Gambogic acid enhances the radiosensitivity of human esophageal cancer cells by inducing reactive oxygen species via targeting Akt/mTOR pathway

Therapeutic implications of signaling pathways and tumor microenvironment interactions in esophageal cancer

Esophageal cancer (EC) is significantly influenced by the tumor microenvironment (TME) and altered signaling pathways. Downregulating these pathways in EC is essential for suppressing tumor development, preventing metastasis, and enhancing therapeutic outcomes. This approach can increase tumor sensitivity to treatments, enhance patient outcomes, and inhibit cancer cell proliferation and spread. The TME, comprising cellular and non-cellular elements surrounding the tumor, significantly influences EC's development, course, and treatment responsiveness. Understanding the complex relationships within the TME is crucial for developing successful EC treatments. Immunotherapy is a vital TME treatment for EC. However, the heterogeneity within the TME limits the application of anticancer drugs outside clinical settings. Therefore, identifying reliable microenvironmental biomarkers that can detect therapeutic responses before initiating therapy is crucial. Combining approaches focusing on EC signaling pathways with TME can enhance treatment outcomes. This integrated strategy aims to interfere with essential signaling pathways promoting cancer spread while disrupting factors encouraging tumor development. Unraveling aberrant signaling pathways and TME components can lead to more focused and efficient treatment approaches, identifying specific cellular targets for treatments. Targeting the TME and signaling pathways may reduce metastasis risk by interfering with mechanisms facilitating cancer cell invasion and dissemination. In conclusion, this integrative strategy has significant potential for improving patient outcomes and advancing EC research and therapy. This review discusses the altered signaling pathways and TME in EC, focusing on potential future therapeutics.

Prodrug Nanosensitizer Overcomes the Radiation Resistance of Hypoxic Tumor

Clinical radiation therapy (RT) is often hindered by the low radiation energy absorption coefficient and the hypoxic features of tumor tissues. Among the tremendous efforts devoted to overcoming the barriers to efficient RT, the application of hypoxic radiosensitizers and cell-cycle-specific chemotherapeutics has shown great potential. However, their effectiveness is often compromised by their limited bioavailability, especially in the hypoxic region, which plays a major role in radioresistance. Herein, to simultaneously improve the delivery efficacy of both hypoxic radiosensitizer and cell-cycle-specific drug, a gambogic acid (GA) metronidazole (MN) prodrug (GM) was designed and synthesized based on GA, a naturally occurring chemotherapeutic and multiple pathway inhibitor, and MN, a typical hypoxic radiosensitizer. In combination with MN-containing block copolymers, the prodrug nanosensitizer (NS) of GM was obtained. Owing to the bioreduction of MN, the as-designed prodrug could be efficiently delivered to hypoxic cells and act on mitochondria to cause the accumulation of reactive oxygen species. The strong G₂/M phase arrest caused by the prodrug NS could further sensitize treated cells to external radiation under hypoxic conditions by increasing DNA damage and delaying DNA repair. After coadministration of the NS with a well-established tissue-penetrating peptide, efficient tumor accumulation, deep tumor penetration, and highly potent chemoradiotherapy could be achieved.

Nanoscale Features of Gambogic Acid Induced ROS-Dependent Apoptosis in Esophageal Cancer Cells Imaged by Atomic Force Microscopy

Gambogic acid (GA), a kind of polyprenylated xanthone derived from Garcinia hanburyi tree, has showed spectrum anticancer effects both in vitro and in vivo with low toxicity. However, up to now, there is little information about the effects of GA on esophageal cancer. In this study, we aim to test the anticancer effects of GA on esophageal cancer EC9706 cells. We established a nanoscale imaging method based on AFM to evaluate the reactive oxygen species- (ROS-) mediated anticancer effects of GA on esophageal cancer regarding the morphological and ultrastructural changes of esophageal cancer cells. The obtained results demonstrated that GA could inhibit cell proliferation, induce apoptosis, induce cell cycle arrest, and induce mitochondria membrane potential disruption in a ROS-dependent way. And using AFM imaging, we also found that GA could induce the damage of cellular morphology and increase of membrane height distribution and membrane roughness in EC9706 cells, which could be reversed by the removal of GA-induced excessive intracellular ROS. Our results not only demonstrated the anticancer effects of GA on EC9706 cells in ROS-dependent mechanism but also strongly suggested AFM as a powerful tool for the detection of ROS-mediated cancer cell apoptosis on the basis of imaging.

