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Biomedical subjects

D C Linch

Publications and source records attributed to D C Linch.

At least 109 records · Page 6Linked to original sources
PubMed1996

The regulation of neutrophil phospholipase A2 by granulocyte-macrophage colony-stimulating factor and its role in priming superoxide production.

Experiments were performed to investigate the relative role of phospholipase A2 (PLA2) in the activation and cytokine-mediated priming of neutrophil superoxide production. PLA2 activity was measured with a radiometric assay which discriminates between PLA2 and the downstream enzyme, 5-lipoxygenase. In cells that had not been primed by prior incubation with granulocyte-macrophage colony stimulating factor (GM-CSF), PLA2 and NADPH oxidase were differentially stimulated by the chemotactic peptide N-formyl-met-leu-phe (FMLP), calcium ionophore, or phorbol ester. In addition, inhibition of PLA2 by mepacrine (0-100 micromol/l) did not concomitantly inhibit FMLP-stimulated superoxide production. These findings suggest that the activity of PLA2 and NADPH oxidase may be uncoupled in the unprimed cell. In cells preincubated with GM-CSF, time- and dose-dependent priming of FMLP-stimulated PLA2 responses were observed and inhibition of PLA2 by mepacrine was accompanied by the inhibition of FMLP-stimulated superoxide production down to the level of unprimed cells. The effect of mepacrine was not due to inhibition of FMLP receptor expression. These data suggest that a mepacrine-sensitive PLA2 may have a role in the GM-CSF mediated priming of superoxide production. Using ionophore-stimulated PLA2 activity as a model, we showed that Bordatella pertussis toxin did not inhibit GM-CSF mediated priming, demonstrating that a pertussis-sensitive GTP-binding protein does not mediate signal transduction from the GM-CSF receptor to PLA2. The tyrosin kinase inhibitor, genestein, selectively inhibited GM-CSF primed but not unprimed PLA2 activity, demonstrating that GM-CSF-mediated priming requires tyrosine kinase activity.

Arachidonic Acid↗
PubMed1996

Demonstration of developing myelodysplasia/acute myeloid leukaemia in haematologically normal patients after high-dose chemotherapy and autologous bone marrow transplantation using X-chromosome inactivation patterns.

Autologous bone marrow or peripheral blood stem cell transplantation may carry an increased risk of secondary myelodysplasia (MDS) and acute myeloid leukaemia (AML), which are already recognized as complications of conventional treatment for lymphoid malignancies. In order to ascertain whether it is possible to detect the evolution of such a clone at an early stage in its development we have studied X-chromosome inactivation patterns (XCIPs) in three informative females who developed abnormal myelopoiesis after high-dose chemotherapy and ABMT. In one patient transplanted for relapsed Hodgkin's disease a leukaemic clone comprising approximately 50% of the patient's myeloid cells was detectable by comparison of peripheral blood granulocyte and T-cell XCIPs when the full blood count and morphology were normal. She presented with AML 7 months later. In two patients transplanted for AML, XCIP analysis was complicated by constitutively skewed Lyonization patterns, nevertheless a progressive alteration could be demonstrated by serial analyses. In one patient a difference was detectable 28 months before presentation with MDS. In the other patient, despite evident mild pancytopenia and alterations in her XCIPs over the past 4 years, she has developed no definitive myelodysplastic features and oligoclonality due to stem cell failure cannot be excluded. These studies show that XCIPs can be used to predict development of MDS/AML in some patients, but the technique is limited by technical variability and frequent constitutional skewing in the haemopoietic system.

Acute Disease↗
PubMed1996

Analysis of granulocyte colony stimulating factor receptor isoforms, polymorphisms and mutations in normal haemopoietic cells and acute myeloid leukaemia blasts.

Deletion mutants of the intracytoplasmic domain of the granulocyte colony stimulating factor receptor (G-CSFR) have shown that it contains a membrane-proximal region which must be conserved to allow the receptor to transduce a mitotic signal, and a C-terminal region necessary for transduction of cell differentiation. Changes in the intracytoplasmic domain may result in the uncoupling of these two processes, as in acute leukaemia, and such alterations could occur either as isoforms or mutations. We have studied the transmembrane domain and intracytoplasmic tail of the G-CSFR in RNA from blood or bone marrow of 11 haematologically normal controls and 40 patients with acute myeloid leukaemia (AML). Two novel transcripts of the receptor were identified, both were minor components and are unlikely to be of major physiological significance. We could find no evidence for altered levels of expression of these transcripts in the AML patients. In addition, only one point mutation was detected in the 40 patients screened by RT-PCR-SSCP, a C-->A substitution at nucleotide 2088 which changes a threonine to asparagine in the transmembrane domain and is probably a polymorphism. These results suggest that abnormalities in the G-CSFR are uncommon in AML.

