Bufalin enhances antitumor effect of paclitaxel on cervical tumorigenesis via inhibiting the integrin α2/β5/FAK signaling pathway

Prospects of focal adhesion kinase inhibitors as a cancer therapy in preclinical and early phase study

INTRODUCTION

FAK, a nonreceptor cytoplasmic tyrosine kinase, plays a crucial role in tumor metastasis, drug resistance, tumor stem cell maintenance, and regulation of the tumor microenvironment. FAK has emerged as a promising target for tumor therapy based on both preclinical and clinical data.

AREAS COVERED

This paper aims to summarize the molecular mechanisms underlying FAK's involvement in tumorigenesis and progression. Encouraging results have emerged from ongoing clinical trials of FAK inhibitors. Additionally, we present an overview of clinical trials for FAK inhibitors, examining their potential as promising treatments. The pertinent studies gathered from databases including PubMed, ClinicalTrials.gov.

EXPERT OPINION

Since the first finding in 1990s, targeting FAK has became the focus of interests in many pharmaceutical companies. Through 30 years' discovery, the industry and academy gradually realized the features of FAK target which may not be a driver gene but a solid defense system for the cancer initiation and development. Currently, the ongoing clinical regimens involving FAK inhibition are all the combination strategies in which FAK inhibitors can further strengthen the cancer cell killing effects of other testing agents. The emerging positive signal in clinical trials foresee targeting FAK as class will be an effective mean to fight against cancers.

Influence of Different Ratios of DSPE-PEG2k on Ester Prodrug Self-Assembly Nanoparticles for Cell Migration and Proliferation Suppression

Background

Bufalin (BFL, an active anti-tumor compound derived from toad venom) is limited in its application due to high toxicity and rapid metabolism of the cardiotonic steroid. Ester prodrug self-assembly nanoparticles have shown significant improved effects in addressing the above-mentioned issues.

Methods

An ester bond was formed between linoleic acid and bufalin to synthesize linoleic acid-bufalin prodrug (LeB). The self-assembly nanoparticles (LeB-PSNs) containing different mass ratios of DSPE-PEG2k and prodrug (6:4, 7:3, 8:2, 9:1 and 10:0) were prepared via co-precipitation method and defined as 6:4-PSNs, 7:3-PSNs, 8:2-PSNs, 9:1-PSNs and LeB-PSNs, respectively. Further, the characterization (particle size, zeta potential, surface morphology and stability) of the nanoparticles was carried out. Finally, we evaluated the impact of different ratios of DSPE-PEG2k on the hydrolysis rate, cytotoxicity, cellular uptake, cell migration and proliferation suppression potential of the prodrug nanoparticles.

Results

The linoleic acid-bufalin prodrug (LeB) was successfully synthesized. Upon the addition of DSPE-PEG2k at different weight ratios, both particle size and polydispersity index (PDI) significantly decreased, while the zeta potential increased remarkably. No significant differences in particle size, PDI and Zeta potential were observed among the 9:1, 8:2 and 7:3 PSNs. Notably, the 8:2 (w/w) DSPE-PEG2k nanoparticles exhibited superior stability, hydrolysis and cellular uptake rates, along with efficient cell cytotoxicity, cell migration and proliferation suppression.

Conclusion

These findings indicate that DSPE-PEG2k could improve the performance of BFL prodrug nanoparticles, namely enhancing stability and achieving adaptive drug release by modulating the hydrolysis rate of esterase. This study therefore provides more opportunities for the development of BFL application.

An overview of the past decade of bufalin in the treatment of refractory and drug-resistant cancers: current status, challenges, and future perspectives

Profound progress has been made in cancer treatment in the past three decades. However, drug resistance remains prevalent and a critical challenge. Drug resistance can be attributed to oncogenes mutations, activated defensive mechanisms, ATP-bind cassette transporters overexpression, cancer stem cells, etc. Chinese traditional medicine toad venom has been used for centuries for different diseases, including resistant cancers. Bufalin is one of the bufadienolides in toad venom that has been extensively studied for its potential in refractory and drug-resistant cancer treatments in vitro and in vivo. In this work, we would like to critically review the progress made in the past decade (2013-2022) of bufalin in overcoming drug resistance in cancers. Generally, bufalin shows high potential in killing certain refractory and resistant cancer cells via multiple mechanisms. More importantly, bufalin can work as a chemo-sensitizer that enhances the sensitivity of certain conventional and targeted therapies at low concentrations. In addition, the development of bufalin derivatives was also briefly summarized and discussed. We also analyzed the obstacles and challenges and provided possible solutions for future perspectives. We hope that the collective information may help evoke more effort for more in-depth studies and evaluation of bufalin in both lab and possible clinical trials.

Improving cellular uptake and bioavailability of periplocymarin-linoleic acid prodrug by combining PEGylated liposome

Periplocymarin (PPM), a cardiac glycoside isolated from Cortex periplocae, has a strong anti-tumor effect against various cancer cells. However, cardiotoxicity and rapid metabolism hinder its clinical applications. In this study, small molecule prodrug was integrated into PEGylated liposome to improve the efficiency of periplocymarin in vivo. The periplocymarin-linoleic acid (PL) prodrug was constructed by conjugating the linoleic acid with PPM via esterification, which was further facilitated to form PEGylated liposome (PL-Lip) through film dispersion. Compared with PL self-assembling nano-prodrug (PL-SNP), PL-Lip showed better colloid stability, sustained drug release kinetics, and enhanced cellular uptake by tumor cells. Notably, PL-Lip performed better than PPM and PL-SNP in terms of tumor distribution and pharmacokinetics, which include bioavailability and half-life. Altogether, the prodrug PEGylated liposome represents a good strategy and method for long-circulating and tumor-targeting delivery of periplocymarin with enhanced clinical application prospect.