The role of autophagy in initiation, progression, TME modification, diagnosis, and treatment of esophageal cancers

Autophagy is a highly conserved metabolic process with a cytoprotective function. Autophagy is involved in cancer, infection, immunity, and inflammation and may be a potential therapeutic target. Increasing evidence has revealed that autophagy has primary implications for esophageal cancer, including its initiation, progression, tumor microenvironment (TME) modification, diagnosis, and treatment. Notably, autophagy displayed excellent application potential in radiotherapy combined with immunotherapy. Radiotherapy combined with immunotherapy is a new potential therapeutic strategy for cancers, including esophageal cancer. Autophagy modulators can work as adjuvant enhancers in radiotherapy or immunotherapy of cancers. This review highlights the most recent data related to the role of autophagy regulation in esophageal cancer.

Function of selected natural antidiabetic compounds with potential against cancer via modulation of the PI3K/AKT/mTOR cascade

Diabetes mellitus (DM) is a metabolic disorder with growing global incidence, as 387 million people were diagnosed in 2014 with an expected projection of 642 million in 2040. Several complications are associated with DM including heart attack, stroke, kidney failure, blindness, and cancer. The latter is the second leading cause of death worldwide accounting for one in every six deaths, with liver, pancreas, and endometrium cancers are the most abundant among patients with diabetes. Phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway plays a vital role in developing a wide array of pathological disorders, among them diabetes and cancer. Natural secondary metabolites that counteract the deleterious effects of reactive oxygen species (ROS) and modulate PI3K/Akt/mTOR pathway could be a promising approach in cancer therapy. Here, 717 medicinal plants with antidiabetic activities were highlighted along with 357 bioactive compounds responsible for the antidiabetic activity. Also, 43 individual plant compounds with potential antidiabetic activities against cancer via the modulation of PI3K/Akt/mTOR cascade were identified. Taken together, the available data give an insight of the potential of repurposing medicinal plants and/or the individual secondary metabolites with antidiabetic activities for cancer therapy.

Silencing c-Jun inhibits autophagy and abrogates radioresistance in nasopharyngeal carcinoma by activating the PI3K/AKT/mTOR pathway

Background

Radioresistance plays an important role in the failure of radiotherapy (RT) for nasopharyngeal carcinoma (NPC), leading to poor prognosis. The purpose of this study was to explore the relationship between the expression of the c-Jun oncogene and the prognosis of NPC. In addition, we investigated the potential mechanisms of c-Jun in the regulation of tumor growth and radioresistance in NPC.

Methods

c-Jun expression in NPC tissues and nasopharyngeal mucosa tissues was evaluated using immunochemistry. c-Jun and its downstream targets were verified by dual-luciferase reporter assays. Inhibitors or activators were used to interfere with the PI3K/AKT/mTOR pathway. Protein expression was analyzed by western blotting. NPC nude mouse xenograft models were used to investigate the potential effects of c-Jun and ionizing radiation in vivo.

Results

The expression of c-Jun in NPC tissues was significantly higher than that in normal nasopharyngeal mucosa (NNM) tissues, and Cox regression analysis revealed that c-Jun overexpression was an independent risk factor for poor prognosis in NPC patients. Both in vitro and in vivo experiments verified that c-Jun targeted PI3K/AKT signaling. We also performed an in vivo study showing that c-Jun knockdown effectively suppressed NPC growth in a xenograft tumor model by autophagy inhibition, and these effects were accompanied by the upregulation of p-PI3K p-AKT, p-mTOR, and P62 and downregulation of LC3-II expression.

Conclusions

High expression of c-Jun was correlated with poor prognosis in NPC patients. c-Jun knockdown increased cell sensitivity to radiation by inhibiting autophagy activation via the PI3K/AKT/mTOR signaling pathway. The present study provides a theoretical basis for a promising treatment for radioresistant NPC by inhibiting c-Jun expression.

