Targeted constitutive activation of signal transducer and activator of transcription 3 in human hepatocellular carcinoma cells by cucurbitacin B. Cancer Chemother Pharmacol. 2009;63:635-642. [PMID: 18521604 DOI: 10.1007/s00280-008-0780-0]

Multifaceted Therapeutic Impacts of Cucurbitacin B: Recent Evidences From Preclinical Studies

The most prevalent and bioactive cucurbitacin is Cucurbitacin B (CuB, C32H46O8), which is a tetracyclic triterpene chiefly present in the Cucurbitaceae family. CuB has a wide spectrum of pharmacological properties namely antioxidant, anticancer, hepatoprotective, anti-inflammatory, antiviral, hypoglycaemic, insecticidal, and neuroprotective properties, owing to its ability to regulate several signaling pathways, including the Janus kinase/signal transducer and activator of transcription-3 (JAK/STAT3), AMP-activated protein kinase (AMPK), nuclear factor (NF)-κB, nuclear factor erythroid 2-related factor-2/antioxidant responsive element (Nrf2/ARE), phosphoinositide 3-kinase (PI3K)/Akt, mitogen-activated protein kinase (MAPK), Hippo-Yes-associated protein (YAP), focal adhesion kinase (FAK), cancerous inhibitor of protein phosphatase-2A/protein phosphatase-2A (CIP2A/PP2A), Wnt and Notch pathways. The present review highlights the medicinal attributes of Cucurbitacin B (CuB) with special emphasis on their signaling pathways to provide key evidence of its therapeutic utility in the near future.

TCM targets ferroptosis: potential treatments for cancer

Ferroptosis is caused by the accumulation of cellular reactive oxygen species that exceed the antioxidant load that glutathione (GSH) and phospholipid hydroperoxidases with GSH-based substrates can carry When the antioxidant capacity of cells is reduced, lipid reactive oxygen species accumulate, which can cause oxidative death. Ferroptosis, an iron-dependent regulatory necrosis pathway, has emerged as a new modality of cell death that is strongly associated with cancer. Surgery, chemotherapy and radiotherapy are the main methods of cancer treatment. However, resistance to these mainstream anticancer drugs and strong toxic side effects have forced the development of alternative treatments with high efficiency and low toxicity. In recent years, an increasing number of studies have shown that traditional Chinese medicines (TCMs), especially herbs or herbal extracts, can inhibit tumor cell growth and metastasis by inducing ferroptosis, suggesting that they could be promising agents for cancer treatment. This article reviews the current research progress on the antitumor effects of TCMs through the induction of ferroptosis. The aim of these studies was to elucidate the potential mechanisms of targeting ferroptosis in cancer, and the findings could lead to new directions and reference values for developing better cancer treatment strategies.

Terpenoid-Mediated Targeting of STAT3 Signaling in Cancer: An Overview of Preclinical Studies

Cancer has become one of the most multifaceted and widespread illnesses affecting human health, causing substantial mortality at an alarming rate. After cardiovascular problems, the condition has a high occurrence rate and ranks second in terms of mortality. The development of new drugs has been facilitated by increased research and a deeper understanding of the mechanisms behind the emergence and advancement of the disease. Numerous preclinical and clinical studies have repeatedly demonstrated the protective effects of natural terpenoids against a range of malignancies. Numerous potential bioactive terpenoids have been investigated in natural sources for their chemopreventive and chemoprotective properties. In practically all body cells, the signaling molecule referred to as signal transducer and activator of transcription 3 (STAT3) is widely expressed. Numerous studies have demonstrated that STAT3 regulates its downstream target genes, including Bcl-2, Bcl-xL, cyclin D1, c-Myc, and survivin, to promote the growth of cells, differentiation, cell cycle progression, angiogenesis, and immune suppression in addition to chemotherapy resistance. Researchers viewed STAT3 as a primary target for cancer therapy because of its crucial involvement in cancer formation. This therapy primarily focuses on directly and indirectly preventing the expression of STAT3 in tumor cells. By explicitly targeting STAT3 in both in vitro and in vivo settings, it has been possible to explain the protective effect of terpenoids against malignant cells. In this study, we provide a complete overview of STAT3 signal transduction processes, the involvement of STAT3 in carcinogenesis, and mechanisms related to STAT3 persistent activation. The article also thoroughly summarizes the inhibition of STAT3 signaling by certain terpenoid phytochemicals, which have demonstrated strong efficacy in several preclinical cancer models.

Natural bioactive compounds and STAT3 against hepatocellular carcinoma: An update

Hepatocellular carcinoma (HCC) is a challenging and very fatal liver cancer. The signal transducer and activator of transcription 3 (STAT3) pathway is a crucial regulator of tumor development and are ubiquitously active in HCC. Therefore, targeting STAT3 has emerged as a promising approach for preventing and treating HCC. Various natural bioactive compounds (NBCs) have been proven to target STAT3 and have the potential to prevent and treat HCC as STAT3 inhibitors. Numerous kinds of STAT3 inhibitors have been identified, including small molecule inhibitors, peptide inhibitors, and oligonucleotide inhibitors. Due to the undesirable side effects of the conventional therapeutic drugs against HCC, the focus is shifted to NBCs derived from plants and other natural sources. NBCs can be broadly classified into the categories of terpenes, alkaloids, carotenoids, and phenols. Most of the compounds belong to the family of terpenes, which prevent tumorigenesis by inhibiting STAT3 nuclear translocation. Further, through STAT3 inhibition, terpenes downregulate matrix metalloprotease 2 (MMP2), matrix metalloprotease 9 (MMP9) and vascular endothelial growth factor (VEGF), modulating metastasis. Terpenes also suppress the anti-apoptotic proteins and cell cycle markers. This review provides comprehensive information related to STAT3 abrogation by NBCs in HCC with in vitro and in vivo evidences.

Potential of cucurbitacin as an anticancer drug

In Chinese medicine, the Cucurbitaceae family contains many compounds known as cucurbitacins, which have been categorized into 12 classes ranging from A to T and more than 200 derivatives. Cucurbitacins are a class of highly oxidized tetracyclic triterpenoids with potent anticancer properties. The eight components of cucurbitacins with the strongest anticancer activity are cucurbitacins B, D, E, I, IIa, L-glucoside, Q, and R. Cucurbitacins have also been reported to suppress JAK-STAT 3, mTOR, VEGFR, Wnt/β-catenin, and MAPK signaling pathways, all of which are crucial for the survival and demise of cancer cells. In this paper, we review the progress in research on cucurbitacin-induced apoptosis, autophagy, cytoskeleton disruption, cell cycle arrest, inhibition of cell proliferation, inhibition of invasion and migration, inhibition of angiogenesis, epigenetic alterations, and synergistic anticancer effects in tumor cells. Recent studies have identified cucurbitacins as promising molecules for therapeutic innovation with broad versatility in immune response. Thus, cucurbitacin is a promising class of anticancer agents that can be used alone or in combination with chemotherapy and radiotherapy for the treatment of many types of cancer.Therefore, based on the research reports in the past five years at home and abroad, we further summarize and review the structural characteristics, chemical and biological activities, and studies of cucurbitacins based on the previous studies to provide a reference for further development and utilization of cucurbitacins.

