Melittin suppresses VEGF-A-induced tumor growth by blocking VEGFR-2 and the COX-2-mediated MAPK signaling pathway

Peptides for microbe-induced cancers: latest therapeutic strategies and their advanced technologies

Cancer is a significant global health concern associated with multiple distinct factors, including microbial and viral infections. Numerous studies have elucidated the role of microorganisms, such as Helicobacter pylori (H. pylori), as well as viruses for example human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus (HCV), in the development of human malignancies. Substantial attention has been focused on the treatment of these microorganism- and virus-associated cancers, with promising outcomes observed in studies employing peptide-based therapies. The current paper provides an overview of microbe- and virus-induced cancers and their underlying molecular mechanisms. We discuss an assortment of peptide-based therapies which are currently being developed, including tumor-targeting peptides and microbial/viral peptide-based vaccines. We describe the major technological advancements that have been made in the design, screening, and delivery of peptides as anticancer agents. The primary focus of the current review is to provide insight into the latest research and development in this field and to provide a realistic glimpse into the future of peptide-based therapies for microbe- and virus-induced neoplasms.

Melittin: a possible regulator of cancer proliferation in preclinical cell culture and animal models

BACKGROUND

Melittin is a water-soluble cationic peptide derived from bee venom that has been thoroughly studied for the cure of different cancers. However, the unwanted interactions of melittin produce hemolytic and cytotoxic effects that hinder their therapeutic applications. To overcome the shortcomings, numerous research groups have adopted different approaches, including conjugation with tumor-targeting proteins, gene therapy, and encapsulation in nanoparticles, to reduce the non-specific cytotoxic effects and potentiate their anti-cancerous activity.

PURPOSE

This article aims to provide mechanistic insights into the chemopreventive activity of melittin and its nanoversion in combination with standard anti-cancer drugs for the treatment of cancer.

METHODS

We looked over the pertinent research on melittin's chemopreventive properties in online databases such as PubMed and Scopus.

CONCLUSION

In the present article, the anti-cancerous effects of melittin on different cancers have been discussed very nicely, as have their possible mechanisms of action to act against different tumors. Besides, it interacts with different signal molecules that regulate the diverse pathways of cancerous cells, such as cell cycle arrest, apoptosis, metastasis, angiogenesis, and inflammation. We also discussed the recent progress in the synergistic combination of melittin with standard anti-cancer drugs and a nano-formulated version of melittin for targeted delivery to improve its anticancer potential.

Recent advances in melittin-based nanoparticles for antitumor treatment: from mechanisms to targeted delivery strategies

As a naturally occurring cytolytic peptide, melittin (MLT) not only exhibits a potent direct tumor cell-killing effect but also possesses various immunomodulatory functions. MLT shows minimal chances for developing resistance and has been recognized as a promising broad-spectrum antitumor drug because of this unique dual mechanism of action. However, MLT still displays obvious toxic side effects during treatment, such as nonspecific cytolytic activity, hemolytic toxicity, coagulation disorders, and allergic reactions, seriously hampering its broad clinical applications. With thorough research on antitumor mechanisms and the rapid development of nanotechnology, significant effort has been devoted to shielding against toxicity and achieving tumor-directed drug delivery to improve the therapeutic efficacy of MLT. Herein, we mainly summarize the potential antitumor mechanisms of MLT and recent progress in the targeted delivery strategies for tumor therapy, such as passive targeting, active targeting and stimulus-responsive targeting. Additionally, we also highlight the prospects and challenges of realizing the full potential of MLT in the field of tumor therapy. By exploring the antitumor molecular mechanisms and delivery strategies of MLT, this comprehensive review may inspire new ideas for tumor multimechanism synergistic therapy.

Neurotoxicity of melittin: Role of mitochondrial oxidative phosphorylation system in synaptic plasticity dysfunction

Melittin (Mel), a main active peptide component of bee venom, has been proven to possess strong antitumor activity. Previous studies have shown that Mel caused severe cell membrane lysis and acted on the central nervous system (CNS). Here, this study was designed to investigate the effects of Mel on CNS and explore the potential mechanism. We confirmed the neurotoxic effect of melittin by in vivo and in vitro experiments. After subcutaneous administration of Mel (4 mg/kg, 8 mg/kg) for 14 days, the mice exhibited obvious depression-like behavior in a dose dependent manner. Besides, RNA-sequencing analysis revealed that oxidative phosphorylation (OXPHOS) signaling pathway was mostly enriched in hippocampus. Consistently, we found that Mel distinctly inhibited the activity of OXPHOS complex I and induced oxidative stress injury. Moreover, Mel significantly induced synaptic plasticity dysfunction in hippocampus via BDNF/TrkB/CREB signaling pathway. Taken together, the neurotoxic effect of Mel was involved in impairing OXPHOS system and hippocampal synaptic plasticity. These novel findings provide new insights into fully understanding the health risks of Mel and are conducive to the development of Mel related drugs.

Melittin induces ferroptosis and ER stress-CHOP-mediated apoptosis in A549 cells

Melittin is a natural polypeptide present in bee venom, with significant anti-tumor activity. Melittin has been reported to induce cell death in lung carcinoma cell line A549 cells, suggesting an excellent potential for treating lung cancer. However, the core mechanism underlying melittin-induced cell death in A549 cells remains unclear. This work reports that melittin induces reactive oxygen species (ROS) burst, upregulates intracellular Fe²⁺ levels, disrupts the glutathione-glutathione peroxidase 4 antioxidant system, and increases lipid peroxide accumulation, eventually inducing cell death, indicating that ferroptosis may be involved in the antitumor effects of melittin in A549 cells. Furthermore, A549 cells treated with the ferroptosis inhibitors ferrostatin-1 and deferoxamine demonstrated that these inhibitors could reverse the cell death induced by melittin, further confirming that melittin induces A549 cell death via ferroptosis. Furthermore, the results also illustrated that melittin activated the endoplasmic reticulum (ER) stress-CHOP (C/EBP homologous protein) apoptotic signal, closely associated with high-level intracellular ROS. The ER stress inhibitor, 4-Phenyl butyric acid, was used to confirm that ER stress-CHOP apoptotic signaling is another molecular mechanism of melittin-induced A549 cell death. Thus, our results demonstrate that ferroptosis and ER stress-CHOP signaling are key molecular mechanisms of melittin-induced cell death in lung cancer.Key policy highlightsMelittin upregulates intracellular Fe²⁺ levels, leading to the accumulation of lipid peroxides in A549 cells.Melittin disrupts the glutathione-glutathione peroxidase 4 antioxidant system in A549 cells.Melittin induces activation of endoplasmic reticulum stress-C/EBP homologous protein apoptosis signal.Ferroptosis and ER stress are the core molecular mechanisms underlying melittin-induced apoptosis in A549 cells.

