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Biomedical subjects

P A Keep

Publications and source records attributed to P A Keep.

32 records · Page 2Linked to original sources
PubMed1984

Analysis of radioimmunodetection of tumors by the subtraction technique.

The subtraction method for radioimmunodetection (RID) of cancer is showing potential as a diagnostic tool. An objective assessment of this technique is needed in order to determine its clinical usefulness. A numerical analysis of the RID scintigrams was developed and applied to 21 RID studies on 20 patients for whom a final diagnosis had been established. The subtraction technique was shown to give rise to artifactual positive regions, which could be avoided by experienced clinicians. When artifact-producing regions were excluded, 97 regions were examined (80 nontumor, 17 tumor-containing). The "background" scintigrams were shown to be good models for nontumor regions of the antibody scintigrams, and tumor and nontumor regions were shown to form statistically distinct groups.

Antibodies↗
PubMed1983

Improved radioimmunodetection of tumours using liposome-entrapped antibody.

The discrimination of radioimmunodetection of tumours is reduced by the presence of circulating radiolabelled antibody (primary antibody). We have prepared liposomes containing an antibody to the primary antibody (secondary antibody), with the intention of complexing and delivering to the liver primary antibody which is not associated with the tumour. In mice bearing xenografts of human tumours which secrete the marker carcinoembryonic antigen (CEA), liposomally entrapped secondary antibody was able to reduce the blood levels of 125I-labelled anti-CEA within 2 h, without reducing the amount of anti-CEA bound to the tumour. We therefore suggest that the use of liposomally entrapped secondary antibody would improve the diagnostic potential of radioimmunodetection of tumours and their metastases.

Animals↗
PubMed1983

A comparison of the content and immunohistochemical patterns of CEA-like activity in human colorectal tumours and nude mouse xenografts.

The immunohistochemical pattern of CEA-like material was examined in sections of five human colonic tumour xenograft lines in nude mice and in the primary tumours from which these lines were derived. Conventional tissue sections were stained by a PAP immunoperoxidase technique, using affinity purified goat anti-CEA as the primary reagent. Normal human and nude mouse tissues were also examined. Saline extracts were made from three of the human tumours and from examples of the respective xenograft lines. The CEA content of extracts was determined by radioimmunoassay. The pattern of CEA-like material was similar in primary tumours and xenografts, but in 3/5 xenograft lines the intensity of specific staining was reduced when compared to that of the respective primary tumour. The three xenograft lines from which extracts were made contained mean values of 22%, 63% and 68% of the CEA activity found in the respective primary tumours, and the data suggested that reduced immunoperoxidase stain intensity seen in some xenografts resulted from the presence of far less antigen than in the corresponding primary tumour. We suggest that some xenograft lines represent subpopulations of cells in the primary tumour which produce less CEA than those of the primary tumour sample examined, although histologically no differences can be identified. No CEA-like activity was detected in normal nude mouse tissues.

Animals↗
PubMed1983

Clearance of injected radioactively labelled antibodies to tumour products by liposome-bound second antibodies.

Liposomes containing anti-goat immunoglobulin were injected 24 h after administration of 125I-labelled goat antibody against the carcinoembryonic antigen (anti-CEA) to groups of nude mice bearing human tumour xenografts, and normal mice. Controls in each group received radioactively labelled anti-CEA only. In liposome-treated mice, blood 125I levels were lower than those of controls 30 min to 24 h after liposome administration, with corresponding accumulation of 125I activity in the liver and spleen for the first 2 h after liposome injection. [14C]Cholesterol or 99mTc labels in the bilayer were eliminated rapidly from the blood, with uptake in the liver and spleen. In xenograft-bearing mice, 125I activity detected in the tumours up to 6 h after liposome injection was identical to that detected in the tumours of controls. However, 24 h after liposome injection a reduction in the tumour concentration of 125I-labelled anti-CEA was obtained, but the tumour/blood radioactivity was still increased. In two mice given 27 mumol lipid, the blood radioactivity count after 24 h was only 5% of that in the controls. In rabbits, 2 h after administration of liposomes containing anti-goat second antibody, the circulating 125I activity had dropped by 28-40%. The results suggest that administration of liposome-entrapped second antibody approximately 2 h prior to external scintigraphy may clear circulating radioactively labelled primary antibody by up to 50%.

Animals↗
PubMed1982

Liposomally entrapped second antibody improves tumour imaging with radiolabelled (first) antitumour antibody.

The usefulness of antibodies directed against tumour products for localisation and therapy of cancer is limited by the large proportion of administered antibody which remains non-specifically in the circulation and extravascular space. Liposomally entrapped second antibody (LESA) directed against the first (antitumour) antibody has been used to accelerate clearance of non-tumour-bound first antibody without affecting its clearance from the tumour. Intravenously administered LESA binds the first antibody and LESA is cleared by the reticuloendothelial system. LESA accelerated clearance of radiolabelled antibody directed against carcinoembryonic antigen (CEA) from the circulation in four of five patients with gastrointestinal cancer, enhancing gamma-camera imaging of the tumour in three of them. These results suggest that LESA can improve the sensitivity and specificity of tumour imaging with radiolabelled antitumour antibody. This strategy may also have the potential to improve the therapeutic ratio of some toxic agents linked to antitumour antibody.

Adolescent↗
PubMed1982

The use of cellulose carbonate-based immunoadsorbents in the isolation of minor allotypic components of rabbit immunoglobulin populations.

