Proteasome Inhibition Contributed to the Cytotoxicity of Arenobufagin after Its Binding with Na, K-ATPase in Human Cervical Carcinoma HeLa Cells

Arenobufagin induces cell apoptosis by modulating the cell cycle regulator claspin and the JNK pathway in nasopharyngeal carcinoma cells

BACKGROUND

The high recurrence rate and incidence of distant metastasis of nasopharyngeal carcinoma (NPC) result in poor prognosis. It is necessary to identify natural compounds that can complement combination radiation therapy. Arenobufagin is commonly used for heart diseases and liver cancer, but its effectiveness in NPC is unclear.

STUDY DESIGN AND METHODS

The effect of arenobufagin-induced apoptosis was measured by a cell viability assay, tumorigenic assay, fluorescence assay, and Western blot assay through NPC-039 and NPC-BM cell lines. The protease array, Western blot assay, and transient transfection were used to investigate the underlying mechanism of arenobufagin-induced apoptosis. An NPC xenograft model was established to explore the antitumor activity of arenobufagin in vivo.

RESULTS

Our findings indicated that arenobufagin exerted cytotoxic effects on NPC cells, inhibiting proliferation through apoptosis activation. Downregulation of claspin was confirmed in arenobufagin-induced apoptosis. Combined treatment with arenobufagin and mitogen-activated protein kinase inhibitors demonstrated that arenobufagin induced NPC apoptosis through the c-Jun N-terminal kinases (JNK) pathway inhibition. Furthermore, arenobufagin suppressed NPC tumor proliferation in vivo.

CONCLUSION

Our results revealed the antitumor effect of arenobufagin in vitro and in vivo. Arenobufagin may have clinical utility in treating NPC due to its suppression of claspin and inhibition of the JNK pathway.

Ephedra alata Seeds Confer Kidney Protection against Early Life Exposure to Acephate by Regulating Oxidative Insult and Activating Autophagy

The aim of the current work was to examine for the first time the nephropreventive capacity of Ephedra alata seed extract (E) against maternal exposure to acephate in rat offspring. The in vivo results revealed that E. alata supplementation for 28 days (40 mg/kg b.w.) significantly attenuated the nephrotoxicity in adult offspring induced by acephate. In fact, it decreased the levels of creatinine and uric acid and increased the albumin content compared to the intoxicated group. The in utero studies showed that E. alata inhibited the renal oxidative stress generated by acephate exposure by reducing lipid peroxidation and enhancing antioxidant biomarker activities (GSH, CAT, and SOD). The inhibition of DNA fragmentation and the improvement of the ultrastructural changes highlighted the prophylactic effect of E. alata in renal tissue. Additionally, the immunofluorescence study showed the upregulation of LC3 gene expression, suggesting the capacity of E. alata extract to stimulate autophagic processes as a protective mechanism. Molecular docking analysis indicated that hexadecasphinganine, the major compound in E. alata, has a higher affinity toward the Na+/K+-ATPase, epithelial sodium channel (ENaC), and sodium hydrogen exchanger 3 (NHE3) genes than acephate. Hexadecasphinganine could be considered a potential inhibitor of the activity of these genes and therefore exerted its preventive capacity. The obtained findings confirmed that E. alata seed extract exerted nephropreventive capacities, which could be related to its bioactive compounds, which possess antioxidant activities.

Toad venom bufadienolides and bufotoxins: An updated review

Bufadienolides, naturally found in toad venoms having steroid-like structures, reveal antiproliferative effects at low doses. However, their application as anticancer drugs is strongly prevented by their Na+ /K+ -ATPase binding activities. Although several kinds of research were dedicated to moderating their Na+ /K+ -ATPase binding activity, still deeper fundamental knowledge is required to bring these findings into medical practice. In this work, we reviewed data related to anticancer activity of bufadienolides such as bufalin, arenobufagin, bufotalin, gamabufotalin, cinobufotalin, and cinobufagin and their derivatives. Bufotoxins, derivatives of bufadienolides containing polar molecules mainly belonging to argininyl residues, are reviewed as well. The established structures of bufotoxins have been compiled into a one-page figure to review their structures. We also highlighted advances in the structure-modification of the structure of compounds in this class. Drug delivery approaches to target these compounds to tumor cells were discussed in one section. The issues related to extraction, identification, and quantification are separated into another section.

