Em08red, a dual functional antiproliferative emodin analogue, is a downregulator of ErbB2 expression and inducer of intracellular oxidative stress

Fong-Pin Liang,1,* Jin-Cherng Lien,1,* Yu-Hua Wu,2 Chien-Shu Chen,2 Shin-Hun Juang1–3 1Graduate Institute of Pharmaceutical Chemistry, 2School of Pharmacy and Department of Pediatrics, Children’s Hospital, 3Department of Medical Research, China Medical University Hospital, Taichung, Taiwan *These authors contributed equally to this work Abstract: Expression of ErbB2 protein is inversely correlated with the prognosis in cancer patients. Consequently, strategies targeting ErbB2 remain an attractive option in treating several types of malignancies, including oral cancer. In addition, many studies have shown that emodin and emodin derivatives are able to inhibit growth of ErbB2-overexpressing tumor cells. In this study, a series of computer modeling-generated emodin analogues were synthesized and tested for their antiproliferative activity against oral cancer cell lines overexpressing ErbB2. Among these analogues, em08red (1,8-dihydroxy-9(10H)-anthracenone) demonstrated potent antiproliferative activity against all three tested ErbB2-overexpressing cell lines, ie, FaDu, HSC3, and OECM1. Treatment with em08red significantly downregulated activation of ErbB2 as well as the ErbB2 protein expression level in the tested cell lines and induced G2 arrest. Antiapoptosis protein (Bcl-xl and Bcl-2) expression levels were also downregulated, and active caspase-3 and caspase-9 was detected in cells after treatment with em08red. Moreover, treatment with em08red stimulated production of cytotoxic reactive oxygen species in treated cells, and this could be partially reversed by pretreatment with N-acetylcysteine. Overall, we demonstrated inhibition of ErbB2 function and induction of reactive oxygen species in tumor cells by em08red, which prevented proliferation of tumor cells and induced apoptotic cell death. Keywords: ErbB2, emodin, em08red, reactive oxygen species, structure-activity relationship&nbsp