Abstract 3803: Obatoclax analogue SC-2001 inhibits STAT3 phosphorylation by enhancing protein tyrosine phosphatase SHP-1 expression and induces apoptosis in human breast cancer cells

Abstract

Background: Interfering the oncogenic STAT3 signaling is considered as promising anti-cancer strategy. Previously, we have reported an obatoclax analogue, SC-2001, as a novel STAT3 inhibitor in hepatocellular carcinoma cells (Cancer Letter 2012). Here, we examined the efficacy and drug mechanism of SC-2001 in breast cancer cells.

Methods: Human breast cancer cell lines were used for in vitro studies. Cell viability was examined by MTT assay. Apoptosis was examined by both flow cytometry and western blot. Signal transduction pathways in cells were assessed by western blot. Small interference RNA was used to knockdown SHP-1. Quantitative RT-PCR was used for assessing gene transcription. In vivo efficacy of SC-2001 was tested in xenografted nude mice.

Results: SC-2001 inhibited cell growth and induced apoptosis in breast cancer cell lines (MDA-MB-468, MDA-MB-231, MDA-MB-453, MCF-7 and HCC 1937). SC-2001 downregulated the phosphorylation of STAT3 (Tyr 705) and subsequently inhibited its transcriptional activities in a dose-dependent manner. STAT3-regulated proteins, including Mcl-1, survivin and cyclin D1, were also repressed by SC-2001. Over-expression of STAT3 in MDA-MB-468 cells protected cells from SC-2001-induced apoptosis. Moreover, SC-2001 enhanced the expression of SHP-1, a negative regulator of STAT3, in a time-dependent manner. The enhanced SHP-1 expression, in conjunction with increased SHP-1 phosphatase activity, was mediated by upregulated transcription. Furthermore, co-immunoprecipitation experiment showed that SC-2001 upregulated SHP-1 expression through enhanced transcription by RFX-1 transcription factor. Importantly, SC-2001 showed efficacious antitumor activity and p-STAT3 downregulation in MDA-MB-468 xenograft tumors.

Conclusion: Our results suggest that SC-2001 induced apoptosis in breast cancer cells, and that this effect is mediated through RFX-1 upregulated SHP-1 expression and SHP-1-dependent STAT3 inactivation.

(Supported by Yen Tjing Ling Medical Foundation; NSC 101-2325-B-075-006, NSC-102-2325-B-075-006 and NSC 100-2325-B-010-007; and V100-D-005-4)

Citation Format: Chun-Yu Liu, Jung-Chen Su, Ling-Ming Tseng, Pei-Yi Chu, Wei-Tien Tai, Chung-Wai Shiau, Kuen-Feng Chen. Obatoclax analogue SC-2001 inhibits STAT3 phosphorylation by enhancing protein tyrosine phosphatase SHP-1 expression and induces apoptosis in human breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3803. doi:10.1158/1538-7445.AM2014-3803