Ethanol Exposure to Ethanol-Oxidizing HEPG2 Cells Induces Intracellular Protein Aggregation

Background: Aggresomes are collections of intracellular protein aggregates. In liver cells of patients with alcoholic hepatitis, aggresomes appear histologically as cellular inclusions known as Mallory–Denk (M–D) bodies. The proteasome is a multicatalytic intracellular protease that catalyzes the degradation of both normal (native) and abnormal (misfolded and/or damaged) proteins. The enzyme minimizes intracellular protein aggregate formation by rapidly degrading abnormal proteins before they form aggregates. When proteasome activity is blocked, either by specific inhibitors or by intracellular oxidants (e.g., peroxynitrite, acetaldehyde), aggresome formation is enhanced. Here, we sought to verify whether inhibition of proteasome activity by ethanol exposure enhances protein aggregate formation in VL-17A cells, which are recombinant, ethanol-oxidizing HepG2 cells that express both alcohol dehydrogenase (ADH) and cytochrome P450 2E1 (CYP2E1). Methods: We exposed ethanol-non-oxidizing HepG2 cells (ADH−/CYP2E1−) or ethanol-oxidizing VL-17A (ADH+/CYP2E1+) to varying levels of ethanol for 24 h or 72 h. After these treatments, we stained cells for aggresomes (detected microscopically) and quantified their numbers and sizes. We also conducted flow cytometric analyses to confirm our microscopic findings. Additionally, aggresome content in liver cells of patients with alcohol-induced hepatitis was quantified. Results: After we exposed VL-17A cells to increasing doses of ethanol for 24 h or 72 h, 20S proteasome activity declined in response to rising ethanol concentrations. After 24 h of ethanol exposure, aggresome numbers in VL-17A cells were 1.8-fold higher than their untreated controls at all ethanol concentrations employed. After 72 h of ethanol exposure, mean aggresome numbers were 2.5-fold higher than unexposed control cells. The mean aggregate size in all ethanol-exposed VL-17A cells was significantly higher than in unexposed control cells but was unaffected by the duration of ethanol exposure. Co-exposure of cells to EtOH and rapamycin, the latter an autophagy activator, completely prevented EtOH-induced aggresome formation. In the livers of patients with alcohol-induced hepatitis (AH), the staining intensity of aggresomes was 2.2-fold higher than in the livers of patients without alcohol use disorder (AUD). Conclusions: We conclude that ethanol-induced proteasome inhibition in ethanol-metabolizing VL-17A hepatoma cells causes accumulation of protein aggregates. Notably, autophagy activation removes such aggregates. The significance of these findings is discussed.

Enhanced Cytotoxic Effects of Arenite in Combination with Active Bufadienolide Compounds against Human Glioblastoma Cell Line U-87

The cytotoxicity of a trivalent arsenic derivative (arsenite, As^III) combined with arenobufagin or gamabufotalin was evaluated in human U-87 glioblastoma cells. Synergistic cytotoxicity with upregulated intracellular arsenic levels was observed, when treated with As^III combined with arenobufagin instead of gamabufotalin. Apoptosis and the activation of caspase-9/-8/-3 were induced by As^III and further strengthened by arenobufagin. The magnitude of increase in the activities of caspase-9/-3 was much greater than that of caspase-8, suggesting that the intrinsic pathway played a much more important role in the apoptosis. An increase in the number of necrotic cells, enhanced LDH leakage, and intensified G₂/M phase arrest were observed. A remarkable increase in the expression level of γH2AX, a DNA damage marker, was induced by As^III+arenobufagin. Concomitantly, the activation of autophagy was observed, suggesting that autophagic cell death associated with DNA damage was partially attributed to the cytotoxicity of As^III+arenobufagin. Suppression of Notch signaling was confirmed in the combined regimen-treated cells, suggesting that inactivation of Jagged1/Notch signaling would probably contribute to the synergistic cytotoxic effect of As^III+arenobufagin. Given that both As^III and arenobufagin are capable of penetrating into the blood-brain barrier, our findings may provide fundamental insight into the clinical application of the combined regimen for glioblastoma.