Alternative Splicing↗
PubMed1996

The retinoblastoma gene (rb1) in acute myeloid leukaemia: analysis of gene rearrangements, protein expression and comparison of disease outcome.

The occurrence of retinoblastoma gene abnormalities in a large subset of various malignancies suggests an important role for this tumour suppressor gene in carcinogenesis, but this varies considerably from one tumour type to another and results in patients with acute myeloid leukaemia (AML) have been controversial. We analysed 106 AML patients and 18 normal controls for RB1 gene rearrangements and 86 AML patients for RB protein (pRB) expression. Southern blot analysis detected no gross gene rearrangements, but several restriction enzyme polymorphisms were observed. By Western blot analysis, 20 patients (23%) had no detectable pRB protein and seven (8%) had truncated pRB bands. Discordance between the DNA and protein data suggests that there may be minor deletions and point mutations in the RB1 gene or abnormalities in the proteins regulating the expression of pRB. No significant differences in the frequency of attainment of complete remission or length of survival were observed between patients with normal and abnormal pRB.

Acute Disease↗
PubMed1996

Amplification of mitochondrial DNA in acute myeloid leukaemia.

There is a long-standing interest in the possible role of mitochondria in malignancy. We sought to discover whether amplification of mitochondrial DNA (mtDNA) occurred in leukaemia, and found it was often remarkably amplified in the blast cells of acute myeloid leukaemia (AML). We used gene dosage experiments to quantify the amount of mtDNA relative to nuclear DNA. DNA extracted from peripheral blood leucocytes or bone marrow of healthy individuals or patients was simultaneously hybridized with a probe for the mitochondrial genome and a control probe for the renin gene on human chromosome 1. Comparative densitometric ratios of approximately 1 were obtained between the two signals in 20 normal control peripheral blood samples. In contrast, comparative ratios in the range of 2-50 were observed in 25 AML samples and 13 of these showed 8-fold or greater amplification of mtDNA relative to normal peripheral blood controls. An additional four cases of AML were investigated at both presentation and remission and showed 3-10-fold amplification of mtDNA at presentation, but no amplification when in clinical remission. 18 cases of chronic granulocytic leukaemia (CGL) were also studied in chronic phase and showed mtDNA dosage levels equivalent to normal peripheral blood controls. However, 8/9 CGL patients showed mtDNA amplification during transformation from chronic phase. We conclude that amplification of mtDNA is an invariable feature of acute myeloid leukaemia and that it may be a useful marker for detecting transformation of CGL.

Acute Disease↗
PubMed1996

Peripheral blood progenitor cell transplantation: where do we stand? Chairman's Summary of the European School of Oncology Task Force meeting Peripheral Blood progenitor cell's held September 29-30, 1995.

Whether or not peripheral stem cells have an unlimited capacity for self renewal is debated. However, everyday haematopoietic requirements are met by progenitors; and it seems that few "real' stem cells are needed. Although we may not yet have identified these "true' stem cells, for practical purposes the long term culture-initiating cells (LTC-ICs) are a close approximation. To date, experience in peripheral blood progenitor cell (PBPC) transplantation is largely confined to non-ablative regimens. It is therefore difficult to determine the number of PBPCs needed to effect long-term reconstitution. The number of tumour cells present among mobilised PBPCs can be reduced using the CD34 affinity column and by positive purging methods. The ex vivo expansion of CD34 cells also has the effect of diluting tumour cell concentration. In clinical use, PBPC transplantation has a proven role in support of high dose chemotherapy in certain haematological and oncological malignancies but the concept of dose intensification is not universally accepted. With the exception of leukaemia, lymphoma, myeloma or relapsed testicular cancer and possibly some subgroups of breast cancer; high dose chemotherapy does not demonstrate a survival benefit. For patients with CML, autografting with Ph- cells appears to become a useful alternative to allogeneic BMT. Allogeneic PBPC transplantation may have potential, though work is preliminary. Cord blood transplantation between matched siblings is viable, but it is not yet clear whether this source will increase the donor pool for adults needing allogeneic transplantation. For gene therapy using haematopoietic cells to be effective, a greatly increased rate of transduction will be needed. Meeting in Paris in September 1995, a European School of Oncology Task Force considered a number of important questions relating to peripheral blood progenitor cell (PBPC) physiology and transplantation. This review is a brief account of their conclusions.

