normal religation activity of the nuclear enzyme topoisomerase II, can induce a secondary acute myeloid leukemia characterized by site-specific DNA rearrangements. The schedule of drug administration appears to be a clinical risk factor for this devastating treatment complication. PURPOSE: We tested the hypothesis that prolonged exposure of leukemia cells in vitro to low concentrations of etoposide, compared with short exposures to high concentrations, could produce equivalent or greater desired cytotoxic effects, with decreased occurrence of undesired site-specific double-stranded DNA recombinational events (i.e., recombinogenesis). METHODS: We used the frequency of V(D)J (variable-diversity-joining) recombinase-mediated deletions of exons 2 and 3 of the hypoxanthine phosphoribosyltransferase (HPRT) gene as a biomarker of etoposide-induced, nonhomologous, site-specific DNA rearrangement. A polymerase chain reaction-based technique was used to measure exon 2 + 3 deletions in human lymphoid leukemia CCRF-CEM cells 6 days after either 4-hour or 24-hour treatment with etoposide at clinically relevant concentrations. Cytotoxic effects of etoposide (determined by the number of viable cells present in the treated compared with the control [i.e., untreated] cells) were measured 6 days after treatment of the cells. The frequency of the exon 2 + 3 deletion following the two treatment-duration conditions was compared by use of the Mantel-Haenszel statistic. All P values resulted from two-sided tests. RESULTS: Cytotoxicity increased with increasing etoposide concentration and exposure duration, as expected. By day 6, the frequency of exon 2 + 3 deletions was significantly higher (global P value = .0003) after the 4-hour treatment than after the 24-hour treatment, regardless of whether the frequency was assessed at etoposide concentrations achieving equivalent (e.g., 95%) cytotoxicity (14.2 x 10(-7) versus 4.1 x 10(-7) or at equivalent etoposide concentrations (e.g., 1 microM) (10.8 x 10(-7) versus 1.3 x 10(-7). Thus, the ratio of desired cytotoxic to undesired recombinogenic effects was higher with the 24-hour schedule. After the treated cells were subcloned at limiting dilutions, the frequency of the exon 2 + 3 deletion increased from 16.3 x 10(-7) to 4.33 x 10(-3), indicating that the recombinational event is not necessarily lethal. CONCLUSION: For all drug concentrations and levels of cytotoxicity studied in CCRF-CEM cells, there was a greater ratio of cytotoxicity to genetic recombination following prolonged exposure to etoposide than following brief exposure. IMPLICATION: These data suggest that recombinogenesis is not inextricably linked to cytotoxicity. If confirmed in the clinical setting, the use of prolonged dosage schedules may provide a means to decrease the risk of etoposide-induced acute myeloid leukemia without compromising treatment efficacy.

Acute Disease↗
PubMed1996

Etoposide causes illegitimate V(D)J recombination in human lymphoid leukemic cells.

Etoposide is one of the most widely used antineoplastics. Unfortunately, the same treatment schedules associated with impressive efficacy are associated with an increased risk of secondary acute myeloid leukemia (AML), which has prompted its withdrawal from some treatment regimens, thereby potentially compromising efficacy against the original tumor. Because etoposide-associated AML is characterized by site-specific illegitimate DNA recombination, we studied whether etoposide could directly cause site-specific deletions of exons 2 and 3 in the hprt gene. Human lymphoid CCRF-CEM cells were treated with etoposide for 4 hours, and DNA was isolated after subculturing. The deletion of exons 2 and 3 from hprt was assayed by a quantitative polymerase chain reaction (PCR) method. In the absence of etoposide treatment, the frequency of deletions of exons 2 and 3 was very low (5.05 x 10(-8)). After exposure to 10 mumol/ L etoposide, the frequency of the exon 2 + 3 deletion was increased immediately after and at 24 hours after etoposide treatment (65 to 89 x 10(-8)) and increased to higher levels (128 to 173 x 10(-8)) after 2 and 6 days of subculture (P < .001 overall). The frequency of the exon 2 + 3 deletion assessed at 6 days of subculture after 4 hours of 0, 0.25, 1, 2.5, 5, and 10 mumol/L etoposide treatment increased with etoposide concentration, ie, 5.05 x 10(-8), 89.2 x 10(-8), 108 x 10(-8), 142 x 10(-8), 163 x 10(-8), and 173 x 10(-8), respectively (P < .0001). Sequencing of a subset of amplified products confirmed the presence of DNA sequences at the breakpoints consistent with V(D)J recombination. By contrast, exon 2 + 3 deletions after etoposide treatment in the myeloid cell lines KG-1A and K562 showed no evidence of V(D)J recombinase in their genesis. We conclude that etoposide can induce the illegitimate site-specific action of V(D)J recombinase on an unnatural DNA substrate after a single treatment in human lymphoid cells.