BETA: a comprehensive benchmark for computational drug-target prediction

Internal validation is the most popular evaluation strategy used for drug-target predictive models. The simple random shuffling in the cross-validation, however, is not always ideal to handle large, diverse and copious datasets as it could potentially introduce bias. Hence, these predictive models cannot be comprehensively evaluated to provide insight into their general performance on a variety of use-cases (e.g. permutations of different levels of connectiveness and categories in drug and target space, as well as validations based on different data sources). In this work, we introduce a benchmark, BETA, that aims to address this gap by (i) providing an extensive multipartite network consisting of 0.97 million biomedical concepts and 8.5 million associations, in addition to 62 million drug-drug and protein-protein similarities and (ii) presenting evaluation strategies that reflect seven cases (i.e. general, screening with different connectivity, target and drug screening based on categories, searching for specific drugs and targets and drug repurposing for specific diseases), a total of seven Tests (consisting of 344 Tasks in total) across multiple sampling and validation strategies. Six state-of-the-art methods covering two broad input data types (chemical structure- and gene sequence-based and network-based) were tested across all the developed Tasks. The best-worst performing cases have been analyzed to demonstrate the ability of the proposed benchmark to identify limitations of the tested methods for running over the benchmark tasks. The results highlight BETA as a benchmark in the selection of computational strategies for drug repurposing and target discovery.

Natural compounds in the regulation of proteostatic pathways: An invincible artillery against stress, ageing, and diseases

Cells have different sets of molecules for performing an array of physiological functions. Nucleic acids have stored and carried the information throughout evolution, whereas proteins have been attributed to performing most of the cellular functions. To perform these functions, proteins need to have a unique conformation and a definite lifespan. These attributes are achieved by a highly coordinated protein quality control (PQC) system comprising chaperones to fold the proteins in a proper three-dimensional structure, ubiquitin-proteasome system for selective degradation of proteins, and autophagy for bulk clearance of cell debris. Many kinds of stresses and perturbations may lead to the weakening of these protective cellular machinery, leading to the unfolding and aggregation of cellular proteins and the occurrence of numerous pathological conditions. However, modulating the expression and functional efficiency of molecular chaperones, E3 ubiquitin ligases, and autophagic proteins may diminish cellular proteotoxic load and mitigate various pathological effects. Natural medicine and small molecule-based therapies have been well-documented for their effectiveness in modulating these pathways and reestablishing the lost proteostasis inside the cells to combat disease conditions. The present article summarizes various similar reports and highlights the importance of the molecules obtained from natural sources in disease therapeutics.

Target identification of anticancer natural products using a chemical proteomics approach

In recent years, there has been a strong demand worldwide for the identification and development of potential anticancer drugs based on natural products. Natural products have been explored for their diverse biological and therapeutic applications from ancient time. In order to enhance the efficacy and selectivity and to minimize the undesired side effects of anti cancer natural products (ANPs), it is essential to understand their target proteins and their mechanistic pathway. Chemical proteomics is one of the most powerful tools to connect ANP target identification and quantification where labeling and non-labeling based approaches have been used. Herein, we have discussed the various strategies to systemically develop selective ANP based chemical probes to characterise their specific and non-specific target proteins using a chemical proteomic approach in various cancer cell lysates.

Molecular mechanisms of bufadienolides and their novel strategies for cancer treatment

Bufadienolides are cardioactive C24 steroids with an α-pyrone ring at position C17. In the last ten years, accumulating studies have revealed the anticancer activities of bufadienolides and their underlying mechanisms, such as induction of autophagy and apoptosis, cell cycle disruption, inhibition of angiogenesis, epithelial-mesenchymal transition (EMT) and stemness, and multidrug resistance reversal. As Na⁺/K⁺-ATPase inhibitors, bufadienolides have inevitable cardiotoxicity. Short half-lives, poor stability, low plasma concentration and oral bioavailability in vivo are obstacles for their applications as drugs. To improve the drug potency of bufadienolides and reduce their side effects, prodrug strategies and drug delivery systems such as liposomes and nanoparticles have been applied. Therefore, systematic and recapitulated information about the antitumor activity of bufadienolides, with special emphasis on the molecular or cellular mechanisms, prodrug strategies and drug delivery systems, is of high interest. Here, we systematically review the anticancer effects of bufadienolides and the molecular or cellular mechanisms of action. Research advancements regarding bufadienolide prodrugs and their tumor-targeting delivery strategies are critically summarized. This work highlights recent scientific advances regarding bufadienolides as effective anticancer agents from 2011 to 2019, which will help researchers to understand the molecular pathways involving bufadienolides, resulting in a selective and safe new lead compound or therapeutic strategy with improved therapeutic applications of bufadienolides for cancer therapy.

