(R)-ErSO

(R)-ErSO is an activator of the anticipatory unfolded protein response (a-UPR).¹ It inhibits protein synthesis and induces intracellular ATP depletion in T47D cells that express estrogen receptor α (ERα), but not MDA-MB-231 cells which lack ERα, when used at a concentration of 1 µM. (R)-ErSO (1 µM) also increases levels of phosphorylated eukaryotic translation initiation factor 2α kinase 3 (EIF2AK3), also known as PERK, eukaryotic translation initiation factor 2α subunit (eIF2α), and AMP-activated protein kinase (AMPK), markers of a-UPR activation, in T47D cells. It is cytotoxic to T47D, TYS, BT474, and ZR-75-1 ERα-positive breast cancer cells (IC₅₀s = 16.4, 11.1, 26.9, and 42.8 nM, respectively). In vivo, (R)-ErSO (40 mg/kg) induces tumor regression in an MCF-7 mouse xenograft model. It also induces tumor regression in an ST941/HI breast cancer patient-derived xenograft (PDX) mouse model.

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1. Boudreau, M.W., Duraki, D., Wang, L., et al. A small-molecule activator of the unfolded protein response eradicates human breast tumors in mice. Sci. Transl. Med. 13(603), eabf1383 (2021).