Bee venom-loaded EGFR-targeting peptide-coupled chitosan nanoparticles for effective therapy of hepatocellular carcinoma by inhibiting EGFR-mediated MEK/ERK pathway

Hepatocellular carcinoma (HCC) is one of the world's most risky diseases due to the lack of clear and cost-effective therapeutic targets. Currently, the toxicity of conventional chemotherapeutic medications and the development of multidrug resistance is driving research into targeted therapies. The nano-biomedical field's potential for developing an effective therapeutic nano-sized drug delivery system is viewed as a significant pharmaceutical trend for the encapsulation and release of numerous anticancer therapies. In this regard, current research is centered on the creation of biodegradable chitosan nanoparticles (CSNPs) for the selective and sustained release of bee venom into liver cancer cells. Furthermore, surface modification with polyethylene glycol (PEG) and GE11 peptide-conjugated bee venom-CSNPs allows for the targeting of EGFR-overexpressed liver cancer cells. A series of in vitro and in vivo cellular analyses were used to investigate the antitumor effects and mechanisms of targeted bee venom-CSNPs. Targeted bee venom-CSNPs, in particular, were found to have higher cytotoxicity against HepG2 cells than SMMC-7721 cells, as well as stronger cellular uptake and a substantial reduction in cell migration, leading to improved cancer suppression. It also promotes cancer cell death in EGFR overexpressed HepG2 cells by boosting reactive oxygen species, activating mitochondria-dependent pathways, inhibiting EGFR-stimulated MEK/ERK pathway, and elevating p38-MAPK in comparison to native bee venom. In hepatocellular carcinoma (HCC)-induced mice, it has anti-cancer properties against tumor tissue. It also improved liver function and architecture without causing any noticeable toxic side effects, as well as inhibiting tumor growth by activating the apoptotic pathway. The design of this cancer-targeted nanoparticle establishes GE11-bee venom-CSNPs as a potential chemotherapeutic treatment for EGFR over-expressed malignancies. Finally, our work elucidates the molecular mechanism underlying the anticancer selectivity of targeted bee venom-CSNPs and outlines therapeutic strategies to target liver cancer.

Stable Loading and Delivery of Melittin with Lipid-Coated Polymeric Nanoparticles for Effective Tumor Therapy with Negligible Systemic Toxicity

Melittin is a potential anticancer candidate with remarkable antitumor activity and ability to overcome tumor drug resistance. However, the clinical applications of melittin are largely restricted by its severe hemolytic activity and nonspecific cytotoxicity after systemic administration. Here, a biocompatible and stable melittin-loaded lipid-coated polymeric nanoparticle (MpG@LPN) formulation that contains a melittin/poly-γ-glutamic acid nanoparticle inner core, a lipid membrane middle layer, and a polyethylene glycol (PEG) and PEG-targeting molecule outer shell was designed. The formulations were prepared by applying a self-assembly procedure based on intermolecular interactions, including electrostatic attraction and hydrophobic effect. The core-shell MpG@LPN presented high efficiency for melittin encapsulation and high stability in physiological conditions. Hemolysis and cell proliferation assays showed that the PEG-modified MpG@LPN had almost no hemolytic activity and nonspecific cytotoxicity even at high concentrations. The modification of targeting molecules on the MpG@LPNs allowed for the selective binding with target tumor cells and cytolytic activity via apoptosis induction. In vivo experiments revealed that MpG@LPNs can remarkably inhibit the growth of tumors without the occurrence of hemolysis and tissue toxicity. Results suggested that the developed MpG@LPN with a core-shell structure can effectively address the main obstacles of melittin in clinical applications and has great potential in cancer treatment.

Applications and evolution of melittin, the quintessential membrane active peptide

Melittin, the main venom component of the European Honeybee, is a cationic linear peptide-amide of 26 amino acid residues with the sequence: GIGAVLKVLTTGLPALISWIKRKRQQ-NH₂. Melittin binds to lipid bilayer membranes, folds into amphipathic α-helical secondary structure and disrupts the permeability barrier. Since melittin was first described, a remarkable array of activities and potential applications in biology and medicine have been described. Melittin is also a favorite model system for biophysicists to study the structure, folding and function of peptides and proteins in membranes. Melittin has also been used as a template for the evolution of new activities in membranes. Here we overview the rich history of scientific research into the many activities of melittin and outline exciting future applications.

Role of Bee Venom and Melittin on Restraining Angiogenesis and Metastasis in γ-Irradiated Solid Ehrlich Carcinoma-Bearing Mice

Pathological angiogenesis and apoptosis evasion are common hallmarks of cancer. The present work was an endeavor to evaluate the influence of bee venom (BV) or its major constituent melittin (MEL) as antiapoptotic and angiogenic regulator modifier on the tumor growth and the cell sensitivity to ionizing radiation targeting the improvement of cancer therapeutic protocols. BV (0.56 mg/kg/day) and MEL (500 µg/kg body weight/day) were injected intraperitoneally to mice bearing 1 cm³ solid tumor of Ehrlich ascites carcinoma (EAC) for 21 consecutive days. Mice were whole-body exposed to 1 Gray (Gy) of γ-radiation (2 fractionated doses). Treatment with BV or MEL markedly suppresses the proliferation of tumor in EAC mice. The concentrations of m-RNA for angiogenic factors (TNF-α, VEGF) as well as MMPs 2 and 9 activities and NO concentration were significantly decreased, combined with improvements in apoptotic regulators (caspase-3 activity) and normal cells redox tone (catalase and free radicals content) compared with EAC mice. Moreover, the histopathological investigation confirms the improvement exerted by BV or MEL in the EAC mice group or EAC + R group. Exposure to γ-radiation sustained the modulatory effect of BV on tumor when compared with EAC + BV mice. Convincingly, the role of BV or MEL as a natural antiangiogenic in the biological sequelae after radiation exposure is verified. Hence, BV and its major constituent MEL might represent a potential therapeutic strategy for increasing the radiation response of solid tumors.

