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M J Embleton

Publications and source records attributed to M J Embleton.

At least 37 records · Page 2Linked to original sources
PubMed1990

A bispecific monoclonal antibody against methotrexate and a human tumour associated antigen augments cytotoxicity of methotrexate-carrier conjugate.

A bispecific monoclonal antibody, reactive with methotrexate (MTX) and a tumour associated antigen (gp72) has been produced by fusing spleen cells from MTX immunised mice with 791T/36/3 (anti-gp72) hybridoma. The hybrid antibody was purified from anti-MTX and anti-gp72 antibodies present in the hybridoma culture supernatant by combinations of affinity chromatography on a MTX-agarose immunoabsorbent and stepwise acid elution from Sepharose-Protein A. A particular feature of the present antibody is that it reacts with conjugated MTX; this would allow in vivo targeting of conjugates, increasing many fold the number of molecules of drug carried or localising to pre-targeted antibody. Dual binding between tumour cell surface antigen and MTX was demonstrated by the ability of the hybrid antibody to bridge between tumour cells and MTX as MTX-HSA conjugate, reaction here being detected by flow cytofluorimetry. Purified hybrid antibody specifically enhanced the in vitro cytotoxicity of MTX-HSA for gp72 positive tumour cells.

Antibodies, Monoclonal↗
PubMed1989

Heterogeneity of hepatocyte antigen expression in rat liver carcinogenesis: concordance between neoplastic nodules and tumours.

Fischer F344 rats were given a cyclical diet of 0.06% 2-acetylaminofluorene (AAF), which progressively induced oval cell proliferation, cirrhosis and hyperplastic (or neoplastic) nodules. Primary liver tumours developed from 7 months after ceasing the diet. Liver samples taken during and after AAF administration and specimens of primary tumours were processed into frozen sections and examined microscopically for morphological changes in cell populations, stained histochemically for gamma-glutamyl transpeptidase (GGTase) and four phosphatases, and stained by the immunoperoxidase technique for the presence of antigens detected by seven anti-liver cell monoclonal antibodies and monoclonal antibodies to six oncoproteins. During and after AAF treatment several of the anti-liver antibodies revealed foci of aberrantly or heterogeneously-stained cells, although anti-oncoprotein antibodies showed no consistent changes. Foci of cells positive for GGTase and heterogeneous for adenosine triphosphatase (ATPase) were also seen. Nodules invariably showed heterogeneous antigenicity, raised GGTase and abnormal ATPase expression. Primary tumours exhibited varying degrees of positivity, negativity and heterogeneity with the anti-liver monoclonal antibodies, and all were positive for GGTase. Comparison between various parameters and different lesions showed the greatest concordance between nodules and tumours, suggesting that nodules are probably the precursors of malignant tumours in this system.

2-Acetylaminofluorene↗
PubMed1988

Reactivity of monoclonal antibodies to oncoproteins with normal rat liver, carcinogen-induced tumours, and premalignant liver lesions.

Monoclonal antibodies to proteins encoded by the ras, myb, myc, erb-B, src and PDGF-2 genes were tested for reactivity with normal rat liver, livers from rats fed with 0.06% 2-acetylaminofluorene (AAF), and premalignant lesions and primary liver tumours from rats given AAF alone or a combined treatment with diethylnitrosamine and AAF. Radioimmunoassays were performed with plasma membrane fractions and total soluble subcellular extracts of the tissues, and immunoperoxidase staining was carried out on frozen tissue sections. All of the antibodies were positive in radioimmunoassays, some more strongly than others, and each antibody bound equally to extracts of different kinds of tissue. Immunohistology revealed significant staining of normal liver by 5 of the 6 antibodies, and only minor qualitative differences of the staining pattern in some tumours and hyperplastic nodules. It was concluded that these antibodies were not able to discriminate sufficiently well between normal, premalignant and malignant rat liver to be of value in identifying the precursor cells of malignant tumours.

2-Acetylaminofluorene↗
PubMed1987

Conjugates of monoclonal antibody 791T/36 with methotrexate in cancer therapy.

