Patterns of HER-family receptor dimerization in trastuzumab susceptible and trastuzumab resistant cell lines

Abstract

2533 Background: HER2 overexpression is associated with accelerated disease progression and poor prognosis in breast cancer. Trastuzumab, a monoclonal antibody targeting the extracellular domain of HER2, is effective in the treatment of metastatic breast cancer. However, most patients treated with trastuzumab eventually develop clinical resistance. To investigate the role of HER-family receptors in trastuzumab resistance, we measured HER-family receptor expression, dimerization, and phosphorylation in trastuzumab susceptible and resistant cell lines. Methods: Cell lysates from trastuzumab susceptible and resistant BT474 and SKBR3 cell lines were obtained from the Arteaga and Esteva laboratories. Proximity-based, multiplexed assays were used to detect and quantify HER1, HER2, and HER3 expression and phosphorylation levels, as well as HER1/HER1, HER1/HER2, HER1/HER3, HER2/HER2, and HER2/HER3 dimers. Samples were incubated with a mixture of HER specific antibodies conjugated either with fluorescent reporter tags (eTags), or biotin, which binds a reporter tag releasing agent (chemical scissor). Reporter molecules are released based on proximity to the scissor in a photochemical reaction and separated by capillary gel electrophoresis. Results: In comparison to trastuzumab susceptible parental cell lines, both SKBR3 and BT474 trastuzumab-resistant cell lines displayed upregulated HER1 expression. Resistant BT474 cell lines exhibited markedly increased levels of HER1/HER2 heterodimers. Increases in HER2 phosphorylation in the trastuzumab resistant SKBR3 cell line were observed, consistent with previous studies implicating trastuzumab in the induction of HER2 phosphorylation. Total HER2 and HER3 levels were similar in trastuzumab susceptible and resistant BT474 cell lines. Conclusions: The development of trastuzumab resistance in these cell line models correlated with HER1 expression and the appearance of HER1:HER2 dimers. Since signaling initiated by such heterodimers is ineffectively antagonized by trastuzumab, these data suggest that selection for proliferative signaling mediated by HER1:HER2 dimers may represent a mechanism of trastuzumab resistance in breast cancer. No significant financial relationships to disclose.