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Experimental Analysis of Apoptotic Thymocyte Engulfment by Macrophages
Published on: May 24, 2019
Structural and functional analysis of the interaction between the agonistic monoclonal antibody Apomab and the
C Adams1, K Totpal, D Lawrence
1Department of Antibody Engineering, Genentech Inc., South San Francisco, CA 94080-4918, USA.
Abstract:
Activation of the proapoptotic receptor death receptor5 (DR5) in various cancer cells triggers programmed cell death through the extrinsic pathway. We have generated a fully human monoclonal antibody (Apomab) that induces tumor cell apoptosis through DR5 and investigated the structural features of its interaction with DR5. Biochemical studies showed that Apomab binds DR5 tightly and selectively. X-ray crystallographic analysis of the complex between the Apomab Fab fragment and the DR5 ectodomain revealed an interaction epitope that partially overlaps with both regions of the Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand binding site. Apomab induced DR5 clustering at the cell surface and stimulated a death-inducing signaling complex containing the adaptor molecule Fas-associated death domain and the apoptosis-initiating protease caspase-8. Fc crosslinking further augmented Apomab's proapoptotic activity. In vitro, Apomab triggered apoptosis in cancer cells, while sparing normal hepatocytes even upon anti-Fc crosslinking. In vivo, Apomab exerted potent antitumor activity as a single agent or in combination with chemotherapy in xenograft models, including those based on colorectal, non-small cell lung and pancreatic cancer cell lines. These results provide structural and functional insight into the interaction of Apomab with DR5 and support further investigation of this antibody for cancer therapy.
Insights
A new antibody, Apomab, effectively triggers cancer cell death by targeting the death receptor 5 (DR5). This antibody shows potent anti-tumor activity in preclinical models, offering a promising new avenue for cancer therapy.
Area of Science:
- Oncology
- Immunology
- Structural Biology
Background:
- The extrinsic apoptosis pathway, initiated by death receptors like death receptor 5 (DR5), is crucial for programmed cell death.
- Targeting DR5 offers a potential strategy for cancer therapy by inducing tumor cell apoptosis.
Purpose of the Study:
- To characterize a fully human monoclonal antibody, Apomab, for its ability to induce tumor cell apoptosis via DR5.
- To elucidate the structural basis of the Apomab-DR5 interaction.
- To evaluate the therapeutic potential of Apomab in preclinical cancer models.
Main Methods:
- Biochemical binding assays to assess Apomab's affinity and selectivity for DR5.
- X-ray crystallography to determine the structural complex of Apomab Fab fragment and DR5 ectodomain.
- In vitro assays to evaluate Apomab's ability to induce DR5 clustering, apoptosis, and signaling complex formation.
- In vivo xenograft studies in mice to assess Apomab's anti-tumor efficacy as a single agent and in combination therapy.
Main Results:
- Apomab demonstrated tight and selective binding to DR5.
- X-ray crystallography revealed the interaction epitope, showing partial overlap with Apo2L/TRAIL binding sites.
- Apomab induced DR5 clustering, formation of the death-inducing signaling complex (DISC) with FADD and caspase-8, and apoptosis in cancer cells.
- Apomab exhibited potent anti-tumor activity in xenograft models of colorectal, non-small cell lung, and pancreatic cancers, sparing normal hepatocytes.
- Fc crosslinking enhanced Apomab's proapoptotic activity.
Conclusions:
- Apomab effectively induces cancer cell apoptosis through DR5 activation.
- Structural and functional data provide insight into Apomab's mechanism of action.
- Apomab shows significant promise as a single-agent or combination therapy for various cancers.
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