Biomedical subjects

N L Davis

Publications and source records attributed to N L Davis.

At least 37 records · Page 2Linked to original sources

PubMed1996

A viral vaccine vector that expresses foreign genes in lymph nodes and protects against mucosal challenge.

A candidate live-virus vaccine strain of Venezuelan equine encephalitis virus (VEE) was configured as a replication-competent vector for in vivo expression of heterologous immunogens. Three features of VEE recommend it for use as a vaccine vector. (i) Most human and animal populations are not already immune to VEE, so preexisting immunity to the vector would not limit expression of the heterologous antigen. (ii) VEE replicates first in local lymphoid tissue, a site favoring the induction of an effective immune response. (iii) Parenteral immunization of rodents and humans with live, attenuated VEE vaccines protects against mucosal challenge, suggesting that VEE vaccine vectors might be used successfully to protect against mucosal pathogens. Upon subcutaneous (s.c.) inoculation into the footpad of mice, a VEE vector containing the complete influenza virus hemagglutinin (HA) gene expressed HA in the draining lymph node and induced anti-HA immunoglobulin G (IgG) and IgA serum antibodies, the levels of which could be increased by s.c. booster inoculation. When immunized mice were challenged intranasally with a virulent strain of influenza virus, replication of challenge virus in their lungs was restricted, and they were completely protected from signs of disease. Significant reduction of influenza virus replication in the nasal epithelia of HA vector-immunized mice suggested an effective immunity at the mucosal surface. VEE vaccine vectors represent an alternative vaccination strategy when killed or subunit vaccines are ineffective or when the use of a live attenuated vaccine might be unsafe.

Animals↗

PubMed1996

An animal model of benign bile-duct stricture, sclerosing cholangitis and cholangiocarcinoma and the role of epidermal growth factor receptor in ductal proliferation.

OBJECTIVE: To adapt an animal model of benign bile-duct stricture, sclerosing cholangitis and cholangiocarcinoma in order to determine if the expression of epidermal growth factor receptor (EGFr) could be used to differentiate these lesions. DESIGN: A prospective control study with blinded interpretation of liver biopsy histology and immunohistochemical staining as the criterion standards. SETTING: A university-affiliated research centre. SUBJECTS: Male Syrian Golden hamsters (40 for benign duct stricture, 29 for sclerosing cholangitis and 27 for cholangiocarcinoma). INTERVENTIONS: Ligation of the common bile duct with 6-0 catgut for benign duct stricture; injection of the biliary tree with 0.15 mL of formalin for sclerosing cholangitis; and weekly subcutaneous injections of 500 mg/kg of di-isopropanolnitrosamine for 10 weeks followed by ligation of the common bile duct with 6-0 catgut for cholangiocarcinoma. Routine histologic preparation of liver biopsies obtained at autopsy 10 weeks postoperatively then immunohistochemical staining of specimens for EGFr. MAIN OUTCOME MEASURES: The development of benign or atypical biliary ductal proliferation, including adenoma and carcinoma formation. The presence or absence of immunohistochemical staining for EGFr. RESULTS: Benign ductal proliferation without atypia was seen in 15 of 21 animals in the bile-duct-stricture group that were sacrificed, in 15 of 24 animals in the sclerosing cholangitis group and in 17 of 18 animals in the cholangiocarcinoma group. Atypical proliferation was seen in 13 of 18 animals with cholangiocarcinoma but not in the other two groups. The differential occurrence of atypical ductal proliferation was statistically significant (p < 0.00001) for both groups. No evidence of EGFr expression was found in any group. CONCLUSION: Although the animal model was valid histologically for comparing benign and malignant biliary disease, EGFr does not play a role in biliary ductal proliferation and so cannot be used to differentiate between benign and malignant lesions.

Animals↗

PubMed1995

Attenuated mutants of Venezuelan equine encephalitis virus containing lethal mutations in the PE2 cleavage signal combined with a second-site suppressor mutation in E1.

