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A T Look

Publications and source records attributed to A T Look.

At least 163 records · Page 9Linked to original sources
PubMed1987

Teniposide plus cytarabine improves outcome in childhood acute lymphoblastic leukemia presenting with a leukocyte count greater than or equal to 100 x 10(9)/L.

Childhood acute lymphoblastic leukemia with an initial leukocyte count greater than or equal to 100 X 10(9)/L responds poorly to conventional chemotherapy. To extend event-free survival (EFS) in this disease, we devised a protocol that specifies intensive 2-week courses of teniposide (VM-26, 165 mg/m2) plus cytarabine (ara-C, 300 mg/m2), before and immediately after standard 4-week remission induction therapy with prednisone, vincristine, and L-asparaginase. The VM-26 and ara-C combination was also administered intermittently for the first year of continuation treatment with oral 6-mercaptopurine and methotrexate. CNS prophylaxis consisted of periodic intrathecal (IT) injections of methotrexate and delayed cranial irradiation. At a median follow-up of 4 years, the estimated EFS rate for 57 consecutive patients with leukocyte counts of 100 to 1,000 X 10(9)/L was 44%, compared with 10% for matched controls (P less than .001). Remission induction rates in the two groups were similar (82% v 72%, P = .16). Twenty-five patients in the VM-26/ara-C group have survived without adverse events for 2.7 to 6.8 years, whereas only nine of the controls achieved more than a year of EFS. The most common complications during early treatment were acute hyperkalemia from rapid tumor cell lysis and infections due to prolonged marrow aplasia. Continuation chemotherapy was well tolerated. We conclude that VM-26 plus ara-C, added to each phase of an otherwise basic regimen of chemotherapy, will substantially improve prognosis in this high-risk form of childhood leukemia.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1987

Combined etoposide and 5-azacitidine in children and adolescents with refractory or relapsed acute nonlymphocytic leukemia: a Pediatric Oncology Group Study.

An intensive regimen of combined etoposide (VP-16) and 5-azacitidine (5-Az) was used to treat 96 children and adolescents with refractory or relapsed acute nonlymphocytic leukemia (ANLL). Patients were given two sequential five-day courses of VP-16, 250 mg/m2 for three days, followed by 5-Az, 300 mg/m2 for two days. An additional five-day course was administered if marrow aplasia was not evident by day 13. A complete remission rate of 45% was achieved with a median of two courses of VP-16 and 5-Az. The outcome of induction therapy was not influenced by prior treatment, blast cell morphology, or disease status on study entry (refractory or relapsed). Twenty-seven patients have relapsed after remission periods of 35 to 920 days (median, 110 days); seven others are free of leukemia for up to 519 days. The effectiveness of VP-16/5-Az combination therapy in patients refractory to anthracyclines and cytarabine indicates a potential role for these compounds in first-line treatment of patients with ANLL.

Adolescent↗
PubMed1987

Hypodiploidy is associated with a poor prognosis in childhood acute lymphoblastic leukemia.

Leukemic cells from 31 (7.6%) of 409 children with newly diagnosed acute lymphoblastic leukemia (ALL) had a hypodiploid karyotype. The patients' ages ranged from 0.8 to 17 years (median, 5 years) and their initial leukocyte counts from 1.0 to 132 X 10(9)/L (median, 12.7 X 10(9)/L). Modal chromosome numbers for the leukemic stem lines were 45 in 26 cases, 28 in two cases, and 26, 36 and 43 in one case each. Seven cases had one to three additional abnormal lines due to clonal evolution. Chromosome 20 was lost most frequently (nine cases). Structural abnormalities--including chromosomal translocations (21 cases), deletions (ten cases), duplications (two cases), or inversions (one case)--were common findings; the nonrandom translocations consisted of the t(1;19)(q23;p13.3) in two pre-B cases and tdic(9;12)(p1?1;p1?2) in three cases of common ALL. When compared with hyperdiploid cases (greater than 50 chromosomes), ALL with hypodiploidy was found to have a poorer outcome and was more likely to be associated with chromosomal translocations, higher serum lactic dehydrogenase levels, and age less than 2 or greater than or equal to 10 years. Moreover, patients with hypodiploid ALL fared as poorly as those with pseudodiploid karyotypes, even though their leukocyte counts and serum lactic dehydrogenase levels were lower and they had a comparable frequency of leukemic cell translocations. Hypodiploidy is therefore an unfavorable karyotypic feature in childhood ALL.