Melittin inhibits the expression of key genes involved in tumor microenvironment formation by suppressing HIF-1α signaling in breast cancer cells

HIF-1α has critical roles in the formation of tumor microenvironment by regulating genes involved in angiogenesis and anaerobic respiration. TME fuels tumors' growth and metastasis and presents therapy with several challenges. Therefore, we aimed to investigate if Melittin disrupts HIF-1α signaling pathway in breast adenocarcinoma cell line MDA-MB-231. Breast adenocarcinoma cell line MDA-MB-231 was cultured in the presence of different doses of Melittin, and MTT assay was carried out to measure Melittin's cytotoxic effects. Cells were exposed to 5% O₂ to mimic hypoxic conditions and Melittin. Western blot was used to measure HIF-1α protein levels. Gene expression analysis was performed using real-time PCR to measure relative mRNA abundance of genes involved in tumor microenvironment formation. Our results revealed that Melittin effectively inhibits HIF-1α at transcriptional and translational/post-translational level. HIF-1α protein and mRNA level were significantly decreased in Melittin-treated groups. It is found that inhibition of HIF-1α by Melittin is through downregulation of NFκB gene expression. Furthermore, gene expression analysis showed a downregulation in VEGFA and LDHA expression due to inhibition of HIF-1α protein by Melittin. In addition, cell toxicity assay showed that Melittin inhibits the growth of MDA-MB-231 cell line through activation of extrinsic and intrinsic apoptotic pathways by upregulating TNFA and BAX expression. Melittin suppresses the expression of genes responsible for formation of TME physiological hallmarks by suppressing HIF-1α signaling pathway. Our results suggest that Melittin can modulate tumor microenvironment by inhibition of VEGFA and LDHA.

Delivery Strategies for Melittin-Based Cancer Therapy

Melittin (MLT) has been studied preclinically as an anticancer agent based on its broad lytic effects in multiple tumor types. However, unsatisfactory tissue distribution, hemolysis, rapid metabolism, and limited specificity are critical obstacles that limit the translation of MLT. Emerging drug delivery strategies hold promise for targeting, controlled drug release, reduced side effects, and ultimately improved treatment efficiency. In this review, we discuss recent advances in the use of diverse carriers to deliver MLT, with an emphasis on the design and mechanisms of action. We further outline the opportunities for MLT-based cancer immunotherapy.

Melittin suppresses growth and induces apoptosis of non-small-cell lung cancer cells via down-regulation of TGF-β-mediated ERK signal pathway

The purpose of this study was to investigate the anti-cancer effect of melittin on growth, migration, invasion, and apoptosis of non-small-cell lung cancer (NSCLC) cells. This study also explored the potential anti-cancer mechanism of melittin in NSCLC cells. The results demonstrated that melittin suppressed growth, migration, and invasion, and induced apoptosis of NSCLC cells in vitro. Melittin increased pro-apoptotic caspase-3 and Apaf-1 gene expression. Melittin inhibited tumor growth factor (TGF)-β expression and phosphorylated ERK/total ERK (pERK/tERK) in NSCLC cells. However, TGF-β overexpression (pTGF-β) abolished melittin-decreased TGF-β expression and pERK/tERK in NSCLC cells. Treatment with melittin suppressed tumor growth and prolonged mouse survival during the 120-day observation in vivo. Treatment with melittin increased TUNEL-positive cells and decreased expression levels of TGF-β and ERK in tumor tissue compared to the control group. In conclusion, the findings of this study indicated that melittin inhibited growth, migration, and invasion, and induced apoptosis of NSCLC cells through down-regulation of TGF-β-mediated ERK signaling pathway, suggesting melittin may be a promising anti-cancer agent for NSCLC therapy.

Formicolides A and B, Antioxidative and Antiangiogenic 20-Membered Macrolides from a Wood Ant Gut Bacterium

Two new macrolides, formicolides A (1) and B (2), were isolated from Streptomyces sp. BA01, a gut bacterial strain of the wood ant (Formica yessensis). Their 20-membered macrocyclic lactone structures were established using NMR and mass spectrometric data. The relative configurations of the formicolides were determined by J-based configuration analysis utilizing ROESY, HETLOC, and HECADE NMR spectroscopic data. Genomic and bioinformatics analysis of the bacterial strain enabled us to identify the type-I polyketide synthase pathway employing a trans-acyltransferase system. The absolute configurations of 1 and 2 are proposed based on detailed analysis of the sequences of the ketoreductases in the modular gene cluster and statistical comparative analysis of the experimental NMR chemical shifts and quantum mechanical calculations. Formicolides A and B (1 and 2) induced quinone reductase activity in murine Hepa-1c1c7 cells and antiangiogenic activity by suppression of tube formation in human umbilical vein endothelial cells.

Antimicrobial Properties of Apis mellifera's Bee Venom

Bee venom (BV) is a rich source of secondary metabolites from honeybees (Apis mellifera L.). It contains a variety of bioactive ingredients including peptides, proteins, enzymes, and volatile metabolites. The compounds contribute to the venom’s observed biological functions as per its anti-inflammatory and anticancer effects. The antimicrobial action of BV has been shown in vitro and in vivo experiments against bacteria, viruses, and fungi. The synergistic therapeutic interactions of BV with antibiotics has been reported. The synergistic effect contributes to a decrease in the loading and maintenance dosage, a decrease in the side effects of chemotherapy, and a decrease in drug resistance. To our knowledge, there have been no reviews on the impact of BV and its antimicrobial constituents thus far. The purpose of this review is to address the antimicrobial properties of BV and its compounds.

