ERD-308 is a highly potent von Hippel-Lindau-based PROTAC degrader of estrogen receptor (ER) for ER positive breast cancer treatment. ERD-308 induces >95% of ER degradation at concentrations as low as 5 nM in both cell lines (DC50 (concentration causing 50% of protein degradation) of 0.17 nM and 0.43 nM in MCF-7 and T47D ER+ cells, respectively).