Bufalin for an innovative therapeutic approach against cancer

Bufalin is an endogenous cardiotonic steroid, first discovered in toad venom but also found in the plasma of healthy humans, with anti-tumour activities in different cancer types. The current review is focused on its mechanisms of action and highlights its very large spectrum of effects both in vitro and in vivo. All leads to the conclusion that bufalin mediates its effects by affecting all the hallmarks of cancer and seems restricted to cancer cells avoiding side effects. Bufalin decreases cancer cell proliferation by acting on the cell cycle and inducing different mechanisms of cell death including apoptosis, necroptosis, autophagy and senescence. Bufalin also moderates metastasis formation by blocking migration and invasion as well as angiogenesis and by inducing a phenotype switch towards differentiation and decreasing cancer cell stemness. Regarding its various mechanisms of action in cancer cells, bufalin blocks overactivated signalling pathways and modifies cell metabolism. Moreover, bufalin gained lately a huge interest in the field of drug resistance by both reversing various drug resistance mechanisms and affecting the immune microenvironment. Together, these data support bufalin as a quite promising new anti-cancer drug candidate.

Identification of key pathways and genes in vestibular schwannoma using bioinformatics analysis

The aim of the present study is to identify novel promising marks and targets of diagnosis, therapy and prognosis for patients with vestibular schwannoma at the molecular level. The gene expression profiles of GSE54934, GSE39645 and GSE56597 datasets were obtained respectively from the Gene Expression Omnibus database. The differentially expressed genes (DEGs) were identified by comparing between gene expression profiles of the vestibular schwannoma tissues and normal tissues. Subsequently, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and protein-protein interaction (PPI) network analysis were performed. The function and pathway enrichment analysis were performed for DEGs with DAVID. Reverse transcription-quantitative PCR were conducted to confirm the expression of BCL2, AGT, IL6 and ITGA2 in human Schwann cells and vestibular schwannoma cells. A total of 4,025, 1,1291 and 1,513 DEGs were identified from GSE54934, GSE56597 and GSE39645 datasets, respectively. GO and KEGG analysis showed that the mutual upregulated genes were mainly enriched in cell division, mitotic nuclear division, and transition of mitotic cell cycle, whilst mutual downregulated genes were enriched in chemical synaptic transmission, neurotransmitter transport, and synaptic vesicle membrane. Subsequently, 20 genes, including BCL2, AGT, IL6 and ITGA2 were selected as hub genes with high degrees after PPI network analysis. The significant differential expression of those genes were detected among vestibular schwannoma tissues compared with normal nerve tissues. In conclusion, BCL2, AGT, IL6 and ITGA2 are significantly higher expressed in vestibular schwannoma tissues compared with human Schwann tissues. The DEGs identified in the present study provide novel targets for the diagnosis and treatment of vestibular schwannoma.

Bufalin induces mitochondrial dysfunction and promotes apoptosis of glioma cells by regulating Annexin A2 and DRP1 protein expression

Background

Glioma is a common primary central nervous system tumour, and therapeutic drugs that can effectively improve the survival rate of patients in the clinic are lacking. Bufalin is effective in treating various tumours, but the mechanism by which it promotes the apoptosis of glioma cells is unclear. The aim of this study was to investigate the drug targets of bufalin in glioma cells and to clarify the apoptotic mechanism.

Methods

Cell viability and proliferation were evaluated by CCK-8 and colony formation assays. Then, the cell cycle and apoptosis, intracellular ion homeostasis, oxidative stress levels and mitochondrial damage were assessed after bufalin treatment. DARTS-PAGE technology was employed and LC–MS/MS was performed to explore the drug targets of bufalin in U251 cells. Molecular docking and western blotting were performed to identify potential targets. siRNA targeting Annexin A2 and the DRP1 protein inhibitor Mdivi-1 were used to confirm the targets of bufalin.

Results

Bufalin upregulated the expression of cytochrome C, cleaved caspase 3, p-Chk1 and p-p53 proteins to induce U251 cell apoptosis and cycle arrest in the S phase. Bufalin also induced oxidative stress in U251 cells, destroyed intracellular ion homeostasis, and caused mitochondrial damage. The expression of mitochondrial division-/fusion-related proteins in U251 cells was abnormal, the Annexin A2 and DRP1 proteins were translocated from the cytoplasm to mitochondria, and the MFN2 protein was released from mitochondria into the cytoplasm after bufalin treatment, disrupting the mitochondrial division/fusion balance in U251 cells.

Conclusions

Our research indicated that bufalin can cause Annexin A2 and DRP1 oligomerization on the surface of mitochondria and disrupt the mitochondrial division/fusion balance to induce U251 cell apoptosis.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02137-x.

Bufalin inhibits the malignant development of non-small cell lung cancer by mediating the circ_0046264/miR-522-3p axis

BACKGROUND

Bufalin is an active component of the traditional Chinese medicine "Chan Su" and is reported to play anti-tumor roles in cancer development, but its functional mechanism is largely unclear. This study intends to explore a potential action mode of bufalin in NSCLC.

MATERIALS AND METHODS

The malignant properties of NSCLC, including cell viability, proliferation, adhesion capacity, migration and invasion, were monitored by cell counting kit-8 (CCK-8), adhesion assay and transwell assay, respectively. The expression of circ_0046264 and miR-522-3p was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of proliferation- and migration-related markers was examined by western blot. The putative relationship between circ_0046264 and miR-522-3p was verified by dual-luciferase reporter assay, RIP assay and RNA pull-down assay. Animal experiments in nude mice were performed to investigate the role of bufalin in vivo.