The design and evaluation of drug-antibody conjugates for tumor therapy is considered with respect to the use of the anti-human osteogenic sarcoma monoclonal antibody designated 791T/36. Conjugates have been constructed by linking antibody to methotrexate; the agent has been linked to antibody, either directly or via a human serum albumin bridging agent. In each case, conjugates have been assessed for retention of antibody reactivity with osteogenic sarcoma target cells by comparing their capacity with that of unmodified antibody in competing with fluorescein isothiocyanate-labeled 791T/36 binding, as measured by flow cytometry. Retention of drug cytotoxicity was evaluated by in vitro cytotoxicity and colony inhibition assays. Conjugates with acceptable retention of drug and antibody reactivities were then examined for in vivo suppression of human tumor xenografts.

Animals↗
PubMed1986

Unsuitability of monoclonal antibodies to oncogene proteins for anti-tumour drug-targeting.

Monoclonal antibodies (MAbs) to ras, sis, erb-B, src, myb and myc oncoproteins were evaluated for their potential to target anti-cancer drugs to malignant cells. Each antibody was tested for reactivity against both fixed and viable cultured human tumour cells by immunofluorescence, and all reacted against a variety of fixed tumour cell preparations. Reactions were also observed against fixed non-malignant cells. None, however, reacted significantly with viable cells. Two antibodies (against ras and myc proteins) were tested for their ability to localize to tumour xenografts in nude mice, and conjugates were constructed by linking these antibodies to methotrexate using human serum albumin as an intermediate carrier. Neither antibody localized to tumour in vivo, and the methotrexate conjugates were not significantly cytotoxic for tumour cells in vitro, in contrast to similar conjugates simultaneously prepared with a proven anti-tumour MAb (791T/36). It was concluded that currently available MAbs to oncogene proteins are not suitable vectors for targeting cytotoxic agents to tumour cells.

Antibodies, Monoclonal↗
PubMed1986

Differentiation between monoclonal antibody-defined antigens on a human osteogenic sarcoma cell line (791T) and tumor-localizing properties of the anti-791T/36 antibody.

Two monoclonal antibodies (anti-791T/36 and anti-791T/48) prepared against an osteogenic sarcoma cell line (791T) following xenogeneic immunization, reacted against the immunizing tumor, but not against normal cells from the tumor-donor, using an indirect 125I-protein A binding assay. Both antibodies cross-reacted with a small number of other osteogenic sarcomas and a few unrelated cell lines from an extensive panel, but the specificity of these cross-reactions was different. Both antibodies were labelled with 125I to detect direct binding to target cells, and the specificity of their reactivity was essentially identical to that observed in the indirect assay. Direct binding of each labelled antibody was inhibited by pretreating target cells with its unlabelled counterpart, but the two antibodies could not inhibit each other. The binding of anti-791T/36 was also not inhibited by pretreating the target cells with sera from the 791-T-tumor donor, which were shown to contain antibody reacting with the autochthonous tumor. It is concluded that 791T has two distinct tumor-associated antigens recognized by the monoclonal antibodies, and furthermore that at least one of these antigens is independent of those recognized by the patient from which the tumor cell line was derived. The efficacy of anti-791T/36 antibody labelled with radioactive iodine was demonstrated for localizing tumor deposits growing in immunodeprived mice.

Animals↗
PubMed1986

Sensitivity and selectivity of ricin toxin A chain-monoclonal antibody 791T/36 conjugates against human tumor cell lines.

Ricin toxin A chain (RTA) was conjugated to monoclonal antibody 791T/36, which was raised originally against human osteogenic sarcoma cell line 791T. The resultant conjugates were characterized and tested for cytotoxicity against a panel of human tumor cell lines representing a defined range of antigenicity with regard to 791T/36. Conjugates were highly cytotoxic for cells expressing high antigen density, inhibiting cell survival at RTA concentrations three to four orders of magnitude lower than that possible with RTA alone. Cytotoxicity of conjugates diminished with decreasing 791T/36 antigen concentration on target cells, but significant effects were seen against cells of low or intermediate antigenicity. Cytotoxicity could be blocked specifically by excess 791T/36 antibody, clearly indicating that antigen binding was a necessary part of the mechanism of action. Comparison with drug-antibody conjugates indicated that RTA immunotoxins are much more active, but discriminate less readily than drug-antibody conjugates between cells of different antigenicity. It is suggested that these properties be taken into account with regard to practical application and future development.

