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 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.

Antitumor Activity of the Hsp90 Inhibitor IPI-504 in HER2-Positive Trastuzumab-Resistant Breast Cancer

“…Accordingly, inhibition of Hsp90 induces proteasomal degradation of HER2 and suppresses growth of breast cancer cells and breast cancer xenograft tumors in vivo (18)(19)(20)(21)(22). The Hsp90 inhibition-mediated degradation of HER2 is enhanced with the addition of trastuzumab (23), and an early clinical trial that combined the Hsp90 inhibitor 17-AAG with trastuzumab has shown signs of efficacy among patients with trastuzumab refractory breast cancer (23,24). 17-AAG is a potent inhibitor of Hsp90, but its clinical development has been hampered by pharmacologic liabilities, including poor aqueous solubility, which could limit patient safety and the therapeutic index.…”

Mechanism-Based Enhanced Delivery of Drug-Loaded Targeted Nanoparticles for Breast Cancer Therapy

“…However by 60 min, the Dox fluorescence was found in the nucleus, confirming diffusion of DOX from the lysosomes, presumably following disintegration under the lysosomal pH, redox conditions and lysosomal proteases, such as Cathepsins. Previous studies from our lab has shown that BIC nanogels with crosslinked ionic cores can be selectively endocytosed into cancer cells, which lack tight epithelial cell junctions, in contrast to normal epithelial cells that form tight junctions (7). The internalization route appeared to be predominantly via the caveolar pathway.…”

Trastuzumab-Doxorubicin Conjugate Provides Enhanced Anti-Cancer Potency and Reduced Cardiotoxicity

“…GA is an inhibitor of HSP90 and is known to down-regulate HER2 levels by diverting endosomal trafficking of HER2 from recycling back to membrane surface [23,34]. A combination study of trastuzumab and 17-AAG (17-(allylamino)-17-demethoxygeldanamycin) showed enhanced HER2 down-regulation [35]. Since uptake of trastuzumab-drug conjugates is dependent on binding of HER2 for internalization, down-regulation of HER2 by GA may decrease uptake of trastuzumab-GA conjugate.…”