Development of Herceptin resistance in breast cancer cells

Background Herceptin, a humanized antibody to HER‐2, is now utilized in the clinic for metastatic breast cancer treatment. The response rate for HER‐2+ patients is only 30% and little is known as to mechanisms of resistance. The mechanism of Herceptin action is also unknown but has been related to c...

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Published in:	Cytometry. Part A Vol. 57A; no. 2; pp. 86 - 93
Main Authors:	Kute, Timothy, Lack, Christopher M., Willingham, Mark, Bishwokama, Bimjhana, Williams, Holly, Barrett, Kathy, Mitchell, Tanita, Vaughn, James P.
Format:	Journal Article
Language:	English
Published:	Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-02-2004
Subjects:	Animals Antibodies, Monoclonal - metabolism Antibodies, Monoclonal - pharmacology Antibodies, Monoclonal - therapeutic use Antibodies, Monoclonal, Humanized Antineoplastic Agents - metabolism Antineoplastic Agents - pharmacology Antineoplastic Agents - therapeutic use breast cancer Breast Neoplasms - drug therapy Breast Neoplasms - metabolism Cell Cycle Proteins - metabolism Cell Line, Tumor Cyclin-Dependent Kinase Inhibitor p27 Down-Regulation Drug Resistance, Neoplasm Female Flow Cytometry Herceptin resistance HER‐2 Humans Mice p27 Receptor, Epidermal Growth Factor - metabolism Trastuzumab Tumor Suppressor Proteins - metabolism
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Summary:	Background Herceptin, a humanized antibody to HER‐2, is now utilized in the clinic for metastatic breast cancer treatment. The response rate for HER‐2+ patients is only 30% and little is known as to mechanisms of resistance. The mechanism of Herceptin action is also unknown but has been related to cell cycle inhibition. Methods The effects of Herceptin and other antibody treatments were determined by cell counting and cell cycle analysis. HER‐2 and p27 expression levels were analyzed by flow cytometry and levels of activated AKT were compared by Western blot analysis. Cellular HER‐2 and p27 expression was measured by immunofluorescence. Results Herceptin treatment of BT‐474 cells results in inhibition of cell growth and arrest in the G1 phase. The efficacy of growth arrest was not directly correlated to the binding affinity of antibodies to Her‐2. Our laboratory has developed cell lines that are resistant to Herceptin treatment. In resistant cell lines, binding of antibodies is not hindered. However, Herceptin has completely lost the ability to inhibit cell proliferation. Yet, the mouse isotype 4D5 maintains significant inhibitory activity upon Herceptin‐resistant clones. Conclusions Herceptin binds effectively to Her‐2 on the cell surface of Herceptin‐resistant cell lines and the level of Her‐2 expression on the cell surface is not downregulated. Herceptin resistance is not due to downregulation of levels of AKT protein expression, although, phosphorylation of AKT is enhanced in resistant lines and could have a role in resistance. Resistance appears to correlate with the loss of nuclear expression of the cyclin‐dependent kinase inhibitor, p27, as defined by immunofluorescence and flow cytometry studies and cdk‐2 binding studies. © 2004 Wiley‐Liss, Inc.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1552-4922 1552-4930
DOI:	10.1002/cyto.a.10095