Discovery of novel nitrogenous heterocyclic-containing quinoxaline-1,4-di-N-oxides as potent activator of autophagy in M.tb-infected macrophages

As a continuation of our research on antimycobacterial agents, a series of novel quinoxaline-1,4-di-N-oxides (QdNOs) containing various nitrogenous heterocyclic moieties at the R₆ position were designed and synthesized. Antimycobacterial activities, as well as the cytotoxic effects, of the compounds were assayed. Four compounds (6b, 6f, 6n, and 6o), characterized by 2-carboxylate ethyl or benzyl ester, 6-imidazolyl or 1,2,4-triazolyl, and a 7-fluorine group, exhibited the most potent antimycobacterial activity against M.tb strain H37Rv (MIC ≤ 0.25 μg/mL) with low toxicity in VERO cells (SI = 169.3-412.1). Compound 6o also exhibited excellent antimycobacterial activity in an M.tb-infected macrophage model and was selected for further exploration of the mode of antimycobacterial action of QdNOs. The results showed that compound 6o was capable of disrupting membrane integrity and disturbing energy homeostasis in M.tb. Furthermore, compound 6o noticeably increased cellular ROS levels and, subsequently, induced autophagy in M.tb-infected macrophages, possibly indicating the pathways of QdNOs-mediated inhibition of intracellular M.tb replication. The in vivo pharmacokinetic (PK) profiles indicated that compounds 6o was acceptably safe and possesses favorable PK properties. Altogether, these findings suggest that compound 6o is a promising antimycobacterial candidate for further research.

The mechanisms and reversal strategies of tumor radioresistance in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of most lethal malignancies with high aggressive potential in the world. Radiotherapy is used as one curative treatment modality for ESCC patients. Due to radioresistance, the 5-year survival rates of patients after radiotherapy is less than 20%. Tumor radioresistance is very complex and heterogeneous. Cancer-associated fibroblasts (CAFs), as one major component of tumor microenvironment (TME), play critical roles in regulating tumor radioresponse through multiple mechanisms and are increasingly considered as important anti-cancer targets. Cancer stemness, which renders cancer cells to be extremely resistant to conventional therapies, is involved in ESCC radioresistance due to the activation of Wnt/β-catenin, Notch, Hedgehog and Hippo (HH) pathways, or the induction of epithelial-mesenchymal transition (EMT), hypoxia and autophagy. Non-protein-coding RNAs (ncRNAs), which account for more than 90% of the genome, are involved in esophageal cancer initiation and progression through regulating the activation or inactivation of downstream signaling pathways and the expressions of target genes. Herein, we mainly reviewed the role of CAFs, cancer stemness, non-coding RNAs as well as others in the development of radioresistance and clarify the involved mechanisms. Furthermore, we summarized the potential strategies which were reported to reverse radioresistance in ESCC. Together, this review gives a systematic coverage of radioresistance mechanisms and reversal strategies and contributes to better understanding of tumor radioresistance for the exploitation of novel intervention strategies in ESCC.

Polyphenol-Mediated Autophagy in Cancer: Evidence of In Vitro and In Vivo Studies

One of the hallmarks of cellular transformation is the altered mechanism of cell death. There are three main types of cell death, characterized by different morphological and biochemical features, namely apoptosis (type I), autophagic cell death (type II) and necrosis (type III). Autophagy, or self-eating, is a tightly regulated process involved in stress responses, and it is a lysosomal degradation process. The role of autophagy in cancer is controversial and has been associated with both the induction and the inhibition of tumor growth. Autophagy can exert tumor suppression through the degradation of oncogenic proteins, suppression of inflammation, chronic tissue damage and ultimately by preventing mutations and genetic instability. On the other hand, tumor cells activate autophagy for survival in cellular stress conditions. Thus, autophagy modulation could represent a promising therapeutic strategy for cancer. Several studies have shown that polyphenols, natural compounds found in foods and beverages of plant origin, can efficiently modulate autophagy in several types of cancer. In this review, we summarize the current knowledge on the effects of polyphenols on autophagy, highlighting the conceptual benefits or drawbacks and subtle cell-specific effects of polyphenols for envisioning future therapies employing polyphenols as chemoadjuvants.