Apoptotic and antimetastatic effect of cucurbitacins in cancer: recent trends and advancement

The Cucurbitaceae family produces a class of secondary metabolites known as cucurbitacins. The eight cucurbitacin subunits are cucurbitacin B, D, E, I, IIa, L glucoside, Q, and R with the most significant anticancer activity. They are reported to inhibit cell proliferation, invasion, and migration; induce apoptosis; and encourage cell cycle arrest, as some of their modes of action. The JAK-STAT3, Wnt, PI3K/Akt, and MAPK signaling pathways, which are essential for the survival and apoptosis of cancer cells, have also been shown to be suppressed by cucurbitacins. The goal of the current study is to summarize potential molecular targets that cucurbitacins could inhibit in order to suppress various malignant processes. The review is noteworthy since it presents all putative molecular targets for cucurbitacins in cancer on a single podium.

Association between the antioxidant properties of SESN proteins and anti-cancer therapies

Since the beginning of SESN protein development, they have attracted highly progressive attention due to their regulatory role in multiple signalling pathways. Through their antioxidant activity and autophagy regulation implication, they can function as powerful antioxidants to reduce oxidative stress in cells. SESN proteins received special attention in the field of regulation of reactive oxygen species level in the cell and its interplay with signalling pathways determining energy and nutrient homeostasis. Since perturbations in these pathways are implicated in cancer onset and development, SESNs might constitute potential novel therapeutic targets of broad interest. In this review, we discuss the impact of SESN proteins on anti-cancer therapy based on naturally occurring compounds and conventionally used drugs that influence oxidative stress and autophagy-induced cellular signalling pathways. The significant changes in reactive oxygen species level and nutrient status in cancer cells generate subsequent biological effect through the regulation of SESN-dependent pathways. Thus, SESN may serve as the key molecule for regulating anti-cancer drugs' induced cellular response.

Cucurbitacin B: A review of its pharmacology, toxicity, and pharmacokinetics

Cucurbitacin B (CuB, C₃₂H₄₆O₈), the most abundant and active member of cucurbitacins, which are highly oxidized tetracyclic triterpenoids. Cucurbitacins are widely distributed in a variety of plants and mainly isolated from plants in the Cucurbitaceae family. CuB is mostly obtained from the pedicel of Cucumis melo L. Modern pharmacological studies have confirmed that CuB has a broad range of pharmacological activities, with significant therapeutic effects on a variety of diseases including inflammatory diseases, neurodegenerative diseases, diabetes mellitus, and cancers. In this study the PubMed, Web of Science, Science Direct, and China National Knowledge Infrastructure (CNKI) databases were searched from 1986 to 2022. After inclusion and exclusion criteria were applied, 98 out of 2484 articles were selected for a systematic review to comprehensively summarize the pharmacological activity, toxicity, and pharmacokinetic properties of CuB. The results showed that CuB exhibits potent anti-inflammatory, antioxidant, antiviral, hypoglycemic, hepatoprotective, neuroprotective, and anti-cancer activities mainly via regulating various signaling pathways, such as the Janus kinase/signal transducer and activator of transcription-3 (JAK/STAT3), nuclear factor erythroid 2-related factor-2/antioxidant responsive element (Nrf2/ARE), nuclear factor (NF)-κB, AMP-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)/Akt, cancerous inhibitor of protein phosphatase-2A/protein phosphatase-2A (CIP2A/PP2A), Wnt, focal adhesion kinase (FAK), Notch, and Hippo-Yes-associated protein (YAP) pathways. Studies of its toxicity and pharmacokinetic properties showed that CuB has non-specific toxicity and low bioavailability. In addition, derivatives and clinical applications of CuB are discussed in this paper.

Prophylactic effects of cucurbitacin B in the EAE Model of multiple sclerosis by adjustment of STAT3/IL-23/IL-17 axis and improvement of neuropsychological symptoms

Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system. Although remarkable progress has been made in treating MS, current therapies are less effective in protecting against the progression of the disease. Since cucurbitacins have shown an extreme range of pharmacological properties, in this study, we aimed to investigate the prophylactic effect of cucurbitacin B (CuB) in the experimental MS model. Experimental autoimmune encephalomyelitis (EAE) induced by subcutaneous immunization of MOG35-55 in C57BL/6 mice. CuB interventions (0.5 and 1 mg/kg, i.p.) were performed every other day from the first day of EAE induction. Assessment of clinical scores and motor function, inflammatory responses, and microglial activation were assessed by qRT-PCR, western blotting, and immunohistochemical (IHC) analyses. CuB (1 mg/kg) significantly decreased the population of CD45⁺ (P < 0.01), CD11b⁺ (P < 0.01) and CD45⁺/CD11b⁺ (P < 0.05) cells in cortical lesions of EAE mice. In addition, activation of STAT3 (P < 0.001), expression of IL-17 A and IL-23 A (both mRNA and protein), and transcription of Iba-1 significantly decreased. On the contrary, CuB (1 mg/kg) significantly increased the transcription of MBP and Olig-2. Furthermore, a significant decrease in the severity of EAE (P < 0.05), and an improvement in motor function (P < 0.05) and coordination (P < 0.05) were observed after treatment with a high dose of CuB. Our results suggest that CuB may have a wide-ranging effect on autoimmune responses in MS via a reduction in STAT3 activation, microgliosis, and adaptation of the IL-23/IL-17 axis. Further studies are needed to investigate the exact effect of CuB in glial cells and its efficiency and bioavailability in other neuroinflammatory diseases.

Benzobis(imidazole) derivatives as STAT3 signal inhibitors with antitumor activity

Polycyclic aromatic systems have been considered good biological probes, but some may also be good scaffolds for drug development. In this study, a series of benzobis(imidazole) derivatives were identified as STAT3 signal inhibitors, among which compound 24 showed significant inhibition of IL-6 induced JAK/STAT3 signalling pathway activation. Moreover, 24 inhibited cancer cell growth and migration, and induced cell apoptosis as well as cycle arrest in human hepatocellular carcinoma cells (HepG2) and oesophageal carcinoma cells (EC109). Compound 24 also displayed obvious antitumor activity in a mouse HepG2 cell xenograft tumor model without affecting the body weight. These results confirmed that 24 was a potential STAT3 signal inhibitor with certain antitumor activity.

