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Biomedical subjects

B S Mitchell

Publications and source records attributed to B S Mitchell.

At least 19 recordsLinked to original sources
PubMed2005

Phase I study of 506U78 administered on a consecutive 5-day schedule in children and adults with refractory hematologic malignancies.

PURPOSE: A phase I study was conducted to determine the maximum-tolerated dose (MTD), toxicity profile, and pharmacokinetics of a novel purine nucleoside, nelarabine, a soluble prodrug of 9-beta-D-arabinosylguanine (araG; Nelarabine), in pediatric and adult patients with refractory hematologic malignancies. PATIENTS AND METHODS: Between April 1994 and April 1997, 93 patients with refractory hematologic malignancies were treated with one to 16 cycles of study drug. Nelarabine was administered daily, as a 1-hour intravenous infusion for 5 consecutive days, every 21 to 28 days. First-cycle pharmacokinetic data, including plasma nelarabine and araG levels, were obtained on all patients treated. Intracellular phosphorylation of araG was studied in samples of leukemic blasts from selected patients. RESULTS: The MTDs were defined at 60 mg/kg/dose and 40 mg/kg/dose daily x 5 days in children and adults, respectively. Dose-limiting toxicity (DLT) was neurologic in both children and adults. Myelosuppression and other significant organ toxicities did not occur. Pharmacokinetic parameters were similar in children and adults. Accumulation of araGTP in leukemic blasts was correlated with cytotoxic activity. The overall response rate was 31%. Major responses were seen in patients with T-cell malignancies, with 54% of patients with T-lineage acute lymphoblastic leukemia achieving a complete or partial response after one to two courses of drug. CONCLUSION: Nelarabine is a novel nucleoside with significant cytotoxic activity against malignant T cells. DLT is neurologic. Phase II and III trials in patients with T-cell malignancies are encouraged.

Adolescent↗
PubMed2004

Student attitudes towards anatomy teaching and learning in a multiprofessional context.

CONTEXT: We carried out a survey of attitudes to learning anatomy amongst students from a range of health care disciplines in a multiprofessional context. SETTING: A joint course called the Common Foundation Programme (CFP) presented by a hospital medical school and a joint university faculty of health and social care sciences in the UK in the first term of the students' courses. PARTICIPANTS: Students following degree courses in biomedical science, medicine, nursing, physiotherapy, diagnostic radiography and therapeutic radiography. OBJECTIVES: To assess student attitudes to cadaveric work, learning anatomy and multiprofessional learning, and to compare student performance between degree courses in an anatomy assessment. DESIGN: A questionnaire was designed that requested demographic information and the students' attitudes to cadaveric work, anatomy learning and multiprofessional learning on a Likert scale. All students sat the same anatomy assessment at the end of the first term. RESULTS: The biomedical science and medical students were the most apprehensive about entering the dissecting room. The biomedical science students enjoyed working in a multidisciplinary group the most. Assessment results varied widely and the physiotherapy and medical students scored more highly than students in other disciplines, although all students had participated in the same course. CONCLUSIONS: It was possible to teach anatomy in the context of the shared learning experience of the CFP, although performance varied widely. Reasons for the differences are discussed and suggestions for the design of multiprofessional courses involving anatomy are made.

Adolescent↗
PubMed2002

Alemtuzumab in previously treated chronic lymphocytic leukemia patients who also had received fludarabine.