Acute Disease↗
PubMed1987

Expression of the human monocyte membrane antigen gp55 by murine fibroblasts after DNA-mediated gene transfer.

Human DNA sequences that contain the gene encoding gp55, a cell surface glycoprotein expressed exclusively on mature human monocytes and monocytic leukemia cells, were isolated in a mouse genetic background. DNA from mature human monocytes was cotransfected with DNA from a molecularly cloned feline sarcoma virus containing the v-fms oncogene into NIH-3T3 cells. Transformed mouse fibroblasts that expressed gp55, based on their reactivity with the MY4, B44.1, or LeuM3 monoclonal antibodies, were selected by fluorescence-activated cell sorting. Regardless of which antibody was used for selection, equivalent binding of all three antibodies was observed for positive transformants. Secondary and tertiary mouse cell transformants were obtained after additional rounds of transfection and cell sorting with the use of DNA from primary and then secondary transformants. Southern blot analysis of the cellular DNA from two independently derived tertiary subclones revealed a limited complement of human sequences, thus indicating that the gene encoding gp55 is included in fewer than 50 kilobases of human DNA. Independently derived tertiary subclones displayed concordant patterns of reactivity with 13 monocyte-specific monoclonal antibodies, thus indicating that each recognized an epitope on the product (gp55) of a single human gene. The 55-kilodalton cell surface polypeptide was specifically immunoprecipitated with a representative monoclonal antibody, 26if, from lysates of enzymatically radioiodinated peripheral blood monocytes and tertiary transformants. We conclude that gp55 is highly immunogenic and that a large number of independently derived monoclonal antibodies specific for human monocytes react with epitopes on this one molecule.

Animals↗
PubMed1986

Clinical pharmacodynamics of high-dose methotrexate in acute lymphocytic leukemia. Identification of a relation between concentration and effect.

High-dose methotrexate (500 to 33,600 mg per square meter of body-surface area) with leucovorin rescue is a common component of therapy for acute lymphocytic leukemia. To increase understanding of the relation between the serum concentration and the effect of methotrexate, we conducted a randomized, prospective study of 108 children with "standard-risk" acute lymphocytic leukemia who were treated with 15 doses of methotrexate (1000 mg per square meter) that were infused over 24 hours. The median length of follow-up was 3.5 years from diagnosis for patients still in remission. Variability between patients in methotrexate clearance produced steady-state serum concentrations that ranged from 9.3 to 25.4 microM. Patients with median methotrexate concentrations of less than 16 microM (n = 59) had a lower probability of remaining in remission (P less than 0.05) than patients with concentrations of 16 microM or more (n = 49). Multivariate analyses indicated that patients with methotrexate concentrations of less than 16 microM were 3 times more likely to have any kind of relapse during therapy (P = 0.01) and 7 times more likely to have a hematologic relapse during therapy (P = 0.001). Stepwise Cox's regression identified leukemic-cell DNA content, methotrexate concentration, and hemoglobin as significant prognostic variables for hematologic relapse (P = 0.0005). We conclude that there is a concentration-effect relation for high-dose methotrexate in acute lymphocytic leukemia and that 1000 mg per square meter infused over a period of 24 hours may not be optimal for patients with relatively fast drug clearance.

Adolescent↗
PubMed1986

Induction failures in childhood acute nonlymphocytic leukemia: etoposide/5-azacytidine for cases refractory to daunorubicin/cytarabine.

