AGR2, a potential prognostic and predictive biomarker and therapeutic to overcome drug resistance in HER2-overexpressing cancer

The development of resistance to HER2-targeted drugs is common. Neratinib, an orally delivered cost effective drug is showing great promise for patients with HER2-overexpressing tumours but, unfortunately, for many the development of resistance is inevitable. In this study spanning novel pairs of cell line models and data from patients samples, we used a broad range of methodologies including mass-spectrometry-based quantitative proteomics, ectopic gene expression, RT-qPCR, immunoblotting, cytotoxicity, proliferation, invasion, and migration assays. We found loss of anterior gradient protein 2 (AGR2) to be prognostic for poor overall survival for patients with HER2-overexpressing tumours, in contrast to what has been reported for estrogen-positive breast cancer. Additionally, we discovered that loss of AGR2 is not only associated with neratinb-resistance, but that its restoration by ectopic AGR2 expression in neratinib-resistance cells partly restores their drug sensitivity. Furthermore, we established that keys metastatic phenotypic traits acquired with neratinib-resistance were blocked by ectopic AGR2 expression in the cells. Taken together, our results show that AGR2 has potential as a prognostic biomarker for outcome from HER2-overexpressing cancer; a predictive biomarker for resistance/response to neratinib; and a potential therapeutic protein for helping restore sensitivity to neratinib and overcoming aggressive cellular traits associated with cancer metastasis. Statement of SignificanceAGR2 loss in HER2-overexpressing cancer is prognostic for poor outcome and predictive for HER2-targeted drug-resistance, with AGR2 re-introduction helping restore drug sensitivity and overcoming phenotypic characteristics key to metastasis.