Low nanomolar concentrations of Cucurbitacin-I induces G2/M phase arrest and apoptosis by perturbing redox homeostasis in gastric cancer cells in vitro and in vivo.

Chao Deng ,M Chen,B Zhang,L Wang,W Zhang,X Zhang,Ying Lv ,Chaoqin Duan ,Wei Kang ,Thai-Yen Ling ,Gengli Duan ,Fan Zhang ,Lei Wu ,Shanshan Shen ,Yue Cao ,Xiaohui Ding ,Shuyun Zhang ,Hongli Yan ,Guohai Xu ,Shenglan Huang ,Xiaoping Zou

doi:10.1038/cddis.2016.13

Abstract

Cucurbitacin-I (Cu-I, also known as Elatericin B or JSI-124) is developed to inhibit constitutive and abnormal activation of STAT3 in many cancers, demonstrating a potent anticancer activity by targeting disruption of STAT3 function. Here, we for the first time systematically studied the underlying molecular mechanisms of Cu-I-induced gastric cancer cell death both in vitro and in vivo. In our study, we show that Cu-I markedly inhibits gastric cancer cell growth by inducing G2/M phase cell cycle arrest and apoptosis at low nanomolar concentrations via a STAT3-independent mechanism. Notably, Cu-I significantly decreases intracellular GSH/GSSG ratio by inhibiting NRF2 pathway to break cellular redox homeostasis, and subsequently induces the expression of GADD45α in a p53-independent manner, and activates JNK/p38 MAPK signaling. Interestingly, Cu-I-induced GADD45α and JNK/p38 MAPK signaling form a positive feedback loop and can be reciprocally regulated by each other. Therefore, the present study provides new insights into the mechanisms of antitumor effects of Cu-I, supporting Cu-I as an attractive therapeutic drug in gastric cancer by modulating the redox balance.

Highlights

Cucurbitacin-I (Cu-I), known as Elatericin B or JSI-124, was originally identified to be a potent selective inhibitor of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway with antiproliferative and antitumor properties.[4,5,6,7] Upon inhibition of STAT3-dependent gene transcription, Cu-I elicits antiproliferative effects in breast, glioma, head and neck squamous carcinoma, and lung cancer cells with activated STAT3 signaling.[4,6,8,9] the anticancer effect and underlying mechanism of Cu-I in human gastric cancer is still elusive
We show that Cu-I markedly inhibits the growth of gastric cancer cell lines by inducing G2/M phase cell cycle arrest and apoptosis at low nanomolar concentrations
Cu-I treatment almost completely inhibited the formation of AGS and HGC-27 cell colonies as determined by colony-formation assays (Figure 1c,Supplementary Figure 1a and 1b). These data support a suppressive role for Cu-I, which might inhibit gastric cancer cell growth at low nanomolar concentrations

Summary

Introduction

Cucurbitacin-I (Cu-I), known as Elatericin B or JSI-124, was originally identified to be a potent selective inhibitor of the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway with antiproliferative and antitumor properties.[4,5,6,7] Upon inhibition of STAT3-dependent gene transcription, Cu-I elicits antiproliferative effects in breast, glioma, head and neck squamous carcinoma, and lung cancer cells with activated STAT3 signaling.[4,6,8,9] the anticancer effect and underlying mechanism of Cu-I in human gastric cancer is still elusive. Mechanistic analysis revealed that the effect of Cu-I is independent of STAT3 signaling but rather involves the disruption of the balance between pro-oxidants (ROS generation) and antioxidants (mainly expressed by the GSH/GSSG ratio). To the best of our knowledge, we revealed for the first time that Cu-I could efficiently inhibit NRF2 and its downstream targets, whose main function is to modulate GSH generation.[10] we confirmed our in vitro observations by showing profound antitumor activity of Cu-I in a xenograft model with no apparent toxicity to the mice. Our findings collectively indicated that Cu-I may become a potential therapeutic agent against human gastric cancer in the future.

Methods

Results

Conclusion