PURPOSE: This phase II pilot study determined the efficacy and safety of alemtuzumab (Campath-1H; Burroughs Wellcome, United Kingdom) in patients with chronic lymphocytic leukemia (CLL), all of whom had previously received fludarabine and other chemotherapy regimens. PATIENTS AND METHODS: Twenty-four patients were treated with intravenous alemtuzumab at six centers in the United States. The target dose of 30 mg over 2 hours, three times weekly, was administered for up to 16 weeks. Responses were evaluated by an independent panel of experts using 1996 National Cancer Institute-sponsored Working Group criteria. Safety assessments included analysis of lymphocyte subpopulations. Antimicrobial prophylaxis was not mandatory. RESULTS: Eight patients (33%) achieved a major response (all partial remissions), with a median time to response of 3.9 months (range, 1.6 to 5.3 months). The median duration of response was 15.4 months (range, 4.6 to >or= 38.0 months), the median time to disease progression was 19.6 months (range, 7.7 to >or= 42.0 months), and the median survival time was 35.8 months (range, 8.8 to >or= 47.1 months). Acute infusion-related events, mainly grades 1 and 2, were most common and most severe in the first week. Ten patients (eight nonresponders and two responders) experienced major infections on-study. Pneumocystis carinii pneumonia was reported in two patients on-study; neither had received prophylaxis. Median CD4+ and CD8+ counts decreased and then began to increase by the end of the study, with further recovery by 1-month follow-up. One of 53 samples obtained from 10 patients had a low titer of alemtuzumab antibodies. CONCLUSION: Alemtuzumab has significant activity in poor-prognosis, fludarabine-treated CLL patients. However, because of a relatively high incidence of opportunistic infections accompanying profound lymphopenia, future protocols should include mandatory prophylaxis.

Adolescent↗
PubMed2002

Anatomic relation between the nuchal ligament (ligamentum nuchae) and the spinal dura mater in the craniocervical region.

There are inconsistencies between the descriptions of the physical connections between the spinal cervical dura and the surrounding tissues. This study was undertaken to clarify the relationship between the spinal dura, the nuchal ligament and the suboccipital muscles. Dissections were performed on embalmed cadavers: in nine the relevant structures were removed en bloc, whereas in one a sagittal section was prepared. In all specimens it was possible to demonstrate continuity in the midline between the nuchal ligament and the posterior spinal dura at the atlanto-occipital and atlanto-axial intervals. No such attachments were found caudal to the arch of the axis. In addition, there was a connective tissue bridge between the deep aspect of the rectus capitis posterior minor muscle to the transverse fibers of the posterior atlanto-occipital membrane that extended laterally to blend with the perivascular tissue of the vertebral arteries. The present study is, we believe, the first to describe continuity between the nuchal ligament and the dura at the atlanto-occipital interspace, and confirms previous descriptions of similar connections at the atlanto-axial level. Knowledge of the exact attachments of the dura may contribute to understanding the biomechanics of the cervical spine and of the possible etiology of some types of cervicogenic headaches.

Aged↗
PubMed2002

Trends in radiological anatomy teaching in the U.K. and Ireland.

AIM: To determine the prevalence of radiological anatomy teaching in modern medical curricula. MATERIALS AND METHODS: The present paper details a survey carried out amongst 21 medical schools in the U.K. and Ireland to determine the variability of the inclusion of radiological anatomy in their different curricula. RESULTS: In all the institutions surveyed teaching of anatomy as revealed by radiological techniques was delivered by anatomy departments. There was considerable variation, however, in the way in which it was delivered, by whom and in the range of radiological material available. Most anatomy departments had links with radiology departments, though the precise arrangements of these also varied. CONCLUSION: This study highlights the need for standardization between anatomy departments with regard to the content and level of radiological anatomy taught to ensure that an appropriate basis for clinical undergraduate training is provided.

Anatomy↗
PubMed2001

Innovative approaches to comprehensive cardiovascular disease risk reduction in clinical and community-based settings.

We have developed, tested, and successfully implemented an affordable, evidence-based, comprehensive cardiovascular disease risk-reduction program for use in primary and secondary prevention settings. The program is administered at hospitals, physician practices, cardiac rehabilitation programs, work sites, shopping malls, and health clubs. The program is also delivered from a call center using the telephone and the Internet. Program staff are guided by a computerized participant management and tracking system. Lifestyle management interventions are based on several behavior change models, primarily social learning theory, the stages of change model, and single concept learning theory. Typically, the program is administered entirely by non-physician healthcare professionals whose services are integrated with the care provided by the participants' physicians. Outcome data have documented the clinical effectiveness of this innovative approach.

