PubMed Health⌕ Search

Biomedical subjects

A G Hall

Publications and source records attributed to A G Hall.

At least 19 recordsLinked to original sources
PubMed2006

Expression levels of asparagine synthetase in blasts from children and adults with acute lymphoblastic leukaemia.

L-asparaginase is active in the treatment of acute lymphoblastic leukaemia (ALL) through the depletion of serum asparagine. Here we report that median asparagine synthetase (AS) mRNA levels were higher in acute myeloid leukaemia (AML) than ALL blasts in both children and adults, with intermediate levels in normal peripheral blood mononuclear cells (NPBMC). NPBMC versus child ALL (Tukeys multiple comparison test, P < 0.05); child ALL versus child AML (P < 0.001) and adult ALL versus adult AML (P < 0.01) were all significant and support the hypothesis that selectivity to treatment with l-asparaginase is due, at least in part, to lower AS expression.

Acute Disease↗
PubMed2005

Relation between genetic variants of the ataxia telangiectasia-mutated (ATM) gene, drug resistance, clinical outcome and predisposition to childhood T-lineage acute lymphoblastic leukaemia.

The T-lineage phenotype in children with acute lymphoblastic leukaemia (ALL) is associated with in vitro drug resistance and a higher relapse-risk compared to a precursor B phenotype. Our study was aimed to investigate whether mutations in the ATM gene occur in childhood T-lineage acute lymphoblastic leukaemia (T-ALL) that are linked to drug resistance and clinical outcome. In all, 20 different single nucleotide substitutions were found in 16 exons of ATM in 62/103 (60%) T-ALL children and 51/99 (52%, P = 0.21) controls. Besides the well-known polymorphism D1853N, five other alterations (S707P, F858L, P1054R, L1472W, Y1475C) in the coding part of ATM were found. These five coding alterations seem to occur more frequently in T-ALL (13%) than controls (5%, P = 0.06), but did not associate with altered expression levels of ATM or in vitro resistance to daunorubicin. However, T-ALL patients carrying these five coding alterations presented with a higher white blood cell count at diagnosis (P = 0.05) and show an increased relapse-risk (5-year probability of disease-free survival (pDFS) = 48%) compared to patients with other alterations or wild-type ATM (5-year pDFS = 76%, P = 0.05). The association between five coding ATM alterations in T-ALL, their germline presence, white blood cell count and unfavourable outcome may point to a role for ATM in the development of T-ALL in these children.

Adolescent↗
PubMed2004

The clinical impact of thiopurine methyltransferase polymorphisms on thiopurine treatment.

Acute lymphoblastic leukaemia (ALL) is the most common malignancy of childhood. Although current treatment results in long term survival in over 70% of cases there is evidence that as many as 50% could have been cured using a less complex regimen with a lower incidence of long term side effects. In previous studies it has been found that thiopurines given as part of continuing therapy are key agents in preventing relapse. However, optimal administration during continuing therapy is often not achieved. Variation in the level of thiopurine methyltransferase (TPMT) activity appears to be a major molecular determinant of the extent of thiopurine metabolism. TPMT activity shows a trimodal distribution pattern. A lack of activity is found in approximately one in 300 Caucasians; approximately 11% have intermediate activity and the remaining 89% high activity. Congenital loss of activity is associated with grossly elevated levels of active drug and profound myelosuppression on exposure to thiopurines. This loss of activity has been attributed to single nucleotide polymorphisms (SNPs) within the TPMT gene. The frequency of SNPs is related to ethnicity, with the most common in Caucasians being TPMT*3A which is characterized by a G to A transition at position 460 with a substitution of alanine for tyrosine at amino acid 154 (A154Y) and a transition of A to G at nucleotide 719 resulting in a change of tyrosine to cysteine at position 240 (Y240C). Polymorphisms have also been identified within the 5' flanking promoter region of the TPMT gene due to a variable number of tandem repeats (VNTR*3-*8). An overview of the polymorphisms identified to date, their implication on the metabolism of the thiopurine drugs and therapeutic importance will be discussed.

Alanine↗
PubMed2002

Loss of nuclear expression of the p33(ING1b) inhibitor of growth protein in childhood acute lymphoblastic leukaemia.