The Inhibition of Gastric Cancer Cells’ Progression by 23,24-Dihydrocucurbitacin E through Disruption of the Ras/Raf/ERK/MMP9 Signaling Pathway

Gastric cancer is considered to be one of the most common causes of cancer death worldwide due to its high recurrence and metastasis rates. The molecule 23,24-Dihydrocucurbitacin E (DHCE) is a cucurbitacin-derived tetracyclic triterpenoid compound that has anti-tumor activity, but the exact mechanism remains to be elucidated. This research aimed to explore the effects of DHCE on human gastric cancer cells and the possible mechanisms. The results showed that DHCE suppressed proliferation, migration, and invasion of gastric cancer cells, as well as induced apoptosis and G2/M phase arrest. Mechanistically, the potential targets and pathways of DHCE were predicted using database screening and verified using a molecular docking study, fluorescence staining, and Western blot. The results indicated that DHCE obviously inhibited the kinase activity of ERK2 via targeting its ATP-binding domain, destroyed F-actin microfilament, and reduced the expression levels of Ras, p-c-Raf, ERK, p-ERK, and MMP9 proteins. Collectively, our study demonstrated that DHCE suppressed gastric cancer cells’ proliferation, migration, and invasion through targeting ERK2 and disrupting the Ras/Raf/ERK/MMP9 signaling pathway. These properties make DHCE a promising candidate drug for the further design and development of novel and effective Ras/Raf/ERK/MMP9 pathway inhibitors for treating gastric cancer.

Chemical diversity of dietary phytochemicals and their mode of chemoprevention

Despite the advancement in prognosis, diagnosis and treatment, cancer has emerged as the second leading cause of disease-associated death across the globe. With the remarkable application of synthetic drugs in cancer therapy and the onset of therapy-associated adverse effects, dietary phytochemicals have been materialized as potent anti-cancer drugs owing to their antioxidant, apoptosis and autophagy modulating activities. With dynamic regulation of apoptosis and autophagy in association with cell cycle regulation, inhibition in cellular proliferation, invasion and migration, dietary phytochemicals have emerged as potent anti-cancer pharmacophores. Dietary phytochemicals or their synthetic analogous as individual drug candidates or in combination with FDA approved chemotherapeutic drugs have exhibited potent anti-cancer efficacy. With the advancement in cancer therapeutics, dietary phytochemicals hold high prevalence for their use as precision and personalized medicine to replace conventional chemotherapeutic drugs. Hence, keeping these perspectives in mind, this review focuses on the diversity of dietary phytochemicals and their molecular mechanism of action in several cancer subtypes and tumor entities. Understanding the possible molecular key players involved, the use of dietary phytochemicals will thrive a new horizon in cancer therapy.

Cucurbitacin B exhibits antitumor effects on CD133+ HepG2 liver cancer stem cells by inhibiting JAK2/STAT3 signaling pathway

Cancer stem cells (CSCs), a crucial cancer cell subpopulation, possess stemness phenotypic characteristics. Cucurbitacin B (CuB), a tetracyclic triterpenoid isolated from Cucurbitaceae, exerts widely pharmacological activities in many diseases. The aim of this study was to enrich, identify liver CSCs and investigate antitumor effects of CuB as well as explore the underlying molecular mechanisms in these liver CSCs. HepG2 cell lines were used for the enrichment of liver CSCs by serum-free medium culture and magnetic-activated cell sorting. The CSC characteristics were analyzed by immunofluorescent staining, sphere-forming, western blot and xenograft tumorigenicity assay. CuB' antitumor effects and underlying molecular mechanism were measured by cell counting kit-8, colony formation, sphere-forming, cell cycle, xenograft and western blot assay. Our results showed that we could enrich 97.29% CD133+ HepG2 cells, which possessed CSC characteristics including re-renewal capacity, proliferative ability, sorafenib resistance, overexpressed stemness-related molecules and enhanced tumorigenic potential. Furthermore, we also found that CuB inhibited cell viability, sphere formation, colony formation and arrested cell cycle at G2/M phase as well as sensitized CD133+ HepG2 cells to sorafenib in vitro and in vivo. Western blot assay indicated that CuB inhibited expression levels of cyclin B1, CDK1, CD133, p-JAK2 and p-STAT3. In conclusion, our findings indicated that CuB could exhibit antitumor effects on CD133+ HepG2 CSCs by inhibiting the Janus kinase 2/signal transducers and activators of transcription-3 signaling pathway, expanding basic and preclinical investigations on liver CSCs.

Induction of ferroptosis in human nasopharyngeal cancer cells by cucurbitacin B: molecular mechanism and therapeutic potential

Cucurbitacin B (CuB) is a widely available triterpenoid molecule that exhibits various biological activities. Previous studies on the anti-tumour mechanism of CuB have mostly focused on cell apoptosis, and research on the ferroptosis-inducing effect has rarely been reported. Herein, we first discovered the excellent cytotoxicity of CuB towards human nasopharyngeal carcinoma cells and elucidated its potential ferroptosis-inducing mechanisms. Morphology alterations of mitochondrial ultrastructure, as observed via transmission electron microscopy, showed that CuB-treated cells undergo ferroptosis. CuB caused intracellular accumulation of iron ions and depletion of glutathione. Detailed molecular mechanism investigation confirmed that CuB both induced widespread lipid peroxidation and downregulated the expression of GPX4, ultimately initiating a multipronged mechanism of ferroptosis. Furthermore, CuB exhibited anti-tumour effects in vitro by inhibiting cellular microtubule polymerization, arresting cell cycle and suppressing migration and invasion. Finally, CuB significantly inhibited tumour progression without causing obvious side effects in vivo. Altogether, our study highlighted the therapeutic potential of CuB as a ferroptosis-inducing agent for nasopharyngeal cancer, and it provided valuable insights for developing effective anti-tumour agents with novel molecular mechanisms derived from natural products.

Sorafenib and CuB exert synergistic antitumor effects against hepatocellular carcinoma cells via inhibition of STAT3 phosphorylation

Sorafenib, the first‐line agent for treatment of advanced hepatocellular carcinoma (HCC), improves median overall survival by approximately 3 months. In the present study, we investigated whether sorafenib combined with cucurbitacin B (CuB), a natural tetracyclic triterpenoid isolated from Cucurbitaceae, exerts enhanced antitumor effects against HCC. Cell viability and colony formation ability were detected by cell‐counting kit‐8 and colony formation assays. Cell cycle and apoptosis were analyzed by flow cytometry. Protein expression was detected by western blotting. HepG2 xenografts in nude mice were used to evaluate in vivo antitumor effects. We report that sorafenib and CuB exhibited synergistic effects on cellular proliferation inhibition and cell apoptosis induction, but not on cell cycle arrest. Furthermore, combination treatment enhanced levels of cleaved caspase 3 and cleaved caspase 9, but suppressed phosphorylation of STAT3. Epidermal growth factor, a potent stimulator of signal transducer and activator of transcription‐3 (STAT3), promoted cell viability and colony formation ability, whereas combination treatment exerted inhibitory effects on epidermal growth factor‐induced STAT3 phosphorylation. Finally, HepG2 xenograft mice cotreated with sorafenib and CuB exhibited reduced tumor progression without notable weight loss. In conclusion, sorafenib and CuB exert synergistic antitumor effects through a pathway that may involve STAT3 phosphorylation, and this may represent a promising therapeutic approach for treatment of HCC.