Temperature-sensitive gel-loaded composite nanomedicines for the treatment of cervical cancer by vaginal delivery

In this study, toad venom (TV) and realgar were loaded into a poloxamer 188/407 (F127/F188)-based temperature-sensitive in situ gel (TISG) and encapsulated in solid lipid nanoparticles (TV-SLN) or ground nano-realgar (NR) to improve drug release and reduce local irritation after vaginal administration. The combination of TV-SLN and NR (TV-SLN/NR) greatly enhanced the inhibition of tumor cell proliferation and was most effective at a dose ratio of 2:3 (w/w). After TV-SLN/NR treatment, S and G0/G1 phase arrest were observed in HeLa and SKOV-3 cells and the inhibitory effects on proliferation were stronger than those in the conventional powder group. The gelation temperature of TV-SLN and NR-loaded TISG (TV-SLN/NR-TISG) using the selected formulation was 33 ± 0.91 °C. The cumulative release of the drug increased as the dissolution of gel progressed, showing a linear relationship (r > 0.99). TV-SLN/NR-TISG enabled the sustained release of cargo by adhesion to the vaginal mucosa and showed excellent biocompatibility during continuous administration for 7 days. We specifically demonstrated the effectiveness of the TISG for the vaginal delivery of TV-SLN and NR, supporting its important clinical implications for the treatment of cervical cancer.

Arenobufagin Promoted Oxidative Stress-Associated Mitochondrial Pathway Apoptosis in A549 Non-Small-Cell Lung Cancer Cell Line

Arenobufagin (ARE) has demonstrated potent anticancer activity in various types of tumor, but the role and mechanism of ARE for lung cancer remain unclear. Oxidative stress exists under normal conditions and is an inevitable state in the body. A variety of noxious stimuli can break the equilibrium state of oxidative stress and promote apoptosis. Here, we used a CCK-8 assay to examine cell viability. We determined oxidative stress damage by measuring levels of intracellular ROS and levels of GSH, SOD, and MDA. Annexin V-FITC/PI double staining assay, as well as the Hoechst 33258 staining, was used to detect ARE-induced apoptosis in A549 cell. Evaluation of the expression level of the specified molecule was indicated by Western blot and qRT-PCR. Loss of function experiment was carried out using NAC pretreatment. The experimental results show that ARE significantly declines in the viability of A549 cells and increases the apoptosis rate of A549 cells. As reflected in cell morphology, the A549 cells showed features of shrinkage and had incompletely packed membranes; the same phenomenon is manifested in Hoechst 33258 staining. Following ARE treatment, the ROS level in A549 cells was rising in a concentration-dependent manner, and so were MDA and GSH levels, while the SOD level was decreasing. Moreover, we found that ARE can decrease mitochondrial membrane potential (MMP), and a cascade of apoptotic processes can be triggered by decreased MMP. Importantly, we found significant changes in protein expression levels and mRNA levels of apoptosis-related proteins. Furthermore, when we used NAC to restrain oxidative stress, the expression levels of apoptosis-related proteins have also changed accordingly. Our data demonstrate that apoptosis in the non-small-cell lung cancer (NSCLC) cell line A549 is caused by oxidative stress due to ARE. Our research also shows that ARE may have the potential to become a targeted therapeutic for the treatment of NSCLC in the future.

Arenobufagin, isolated from toad venom, inhibited epithelial-to-mesenchymal transition and suppressed migration and invasion of lung cancer cells via targeting IKKβ/NFκB signal cascade

ETHNOPHARMACOLOGICAL RELEVANCE

Lung cancer is the leading cause of cancer incidence and mortality worldwide. Arenobufagin (Arg), a representative natural bufadienolide compound, is one of the major bioactive components isolated from toad venom ("Chan Su"named in Chinese to treat multifarious clinical neoplasms in China). However, the underlying molecular mechanisms that Arg inhibited the metastasis of lung cancer cells remain poorly understood.

MATERIALS AND METHODS

The mobility capacities of lung cancer cells treated with Arg were evaluated using wound healing assay. The anti-migratory and anti-invasive effects of Arg on lung cancer cells were investigated by transwell invasion assay and matrigel invasion assay. iTRAQ-labeled LC-MS proteomics was used to analyze the potential proteins related to metastasis in lung cancer cells treated with Arg and differentially-expressed proteins related to EMT and NFκB signaling cascade were further confirmed by Western blotting assay. The changed subcellular localization of p65 in lung cancer A549 and H1299 cells treated with Arg was detected by immunofluorescence staining. Molecular docking and molecular dynamic (MD) simulation assay were performed to verify the binding between Arg and IKKα/IKKβ. siRNA knockdown was used to check whether Arg inhibited EMT of lung cancer cells via targeting NFκB signaling cascade, which was further verified by in vivo study of lung cancer cell xenograft mice model and pulmonary metastasis mice model accompanying with immunohistochemical and hematoxylin-eosin (HE) staining.