Treatment with a combination of daunorubicin (45 mg/m2 IV, days 1-3) and cytarabine (100 mg/m2 continuous IV infusion, days 4-10) failed to induce complete remission in 31 of 87 children (36%) with acute nonlymphocytic leukemia (ANLL). Six patients with monocytic or promyelocytic leukemia died before day 14 of therapy from complications of hyperleukocytosis and coagulopathy; an additional 10 failed because of fatal infections associated with drug-induced marrow hypoplasia, and the remaining 15 had residual leukemia despite receiving two courses of daunorubicin and cytarabine. Alternative therapy with etoposide (250 mg/m2, IV, days 1-3, 7-9) and 5-azacytidine (300 mg/m2 IV, days 4, 5, 9, 10) induced complete remission in nine (60%) of the 15 patients with resistant leukemia. Among the six children who failed to respond to either regimen, three had cytochemical and immunophenotypic features indicative of acute mixed-lineage leukemia, and one had monosomy 7 syndrome. Our findings suggest that the addition of etoposide and 5-azacytidine to a basic daunorubicin-cytarabine regimen would increase remission induction rates in childhood ANLL. Careful determination of pretreatment characteristics, including blast cell immunophenotype and cytogenetic properties, are needed to identify unusual cases of ANLL that may require selective therapy.

Acute Disease↗
PubMed1986

Unfavorable presenting clinical and laboratory features are associated with CALLA-negative non-T, non-B lymphoblastic leukemia in children.

Twenty-four (5.7%) of 424 children with newly diagnosed acute lymphoblastic leukemia (ALL) were found to have blast cells that expressed HLA-DR antigens but not the common ALL antigen (CALLA), E-rosette receptors, T-cell antigens, or cytoplasmic or surface immunoglobulins. Each of the eight cases tested expressed the B-cell associated antigen B4, but not B1 or B2 antigen. Myeloid-associated antigens were not present in any of the 10 cases tested. By comparison with common (CALLA+ B-cell precursor) ALL, patients having this immunophenotype were more likely to be children less than 2 yr of age (p less than 0.001), to have higher initial leukocyte counts (p less than 0.001), and to have blast cells with a DNA index less than 1.16 (p = 0.05), a pseudodiploid karyotype (p = 0.01) and a chromosomal translocation (p = 0.003). The presence of any chromosomal translocation in these CALLA- ALL was related to measures of increased leukemic cell burden including higher leukocyte counts, larger liver and spleen sizes and higher serum lactic dehydrogenase levels. While the patients were entered into several treatment arms of two protocols, the CALLA- cases appeared to have lower remission rate (p = 0.06) and shorter event-free survival time (p = 0.05) than did those with common ALL. The association with clinical and laboratory features of known adverse prognostic significance provides some explanation for the poor treatment outcome of CALLA- ALL.

Antigens, Neoplasm↗
PubMed1986

Inverse relationship between megakaryocyte buoyant density and maturity.

We examined the relationship between rat megakaryocyte buoyant density and maturation stage in continuous Percoll density gradients. An average of 88% of megakaryocytes had buoyant densities less than 1.054 g/ml. There was an inverse relationship between megakaryocyte buoyant density and maturation. Morphologically mature forms comprised 90% of the megakaryocytes with buoyant densities of 1.030-1.033 g/ml. In contrast, immature morphology was present in three-quarters of megakaryocytes with buoyant densities of 1.042-1.046 g/ml. These morphological findings were confirmed by [3H]thymidine labelling studies. Cell viability assessed by trypan blue exclusion was highest among more dense megakaryocytes of which the majority were immature. The lowest trypan blue exclusion was found in the less dense, predominantly mature megakaryocytes indicating that these cells are more susceptible to membrane damage during marrow suspension. Megakaryocyte DNA content distributions and platelet antigen levels, determined by two-colour flow cytometry, were also related to megakaryocyte density; the more dense megakaryocytes showed an approximately two-fold higher proportion of 8N cells and less platelet antibody binding than did less dense megakaryocytes. These studies suggest that megakaryocytes can be fractionated according to their buoyant densities into immature and mature populations suitable for molecular studies of differentiation.

