Antibody-mediated targeting in the treatment and diagnosis of cancer: an overview

Conjugation of doxorubicin to monoclonal anti-carcinoembryonic antigen antibody via novel thiol-directed cross-linking reagents

In order to improve the available methods to produce an immunoconjugate the use of longer heterobifunctional cross-linking reagents were investigated. Two new maleimidobenzoyl spacers have been synthesized in a one step process from 4-maleimidobenzoic acid. The new heterobifunctional cross-linking reagents were fully characterized by their IR, 1H NMR, 13C NMR and mass spectra. These spacers are selectively attached to NH2-3' of the daunosamine moiety of doxorubicin. The spacer-doxorubicin derivatives were also characterized by 1H NMR spectrometry before coupling to thiol groups of thiolated anti-carcinoembryonic antigen (CEA) monoclonal antibody (11-285-14). These conjugates contain 1.51-3.44 molecules of drug for each molecule of monoclonal antibody (MAb).

Increased yields of IgG2a- and IgG3-secreting hybridomas after fusion of B cells from mice with autoimmune diseases

Hybridoma technology has made the production of antigen-specific monoclonal antibodies feasible and almost routine, but the production of certain biologically desirable antibody isotypes has remained difficult. Three strains of autoimmune mice (MRL/l, NZB, and BXSB) were compared to a normal strain (BALB/c), in fusions with a BALB/c myeloma (NS-1) in order to study the rescue of relevant isotypes with the desired antigenic specificities. Mice from these four strains were immunized with colon carcinoma cells, and the hybridoma supernatants from thirty fusions were analyzed for (1) reactivity with cell surface determinants on the immunizing cell line; and (2) Ig class and subclass isotypes. We found that compared to BALB/c mice, MRL/l mice produced greater numbers, and NZB and BXSB mice comparable numbers, of cell surface-reactive hybridoma clones per fusion. MRL/l mice produced the largest number and highest percentage of cell-surface reactive IgG2a (22.4%) and IgG3 (10.6%) producing clones, followed by NZB mice which produced predominantly IgG2a clones (12.3%). BXSB mice, which have latent autoimmune disease, showed no significant difference from normal BALB/c controls (IgG2a:0.7% and IgG3:1.9% vs. IgG2a:4.8% and IgG3:4.8%). The increase in IgG2a and IgG3 clones derived from MRL/l mice was age-dependent, correlating with the age at which abnormal proliferation of T cell and splenic enlargement occurs (2-4 months). We conclude that MRL/l mice are useful for generating monoclonal antibodies of the IgG2a or IgG3 isotype, provided fusions are performed at the time of maximal lymphoproliferation.

A fluorouridine-anti-CEA immunoconjugate is therapeutically effective in a human colonic cancer xenograft model

5-fluorouridine (FUR), an antineoplastic agent, was site-specifically conjugated to the carbohydrate moiety of a anticarcinoembryonic antigen (CEA) monoclonal antibody (MAb) by using amino-dextran as the intermediate carrier. The final immunoconjugate contains approximately 30-35 molecules of FUR per molecule of immunoglobulin, has immunoreactivity retained as examined by flow cytometry, and is cytotoxic to the target cells as examined by 75selenomethionine incorporation studies. In the GW-39/nude mouse model, the conjugate remained efficient in targeting the human colonic tumor and possessed greater inhibitory growth effects on the subcutaneous tumor than free FUR or an irrelevant antibody conjugate. In addition, the reduced host toxicity of the conjugate may permit the use of this agent in a high-dose therapy of this tumor system.

Interleukin 2 receptor-targeted cytotoxicity. Receptor binding requirements for entry of a diphtheria toxin-related interleukin 2 fusion protein into cells

The receptor binding requirements for entry of the NAD+ ADP-ribosyltransferase component of DAB486-IL 2 into target cells were examined. Experiments utilizing cell lines bearing either high-affinity or individual subunits of the interleukin 2 receptor (IL 2R) as well as human peripheral blood mononuclear cells with natural killer activity demonstrate that the high-affinity receptor facilitates delivery of fragment A from DAB486-IL 2 to the cytosol approximately 1000 times more efficiently than either the intermediate-(p75) or low-affinity (p55) forms of the IL 2R. We show that elongation factor 2 (EF-2) in these cells is not quantitatively or qualitatively altered indicating that the relative resistance to intoxication displayed by IL 2R variant cell lines cannot be attributed to an altered intracellular target of the hybrid toxin. We also demonstrate that an alteration in the binding of DAB486-IL 2 to the p75 subunit of the IL 2R may account for the selective cytotoxicity of DAB486-IL 2 for cells bearing the heterodimeric high-affinity IL 2R.

Chromatography of functionalized liposomes and their components

The antitumour drug 1-beta-D-arabinofuranosylcytosine (ara C) was acylated by means of oleic acid anhydride, resulting in the prodrug N4-oleoyl-ara C. Together with a lipophilic biotin derivative, this lipophilic prodrug was incorporated into the bilayer membrane of unilamellar liposomes prepared by means of the detergent dialysis method. On addition of these biotinylated prodrug-liposomes to an excess of avidin, biotin residues were complexed with avidin. The unreacted avidin was removed by chromatography on the Ultrogel AcA-22 column. The prodrug-liposome-avidin complex was coupled to biotinylated monoclonal antibodies through the free binding sites of the immobilized avidin. Unreacted antibodies were removed by chromatography on an Ultrogel AcA-22 column. In vitro, the liposome-antibody complexes selectively bound to cells which were recognized by the monoclonal antibodies linked to the liposomes. For this reason, a promising strategy towards a specific chemotherapy of cancer is expected.

Interleukin 2 receptor-targeted cytotoxicity. Interleukin 2 receptor-mediated action of a diphtheria toxin-related interleukin 2 fusion protein

The IL-2 toxin-mediated inhibition of protein synthesis in high affinity IL-2-R-positive murine and human T cell lines has been examined. Both excess free IL-2 and mAb to the Tac epitope of the p55 subunit of IL-2-R are shown to block the action of IL-2 toxin; whereas, agents that interact with other receptors or antigens on the T cell surface have no effect. We show that IL-2 toxin, like diphtheria toxin, must pass through an acidic vesicle in order to intoxicate target T cells. Finally, we demonstrate that the IL-2 toxin-mediated inhibition of protein synthesis in both human and murine T cells that bear the high affinity IL-2-R is due to the classic diphtheria toxin fragment A-catalyzed ADP ribosylation of elongation factor 2.