RESULTS

Bufalin treatment inhibited cell viability, colony formation, cell adhesion capacity, migration and invasion in NSCLC cells. Bufalin facilitated the expression of circ_0046264, and circ_0046264 overexpression also inhibited NSCLC cell viability, colony formation, cell adhesion capacity, migration and invasion. Besides, circ_0046264 knockdown partially counteracted the effects of bufalin. Further, miR-522-3p was identified as a target of circ_0046264, and its deficiency reversed the effects of circ_0046264 knockdown to suppress malignant activities of NSCLC cells. In addition, bufalin restrained the tumor growth and development in vivo via enhancing the expression of circ_0046264.

CONCLUSION

Bufalin played an anti-tumor role in NSCLC by modulating the circ_0046264/miR-522-3p pathway, which might be a potential functional mechanism of bufalin in NSCLC.

Bufalin: A Systematic Review of Research Hotspots and Antitumor Mechanisms by Text Mining and Bioinformatics

Bufalin is an anticancer drug extract from traditional Chinese medicine. Several articles about bufalin have been published. However, the literature on bufalin has not yet been systematically studied. This study aimed to identify the study status and knowledge structures of bufalin and to summarize the antitumor mechanism. Data were retrieved and downloaded from the PubMed database. The softwares of BICOMB, gCLUTO, Ucinet 6.0, and NetDraw2.084 were used to analyze these publications. The bufalin related genes were recognized and tagged by ABNER software. Then these BF-related genes were performed by Gene Ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis, and protein-protein interaction (PPI) network analysis. A total of 474 papers met the search criteria from 2000 to 2019. By biclustering clustering analysis, the 50 high-frequency main MeSH terms/subheadings were classified into 5 clusters. The clusters of drug therapy and the mechanism of bufalin were hotspot topics. A total of 50 genes were identified as BF-related genes. PPI network analysis showed that inducing apoptosis was the main effect of bufalin, and apoptosis-related gene Caspase 3 was the most reported by people. Bufalin could inhibit the proliferation, invasion, and metastasis of cancer cells through multiple signaling pathways, such as PI3K/AKT, Hedgehog, MAPK/JNK, Wnt/[Formula: see text]-catenin, TGF-[Formula: see text]/Smad, Integrin signaling pathway, and NF-KB signaling pathway via KEGG analysis. Through the quantitative analysis of bufalin literature, we revealed the research status and hot spots in this field and provided some guidance for further research.

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.

Bufalin reverses multidrug resistance by regulating stemness through the CD133/nuclear factor-κB/MDR1 pathway in colorectal cancer

Recent studies have shown that MDR could be induced by the high stemness of cancer cells. In a previous study, we found bufalin could reverse MDR and inhibit cancer cell stemness in colorectal cancer, but the relationship between them was unclear. Here we identified overexpressing CD133 increases levels of Akt/nuclear factor‐κB signaling mediators and MDR1, while increasing cell chemoresistance. Furthermore, bufalin reverses colorectal cancer MDR by regulating cancer cell stemness through the CD133/nuclear factor‐κB/MDR1 pathway in vitro and in vivo. Taken together, our results suggest that bufalin could be developed as a novel 2‐pronged drug that targets CD133 and MDR1 to eradicate MDR cells and could ultimately be combined with conventional chemotherapeutic agents to improve treatment outcomes for patients with colorectal cancer.

Anti-tumor Activity of Bufalin by Inhibiting c-MET Mediated MEK/ERK and PI3K/AKT Signaling Pathways in Gallbladder Cancer

Gallbladder cancer is one of the most common malignant tumors in the biliary tract. In recent years, the chemotherapy treatment for gallbladder carcinoma has exhibited obvious characteristics of drug resistance and insensitivity, and one of the main factors is the existence of cancer stem cells. Here in this study, the effect of Bufalin on gallbladder cancer (GBC-SD) cells and the related mechanism were studied. The results indicated that Bufalin could inhibit the growth of gallbladder carcinoma both in vivo and in vitro. According to the biological behavior analysis, Bufalin induced apoptosis, inhibited the propagation, migration and invasion of GBC-SD cells, and blocked cell cycle at the G2/M stage. Besides, Bufalin inhibited the tumor sphere formation capability of gallbladder carcinoma in matrigel, reduced the expression of multiple stemness-associated proteins, including Oct4, Sox2 and the stem cell-surface marker proteins CD133 and CD44. Western blot assay showed that Bufalin inhibited MEK/ERK and PI3-K/AKT signaling pathways by inhibiting the expression of p-c-Met, which in turn affected the expression of apoptosis-related protein Mcl-1, and the invasion-associated proteins E-cadherin, MMP9 and Snail. Bufalin was found to have an inhibitory effect on the GBC-SD cell growth and reduce the self-renewal and characteristic of gallbladder cancer stem cells. It enhanced the chemotherapeutic sensitivity and reduced the metastasis of gallbladder carcinoma. In conclusion, Bufalin can be used as a new promising anticancer drug for gallbladder cancer patients who are resistant to traditional chemotherapy.