Animals↗
PubMed1986

The amino-terminal domain of the v-fms oncogene product includes a functional signal peptide that directs synthesis of a transforming glycoprotein in the absence of feline leukemia virus gag sequences.

The nucleotide sequence of a 5' segment of the human genomic c-fms proto-oncogene suggested that recombination between feline leukemia virus and feline c-fms sequences might have occurred in a region encoding the 5' untranslated portion of c-fms mRNA. The polyprotein precursor gP180gag-fms encoded by the McDonough strain of feline sarcoma virus was therefore predicted to contain 34 v-fms-coded amino acids derived from sequences of the c-fms gene that are not ordinarily translated from the proto-oncogene mRNA. The (gP180gag-fms) polyprotein was cotranslationally cleaved near the gag-fms junction to remove its gag gene-coded portion. Determination of the amino-terminal sequence of the resulting v-fms-coded glycoprotein, gp120v-fms, showed that the site of proteolysis corresponded to a predicted signal peptidase cleavage site within the c-fms gene product. Together, these analyses suggested that the linked gag sequences may not be necessary for expression of a biologically active v-fms gene product. The gag-fms sequences of feline sarcoma virus strain McDonough and the v-fms sequences alone were inserted into a murine retroviral vector containing a neomycin resistance gene. Both constructs were biologically active when transfected into NIH 3T3 cells and produced morphologically transformed foci at equivalent efficiencies. When transfected into a cell line (psi 2) expressing complementary viral gene functions, G418-resistant (Neor) cells containing either of these vector DNAs produced high titers of transforming viruses. Analysis of proteins produced in cells containing the vector lacking gag gene sequences showed that gP180gag-fms was not synthesized, whereas normal levels of both immature gp120v-fms and mature gp140v-fms were detected. The glycoprotein was efficiently transported to the cell surface, and it retained wild-type tyrosine kinase activity. We conclude that a cryptic hydrophobic signal peptide sequence in v-fms was unmasked by gag deletion, thereby allowing the correct orientation and transport of the v-fms gene product within membranous organelles. It seems likely that the proteolytic cleavage of gP180gag-fms is mediated by signal peptidase and that the amino termini of gp140v-fms and the c-fms gene product are identical.

Amino Acid Sequence↗
PubMed1986

Molecular cloning, expression, and chromosomal localization of the gene encoding a human myeloid membrane antigen (gp150).

DNA from a tertiary mouse cell transformant containing amplified human sequences encoding a human myeloid membrane glycoprotein, gp150, was used to construct a bacteriophage lambda library. A single recombinant phage containing 12 kilobases (kb) of human DNA was isolated, and molecular subclones were then used to isolate the complete gp150 gene from a human placental genomic DNA library. The intact gp150 gene, assembled from three recombinant phages, proved to be biologically active when transfected into NIH 3T3 cells. Molecular probes from the gp150 locus annealed with a 4.0-kb polyadenylated RNA transcript derived from human myeloid cell lines and from tertiary mouse cell transformants. The gp150 gene was assigned to human chromosome 15, and was subchromosomally localized to bands q25-26 by in situ hybridization. The chromosomal location of the gp150 gene coincides cytogenetically with the region assigned to the c-fes proto-oncogene, another human gene specifically expressed by myeloid cells.

Antigens, Surface↗
PubMed1986

Hyperdiploidy and chromosomal rearrangements define the anaplastic variant of Wilms' tumor.