The PE2 cleavage signal in a full-length cDNA clone of the alphavirus Venezuelan equine encephalitis virus (VEE) was ablated by site-directed mutagenesis. RNA transcripts derived from the resulting plasmids programmed the production of nonviable particles upon transfection of baby hamster kidney (BHK) cells. However, the mutant RNAs also gave rise to a small proportion of viable revertants. Analysis of these biological revertants and their molecularly cloned homologs demonstrated that second-site suppressor mutations at either E2 position 243 or E1 position 253 were able to restore viability to PE2 cleavage signal mutants. The viable revertants incorporated unprocessed PE2 into particles which showed normal infectivity for BHK cells, but reduced ability to grow in C6/36 mosquito cells. A mutant carrying a lethal PE2 cleavage signal mutation in combination with a suppressor at E1 253 was either avirulent or highly attenuated in adult mice when inoculated by the subcutaneous, intracerebral, or intranasal route and conferred complete protection against both intraperitoneal and intranasal challenge with virulent VEE. These results indicate the close functional association of the E2 and E1 proteins in the alphavirus spike. They also have implications for the design of recombinant live virus vaccines for VEE, for other alphaviruses, and for other viruses that use a similar mechanism for glycoprotein maturation.

Amino Acid Sequence↗

PubMed1995

Specific restrictions in the progression of Venezuelan equine encephalitis virus-induced disease resulting from single amino acid changes in the glycoproteins.

The pathogenesis of Venezuelan equine encephalitis virus (VEE) was examined in the mouse model using V3000, a virus derived from a molecular clone of the Trinidad donkey strain of VEE. These results were compared in parallel experiments with avirulent mutants of VEE derived by site-directed mutagenesis of the clone. Adult mice, inoculated subcutaneously in their left rear footpad with V3000, were followed in a time course study for 6 days in which 15 organs were tested for histopathological changes, for the presence of viral antigen by immunohistochemical staining, for the presence of viral nucleic acid by in situ hybridization analysis, and for content of viable virus. Virus was detected in the footpad inoculation site, but until 12 hr postinoculation (pi), the level of virus did not suggest early viral replication. By 4 hr pi, however, replication of V3000 was evident in the draining popliteal lymph node. At this early time point, no virus could be isolated from any other organ examined. At 12 hr, a significant serum viremia was observed, and virus was detected at a low level in a number of well vascularized organs, including spleen, heart, lung, liver, kidney, and adrenal gland. By 18 hr, high virus titers were present in serum and all the lymphoid organs examined, and these tissues appeared to be the major peripheral sites of V3000 replication. Virus in serum and peripheral organs was cleared by 3-4 days pi. In a second phase of the infection, V3000 invaded the central nervous system (CNS), replicated predominantly in neurons, and persisted in the brain until death by encephalitis. Pathologic findings as well as the results of immunocytochemical and in situ hybridization examination were generally coordinate with virus titration. A site-directed mutant of V3000, V3010, contained a mutation in the gene for the E2 glycoprotein at codon 76 (Glu to Lys) which rendered it avirulent after footpad inoculation. Detection of V3010 replication in the draining lymph node was sporadic and was sometimes delayed to as long as 3 days pi. Infrequent and/or delayed virus spread to other sites also was observed. Analogous experiments were performed with other mutants which were avirulent by the footpad inoculation route: V3014, a mutant differing from V3000 at three loci (E2 Lys 209, E1 Thr 272, and E2 Asn 239), as well as single-site mutants V3032 (E2 Lys 209) and V3034 (E1 Thr 272).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Detection of squamous neoplasia by fluorescence imaging comparing porfimer sodium fluorescence to tissue autofluorescence in the hamster cheek-pouch model.

BACKGROUND: Early neoplastic changes in the oral cavity may be difficult to detect. Fluorescence imaging using porphyrin-derived drugs has been used to enhance detection of neoplasia. Autofluorescence has also been used for this purpose. This paper compares autofluorescence to porfimer sodium-induced fluorescence in the detection of neoplasia in the hamster cheek-pouch model. MATERIALS AND METHODS: Neoplasia was induced in the hamster cheek pouch by the application of 9,10-dimethyl-1,2-benzanthracene. Animals were imaged either with injection of drug (porfimer sodium) or without drug (autofluorescence). Imaging was carried out using a laser-induced fluorescence detection system. Biopsies were performed on imaged sections and histologic grades were assigned. RESULTS: Porfimer sodium fluorescence provided 100% sensitivity and specificity in detection of neoplasia. The sensitivity and specificity with autofluorescence was 76% and 83%, respectively. CONCLUSIONS: Autofluorescence provides an accurate means of detecting early neoplastic changes in the hamster cheek-pouch model; however, porfimer sodium imaging does improve detection rates.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1995

An evaluation of prognostic scoring systems in patients with follicular thyroid cancer.

