Abstract 5362: The role of adam10 in trastuzumab resistance of her2 positive breast cancer cell lines
Authors: Feldinger Katharina , Gijsen Merel , Kong Anthony 
Published: June 2012

Abstract
Members of a disintegrin and metalloproteases (ADAMs) are responsible for shedding of a variety of ErbB ligands. One of them, ADAM10, has been shown to cleave several pro-ligands, including betacellulin and HB-EGF. ADAM10 further may play a role in trastuzumab resistance since it is also responsible for HER2 shedding, thereby removing the binding site for trastuzumab. It was reported that ADAM10 inhibitor INCB 7839 could reduce HER2 cleavage in patients with HER2 positive breast cancer. However, a direct correlation of trastuzumab treatment and ADAM10 and the precise role of ADAM10 in trastuzumab resistance have not been elucidated. The aim of this project is therefore to investigate the role of ADAM10 in trastuzumab treatment and resistance in HER2 positive breast cancer cell lines.
Using western blot, we showed that one hour of trastuzumab treatment leads to an upregulation of ADAM10 in conditioned medium and cell lysates of BT474 cells, which was correlated with an elevated level of betacellulin. Additionally, the use of a specific ADAM10 inhibitor in turn leads to downregulation of betacellulin levels in culture medium. Whereas one hour of trastuzumab treatment could not decrease pHER2, its combination with ADAM10 inhibitor reduced pHER2 level. To further investigate the role of ADAM10 in relation to trastuzumab treatment, we used cell viability studies to assess the effect of a specific ADAM10 inhibitor with or without trastuzumab treatment. Although monotherapy with ADAM10 inhibitor only had minimal influence, combining it with trastuzumab significantly enhanced trastuzumab in reducing cell proliferation of BT474 cells. Interestingly, the addition of ADAM10 inhibitor to trastuzumab exerts an even greater inhibition of cell proliferation in the BT474 trastuzumab resistant cell line.
Since the N-domain of ADAM10 was shown to be cleaved by ADAM9 in other cell lines, we also assessed ADAM9 level in response to trastuzumab treatment. In BT474 lysates, ADAM9 level was increased after one hour of treatment, correlating with increased ADAM10 level in the medium. ADAM9 level was also found to be increased in the trastuzumab-resistant HER2 positive cell line in comparison to the sensitive cell line.
Thus, ADAM10 as well as ADAM9 may play a key role in trastuzumab resistance in HER2 positive breast cancer cells. Our results suggest that the increased level of ADAM10 results in HER ligand sheddase which in turn may lead to the activation of HER receptors and the maintenance of pHER2. We demonstrated that ADAM10 inhibitor in combination with trastuzumab is able to decrease pHER2 and potentiate the trastuzumab effect in HER2 positive breast cancer cells. The role of ADAM9 in its regulation of ADAM10 in relation to trastuzumab treatment is currently under investigation. We recommend that inhibition of ADAM10 should be considered as a potential strategy to improve trastuzumab response in HER2 positive breast cancer patients.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5362. doi:10.1158/1538-7445.AM2011-5362