Gambogic acid: A shining natural compound to nanomedicine for cancer therapeutics

The United States Food and Drug Administration has permitted number of therapeutic agents for cancer treatment. Most of them are expensive and have some degree of systemic toxicity which makes overbearing in clinical settings. Although advanced research continuously applied in cancer therapeutics, but drug resistance, metastasis, and recurrence remain unanswerable. These accounts to an urgent clinical need to discover natural compounds with precisely safe and highly efficient for the cancer prevention and cancer therapy. Gambogic acid (GA) is the principle bioactive and caged xanthone component, a brownish gamboge resin secreted from the of Garcinia hanburyi tree. This molecule showed a spectrum of biological and clinical benefits against various cancers. In this review, we document distinct biological characteristics of GA as a novel anti-cancer agent. This review also delineates specific molecular mechanism(s) of GA that are involved in anti-cancer, anti-metastasis, anti-angiogenesis, and chemo-/radiation sensitizer activities. Furthermore, recent evidence, development, and implementation of various nanoformulations of gambogic acid (nanomedicine) have been described.

Autophagy modulators for the treatment of oral and esophageal squamous cell carcinomas

Oral squamous cell carcinomas (OSCC) and esophageal squamous cell carcinomas (ESCC) exhibit a survival rate of less than 60% and 40%, respectively. Late-stage diagnosis and lack of effective treatment strategies make both OSCC and ESCC a significant health burden. Autophagy, a lysosome-dependent catabolic process, involves the degradation of intracellular components to maintain cell homeostasis. Targeting autophagy has been highlighted as a feasible therapeutic strategy with clinical utility in cancer treatment, although its associated regulatory mechanisms remain elusive. The detection of relevant biomarkers in biological fluids has been anticipated to facilitate early diagnosis and/or prognosis for these tumors. In this context, recent studies have indicated the presence of specific proteins and small RNAs, detectable in circulating plasma and serum, as biomarkers. Interestingly, the interplay between biomarkers (eg, exosomal microRNAs) and autophagic processes could be exploited in the quest for targeted and more effective therapies for OSCC and ESCC. In this review, we give an overview of the available biomarkers and innovative targeted therapeutic strategies, including the application of autophagy modulators in OSCC and ESCC. Additionally, we provide a viewpoint on the state of the art and on future therapeutic perspectives combining the early detection of relevant biomarkers with drug discovery for the treatment of OSCC and ESCC.

Gambogic acid increases the sensitivity to paclitaxel in drug‑resistant triple‑negative breast cancer via the SHH signaling pathway

Paclitaxel is the most frequently used therapy regimen for triple-negative breast cancer (TNBC). However, chemoresistance frequently occurs, leading to enhanced failure rates of chemotherapy in TNBC; therefore, novel biological therapies are urgently needed. Gambogic acid (GA) has potent anticancer effects and inhibits tumor growth in several types of human cancer. However, the effects of GA on paclitaxel-resistant TNBC remain unknown. In the present study, the Cell Counting Kit-8 assay was used to examine the effect of GA and/or paclitaxel on the viability of TNBC cells; flow cytometry was used to examine the effects of GA on cell apoptosis; and western blotting and reverse transcription-quantitative PCR were used to determine the effects of GA on the expression of sonic hedgehog (SHH) signaling pathway target genes. The present results indicated that GA significantly inhibited the viability and enhanced the rate of apoptosis in paclitaxel-resistant MDA-MB-231 cells via activating the SHH signaling pathway. In vivo experiments confirmed that GA treatment enhanced the sensitivity of MDA-MB-231 cells to paclitaxel via the SHH signaling pathway. In conclusion, the combination of GA with paclitaxel may increase the antitumor effects on paclitaxel-resistant TNBC via downregulating the SHH signaling pathway.