BACKGROUND: Prognostic scoring systems for thyroid cancer have not been investigated in patients with pure follicular cancer; thus, the purpose of this study was to compare the following prognostic indices: the European Organization for Research and Treatment of Cancer (EORTC) method; the Age, Grade, Extent, Size (AGES) score; and the Age, Metastasis, Extent, Size (ALIES) score. PATIENTS AND METHODS: A retrospective study reviewing 122 patients actively treated between 1955 and 1990 was conducted. Scoring systems were calculated and survival analysis completed. AGES low-risk patients were analyzed with respect to known risk factors. RESULTS: The AGES scoring system significantly defined low- and high-risk groups (P = 0.0041); the ratio of deaths between high-versus low-risk groups was 1.9:1. EORTC scores distinguished four risk groups (P = 0.002). The AMES scoring system did not significantly assign risk. In multivariate analysis of low-risk AGES patients, age, perithyroidal tissue involvement, and positive frozen section reached statistical significance. CONCLUSIONS: The AGES and EORTC scoring systems best defined low- and high-risk groups of patients with pure follicular cancer, although the separation between groups was low.

Adenocarcinoma, Follicular↗

PubMed1994

A molecular genetic approach to the study of Venezuelan equine encephalitis virus pathogenesis.

Viral pathogenesis can be described as a series of steps, analogous to a biochemical pathway, whose endpoint is disease of the infected host. Distinct viral functions may be critical at each required step. Our genetic approach is to use Venezuelan equine encephalitis virus (VEE) mutants blocked at different steps to delineate the process of pathogenesis. A full-length cDNA clone of a virulent strain of VEE was used as a template for in vitro mutagenesis to produce attenuated single-site mutants. The spread of molecularly cloned parent or mutant viruses in the mouse was monitored by infectivity, immunocytochemistry, in situ hybridization and histopathology. Virulent VEE spread through the lymphatic system, produced viremia and replicated in several visceral organs. As virus was being cleared from these sites, it began to appear in the brain, frequently beginning in the olfactory tracts. A single-site mutant in the E2 glycoprotein appeared to block pathogenesis at a very early step, and required a reversion mutation to spread beyond the site of inoculation. The feasibility of combining attenuating mutations to produce a stable VEE vaccine strain has been demonstrated using three E2 mutations.

Amino Acid Sequence↗

PubMed1994

A multicenter review of the treatment of major truncal necrotizing infections with and without hyperbaric oxygen therapy.

To examine the effectiveness of hyperbaric oxygen (HBO) therapy in the treatment of major truncal necrotizing infections, a retrospective (1980 to 1992) analysis of the medical records of 30 patients treated with HBO therapy and 24 patients treated without HBO therapy was undertaken. The two groups were similar; however, there was a selection bias towards more frequent clostridial infections in a younger population in the HBO group. There was no difference in length of hospital stay, intensive care unit (ICU) stay, or duration of antibiotic therapy between groups. The mortality rates were 9/30 (30%) in the HBO group versus 10/24 (42%) (nonsignificant difference) in the non-HBO group. The total number of operations was greater in the HBO-treated group. This study failed to show that the use of HBO in the treatment of major truncal necrotizing infections statistically reduced mortality or the number of débridements. We believe, however, that the apparent selection bias and the trend towards increased survival in the HBO-treated group (12%) justifies the continued use of and research with HBO therapy.

Anti-Bacterial Agents↗

PubMed1994

Differentiation of thyroid neoplasms by evaluating epithelial membrane antigen, Leu-7 antigen, epidermal growth factor receptor, and DNA content.

