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Kinetics of anti-carcinoembryonic antigen antibody internalization: effects of affinity, bivalency, and stability.

ABSTRACT: Theoretical analyses suggest that the cellular internalization and catabolism of bound antibodies contribute significantly to poor penetration into tumors. Here we quantitatively assess the internalization of antibodies and antibody fragments against the commonly targeted antigen carcinoembryonic antigen (CEA). Although CEA is often referred to as a non-internalizing or shed antigen, anti-CEA antibodies and antibody fragments are shown to be slowly endocytosed by LS174T cells with a half-time of 10-16 h, a time scale consistent with the metabolic turnover rate of CEA in the absence of antibody. Anti-CEA single chain variable fragments (scFvs) with significant differences in affinity, stability against protease digestion, and valency exhibit similar uptake rates of bound antibody. In contrast, one anti-CEA IgG exhibits unique binding and trafficking properties with twice as many molecules bound per cell at saturation and significantly faster cellular internalization after binding. The internalization rates measured herein can be used in simple computational models to predict the microdistribution of these antibodies in tumor spheroids.

SUBMITTER: Schmidt MM

PROVIDER: S-EPMC2840397 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature

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Kinetics of anti-carcinoembryonic antigen antibody internalization: effects of affinity, bivalency, and stability.

Schmidt Michael M MM Thurber Greg M GM Wittrup K Dane KD

Cancer immunology, immunotherapy : CII 20080412 12

Theoretical analyses suggest that the cellular internalization and catabolism of bound antibodies contribute significantly to poor penetration into tumors. Here we quantitatively assess the internalization of antibodies and antibody fragments against the commonly targeted antigen carcinoembryonic antigen (CEA). Although CEA is often referred to as a non-internalizing or shed antigen, anti-CEA antibodies and antibody fragments are shown to be slowly endocytosed by LS174T cells with a half-time of ...[more]

PMID: 18408925

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Project description:Antibody drugs are widely used in cancer therapy, but conditions to maximize tumor penetration and efficacy have yet to be fully elucidated. In this study, we investigated the impact of antibody binding affinity on tumor targeting and penetration with affinity variants that recognize the same epitope. Specifically, we compared four derivatives of the C6.5 monoclonal antibody (mAb), which recognizes the same HER2 epitope (monovalent K(D) values ranging from 270 to 0.56 nmol/L). Moderate affinity was associated with the highest tumor accumulation at 24 and 120 hours after intravenous injection, whereas high affinity was found to produce the lowest tumor accumulation. Highest affinity mAbs were confined to the perivascular space of tumors with an average penetration of 20.4 ± 7.5 μm from tumor blood vessels. Conversely, lowest affinity mAbs exhibited a broader distribution pattern with an average penetration of 84.8 ± 12.8 μm. In vitro internalization assays revealed that antibody internalization and catabolism generally increased with affinity, plateauing once the rate of HER2 internalization exceeded the rate of antibody dissociation. Effects of internalization and catabolism on tumor targeting were further examined using antibodies of moderate (C6.5) or high-affinity (trastuzumab), labeled with residualizing ((111)In-labeled) or nonresidualizing ((125)I-labeled) radioisotopes. Significant amounts of antibody of both affinities were degraded by tumors in vivo. Furthermore, moderate- to high-affinity mAbs targeting the same HER2 epitope with monovalent affinity above 23 nmol/L had equal tumor accumulation of residualizing radiolabel over 120 hours. Results indicated equal tumor exposure, suggesting that mAb penetration and retention in tumors reflected affinity-based differences in tumor catabolism. Together, these results suggest that high-density, rapidly internalizing antigens subject high-affinity antibodies to greater internalization and degradation, thereby limiting their penetration of tumors. In contrast, lower-affinity antibodies penetrate tumors more effectively when rates of antibody-antigen dissociation are higher than those of antigen internalization. Together, our findings offer insights into how to optimize the ability of therapeutic antibodies to penetrate tumors.

Dataset Information

Kinetics of anti-carcinoembryonic antigen antibody internalization: effects of affinity, bivalency, and stability.

Publications

Kinetics of anti-carcinoembryonic antigen antibody internalization: effects of affinity, bivalency, and stability.

Similar Datasets

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