Base Sequence↗
PubMed1996

P-glycoprotein: a major determinant of rifampicin-inducible expression of cytochrome P4503A in mice and humans.

The P-glycoprotein (Pgp) efflux pump can influence the hepatocellular concentration of xenobiotics that are modulators and substrates of cytochrome P4503A (CYP3A). We tested the hypothesis that Pgp is a determinant of drug-inducible expression of CYP3A. The magnitude of CYP3A induction by rifampicin was compared in the human parental colon carcinoma cell line LS 180/WT (wild type) and in two derivative clones overexpressing the human multidrug resistance gene MDR1 (also designated PGY1) because of either drug selection (LS 180/ADR) or transfection with MDRI cDNA (LS 180/MDR). In both MDR1 cDNA-overexpressing clones, rifampicin induction of CYP3A mRNA and protein was decreased and required greater rifampicin concentrations compared with parental cells. The role of Pgp in regulation of CYP3A expression in vivo was analyzed in mice carrying a targeted disruption of the mdr1a mouse gene. Oral treatment with increasing doses of rifampicin resulted in elevated drug levels in the livers of mdr1a (-/-) mice compared with mdr1a (+/+) mice at all doses. Consistent with the enhanced accumulation of rifampicin in mdr1a (-/-) mice, lower doses of rifampicin were required for induction of CYP3A proteins, and the magnitude of CYP3A induction was greater at all doses of rifampicin in mdr1a (-/-) mice compared with mdr1a (+/+) mice. We conclude that Pgp-mediated transport is a critical element influencing the CYP3A inductive response.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Accumulation of methotrexate polyglutamates in lymphoblasts is a determinant of antileukemic effects in vivo. A rationale for high-dose methotrexate.

Methotrexate (MTX) is one of the most widely used drugs for the treatment of childhood acute lymphoblastic leukemia (ALL) and is commonly given in high doses. However, the rationale for high-dose MTX (HDMTX) has been challenged recently. To determine whether higher MTX polyglutamate (MTXPG) concentrations in ALL blasts translate into greater antileukemic effects, 150 children with newly diagnosed ALL were randomized to initial treatment with either HDMTX (1,000 mg/m2 intravenously over 24 h) or lower-dose MTX (30 mg/m2 by mouth every 6 h x 6). ALL blasts accumulated higher concentrations of MTXPG and long-chain MTXPG (MTXPGLC) after HDMTX (P < 0.00001). Of 101 patients evaluable for peripheral blast cytoreduction, MTXPG concentrations were higher in patients whose blast count decreased within 24 h (P = 0.005) and in those who had no detectable circulating blasts within 4 days (P = 0.004). The extent of inhibition of de novo purine synthesis in ALL blasts was significantly related to the blast concentration of MTXPGLC (IC95% = 483 pmol/10(9) blasts). The percentage of patients with 44-h MTXPGLC exceeding the IC95% was greater after HDMTX (81%) than LDMTX (46%, P < 0.0001). These data indicate that higher blast concentrations of MTXPG are associated with greater antileukemic effects, establishing a strong rationale for HD-MTX in the treatment of childhood ALL.

Adolescent↗
PubMed1996

Are the major effects of P-glycoprotein modulators due to altered pharmacokinetics of anticancer drugs?

Agents (modulators) that reverse the in vitro resistance of tumor cells to anticancer drugs that are substrates for P-glycoprotein (Pgp, the product of the MDR1 gene) have been given to patients concurrently with anticancer drugs in an attempt to improve therapeutic response. The vast majority of investigations into these drugs indicate that Pgp modulators decrease the systemic clearance of anticancer drugs, thus potentially nonselectively increasing exposure to normal and malignant cells and thereby potentially increasing the severity and/or incidence of adverse effects associated with the anticancer therapy. Mechanisms by which Pgp modulators could alter the pharmacokinetics of the anticancer agent include competition for cytochrome P450 intestinal or liver metabolism, inhibition of Pgp-mediated biliary excretion or intestinal transport, or inhibition of renal elimination. It is suggested that administration of Pgp modulators is unlikely to improve the therapeutic index for anticancer drugs unless agents that lack significant pharmacokinetic interactions are found. Moreover, it will likely be required that there be some cancer-tissue selectivity for modulators in order to avoid collaterally increasing the sensitivity of normal Pgp-expressing tissues to the anticancer drug.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Simultaneous characterization of glutathione S-transferase M1 and T1 polymorphisms by polymerase chain reaction in American whites and blacks.