The expression of epithelial membrane antigen (EMA), Leu-7 antigen, epidermal growth factor receptor (EGFr), and deoxyribonucleic acid (DNA) content in 40 thyroid nodules was investigated to identify those factors that might differentiate these lesions or correlate to their prognosis. There were 22 carcinomas (16 papillary, 4 follicular, 1 anaplastic, 1 medullary) and 18 benign lesions prospectively obtained between 1989 and 1993. Patients' charts were reviewed to establish a database of known clinical prognostic indicators. Expression of EMA and Leu-7 was significant in malignant lesions when compared to benign lesions (P < 0.02 and P < 0.001). EMA was expressed significantly more frequently by follicular carcinomas than by follicular adenomas (P < 0.03). Leu-7 antigen was expressed by all papillary carcinomas. Neither of these antigens showed any association with known clinical prognostic indicators. EGFr expression neither differentiated benign from malignant lesions nor correlated with prognostic factors. The presence of aneuploidy correlated with poor tumor differentiation (P < 0.02), but did not distinguish benign from malignant lesions. These results suggest that EMA expression may be useful for confirming malignancy in follicular neoplasms and that the expression of Leu-7 antigen can assist in distinguishing papillary carcinoma from benign lesions with pseudopapillae.

Adolescent↗

PubMed1994

Lethality of PE2 incorporation into Sindbis virus can be suppressed by second-site mutations in E3 and E2.

Sindbis virions contain two glycoproteins, E1 and E2. E2 is produced initially as a precursor, PE2, from which the amino-terminal 64 amino acids are cleaved by a cellular protease at a late stage in virion maturation. A mutation at E2 position 1 (Arg to Asn) was placed into Sindbis virus AR339 by site-directed mutagenesis of a full-length AR339 cDNA clone, pTRSB, to produce pTRSB-N. The mutation created a signal for N-linked glycosylation immediately adjacent to the PE2 cleavage signal. Virions derived from pTRSB-N were glycosylated at E2 position 1, and they quantitatively incorporated PE2 in place of E2. When pTRSB-N transcripts were electroporated into BHK-21 cells, TRSB-N particles were released with nearly normal efficiency; however, the specific infectivity of TRSB-N particles was very low. Analysis of seven infectious revertants of TRSB-N revealed that reversion was linked to (i) mutations that eliminated the signal for N-linked glycosylation and thus restored the PE2 cleavage phenotype or (ii) conservation of the PE2 cleavage defect combined with incorporation of suppressor mutations in E3 or E2. The genotype of each revertant was reconstructed in the genetic background of TRSB-N, and each reverting mutation also was replaced individually into the genetic background of wild-type virus (TRSB). Each PE2-containing revertant was attenuated in newborn CD-1 mice and replicated poorly in cultured mosquito cells (C6/36). Reverting mutations in the genetic background of TRSB did not reduce virulence in mice or growth in mosquito cells, suggesting that the phenotypes of attenuation in mice and reduced growth in mosquito cells were linked to failure of PE2 cleavage and not to the reverting mutations themselves.

Amino Acid Sequence↗

PubMed1993

Photodynamic therapy of squamous cell carcinoma. An evaluation of a new photosensitizing agent, benzoporphyrin derivative and new photoimmunoconjugate.

Photodynamic therapy for cancer depends on the relatively selective distribution of photosensitizing agents to malignant as compared with normal tissues, rendering the malignant cells more susceptible to light-mediated damage. Photodynamic therapy has been used with only moderate success to date. The purpose of this study was to compare a new photosensitizing agent, benzoporphyrin derivative (BPD), to the standard agent presently in use, photofrin II, in a hamster cheek pouch model of squamous cell carcinoma. As well we have investigated the potential of using a tumour-specific monoclonal antibody-BPD conjugate to improve the tumour localizing properties of BPD. Treatment consisted of photodynamic therapy with either photofrin II, BPD, or a tumour-specific anti-epidermal growth factor receptor-BPD conjugate. Control groups of light alone, anti-EGFr, tumour non-specific MoAb, and tumour non-specific MoAb-BPD conjugate were included with the contralateral cheek pouch of each animal acting as a dark control. An assessment of differential delivery of BPD to tumour and to normal mucosa was undertaken using a spectrophotometric assay. Parametric statistical analysis included Student's t-tests and linear regression while non-parametric analysis was undertaken using Fisher's exact test. Animals receiving BPD alone demonstrated tumour-to-tissue levels of approximately 2:1 while animals receiving the tumour-specific anti-EGFr-BPD conjugate had significantly better tumour:tissue ratios of 26:1 (P < 0.005). Animals treated with photofrin II had a 1 month cancer-free survival of 27% while animals treated with BPD had an improved survival of 67% (P = 0.03). The group treated with the tumour-specific anti-EGFr-BPD conjugate at a twentieth the total dose of BPD had an 80% 1 month cancer-free survival which was not statistically different from the group treated with BPD alone. Benzoporphyrin appears to be a more effective photosensitizing agent than Photofrin II and its tumour selectivity can be improved using a tumour specific monoclonal antibody conjugate.

