Antibodies as carriers of cancer chemotherapeutic agents

Inhibition of human renal cancer by monoclonal antibody targeted methotrexate-containing liposomes in an ascites tumor model

The monoclonal antibody DAL K29 against a human renal cell carcinoma associated cell surface antigen was covalently linked to small unilamellar lipid vesicles (SUV) containing the antifolate, methotrexate (MTX), with full retention of antibody activity. In an ascites tumor model developed after intraperitoneal inoculation of 5 x 10(6) cells of the human kidney cancer line Caki-1 per pristane primed nude mouse, the DAL K29 linked MTX-containing SUV was a more potent tumor inhibitor (P less than 0.0005) than the drug or MAB alone, MTX-containing SUV, a mixture of DAL K29 and MTX-containing SUV or MTX-containing SUV linked to an isotype matched nontumor specific IgG.

Antibody mediated targeting of radioisotopes, drugs and toxins in diagnosis and treatment

The recent resurgence of interest in site specific delivery of radioisotopes, chemotherapeutic drugs and toxins for the diagnosis and treatment of cancer, and for the selective manipulation of the immune system, can be directly related to the need for improved diagnosis and the fact that for many cancers, for example lung, colon and gastric, the conventional treatments of surgery, radiotherapy and chemotherapy have reached a plateau in terms of the number of patients cured. To date, because of their specificity, the major emphasis has been on the use of antibodies as carriers and extensive in vitro, in vivo preclinical and clinical evaluation is underway. The aim of this article is to review recent progress, highlight avenues being explored to overcome limitations and to indicate new approaches that are evolving in antibody mediated targeting.

Priorities in experimental therapeutics--a surfeit of riches

Experimental therapeutics plays a key role in determining which areas of basic biological research are developed to see if they can be of use in cancer medicine. The recent expansion in our basic knowledge about biology and cancer makes difficult the choice of what areas should be developed. Six such areas are reviewed and assessed. Several hold the promise of improving the management of cancer. More important, developmental therapeutics itself adds to our basic knowledge of cancer and this in turn may indicate those areas which, if developed, will lead to cure of this disease.

Inhibition of human renal cancer by methotrexate linked to a monoclonal antibody

The monoclonal antibody DAL K29 against a human renal cell carcinoma associated cell surface antigen was covalently linked to the antifolate methotrexate with full retention of antibody reactivity and partial retention of drug activity. In a colony inhibition assay, antibody-conjugated methotrexate was 400% more potent in inhibiting the growth of the human kidney cancer line Caki-1 than equimolar amounts of the free drug. Comparable amounts of the antifolate linked to normal mouse IgG did not inhibit the growth of Caki-1 cells. Furthermore, the methotrexate-DAL K29 conjugate had no effect on the two nontarget human cell lines tested, melanoma M21 and B cell leukemia D10-1 cells, even when the conjugate contained amounts of methotrexate equivalent to the 50% inhibitory concentration of the free drug for the nontarget cell lines or an amount equivalent to the 50% inhibitory concentration of the conjugated drug for Caki-1 cells.

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.

Selective killing of T lymphocytes by phototoxic liposomes

Two-fold specificity in drug delivery obtained through the localized activation of drugs by physical means and the attachment of drugs to proteins that bind to target cells might be used for highly selective cancer chemotherapy or for immunosuppression. Toward this end, a monoclonal antibody against an antigen on the surface of T lymphocytes was covalently attached to liposomes containing a phototoxic drug, pyrene, bound to the lipid bilayer. When unfractionated peripheral blood lymphocytes, or B- and T-cell lines, were irradiated after treatment with these liposomes, T cells were killed while B cells were spared, demonstrating the validity of the approach in a simple in vitro assay.