Flow cytometric measurement of the DNA content of Wilms' tumor cells revealed a striking correspondence with the histologic subtype and treatment outcome. In the 48 cases studied, a hyperdiploid DNA content ranging from 1.7 to 3.2 times the result for normal diploid cells distinguished all but one of the ten anaplastic tumors. Lower values, from 1.0 to 1.4 times the diploid DNA content, characterized the nonanaplastic specimens. By Kaplan-Meier analysis, the probability of achieving 3 years of relapse-free survival was significantly lower in the group with higher DNA content (0.42 v 0.87, P less than .01). Analysis of banded chromosomes for a subset of 22 patients contributed important information beyond the flow cytometric study. Cases of anaplasia associated with poorer responses to therapy showed numerous complex translocations, whereas all others lacked such changes. By combining flow cytometric techniques and conventional methods of chromosome analysis, it should be possible to identify those patients with Wilms' tumor who are most likely to fail therapy. The biologic implication of these findings is that the development of clinical drug resistance in Wilms' tumor is a result of the genetic instability of the malignant clone.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1986

Cytogenetic features and serum lactic dehydrogenase level predict a poor treatment outcome for children with pre-B-cell leukemia.

Leukemic cells from 89 (24%) of 369 children with newly diagnosed acute lymphoblastic leukemia (ALL) were found to have a pre-B immunophenotype. By comparison with blasts having the common ALL phenotype, the pre-B cells were more likely to have a DNA index less than 1.16 (P = 0.02), a pseudodiploid karyotype (P less than 0.001), and a chromosomal translocation (P = 0.001). Increased serum lactic dehydrogenase levels (P = 0.001) were also characteristic of pre-B ALL; otherwise, the clinical and laboratory features of the two groups were similar. A nonrandom chromosomal translocation, t(1;19)(q23;p13.3), was identified in blast cells from 16 (23%) of the 70 patients with pre-B ALL and adequate chromosome banding studies; different translocations were found in 11 of the remaining patients. The presence of any chromosomal translocation in the pre-B group was significantly related to a higher leukocyte count, an increased level of serum lactic dehydrogenase, an increased percentage of S-phase cells, black race, and a blast cell DNA index less than 1.16. Four presenting features were found to confer an increased risk of treatment failure among pre-B patients: pseudodiploidy, chromosomal translocation, black race, and higher serum lactic dehydrogenase level. In a multivariate analysis, pseudodiploidy emerged as the strongest factor for predicting relapse in pre-B ALL. The frequent association of chromosomal abnormalities of known adverse prognostic significance and high serum lactic dehydrogenase levels with pre-B-cell ALL explains, at least in part, the poor treatment outcome reported for children with this subtype of leukemia.

Adolescent↗
PubMed1986

Reversal of Vinca alkaloid resistance but not multiple drug resistance in human leukemic cells by verapamil.

We examined the ability of verapamil, a Ca2+ channel blocker, to overcome Vinca alkaloid and multiple drug resistance in our CEM/VLB100 and CEM/DOX human leukemic lymphoblasts. Compared with the parent CCRF-CEM cells, CEM/VLB100 cells are approximately equal to 200- to 800-fold resistant to vinblastine and express cross-resistance to vincristine, doxorubicin, and other "natural product" drugs, as determined by comparing 50% inhibitory concentrations in a 48-h growth inhibition assay. Verapamil (10 microM) decreased the 50% inhibitory concentrations for Vinca alkaloids in CEM/VLB100 cells by approximately equal to 75- to 85-fold but caused only slight (approximately equal to 2- to 5-fold) decreases in 50% inhibitory concentrations for anthracyclines, epipodophyllotoxins, and other tubulin-binding drugs (colchicine and podophyllotoxin). Qualitatively similar results were obtained with doxorubicin-resistant cells, termed CEM/DOX; verapamil caused a 19-fold increase in doxorubicin toxicity but 67- and 3500-fold increases in the toxicities of vinblastine and vincristine, respectively. These results indicate that the effect of verapamil is relatively greater for Vinca alkaloids, with less pronounced effects for the other natural product drugs against which these cells express multiple drug resistance. In flow cytometric studies, individually nontoxic or minimally toxic concentrations of vinblastine plus verapamil caused measurable accumulation in the G2 + M phase as early as 4 h after the drug combination was added to cultures of CEM/VLB100 cells; this finding correlated with a comparable increase in the number of cells in mitosis and measurable decreases in the total number of cells. Since similar effects on cell cycle distribution, percentage of cells in mitosis, and cell number were seen when CEM/VLB100 cells were treated with toxic concentrations of vinblastine alone, we conclude that the primary toxicity of the vinblastine-verapamil combination stems from the alkaloid. Further, the rapid lytic effect of the drug combination was associated with cellular vacuolization. The vacuoles did not stain for lipids, and increases in their number were evident within 2 to 4 h after drug treatment. We suggest that verapamil enhances Vinca alkaloid cytotoxicity by altering "cryptic" cytotoxic targets, possibly related to these vacuoles, through some as yet undefined membrane effect.