Adaptation, Psychological↗
PubMed2001

Nutritional support of the pediatric trauma patient: a practical approach.

It is mandatory to evaluate and develop a plan for nutritional support for all injured children who are hospitalized. Although most childre" will rapidly resume normal oral intake, more severely injured children should be started on parenteral or enteral nutrition as soon as possible after admission. The mode of delivery and composition of nutritional support differ depending on the clinical setting and can change during the recovery period. Development of an initial plan and modification of the plan depending on the child's response will most effectively meet the metabolic demands after injury.

Child↗
PubMed2001

Tumor uptake and elimination of 2',2'-difluoro-2'-deoxycytidine (gemcitabine) after deoxycytidine kinase gene transfer: correlation with in vivo tumor response.

PURPOSE: We hypothesized that tumor uptake and elimination of 2',2'-difluoro-2'-deoxycytidine/2',2'-difluoro-2'-deoxycytidine 5'-triphosphate (dFdCyd/dFdCTP) would be altered after dCK gene transfer and that this change would result in an enhanced cytotoxic effect. To test this hypothesis, we examined dFdCyd/dFdCTP uptake and clearance in HT-29 human colon carcinoma xenografts in nude mice by high-performance liquid chromatography (HPLC) and fluorine-19 magnetic resonance spectroscopy (F-19 MRS). EXPERIMENTAL DESIGN: HT-29 tumors were grown from cells infected with either the retroviral vector alone (LNPO-LacZ) or vector containing the dCK gene (LNPO-dCK). HPLC and F-19 MRS analyses were performed after a single 160 mg/kg i.p. injection of dFdCyd. Tumor response was determined in animals receiving a similar dosing schedule of dFdCyd. RESULTS: HPLC experiments revealed an increased tumor accumulation of dFdCTP in xenografts overexpressing dCK compared with wild-type controls (P < or = 0.05). dFdCTP in the dCK-infected tumors was easily identified at 24 h postinjection. Conversely, no dFdCTP could be detected in the control xenografts 14 h postinjection. Subsequent F-19 MRS experiments confirmed an altered uptake, revealing a 2.5-fold greater accumulation of dFdCyd/dFdCTP in the dCK xenografts. Whereas a modest tumor growth delay was observed in the wild-type tumors receiving dFdCyd, dCK xenografts demonstrated a marked tumor growth delay following treatment (P < or = 0.05). CONCLUSIONS: These data support the hypothesis that increased expression of dCK cDNA in HT-29 xenografts results in an enhanced dFdCTP accumulation and prolonged elimination kinetics, and ultimately a potentiated in vivo tumor response to dFdCyd. Related to these effects, changes in the overall tumor metabolism of dFdCyd/dFdCTP was detectable by noninvasive F-19 MRS. These data are relevant to future preclinical and clinical studies evaluating dCK gene transfer and dFdCyd therapy.

Animals↗
PubMed2000

Human cytosolic 5'-nucleotidase I: characterization and role in nucleoside analog resistance.

Nucleoside analogs are important in the treatment of hematologic malignancies, solid tumors, and viral infections. Their metabolism to the triphosphate form is central to their chemotherapeutic efficacy. Although the nucleoside kinases responsible for the phosphorylation of these compounds have been well described, the nucleotidases that may mediate drug resistance through dephosphorylation remain obscure. We have cloned and characterized a novel human cytosolic 5'-nucleotidase (cN-I) that potentially may have an important role in nucleoside analog metabolism. It is expressed at a high level in skeletal and heart muscle, at an intermediate level in pancreas and brain, and at a low level in kidney, testis, and uterus. The recombinant cN-I showed high affinity toward dCMP and lower affinity toward AMP and IMP. ADP was necessary for maximal catalytic activity. Expression of cN-I in Jurkat and HEK 293 cells conferred resistance to 2-chloro-2'-deoxyadenosine, with a 49-fold increase in the IC(50) in HEK 293 and a greater than 400-fold increase in the IC(50) in Jurkat cells. Expression of cN-I also conferred a 22-fold increase in the IC(50) to 2',3'-difluorodeoxycytidine in HEK 293 cells and an 82-fold increase in the IC(50) to 2',3'-dideoxycytidine in Jurkat cells. These data indicate that cN-I may play an important role in the regulation of physiological pyrimidine nucleotide pools and may also alter the therapeutic efficacy of certain nucleoside analogs.