Ouabain reduces the expression of the adhesion molecule CD18 in neutrophils

Ouabain, a hormone that inhibits Na⁺/K⁺-ATPase, modulates many aspects of the inflammatory response. It has been previously demonstrated that ouabain inhibits neutrophil migration in several inflammation models in vivo, but little is known about the mechanisms underlying this effect. Thus, this work aimed to evaluate the effect of ouabain on molecules related to neutrophil migration. For this purpose, neutrophils obtained from mouse bone marrow were treated with ouabain (1, 10, and 100 nM) in vitro. Neutrophil viability was assessed by annexin V/propidium iodide staining. Ouabain treatment did not affect neutrophil viability at different times (2, 4, and 24 h). However, basal neutrophil viability was decreased after 4 h. Thus, we assessed the effect of ouabain on the adhesion molecule CD18, an integrin β2 chain protein, and on the chemokine receptor CXCR2 after 2 h of treatment. CD18 expression was reduced (by 30%) by 1 nM ouabain. However, the expression of CXCR2 on the neutrophil membrane was not affected by ouabain treatment (1, 10, and 100 nM). Moreover, ouabain (1, 10, and 100 nM) did not modulate the zymosan-induced secretion of CXCL1 (a chemokine receptor CXCR2 ligand) in macrophage cultures. These data suggest that the inhibitory effect of ouabain on neutrophil migration is related to reduced CD18 expression, indicating a novel mechanism of action.

New therapeutic aspects of steroidal cardiac glycosides: the anticancer properties of Huachansu and its main active constituent Bufalin

Aim of the review

In the past decade, increasing research attention investigated the novel therapeutic potential of steroidal cardiac glycosides in cancer treatment. Huachansu and its main active constituent Bufalin have been studied in vitro, in vivo and clinical studies. This review aims to summarize the multi-target and multi-pathway pharmacological effects of Bufalin and Huachansu in the last decade, with the aim of providing a more comprehensive view and highlighting the recently discovered molecular mechanisms.

Results

Huachansu and its major derivative, Bufalin, had been found to possess anti-cancer effects in a variety of cancer cell lines both in vitro and in vivo. The underlying anti-cancer molecular mechanisms mainly involved anti-proliferation, apoptosis induction, anti-metastasis, anti-angiogenesis, epithelial-mesenchymal transition inhibition, anti-inflammation, Na⁺/K⁺-ATPase activity targeting, the steroid receptor coactivator family inhibitions, etc. Moreover, the potential side-effects and toxicities of the toad extract, Huachansu, and Bufalin, including hematological, gastrointestinal, mucocutaneous and cardiovascular adverse reactions, were reported in animal studies and clinic trails.

Conclusions

Further research is needed to elucidate the potential drug-drug interactions and multi-target interaction of Bufalin and Huachansu. Large-scale clinical trials are warranted to translate the knowledge of the anticancer actions of Bufalin and Huachansu into clinical applications as effective and safe treatment options for cancer patients in the future.

Antagonistic anticancer effect of paclitaxel and digoxin combination

Despite the growing interest in the antitumor effect of cardiotonic steroids, combination treatments with well-established chemotherapy drugs like paclitaxel have been rarely investigated. Moreover, paclitaxel has been suggested as a Na⁺ /K⁺ -ATPase inhibitor. Here we investigated the effect of paclitaxel and digoxin alone or in combination on the viability of human lung (A549) and cervical cancer (HeLa) cell lines and the inhibitory effect of paclitaxel on several mammalian Na⁺ /K⁺ -ATPases. Although the viability of both tumor cell lines was concentration-dependently affected by digoxin treatment after 48 hours (A549 IC₅₀  = 31 nM and HeLa IC₅₀  = 151 nM), a partial effect was observed for paclitaxel, with a maximal inhibitory effect of 45% at 1000 nM with A549 and around 70% with HeLa cells (IC₅₀  = 1 nM). Although the two drugs were cytotoxic, their combined effect in HeLa cells was revealed to be antagonistic, as estimated by the combination index. No direct inhibitory effect of paclitaxel was detected in human, pig, rat, and mouse Na⁺ /K⁺ -ATPase enzymes, but high concentrations of paclitaxel decreased the Na⁺ /K⁺ -ATPase activity in HeLa cells after 48 hours without affecting protein expression. Our findings demonstrate that, under our conditions, paclitaxel and digoxin cotreatment produce antagonistic cytotoxic effects in HeLa cells, and the mechanism of action of paclitaxel does not involve a direct inhibition of Na⁺ /K⁺ -ATPase. More studies shall be designed to evaluate the consequences of the interaction of cardiotonic steroids and chemotherapy drugs.

Anti-tumor effects and 3D-quantitative structure-activity relationship analysis of bufadienolides from toad venom

Toad venom (venenum bufonis, also called Chan'su) has been widely used for centuries in China to treat different diseases, especially for cancer. Bufadienolides are mainly responsible for the anti-cancer effects of toad venom. However, systematic chemical composition and cytotoxicity as well as key pharmacophores of these bufadienolides from toad venom have not yet been defined clearly. To enrich the understanding of the diversity of bufadienolides and to find bufadienolides with better activities from toad venom. This study was carried out to isolate chemical constituents, research their anti-tumor effects and mechanisms by MTT assay, flow cytometry and Western blotting, and develop a CoMFA and CoMSIA quantitative structure-activity relationship (QSAR) model for illustrating the vital relationship between the chemical structures and cytotoxicities. Among 47 natural bufadienolides, most of bufadienolides (21 compounds isolated in this study and 26 compounds isolated previously) could significantly inhibit the proliferation of cancer cells, and compounds 1, 8, 12, 18 and 19 showed the most potent inhibitory activity against four types of human tumor cells. Compound 18 induced G₂/M cell cycle arrest and apoptosis. Moreover, 3D contour maps generated from CoMFA and CoMSIA identified several pharmacophores of bufadienolides responsible for the anti-tumor activities. Our study might provide reliable information for future structure modification and rational drug design of bufadienolides with anticancer activities in medical chemistry.