Cell Cycle↗
PubMed1986

Chromosomal translocations play a unique role in influencing prognosis in childhood acute lymphoblastic leukemia.

Certain types of chromosomal abnormalities have been shown to exert strong independent influence on treatment outcome in acute lymphoblastic leukemia (ALL). To identify the changes most closely associated with prognosis, we analyzed the completely banded blast cell karyotypes of 161 children with this disease. One hundred twenty-five cases had one or more chromosomal abnormalities, with 45 showing translocations. The frequency of translocations was highest (58%) among patients with pseudodiploid karyotypes and lowest (0%) in the hyperdiploid group defined by 51 or more chromosomes. During the maximum 6-year follow-up period, 30 of the 45 patients with a translocation failed therapy, compared with only 27 of the 116 who lacked this feature. Life-table estimates of event-free survival indicate that only 14% of the translocation group will be in complete remission at 3 years. The percentages of failures associated with random and nonrandom translocations were virtually identical (68% v 65%). When entered in a Cox proportional hazards model with seven other types of chromosomal abnormalities, and then with 11 clinical and laboratory variables of known prognostic value in ALL, translocation emerged as the strongest single predictor of treatment outcome (P less than 0.0001). The model indicated that translocation increases the risk of treatment failure six times by comparison with the absence of this feature. These findings offer an explanation for the majority of early treatment failures in childhood ALL, including those previously attributed to ploidy classification.

Child↗
PubMed1986

Amplification of genes encoding human myeloid membrane antigens after DNA-mediated gene transfer.

Spontaneous amplification of genes encoding two different human myeloid surface antigens was observed after DNA-mediated gene transfer of cellular DNA from the human myeloid cell line HL-60 into NIH-3T3 mouse fibroblasts. Transformed recipient cells with highly amplified expression of either of two donor membrane polypeptides, gp150 or p67, were isolated with a fluorescence-activated cell sorter (FACS), using monoclonal antibodies specific for human myeloid cells. Immunoprecipitation of enzymatically radioiodinated polypeptides from the surface of transformed NIH-3T3 cells confirmed that expression of these proteins was amplified tenfold to 20-fold in comparison to their expression on human myeloid cell lines. The cellular DNA of cloned secondary and tertiary transformants expressing high levels of gp150 and p67 contained amplified sets of DNA restriction fragments that hybridized with human repetitive DNA sequences. Cytogenetic analysis of subclones overexpressing gp150 revealed extrachromosomal double minutes (DMs), whose presence correlated with the unstable expression of the membrane polypeptide. Human sequences in gp150-positive clones did not localize to chromosomes, consistent with their association with extrachromosomal DMs. By contrast, p67-positive subclones stably expressed the antigen, and in situ hybridization to metaphase spreads demonstrated that amplified human DNA sequences were integrated into a specific marker chromosome. Cytogenetic analysis of the parental NIH-3T3 subclone used in these studies disclosed DMs in a low percentage of metaphases, suggesting that the recipient cells have a propensity for amplifying donor DNA.

Animals↗
PubMed1985

Abnormalities of chromosomes 1 and 11 in Wilms' tumor.

Cytogenetic studies were performed successfully on 14 cases of Wilms' tumor. Six cases had detectable rearrangements of 11p, and 7 cases had structural abnormalities of chromosome #1. Two cases with advanced stage disease showed multiple translocations, resulting in hypodiploidy with a normal DNA complement.

Child↗