Biomedical subjects

S Langdon

Publications and source records attributed to S Langdon.

12 recordsLinked to original sources

PubMed2004

A high-wavenumber boundary-element method for an acoustic scattering problem.

In this paper we show stability and convergence for a novel Galerkin boundary-element-method approach to the impedance boundary-value problem for the Helmholtz equation in a half-plane with piecewise constant boundary data. This problem models, for example, outdoor sound propagation over inhomogeneous flat terrain. To achieve a good approximation with a relatively low number of degrees of freedom we employ a graded mesh with smaller elements adjacent to discontinuities in impedance, and a special set of basis functions for the Galerkin method so that, on each element, the approximation space consists of polynomials (of degree nu) multiplied by traces of plane waves on the boundary. In the case where the impedance is constant outside an interval [a,b], which only requires the discretization of [a,b], we show theoretically and experimentally that the L(2) error in computing the acoustic field on [a,b] is O(log(nu+3/2)|k(b-a)|M(-(nu+1)), where M is the number of degrees of freedom and k is the wavenumber. This indicates that the proposed method is especially commendable for large intervals or a high wavenumber. In a final section we sketch how the same methodology extends to more general scattering problems.

Journal Article↗

PubMed2000

Tamoxifen increases apoptosis but does not influence markers of proliferation in an MCF-7 xenograft model of breast cancer.

Twenty-four nude mice bearing MCF-7 breast cancer cells grown as xenografts and treated with tamoxifen (2.5 mg slow-release pellet) were studied for up to 35 days. Tumour size was measured in 2 dimensions at regular time-intervals and tumours were harvested on each of days 2, 4, 7, 14, 28 and 35 after the start of treatment. Control animals (8) received no treatment and the tumours were harvested after 0 or 35 days. Tumour sections were assessed for prevalence of apoptosis and mitosis and examined immunocytochemically for Ki(67)(MIB-1) and bcl-2 expression. Tumours increased in size during tamoxifen-treatment, but at a significantly slower rate (max. 2.6-fold) than in the untreated control animals; thus tumours not actually regressing may, nevertheless, be responding significantly to tamoxifen. MIB-1 and bcl-2 immunostaining and mitosis failed to show any consistent change over the period of study. Apoptosis, however, increased progressively and significantly to day-28 in tamoxifen-treated tumours, reaching approximately a 5-fold increase over day-0 values, then decreasing again to nearly 3-fold by day-35 (P= 0.0002). The apoptosis: mitosis ratio in treated tumours also increased to approximately 10-fold on day-28 over day-0 values, decreasing to nearly 4-fold by day-35 (P= 0.037). Within the treated group, apoptosis was significantly inversely correlated with both mitosis (R = -0.38, P= 0.03) and expression of bcl-2 (R = -0.48, P= 0.0056) and strongly positively correlated with both time on tamoxifen (R = +0.63, P= 0.0003) and the % inhibition of growth by tamoxifen (R = +0.58,P = 0.0012) in the 28 individual, treated tumours (estimated relative to the mean growth rate in the controls). The apoptosis: mitosis ratio was also inversely correlated with bcl-2 expression (R = -0.56, P= 0.0021) and positively correlated with both time on tamoxifen (R = +0.50, P= 0.0068) and % inhibition of growth (R = +0.56, P= 0.0019). In this hormone-sensitive tumour model for breast cancer, in which tamoxifen caused inhibition rather than regression, it was not possible to detect significant changes in the marker proteins Ki(67)and bcl-2, or in the prevalence of mitosis in relation to treatment; these factors may therefore not be accurate indices of response to tamoxifen in all situations. By contrast, however, tamoxifen induced a significant, early increase in the prevalence of apoptosis associated with inhibition of tumour growth and an inverse relationship in both mitosis and bcl-2 expression, suggesting that apoptosis may be an accurate and sensitive early marker of even a moderate response to tamoxifen.

Journal Article↗

PubMed1997

Tamoxifen induced apoptosis in ZR-75 breast cancer xenografts antedates tumour regression.