Antibodies, Monoclonal↗
PubMed1985

Antitumor properties of vindesine-monoclonal antibody conjugates.

The anticancer alkaloid vindesine (VDS) was conjugated to four mouse monoclonal antibodies recognizing human tumor-associated antigens. The antibodies were 96.5 (antimelanoma, IgG2a); 791T/36 (antiosteogenic sarcoma, IgG2b); 11.285.14, and 14.95.55 (anticarcinoembryonic antigen, IgG1 and IgG2a respectively). Conjugates VDS-96.5 and VDS-791T/36 were tested in vitro and shown to be specifically cytotoxic for target cells expressing the appropriate antigen. The in vivo effects of the antibodies and conjugates were tested against human tumor xenografts in athymic or immunodeprived mice using multiple treatments. Conjugate VDS-96.5 retarded the initial growth of a melanoma xenograft, whereas free antibody was without effect. Similarly, VDS-791T/36 but not free antibody retarded the growth of osteogenic sarcoma 791T. The most marked antitumor effects observed were those obtained with VDS conjugates of the anti-CEA antibodies against a colorectal tumor xenograft. Antibody 14.95.55 suppressed tumor growth both alone and as a VDS conjugate, whereas 11.285.14 produced only a slight effect alone but an almost complete and lasting suppression of tumor growth as a VDS conjugate. Free VDS had little effect at nontoxic levels. Acute studies showed that VDS-11.285.14 conjugate was considerably less toxic than free VDS in Balb/c mice.

Animals↗
PubMed1985

Studies on the mechanism of action of an antibody-targetted drug-carrier conjugate.

A conjugate of methotrexate-substituted human serum albumin (HSA) coupled to a monoclonal antibody (791T/36) recognizing osteogenic sarcoma cell lines has been reported previously to have good cytotoxicity and specificity in vitro (Garnett et al., 1983). Cytotoxicity was assessed by the median inhibition (IC50) of [75Se]selenomethionine uptake resulting from a 24-h incubation of conjugate with antigen-bearing 788T or 791T osteogenic sarcoma cell lines. In the present work, the properties of this conjugate have been investigated to determine whether cytotoxicity is optimal with respect to binding activity, and aspects of the mechanism of action investigated by the effects of specific inhibitors of biochemical processes on conjugate cytotoxicity. Conjugate cytotoxicity was reduced by ammonium chloride suggesting that endocytosis and an acidic internal compartment were involved in the mechanism of action. The specific inhibitors of proteinases leupeptin and E64 also reduced conjugate cytotoxicity, while the inhibitors pepstatin A and chymostatin had no effect, demonstrating that cysteine proteinases were involved. The inhibitor of methotrexate transport, folinic acid, reduced the cytotoxicity of conjugate more than that of free methotrexate whereas folic acid had no effect on either, indicating that the methotrexate transport system may still be involved but in a different manner to the free drug. The cytotoxicity of these conjugates is probably near optimal for maximum selectivity.

Antibodies, Monoclonal↗
PubMed1984

Immunohistochemical localization of Y hapten and the structurally related H type-2 blood-group antigen on large-bowel tumours and normal adult tissues.

The monoclonal antibody C14/1/46/10 which defines the Y hapten carbohydrate antigen (Brown et al., 1983) was shown, by the indirect immunoperoxidase technique, to stain tissue sections of 96% of colo-rectal adenocarcinomas and 100% of colo-rectal adenomas. In contrast, a monoclonal antibody defining the related H type-2 blood-group antigen was found to stain 86% of adenocarcinomas and 32% of adenomas. In adenocarcinomas the percentage of cells stained for both antigens was, on average, greater in group O than in group A patients. In adenomas a focal pattern of expression was observed, for both Y hapten and H type-2 antigen, that was characteristic of group A but not group O adenocarcinomas. In the normal mucosa of the distal colon, whilst H type-2 antigen was absent, Y hapten was found in the immature cells of the crypt bases. A comparison of the cellular phenotypes present in adenocarcinomas, adenomas and normal mucosa of the distal colon supports the adenoma-carcinoma sequence hypothesis for the genesis of colo-rectal carcinomas. In normal adult tissues Y hapten was predominantly found on epithelial cells whilst nervous tissues, muscles and connective tissues were negative. The expression of Y hapten in several positive tissues was dependent upon secretor status. A comparison of the expression of Y hapten and H type 2 antigen on normal adult tissues revealed that all of the permutations of expression of these two structurally related antigens were possible.