Bufalin induces apoptosis via mitochondrial ROS-mediated caspase-3 activation in HCT-116 and SW620 human colon cancer cells

OBJECTIVE

Bufalin has been reported to kill various types of cancer including human colorectal cancer. Our previous study demonstrated that bufalin induced cell death via autophagy in HT-29 and Caco-2 colon cancer cells, but the action of bufalin remains unclear. This study was conducted to investigate the role of bufalin in other colon cancer HCT-116 and SW620 cells as well as its potential mechanism.

METHODS

The effect of bufalin in HCT-116 and SW620 colon cancer cells was detected by assessing cell viability and cell death. Apoptotic cells were analyzed by Western blot and trypan blue dye exclusion assay. Mitochondrial ROS production was analyzed by flow cytometry after DCFDA and DHR-123 staining. The potential mechanism was investigated via pharmacological inhibitors.

RESULTS

Bufalin had high potency against HCT-116 and SW620 cells with IC50 values of 12.823 ± 1.792 nM and 26.303 ± 2.498 nM in HCT-116 and SW620 cells, respectively. Bufalin decreased cell viability, increased cell death as well as caspase-3 downstream target (cleaved PARP) accumulation, and these actions were significantly blocked by pan-caspase inhibitor zVAD-FMK. Mechanistically, ROS production, but neither the NAD(P)H oxidase, AMPK, ERK nor p38, is responsible for bufalin-induced apoptotic cell death. Moreover, bufalin-induced ROS generation is derived from mitochondria.

CONCLUSION

Bufalin significantly induces apoptosis in HCT-116 and SW620 colon cancer cells via mitochondrial ROS-mediated caspase-3 activation. We believe that our novel findings will greatly alter our current understanding on the anti-cancer mechanism of bufalin in colon cancer cells and will pave the way for further exploiting the clinical application.

Regulation and functions of integrin α2 in cell adhesion and disease

Integrins are cell adhesion molecules that are composed of an alpha (α) subunit and a beta (β) subunit with affinity for different extracellular membrane components. The integrin family includes 24 known members that actively regulate cellular growth, differentiation, and apoptosis. Each integrin heterodimer has a particular function in defined contexts as well as some partially overlapping features with other members in the family. As many reviews have covered the general integrin family in molecular and cellular studies in life science, this review will focus on the specific regulation, function, and signaling of integrin α2 subunit (CD49b, VLA-2; encoded by the gene ITGA2) in partnership with β1 (CD29) subunit in normal and cancer cells. Its roles in cell adhesion, cell motility, angiogenesis, stemness, and immune/blood cell regulations are discussed. The pivotal role of integrin α2 in many diseases such as cancer suggests its potential to be used as a novel therapeutic target.

Circular RNAs: Functions and Prospects in Glioma

Improving the survival rate of patients with glioma, a malignant tumor of the human brain has become increasingly important. In recent years, the function of circular RNAs (circRNAs) in different diseases and the pathophysiological mechanisms involved have been elucidated. In the pathophysiological mechanism, the primary function of circRNAs is to act as microRNA sponges. An increasing number of studies have found that circRNAs are differentially expressed in gliomas and regulate the occurrence, proliferation, and invasion of glioma and thus may be potential markers for the diagnosis of gliomas. Additionally, some circRNAs have been associated with glioma staging and may be useful in determining prognosis. Based on the stability and high conservation of circRNAs, we believe that circRNAs may have molecular targets that are useful for the treatment of glioma. In this review, we summarize the current research regarding the role of circRNAs in gliomas, discuss the potential value and role of circRNAs in gliomas, and provide new perspectives for future research.

Bufalin-loaded vitamin E succinate-grafted-chitosan oligosaccharide/RGD conjugated TPGS mixed micelles demonstrated improved antitumor activity against drug-resistant colon cancer

Background

Multidrug resistance (MDR) is the major reason for the failure of chemotherapy in colon cancer. Bufalin (BU) is one of the most effective antitumor active constituents in Chansu. Our previous study found that BU can effectively reverse P-glycoprotein (P-gp)-mediated MDR in colon cancer. However, the clinical application of BU is limited due to its low solubility in water and high toxicity. In the present study, a multifunctional delivery system based on vitamin-E- succinate grafted chitosan oligosaccharide (VES-CSO) and cyclic (arginine-glycine-aspartic acid peptide) (RGD)-modified d-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) was prepared by emulsion solvent evaporation method for targeted delivery of BU to improve the efficacy of drug-resistant colon cancer therapy.

Methods

The cytotoxicity of BU-loaded micelles against drug-resistant colon cancer LoVo/ADR and HCT116/LOHP cells was measured by CCK-8 assay. The cellular uptake, Rho123 accumulation, and cell apoptosis were determined by flow cytometry. The expression of apoptosis-related protein and P-gp was measured by Western blot assay. The antitumor activity of BU-loaded micelles was evaluated in LoVo/ADR-bearing nude mice.

Results

BU-loaded VES-CSO/TPGS-RGD mixed micelles (BU@VeC/T-RGD MM) were 140.3 nm in diameter with zeta potential of 8.66 mV. The BU@VeC/T-RGD MM exhibited good stability, sustained-release pattern, higher intracellular uptake, and greater cytotoxicity in LoVo/ADR cells. Furthermore, the mechanisms of the BU@VeC/T-RGD MM to overcome MDR might be due to enhanced apoptosis rate and P-gp efflux inhibition. Subsequently, in vivo studies confirmed an enhanced therapeutic efficiency and reduced side effects associated with BU@VeC/T-RGD MM compared with free BU, owing to the enhanced permeation and retention effect, improved pharmacokinetic behavior, and tumor targeting, which lead to MDR-inhibiting effect in LoVo/ADR-bearing nude mice.