RESULTS

Arg suppressed the wound closure of lung cancer cells using wound healing assay. Moreover, Arg significantly inhibited the migration and invasion of lung cancer cells by transwell invasion assay and matrigel invasion assay. 24 unique differentially-expressed proteins related to metastasis in lung cancer cells treated with Arg were identified using iTRAQ-labeled LC-MS proteomics and 14 differentially-expressed proteins related to EMT were further confirmed by Western blotting assay. Arg significantly decreased the phosphorylation of IKKβ, IκBα and p65 in the cytoplasm of lung cancer cells by Western blotting assay, and remarkably reduced the release of p65 from the cytoplasm to the nucleus. Arg could be bound in the ATP binding pocket of IKKα and IKKβ by molecular docking assay, and MD simulation assay further demonstrated that Arg binding to the ATP-binding pocket of IKKβ was very stable in 300 ns MD simulation, compared with the binding of Arg and IKKα. IKKβ/NFκB signaling cascade was also involved in the inhibitory effect of Arg on EMT of lung cancer cells by siRNA knockdown assay. The study of lung cancer cell xenograft mice model and pulmonary metastasis mice model in vivo indicated that Arg inhibited EMT and suppressed migration and invasion of lung cancer cells via downregulating IKKβ/NFκB signaling cascade.

CONCLUSION

In the present study, we explored the molecular mechanism of Arg prohibiting the metastasis of lung cancer cells in vitro and in vivo, which displayed Arg could target IKKβ to inactive NFκB signaling cascade and further change the expression of proteins related to EMT. These results highlight the potential of toad venom as a potential chemotherapeutic agent and warrant its development as the clinical therapy for lung cancer.

Drug-target prediction utilizing heterogeneous bio-linked network embeddings

To enable modularization for network-based prediction, we conducted a review of known methods conducting the various subtasks corresponding to the creation of a drug-target prediction framework and associated benchmarking to determine the highest-performing approaches. Accordingly, our contributions are as follows: (i) from a network perspective, we benchmarked the association-mining performance of 32 distinct subnetwork permutations, arranging based on a comprehensive heterogeneous biomedical network derived from 12 repositories; (ii) from a methodological perspective, we identified the best prediction strategy based on a review of combinations of the components with off-the-shelf classification, inference methods and graph embedding methods. Our benchmarking strategy consisted of two series of experiments, totaling six distinct tasks from the two perspectives, to determine the best prediction. We demonstrated that the proposed method outperformed the existing network-based methods as well as how combinatorial networks and methodologies can influence the prediction. In addition, we conducted disease-specific prediction tasks for 20 distinct diseases and showed the reliability of the strategy in predicting 75 novel drug-target associations as shown by a validation utilizing DrugBank 5.1.0. In particular, we revealed a connection of the network topology with the biological explanations for predicting the diseases, 'Asthma' 'Hypertension', and 'Dementia'. The results of our benchmarking produced knowledge on a network-based prediction framework with the modularization of the feature selection and association prediction, which can be easily adapted and extended to other feature sources or machine learning algorithms as well as a performed baseline to comprehensively evaluate the utility of incorporating varying data sources.

Affinity-Based Protein Profiling Reveals Cellular Targets of Photoreactive Anticancer Inhibitors

Affinity-based protein profiling has proven to be a powerful method in target identification of bioactive molecules. Here, this technology was applied in two photoreactive anticancer inhibitors, arenobufagin and HM30181. Using UV irradiation, these photoreactive reagents can covalently cross-link to target proteins, leading to a covalent binding with target proteins. Moreover, the cellular on/off targets of these two molecules, including ATP1A1, MDR1, PARP1, DDX5, NOP2, RAB6A, and ERGIC1 were first identified by affinity-based protein profiling and bioimaging approaches. The protein hit, PARP1, was further validated to be involved in the function of the anticancer effects.

Novel therapeutic approaches of natural oil from black seeds and its underlying mechanisms against kidney dysfunctions in haloperidol-induced male rats

BACKGROUND

Antipsychotic drugs could be nephrotoxic in schizophrenia patients.

