Saikosaponin-d, a novel SERCA inhibitor, induces autophagic cell death in apoptosis-defective cells

Abstract

Autophagy is an important cellular process that controls cells in a normal homeostatic state by recycling nutrients to maintain cellular energy levels for cell survival via the turnover of proteins and damaged organelles. However, persistent activation of autophagy can lead to excessive depletion of cellular organelles and essential proteins, leading to caspase-independent autophagic cell death. As such, inducing cell death through this autophagic mechanism could be an alternative approach to the treatment of cancers. Recently, we have identified a novel autophagic inducer, saikosaponin-d (Ssd), from a medicinal plant that induces autophagy in various types of cancer cells through the formation of autophagosomes as measured by GFP-LC3 puncta formation. By computational virtual docking analysis, biochemical assays and advanced live-cell imaging techniques, Ssd was shown to increase cytosolic calcium level via direct inhibition of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pump, leading to autophagy induction through the activation of the Ca2+/calmodulin-dependent kinase kinase–AMP-activated protein kinase–mammalian target of rapamycin pathway. In addition, Ssd treatment causes the disruption of calcium homeostasis, which induces endoplasmic reticulum stress as well as the unfolded protein responses pathway. Ssd also proved to be a potent cytotoxic agent in apoptosis-defective or apoptosis-resistant mouse embryonic fibroblast cells, which either lack caspases 3, 7 or 8 or had the Bax-Bak double knockout. These results provide a detailed understanding of the mechanism of action of Ssd, as a novel autophagic inducer, which has the potential of being developed into an anti-cancer agent for targeting apoptosis-resistant cancer cells.

The Anticancer Agent Di-2-pyridylketone 4,4-Dimethyl-3-thiosemicarbazone (Dp44mT) Overcomes Prosurvival Autophagy by Two Mechanisms

“…Studies have reported that cytotoxic drugs can induce autophagic cell death when the apoptotic pathway is non-functional (32,37). In this study, Dp44mT was found to induce classical markers of both autophagy (Fig.…”

“…In contrast, previous studies have also reported a prodeath function of persistent autophagy where blocking the autophagic response using the inhibitor 3-methyladenine or the silencing of autophagy genes ATG5, ATG7, and BECN1 inhibited cell death (35,36). Furthermore, in response to various agents, apoptosis-resistant fibroblasts undergo cell death associated with autophagosome/autolysosome accumulation (37,38). These findings indicate the role of autophagic cell death as an alternative death mechanism to apoptosis (37,38).…”

“…Furthermore, in response to various agents, apoptosis-resistant fibroblasts undergo cell death associated with autophagosome/autolysosome accumulation (37,38). These findings indicate the role of autophagic cell death as an alternative death mechanism to apoptosis (37,38).…”

Combination of graphene oxide–silver nanoparticle nanocomposites and cisplatin enhances apoptosis and autophagy in human cervical cancer cells

“…76,77 Chemotherapy-induced inhibitory effects on cell viability and cell proliferation usually leads to the demise of cancer cells, which can be mediated by either apoptotic or autophagic pathways. Previous studies have indicated that autophagy can act as both an inhibitor and enabler of programmed cell death.…”

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

“…It has been reported that the overexpression of genes encoding core components of autophagic pathways, such as Beclin 1, can inhibit various cancer types (9), and the induction of autophagy with the use of chemotherapy and radiotherapy helps to remove damaged and mutated cells, thereby reducing tumor size (10). In addition, autophagy is suggested to be an effective approach to alleviate treatment resistance in apoptosis-defective tumor cells (11). Although the definite mechanism underlying autophagic cell death still remains to be elucidated, autophagy can function as a suppressor of cancer, which makes it a promising therapeutic target.…”