Highly antiproliferative copper(II) complexeswith Schiffbases derived from indolo[3,2-d]benzazepines and2-formyl- and 2-acetylpyridine have been synthesized and characterized.Western blot analysis of endoplasmic reticulum stress biomarkers PERK,BIP, and Ero-1-Lα after treatment of breast cancer cells MDA-MB-231with increasing concentrations of lead drug candidate 4 revealed ER stress activation and production of toxic ROS, whichfinally led to cell death. Here, EIF2AK3 is linked to breast cancer.