Conclusion

Our results demonstrated that VeC/T-RGD MM could be developed as a potential delivery system for BU to improve its antitumor activity against drug-resistant colon cancer.

Bufalin suppresses the proliferation and metastasis of renal cell carcinoma by inhibiting the PI3K/Akt/mTOR signaling pathway

Bufalin, one of the active ingredients of the Chinese drug Chan su, exhibits significant antitumor activity against various cancer types. However, the role of bufalin in renal cell carcinoma (RCC) remains unclear. In the present study, it was demonstrated that bufalin inhibited cell proliferation, blocked the cell cycle in the G2/M phase, and reduced the metastasis of human RCC ACHN cells via the upregulation of p21^waf/cip1 and E-cadherin and the downregulation of cyclin dependent kinase 1, cyclin B1, N-cadherin, and hypoxia-inducible factor-1α (HIF-1α). Further mechanistic study revealed that bufalin reduced the expression of phosphorylated (phospho)-Akt and phospho-mammalian target of rapamycin (mTOR). Moreover, HIF-1α expression may be regulated through the inhibition of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling pathway. Thus, the present results suggest that bufalin induces cell cycle arrest and suppresses metastasis; this process may be associated with the PI3K/Akt/mTOR signaling pathway. Accordingly, it is suggested that bufalin is a therapeutic agent for RCC.

Bufalin inhibits glycolysis-induced cell growth and proliferation through the suppression of Integrin β2/FAK signaling pathway in ovarian cancer

Bufalin is the major digoxin-like component of the traditional Chinese medicine Chansu and has obvious anti-tumor effect in major malignancies, but the role of bufalin in glucose metabolism in ovarian cancer remains illustrated. Here, we sought to elucidate the regulatory function of bufalin on cell glucose metabolism in ovarian cancer. The treatment of bufalin on ovarian cancer cells effectively inhibited glucose uptake and lactate production in ovarian cancer cells. The expression levels of glycolysis-related proteins, including GLUT4, LDHB and HK2, were decreased by the treatment of bufalin detected by qRT-PCR and immunoblotting. Mechanistically, bufalin exerted its anti-tumor effect by targeting ITGB2/FAK signaling pathway in vitro and in vivo, which could be rescued by the introduction of ITGB2 cDNA in ovarian cancer cells. These findings provide evidence that bufalin inhibited cellular glycolysis-induced cell growth and proliferation through repression of the ITGB2/FAK pathway, indicating that bufalin may be developed as a chemotherapeutic agent to treat ovarian cancer.

Modulatory effects of bufalin, an active ingredient from toad venom on voltage-gated sodium channels

Chan-su (toad venom) has been used as an analgesic agent in China from ancient to modern times. Bufalin, a non-peptide toxin extracted from toad venom, is considered as one of the analgesic components. The molecular mechanism underlying the anti-nociceptive effects of bufalin remains unclear so far. In this study, we investigated the pharmacological effects of bufalin on pain-related ion channels as well as animal models through patch clamping, calcium imaging and animal behavior observation. Using the whole-cell recording, bufalin caused remarkable suppressive effect on the peak currents of Nav channels (voltage gated sodium channels, VGSCs) of dorsal root ganglion neuroblastomas (ND7-23 cell) in a dose-dependent manner. Bufalin facilitated the voltage-dependent activation and induced a negative shift on the fast inactivation of VGSCs. The recovery kinetics of VGSCs were significantly slowed and the recovery proportion were reduced after administering bufalin. However, bufalin prompted no significant effect not only on Kv4.2, Kv4.3 and BK channels heterologously expressed in HEK293T cells, but also on the capsaicin and allyl isothiocyanate induced Ca²⁺ influx. What's more, bufalin could observably relieve formalin-induced spontaneous flinching and licking response as well as carrageenan-induced thermal and mechanical hyperalgesia in dose-dependent manner in agreement with the results of in vitro experiments. The present results imply that the remarkable anti-nociceptive effects produced by bufalin are probably ascribed to its specific regulation on Nav channels. Bufalin inhibits the Nav channels in a dose-dependent manner, which will provide references for the optimal dose selection of analgesia drugs.

Programmed death ligand 1 promotes lymph node metastasis and glucose metabolism in cervical cancer by activating integrin β4/SNAI1/SIRT3 signaling pathway

Although PD-L1 has been shown to play a well-characterized role in inhibiting antitumor immunity via engagement of its receptor PD-1 in T lymphocytes, little is known about the tumor cell-intrinsic function of PD-L1 and its association with prognosis. Here, we investigate this issue and dissect the molecular mechanisms underlying the role of PD-L1 in glucose metabolism, proliferation, migration, and invasion in human cervical cancer cells. As a result, we found that PD-L1 overexpression in cervical cancer cells increases glucose metabolism and metastasis-related behaviors. Mechanistically, PD-L1 bound directly to integrin β4 (ITGB4), activating the AKT/GSK3β signaling pathway and consequently inducing the expression of the transcriptional repressor SNAI1. SNAIL in turn influenced the expression of genes involved in the epithelial-to-mesenchymal transition and regulated glucose metabolism by inhibiting SIRT3 promoter activity. High expression of PD-L1 and ITGB4 in human cervical carcinomas was significantly associated with lymph node metastasis and poor prognosis. Finally, ¹⁸F-fluorodeoxyglucose microPET/CT and bioluminescence imaging analyses of cervical xenograft tumors in mice revealed that PD-L1 overexpression markedly increases tumor glucose uptake and promotes lymph node metastasis. Together, these results demonstrate that PD-L1 can promote the growth and metastasis of cervical cancer by activating the ITGB4/SNAI1/SIRT3 signaling pathway, and also suggest the possibility of targeting PD-L1 and its downstream effectors as a potential approach for interfering with cervical cancer growth and metastasis.

