Plant sesquiterpene lactone derivatives deregulate mitochondrial function and induce paraptosis-like cell death in triple negative breast cancer cells
Jeng-Yuan Shiau1, Yong-Qun Chang1, Kyoko Nakagawa-Goto2, Kuo-Hsiung Lee3, and Lie-Fen Shyur1*
1Agricultural Biotechnology Research Center, Academia Sinica, Taiwan; 2 College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan; 3 Natural Products Research Laboratories, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
Triple negative breast cancer (TNBC) is a highly metastatic cancer with poor prognosis which presents a clinical challenge due to lack of efficient target for therapy. Previously we observed that a plant germacranolide sesquiterpene lactone deoxyelephantopin (DET) and its novel derivative DETD-35 are effective in inhibiting TNBC cell activity in vitro and in vivo through induction of reactive oxygen species (ROS) in the MDA-MB-231 cancer cells, subsequently induction of endoplasmic reticulum (ER) stress and cell apoptosis. In this study, we further observed that both DET and DETD-35 can cause loss of mitochondrial membrane potential and increase of the expression of voltage-dependent anion channel 1 (VDAC1), an important protein of mitochondria-mediated apoptosis. Meanwhile, we treated TNBC cells with an in-house design DET-near infrared (NIR) fluorescent conjugate which was found co-localized with VDAC1 in mitochondria within a 4 h treatment time. A longer treatment (24 h) with either compound significantly promoted cell swelling and massive cytoplasmic vacuole formation originated from the swelling of ER or mitochondria, and the phenotypic changes in cancer cells were reversed by pretreatment with ROS scavenger N-acetylcysteine and protein synthesis inhibitor, cycloheximide. The results indicate that both compound treatments caused paraptotic programmed cell death in TNBC cells. Moreover, cytosolic calcium level and autophagosomal LC3 protein were accumulated in treated cells, while knockdown of LC3 gene by shRNA attenuated anti-proliferative activity of DET or DETD-35 in TNBC cells. Overall, this study provides novel mechanistic insights of plant sesquiterpene lactone derivatives on inhibiting TNBC cell activities through induction of mitochondria dysfunction and paraptosis-like cell death that support the potential use of such plant-derived agents in TNBC intervention.