BACKGROUND/AIMS: p33(ING1b) is a tumour suppressor protein involved in growth control and apoptosis. Suppression of p33(ING1b) expression is associated with the loss of cellular growth control and immortalisation, whereas its overexpression causes cell cycle arrest. Moreover, normal p33(ING1b) expression is essential for optimal function of p53. Acute lymphoblastic leukaemia (ALL) is the most common malignancy of childhood, accounting for one third of all childhood malignancies. A variety of cytogenetic abnormalities have been described but there is no single abnormality common to all cases. Deregulation of the TP53 pathway is a common genetic abnormality in human malignancies. However, TP53 mutations are uncommon in ALL. It is possible that alternative mechanisms of regulation of the TP53 apoptosis pathway, such as modulation of p33(ING1b) expression, may be important in ALL. The aim of this study was to assess the expression of p33(ING1b) in childhood ALL. METHODS: One hundred and forty five patients with childhood ALL were investigated in this immunohistochemical study of the expression of p33(ING1b). RESULTS: Loss of nuclear expression of p33(ING1b) was seen in 78% of cases. This was associated with increased cytoplasmic expression of the protein. Kaplan Meier survival analysis demonstrated a trend towards a better prognosis for patients with tumours that had lost nuclear p33(ING1b). CONCLUSION: These results suggest that the loss of nuclear p33(ING1b) expression may be an important molecular event in the pathogenesis of childhood ALL.

Adolescent↗
PubMed2001

The use of denaturing high-pressure liquid chromatography for the detection of mutations in thiopurine methyltransferase.

The level of expression of the enzyme thiopurine methyltransferase (TPMT) is an important determinant of the metabolism of drugs used both in the treatment of acute leukaemia (6-mercaptopurine and 6-thioguanine) and as an immunosuppressant in patients with autoimmune diseases or following organ transplantation (azathioprine). Studies of enzyme activity in red blood cells have shown that TPMT expression displays genetic polymorphism with 11% of individuals having intermediate and one in 300 undetectable levels. Patients with biallelic mutations and undetectable enzyme activity suffer life-threatening myelosuppression when treated with conventional doses of these drugs. Patients with intermediate activity have an increased risk of drug-associated toxicity. In the Caucasian populations studied to date, intermediate activity is associated with mutations at two sites of the TPMT gene, G460A and A719G (designated TPMT*3A), in 80% of cases. Detection of these mutations has, to date, been based on the analysis of restriction digests of PCR products. In order to simplify this process we have investigated the ability of denaturing high pressure liquid chromatography (DHPLC) to detect the A719G mutation. DHPLC of PCR products from 15 known heterozygotes (TPMT*3A/TPMT*1) and 18 known homozygotes (TPMT*1/TPMT*1) gave a clear pattern difference between the groups and 100% concordance with the results of restriction digests. These results suggest DHPLC represents a valuable technique for accurate and rapid detection of pharmacologically important mutations in the TPMT gene.

Antineoplastic Agents↗
PubMed2001

Raised blast glutathione levels are associated with an increased risk of relapse in childhood acute lymphocytic leukemia.

A preliminary study has linked raised blast glutathione levels with chemoresistance in acute myeloid and lymphoblastic leukemia in adults and children. In this study, therefore, the relationship between leukemic blast glutathione levels and prognosis in childhood acute lymphoblastic leukemia (ALL) was investigated. A total of 77 childhood ALL samples were analyzed, 62 at initial presentation and 15 at relapse. A 20-fold interindividual variation in glutathione levels at presentation (median, 6.54 nmol/mg protein; range, 1.37 to 27.9) was demonstrated. The median level in T-lineage ALL was 2. 3-fold higher than in B-lineage ALL (Mann-Whitney test, P <.0001). There was a significant correlation between presenting white cell count (WBC) and glutathione level (Spearman rank correlation coefficient, rho = 0.45, P =.001). A high DNA index correlated with low glutathione levels (Mann-Whitney test, P =.013). There was no significant relationship between glutathione levels and in vitro drug sensitivity. Patients with glutathione levels above the median had a significantly greater risk of relapse (log-rank test statistic, 5.55; P =.018), and the overall survival rate was significantly reduced (log-rank test statistic, 4.38; P =.04). Multivariate analysis demonstrated that glutathione concentration was of independent prognostic value when assessed in conjunction with age, gender, WBC, and immunophenotype. The association of elevated blast glutathione levels with an increased risk of relapse suggests that glutathione-depleting agents may be of therapeutic value in patients who present with a high WBC.

Actuarial Analysis↗
PubMed2001

The role of AP-1 in glucocorticoid resistance in leukaemia.