Cucurbitacins: A Focus on Cucurbitacin E As A Natural Product and Their Biological Activities

For the last years, different types of cucurbitacins have been extracted from various species of Cucurbitaceae family. For this review, all related papers were accumulated by searching electronic databases in the English language, including PubMed, Scopus, and Google Scholar. The keywords of cucurbitacin, cucumber anticancer therapy, cytotoxic effects, chemotherapy, and inhibitor effect were searched until February 2020. According to the result of this review, cucurbitacin E as a tetracyclic triterpenes compound, has been exhibited cell cycle arrest, anti-inflammatory and anticancer activities. It showed tumor proliferation prevention, induction of apoptosis or synergistically acts with other established antitumor compounds and cytokines throughout many molecular mechanisms. In a function-structure association manner, cucurbitacin E can inhibit Janus kinas2 (JAK2) phosphorylation, the signal transducer activator of transcription 3 (STAT3) and subsequently block these pathways, which seems to be the main mechanism of its activity. Future studies could target its detection in uninvestigated sources, subsequently its derivatives to improve their anticancer activity.

Development and Evaluation of Cucurbitacin B Microemulsion: the Effect of Oil Phase and Aqueous Phase on Drug Percutaneous Absorption Based on ATR-FTIR Spectroscopy and Molecular Modeling

The present study aimed to develop a cucurbitacin B microemulsion (CuB-ME) and investigate the mechanism of the enhanced drug skin absorption at the molecular level. Firstly, the pseudo-ternary phase diagrams were developed to evaluate the effect of composition on microemulsion properties systematically. The formulation composition types and ratios of oil phase, surfactant, co-surfactant, and aqueous phase were optimized by an in vitro skin permeation experiment, and the optimized formula was confirmed with the pharmacodynamics study. Furthermore, the molecular mechanism of enhanced skin permeation was investigated using ATR-FTIR and molecular modeling. As a result, the optimized CuB-ME formulation was composed of Azone:Tween 80:ethanol:water = 2.5:16.9:5.6:75.0 (w/w/w/w). The oil phase improved skin permeation by disordering the stratum corneum intercellular liquid, while the aqueous phase impacted the particle size of the microemulsion and permeability coefficient of the drug. Besides, the hydration state of skin lipid also enhanced drug permeation by the interaction of water and the polar head of ceramide. The in vitro skin permeation amount was 45.47 ± 10.39 μg/cm², and no significant skin irritation was observed. The pharmacodynamics study demonstrated that CuB-ME had a significant therapeutic effect on the animal tumor model. In conclusion, the CuB-ME was developed successfully and the effect of the oil phase and aqueous phase on drug skin permeation was clarified at the molecular level.

Cucurbitacins as Anticancer Agents: A Patent Review

BACKGROUND

Cucurbitacins belong to a group of tetracyclic triterpenoids that display a wide range of biological effects. In the past, numerous cucurbitacins have been isolated from natural sources and many active compounds have been synthesized using the privileged scaffold in order to enhance its cytotoxic effects.

OBJECTIVE

This review covers patents on the therapeutic effects of natural cucurbitacins and their synthetic analogs published during the past decade. By far, the majority of patents published are related to cancer and Structure-Activity Relationships (SAR) of these compounds are included to lend gravitas to this important class of natural products.

METHODS

The date about the published patents was downloaded via online open access patent databases.

RESULTS

Cucurbitacins display significant cytotoxic properties, in particular cucurbitacins B and D which possess very potent effects towards a number of cancer cells. Numerous cucurbitacins isolated from natural sources have been derivatized through chemical modification at the C(2)-OH and C(25)- OH groups. Most importantly, an acyl ester of the C(25)-OH and, iso-propyl, n-propyl and ethyl ether groups of the C(2)-OH demonstrated the most increased cytotoxic activity.

CONCLUSION

The significant cytotoxic effects of natural and semi-synthetic cucurbitacins make them attractive as new drug candidates. Moreover, cucurbitacins have the capability to form conjugates with other anticancer drugs which will synergistically enhance their anticancer effects. The authors believe that in order to get lead compounds, there should be a greater focus on the synthesis of homodimers, heterodimers, and halo derivatives of cucurbitacins. In the opinion of the authors the analysis of the published patents on the cucurbitacins indicates that these compounds can be developed into a regimen to treat a wide spectrum of cancers.

Sestrins as a Therapeutic Bridge between ROS and Autophagy in Cancer

The regulation of Reactive Oxygen Species (ROS) levels and the contribution therein from networks regulating cell metabolism, such as autophagy and the mTOR-dependent nutrient-sensing pathway, constitute major targets for selective therapeutic intervention against several types of tumors, due to their extensive rewiring in cancer cells as compared to healthy cells. Here, we discuss the sestrin family of proteins—homeostatic transducers of oxidative stress, and drivers of antioxidant and metabolic adaptation—as emerging targets for pharmacological intervention. These adaptive regulators lie at the intersection of those two priority nodes of interest in antitumor intervention—ROS control and the regulation of cell metabolism and autophagy—therefore, they hold the potential not only for the development of completely novel compounds, but also for leveraging on synergistic strategies with current options for tumor therapy and classification/stadiation to achieve personalized medicine.

Pharmacokinetics of cucurbitacin B from Trichosanthes cucumerina L. in rats

BACKGROUND

Cucurbitacin B is the major bioactive constituent in Trichosanthes cucumerina L. fruits, which the pharmacological properties have been studied for decades particularly an anti-tumor activity. The pharmacokinetic profile of this compound is still limited and investigation is needed for further phytopharmaceutical product development. This study aimed to investigate the pharmacokinetic profile of cucurbitacin B after administering the compound at different doses and routes to rats.

METHODS

Male Wistar rats (n = 6) were treated by cucurbitacin B extracted from Trichosanthes cucumerina L. The cucurbitacin B was administered at 0.1 mg/kg intravenously or by oral gavage at 2-4 mg/kg. Blood samples and internal organs were collected serially within 24 h after administration. Urine and feces were collected from time 0 to 48 h. The level of cucurbitacin B in biological samples was determined by liquid chromatography-tandem mass spectrometry.

RESULTS

The absolute oral bioavailability of cucurbitacin B was approximately 10%. The maximum concentration in plasma after normalization by dose ranged from 4.85-7.81 μg/L and the time to reach maximum value was approximately within 30 min after oral dosing. The level of cucurbitacin B in plasma increased proportionally to the given dose. After intravenous administration, cucurbitacin B had a large volume of distribution of about 51.65 L/kg and exhibited a high tissue to plasma concentration ratio, approximately 60 to 280-fold in several organs. Negligible amount of unchanged cucurbitacin B could be detected in urine and feces and accounted less than 1% of administered dose.