Animals↗

PubMed1992

Prognostic markers of colorectal cancer: an evaluation of DNA content, epidermal growth factor receptor, and Ki-67.

Between January 1989 and August 1991, 62 patients undergoing resection for colorectal adenocarcinoma were assessed in a prospective fashion on the basis of various tumor characteristics that are thought to indicate prognosis. Parameters measured included epidermal growth factor receptor (EGFr) expression, a cell membrane receptor known to be overexpressed in a variety of tumors, Ki-67, a monoclonal antibody marker of cell proliferation, as well as flow cytometry and standard histologic examination. Statistical analysis included chi square with Yates correction when appropriate, Wilcoxon W, and multivariate logistic regression. EGFr positive tumors were associated with worse Dukes' stage (27% of EGFr negative tumors were Dukes' C or D vs. 58% of EGFr positive tumors, P = 0.03), as well as more aneuploid characteristics by flow cytometry (48% EGFr negative = aneuploid vs. 82% EGFr positive = aneuploid, P = 0.01). Lymphatic invasion was more frequent in EGFr positive tumors (P = 0.03). These factors proved to be independent of each other by multivariate analysis. Ki-67 did not correlate with any of the measured parameters and was of extremely limited use in the evaluation of the study population. Multivariate analysis indicated that aneuploid tumors were associated with worse Dukes' stage than diploid tumors. Histologic parameters such as lymphatic and vascular invasion as well as histologic grade are compared to the other parameters involved with prognosis.

Adenocarcinoma↗

PubMed1992

Impact of cervical lymph node metastases from squamous cell cancer of the lip.

The records of 123 patients with squamous cell cancer of the lip presenting to the Vancouver Clinic of the British Columbia Cancer Agency from 1984 and 1988 were reviewed, and 4 were excluded from the study for various reasons. Initial treatment was surgery in 40, radiotherapy in 61, and combined in 18 patients. The primary tumor was staged as TIS in 11, T1 in 57, T2 in 24, T3 in 15, T4 in 1, and undetermined in 11. Follow-up continued for a minimum of 2 years in all but five patients. Lymph node metastases developed in 19 patients, representing 18% of the 108 patients with invasive cancer. The size of the primary tumor correlated with the likelihood of metastases. The neck disease was controlled in only 8 of the 19 patients with metastases, whereas control of the primary tumor was achieved in all but 3 patients. It is concluded that the development of node metastases in patients with lip cancer is more frequent than commonly appreciated and is associated with a high mortality rate. Close follow-up is essential to allow early detection of neck involvement. Aggressive surgery is indicated when such involvement becomes evident.

Adult↗

PubMed1992

Efficacy of 131I ablation following thyroidectomy in patients with invasive follicular thyroid cancer.

The role of thyroid ablation following thyroidectomy for invasive follicular cancer remains controversial. The use of iodine 131 (131I) ablation as adjuvant therapy may facilitate follow-up of patients in whom serum thyroglobulin levels and 131I total body scans are used to detect metastatic disease. It is uncertain if 131I ablation improves survival of patients with follicular thyroid cancer. Thus, the purpose of this study was to determine if survival is enhanced following ablation, with particular reference to those patients with minimally invasive cancer. Between the years 1955 to 1988, 142 patients with invasive thyroid follicular cancer were treated at the British Columbia Cancer Agency, of whom 71 had minimal invasion and no extrathyroidal extension of tumor. In this group of patients, 46 underwent hormone suppression only, 17 had ablation, and 8 had neither. The average follow-up was 9 years and extended beyond 15 years in many patients. Data were entered in a mainframe computer, and Kaplan-Meier survival analysis was used, comparing crude survival, disease-specific survival, and disease-free survival. There was no significant difference between groups. In patients with follicular thyroid cancer and capsular invasion only, 131I ablation does not improve survival compared with patients treated with thyroid hormone suppression only.