Glucocorticoids are used in the treatment of acute lymphoblastic leukaemia (ALL) and chronic lymphocytic leukaemia (CLL) but many patients develop glucocorticoid resistance on relapse. The ligand-activated glucocorticoid receptor inhibits activity of the AP-1 transcription factor and the purpose of this study was to test the hypothesis that up-regulation or overexpression of AP1-binding activity may be an important mechanism of glucocorticoid resistance in ALL and CLL. In vitro sensitivity of patient blasts to prednisolone was measured using th

Adult↗
PubMed2001

Recent advances in the pharmacogenomics of thiopurine methyltransferase.

The thiopurine drugs (6-mercaptopurine, 6-thioguanine and azathioprine) are commonly used cytotoxic agents and immunosuppressants. One important route for the metabolism of these agents is methylation, mediated by thiopurine methyltransferase (TPMT). It is now well established that inter-individual variation in sensitivity to thiopurines can be due to the presence of common genetic polymorphisms affecting the TPMT gene. More recently variations in the number of tandem repeats in the 5' promoter region have been shown to influence TPMT expression in vitro. In this article, we review recent advances in the understanding of the range of inter-individual variation that may be involved in the open reading frame or promoter region of the TPMT gene. We also review the data which have been published regarding the influence such variations may have on both the clinical efficacy and toxicity of the thiopurine drugs.

Animals↗
PubMed2001

Topoisomerase II alpha and II beta expression in childhood acute lymphoblastic leukaemia: relation to prognostic factors and clinical outcome.

BACKGROUND/AIMS: Many regimens used in the treatment of childhood acute lymphoblastic leukaemia (ALL) include Daunorubicin or Etoposide, which act as topoisomerase poisons. It has been suggested that there may be a relation between topoisomerase expression and response to topoisomerase poisons, based mainly on results from in vitro studies. Therefore, the aim of this study was to investigate this relation in a clinical setting and determine whether topoisomerase II alpha and II beta might be of predictive value in ALL. METHODS: Cellular expression of topoisomerases II alpha and II beta was assessed in 177 cases of ALL by immunohistochemistry using monoclonal antibodies to the two enzymes. The percentages of cell nuclei showing positive staining for topoisomerase II alpha and II beta expression were assessed. RESULTS: Taking the series as a whole, a clear separation of survival curves was seen with the established prognostic markers white blood cell (WBC) count, CD10 status, and sex. However, topoisomerase II alpha and II beta expression showed no relation to survival. No association was found between the topoisomerases and the prognostic markers CD10 and WBC count; however, topoisomerase II alpha expression was found to be related to sex, with expression being lower in girls (p = 0.002). CONCLUSIONS: These results suggest that the response to topoisomerase poisons cannot be predicted by the assessment of topoisomerase II alpha and II beta expression as defined by immunohistochemistry.

Adolescent↗
PubMed2001

Mismatch repair defects as a cause of resistance to cytotoxic drugs.

In this short review, we aim to bring together the most recent evidence implicating mismatch repair pathway defects as a cause of drug resistance to a spectrum of chemotherapeutic agents in a variety of cancers. Experimental and clinical studies are discussed and possible strategies that may be employed to overcome the multidrug resistant phenotype afforded by such defects.

Base Pair Mismatch↗
PubMed2001

Pharmacogenetics of cytotoxic drugs.

The main genetic polymorphisms affecting the metabolism and transport of cytotoxic drugs are discussed in this review. Likely future approaches to pharmacogenetics and emerging technologies, such as tumor classification using microarray analysis, are also considered.

Antineoplastic Agents↗
PubMed2000

A comparison of molecular and enzyme-based assays for the detection of thiopurine methyltransferase mutations.

S-Methylation by thiopurine methyltransferase (TPMT) is an important route of metabolism for the thiopurine drugs. About one in 300 individuals are homozygous for a TPMT mutation associated with very low enzyme activity and severe myelosuppression if treated with standard doses of drug. To validate the use of molecular genetic techniques for the detection of TPMT deficiency, we have determined red blood cell TPMT activity in 240 adult blood donors and 55 normal children. Genotype was determined by restriction fragment length analysis of polymerase chain reaction products in a cohort of 79 of the blood donors and five cases of azathioprine-induced myelosupression, and this confirmed a close relationship between genotype and phenotype. In 17 of the 24 cases in which mutations were found, DNA was also available from remission bone marrow. In one of these cases, DNA from the remission marrow sample indicated the presence of a non-mutated allele that had not been seen in the blast DNA sample obtained at presentation. These results indicate that polymerase chain reaction-based assays give reliable and robust results for the detection of TPMT deficiency, but that caution should be exercised in relying exclusively on DNA obtained from lymphoblasts in childhood leukaemia.

Adolescent↗
PubMed1999

Increased BAX expression is associated with an increased risk of relapse in childhood acute lymphocytic leukemia.