Antineoplastic Agents↗
PubMed1996

The beta subunit common to the GM-CSF, IL-3 and IL-5 receptors is highly polymorphic but pathogenic point mutations in patients with acute myeloid leukaemia (AML) are rare.

The intracytoplasmic tail of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) beta c chain is essential for the activation of ligand-mediated signal transduction pathways in myeloid cells. Alterations in this region could deregulate normal signalling processes. We have therefore used RT-PCR-SSCP analysis of the receptor tail to look for point mutations in RNA from 35 patients with acute myeloid leukaemia (AML) and 10 haematologically normal controls. Patterns differing from those of the haemopoietic cell line TF-1 were detected in 25/35 (71%) AML patients and 8/10 (80%) normal controls. A total of six base substitutions were identified by sequencing. Three were conservative for the amino acid involved, three led to amino acid differences, valine652-->methionine, glycine647-->valine and proline603-->threonine. One alteration was found only in a normal control, the other five were all found in both AML patients and normal controls suggesting that they were DNA polymorphisms. Two substitutions were particularly common with allele frequencies of 0.23 (G1972-->A, unchanged proline648) and 0.13 (C1306-->T, unchanged serine426). These results indicate that the GM-CSFR beta c chain is highly polymorphic but point mutations of the intracytoplasmic tail do not appear to contribute frequently to the pathogenesis of AML.

Base Sequence↗
PubMed1996

Variable expression of p16 protein in patients with acute myeloid leukemia without gross rearrangements at the DNA level.

The p16 protein is an inhibitor of cyclin-dependent kinases (cdk) 4 and 6. Both cdk4 and cdk6 phosphorylate the retinoblastoma protein (pRb) and are thought to be required for cell proliferation. Mutations and homozygous deletions in the p16 gene have been found in a number of cell lines but the incidence of abnormalities in primary tumours is controversial. We have studied the p16 gene in 76 cases of acute myeloid leukemia (AML) and 18 hematologically normal controls by quantitative Southern blotting. No deletions or rearrangements were detected. Twenty-five cases also showed no abnormal band patterns by RT-PCR-SSCP analysis of the coding sequence. We analyzed 60 AML samples for p16 protein expression by Western blot analysis. A reduced level of p16 was observed in six cases, however, none of them showed methylation of the 5'-CpG island. Over-expression of p16 protein was detected in six cases. Studies in cell lines have suggested a feedback loop between p16 and pRb with a futile overproduction of p16 protein in cells containing abnormal pRb. In accordance with these findings, four of the AML cases with high levels of p16 had abnormal pRb (two alteration in band size, two absent). From our data we suggest that gross abnormalities in the p16 gene are rare in AML, but that p16 levels are variable and high levels are associated with pRb abnormalities in a subset of cases.

Acute Disease↗
PubMed1996

Expression of two alternatively spliced forms of the 5' untranslated region of the GM-CSF receptor alpha chain mRNA.

The granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) is composed of at least two chains (alpha and beta). The alpha chain binds GM-CSF specifically with low affinity, and the binding is converted to high affinity when the alpha chain is associated with the beta chain. To date, there are at least six isoforms described for the GM-CSFR alpha, all involving alternative splicing at the 3' end, which alters the coding region and hence the protein produced. To detect variants at the 5' end of the GM-CSFR alpha mRNA, RNAse protection and reverse transcriptase polymerase chain reaction (RT-PCR) assays were performed using a probe spanning nucleotides 102-392 and pairs of primers covering exons 1-4. in addition to the expected full-length transcript, two mRNAs were detected, one containing a deletion of 24 nucleotides by alternative splicing at the 3' end of exon 2 (exon 2b-deleted isoform) and another in which exon 2 was completely deleted (exon 2-deleted isoform). Together, the isoforms were more highly expressed form). Together, the isoforms were more highly expressed than the full-length sequence (TF-1 cells: full-length 36 +/- 2.8% vs. exon 2-deleted isoforms 64 +/- 5.5%). These isoforms were detected in primary hematopoietic cells, blasts from patients with acute myeloid leukemia (AML), and malignant cell lines and the relative mRNA expression for the isoforms, was always similar to that of TF-1 cells. As sequences in the 5'untranslated region can be involved in the modulation of translational efficiency, translation of constructs constructs corresponding to these exon 2 deleted isoforms was assessed using an in vitro reticulocyte lysate system. Deletion of exon 2 resulted in significantly lower in vitro translation of the receptor protein relative to the full-length sequence (53, 56, and 76% in three separate batches of reticulocytes), while deletion of exon 2b resulted in higher translation of the sequence (164, 128, and 305%; p = 0.01). These data suggest a mechanism by which expression of the GM-CSFR alpha protein may be regulated by alternatively spliced transcripts with different translational efficiencies.