Melittin inhibits proliferation, migration and invasion of bladder cancer cells by regulating key genes based on bioinformatics and experimental assays

The antitumour effect of melittin (MEL) has recently attracted considerable attention. Nonetheless, information regarding the functional role of MEL in bladder cancer (BC) is currently limited. Herein, we investigated the effect of MEL on critical module genes identified in BC. In total, 2015 and 4679 differentially expressed genes (DEGs) associated with BC were identified from the GSE31189 set and The Cancer Genome Atlas database, respectively. GSE‐identified DEGs were mapped and analysed using Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes analyses to determine BC‐involved crucial genes and signal pathways. Coupled with protein–protein interaction network and Molecular Complex Detection analyses, Modules 2 and 4 were highlighted in the progression of BC. In in‐vitro experiments, MEL inhibited the proliferation, migration, and invasion of UM‐UC‐3 and 5637 cells. The expression of NRAS, PAK2, EGFR and PAK1 in Module 4—enriched in the MAPK signalling pathway—was significantly reduced after treatment with MEL at concentrations of 4 or 6 μg/mL. Finally, quantitative reverse transcription‐polymerase chain reaction and Western blotting analyses revealed MEL inhibited the expression of genes at the mRNA (ERK1/2, ERK5, JNK and MEK5), protein (ERK5, MEK5, JNK and ERK1/2) and phosphorylation (p‐ERK1/2, p‐JNK, and p‐38) levels. This novel evidence indicates MEL exerts effects on the ERK5‐MAK pathway—a branch of MAPK signalling pathway. Collectively, these findings provide a theoretical basis for MEL application in BC treatment.

Vascular endothelial growth factor A/Vascular endothelial growth factor receptor 2 axis promotes human dental pulp stem cell migration via the FAK/PI3K/Akt and p38 MAPK signalling pathways

AIM

To investigate the effects of vascular endothelial growth factor A (VEGFA) and the underlying molecular mechanisms on the migration of human dental pulp stem cells (hDPSCs).

METHODOLOGY

The expression of VEGFA in inflammatory pulp tissue and lipopolysaccharide (LPS)-stimulated dental pulp cells was examined by immunofluorescence staining and qRT-PCR. The migration of hDPSCs was detected using transwell migration and wound healing assays. The activation of FAK, PI3K, Akt and p38 signalling was evaluated by Western blot analysis. Silence RNA (siRNA) technology was utilized to knockdown the expression of VEGFR1 (Flt-1) and VEGFR2 (Flk-1/KDR). PF573228 (inhibitor of FAK), LY294002 (inhibitor of PI3K), SB203580 (inhibitor of p38) and SU5416 (inhibitor of VEGFR2) were employed to investigate the effect of VEGFA on the migratory mechanism of hDPSCs. Data were analysed statistically using the Student's t-test or one-way ANOVA.

RESULTS

The expression levels of VEGFA in inflammatory pulp tissue in vivo and LPS-stimulated dental pulp cells in vitro were significantly greater than those in the control groups (P < 0.05). Vascular endothelial growth factor A promoted the migration of hDPSCs in a concentration-dependent manner. Several signalling pathways, including FAK, PI3K, Akt and p38, were activated by VEGFA in a dose- and time-dependent manner in hDPSCs. The VEGFA-induced migration of hDPSCs was significantly inhibited with drug inhibitors such as PF573228, LY294002, SB203580 or SU5416 (P < 0.05). These signalling pathways activated by VEGFA stimulation were significantly suppressed by pre-treatment with inhibitor of VEGFR2 (SU5416) or transfection with siRNA of VRGFR2 (P < 0.05) but not VEGFR1 siRNA.

CONCLUSIONS

Vascular endothelial growth factor A/VEGFR2 axis promoted the migration of hDPSCs via the FAK/PI3K/Akt and p38 MAPK signalling pathways. These findings reveal a novel molecular mechanism for cell migration of hDPSCs, which may contribute to the remodelling of pulp tissue and dentine.

Identification of angiogenesis-inhibiting peptides from Chan Su

Chan Su is a traditional medicine prepared from toxic secretions from the auricular and skin glands of Chinese toads. Previous studies show that active components in Chan Su can inhibit the proliferation of tumor cells. To study the effect of Chan Su peptides on angiogenesis, fresh Chan Su was collected and its component peptides were isolated by an extraction and precipitation method. A high-performance liquid chromatography (HPLC) fingerprint of the Chan Su component peptides revealed that there were more than 18 peptide component peaks. We demonstrate that Chan Su peptides inhibit angiogenesis in vitro by inhibiting human umbilical vein endothelial cell (HUVEC) proliferation and tube formation in a dose-dependent manner. Western blots indicated that Chan Su peptides inhibited the protein expression of VEGF165 and Ras, leading us to conclude that Chan Su peptide components exert anti-angiogenic effects by suppressing the VEGF165-VEGFR2-Ras signalling pathway. Finally, we identified the partial amino acid sequences of seven Chan Su peptides using the shotgun proteomics method.

Melittin Constrains the Expression of Identified Key Genes Associated with Bladder Cancer

This work is aimed at investigating the effect of melittin on identified key genes in bladder cancer (BC) and further providing a theoretical basis for BC treatment. GSE35014 downloaded from the Gene Expression Omnibus (GEO) database was used to screen differentially expressed genes (DEGs) in BC cells and control. Results showed that a total of 389 upregulated and 169 downregulated genes were identified. Subsequently, GO analysis, KEGG pathway enrichment analysis, and PPI network analysis were employed to disclose the crucial genes and signaling pathways involved in BC. Fifteen module-related DEGs and their associated signaling pathways were obtained according to the PPI network and modular analyses. Based on the analysis of articles retrieved in the PubMed database, we found that melittin could induce apoptosis and constrain the progression of tumor cells as a result of regulating critical cancer-related signaling pathways, such as PI3K-Akt and TNF signaling pathways. Furthermore, PI3K-Akt and TNF signaling pathways were also found to be associated with module-related DEGs according to biological analyses. At last, qRT-PCR analysis demonstrated that melittin could constrain the expression of module-related DEGs (LPAR1, COL5A1, COL6A2, CXCL1, CXCL2, and CXCL3) associated with PI3K-Akt and TNF signaling pathways in BC cells. Functional assays revealed that melittin could constrain the proliferative and migrated abilities of BC cells. Conjointly, these findings provide a theoretical basis for these six genes as drug-sensitive markers of melittin in BC treatment.