CONCLUSION

Cucurbitacin B had low oral bioavailability, but could be distributed extensively into internal organs with a high volume of distribution and tissue to plasma ratio. Only negligible amounts of unchanged cucurbitacin B were excreted via urine and feces suggesting that the compound might be biotransformed before undergoing an excretion. Further studies of the metabolic pathway and tissue uptake mechanism are required to strategize the future development of cucurbitacin B into clinical studies.

Cucurbits Plants: A Key Emphasis to Its Pharmacological Potential

Cucurbita genus has received a renowned interest in the last years. This plant species, native to the Americas, has served worldwide folk medicine for treating gastrointestinal diseases and intestinal parasites, among other clinical conditions. These pharmacological effects have been increasingly correlated with their nutritional and phytochemical composition. Among those chemical constituents, carotenoids, tocopherols, phenols, terpenoids, saponins, sterols, fatty acids, and functional carbohydrates and polysaccharides are those occurring in higher abundance. However, more recently, a huge interest in a class of triterpenoids, cucurbitacins, has been stated, given its renowned biological attributes. In this sense, the present review aims to provide a detailed overview to the folk medicinal uses of Cucurbita plants, and even an in-depth insight on the latest advances with regards to its antimicrobial, antioxidant and anticancer effects. A special emphasis was also given to its clinical effectiveness in humans, specifically in blood glucose levels control in diabetic patients and pharmacotherapeutic effects in low urinary tract diseases.

Synthesis of Cucurbitacin B Derivatives as Potential Anti-Hepatocellular Carcinoma Agents

Cucurbitacin B shows potent activity against tumor cells, but its high toxicity limits its application in the clinic. A series of cucurbitacin B derivatives was synthesized and evaluated for their anti-hepatocellular carcinoma (HCC) activities against the HepG-2 cell line. These compounds were also tested for their toxicity against the L-O2 normal cell line. The compound with the most potential, 10b, exhibited potent activity against the HepG-2 cell line with an IC50 value of 0.63 μM. Moreover, compound 10b showed the highest TI value (4.71), which is a 14.7-fold improvement compared to its parent compound cucurbitacin B. A preliminary molecular mechanism study of 10b indicated that 10b could inhibit P-STAT3 to induce the activation of mitochondrial apoptotic pathways. An in vivo acute toxicity study indicated that the compound 10b has preferable safety and tolerability compared with cucurbitacin B. These findings indicate that compound 10b might be considered as a lead compound for exploring effective anti-HCC drugs.

Isolation of anticancer constituents from Cucumis prophetarum var. prophetarum through bioassay-guided fractionation

BACKGROUND

Cucumis prophetarum var. prophetarum is used in Saudi folk medicine for treating liver disorders and grows widely between Abha and Khamis Mushait City, Saudi Arabia.

METHODS

Bioassay-guided fractionation and purification were used to isolate the main active constituents of Cucumis prophetarum var. prophetarum fruits. These compounds were structurally elucidated using NMR spectroscopy, mass spectral analyses and x-ray crystallography. All fractions, sub-fractions and pure compounds were screened for their anticancer activity against six cancer cell lines.

RESULTS

The greatest cytotoxic activity was found to be in the ethyl acetate fraction, resulting in the isolation of five cucurbitacin compounds [E, B, D, F-25 acetate and Hexanorcucurbitacin D]. Among the cucurbitacins that were isolated and tested cucurbitacin B and E showed potent cytotoxicity activities against all six human cancer cell lines.

CONCLUSION

Human breast cancer cell lines were found to be the most sensitive to cucurbitacins. Preliminary structure activity relationship (SAR) for cytotoxic activity of Cucurbitacins against human breast cancer cell line MDA-MB-231 has been reported.

Novel pregnenolone derivatives modulate apoptosis via Bcl-2 family genes in hepatocellular carcinoma in vitro

A series of pregnenolone derivatives were synthesized and assessed for anti-cancer activity against hepatocellular carcinoma cell line (HepG2). The synthesized hetero-steroids (compounds 3, 4, 5, 6, 7, 8a and 8b) were evaluated for their cytotoxic activities using MTT (3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide) assay. Apoptotic activity was assessed using dual acridine orange/ethidium bromide staining method and DNA fragmentation assay. Pro-apoptotic genes (Bax and Bak) and anti-apoptotic genes (Bcl-2 and Bcl-xL) were analyzed using quantitative real time PCR. The results revealed that compounds 4 and 6 displayed cytotoxic activity (IC_50s, 36.97 ± 2.18 and 18.46 ± 0.64 μM, respectively), while compounds 5 and 7 exhibited weak cytotoxic activity (IC_50s, 93.87 ± 8.30 μM and 93.48 ± 4.14 μM, respectively). All synthesized heterocyclic pregnenolone derivatives induced apoptosis through DNA fragmentation. Compounds 4 and 6 increased early and late apoptotic cell percentages while compounds 3, 5, 7 and 8b increased either early or late apoptotic cell percentage. Moreover, compounds 3, 6 and 8b up-regulated the expression level of Bak gene. On the other hand, compounds 4, 5, 7 and 8a down-regulated the Bcl-2 expression level, besides, compounds 5, 7 and 8a down-regulated the Bcl-xL expression level. Compounds 5, 7, 8a and 8b increased the Bak/Bcl-xL ratio, besides, compound 8a raised the Bax/Bcl-xL ratio whereas compound 5 elevated Bax/Bcl-2 and Bak/Bcl-2 ratios. The present work introduced novel pro-apoptotic pregnenolone derivatives that acted against HepG2 cells through DNA fragmentation, apoptotic morphological changes and were able to increase the pro-apoptotic/anti-apoptotic ratios of Bcl-2 family genes. This study particularly revealed that the cytotoxic compound 4 is the most promising pro-apoptotic compound among other synthesized derivatives where it induced apoptosis (late and early) through the down-regulation of Bcl-2 gene expression level.