5'-Nucleotidase↗
PubMed2000

A modified diffuse reflectance infrared Fourier transform spectroscopy cell for depth profiling of ceramic fibers.

A modified diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS) accessory was used to analyze the surface properties of alumino-silicate fibers. The modifications are simple and involve a different way of performing depth-profiling from traditional DRIFTS by removing approximately 2 mm of salt from a full cup prior to placing the sample in for depth profiling. This method proved successful in elucidating the effects of quenching alumino-silicate fibers in mineral oil versus quenching in an air stream.

Aluminum Silicates↗
PubMed2000

Inhibition of T lymphocyte activation in mice heterozygous for loss of the IMPDH II gene.

Inosine 5'-monophosphate dehydrogenase (IMPDH) is the rate-limiting enzyme in the de novo synthesis of guanine nucleotides, which are also synthesized from guanine by a salvage reaction catalyzed by the X chromosome-linked enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Since inhibitors of IMPDH are in clinical use as immunosuppressive agents, we have examined the consequences of knocking out the IMPDH type II enzyme by gene targeting in a mouse model. Loss of both alleles of the gene encoding this enzyme results in very early embryonic lethality despite the presence of IMPDH type I and HPRT activities. Lymphocytes from IMPDH II(+/-) heterozygous mice are normal with respect to subpopulation distribution and respond normally to a variety of mitogenic stimuli. However, mice with an IMPDH II(+/-), HPRT(-/o) genotype demonstrate significantly decreased lymphocyte responsiveness to stimulation with anti-CD3 and anti-CD28 antibodies and show a 30% mean reduction in GTP levels in lymphocytes activated by these antibodies. Furthermore, the cytolytic activity of their T cells against allogeneic target cells is significantly impaired. These results demonstrate that a moderate decrease in the ability of murine lymphocytes to synthesize guanine nucleotides during stimulation results in significant impairment in T-cell activation and function.

Animals↗
PubMed1999

Association of terminal deoxynucleotidyl transferase with Ku.

Terminal deoxynucleotidyl transferase (TdT) catalyzes the addition of nucleotides at the junctions of rearranging Ig and T cell receptor gene segments, thereby generating antigen receptor diversity. Ku is a heterodimeric protein composed of 70- and 86-kDa subunits that binds DNA ends and is required for V(D)J recombination and DNA double-strand break (DSB) repair. We provide evidence for a direct interaction between TdT and Ku proteins. Studies with a baculovirus expression system show that TdT can interact specifically with each of the Ku subunits and with the heterodimer. The interaction between Ku and TdT is also observed in pre-T cells with endogenously expressed proteins. The protein-protein interaction is DNA independent and occurs at physiological salt concentrations. Deletion mutagenesis experiments reveal that the N-terminal region of TdT (131 amino acids) is essential for interaction with the Ku heterodimer. This region, although not important for TdT polymerization activity, contains a BRCA1 C-terminal domain that has been shown to mediate interactions of proteins involved in DNA repair. The induction of DSBs in Cos-7 cells transfected with a human TdT expression construct resulted in the appearance of discrete nuclear foci in which TdT and Ku colocalize. The physical association of TdT with Ku suggests a possible mechanism by which TdT is recruited to the sites of DSBs such as V(D)J recombination intermediates.

Animals↗
PubMed1999

Tissue-specific regulation of the ecto-5'-nucleotidase promoter. Role of the camp response element site in mediating repression by the upstream regulatory region.

