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Biological rationale for HER2/neu (c-erbB2) as a target for monoclonal antibody therapy
1Division of Hematology/Oncology, UCLA School of Medicine, Los Angeles, CA 90095, USA.
Abstract:
The physical characteristics of tumor antigens that would make the most ideal targets for antibody therapeutics include cell surface expression; high, stable expression levels in tumor cells; low or absent expression in normal tissues; lack of a soluble form of the antigenic target; and lack of internalization of the antigen/antibody complex. HER2/neu is a 185-kd surface membrane protein that is overexpressed in approximately 25% of human breast cancers due to amplification of the HER2 gene. Overexpression of the gene results in ligand-independent activation of HER2 kinase, causing mitogenic signal transduction and increased cell proliferation. Consequently, patients with this alteration have a worse clinical prognosis. Trastuzumab (Herceptin; Genentech, Inc, So. San Francisco, CA), a humanized anti-HER2 monoclonal antibody, has significant clinical activity against metastatic breast cancers with HER2/neu overexpression, despite the fact that the p185HER2 protein product lacks some of the ideal characteristics of tumor antigens listed above. We propose that the efficacy of trastuzumab may be explained on the basis of its effects on signal transduction, which is independent from its immune mechanism(s) of action. Furthermore, trastuzumab is synergistic with some chemotherapeutic drugs, resulting in improved therapeutic efficacy. Thus, in the case of trastuzumab, a clear distinction may be drawn between the use of monoclonal antibodies as immuneactive agents and their use to achieve a desired cellular/biochemical activity.
Insights
Trastuzumab, an anti-HER2 antibody, shows clinical activity in breast cancer by affecting HER2 signaling pathways, not just immune responses. It also works synergistically with chemotherapy.
Area of Science:
- Oncology
- Immunology
- Molecular Biology
Background:
- Ideal tumor antigens for antibody therapeutics possess specific characteristics like cell surface expression and lack of internalization.
- HER2/neu, a surface protein, is overexpressed in ~25% of breast cancers, correlating with a poor prognosis.
- Trastuzumab is a humanized anti-HER2 monoclonal antibody with clinical activity in HER2-overexpressing metastatic breast cancers.
Purpose of the Study:
- To investigate the mechanism of action of trastuzumab in HER2-overexpressing breast cancer.
- To explore whether trastuzumab's efficacy is primarily due to immune mechanisms or cellular/biochemical effects.
- To examine the synergistic effects of trastuzumab with chemotherapeutic agents.
Main Methods:
- Analysis of HER2/neu protein characteristics and its role in breast cancer.
- Evaluation of trastuzumab's clinical activity in metastatic breast cancer patients with HER2/neu overexpression.
- Assessment of trastuzumab's impact on signal transduction pathways.
- Investigation of synergistic interactions between trastuzumab and chemotherapeutic drugs.
Main Results:
- Trastuzumab demonstrates significant clinical activity despite HER2/neu lacking ideal tumor antigen characteristics.
- The efficacy of trastuzumab may be attributed to its effects on signal transduction, independent of immune mechanisms.
- Trastuzumab exhibits synergistic effects when combined with certain chemotherapeutic drugs, enhancing therapeutic outcomes.
Conclusions:
- Trastuzumab's efficacy in HER2-overexpressing breast cancer is likely mediated by its impact on cellular signal transduction.
- A distinction can be made between trastuzumab's immune-mediated actions and its direct cellular/biochemical activities.
- Trastuzumab represents a valuable therapeutic agent, particularly in combination regimens for metastatic breast cancer.