Sestrin-3 modulation is essential for therapeutic efficacy of cucurbitacin B in lung cancer cells

Many purified compounds from dietary sources have been investigated for their anticancer activities. The main issue with most agents is their effectiveness at high doses which generally could not be delivered to humans through dietary consumption. Here, we observed that cucurbitacin B, a tetracyclic triterpenoid present in pumpkins, gourds and squashes, exhibits antiproliferative effects on human non-small cell lung cancer (NSCLC) cells at nanomolar concentrations. Treatment with cucurbitacin B (0.2-0.6 μM; 24 h) was found to result in decrease in the viability of EGFR-wild type (A549 and H1792) and EGFR-mutant lung cancer cells (H1650 and H1975) and reduction in cell-colonies but had only minimal effect on normal human bronchial epithelial cells. Treatment with cucurbitacin B also caused inhibition of PI3K/mTOR and signal transducer and activator of transcription (STAT)-3 signaling along with simultaneous activation of AMPKα levels in both EGFR-wild type and EGFR-mutant lung cancer cells. Cucurbitacin B caused specific increase in the protein and mRNA expression of sestrin-3 in EGFR-mutant lung cancer cells, but not in EGFR-wild type cells. Treatment with cucurbitacin B to sestrin-3 siRNA treated EGFR-mutant cells further amplified the decrease in cell-viability and caused more sustained G2-phase cell cycle arrest, suggesting that these effects are mediated partly through sestrin-3. We also found that sestrin-3 has a role in the induction of apoptosis by cucurbitacin B in both EGFR-wild type and EGFR-mutant lung cancer cells. These findings suggest novel mechanism by the modulation of sestrin-3 for the action of cucurbitacin B and suggest that it could be developed as an agent for therapy of NSCLC.

Cucurbitacin B inhibits cell proliferation and induces apoptosis in human osteosarcoma cells via modulation of the JAK2/STAT3 and MAPK pathways

Osteosarcoma (OS) is the most commonly diagnosed tumor of the bones in children and young adults. Even with conventional therapies the 5-year survival rate is ~65% in patients with OS. Considering the side effects and aggressiveness of malignant bone tumors, research is focussing on multi-targeted strategies in treatment. Cucurbitacin B, a triterpenoid compound has been demonstrated to induce apoptosis in various cancer cell types. The Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signalling cascades and mitogen activated protein kinases (MAPK) signalling cascades are critical regulators of tumorigenesis. The present study assessed the influence of cucurbitacin B on the viability and expression of MAPKs and proteins of the JAK2/STAT3 cascades in human OS cells (U-2 OS). Cucurbitacin B (20-100 µM) significantly reduced cell viability (P<0.05) and induced apoptosis, as assessed by MTT and Annexin V/propidium iodide staining, along with inhibiting cell migration. Gelatin zymography revealed supressed activities of matrix metalloproteinase (MMP-)2 and 9. Furthermore, cucurbitacin B effectively upregulated the apoptotic pathway and caused the effective inhibition of MAPK signalling and JAK2/STAT3 cascades. Multifold suppression of vascular endothelial growth factor by cucurbitacin B was also observed, indicating inhibition of angiogenesis. Thus, by downregulating major pathways-MAPK and JAK2/STAT3 and MMPs, cucurbitacin B has potent anti-proliferative and anti-metastatic effects that require further investigation with regards to cancer treatment.

Inhibition of paclitaxel resistance and apoptosis induction by cucurbitacin B in ovarian carcinoma cells

Ovarian cancer is the leading cause of mortality among all gynecological malignancies. Drug resistance is a cause of ovarian cancer recurrence and low rate of overall survival. There is a requirement for more effective treatment approaches. Cucurbitacin B (CuB) is an antineoplastic agent derived from traditional Chinese medicinal herbs. Its activity against paclitaxel-resistant human ovarian cancer cells has, however, not yet been established. The purpose of the present study was to investigate the effect and mechanism of CuB on human paclitaxel-resistant ovarian cancer A2780/Taxol cells. Cell viability was evaluated by a cell counting assay, while cell cycle arrest and apoptosis were assessed by microscopy and flow cytometry, and proteins associated with apoptotic pathways and drug resistance were evaluated by western blotting. The present results demonstrated that CuB exerts dose- and time-dependent cytotoxicity against the ovarian cancer A2780 cell line, with half-maximal inhibitory concentration (IC₅₀) values 0.48, 0.25 and 0.21 µM following 24, 48 and 72 h of incubation, respectively. Compared with its sensitive counterpart, A2780, paclitaxel-resistant A2780/Taxol cells had almost identical IC₅₀ values. Cell cycle analysis demonstrated that treatment with CuB may induce cell cycle arrest at the G₂/M phase of the cell cycle in the two cell lines. As revealed by Annexin V/propidium iodide-labeled flow cytometry and Hoechst 33258 staining, CuB-induced apoptosis was accompanied by activation of caspase-3 and downregulation of B-cell lymphoma-2. Western blotting demonstrated that CuB may enhance the expression of p53 and p21 in the two cell lines. CuB may also downregulate the expression of P-glycoprotein. These results indicate that CuB may exert a therapeutic effect on paclitaxel-resistant human ovarian cancer.

Doxorubicin has a synergistic cytotoxicity with cucurbitacin B in anaplastic thyroid carcinoma cells

In this study, the combined effect of doxorubicin with cucurbitacin B on survival of anaplastic thyroid carcinoma cells was evaluated. For experiments, 8505C and CAL62 human anaplastic thyroid carcinoma cells were used. Cell viability, the percentage of viable cells, and cytotoxic activity were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, multiplexed cytotoxicity assay, and cytotoxicity assay, respectively. Reactive oxygen species production was measured. In experiments, doxorubicin and cucurbitacin B reduced cell viability in a dose- and time-dependent manner. Cotreatment of doxorubicin and cucurbitacin B, compared with treatment of doxorubicin alone, decreased the percentage of viable cells and increased cytotoxic activity. All of the combination index values were lower than 1.0, suggesting the synergism between doxorubicin and cucurbitacin B in induction of cytotoxicity. In cells treated with both doxorubicin and cucurbitacin B, compared with doxorubicin alone, the protein levels of cleaved poly(adenosine diphosphate-ribose) polymerase and cyclooxygenase 2 and reactive oxygen species production were enhanced. In contrast, the protein levels of B-cell chronic lymphocytic leukemia/lymphoma 2 and survivin and B-cell chronic lymphocytic leukemia/lymphoma 2/B-cell chronic lymphocytic leukemia/lymphoma 2-associated x protein ratio were diminished. The protein levels of Janus kinase 2 and signal transducer and activator of transcription 3 were reduced, while phospho-extracellular signal-regulated kinase 1/2 protein levels were elevated without change in total extracellular signal-regulated kinase 1/2 protein levels. These results suggest that doxorubicin synergizes with cucurbitacin B in induction of cytotoxicity in anaplastic thyroid carcinoma cells. Moreover, synergistic cytotoxicity of doxorubicin with cucurbitacin B is mediated by B-cell chronic lymphocytic leukemia/lymphoma 2 family proteins, survivin, and reactive oxygen species and modulated by Janus kinase 2/signal transducer and activator of transcription 3 and extracellular signal-regulated kinase 1/2 in anaplastic thyroid carcinoma cells.