We have isolated the 5' region of the ecto-5'-nucleotidase (low K(m) 5'-NT) gene and established that a 969-base pair (bp) fragment confers cell-specific expression of a CAT reporter gene that correlates with the expression of endogenous ecto-5'-NT mRNA and enzymatic activity. A 768-bp upstream negative regulatory region has been identified that conferred lymphocyte-specific negative regulation in a heterologous system with a 244-bp deoxycytidine kinase core promoter. DNase I footprinting identified several protected areas including Sp1, Sp1/AP-2, and cAMP response element (CRE) binding sites within the 201-bp core promoter region and Sp1, NRE-2a, TCF-1/LEF-1, and Sp1/NF-AT binding sites in the upstream regulatory region. Whereas the CRE site was essential in mediating the negative activity of the upstream regulatory region in Jurkat but not in HeLa cells, mutation of the Sp1/AP-2 site decreased promoter activity in both cell lines. Electrophoretic mobility shift assay analysis of proteins binding to the CRE site identified both ATF-1 and ATF-2 in Jurkat cells. Finally, phorbol 12-myristate 13-acetate increased the activity of both the core and the 969-bp promoter fragments, and this increase was abrogated by mutations at the CRE site. In summary, we have identified a tissue-specific regulatory region 5' of the ecto-5'-NT core promoter that requires the presence of a functional CRE site within the basal promoter for its suppressive activity.

5'-Nucleotidase↗
PubMed1999

ATP and phosphate reciprocally affect subunit association of human recombinant High Km 5'-nucleotidase. Role for the C-terminal polyglutamic acid tract in subunit association and catalytic activity.

IMP-specific, High Km 5'-nucleotidase (EC 3.1.3.5) is an ubiquitous enzyme, the activity of which is highly regulated by substrate, ATP, and inorganic phosphate. The cDNA encoding this enzyme has recently been cloned and found to contain a unique stretch of nine glutamic and four aspartic acid residues at the C-terminus. To study the effects of this acidic tail, and of ATP and inorganic phosphate on enzyme function, we generated several structural modifications of the 5'-nucleotidase cDNA, expressed the corresponding proteins in Escherichia coli and compared their molecular and kinetic properties. As with the enzyme purified from human placenta, all recombinant proteins were activated by ATP and inhibited by inorganic phosphate. Although the S0.5-values were higher, the specific activities of the purified protein variants (except that truncated at the C-terminus) were similar. The molecular mass of the full-length enzyme subunit has been estimated at 57.3 kDa and the molecular mass of the native protein, as determined by gel-filtration chromatography, was estimated to be 195 kDa. Increasing the concentration of NaCl to 0.3 M promoted oligomerization of the protein and the formation of aggregates of 332 kDa. ATP induced further oligomerization to 715 kDa, while inorganic phosphate reduced the estimated molecular mass to 226 kDa. In contrast to the truncation of 30 amino acids at the N-terminus, which did not alter enzyme properties, the removal of the polyglutamic/aspartic acid tail of 13 residues at the C-terminus caused profound kinetic and structural changes, including a 29-fold decrease in specific activity and a significant increase in the sensitivity to inhibition by inorganic phosphate in the presence of AMP. Structurally, there was a dramatic loss of the ability to form oligomers at physiological salt concentration which was only partially restored by the addition of NaCl or ATP. These data suggest an important function of the polyglutamic acid tract in the process of association and dissociation of 5'-nucleotidase subunits.

5'-Nucleotidase↗
PubMed1999

Nucleotide pool imbalance and adenosine deaminase deficiency induce alterations of N-region insertions during V(D)J recombination.

Template-independent nucleotide additions (N regions) generated at sites of V(D)J recombination by terminal deoxynucleotidyl transferase (TdT) increase the diversity of antigen receptors. Two inborn errors of purine metabolism, deficiencies of adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP), result in defective lymphoid development and aberrant pools of 2'-deoxynucleotides that are substrates for TdT in lymphoid precursors. We have asked whether selective increases in dATP or dGTP pools result in altered N regions in an extrachromosomal substrate transfected into T-cell or pre-B-cell lines. Exposure of the transfected cells to 2'-deoxyadenosine and an ADA inhibitor increased the dATP pool and resulted in a marked increase in A-T insertions at recombination junctions, with an overall decreased frequency of V(D)J recombination. Sequence analysis of VH-DH-JH junctions from the IgM locus in B-cell lines from ADA-deficient patients demonstrated an increase in A-T insertions equivalent to that found in the transfected cells. In contrast, elevation of dGTP pools, as would occur in PNP deficiency, did not alter the already rich G-C content of N regions. We conclude that the frequency of V(D)J recombination and the composition of N-insertions are influenced by increases in dATP levels, potentially leading to alterations in antigen receptors and aberrant lymphoid development. Alterations in N-region insertions may contribute to the B-cell dysfunction associated with ADA deficiency.