Bufalin inhibits glioblastoma growth by promoting proteasomal degradation of the Na+/K+-ATPase α1 subunit

Chansu is a traditional Chinese medicine that is generally recognized as a specific inhibitor of Na⁺/K⁺-ATPase. Bufalin, an active component of Chansu, is an endogenous steroid hormone with great potential as a cancer treatment. However, the mechanism by which it exerts its antitumor activity requires further research. Currently, the α1 subunit of Na⁺/K⁺-ATPase (ATP1A1) is known to exert important roles in tumorigenesis, and the precise mechanisms underlying the effect of Bufalin on the Na⁺/K⁺-ATPase α1 subunit was therefore investigated in this study to determine its role in glioblastoma treatments. The effect of ATP1A1 on the sensitivity of glioblastoma cells to Bufalin was investigated using MTT assays, RT-PCR and siRNA. Western blot was also used to explore the important roles of the ubiquitin-proteasome pathway in the Bufalin-mediated inhibition of ATP1A1. Xenografted mice were used to examine the anti-tumor activity of Bufalin in vivo. LC-MS/MS analysis was performed to determine the ability of Bufalin to traverse the blood-brain barrier (BBB). The results indicated that Bufalin inhibited the expression of ATP1A1 in glioblastoma by promoting the activation of proteasomes and the subsequent protein degradation of ATP1A1, while Bufalin had no effect on ATP1A1 protein synthesis. Bufalin also inhibited the expression of ATP1A1 in xenografted mice and significantly suppressed tumor growth. These data should contribute to future basic and clinical investigations of Bufalin. In conclusion, Bufalin significantly inhibited the expression of ATP1A1 in glioblastoma cells by activating the ubiquitin-proteasome signaling pathway. Bufalin may therefore have the potential to be an effective anti-glioma drug for human glioblastoma in the future.

Bufalin reverses ABCB1-mediated drug resistance in colorectal cancer

Multidrug resistance (MDR), mainly mediated by ABCB1 transporter, is a major cause for chemotherapy failure. Bufalin (BU), an active component of the traditional Chinese medicine chan’su, has been reported to have antitumor effects on various types of cancer cells. The purpose of this present study was to investigate the reversal effect of BU on ABCB1-mediated multidrug resistance in colorectal cancer. BU at safe concentration (5, 10, 20 nM) could reverse chemosensitivity of ABCB1-overexpression HCT8/ADR, LoVo/ADR and HCT8/ABCB1 nearly back to their parental cells level. In addition, results from the drug accumulation studies revealed that BU was able to enhance intracellular accumulation of doxorubicin (DOX) and Rhodamine 123 (Rho-123) in a dose-dependent manner. Furthermore, Western blot assays showed that BU significantly inhibited the expression level of ABCB1 protein. Meanwhile, BU stimulated the ATPase activity of ABCB1, which suggested that BU might be a substrate of ABCB1. More interestingly, docking analysis predicted that BU could be docked into the large hydrophobic drug-binding cavity of human ABCB1. Importantly, BU remarkable increased the effect of DOX against the ABCB1 resistant HCT8/ADR colorectal cell xenografts in nude mice, without inducing any obvious toxicity. Overall, we concluded that BU efficiently reversed ABCB1-mediated MDR through not only inhibited the efflux function of ABCB1, but also down-regulate its protein expression, which might represent a potential and superior ABCB1 modulator in colorectal cancer.

Molecular mechanisms underlying the antimetastatic activity of bufalin

Bufalin is a monomer compound extract from Chansu, which is a traditional Chinese medicine obtained from the skin and parotid venom glands of toads, such as Bufo bufo gargarizans Cantor and Bufo melanostictus Schneider. Chansu had been used in traditional Chinese medicine for >1,000 years due to its cardiac, anti-inflammatory and anticancer properties. Previous studies identified bufalin as the main anticancer compound of Chansu, and recent evidence has corroborated its anticancer properties. Bufalin inhibits cancer cell proliferation, induces cell cycle arrest, induces cancer cell apoptosis, inhibits neovascularization, induces cell differentiation, inhibits cancer metastasis and invasion, and enhances chemotherapeutic drug sensitivity. However, the function and mechanism of bufalin in metastatic cancer cells have not yet been expounded. The aim of the present review was to discuss the recent progress and prospects of bufalin in the prevention of cancer metastasis, particularly in inhibiting epithelial-to-mesenchymal transition.

Silencing of cZNF292 circular RNA suppresses human glioma tube formation via the Wnt/β-catenin signaling pathway

CircRNA is a novel type of RNA molecule formed by a covalently closed loop which have no 5'-3' polarity and possess no polyA tail and relatively stable due to the cyclic structure. Therefore, they may serve as potential targets and diagnosis biomarkers for tumor therapy. cZNF292 is an important circular oncogenic RNA and plays a critical role in the progression of tube formation. This study is aimed at exploring the role of cZNF292 in human glioma tube formation and its potential mechanism of action. We found that cZNF292 silencing suppresses tube formation by inhibiting glioma cell proliferation and cell cycle progression. Cell cycle progression in human glioma U87MG and U251 cells was halted at S/G2/M phase via the Wnt/β-catenin signaling pathway and related genes such as PRR11, Cyclin A, p-CDK2, VEGFR-1/2, p-VEGFR-1/2 and EGFR. The results suggest that cZNF292 silencing plays an important role in the tube formation process and has potential for application as a therapeutic target and biomarker in glioma.