Adenocarcinoma↗

PubMed1992

Detection of squamous cell cancer and pre-cancerous lesions by imaging of tissue autofluorescence in the hamster cheek pouch model.

Early detection of invasive and pre-invasive neoplasms of the aerodigestive tract will ultimately improve the management of patients with these lesions. This paper describes the use of quantitative fluorescence imaging of early squamous cell carcinomas in an animal model. Dysplasia, carcinoma in situ and invasive cancers were imaged exploiting tumour autofluorescence. Mapped biopsies were obtained from areas imaged determining a sensitivity of 100% and specificity of 80%. Autofluorescence imaging is an excellent method of detecting neoplasms of the aerodigestive tract.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1992

Correlation of epidermal growth factor receptor and c-erbB2 oncogene product to known prognostic indicators of colorectal cancer.

Both epidermal growth factor receptor (EGFr) and the oncogene product of c-erbB2 have been shown to be expressed by human malignancies, and in some cases to relate to clinical outcomes. This study investigates the correlation between the presence of these receptor proteins and known prognostic indicators of colorectal cancer. Indirect immunoperoxidase staining of 32 freshly frozen surgical specimens revealed an overall expression of EGFr and c-erbB2 of 43% and 38%, respectively. A significantly higher rate of EGFr expression was found in tumours of more advanced stage (Dukes C and D), poor differentiation and those exhibiting vascular and lymphatic invasion. The presence of the c-erbB2 protein did not correlate with any of these variables. Expression of these molecules appeared to be independent and positive staining for both receptors occurred in only 19% of cases. EGFr may play a future role as a prognostic tool in colorectal cancer.

Adult↗

PubMed1991

Clinical parameters predictive of malignancy of thyroid follicular neoplasms.

Needle aspiration biopsy is commonly employed in the evaluation of thyroid nodules. Unfortunately, the cytologic finding of a "follicular neoplasm" does not distinguish between a thyroid adenoma and a follicular cancer. The purpose of this study was to identify clinical parameters that characterize patients with an increased risk of having a thyroid follicular cancer who preoperatively have a "follicular neoplasm" identified by needle aspiration biopsy. A total of 395 patients initially treated at Vancouver General Hospital and the British Columbia Cancer Agency between the years of 1965 and 1985 were identified and their data were entered into a computer database. Patients with thyroid adenomas were compared to patients with follicular cancer using the chi-square test and Student's t-test. Statistically significant parameters that distinguished patients at risk of having a thyroid cancer (p less than 0.05) included age greater than 50 years, nodule size greater than 3 cm, and a history of neck irradiation. Sex, family history of goiter or neoplasm, alcohol and tobacco use, and use of exogenous estrogen were not significant parameters. Patients can be identified preoperatively to be at an increased risk of having a follicular cancer and accordingly appropriate surgical resection can be planned.

Adenocarcinoma↗

PubMed1991

Surgical versus percutaneous drainage of intra-abdominal abscesses.

The records of 83 patients with intra-abdominal abscesses treated between 1986 and 1990 were reviewed to determine if there were significant differences in the outcome of patients treated by surgical drainage (n = 41) or percutaneous drainage (n = 42). The two groups were matched for age, abscess location, and etiology. Parametric statistical evaluations included the Student's t test as well as analysis of variance; nonparametric statistics used were chi-square and Wilcoxon rank sums. No significant difference was found in mortality (surgical 14% versus percutaneous 12%) or morbidity (surgical 26% versus percutaneous 29%). The duration of hospital stay was similar. Although there was no significant difference between the two groups in severity of illness as measured by APACHE II scores, these scores were significant in determining prognosis. APACHE II scores were significantly higher in non-survivors of both groups (23 versus 13) and also higher in those developing complications. A subgroup of patients with diverticular abscess was identified in whom percutaneous drainage enabled later resection with primary anastomosis without complication. This study indicates that percutaneous drainage of an intra-abdominal abscess is as efficacious as surgical drainage and that APACHE II scores are prognostic of both potential mortality and morbidity.

Abdomen↗