Adenosine Deaminase↗
PubMed1999

The use of the lectin Helix pomatia agglutinin (HPA) as a prognostic indicator and as a tool in cancer research.

Progress in treatment for cancer has enabled extension of the disease-free interval, and of the quality of life for patients, but there has been very little improvement in overall survival rates. The main reason for this has been the ineffectiveness of current therapies to kill all the cancer cells once they have spread to distant sites to form metastatic deposits. One marker which has proved to be useful in identifying those cancers which have the potential to spread is the lectin Helix pomatia agglutinin (HPA). In clinical studies, HPA binding to primary tumours in tissue sections has been of prognostic value in breast, colon and gastric cancer, while no prognostic significance for HPA could be detected in tumours of the head and neck. These studies hence indicate that HPA is best suited to recognise a glycotope on adenocarcinomas. In several studies, HPA reactivity is equal or superior to other classical markers of metastatic potential. Since HPA is a marker of prognosis at the level of individual tumour cells, human tumour cell lines were screened for their HPA positivity. When transplanted into severe combined immunodeficient (scid) mice, HPA positive human breast and colon cancer cells metastasised while HPA negative cancer cell lines in general did not. In order to define HPA binding glycotopes at the molecular level, isolated cell membrane glycoproteins were exposed to labelled HPA on nitrocellulose membranes after Western blotting procedure. The majority of the isolated cell membrane glycoproteins bound HPA indicating that not a single HPA binding glycoprotein exists, which is associated with the metastatic phenotype. Functional investigations using the human/scid mouse chimeras will aid in the identification of those HPA positive glycoproteins which are functionally involved in the metastatic cascade.

Animals↗
PubMed1998

Effects of guanine nucleotide depletion on cell cycle progression in human T lymphocytes.

Depletion of guanine nucleotide pools after inhibition of inosine monophosphate dehydrogenase (IMPDH) potently inhibits DNA synthesis by arresting cells in G1 and has been shown to induce the differentiation of cultured myeloid and erythroid cell lines, as well as chronic granulocytic leukemic cells after blast transformation. Inhibitors of IMPDH are also highly effective as immunosuppressive agents. The mechanism underlying these pleiotropic effects of depletion of guanine nucleotides is unknown. We have examined the effects of mycophenolic acid (MPA), a potent IMPDH inhibitor, on the cell cycle progression of activated normal human T lymphocytes. MPA treatment resulted in the inhibition of pRb phosphorylation and cell entry into S phase. The expression of cyclin D3, a major component of the cyclin-dependent kinase (CDK) activity required for pRb phosphorylation, was completely abrogated by MPA treatment of T cells activated by interleukin-2 (IL-2) and leucoagglutinin (PHA-L), whereas the expression of cyclin D2, CDK6, and CDK4 was more mildly attenuated. The direct kinase activity of a complex immunoprecipitated with anti-CDK6 antibody was also inhibited. In addition, MPA prevented the IL-2-induced elimination of p27(Kip1), a CDK inhibitor, and resulted in the retention of high levels of p27(Kip1) in IL-2/PHA-L-treated T cells bound to CDK2. These results indicate that inhibition of the de novo synthesis of guanine nucleotides blocks the transition of normal peripheral blood T lymphocytes from G0 to S phase in early- to mid-G1 and that this cell cycle arrest results from inhibition of the induction of cyclin D/CDK6 kinase and the elimination of p27(Kip1) inhibitory activity.

Cell Cycle↗