Cardiac glycoside bufalin blocks cancer cell growth by inhibition of Aurora A and Aurora B activation via PI3K-Akt pathway

In our previous study, cardiac glycosides including bufalin, a group of sodium pump (Na+/K+-ATPase) inhibitors widely used to treat heart failure for many years, have been demonstrated to induce a delay of mitotic entry and mitotic arrest in many cancer cells. However, the underlying mechanism remains poorly understood. Here, we reported for the first time that cardiac glycoside bufalin induced mitotic entry delay and prometaphase arrest by inhibition of activation of Aurora A/B. Furthermore, cardiac glycoside bufalin prevented Aurora A recruitment to mitotic centrosomes and Aurora B recruitment to unattached kinetochores. Mechanistically, bufalin and knockdown of sodium pump inhibited PI3K-Akt pathway, which in turn inhibit the activation of Aurora A/B, followed by a delay in mitotic entry and mitotic arrest. These actions were reversed by overexpression of Akt. In addition, ERK, mTOR, and ROS are not involved in bufalin-mediated downregulation of active form of Aurora A/B. Taken together, cardiac glycoside bufalin induces mitotic entry delay and mitotic arrest in cancer cells through inhibition of Aurora A/B activation via PI3K-Akt pathway. Based on this novel finding we could suggest that targeting PI3K-Akt pathway may have therapeutic value for the treatment of cancers associated with sodium pump overexpression.

Bufalin Suppresses Migration and Invasion of Hepatocellular Carcinoma Cells Elicited by Poly (I:C) Therapy

The Toll-like receptor 3 (TLR3) agonists as polyriboinosinic–polyribocytidylic acid (poly (I:C)) have been implicated as potential immunotherapy adjuvant for cancer whereas the exact roles of TLR3 agonists in hepatocellular carcinoma (HCC) treatment have not been clearly evaluated. In consistent with previous reports, we found that poly (I:C) triggering of TLR3 inhibited cell proliferation and induced apoptosis in HCC cells. However, poly (I:C), when used at lower concentration that cannot remarkably inhibit proliferation and induce apoptosis in HCC cells, enhanced the migration and invasion in vitro and the metastasis in vivo. More importantly, we found that bufalin, a prominent component of toad venom, could suppress poly (I:C)-inspired migration, invasion and metastasis of HCC cells despite that bufalin could not potentiate poly (I:C)-induced inhibition of proliferation and induction of apoptosis. In MHCC97 H cells, bufalin impaired poly (I:C)-induced activation of Tank-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) pathway and NF-κB pathway. Inhibitor for TBK1 but not NF-κB suppressed poly (I:C)-inspired migration and invasion, which was further supported by using TBK1 deficient (Tbk1^–/–) cells. In another model using poly (I:C) transfection, bufalin could also suppress the migration and invasion of HCC cells, which was not observed in Tbk1^–/– MHCC97 H cells. Our data suggest that bufalin can suppress the metastasis of HCC cells in poly (I:C) therapy by impairing TBK1 activation, indicating that bufalin may be used in combination with poly (I:C) therapy in HCC treatment for the sake of reversing poly (I:C)-triggered metastasis of HCC cells.

Long non-coding RNA PAR5 inhibits the proliferation and progression of glioma through interaction with EZH2

Emerging evidence suggests that long non-coding RNAs (lncRNAs) may be involved in modulating various aspects of tumor biology and serve as potential therapeutic targets as well as novel biomarkers in the treatment of glioma. The present study investigated the role of lncRNA, Prader Willi/Angelman region RNA 5 (PAR5; also known as PWAR5), in glioma and its clinical significance in glioma cases. The expression levels of PAR5 were determined in clinical samples and U87, U251 cells using real-time reverse transcription quantitative polymerase chain reaction (qRT-PCR) analysis. The effects of PAR5 on cell proliferation, migration and invasion were determined using in vitro assays. RNA immunoprecipitation (RIP) and RNA pull-down assays, as well as the evauation of the expression of various oncogenes were carried out to reveal the underlying mechanisms. We found that PAR5 was significantly downregulated in glioma tissues and cell lines. Furthermore, PAR5 expression was negatively correlated with tumor size, World Health Organization (WHO) grade and Karnofsky performance score (KPS). Patients with low PAR5 expression in tumors had a worse overall survival compared to those with higher expression. Finally, in vitro restoration of PAR5 expression inhibited human glioma cell proliferation, invasion and migration by binding to EZH2 and regulating oncogene expression. This finding may provide a therapeutic approach for the future treatment of glioma.

Bufalin attenuates cancer-induced pain and bone destruction in a model of bone cancer

Bufalin is a natural anti-inflammatory small molecule. Given the close relationship between inflammation and cancer, many scholars have studied the effect of bufalin on cancer in vitro, but in vivo research is still lacking. A murine bone cancer model was used in this study. We conducted pain sensitive test on mice with bone cancer, by nocifensive behavior, mechanical allodynia, and thermal hyperalgesia. Serum levels of bone loss markers with bufalin treatment were measured by ELISA. Expressions of osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) were analyzed in bufalin-treated mice by real-time PCR and Western blot. Cannabinoid 2 receptor (CB2) inverse agonist AM630 was administrated to mice with bone cancer together with bufalin. Bufalin relieved cancer-induced pain and bone destruction in the murine bone cancer model. Serum levels of bone loss markers after bufalin treatment were reduced. Bufalin upregulated OPG and downregulated RANKL. The CB2 receptor inverse agonist, AM630, reduced the pain relief of bufalin treatment in the mouse bone cancer model. This study demonstrates that bufalin relieves cancer-induced pain and bone destruction, which is mediated through the CB2 receptor.