Apoptotic Pathway as the Therapeutic Target for Anticancer Traditional Chinese Medicines

Cancer is a leading cause of morbidity and mortality worldwide. Apoptosis is a process of programmed cell death and it plays a vital role in human development and tissue homeostasis. Mounting evidence indicates that apoptosis is closely related to the survival of cancer and it has emerged as a key target for the discovery and development of novel anticancer drugs. Various studies indicate that targeting the apoptotic signaling pathway by anticancer drugs is an important mechanism in cancer therapy. Therefore, numerous novel anticancer agents have been discovered and developed from traditional Chinese medicines (TCMs) by targeting the cellular apoptotic pathway of cancer cells and shown clinically beneficial effects in cancer therapy. This review aims to provide a comprehensive discussion for the role, pharmacology, related biology, and possible mechanism(s) of a number of important anticancer TCMs and their derivatives mainly targeting the cellular apoptotic pathway. It may have important clinical implications in cancer therapy.

Gambogic acid regulates the migration and invasion of colorectal cancer via microRNA-21-mediated activation of phosphatase and tensin homolog

Gambogic acid (GA) has been reported to inhibit cancer cell proliferation and migration and enhance apoptosis. Several signaling pathways were identified to be involved in GA function, including PI3K/Akt, caspase-3 apoptosis and TNF-α/NF-κB. However, to the best of our knowledge, the association between miRNA and GA has not been explored. The present study initially demonstrated that GA could inhibit HT-29 cancer cell proliferation using an MTT assay. In addition, a Transwell assay and a wound-healing assay respectively indicated that GA inhibited HT-29 cancer cell invasion and migration, which was also confirmed by the increased MMP-9 protein expression. Furthermore, GA induced the apoptosis of HT-29 cancer cells in an Annexin V and PI double staining assay. Moreover, treatment with GA significantly decreased miR-21 expression in these cells. Additionally, western blot analysis demonstrated that GA treatment enhanced the activation of phosphatase and tensin homolog (PTEN) along with the suppression of PI3K and p-Akt. Furthermore, miR-21 mimics reversed all the aforementioned activities of GA, which indicated that miR-21 was the effector of GA and blocked PI3K/Akt signaling pathway via enhancing PTEN activity. In summary, GA induced HT-29 cancer cell apoptosis via decreasing miR-21 expression and blocking PI3K/Akt, which may be a useful novel insight for future CRC treatment.

Glutaredoxin 3 promotes nasopharyngeal carcinoma growth and metastasis via EGFR/Akt pathway and independent of ROS

Glutaredoxin 3 (GLRX3) is antioxidant enzyme, maintaining a low level of ROS, thus contributing to the survival and metastasis of several types of cancer. However, the expression and functions of GLRX3 have not been addressed in nasopharyngeal carcinoma (NPC). In this study, we found that GLRX3 was overexpressed in NPC. Knockdown of GLRX3 in NPC cell lines inhibited proliferation in vitro, tumorignesis in vivo, and colony formation. In addition, GLRX3 knockdown decreased the migration and invasion capacity of NPC cells by reversing the epithelial-mesenchymal transition (EMT). Furthermore, stabilization of GLRX3 was positively related to with epidermal growth factor receptor (EGFR) expression and negatively with ROS generation. Phosphorylation of Akt, a key downstream effector, was induced by EGFR signaling but did not rely on increasing ROS level in NPC cells. GLRX3 might be an oncoprotein in NPC, playing important roles in increasing redox reaction and activating EGFR/ Akt signals, so it may be a therapeutic target for NPC.

Therapeutic potential of gambogic acid, a caged xanthone, to target cancer

Natural compounds have enormous biological and clinical activity against dreadful diseases such as cancer, as well as cardiovascular and neurodegenerative disorders. In spite of the widespread research carried out in the field of cancer therapeutics, cancer is one of the most prevalent diseases with no perfect treatment till date. Adverse side effects and the development of chemoresistance are the imperative limiting factors associated with conventional chemotherapeutics. For this reason, there is an urgent need to find compounds that are highly safe and efficacious for the prevention and treatment of cancer. Gambogic acid (GA) is a xanthone structure extracted from the dry, brownish gamboge resin secreted from the Garcinia hanburyi tree in Southeast Asia and has inherent anti-cancer properties. In this review, the molecular mechanisms underlying the targets of GA that are liable for its effective anti-cancer activity are discussed that reveal the potential of GA as a pertinent candidate that can be appropriately developed and designed into a capable anti-cancer drug.