ABO Blood-Group System↗
PubMed1984

Antigenicity and drug susceptibility of human osteogenic sarcoma cells "escaping" a cytotoxic methotrexate-albumin-monoclonal antibody conjugate.

Cells of osteogenic sarcoma line 791T were treated in vitro with a selectively cytotoxic methotrexate-human serum albumin-monoclonal antibody conjugate at concentrations which were toxic but allowed the "escape" of a small number of tumour cell colonies (less than 0.3% compared with controls). These colonies were propagated as clones in order to test their expression of the monoclonal antibody ( 791T /36)-defined antigen and their resistance to methotrexate (MTX) by comparison with parental cells. Most of the conjugate-treated clones were incapable of prolonged growth and died out, in contrast to untreated 791T clones which virtually always grow progressively. Only four treated clones grew at rates comparable with the parental line. Flow cytofluorometric analysis indicated that the surviving clones expressed normal or enhanced amounts of 791T /36-defined antigen and clonogenic assays demonstrated that they were sensitive to cytotoxicity by MTX. As could be predicted from these results, further exposure to the conjugate inhibited growth of the clones at doses comparable with those active against parental 791T cells. It is concluded that tumour cell clones emerging after exposure to a toxic concentration of a drug-antibody conjugate are not necessarily modified resistant clones, but may have severely impaired long-term growth potential or be susceptible to further contact with the same conjugate.

Antibodies, Monoclonal↗
PubMed1984

Monoclonal antitumour antibodies for tumour detection and therapy.

The potential of anti-tumour monoclonal antibodies for tumour detection and therapy are considered. Immunoscintigraphy of patients following injection of monoclonal antibodies labelled with gamma-emitting radionuclides has been successfully used to detect a range of human cancers including carcinomas of colon, breast and ovary and osteogenic sarcomas. This application of monoclonal antibodies is considered with respect to the design of imaging procedures and the clinical usefulness of the techniques. Another potentially useful application of anti-tumour monoclonal antibodies is for targeting therapeutic agents. This approach is considered particularly with respect to the use of antibodies for targeting cytotoxic drugs.

Animals↗
PubMed1984

Experience in the preparation and experimental use of immunocytostatics.

Vindesine (VDS) was coupled directly to a monoclonal antibody (791T/36) raised against a human osteogenic sarcoma cell line, and methotrexate (MTX) was coupled to 791T/36 via an intervening human serum albumin (HSA) bridge. Both the VDS-791T/36 and MTX-HSA-791T/36 conjugates were cytotoxic in vitro specifically for tumour target cells expressing the 791T/36-defined antigen, while the free drug in each case was indiscriminately toxic to all target cells. The VDS-791T/36 conjugate retarded growth of osteogenic sarcoma xenografts in immunodeprived mice when administered in multiple doses. Free 791T/36 did not significantly affect tumour growth. VDS was tumour inhibitory, but was toxic to the mice at a total dose of 20 micrograms per kg body weight, while VDS-791T/36 conjugate was not toxic at total doses incorporating VDS at up to 45 mg per kg. It is suggested that this is due to selectivity conferred upon the conjugate by the antibody moiety, and that such conjugates may offer considerable potential as anti-cancer agents.

Animals↗
PubMed1984

Antibodies against osteosarcoma and colon cancer.

Two monoclonal antibodies with anti-human tumour reactivity were produced by murine hybridomas. One, 791T/36, is an IgG2b which was raised against a cultured human osteogenic sarcoma cell line, 791T. This antibody reacts with a high proportion of osteogenic sarcomas, and also with other tumour types. It has been used successfully as a tumour localising antibody in vivo and a targeting agent in vitro. The other antibody, C14/1/46, was raised against a human colonic adenoma. An IgM antibody, it reacts with most colorectal carcinoma cells but only with a small subpopulation of cells within the normal mucosa. It has been shown to recognise a difucosylated Type-2 blood-group chain, which has raised expression in colorectal carcinoma tissue.

Animals↗