Nanostructured Peptidotoxins as Natural Pro-Oxidants Induced Cancer Cell Death via Amplification of Oxidative Stress

Melittin (Mel), one of the host defense peptides derived from the venom of honeybees, demonstrates substantial anticancer properties, which is attributed to augmenting reactive oxygen species (ROS) generation. However, little has been reported on its pro-oxidation capacity in cancer oxidation therapy. In this study, an ROS amplifying nanodevice was fabricated through direct complexation of two natural pro-oxidants, Mel and condensed epigallocatechin gallate (pEGCG). The obtained nanocomplex (NC) was further covered with phenylboronic acid derivatized hyaluronic acid (pHA) through the ROS-responsive boronate ester coordination bond to produce pHA-NC. Upon undergoing receptor-mediated endocytosis into cancer cells, the inner cores of pHA-NC will be partially uncovered once pHA corona is degraded by hyaluronidase and will then escape from the lysosome by virtue of cytolytic Mel. The elevated ROS level in the tumor cytoplasm can disrupt the boronate ester bond to facilitate drug release. Both Mel and pEGCG could synergistically amplify oxidative stress and prolong ROS retention in cancer cells, leading to enhanced anticancer efficacy. This ROS cascade amplifier based on selective coordination bond and inherent pro-oxidation properties of natural ingredients could detect and elevate intracellular ROS signals, potentiating to move the tumor away from its homeostasis and make the tumor vulnerable. Compared to previously reported chemosynthetic pro-oxidants, the ROS self-sufficient system, fully composed of natural medicine, from this study provides a new insight in developing cancer oxidation therapy.

Combination of cecropinXJ and LY294002 induces synergistic cytotoxicity, and apoptosis in human gastric cancer cells via inhibition of the PI3K/Akt signaling pathway

The aim of the present study was to investigate the cytotoxic and apoptotic effects of cecropinXJ against human gastric cancer BGC823 cells, either alone, or in combination with a specific phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. Cell viability and the apoptosis rate were measured using flow cytometry with Annexin-V staining. Additionally, the expression levels of several RAC-α serine/threonine kinase (Akt) phosphorylation-associated proteins and apoptosis-regulating proteins were evaluated by western blot analysis. It was observed that the combination of cecropinXJ and LY294002 resulted in significant synergistic cytotoxic and apoptosis effects, as compared with any single agent alone, in a dose-dependent manner. Corresponding to enhanced apoptosis, the expression levels of certain apoptosis-regulating proteins were changed, the most notable being the upregulation of caspase-3, B-cell lymphoma-2 (Bcl-2)-associated death promotor, Bcl-2 homologous antagonist killer, Bcl-2 interacting killer, Bcl-2-like protein 11, Bcl-2-like protein 4 and cytochrome c, and the downregulation of phosphorylated-Bad and Bcl-2 proteins. The present study provided a novel therapeutic regimen for the use of the cecropinXJ in combination with LY294002 for the treatment of gastric cancer.

Melittin suppresses tumor progression by regulating tumor-associated macrophages in a Lewis lung carcinoma mouse model

Tumor-associated macrophages (TAM) are a major component of tumor stroma. It has been reported that TAMs have M2-like phenotype and facilitate tumor progression by promoting angiogenesis and immunosuppression. Melittin, a major polypeptide of bee venom, has been widely studied as an anti-cancer drug due to its cytotoxicity to malignant cells. However, very little is known regarding the effect of melittin on immune cells in the tumor microenvironment. This study focuses on the effect of melittin on TAMs in a Lewis lung carcinoma mouse model. Melittin inhibited the rapid tumor growth compared to the control in vivo. Melittin increased the M1/M2 ratio of TAMs by selectively reducing the number of CD206⁺ M2-like TAMs while not altering the population of CD86⁺ M1-like TAMs. Melittin also preferentially binds to M2 macrophages, and this binding was not associated with phagocytosis. Gene and protein expression of vascular endothelial growth factor (Vegf) and mannose receptor C type 1 (Mrc1/CD206) was reduced in M2-like bone marrow-derived macrophages by melittin treatment, but there was no significant change in the gene level of Vegf and FMS-like tyrosine kinase 1 (Flt1/VEGFR1) in tumor cells in vitro. Additionally, the levels of VEGF and CD31, markers of angiogenesis, were significantly decreased by melittin treatment in tumor tissues. This study revealed a novel role for melittin in tumor treatment and suggested that melittin could be a promising therapeutic agent for targeting M2-like TAMs.

Melittin, a major peptide component of bee venom, and its conjugates in cancer therapy

Melittin (MEL), a major peptide component of bee venom, is an attractive candidate for cancer therapy. This agent has shown a variety of anti-cancer effects in preclinical cell culture and animal model systems. Despite a convincing efficacy data against variety of cancers, its applicability to humans has met with challenges due to several issues including its non-specific cytotoxicity, degradation and hemolytic activity. Several optimization approaches including utilization of nanoparticle based delivery of MEL have been utilized to circumvent the issues. Here, we summarize the current understanding of the anticancer effects of bee venom and MEL on different kinds of cancers. Further, we also present the available information for the possible mechanism of action of bee venom and/or MEL.

Melittin inhibits tumor growth and decreases resistance to gemcitabine by downregulating cholesterol pathway gene CLU in pancreatic ductal adenocarcinoma

Melittin is a Chinese traditional medicine for treating chronic inflammation, immunological diseases and cancers, however, the efficacy of melittin and its mechanism for treating pancreatic ductal adenocarcinoma (PDAC) are still unknown. Here we investigated the anti-cancer activity of melittin and its regulated mechanism(s) in the PDAC models. Melittin was found to suppress tumor growth by promoting cell apoptosis and cell-cycle arrest. Interestingly, the microarray analyses demonstrated that melittin significantly regulated cholesterol biosynthesis pathway during treatment. For instance, the cholesterol pathway gene clusterin (CLU) was highly downregulated by melittin which also enhanced gemcitabine sensitivity in PDAC cells by inhibiting CLU expression. In contrast, overexpression of CLU significantly diminished melittin mediated tumor suppression and gemcitabine sensitization, suggesting that CLU is the target of melittin. Furthermore, in the xenograft mouse model, the combination therapy of melittin and gemcitabine is more efficacious for inhibiting PDAC tumor growth than either single regimen. Taken together, our study has indicated that melittin is capable of suppressing tumor growth and promoting gemcitabine sensitivity in PDAC by downregulating cholesterol pathway.

