Blockade of retrograde transport in triple negative breast cancer excludes ErbB-2 isoforms from the nucleus and abrogates tumor growth

Abstract Triple negative breast cancer (TNBC) is clinically defined by the absence of estrogen and progesterone receptors and the lack of membrane overexpression or gene amplification of the receptor tyrosine kinase ErbB-2/HER2. Due to its heterogeneity, clinical biomarkers and targeted therapies for this disease remain elusive, and chemotherapy has been the standard of care for early and metastatic TNBC. ErbB-2 is classically located at the membrane of BC cells, where it triggers signalling cascades and promotes oncogenesis. However, we have demonstrated that ErbB-2 is also localized in the nucleus (NErbB-2) of TNBC cells and primary tumors, from where it drives growth. We also discovered that TNBC expresses both wild-type ErbB-2 (WTErbB-2) and alternative ErbB-2 isoform c (ErbB-2c). ErbB-2 migrates to the nucleus via retrograde transport. The small molecule Retro-2 is a non-toxic inhibitor of the retrograde transport route that protects cells from the deleterious effects of toxins and viruses. Here, we revealed that Retro-2 evicts both WTErbB-2 and ErbB-2c from the nuclei. Using BC models from several molecular subtypes, we demonstrated that Retro-2 specifically halts the proliferation of cells expressing NErbB-2 in a dose-dependent manner, whilst did not inhibit cell proliferation in the ErbB-2-negative MCF10A normal breast cell line. Additionally, Retro-2 decreased the expression of genes induced by NErbB-2 (cyclin D1 and Erk5) and promoted cell cycle arrest at G0/G1 phase and apoptosis. Even more, in preclinical models (including xenografts and tumor explants), Retro-2 treatment resulted in the eviction of NErbB-2 and abrogation of tumor growth. Our mechanistic studies demonstrated that Retro-2 induces a differential accumulation of WTErbB-2 at the early endosomes and plasma membrane, and of ErbB-2c at the Golgi, further preventing its sorting to the endoplasmic reticulum. These findings shed light both on Retro-2 action on endogenous protein cargoes undergoing retrograde transport and on the biology of ErbB-2 splicing variants. Together, our present discoveries provide evidence for the rational repurposing of Retro-2 as a novel therapeutic agent for TNBC. Citation Format: Santiago Madera, Franco Izzo, Maria F. Chervo, Agustina Dupont, Violeta A. Chiauzzi, Sofia Bruni, Ezequiel Petrillo, Diego Montero, Sharon Merin, Maria F. Mercogliano, Cecilia J. Proietti, Roxana Schillaci, Rosalia I. Cordo Russo, Patricia V. Elizalde. Blockade of retrograde transport in triple negative breast cancer excludes ErbB-2 isoforms from the nucleus and abrogates tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 344.