Cellulose trans-2,3-carbonate has been used as a new insoluble matrix for the simple coupling of a1- and b4-positive rabbit immunoglobulin to make immunoadsorbents capable of purifying from serum, with great efficiency, alloantibodies to these allotypic determinants. The antibodies have themselves been conjugated to prepare specific antibody immunoadsorbents of high binding activity for their allotypic target molecules. With these anti-allotypic solid-phase reagents it has been possible to affinity purify a1- and b4-positive immunoglobulin molecules and to deplete serum immunoglobulin of these molecules to leave in the eluates only the allotypically uncontaminated minor immunoglobulin components which are a-negative or b-negative (lambda chain-bearing) molecules. lambda chain molecules were also purified in very small quantities by affinity chromatography on a sheep anti-rabbit lambda chain column. This method of purifying minor populations of rabbit immunoglobulin from normal serum by special immunoadsorbent applications offers new opportunities to study the products of rarely expressed immunoglobulin genes in normal rabbits.

Animals↗
PubMed1982

The distribution of parenterally administered antibody to CEA in colorectal xenografts. Preliminary findings.

Autoradiography was used to identify the distribution of parenterally administered anti-CEA in human colorectal tumours xenografted to nude mice. Four xenograft lines were studied: three mucinous adenocarcinomas of various degrees of differentiation and one undifferentiated tumour. 125Iodine-labelled, affinity purified goat anti-CEA was given intravenously to xenograft-bearing mice, who were killed at intervals thereafter up to 7 days. Autoradiograms were prepared by both conventional methods and the Appleton 'diffusible compound' technique which is designed to avoid possible translocation and extraction of labelled antibody tracer during tissue processing. Control experiments were done using a non-specific goat gamma-globulin. By combining autoradiography with a PAP-immunoperoxidase method of demonstrating CEA, anti-CEA was found to be preferentially retained at extracellular sites of CEA-positive material within viable tumour areas. Cell surface retention was not observed. At all times following administration more antibody was detected within necrotic areas, extracellular spaces and stromal connective tissue than within the tumour cell compartment. These preliminary results are discussed in relation to the possibility of using anti-CEA as a carrier to deliver chemotherapeutic agents into colorectal tumours. The suitability of diffusible compound and conventional autoradiography for studies of this nature are also examined.

Animals↗
PubMed1981

Application of monoclonal antibodies to purified CEA in clinical radioimmunoassay of human serum.

Double-antibody radioimmunoassay using a mouse monoclonal anti-CEA (MA/1) has been used to measure CEA in human serum. Low levels of MA/1-binding CEA have been found in serum from normal individuals and moderately raised levels are sometimes associated with certain non-malignant diseases. As with conventional anti-CEA, the MA/1 antibodies can recognize significant amounts of CEA in serum from patients with a variety of solid tumours. However they appear to recognize a different immunodeterminant and possibly a different population of CEA molecules to, or a subset of, those measured by two routine assays. Studies in which the MA/1 assay was directly compared with the results of the Charing Cross routine and Abbott EIA assays have indicated that different immunological forms of CEA may be expressed in the course of tumour progression but no prognostic value was evident in this study. Our results stress the need to resolve immunological specificities expressed by CEA-like molecules and evaluate their clinical importance.

Adult↗
PubMed1981

Relationship of serum CEA levels to tumour size and CEA content in nude mice bearing colonic-tumour xenografts.

The relationship of serum carcinoembryonic antigen (CEA) levels to tumour size and antigen content was studied in nude mice bearing well differentiated, mucinous human colonic-tumour xenografts. Blood samples were taken from normal nude mice and others bearing xenografts, whose size had been calculated from in vivo measurements; saline and KCl extracts were made of a proportion of these tumours. Sera and tissue extracts were assayed for CEA activity by double-antibody radioimmunoassay. Extracts were also made from the livers and spleens of tumour-bearing and normal nude mice. All normal sera and 78% of sera from tumour-bearing animals had CEA values less than 11.4 ng/ml. No clear correlation was found between serum CEA levels greater than 11.4 ng/ml and tumour size or weight, or between serum CEA and tumour CEA concentrations or total CEA burden. The concentration of CEA in those tumours tested varied from 1 to 22 microgram/g. Our results confirm and extend the conclusions reached by others (Stragand et al., 1980) studying the significance of serum CEA levels with xenograft model systems. The complexity of factors contributing to circulating CEA is discussed in the light of our findings.

Animals↗
PubMed1978

Extraction of CEA from tumour tissue, foetal colon and patients' sera, and the effect of perchloric acid.

The use of perchloric acid and water for the extraction of CEA from tumour and foetal tissues has been investigated. In the case of tumour, lower recoveries of CEA were obtained from perchloric acid extracts than from aqueous extracts of the same tissue. CEA has also been extracted with 3M KCl solution from insoluble perchloric acid residues of tumour homogenates and cancer patients' serum. Whilst a large proportion of CEA activity recovered from tumour was associated with the perchloric acid residue, the corresponding amounts from serum were very small. CEA elution volumes for each extract, obtained by assay of Sephadex G-200 column fractions, showed significant heterogeneity in molecular size. The purified CEA pools also showed quantitative variations in the binding profiles on Con A-Sepharose. It has been shown that perchloric acid modifies the carbohydrate in CEA, thus altering its Con A-binding properties. Preliminary experiments with foetal colon have demonstrated that, unlike colorectal CEA, a significant proportion of foetal CEA was not bound to ConA. Comparative immunodiffusion showed immunological identity of CEA from the various extracts, although the purified aqueous extract produced an additional precipitin reaction, indicating a second antigen which is relatively unstable or less soluble in perchloric acid.

Bronchial Neoplasms↗