Anti-cancer effect of bee venom on colon cancer cell growth by activation of death receptors and inhibition of nuclear factor kappa B

Bee venom (BV) has been used as a traditional medicine to treat arthritis, rheumatism, back pain, cancerous tumors, and skin diseases. However, the effects of BV on the colon cancer and their action mechanisms have not been reported yet. We used cell viability assay and soft agar colony formation assay for testing cell viability, electro mobility shift assay for detecting DNA binding activity of nuclear factor kappa B (NF-κB) and Western blotting assay for detection of apoptosis regulatory proteins. We found that BV inhibited growth of colon cancer cells through induction of apoptosis. We also found that the expression of death receptor (DR) 4, DR5, p53, p21, Bax, cleaved caspase-3, cleaved caspase-8, and cleaved caspase-9 was increased by BV treatment in a dose dependent manner (0–5 μg/ml). Consistent with cancer cell growth inhibition, the DNA binding activity of nuclear factor kappa B (NF-κB) was also inhibited by BV treatment. Besides, we found that BV blocked NF-κB activation by directly binding to NF-κB p50 subunit. Moreover, combination treatment with BV and p50 siRNA or NF-κB inhibitor augmented BV-induced cell growth inhibition. However, p50 mutant plasmid (C62S) transfection partially abolished BV-induced cell growth inhibiton. In addition, BV significantly suppressed tumor growth in vivo. Therefore, these results suggested that BV could inhibit colon cancer cell growth, and these anti-proliferative effects may be related to the induction of apoptosis by activation of DR4 and DR5 and inhibition of NF-κB.

Effects of Animal Venoms and Toxins on Hallmarks of Cancer

Animal venoms are a cocktail of proteins and peptides, targeting vital physiological processes. Venoms have evolved to assist in the capture and digestion of prey. Key venom components often include neurotoxins, myotoxins, cardiotoxins, hematoxins and catalytic enzymes. The pharmacological activities of venom components have been investigated as a source of potential therapeutic agents. Interestingly, a number of animal toxins display profound anticancer effects. These include toxins purified from snake, bee and scorpion venoms effecting cancer cell proliferation, migration, invasion, apoptotic activity and neovascularization. Indeed, the mechanism behind the anticancer effect of certain toxins is similar to that of agents currently used in chemotherapy. For example, Lebein is a snake venom disintegrin which generates anti-angiogenic effects by inhibiting vascular endothelial growth factors (VEGF). In this review article, we highlight the biological activities of animal toxins on the multiple steps of tumour formation or hallmarks of cancer. We also discuss recent progress in the discovery of lead compounds for anticancer drug development from venom components.

The antibacterial peptide from Bombyx mori cecropinXJ induced growth arrest and apoptosis in human hepatocellular carcinoma cells

CecropinXJ is a cationic antimicrobial peptide originally isolated from the larvae of Bombyx mori. The anticancer effect of cecropinXJ has been reported in various tumor cells, including leukemia, gastric and esophageal cancer cells. However, the activity of cecropinXJ on hepatocellular carcinoma (HCC) and its underlying mechanism have not been investigated to date. Therefore, the present study investigated the efficacy and associated mechanism of cecropinXJ in Huh-7 cells. Flow cytometric analysis was performed to determine the presence of cell cycle arrested and apoptotic cells. CecropinXJ significantly inhibited the growth of Huh-7 cells in a dose- and time-dependent manner. CecropinXJ treatment for 24 h induced S cell cycle arrest and apoptosis, in addition to loss of the mitochondrial membrane potential, in hepatoma cells. CecropinXJ induced HCC cell apoptosis by activating caspase-3 and poly(ADP-ribose) polymerase. Furthermore, cecropinXJ downregulated the expression of B-cell lymphoma 2 (Bcl-2), while upregulated the expression of Bcl-2-associated death promoter and Bcl-2-associated X protein. In conclusion, the results of the present study suggest that cecropinXJ may be an active anti-HCC agent and provide novel insights into the mechanism of cecropinXJ.

Melittin-MIL-2 fusion protein as a candidate for cancer immunotherapy

BACKGROUND

Cytokine fusion protein that modulates the immune response holds great potential for cancer immunotherapy. IL-2 is an effective treatment against advanced cancers. However, the therapeutic efficacy of IL-2 is limited by severe systemic toxicity. Several mutants recombinant IL-2 can increase antitumor activity and minimize systemic toxicity. Melittin is an attractive anticancer candidate because of its wide-spectrum lytic properties. We previously generated a bifunctional fusion protein melittin-MIL-2, composed of melittin and a mutant IL-2. The melittin-MIL-2 inhibited the growth of human ovarian cancer SKOV3 cells in vitro and in vivo tumor growth. However, whether this antitumor effect could also be used in cancer immunotherapy was unknown. To assess its cancer immunotherapy potential, we further investigated its more effective antitumor immune response and antitumor effect against cancers of different tissue origins in vitro and in vivo.

METHODS

The specific IL-2 activity of the melittin-MIL-2 fusion protein was tested on the cytokine growth dependent cell line CTLL-2. The cytolytic activity was detected by standard 4-h (51)Cr-release assays. PBMC stimulation in response to the melittin-MIL-2 was determined by IFN-γ release assay. We observed the cancer cell proliferation of different tissue origins by MTT assay. The ability of melittin-MIL-2 to inhibit tumor growth in vivo was evaluated by using human liver (SMMC-7721 cancer cells), lung (A549 cancer cells) and ovarian (SKOV3 cancer cells) cancer xenograft models. To assess the immunity within the tumor microenvironment, the level of some cytokines including IFN-γ, TNF-α, IL-12 and IL-4 was analyzed by ELISA. We injected the MDA-MB-231 cells and the melittin-MIL-2 into mice, and the anti-metastatic effect was examined by counting nodules in the lung.

RESULTS

The melittin-MIL-2 was more effective in inducing T cell and NK-cell cytotoxicity. The fusion protein significantly increased IFN-γ production in PBMCs. In vitro, the melittin-MIL-2 mediated immune cells killing or directly killed the cancer cell lines of different tissue origins. In vivo, the fusion protein exhibited stronger inhibition on the growth of transplanted human tumors compared to rIL-2. The melittin-MIL-2 treatment promoted the IFN-γ secretion in tumor tissues and decreased the immunosuppressive cells in vivo. Furthermore, the fusion protein reduced lung metastasis of breast cancer.