Studies in cell lines have indicated that expression of the BCL-2 family of proteins is an important determinant of chemotherapy-induced apoptosis; however, the level of expression of these proteins in childhood acute lymphoblastic leukemia (ALL) has not been extensively reported. Using quantitative Western blotting we have determined the level of expression of BCL-2, BAX, MCL-1, and BCL-X in lymphoblasts from 47 children with ALL (33 at presentation only, 4 at relapse only, and 10 at both presentation and on relapse). Results were determined as a ratio to actin as an internal control. BCL-2, BAX, and MCL-1 were detected in all samples. BCL-XL was only detected in 6 cases (4 at presentation and 2 at relapse) and BCL-XS in none. No correlation was found between expression and white blood cell count, age at diagnosis, gender, or blast karyotype. BCL-2 levels and the BCL/BAX and MCL-1/BAX ratios were found to be significantly higher in B-lineage as compared with T-lineage disease (P <.003,.02, and.02, respectively). No consistent pattern of change in expression was noted in the 10 cases studied at both presentation and relapse. Kaplan-Meier analysis showed a significant correlation between high BAX expression and an increased probability of relapse (P <.05 by the log rank test), suggesting that chemosensitivity in leukemic blasts may be regulated by factors that override the BCL-2 pathway.

Adolescent↗
PubMed1999

Glutathione and the regulation of cell death.

The association of elevated levels of glutathione and glutathione S-transferases with the development of resistance to alkylating agents was established more than 10 years ago. Although numerous similar reports have appeared since this time work in this area has tended to dwindle as interest has become focused on more fashionable areas of drug resistance research. However, over the past 3 or 4 years there has been a revival of interest in the study of glutathione and glutathione utilising enzymes driven by recent discoveries which have implicated redox balance as an important regulator of cell death and transmembrane drug transport. In this brief review I highlight some of the more rapid areas of advance.

ATP-Binding Cassette Transporters↗
PubMed1999

Evidence for the involvement of the glutathione pathway in drug resistance in AML.

We have studied altered drug detoxification through the glutathione pathway as a possible mechanism of resistance in 38 patients with AML. GST alpha, mu and pi expressions were determined using immunocytochemistry, the median percentages of positive cells being 73% (range 0-98), 55% (range 0-99) and 97% (range 80-100) respectively. MRP expression was measured using MRPm6 MoAb and flow cytometry. Results were expressed as the ratio of fluorescence associated with MRP over that of an isotype matched control (median, 1.32; range 0.95-2.15). Statistical analyses showed a significant increase in GST alpha expression in blast cells showing in vitro resistance to doxorubicin, with a median value of 78% positive cells compared to 41% in the sensitive group (p < 0.02). There was a significant reduction, however, in GST mu expression from a median value of 60% in newly presenting patients to 40% in a group of patients who had received previous cytotoxic therapy (p < 0.02). Interestingly, patients with high GST mu expression appeared to co-express MRP (p < 0.05). In vitro drug modulation studies, comparing the cytotoxic effect of doxorubicin +/- ethacrynic acid at 6.5 microM resulted in only one significant increase in sensitivity (2.6-fold), out of 22 comparisons. These results support the theory that altered detoxification through the glutathione pathway contributes towards drug resistance in AML. Further studies using fresh blast cells are required to elucidate the importance of this mechanism for individual patients.

ATP-Binding Cassette Transporters↗
PubMed1999

Glutathione in childhood acute leukaemias.

In order to test the hypothesis that glutathione (GSH) is an important determinant of treatment response in childhood acute leukaemia, blast cell GSH levels were studied in a cohort of children with acute lymphoblastic (ALL) and acute myeloid (AML) leukaemia. In both ALL and AML, several indicators of poor prognosis are well established but the underlying molecular mechanisms leading to resistant disease are still poorly understood. GSH is an intracellular thiol implicated in the development of cytotoxic drug resistance and appears to be involved in the control of cell proliferation and apoptosis. In this study, total GSH was measured in cryopreserved blasts from 62 childhood ALL and 13 AML patients. In ALL, high GSH levels were associated with a relatively poor prognosis. A positive correlation was demonstrated between the GSH level and presenting white cell count (WCC). GSH levels were significantly higher in T lineage ALL compared with B lineage and in AML blasts compared with ALL. These results are supportive of GSH as prognostic indicator in childhood leukaemia and may suggest one mechanism of treatment failure. They imply that it may be possible to improve chemosensitivity by the use of known modulators of GSH synthesis.

Adolescent↗