Cucurbitacin B inhibits the stemness and metastatic abilities of NSCLC via downregulation of canonical Wnt/β-catenin signaling axis

Lack of effective anti-metastatic drugs creates a major hurdle for metastatic lung cancer therapy. For successful lung cancer treatment, there is a strong need of newer therapeutics with metastasis-inhibitory potential. In the present study, we determined the anti-metastatic and anti-angiogenic potential of a natural plant triterpenoid, Cucurbitacin B (CuB) against non-small cell lung cancer (NSCLC) both in vitro and in vivo. CuB demonstrated a strong anti-migratory and anti-invasive ability against metastatic NSCLC at nanomolar concentrations. CuB also showed significant tumor angiogenesis-inhibitory effects as evidenced by the inhibition of migratory, invasive and tube-forming capacities of human umbilical vein endothelial cells. CuB-mediated inhibition of angiogenesis was validated by the inhibition of pre-existing vasculature in chick embryo chorio-allantoic membrane and matrigel plugs. Similarly, CuB inhibited the migratory behavior of TGF-β1-induced experimental EMT model. The CuB-mediated inhibition of metastasis and angiogenesis was attributable to the downregulation of Wnt/β-catenin signaling axis, validated by siRNA-knockdown of Wnt3 and Wnt3a. The CuB-mediated downregulation of Wnt/β-catenin signaling was also validated using 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis model in vivo. Collectively, our findings suggest that CuB inhibited the metastatic abilities of NSCLC through the inhibition of Wnt/β-catenin signaling axis.

Cucurbitacins: A Systematic Review of the Phytochemistry and Anticancer Activity

Cucurbitacins are highly oxidized tetracyclic triterpenoids that are widely present in traditional Chinese medicines (Cucurbitaceae family), possess strong anticancer activity, and are divided into 12 classes from A to T with over 200 derivatives. The eight most active cucurbitacin components against cancer are cucurbitacin B, D, E, I, IIa, L glucoside, Q, and R. Their mechanisms of action include antiproliferation, inhibition of migration and invasion, proapoptosis, and cell cycle arrest promotion. Cucurbitacins are also found to be the inhibitors of JAK-STAT3, Wnt, PI3K/Akt, and MAPK signaling pathways, which play important roles in the apoptosis and survival of cancer cells. Recently, new studies have discovered synergistic anticancer effects by using cucurbitacins together with clinically approved chemotherapeutic drugs, such as docetaxel and methotrexate. This paper provides a summary of recent research progress on the anticancer property of cucurbitacins and the various intracellular signaling pathways involved in the regulation of cancer cell proliferation, death, invasion, and migration. Therefore, cucurbitacins are a class of promising anticancer drugs to be used alone or be intergraded in current chemotherapies and radiotherapies to treat many types of cancers.

Treatment with cucurbitacin B alone and in combination with gefitinib induces cell cycle inhibition and apoptosis via EGFR and JAK/STAT pathway in human colorectal cancer cell lines

The epidermal growth factor receptor (EGFR) associated with signaling pathways, such as Janus kinase (JAK)/signal transducer and activator of transcription (STAT), plays an important role in colorectal cancers (CRCs). Gefitinib (Gef) is an orally active inhibitor targeting the adenosine tri phosphate-binding domain of EGFR, and cucurbitacin B (CuB) is a selective inhibitor of JAK/STAT signaling with potent antitumor activity via suppression of STAT3 phosphorylation, but the underlying mechanism is not clear. We aimed to investigate the apoptotic and antiproliferative effects of CuB as a single agent and in combination with Gef on both HT-29 and HCT-116 cell lines. Cell proliferation, cell cycle distribution, and apoptosis were evaluated using viability assay, fluorescent microscopy, cytotoxicity assay, proliferation, DNA fragmentation, and cleaved caspase 3 levels. Real-time polymerase chain reaction and Western blot analyses were performed to determine the expression of relevant genes and proteins including antiapoptotic, proapoptotic, and cell cycle regulation. EGFR, phosphorylated EGFR (pEGFR), STAT3, and pSTAT3 proteins were evalutaed with Western blot analysis. Our results showed that, compared to CuB alone, CuB plus Gef treatment caused a significant growth and cell cycle inhibition and induced apoptosis in both cell lines. Also CuB plus Gef treatment decreased DNA synthesis rate more effectively than CuB alone. Treatment with CuB alone and in combination with Gef decreased the expression levels of B-Cell CLL/Lymphoma 2 (Bcl-2), BCL2-like 1 (BCL2L1), cyclin D1, pSTAT3, and pEGFR and increased the expression levels of Bcl-2-like protein 4, Bcl-2 homologous antagonist/killer, Bcl-2-associated death promoter, Bcl-2-like protein 11, and p27kip1 levels. Our results suggest that treatment with CuB alone and more likely in combination with Gef may be a considerable alternative therapeutic approach for CRC, at least in vitro.

Cucurbitacin B induces DNA damage and autophagy mediated by reactive oxygen species (ROS) in MCF-7 breast cancer cells

Cucurbitacin B (Cuc B), a natural compound extracted from cucurbitaceous plants, demonstrated potent anticancer activities, while the underlying mechanisms remain unclear. We investigated the anticancer effect of Cuc B on MCF-7 breast cancer cells. Cuc B drastically decreased cell viability in a concentration-dependent manner. Cuc B treatment caused DNA damage, as shown by long tails in the comet assay and increased γH2AX protein expression. Immunofluorescence staining showed that Cuc B treatment induced nuclear γH2AX foci. Cuc B activated DNA damage pathways by phosphorylation of ATM/ATR [two large phosphatidylinositol-3-kinase-like kinase family (PIKKs) members]. Furthermore, it also induced autophagy, as evidenced by monodansylcadaverine (MDC) staining and autophagic protein expression. In addition, Cuc B treatment led to increased reactive oxygen species (ROS) formation, which was inhibited by N-acetyl-L-cysteine (NAC) pretreatment. NAC pretreatment inhibited Cuc-B-induced DNA damage and autophagy. Taken together, these results suggest that ROS-mediated Cuc-B-induced DNA damage and autophagy in MCF-7 cells, which provides new insights into the anticancer molecular mechanism of Cuc B.

Improve bile duct-targeted drug delivery and therapeutic efficacy for cholangiocarcinoma by cucurbitacin B loaded phospholipid complex modified with berberine hydrochloride

In present study, a novel phospholipid complex loaded cucurbitacin B modified with berberine hydrochloride (CUB-PLC-BER) was prepared by a simple solvent evaporation method with the aim of improving bile duct-targeted drug delivery and therapeutic efficacy for cholangiocarcinoma (CC). The complex's physicochemical properties were systemically investigated in terms of scanning electron microscopy (SEM), x-ray diffraction (XRD) and infrared absorption spectroscopy (IR). In vivo and in vitro antitumor studies, CUB-PLC-BER and the unmodified cucurbitacin B-phospholipid complex (CUB-PLC) presented stronger antitumor efficacy against human cholangiocarcinoma cells (QBC939 cells) than free cucurbitacin B (CUB), while phospholipids (PL) itself had no significant toxicity. Besides that, CUB-PLC showed the advantage over the free CUB and CUB-PLC-BER with regard to the inhibition of tumor growth in vivo antitumor study. Failure to establish the orthotopic CC model, the study attempted to measure the level of CUB in plasma and in bile to explore bile duct-targeted effect indirectly. In the pharmacokinetics study in rats, the average values of Cmax and AUC0-8h of CUB-PLC-BER group in rat bile were higher than those of CUB-PLC, while an opposite result was found in plasma. Meanwhile, the Cmax, AUC0-8h and AUC0-24h of CUB were the least both in plasma and in bile. The results indicated that the CUB-PLC-BER tended to provide a high and prolonged drug concentration to bile duct, and PL played a central role in internalizing CUB into cells to improve the water insoluble drug's permeability, which was of great benefit to enhance the bioavailability of CUB and improve therapeutic efficacy of CC. These results elucidated the potential of CUB-PLC-BER as drug delivery system for improving bile duct-targeted and therapeutic efficacy for CC.

