The in vitro and in vivo Anti-Tumor Effect of KO-202125, a Sauristolactam derivative, on Estrogen Receptor-Negative Human Breast Cancer Cells

Abstract

Estrogen receptor (ER)-negative breast cancer cells that show more aggressive phenotype are resistant to conventional hormonal therapy, discovery of more effective new drugs for ER-negative breast cancer therapy has been required. Here, we investigated the in vitro and in vivo anti-tumor effects and associated mechanisms of KO-202125, one of chemically synthesized aristolactam analogs which is altered its side chain to have the lowest toxicity, in MDA-MB-231 and SK-BR-3 breast cancer cells, which are ER-negative and overexpressing EGFR family. In these cell lines, cell growth was attenuated by KO-202125 in a dose- and time- dependent manner. KO-202125 also inhibited signaling pathways involved in cell proliferation through EGFR inactivation. Upon KO-202125 treatment, EGFR phosphorylation at Tyr1068 was reduced in MDA-MB-231 cells which have high EGFR expression while c-ErbB2 expression and phosphorylation was unchanged in SK-BR-3 cells which overexpress c-ErbB2. Their downstream effector Akt was inactivated as evidenced by reduced phosphorylated protein in both cell lines. Moreover, suppressed Akt activity by KO-202125 also inhibited Akt-mediated Wnt/b-catenin signaling pathway. Reduced phosphorylation of GSK-3b at Ser9 led to inhibition of nuclear translocation of b-catenin and consequent downregulation of cyclin D1 expression. In addition, Akt-mediated p27Kip1 phosphorylation at Thr157 was decreased by KO-202125 treatment, and consistently, the nuclear import of p27Kip1 was increased that is implicated with increase in functional p27Kip1. Moreover, KO-202125 was effective in vivo as well as in vitro. Treatment of the nude mice injected with MDA-MB-231 cells with KO-202125 efficiently inhibited the tumor growth without any toxicity. Collectively, our results show the possibility of KO-202125 as an effective therapeutic agent for inhibiting growth of ER-negative breast cancers through inhibition of EGFR and Akt activity, and Akt-mediated signaling pathway.