Human glutathione S-transferase (GST) M1 and T1 enzymes exhibit genetic polymorphism, with a percentage of normal individuals exhibiting a homozygous deletion of the relevant genes. We established a differential polymerase chain reaction (PCR) technique to simultaneously characterize inactivating mutations responsible for the null alleles of GSTM1 and GSTT1. Primers for GSTM1,GSTT1,and for beta-globin (as a positive control) were used to simultaneously amplify all three gene products from leukocyte DNA from 416 normal healthy human volunteers. Identical GSTM1 and CSTT1 genotypes were obtained using nine samples processed either separately or simultaneously for GSTM1 and GSTT1. The frequency of the null genotype for GSTM1 was higher in whites (114/213 or 53.5% vs 56/203 or 27.6%, p < 0.001) and for GSTT1 was higher in blacks (49/203 or 24.1% vs 32/213 or 15.0%, p = 0.019). The observed frequency of the 'double null' genotype for both GSTM1 and GSTT1 was not significantly different from that predicted if both polymorphisms were independent (p = 0.102) and did not differ by race (p = 0.120) or sex (p = 0.800). There was a higher frequency of the GSTM1 null genotype among females than males (92/202 or 45.5% vs 78/214 or 36.4%, p = 0.049). These results demonstrate that this PCR method is a simple and reliable tool to simultaneously characterize both GSTM1 and GSTT1 null genotypes.

Adolescent↗
PubMed1996

Genetic polymorphism of thiopurine S-methyltransferase: clinical importance and molecular mechanisms.

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurines such as mercaptopurine and thioguanine. TPMT activity exhibits genetic polymorphism, with about 1 in 300 inheriting TPMT-deficiency as an autosomal recessive trait. If treated with standard dosages of thiopurines. TPMT-deficient patients accumulate excessive thioguanine nucleotides (TGN) in hematopoietic tissues, leading to severe hematopoietic toxicity that can be fatal. However, TPMT-deficient patients can be successfully treated with a 10-15-fold lower dosage of these medications. The human gene encoding polymorphic TPMT has been cloned and characterized, and two mutant alleles have recently been isolated from TPMT-deficient and heterozygous patients (TPMT*2, TPMT*3), permitting development of PCR-based methods to identify TPMT-deficient and heterozygous patients prior to therapy. TPMT*3 is the predominant mutant allele in American whites, accounting for about 75% of mutations in this population. Ongoing studies aim to better define the influence of TPMT activity on thiopurine efficacy, to identify additional mutant alleles and determine their frequency in different ethnic groups, to elucidate the mechanism(s) for loss of function of mutant proteins, to identify potential endogenous substrates and to define the molecular mechanisms of TPMT regulation. Together, these advances bold the promise of improving the safety and efficacy of thiopurine therapy.

Alleles↗
PubMed1996

Etoposide achieves potentially cytotoxic concentrations in CSF of children with acute lymphoblastic leukemia.

PURPOSE: Although epipodophyllotoxins are commonly used in contemporary treatment regimens for acute lymphoblastic leukemia (ALL), their potential role in CNS-directed therapy has received little attention. We prospectively studied 20 children during initial remission of ALL and 16 children at relapse to assess CSF penetration of etoposide. METHODS: Simultaneous plasma and CSF concentrations were assessed at a median of 2.8 hours (range, 0.4 to 5.3) after an intravenous (i.v.) or oral dose in 41 paired samples. RESULTS: Etoposide given at 300 mg/m2 i.v. to patients during first remission and at 50 or 25 mg/m2 orally to those in relapse resulted in median CSF levels of 0.175 mumol/L (range, .066 to 2.12), 0.011 mumol/L (range, .004 to .032), and 0.007 mumol/L (range, .003 to .014), respectively. The CSF etoposide concentration was > or = 10 nmol/L in 20 of 20, five of 10, and two of 11 courses following 300 mg/m2 i.v., 50 mg/m2 orally, and 25 mg/m2 orally, respectively, and was positively related to both the concurrent etoposide plasma concentration (R2 = .64) and to dose (R2 = .73). The median ratio of CSF to plasma concentration was 0.30% (range, 0.09% to 3.12%), which was not related to dose, plasma concentration, or time postdose at which samples were obtained, but was positively correlated with the CSF protein concentration (R2 = 0.43, P = .006). Both the absolute etoposide CSF concentrations (P = .008) and the ratio of CSF to plasma concentrations (P = .023) were higher among first-remission patients who had CSF leukemic blasts at diagnosis compared with those without CSF blasts. CONCLUSION: Because etoposide concentrations as low as 10 nmol/L may be cytotoxic in vitro, prolonged daily oral low-dose (50 mg/m2) or conventional i.v. doses of etoposide may contribute to successful CNS-directed therapy in children with ALL.

Administration, Oral↗