Autophagy in 5-Fluorouracil Therapy in Gastrointestinal Cancer: Trends and Challenges

Objective:

5-Fluorouracil (5-FU)-based combination therapies are standard treatments for gastrointestinal cancer, where the modulation of autophagy is becoming increasingly important in offering effective treatment for patients in clinical practice. This review focuses on the role of autophagy in 5-FU-induced tumor suppression and cancer therapy in the digestive system.

Data Sources:

All articles published in English from 1996 to date those assess the synergistic effect of autophagy and 5-FU in gastrointestinal cancer therapy were identified through a systematic online search by use of PubMed. The search terms were “autophagy” and “5-FU” and (“colorectal cancer” or “hepatocellular carcinoma” or “pancreatic adenocarcinoma” or “esophageal cancer” or “gallbladder carcinoma” or “gastric cancer”).

Study Selection:

Critical reviews on relevant aspects and original articles reporting in vitro and/or in vivo results regarding the efficiency of autophagy and 5-FU in gastrointestinal cancer therapy were reviewed, analyzed, and summarized. The exclusion criteria for the articles were as follows: (1) new materials (e.g., nanomaterial)-induced autophagy; (2) clinical and experimental studies on diagnostic and/or prognostic biomarkers in digestive system cancers; and (3) immunogenic cell death for anticancer chemotherapy.

Results:

Most cell and animal experiments showed inhibition of autophagy by either pharmacological approaches or via genetic silencing of autophagy regulatory gene, resulting in a promotion of 5-FU-induced cancer cells death. Meanwhile, autophagy also plays a pro-death role and may mediate cell death in certain cancer cells where apoptosis is defective or difficult to induce. The dual role of autophagy complicates the use of autophagy inhibitor or inducer in cancer chemotherapy and generates inconsistency to an extent in clinic trials.

Conclusion:

Autophagy might be a therapeutic target that sensitizes the 5-FU treatment in gastrointestinal cancer.

Two new xanthone epimers from the processed gamboge

Two new xanthones, gambogollic acid (1), epigambogollic acid (2), together with three rare compounds, gambogellic acid (3), epigambogellic acid (4) and gambogic acid (5), were isolated from the processed gamboge. The new structures were determined by 1D and 2D NMR spectroscopic analysis. And the cytotoxicity of these five compounds was evaluated against human hepatoma carcinoma and human lung adenocarcinoma cell. Two new compounds showed excellent antitumor activity. All five compounds exhibited inhibitory effect against SMMC-7221cell and A549 cell.

Combination of gambogic acid with cisplatin enhances the antitumor effects on cisplatin-resistant lung cancer cells by downregulating MRP2 and LRP expression

Cisplatin resistance is a main clinical problem of lung cancer therapy. Gambogic acid (GA) could prohibit the proliferation of a variety of human cancer cells. However, the effects of GA on cisplatin-resistant lung cancer are still unclear. The objective of the present study was to find out the antitumor effects of GA on cisplatin-resistant human lung cancer A549/DDP cells and further explore its underlying mechanisms. Cell Counting Kit-8 assay was used to observe the impacts of GA and/or cisplatin on the proliferation of lung cancer cells; flow cytometry was used to detect the effects of GA on cell cycle and apoptosis; Western blot was used to examine the effects of GA on the expression of lung resistance protein (LRP) and multidrug resistance-associated protein 2 (MRP2) protein in A549/DDP cells. Our results showed that GA dose- and time-dependently prohibited the proliferation and induced significant cell apoptosis in A549 and A549/DDP cells. GA also induced G0/G1 arrest in both A549/DDP and A549 cells. Moreover, GA upregulated protein expression level of cleaved caspase-3 and Bax and downregulated protein expression level of pro-caspase-9 and Bcl-2 in time- and dose-dependent way in A549/DDP cells. GA combined with cisplatin enhanced the cells apoptotic rate and reduced the cisplatin resistance index in A549/DDP cells. In addition, GA reduced the MRP2 and LRP protein expression level in A549/DDP cells. GA inhibits the proliferation, induces cell cycle arrest and apoptosis in A549/DDP cells. Combination of GA with cisplatin enhances the antitumor effects on cisplatin-resistant lung cancer cells by downregulating MRP2 and LRP expression.