title: A combination of Trastuzumab and 17-AAG induces enhanced ubiquitinylation and lysosomal pathway-dependent ErbB2 degradation and cytotoxicity in ErbB2-overexpressing breast cancer cells.
abstract: ErbB2 (or Her2/Neu) overexpression in breast cancer signifies poorer prognosis, yet it has provided an avenue for targeted therapy as demonstrated by the success of the humanized monoclonal antibody Trastuzumab (Herceptin). Resistance to Trastuzumab and eventual failure in most cases, however, necessitate alternate ErbB2-targeted therapies. HSP90 inhibitors such as 17-allylaminodemethoxygeldanamycin (17-AAG), potently downregulate the cell surface ErbB2. While the precise mechanisms of Trastuzumab or 17-AAG action remain unclear, ubiquitinylation-dependent proteasomal or lysosomal degradation of ErbB2 appears to play a substantial role. As Trastuzumab and 17-AAG induce the recruitment of distinct E3 ubiquitin ligases, Cbl and CHIP respectively, to ErbB2, we hypothesized that 17-AAG and Trastuzumab combination could induce a higher level of ubiquitinylation and downregulation of ErbB2 as compared to single drug treatments. We present biochemical and cell biological evidence that combined 17-AAG and Trastuzumab treatment of ErbB2-overexpressing breast cancer cell lines leads to enhanced ubiquitinylation, downregulation from the cell surface and lysosomal degradation of ErbB2. Importantly, combined 17-AAG and Trastuzumab treatment induced synergistic growth arrest and cell death specifically in ErbB2-overexpressing but not in ErbB2-low breast cancer cells. Our results suggest the 17-AAG and Trastuzumab combination as a mechanism-based combinatorial targeted therapy for ErbB2-overexpressing breast cancer patients.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, UNMC-Eppley Cancer Center, College of Medicine, University of Nebraska Medical Center, Omaha, NE 68198-6805, USA. sraja@unmc.edu
authors.forename: Srikumar M
authors.initials: SM
authors.lastname: Raja
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Clubb
authors.forename: Mitra
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authors.lastname: Bhattacharyya
authors.forename: Manjari
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authors.lastname: Dimri
authors.forename: Hao
authors.initials: H
authors.lastname: Cheng
authors.forename: Wei
authors.initials: W
authors.lastname: Pan
authors.forename: Cesar
authors.initials: C
authors.lastname: Ortega-Cava
authors.forename: Alagarsamy
authors.initials: A
authors.lastname: Lakku-Reddi
authors.forename: Mayumi
authors.initials: M
authors.lastname: Naramura
authors.forename: Vimla
authors.initials: V
authors.lastname: Band
authors.forename: Hamid
authors.initials: H
authors.lastname: Band