Acute Disease↗
PubMed1996

Quantification of X-chromosome inactivation patterns in haematological samples using the DNA PCR-based HUMARA assay.

Quantification of X-chromosome inactivation patterns (XCIPs) using PCR amplification of the human androgen receptor (HUMARA) locus is potentially valuable in a range of haematological disorders. Of 236 females screened, 203 (86%) were heterozygous. For quantitative XCIPs it was necessary to limit the number of PCR cycles to 20 to reduce preferential amplification of shorter alleles. The optimized PCR method was compared with Southern blotting results using either PGK, HPRT or M27beta in 51 haematologically normal females and blast cells from 27 patients with acute myeloid leukaemia (AML). Reproducible XCIP results were obtained in all 78 samples using digestion with Hpa II prior to amplification (median difference in duplicate values 3%, range 0-17%) and they correlated well with Southern blotting results, r=0.966. Greater variability was observed in the results using Hha I digestion (median difference 4%, range 0-48%). There were marked inconsistencies in repeated analyses of three AML samples and although the HUMARA-Hha I results correlated well overall with Southern blotting in the remaining 75 samples (r=0.922), in nine samples there were still discrepancies with > or = 20% difference between the two values. These results suggest that PCR analysis of the HUMARA locus in Hpa II-digested DNA is suitable for the quantification of XCIPs in haematological samples but results with Hha I should be treated with caution.

Alleles↗
PubMed1996

Peripheral blood stem cell support does not accelerate haemopoietic recovery from miniBEAM chemotherapy.

Intermediate-dose salvage therapy is frequently given for relapsed and resistant lymphomas and is usually intensely myelosuppressive. In an attempt to reduce the haematological toxicity of miniBEAM, one of the commonly used salvage regimens, peripheral blood stem cell (PBSC) support was given to 21 consecutive patients who received miniBEAM chemotherapy. The outcome was compared with a non-randomised control group of consecutive patients who were similar to the supported group apart from the fact that it was not possible to collect PBSC before miniBEAM therapy. Apart from a small, marginally significant difference between the supported and unsupported groups in the number of days for which intravenous antibiotics were required, there were no other differences between the two groups in supportive care required and times to haematological recovery. In conclusion, PBSC support does not accelerate haematological recovery from miniBEAM therapy.

Adolescent↗
PubMed1995

Accessory cells do not contribute to G-CSF or IL-6 production nor to rapid haematological recovery following peripheral blood stem cell transplantation.

Haemopoietic recovery is more rapid after peripheral blood stem cell (PBSC) transplantation than after autologous bone marrow transplantation, and the aim of this study was to assess the role of the large number of lymphocytes and monocytes (accessory cells) in a PBSC leukapheresis product in this rapid regeneration. Haematological recovery was therefore assessed in 10 PBSC recipients with lymphoma or myeloma in whom monocytes and T cells were depleted by a median of 2.3 and 3.3 logs by CD34+ cell selection using the CEPRATE SC stem cell concentration system and compared with recovery in 59 recipients who received whole PBSC. After allowing for the number of progenitor cells reinfused, there was no significant delay in engraftment induced by accessory cell depletion. Plasma levels of granulocyte-colony stimulating factor (G-CSF), granulocyte/monocyte-colony stimulating factor (GM-CSF), interleukin-6 (IL-6), stem cell factor (SCF) and macrophage-inhibition factor-alpha (MIP-1-alpha) during the transplant procedure were similar whether or not accessory cells were given. The G-CSF and IL-6 levels rose between days 5 and 14 post transplantation to approximately 1 ng/ml and 50 pg/ml respectively. This study indicates that accessory cells reinfused with PBSC collections are not responsible for the subsequent cytokine profile or rapid haematological recovery.

Adolescent↗
PubMed1995

BEAM chemotherapy and autologous bone marrow transplantation for patients with relapsed or refractory non-Hodgkin's lymphoma.