CONCLUSIONS

This study provides the evidence that the melittin-MIL-2 can produce stronger immune stimulation and antitumor effects, and the fusion protein is a potent candidate for cancer immunotherapy.

Preparation and Characterization of Gelonin-Melittin Fusion Biotoxin for Synergistically Enhanced Anti-Tumor Activity

PURPOSE

To investigate the applicability of fusion biotoxins combining pore-forming toxins (PFTs) and ribosome-inactivating proteins (RIPs) for the anti-cancer treatment.

METHODS

Membrane active PFTs tend to destabilize cell membranes of tumor cells, but lack a warhead inducing significant cause of cell death. Cell-impermeable RIPs possess a powerful warhead, yet not able to enter the tumor cells. To address these challenges for anti-tumor effects, we introduced a fusion strategy of conjugating melittin (a PFT) and gelonin (a type 1 RIP) via chemical and recombinant methods, followed by in vitro assays and in vivo animal studies.

RESULTS

In vitro characterization results confirmed that the chimeric gelonin-melittin fusion proteins retained equivalent intrinsic activity to that of unmodified gelonin in inhibiting protein translation. However, chemically conjugated gelonin-melittin (cGel-Mel) and recombinant chimeric gelonin-melittin fusion (rGel-Mel) exhibited greater cell uptake, yielding a significantly enhanced cytotoxic activity over treatment of gelonin, melittin or physical mixture of gelonin and melittin. Remarkably, cGel-Mel and rGel-Mel displayed 32- and 10-fold lower IC50 than gelonin in the cell lines. The superior anti-tumor efficacy of multivalent cGel-Mel to monovalent rGel-Mel suggested that valency could be a crucial factor for the extent of melittin-mediated cell uptake. Tumoricidal effects observed from animal studies were in good accordance with our findings from the cellular assays.

CONCLUSIONS

This study successfully demonstrated that fusion of biotoxins could provide a simple yet effective way to synergistically augment their anti-tumor activity.

Melittin induces human gastric cancer cell apoptosis via activation of mitochondrial pathway

AIM: To investigate the apoptotic effects of melittin on SGC-7901 cells via activation of the mitochondrial signaling pathway in vitro.

METHODS: SGC-7901 cells were stimulated by melittin, and its effect on proliferation and apoptosis of was investigated by methyl thiazolyl tetrazolium assay, morphologic structure with transmission electron microscopy, annexin-V/propidium iodide double-staining assay, measuring mitochondrial membrane potential (MMP) levels, and analyzing reactive oxygen species (ROS) concentrations were analyzed by flow cytometry. Cytochrome C (Cyt C), apoptosis-inducing factor (AIF), endonuclease G (Endo G), second mitochondria-derived activator of caspases (Smac)/direct IAP binding protein with low isoelectric point (Diablo), and FAS were analyzed by western blot. The expression of caspase-3 and caspase-8 was measured using activity assay kits.

RESULTS: Melittin was incubated at 1.0, 2.0, 4.0, or 6.0 μg/mL for 1, 2, 4, 6, or 8 h and showed a time- and concentration-dependent inhibition of SGC-7901 cell growth. Melittin induced SGC-7901 cell apoptosis, which was confirmed by typical morphological changes. Treatment with 4 μg/mL melittin induced early apoptosis of SGC-7901 cells, and the early apoptosis rates were 39.97% ± 3.19%, 59.27% ± 3.94%, and 71.50% ± 2.87% vs 32.63% ± 2.75% for 1, 2, and 4 h vs 0 h (n = 3, P < 0.05); the ROS levels were 616.53% ± 79.78%, 974.81% ± 102.40%, and 1330.94% ± 93.09% vs 603.74% ± 71.99% (n = 3, P < 0.05); the MMP values were 2.07 ± 0.05, 1.78 ± 0.29, and 1.16 ± 0.25 vs 2.55 ± 0.42 (n = 3, P < 0.05); caspase-3 activity was significantly higher compared to the control (5492.3 ± 321.1, 6562.0 ± 381.3, and 8695.7 ± 449.1 vs 2330.0 ± 121.9), but the caspase activity of the non-tumor cell line L-O2 was not different from that of the control. With the addition of the caspase-3 inhibitor (Ac-DEVD-CHO), caspase-3 activity was significantly decreased compared to the control group (1067.0 ± 132.5 U/g vs 8695.7 ± 449.1 U/g). The expression of the Cyt C, Endo G, and AIF proteins in SGC-7901 cells was significantly higher than those in the control (P < 0.05), while the expression of the Smac/Diablo protein was significantly lower than the control group after melittin exposure (P < 0.01). Ac-DEVD-CHO did not, however, have any effect on the expression of caspase-8 and FAS in the SGC-7901 cells.

CONCLUSION: Melittin can induce apoptosis of human gastric cancer (GC) cells through the mitochondria pathways, and it may be a potent agent in the treatment of human GC.

Melittin suppresses cathepsin S-induced invasion and angiogenesis via blocking of the VEGF-A/VEGFR-2/MEK1/ERK1/2 pathway in human hepatocellular carcinoma

Melittin, a significant constituent of Apis mellifera (honeybee) venom, is a water-soluble toxic peptide that has traditionally been used as an antitumor agent. However, the underlying mechanisms by which it inhibits tumor cell growth and angiogenesis remain to be elucidated. In the present study, screening for increased cathepsin S (Cat S) expression levels was performed in MHCC97-H cells and various other hepatocellular carcinoma cell lines by reverse transcription-polymerase chain reaction and western blot analysis. A pcDNA3.1-small hairpin RNA (shRNA)-Cat S vector was stably transfected into MHCC97-H cells (shRNA/MHCC97-H) in order to knockdown the expression of Cat S. The effects resulting from the inhibition of Cat S-induced proliferation, invasion and angiogenesis by melittin were examined using cell proliferation, cell viability, flat plate colony formation, migration, wound healing, Transwell migration and ELISA assays. In order to substantiate the evidence for melittin-mediated inhibition of Cat S-induced angiogenesis, Cat S RNA was transfected into primary human umbilical vein endothelial cells (Cat S-HUVECs) to induce overexpression of the Cat S gene. The effects of melittin on HUVECs were examined using Transwell migration and tube formation assays. The findings demonstrated that melittin was able to significantly suppress MHCC97-H cell (Mock/MHCC97-H) proliferation, invasion and angiogenesis, as well as capillary tube formation of Cat S-HUVECs, in a dose-dependent manner. However, proliferation, invasion and angiogenesis in shRNA/MHCC97-H and in native HUVECs (Mock-HUVECs) were unaffected. In addition, melittin specifically decreased the expression of phosphorylated (activated) Cat S, and components of the vascular endothelial growth factor (VEGF)-A/VEGF receptor 2 (VEGFR-2)/mitogen-activated protein kinase kinase 1 (MEK1)/extracellular signal-regulated kinase (ERK)1/2 signaling pathway in Mock/MHCC97-H cells. In conclusion, the inhibition of tumor cell growth and anti-angiogenic activity exerted by melittin may be associated with anti-Cat S actions, via the inhibition of VEGF-A/VEGFR-2/MEK1/ERK1/2 signaling.

