Induction of apoptosis by cross-linking antibodies bound to human B-lymphoma cells: expression of Annexin V binding sites on the antibody cap.

Unlabelled: There are many reports that cross-linking antibodies (Abs) bound to the surface of B-lymphoma cells can induce apoptosis and/or cell death, especially with anti-CD20 Abs. This study was intended to extend our understanding of these effects. To determine if CD20 is a unique target in this respect, or whether Abs to other antigens would have similar effects, six Abs were tested, with and without cross-linking with a secondary Ab, on three target cell lines.

Characterization of antibody-containing vesicles shed from B-lymphoma cell lines: exposure of annexin V binding sites.

Antibodies (Abs) to CD20 or HLA-DR, after binding to the B-lymphoma cell line RL following an overnight incubation at 37 degrees C, accumulate in the form of shed vesicles, which develop in the center of the cell clusters that are spontaneously formed by this cell line. These vesicles coalesce into fairly stable large structures, which we refer to as conglomerates of shed vesicles (CSVs). In the present study, we have extended our previous investigations into the nature of this material.

Deferoxamine as a chelator for 67Ga in the preparation of antibody conjugates.

(67)Ga antibodies (Abs) have been shown to be effective agents for single-cell killing due to the Auger electrons emitted, but their specific activities have not been as high as desired. We therefore evaluated deferoxamine (DFO) as a chelator, as opposed to the cyclic chelator NOTA, which was used previously. Use of DFO for Ab conjugation to (67)Ga was reported previously by several laboratories.

In vitro cytotoxicity of carcinoma cells with 111In-labeled antibodies to HER-2.

Antibodies conjugated to radionuclides emitting low-energy electrons, which include Auger electrons and some conversion electrons, were recently shown to efficiently kill cells bearing a high density of the antigen recognized. The primary purpose of this study was to determine if such killing could be obtained with anti-HER-2 antibodies conjugated to (111)In, using the chelator benzyl-diethylenetriaminepentaacetic acid, or (125)I. Target cells were the breast carcinoma SK-BR-3 and the ovarian carcinoma SK-OV-3.

177Lu-antibody conjugates for single-cell kill of B-lymphoma cells in vitro and for therapy of micrometastases in vivo.

Antibodies (Abs) conjugated to 177Lu, a relatively low-energy beta-particle emitter, were evaluated in vitro for their cytotoxic activity and in vivo for their therapeutic activity against disseminated B-cell lymphoma xenografts in SCID mice. 177Lu was compared with other beta-particle emitters ((131)I and 90Y), and also with emitters of low-energy electrons (LEEs, meaning Auger and conversion electrons of < 50 keV). The Abs used reacted with CD20, CD74 or HLA-DR, and the target cell was the Raji B lymphoma.

Therapy of small subcutaneous B-lymphoma xenografts with antibodies conjugated to radionuclides emitting low-energy electrons.

Purpose: Radionuclides emitting low-energy electrons (Auger and conversion electrons of <50 keV) are potentially useful for cancer therapy when conjugated to an antibody, because they can irradiate the cell to which they bind while producing relatively little irradiation of surrounding cells and tissues. We showed previously the ability of such antibody conjugates to treat micrometastatic, disseminated human B-lymphoma in a severe combined immunodeficient mouse model using an anti-CD74 antibody. In this study, we have evaluated the ability of such conjugates to treat s.

In vitro toxicity of A-431 carcinoma cells with antibodies to epidermal growth factor receptor and epithelial glycoprotein-1 conjugated to radionuclides emitting low-energy electrons.

Purpose: The ability of antibodies (Abs) conjugated to radionuclides emitting low-energy electrons to specifically kill nonadherent lymphoma target cells in vitro was demonstrated previously. This study extends this work to adherent carcinoma cells. The fact that these cells are spread out on plastic can potentially make it more difficult to deliver radiation to the nucleus from decays in the cytoplasm or on the cell surface.

Experimental therapy of disseminated B-Cell lymphoma xenografts with 213Bi-labeled anti-CD74.

A (213)Bi-labeled antibody to CD74 was evaluated as a therapeutic agent for B-cell lymphoma. The alpha-particle emission, with a half-life of 46 min, is appropriate for therapy of micrometastases. The labeled Ab retained full immunoreactivity, and was potent at single-cell kill of the Raji B-lymphoma cell line.

A comparison of 4 radionuclides conjugated to antibodies for single-cell kill.

Unlabelled: We previously found that (67)Ga was more potent and more specific in single-cell kill than other Auger electron emitters and beta-particle emitters, using an anti-CD74 antibody (Ab) (major histocompatibility complex [MHC] class II invariant chain). Because anti-CD74 Abs follow an unusual processing pathway, with rapid delivery in very large amounts to lysosomes, it was important to determine if similar results would be obtained with other, more typical Abs.

Methods: Target cells were Raji B-lymphoma cells, and the Abs tested were antimature MHC class II antigen (lacking the invariant chain) and anti-CD20, both of which react with high-density antigens.

Rapid blood clearance of injected mouse IgG2a in SCID mice.

SCID mice were found to have rapid blood clearance of injected mouse IgG2a antibodies (Ab), while IgG1 Ab were cleared normally. This effect varied depending on the strain of SCID mice, being very rapid in most Taconic ICR mice and slower in C.B-17 mice.

Intracellular accumulation of the anti-CD20 antibody 1F5 in B-lymphoma cells.

In previous experiments, 125I-labeled 1F5 (anti-CD20)was found to kill B-lymphoma cells efficiently and specifically.Unexpectedly, the number of antibody (Ab) molecules taken up per cell was much larger than the number of antigen sites on the cell surface. The present studies were designed to explain this apparent discrepancy.

Antibody localization to B-cell lymphoma xenografts in immunodeficient mice: importance of using residualizing radiolabels.

Antibody (Ab) localization to Raji B-cell lymphoma xenografts in severe combined immunodeficient (SCID) mice was investigated using three Abs: anti-CD20; anti-CD147; and anti-MHC class II. These antigens are all high-density cell surface antigens, and the Abs are all considered to be slowly internalized and catabolized, with catabolism primarily due to the basal turnover rate of cell surface constituents. Unexpectedly, specific Ab uptake was demonstrated only when residualizing labels were used.

Use of galactosylated-streptavidin as a clearing agent with 111In-labeled, biotinylated antibodies to enhance tumor/non-tumor localization ratios.

Optimal tumor imaging using radiolabeled antibodies (Abs) depends on obtaining the highest possible tumor/non-tumor localization ratios. To increase this ratio, in a mouse xenograft model system, we induced rapid blood clearance of the Ab after extensive penetration of a solid tumor, at 24 hr after Ab injection. By using galactosylated streptavidin (gal-SA) as a clearing agent for biotinylated Abs, and by using an 111In-DTPA (diethylenetriaminepentaacetic acid) label, clearance was directed to hepatocytes (as opposed to Kupffer cells), and the radiolabel was excreted by the hepatocytes into bile, thereby reducing accumulation in the liver.