Cyclovirobuxine D Induces Autophagy-Associated Cell Death via the Akt/mTOR Pathway in MCF-7 Human Breast Cancer Cells

Abstract

Abstract. Autophagy is a highly regulated and multi-step biological process that serves to remove damaged cytoplasmic components and organelles. It has been suggested that the activation of autophagy may be a promising therapeutic strategy for cancer treatment by triggering cell death. In this study, we reported that cyclovirobuxine D (CVB-D), an alkaloid component in a traditional Chinese herb, could induce autophagy in the MCF-7 human breast cancer cell line. CVB-D inhibited the viability of MCF-7 cells in a concentration-and time-dependent manner. Activation of autophagy was characterized by transmission electron microscopy, monodansylcadaverine staining, and expression of autophagy marker microtubule-associated protein 1 light chain 3 (LC3). After CVB-D treatment, a clear accumulation of autophagosomes was observed accompanied with elevated LC3 fluorescent puncta. Western blot analysis revealed that CVB-D significantly promoted the conversion from LC3-I to LC3-II and the expression of autophagy-related protein 5 (ATG5), which are both essential for autophagosome formation. On the other hand, CVB-D-induced autophagy and decrease in cell viability could be blocked by 3-methyladenine, a well-established autophagy inhibitor. Moreover, CVB-D attenuated the phosphorylation of Akt and mTOR, two pivotal suppressors in autophagy pathways. These findings shed new light on the pharmacological actions and mechanism of CVB-D and may support the potential utility of autophagy inducers in cancer treatment.

Natural Compounds As Modulators of Non-apoptotic Cell Death in Cancer Cells

“…Mollugin, a bioactive phytochemical isolated from Rubia cordifolia L ., exhibited anticancer activity against various cancer cells [246]. Further experiments demonstrated that PI3K/AKT/mTOR/ p70RS6K and ERK signaling pathways participated in mollugin-induced autophagy and apoptosis [247]. Cyclovirobuxine D (CVB-D) could induce autophagy in the MCF-7 human breast cancer cell line evidenced by accumulation of autophagosomes and elevated LC3B fluorescent puncta, as well as increased LC3B-I-to-LC3B-II conversion, and the expression of ATG5, as described in [247].…”

“…Further experiments demonstrated that PI3K/AKT/mTOR/ p70RS6K and ERK signaling pathways participated in mollugin-induced autophagy and apoptosis [247]. Cyclovirobuxine D (CVB-D) could induce autophagy in the MCF-7 human breast cancer cell line evidenced by accumulation of autophagosomes and elevated LC3B fluorescent puncta, as well as increased LC3B-I-to-LC3B-II conversion, and the expression of ATG5, as described in [247]. CVB-D-induced autophagy and decrease in cell viability could be blocked by 3-MA [247].…”

Poly(ADP‐ribose) polymerase 1 induces cardiac fibrosis by mediating mammalian target of rapamycin activity

“…40 The intensity of protein bands was measured by using the Lab Works software (Bio-Rad, Berkeley, CA). Primary antibodies against α-tubulin (diluted 1:5000) were from Sigma-Aldrich (St Louis, MO).…”

Autophagy regulation in the development and treatment of breast cancer

“…Natural products such as cyclovirobuxine D (CVB-D), an alkaloid component isolated from the roots of Buxus microphylla var. Sinica, are often used as direct or indirect sources to enhance the efficacy of chemotherapy or ameliorate its side effects [67]. A recent study reported carnosol, a naturally occurring polyphenol, being an inducer of ROS-mediated Beclin-1-independent autophagy and apoptosis in triple negative MDA-MB-231 cell line [68].…”