The ZR-75-1 ER positive breast cancer cell line, xenografted in female nude mice, has been used to determine the effect of tamoxifen on cell proliferation (as measured by mitosis) and cell death (as evidenced by apoptosis and necrosis). After 2 days treatment, there was a significant rise in apoptosis (p < 0.05), whereas a fall in mitosis was not apparent until 7 days (p < 0.05). Furthermore there was an increase in the apoptotic:mitotic ratio on day 7 (p < 0.05). These changes antedated tumour regression, which did not reach not significance until day 14. Tamoxifen did not increase necrosis (which significantly decreased in treated tumours once they had regressed (p < 0.01). In contrast tamoxifen treatment of xenografted MDA-MB-231 ER-negative breast cancer cells produced no significant effects on growth, apoptosis, or mitosis. This study presents clear evidence for tamoxifen inducing apoptosis in ZR-75-1 xenografts (but not MDA-MB-231 tumours). Since changes in apoptosis and mitosis antedate tumour regression, their assessment may provide the potential by which to predict tumour response to tamoxifen therapy.

Animals↗

PubMed1997

Adrenaline degradation in general practice.

The general practitioner's (GP's) doctor's bag is exposed to extreme temperatures that may affect the stability of the drugs it contains. Adrenaline (1:1000 solution) is more stable than previous studies would suggest. GPs carry out-of-date drugs despite stating that they regularly check expiry dates.

Ambulatory Care↗

PubMed1994

The c-kit proto-oncogene receptor is expressed on a subset of human CD3-CD4-CD8- (triple-negative) thymocytes.

The c-kit receptor is a tyrosine-kinase transmembrane receptor first identified as an oncogene in the HZ4-feline leukemia virus and later found to be important in hematopoiesis in mice. The ligand for this receptor (Steel factor) can stimulate hematopoiesis both in vitro and in vivo. To study the pattern of c-kit receptor expression in normal human hematopoietic progenitor cells, we prepared a monoclonal antibody (9B9) against human c-kit receptor by using a synthetic peptide (amino acids 476-501) from the extracellular domain of c-kit receptor to immunize Balb/c mice. Monoclonal antibody 9B9 bound to recombinant c-kit protein, the erythroleukemic line HEL, the megakaryocytic line MEG-01, and the murine mast cell line P815. Monoclonal antibody 9B9 also bound to the surface of the CD7+CD3-CD4-CD8- T cell lymphoid cell lines DU.528 and HSB2T, and also to 1 to 4% of normal bone-marrow cells. The majority (67 +/- 6%) of CD34+ bone-marrow progenitor cells coexpressed c-kit receptor. Flow-cytometry analysis of immature CD3-CD4-CD8- (triple-negative) thymocytes indicated 30 +/- 9.5% expressed the c-kit receptor, and thymidine incorporation assay revealed that the receptor is functional. Indirect fluorescent microscopy of human thymic tissue, using a monoclonal antibody against Steel factor, revealed its presence on scattered mononuclear cells within the intralobular septae and the subcapsular cortex, which are regions where the triple-negative thymocytes are also localized. These data provide evidence that the c-kit receptor is present on human hematopoietic bone marrow and intrathymic T cell progenitor cells, and that it likely plays a role in early T cell lymphopoiesis.

Antibodies, Monoclonal↗

PubMed1993

Characterization of the aryl hydrocarbon receptor and aryl hydrocarbon responsiveness in human ovarian carcinoma cell lines.

The human ovarian carcinoma cell lines PE01, PE04, and PE06 express the estrogen receptor and studies with the PE04 cells have shown that tamoxifen inhibits 17 beta-estradiol-induced proliferation. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a broad spectrum antiestrogen which works through the aryl hydrocarbon receptor. Incubation of the three cell lines with [3H]TCDD followed by isolation of nuclear extracts showed that the PE01, PE04, and PE06 cells express the aryl hydrocarbon receptor (23 to 87 fmol/mg protein) which exhibits sedimentation properties (7.5 to 7.9 S) on sucrose gradients similar to that observed in other mammalian species. Aryl hydrocarbon responsiveness was determined by the induction of P4501A1 mRNA levels and ethoxyresorufin O-deethylase activity by TCDD. Induction of both parameters was observed only in the PE04 cells. Gel mobility shift assays with a consensus dioxin-responsive element (DRE, 26-mer) showed that after incubation of the nuclear extracts from the 3 cell lines with 32P-DRE a retarded band formed only with nuclear receptor complex from PE04 cells. 17 beta-Estradiol stimulated proliferation of the PE04 and PE06 but not the PE01 cells; 1 nM TCDD alone either did not affect or inhibited the growth of these cells and 1 nM TCDD significantly inhibited the 17 beta-estradiol-induced proliferation of the PE04 and PE06 cells. Treatment of the PE04 cells with 1 nM 17 beta-estradiol resulted in a time-dependent enhanced secretion of the M(r) 52,000 protein (procathepsin D) and, after 48 h, a 51% increase in the secretion of this protein was observed. Cotreatment of the PE04 cells with 0.1 or 1.0 nM TCDD completely inhibited the 17 beta-estradiol-induced secretion of the M(r) 52,000 protein. These data show that TCDD exhibits antiestrogenic activity in estrogen receptor-positive ovarian carcinoma cell lines; however, in the PE06 cells, there was no correlation between the effects of TCDD on the induction of CYP1A1 gene expression and the results of the gel shift assay (i.e., nonresponsiveness) versus the observed antiestrogenic activity.