PURPOSE: To evaluate the outcome of patients with relapsed or resistant non-Hodgkin's lymphoma (NHL) undergoing high-dose chemotherapy and autologous bone marrow transplantation (ABMT) and to determine the main prognostic factors. PATIENTS AND METHODS: One hundred seven patients with relapsed or resistant intermediate-/high-grade NHL underwent high-dose carmustine, etoposide, cytarabine, and melphalan (BEAM) chemotherapy and ABMT at University College Hospitals between September 1981 and February 1993. The minimum follow-up duration of all patients is 6 months. RESULTS: At 3 months, the overall response rate to BEAM and ABMT was 73% (41% complete response and 32% partial response). The 5-year actuarial overall survival and progression-free survival rates were 41% and 35%, respectively. The early procedure-related mortality rate was 7% (eight of 107 patients). On multivariate analysis, the main prognostic factor was disease status at the time of ABMT. Patients with chemosensitive disease had an actuarial 5-year survival rate of 49% at 5 years compared with 13% for those with chemoresistant disease (P < .001). For patients considered to have chemosensitive disease at the time of transplantation, there is a significant difference in the actuarial progression-free survival rates for those who received high-dose therapy after attaining a partial response to first-line therapy (69% at 5 years) as compared with those with sensitive but relapsed disease (32% at 5 years) (P = .003). CONCLUSION: Patients with chemosensitive disease benefit most from high-dose chemotherapy, and those who receive such therapy early after achieving a partial response to first-line therapy have a high rate of cure.

Adolescent↗
PubMed1995

Dose intensification of etoposide in the BEAM ABMT protocol for malignant lymphoma.

We have previously demonstrated a dose response relationship in Hodgkin's disease for the combination of BCNU, VP16, Ara C and Melphalan, with the superior efficacy of the BEAM regimen requiring haemopoietic support, compared with miniBEAM. To further exploit this, we have attempted to escalate the VP16 dose in BEAM. The standard etoposide dose is 200 mg/m2 IV for four days. Thirty seven patients with refractory lymphoma received 400 mg/m2/day of etoposide, and 13 patients 600 mg/m2/day, in addition to BCNU, cytarabine, and melphalan. Toxicity and outcome parameters were compared in the preceding 40 patients, who received 200 mg/m2/day etoposide. The toxic mortality with 400 mg/m2/day of etoposide (3%) was identical to that for the standard BEAM regimen (5%). Two procedure related deaths occurred in the highest VP16 dose group (15%). The morbidity of the lower etoposide dose regimens was comparable, but 600 mg/m2/day induced significantly greater gastrointestinal toxicity. Twelve of the 13 patients receiving this dose suffered grade II-IV mucositis, with stomatitis, dysphagia and prolonged diarrhoea; 5 haemodynamically significant gastrointestinal haemorrhage, and 1 fatal toxic colitis. Granulocyte colony stimulating factor did not influence the nonhaematological toxicity. The three month response rates were similar (91%) in all dose cohorts. The maximum tolerable etoposide dose within the BEAM regimen is thus 400 mg/m2 for four days.

Adolescent↗
PubMed1995

Delayed neutrophil recovery after BEAM chemotherapy and autologous bone marrow transplantation for lymphoma is not associated with increased mortality from infection.

Administration of high-dose cytotoxic therapy with autologous bone marrow transplantation (BMT) results in prolonged cytopenia and significant morbidity and mortality. Several groups have reported that the administration of recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) to patients with delayed haematological recovery following autologous BMT may accelerate neutrophil recovery and decrease mortality. We have determined the prevalence and natural history of delayed neutrophil recovery following BEAM chemotherapy and autologous BMT for malignant lymphoma in 261 patients treated at a single institution without the use of haemopoietic growth factors. Forty of 261 (15%) patients took > 28 days to reach an absolute neutrophil count (ANC) > 0.5 x 10(9)/L; 29 of these 40 (73%) with delayed engraftment reached an ANC > 0.5 x 10(9)/L by day +42. Five patients with delayed engraftment died before day +100, two of progressive lymphoma, one from unirradiated blood product-related GVHD and two of interstitial pneumonitis (IP). The patients with IP had negative culture and bronchoscopic examinations and onset of assisted ventilation was day +15 and +18, respectively. These results show a high rate of relatively rapid spontaneous recovery in individuals with delayed neutrophil recovery after BEAM plus autologous BMT with a low incidence of death from infection.

Adolescent↗