Preparation and functional characterization of human vascular endothelial growth factor-melittin fusion protein with analysis of the antitumor activity in vitro and in vivo

Vascular endothelial growth factor and its tyrosine kinase receptors have been identified as key mediators of the regulation of pathologic blood vessel growth and maintenance in the promotion of angiogenesis and tumor growth. Therefore, an alternative approach to destroying tumor endothelium would be to make this tissue particularly sensitive to VEGF-mediated drug delivery. To verify this hypothesis, we generated a protein containing VEGF165 fused to melittin. Melittin is a small linear peptide composed of 26 amino acid residues that can exert toxic or inhibitory effects on many types of tumor cells. This protein is a cytolytic peptide that attacks lipid membranes, leading to significant toxicity. In the present study, the Pichia pastoris expression system was used to express the fusion protein. Under optimal conditions, stable VEGF165-melittin production was achieved using a series of purification steps. The activity of VEGF165-melittin fusion protein was compared with melittin for its ability to suppress the growth of tumor cell line in vitro. The fusion toxin selectively inhibited growth of human hepatocellular carcinoma HepG-2 cell line with high expression of VEGFR-2. We found that sensitivity of VEGFR-2 transfected 293 cells to VEGF165-melittin enhanced as the cellular VEGFR-2 density increased. In an in vivo initial experiment, the fusion protein inhibited tumor growth in xenografts assays. Furthermore, successful expression and characterization of the fusion protein demonstrated its efficacy for use as a novel treatment strategy for cancer.

Three valuable peptides from bee and wasp venoms for therapeutic and biotechnological use: melittin, apamin and mastoparan

While knowledge of the composition and mode of action of bee and wasp venoms dates back 50 years, the therapeutic value of these toxins remains relatively unexploded. The properties of these venoms are now being studied with the aim to design and develop new therapeutic drugs. Far from evaluating the extensive number of monographs, journals and books related to bee and wasp venoms and the therapeutic effect of these toxins in numerous diseases, the following review focuses on the three most characterized peptides, namely melittin, apamin, and mastoparan. Here, we update information related to these compounds from the perspective of applied science and discuss their potential therapeutic and biotechnological applications in biomedicine.

CecropinXJ inhibits the proliferation of human gastric cancer BGC823 cells and induces cell death in vitro and in vivo

We have shown that an antimicrobial peptide (AMP) cecropinXJ isolated from the larvae of Bombyx mori selectively inhibits the proliferation of cancer cells. However, the mechanism remains to be determined. In the present study, we examined the antitumor activity of cecropinXJ against human gastric cancer BGC823 cells and explored the mechanism. The results showed that cecropinXJ inhibited the growth of gastric cancer BGC823 cells in vitro and in vivo. MTT and colony formation assays indicated that cecropinXJ suppressed cell proliferation and reduced colony formation of BGC823 cells in a dose- and time-dependent manner, but without inhibitory effect on normal gastric epithelia GES-1 cells. S-phase arrest in BGC823 cells was observed after treatment with cecropinXJ. Annexin V/PI staining suggested that cecropinXJ induced both early and late phases of apoptosis through activation of mitochondrial-mediated caspase pathway, upregulation of Bax expression and downregulation of Bcl-2 expression. Additionally, cecropinXJ treatment increased reactive oxygen species (ROS) production, disrupted the mitochondrial membrane potential (Δψm) and led to release of cytochrome c. Importantly, in vivo study showed that cecropinXJ significantly prevented the growth of xenograft tumor in the BGC823-bearing mice, possibly mediated by the induction of apoptosis and inhibition of angiogenesis. These results suggest that cecropinXJ may be a promising therapeutic candidate for the treatment of gastric cancer.

Anti-tumor effects of melittin

Melittin is a major active component of bee venom, and it exhibits strong biological activity. Recent reports have demonstrated that melittin has anti-tumor effects on many kinds of tumor cells through direct interaction with cell transduction mediators and influencing cellular signaling pathways, induction of apoptotic or necrotic cell death, and inhibition of growth and proliferationin vivo or in vitro. Nanotechnology and genetic engineering provide technical support to the safe and targeted delivery of melittin to the body. This review summarizes recent findings on the anti-tumor potential of melittin in tumors of different types.

Peptide-based cancer therapy: opportunity and challenge

Cancer is one of the leading causes of death worldwide. Conventional cancer therapies mainly focus on mass cell killing without high specificity and often cause severe side effects and toxicities. Peptides are a novel class of anticancer agents that could specifically target cancer cells with lower toxicity to normal tissues, which will offer new opportunities for cancer prevention and treatment. Anticancer peptides face several therapeutic challenges. In this review, we present the sources and mechanisms of anticancer peptides and further discuss modification strategies to improve the anticancer effects of bioactive peptides.

Let-7c inhibits A549 cell proliferation through oncogenic TRIB2 related factors

MicroRNAs have tumor suppressive or oncogenic roles in carcinogenesis. This study aimed to investigate the mechanism of let-7c in suppressing lung cancer cell proliferation. First, let-7c was revealed to be able to inhibit lung adenocarcinoma cell proliferation significantly. TRIB2 was further demonstrated to be a novel target and negatively regulated by let-7c. As downstream signals of TRIB2, the activities of C/EBP-α and phosphorylated p38MAPK were increased obviously in let-7c-treated cells compared with controls. Our results demonstrate that, through regulating the expression of TRIB2 and its downstream factors, let-7c can effectively inhibit A549 cell proliferation in vitro and in vivo.