Adenocarcinoma↗

PubMed1993

Electrical stunning of red deer (Cervus elaphus).

Eighteen of 23 red deer (Cervus elaphus) at a deer slaughtering premises were successfully stunned with an apparatus modified from that normally used to stun sheep. The five unsuccessful electrical stuns were associated with poor head restraint and poor head contact by the electrodes. The median stunning current was 0.9 A, and in the majority of cases the duration of stunning was less than 1 second. The signs of the electrically induced epileptiform seizures in the deer were dissimilar to those seen in sheep, cattle and pigs, in that the initial tonic phase was less marked, and of shorter duration. A similar shorter and less obvious tonic phase was noted in four deer shot with a captive bolt pistol. Two animals which were electrically stunned, and bled within 10 seconds, showed no signs of recovery while bleeding. The electroencephalograms of four deer stunned with currents of 1.3 A for a duration of either 0.5 or 1.0 seconds were recorded under more controlled conditions. All four animals developed electroencephalograms typical of an epileptiform seizure. The animals exhibited behavioural reactions similar to the other 18 animals in the trial at the deer slaughtering premises and were rendered unconscious for between 54 and 122 seconds. The electroencephalogram activity amplitude was greater than that recorded immediately before stunning and took between 6 and 9 seconds to build up to maximum value. It is concluded that, providing the heads of deer are adequately restrained, head-only electrical stunning can be incorporated into a humane method of slaughter for deer.

Journal Article↗

PubMed1992

Phase II preclinical drug screening in human tumor xenografts: a first European multicenter collaborative study.

In a European joint project carried out in 6 laboratories a disease-oriented program was set up consisting of a panel of 7 tumor types, each represented by 4 to 8 different human tumor lines, for secondary screening of promising anticancer drugs. Human tumor lines were selected on the basis of differences in histology, growth rate, and sensitivity to conventional cytostatic agents. Xenografts were grown s.c. in nude mice, and treatment was started when tumors reached a mean diameter of 6 mm in groups of mice where at least 6 tumors were evaluable. Drugs were given at the maximum tolerated dose. For evaluation of drug efficacy, median tumor growth curves were drawn, and specific growth delay and treated/control x 100% were calculated. Doxorubicin (8 mg/kg i.v. days 1 and 8) was effective (treated/control < 50%, and specific growth delay > 1.0) in 0 of 2 breast cancers, 1 of 3 colorectal cancers, 2 of 5 head and neck cancers, 3 of 6 non-small cell lung cancers, 4 of 6 small cell lung cancers, 0 of 3 melanomas, and 3 of 6 ovarian cancer lines. Amsacrine (8 mg/kg i.v. days 1 and 8) was not effective, while datelliptium (35 mg/kg i.p. days 1 and 8) was active against 2 of 6 small cell lung cancer lines. Brequinar sodium (50 mg/kg i.p. days 1-5) showed efficacy in 4 of 5 head and neck cancers, 5 of 8 non-small cell lung cancers, and 4 of 5 small cell lung cancer lines. The project has been shown to be a feasible approach. Clinical activity for doxorubicin and inactivity for amsacrine against solid tumor types was confirmed in the human tumor xenograft panel. Additional anticancer drugs will be studied in the European joint project to further define the reliability of this novel, promising screening approach.

Amsacrine↗

PubMed1992

Broad spectrum neuropeptide antagonists inhibit the growth of small cell lung cancer in vivo.