METHODS

The present study investigated the protective effect of oil from black seed on kidney dysfunctions using several biological approaches in adult rats. The animals were divided into six groups (n=10): normal control rats; haloperidol (HAL)-induced rats: induced rats were pre-, co- and post-treated with black seed oil (BSO), respectively, and the last group was treated with the oil only. The treatment was done through oral administration, and the experiment lasted 14 days.

RESULTS

Therapeutic administration of HAL to rats caused reduction in both enzymatic and non-enzymatic proteins mediated by stable OH˙ and DPPH free radicals. K+, Na+ and MDA contents as well as 51 nucleotidase, aldose-reductase activities were increased with corresponding decrease in the activity of lactate dehydrogenase (LDH) in HAL-induced toxicity rats. Contrariwise, differential treatments with BSO prevented and reversed the nephrotoxicity by depleting K+, Na+, MDA contents and aldose-reductase activity, and AMP hydrolysis with increased adenosine triphosphate (ATP) in the PMFs of rat kidney. The cytotoxicity of HAL elicited on both inner renal cortex and outer medulla was equally alleviated by combined active molecules of oil from black seed (OBS). However, pre-, co- and post-treatment demonstrate significant approaches in averting nephrotoxicity of neuroleptic drug (HAL) via several biological mechanisms.

CONCLUSIONS

This study therefore validates the use of black seed oil as therapy particularly for individuals with renal dysfunctions.

Prognostic significance of sodium-potassium ATPase regulator, FXYD3, in human hepatocellular carcinoma

The clinical significance of the sodium-potassium ATPase regulator FXYD domain-containing ion transport regulator 3 (FXYD3) has been demonstrated in a number of types of cancer. However, the role of this protein in human hepatocellular carcinoma (HCC) remains to be elucidated. In the present study, 217 HCC tissue samples were analyzed to evaluate the expression and prognostic significance of FXYD3 in HCC. Reverse transcription-quantitative polymerase chain reaction was used to analyze the mRNA expression of FXYD3 in 80 primary HCC specimens and paired non-cancerous liver tissue samples, while western blotting was used to analyze the protein expression level of FXYD3 in another 24 pairs. These analyses demonstrated that the expression level of FXYD3 was significantly increasedb at the mRNA and protein levels in HCC tumor tissues compared with adjacent non-cancerous tissues. Immunohistochemical analysis of 137 paraffin-embedded HCC tissue samples indicated that the expression of FXYD3 was associated with HCC clinicopathological characteristics. Kaplan-Meier analysis demonstrated that patients with high FXYD3 protein expression (n=60) experienced significantly poorer overall survival time compared with patients with low FXYD3 protein expression (n=77) (P<0.001). Multivariate analysis demonstrated that FYXD3 protein expression level (hazard ratio, 2.137; 95% confidence interval, 1.224–3.732; P=0.008) was an independent prognostic factor in patients with HCC. Overall, the results indicated that FXYD3 expression levels were higher in HCC tumor tissues than in adjacent non-cancerous tissues, and that the FXYD3 protein may serve as a prognostic marker for HCC.

Arenobufagin Induces Apoptotic Cell Death in Human Non-Small-Cell Lung Cancer Cells via the Noxa-Related Pathway

Arenobufagin, an active component isolated from the traditional Chinese medicine Chan Su, exhibits anticancer influences in several human malignancies. However, the effects and action mechanisms of arenobufagin on non-small-cell lung cancer (NSCLC) are still unknown. In this study, we reported that arenobufagin acted through activation of Noxa-related pathways and promoted apoptotic cell death in human NSCLC cells. Our results revealed that arenobufagin-induced apoptosis was caspase-dependent, as evidenced by the fact that caspase-9, caspase-3 and poly (ADP-ribose) polymerase (PARP) were cleaved, and pretreatment with a pan-caspase inhibitor Z-VAD-FMK inhibited the pro-apoptosis effect of arenobufagin. Mechanistically, we further found that arenobufagin rapidly upregulated the expression of the pro-apoptosis protein Noxa, and abrogated the anti-apoptosis protein Mcl-1, a major binding partner of Noxa in the cell. More importantly, the knockdown of Noxa greatly blocked arenobufagin-induced cell death, highlighting the contribution of this protein in the anti-NSCLC effects of arenobufagin. Interestingly, arenobufagin also increased the expression of p53, a direct transcriptional activator for the upregulation of the Noxa protein. Taken together, our results suggest that arenobufagin is a potential anti-NSCLC agent that triggers apoptotic cell death in NSCLC cells through interfering with the Noxa-related pathway.