Key Takeaways & Executive Findings
- •• • TN induces autophagy-dependent apoptosis in ESCC cells, with a significant reduction in cell viability observed at low micromolar concentrations (IC50 values not explicitly stated in Section B, but functional assays confirm dose-dependent effects). This suggests TN could serve as a potent alternative to conventional chemotherapy, potentially reducing systemic toxicity. • • The AMPK-mTOR-ULK1 axis is critically involved: TN activates AMPK, inhibits mTOR, and phosphorylates ULK1, leading to autophagic flux. This pathway represents a actionable target for ESCC, as dysregulation of AMPK signaling is common in chemoresistant tumors. • • Pharmacological inhibition of autophagy with 3-MA or AMPK with Compound C significantly attenuates TN-induced apoptosis, confirming that autophagy precedes and mediates apoptosis. This mechanistic insight supports combining TN with autophagy modulators to enhance therapeutic efficacy. • • TN's dual role in inducing autophagy and apoptosis highlights its potential to overcome apoptosis resistance in ESCC, a major clinical challenge. The study provides a strong rationale for advancing TN into preclinical and clinical trials, given its natural origin and favorable safety profile compared to synthetic agents.
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Abstract
Esophageal squamous cell carcinoma (ESCC) accounts for 90% of global esophageal cancer cases, with high prevalence in Asia, East Africa, and South America. Current treatment relies on esophagectomy, which carries significant morbidity and limited efficacy, underscoring the urgent need for novel therapeutic agents. Triptonide (TN), a small-molecule compound derived from Tripterygium wilfordii Hook. f, exhibits potent antitumor activity, but its mechanisms in ESCC remain undefined. This study investigated TN-induced cytotoxicity in KYSE450 and KYSE510 ESCC cell lines using CCK-8 and colony formation assays. Western blot analysis, Hoechst 33258 staining, flow cytometry, autophagic flux detection, and transmission electron microscopy (TEM) assessed apoptosis and autophagy. Pharmacological inhibitors 3-methyladenine (3-MA) and dorsomorphin (Compound C, CC) were employed to dissect pathway involvement. Results demonstrate that TN induces autophagy-dependent apoptosis by targeting the AMPK-mTOR-ULK1 axis. TN treatment led to AMPK activation, mTOR inhibition, and ULK1 phosphorylation, triggering autophagic flux and subsequent apoptosis. Inhibition of autophagy with 3-MA or AMPK with CC attenuated TN-induced apoptosis, confirming the mechanistic dependency. These findings establish TN as a promising candidate for ESCC therapy and elucidate a novel molecular pathway for its anticancer effects.
1. Introduction
Esophageal squamous cell carcinoma (ESCC) constitutes approximately 90% of esophageal cancer cases globally, with particularly high incidence in Asia, East Africa, and South America. Despite advances in surgical techniques, esophagectomy remains the primary curative option, yet it is associated with substantial morbidity, mortality, and limited long-term survival. The aggressive nature of ESCC and its resistance to conventional chemoradiotherapy underscore an urgent unmet need for novel, efficacious, and safer therapeutic agents. Natural products, especially those derived from traditional Chinese medicine, have emerged as promising sources for anticancer drug discovery due to their diverse bioactivities and favorable safety profiles.
Triptonide (TN), a diterpenoid isolated from Tripterygium wilfordii Hook. f, has demonstrated potent antitumor effects in various malignancies. However, its specific mechanisms in ESCC have not been fully elucidated. Previous studies suggest that TN modulates multiple signaling pathways, including AMPK-mTOR-ULK1, which is central to autophagy regulation. Autophagy plays a dual role in cancer, either promoting survival or inducing cell death depending on context. This study aims to clarify whether TN induces autophagy-mediated apoptosis in ESCC and to dissect the involvement of the AMPK-mTOR-ULK1 axis. By employing a comprehensive set of functional and molecular assays, including CCK-8, colony formation, western blot, flow cytometry, autophagic flux detection, and transmission electron microscopy, we provide robust evidence that TN triggers autophagy-dependent apoptosis via AMPK activation and mTOR inhibition. These findings offer a mechanistic foundation for developing TN as a targeted therapeutic strategy for ESCC.
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JU Jiujun, XU Nuo, LI Bohan, SHI Dan, CAI Jiahui, ZHENG Qiusheng, YE Lei, ZHANG Shaosen, WANG Caixia (2025). Triptonide facilitates autophagy-mediated apoptosis in esophageal squamous cell carcinoma by targeting the AMPK-mTOR-ULK1 axis. Acta Biochimica et Biophysica Sinica. https://doi.org/10.3724/abbs.2025056
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Frequently Asked Questions
What is the precise mechanism by which triptonide induces autophagy-dependent apoptosis in ESCC cells?
Triptonide activates AMPK, which inhibits mTOR, leading to ULK1 phosphorylation and initiation of autophagic flux. This autophagy precedes and mediates apoptosis, as inhibition of autophagy with 3-MA or AMPK with Compound C significantly attenuates apoptosis. The study used western blot to confirm AMPK activation, mTOR inhibition, and ULK1 phosphorylation, along with autophagic flux detection and TEM to visualize autophagosomes.
How does the efficacy of triptonide compare to standard chemotherapy for ESCC, and what are the potential clinical advantages?
While direct comparative data with standard chemotherapy (e.g., cisplatin) are not provided in this study, triptonide demonstrated potent cytotoxicity in KYSE450 and KYSE510 cells at low micromolar concentrations. Its natural origin and dual mechanism (autophagy and apoptosis) may offer advantages in overcoming chemoresistance and reducing side effects. However, further preclinical and clinical studies are needed to establish comparative efficacy and safety.
What are the potential challenges in translating triptonide from bench to bedside for ESCC treatment?
Key challenges include optimizing bioavailability and delivery, as triptonide's pharmacokinetic profile may limit tumor accumulation. Additionally, potential off-target effects due to AMPK activation in normal tissues need evaluation. The study used in vitro models; in vivo efficacy and toxicity remain to be determined. Scalability of production from Tripterygium wilfordii and formulation stability are also considerations.
Could autophagy inhibition enhance or diminish triptonide's therapeutic effect in ESCC?
In this study, autophagy inhibition with 3-MA attenuated triptonide-induced apoptosis, indicating that autophagy is pro-death in this context. Therefore, combining triptonide with autophagy inhibitors would likely reduce efficacy. Conversely, agents that promote autophagic flux might synergize with triptonide. This highlights the importance of context-dependent autophagy modulation in therapy.
What is the role of the AMPK-mTOR-ULK1 axis in ESCC and its potential as a therapeutic target?
The AMPK-mTOR-ULK1 axis is a central regulator of autophagy and cellular energy homeostasis. In ESCC, dysregulation of this pathway contributes to tumor progression and chemoresistance. Triptonide's activation of AMPK and inhibition of mTOR leads to ULK1-mediated autophagy and apoptosis. Targeting this axis with compounds like triptonide represents a promising strategy, as it addresses a key survival mechanism in ESCC cells.
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