The proliferation of small cell lung cancer (SCLC) cells appears sustained by multiple autocrine and paracrine circuits involving Ca2+ mobilizing neuropeptides. Consequently, broad spectrum neuropeptide antagonists which inhibit SCLC growth in vitro have been suggested as potential anticancer agents. Here we evaluated this hypothesis using xenografts of WX322 cells, a SCLC cell line that responds to multiple Ca2+ mobilizing neuropeptides. The broad spectrum neuropeptide antagonists [Arg6,D-Trp7,9,MePhe8]substance P(6-11) and [D-Arg1,D-Phe5,Trp7,9Leu11[substance P were shown to inhibit the growth of WX322 xenografts in nude mice. Similar results were obtained with xenografts of the SCLC cell line H69. The results indicate that broad spectrum neuropeptide antagonists can inhibit the growth of SCLC in vivo and suggest that these antagonists could be useful in the treatment of SCLC.

Animals↗

PubMed1992

Growth of small cell lung cancer cells: stimulation by multiple neuropeptides and inhibition by broad spectrum antagonists in vitro and in vivo.

Neuropeptides are increasingly implicated in the control of cell proliferation and their mechanisms of action are attracting intense interest. The early complex cascade of events initiated by peptides of the bombesin family including gastrin-releasing peptide is increasingly understood. The cause-effect relationships and temporal organization of these early signals and molecular events provide a paradigm for the study of other growth factors and mitogenic neuropeptides and illustrate the activation and interaction of a variety of signaling pathways. These peptides may also act as autocrine growth factors for certain small cell lung cancer cells. The results discussed here strongly suggest that the autocrine growth loop of bombesin-like peptides may be only a part of an extensive network of autocrine and paracrine interactions involving a variety of Ca(2+)-mobilizing neuropeptides in small cell lung cancer including bradykinin, cholecystokinin, galanin, neurotensin, and vasopressin. In this context, broad spectrum antagonists that prevent the function of multiple Ca(2+)-mobilizing receptors are of special interest. These antagonists block neuropeptide mediated signals and inhibit small cell lung cancer growth in vitro and in vivo. Thus, broad spectrum neuropeptide antagonists constitute potential anticancer agents.

Amino Acid Sequence↗

PubMed1992

Comparative antitumour activity of vinblastine-isoleucinate and related vinca alkaloids in human tumour xenografts.

The antitumour activity of the investigational agent vinblastine-isoleucinate (V-LEU) was compared with vintriptol, another investigational agent of the same series of vinblastine-23-oyl amino acid derivatives, and vinblastine, their clinically active parent compound, in a panel of nine human tumour xenografts growing subcutaneously in nude mice. Compounds were administered intravenously at equitoxic doses twice weekly. As assessed by optimal tumour growth inhibition and tumour growth delay, vinblastine, V-LEU and vintriptol exhibited antitumour activity in 8/9, 7/9 and 4/7 human tumour xenografts, respectively. When growth curves and numbers of complete remissions were compared, V-LEU was the most active agent in two malignant melanoma lines (THXO and LOX p28) and two small cell lung carcinoma lines tested (LXFS 538 and WX 322), whereas vinblastine was more active against the two colorectal carcinomas (CXF 243 and CXF 280). Notably, the non small cell lung carcinoma (NSCLC) line AHXOL was resistant to the three agents. The results of this study suggest that V-LEU was as active as vinblastine in most tumour lines, exhibiting superior antitumour activity in malignant melanoma, SCLC and breast cancer lines. The decision to bring this compound into clinical trial shall await further confirmation of these preclinical results and the evaluation of its toxicity profile in relation to other vinca alkaloids.

Animals↗

PubMedDate not supplied

The transfer and persistence of automotive carpet fibres on shoe soles.

The transfer and persistence of automotive carpet fibres to shoe soles was investigated. It was found that fibres were transferred with the normal activity of a car passenger. Carpet type and shoe sole parameters were significant determinants in the number of fibres that transferred. The average number of fibres was between about one and 33 per sole. Fibres that had been transferred after normal activity only persisted for a few minutes after walking. A survey of the shoe soles of people about to leave their car showed that fibres were usually present. The majority of shoe soles surveyed had less than five fibres with the greatest number of fibres found being 14. The likelihood of finding a large number of fibres on such soles is rare. Fibre composition of automotive carpets showed a high degree of variation. Grey was seen to be a common colour irrespective of the colour of the vehicle body.

Automobiles↗