Abstract 1865: Tumor microenvironment ameliorating effect of E7130 sensitized ER+ breast cancer against fulvestrant

Abstract Introduction and objectives: E7130 is a novel anti-cancer agent created from a total synthetic study of the natural compound norhalichondrin B, and is evaluated in a clinical study currently (NCT03444701). Previous pre-clinical study reported that E7130 had both cancer cell proliferation inhibitory activity and tumor microenvironment ameliorating activities featuring vascular remodeling effect and anti-CAF (cancer-associated fibroblasts) effect. Intratumoral hypoxia induces tumor malignancy and causes resistance against anti-cancer drugs including anti-estrogen agents (eg fulvestrant). It is hypothesized that vascular remodeling effect of E7130 mitigates hypoxia-induced resistant mechanism of ER (estrogen receptor) + breast cancer against anti-estrogen agents, resulting in improving anti-tumor activity of fulvestrant in combination with E7130. Experimental procedure: ERα expression levels in human ER+ breast cancer cell lines under hypoxic or normoxic culture condition were examined by FCM (flow cytometry) analysis. The histological changes after treatment with E7130 were examined by immunohistochemical analyses in the MCF-7 subcutaneous xenograft model. Anti-tumor activity of E7130 in combination with fulvestrant were examined in concurrent and in sequential treatment in the MCF-7 model. Summary: In vitro hypoxic culture condition down-regulated ERα expression in MCF-7 and T-47D compared with normoxic condition. E7130 had no effect on the ERα expression level in the cancer cells in vitro. On the contrary, E7130 increased ERα expression level in the cancer cells concomitantly with an increase of CD31-positive endothelial cell number (ie vascular remodeling effect) in MCF-7 xenograft tumor. These results suggested that E7130 up-regulated ERα expression in cancer cells not by cell-autonomous manner but by mitigating intratumoral hypoxia via its vascular remodeling effect. Concurrent combination therapy of E7130 at 90 μg/kg with fulvestrant at 250 mg/kg significantly inhibited the tumor growth compared with each monotherapy. In sequential combination therapy, pretreatment of E7130 followed by fulvestrant showed superior anti-tumor activity to posttreatment of E7130 following fulvestrant. Severe body weight loss was not observed in any treatment groups. Conclusions: The vascular remodeling effect of E7130 increased ERα expression in cancer cells in vivo, and sensitized ER+ breast cancer against fulvestrant to achieve promising combinational anti-tumor activity. Our data provides compelling evidence that E7130 attenuates tumor malignancy by its tumor microenvironment ameliorating effects and improves current anti-cancer therapy in combination with other drugs. Citation Format: Takanori Abe, Satoshi Kawano, Ken Ito, Taro Semba, Kimiyo Tabata, Hiroki Jozawa, Osamu Asano, Yoshito Kishi. Tumor microenvironment ameliorating effect of E7130 sensitized ER+ breast cancer against fulvestrant [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1865.