Natural compound So-2 suppresses triple-negative breast cancer through inducing ferroptosis via downregulating transcription factor E2F7.

Triple-negative breast cancer (TNBC), accounting for about 15∼18% of all breast cancers, is notorious for its poor prognosis, high rate of relapse and short overall survival. Because of lacking effective therapeutic targets or drugs, treatment of TNBC in clinical encounters great obstacle. Siegesbeckiaorientalis L. have been used as a traditional Chinese medicine "Xi-Xian-Cao" for centuries with multiple medicinal benefits including cancerous treatment. We have reported the isolation of twenty-seven germacranolides including So-2 from the aerial parts of S. orientalis with potent cytotoxicity against breast cancer cells. The studyaims to verified the anti-TNBC function of the natural compound So-2 both in vitro and vivo and uncover the underlying mechanism. The results showed that So-2 caused cell cycle arrest and suppress TNBC cell proliferation and migration. Also, So-2 was first identified to be a bona fide ferroptosis inducer in TNBC cells. So-2 effectively suppressed tumor growth of TNBC by using an orthotopic transplantation tumor model. We also characterized the oncogenic role of the transcription factor E2F7 in TNBC. E2F7 was demonstrated to be involved in the ferroptosis-inducing and tumor suppression effect of So-2. Altogether, So-2 exhibits inhibitory effect on TNBC both in vitro and vivo by inducing TNBC ferroptosis via downregulating the expression of E2F7. These findings provide valuable insight into the pathogenesis of TNBC. The natural compound So-2, isolated from Chinese traditional medicine, might be a prospective drug candidate in TNBC therapy.

GBE attenuates arsenite-induced hepatotoxicity by regulating E2F1-autophagy-E2F7a pathway and restoring lysosomal activity.

Arsenic is an environmental toxicant. Its overdose can cause liver damage. Autophagy has been reported to be involved in arsenite (iAs3+ ) cytotoxicity and plays a dual role in cell proliferation and cell death. However, the effect and molecular regulative mechanisms of iAs3+ on autophagy in hepatocytes remains largely unknown. Here, we found that iAs3+ exposure lead to hepatotoxicity by inducing autophagosome and autolysosome accumulation. On the one hand, iAs3+ promoted autophagosome synthesis by inhibiting E2F1/mTOR pathway in L-02 human hepatocytes. On the other, iAs3+ blocked autophagosome degradation partially via suppressing the expression of INPP5E and Rab7 as well as impairing lysosomal activity. More importantly, autophagosome and autolysosome accumulation induced by iAs3+ increased the protein level of E2F7a, which could further inhibit cell viability and induce apoptosis of L-02 cells. The treatment of Ginkgo biloba extract (GBE) effectively reduced autophagosome and autolysosome accumulation and thus alleviated iAs3+ -induced hepatotoxicity. Moreover, GBE could also protect lysosomal activity, promote the phosphorylation level of E2F1 (Ser364 and Thr433) and Rb (Ser780) as well as suppress the protein level of E2F7a in iAs3+ -treated L-02 cells. Taken together, our data suggested that autophagosome and autophagolysosome accumulation play a critical role for iAs3+ -induced hepatotoxicity, and GBE is a promising candidate for intervening iAs3+ induced liver damage by regulating E2F1-autophagy-E2F7a pathway and restoring lysosomal activity.