Inhibitory effect of cucurbitacin B on imiquimod-induced skin inflammation

Psoriasis is a common skin disease, of which pathogenesis involves the increase of inflammatory reaction in epidermal cells. In an attempt to find therapeutics for psoriasis, we found that cucurbitacin B has an inhibitory potential on imiquimod-induced inflammation of keratinocytes. Cucurbitacin B significantly inhibited imiquimod-induced expression of crucial psoriatic cytokines, such as IL-8 and CCL20, via down-regulation of NF-κB and STAT3 signaling pathway in human keratinocytes. In addition, keratinocyte proliferation was markedly inhibited by cucurbitacin B. The potential beneficial effect of cucurbitacin B on psoriasis was further validated in imiquimod-induced psoriasiform dermatitis of experimental animal. Topical application of cucurbitacin B resulted in significant reduction of epidermal hyperplasia and inflammatory cytokines production, and ameliorated the psoriatic symptom. Taken together, these results suggest that cucurbitacin B may be a potential candidate for the treatment of psoriasis.

Cucurbitacin B inhibits proliferation and induces apoptosis via STAT3 pathway inhibition in A549 lung cancer cells

Natural products are a great source of cancer chemotherapeutic agents. The present study was conducted to investigate whether cucurbitacin B (CuB), one of the most potent and widely used cucurbitacins, inhibits proliferation and induces apoptosis in the A549 lung cancer cell line. Furthermore, CuB induced apoptosis of A549 cells in a concentration-dependent manner, as determined by fluorescence microscopy, flow cytometry and transmission electron microscopy. The present study also demonstrated that CuB dose-dependently inhibited lung cancer cell proliferation, with cell cycle inhibition and cyclin B1 downregulation. Apoptosis induced by CuB was shown to be associated with cytochrome c release, B-cell lymphoma 2 downregulation and signal transducer and activator of transcription 3 pathway inhibition. CuB may prove to be a useful approach for the chemotherapy of lung cancer.

Cucurbitacin E induces cell cycle G2/M phase arrest and apoptosis in triple negative breast cancer

Triple negative breast cancer (TNBC) is a highly aggressive form of breast cancer resistant to many common treatments. In this study, we compared the effects of 12 phytochemical drugs on four cancer cell lines, and noticed that Cucurbitacin E (CuE) significantly inhibited TNBC cell growth by inducing cell cycle G2/M phase arrest and apoptosis. CuE reduced expression of Cyclin D1, Survivin, XIAP, Bcl2, and Mcl-1 in MDA-MB-468 and SW527, and within MDA-MB-468, CuE significantly increased activation of JNK and inhibited activation of AKT and ERK. Collectively, these results suggest that CuE may be a viable compound for developing novel TNBC therapeutics.

Inactivation of ATP citrate lyase by Cucurbitacin B: A bioactive compound from cucumber, inhibits prostate cancer growth

Prostate cancer, a leading cause of cancer-related deaths in males, is well recognized as having late disease on-set (mostly at age 60-70) and showing slow/latent disease development, and strategies to prevent cancer formation in late manhood may have significant health impacts. Cucurbitacin B (CuB) is a naturally occurring compound that is found abundantly in cucumbers and other vegetables, and it is known to exert anti-cancer activities (primarily via apoptosis-induction) in several human cancers. However, its chemopreventive potential for prostate cancer has not yet been investigated. Here, we reported that CuB significantly and specifically inhibited prostate cancer cell growth with low IC50 (~0.3 μM; PC-3 and LNCaP), accompanied by marked apoptosis (Caspase 3/7 activation, PARP cleavage, increase of Annexin V-Alexa Fluor 488 (Alexa488)+ cells and accumulation of Sub-G0/G1 population), whereas normal human prostate epithelial cells (PrEC) were CuB-insensitive. Using a chemopreventive model, pre-treatment of mice with CuB (2 weeks before PC-3 prostate cancer cell implantation) significantly reduced the rate of in vivo tumor-formation. A 79% reduction in tumor size (accompanied by marked in situ apoptosis) was observed in the CuB-treated group (with no noticeable toxicity) vs. controls at day 31. Strikingly, mechanistic investigations demonstrated that CuB drove dose-dependent inhibition of ATP citrate lyase phosphorylation (ACLY; an important enzyme for cancer metabolism) both in vitro and in the CuB-chemopreventive mouse model. Importantly, ACLY over-expression abrogated CuB's apoptotic effects in prostate cancer cells, confirming ACLY as a direct target of CuB. Thus, CuB harbors potent chemopreventive activity for prostate cancer, and we revealed a novel anti-tumor mechanism of CuB via inhibition of ACYL signaling in human cancer.

Cucurbitacin B induced ATM-mediated DNA damage causes G2/M cell cycle arrest in a ROS-dependent manner

Cucurbitacins are a class of triterpenoids widely distributed in plant kingdom with potent anti-cancer activities both in vitro and in vivo by inducing cycle arrest, autophagy, and apoptosis. Cucurbitacin B (Cuc B), could induce S or G2/M cell cycle arrest in cancer cells while the detailed mechanisms remain to be clear. This study was designed to precisely dissect the signaling pathway(s) responsible for Cuc B induced cell cycle arrest in human lung adenocarcinoma epithelial A549 cells. We demonstrated that low concentrations of Cuc B dramatically induced G2/M phase arrest in A549 cells. Cuc B treatment caused DNA double-strand breaks (DSBs) without affecting the signal transducer and activator of transcription 3 (STAT3), the potential molecular target for Cuc B. Cuc B triggers ATM-activated Chk1-Cdc25C-Cdk1, which could be reversed by both ATM siRNA and Chk1 siRNA. Cuc B also triggers ATM-activated p53-14-3-3-σ pathways, which could be reversed by ATM siRNA. Cuc B treatment also led to increased intracellular reactive oxygen species (ROS) formation, which was inhibited by N-acetyl-l-cysteine (NAC) pretreatment. Furthermore, NAC pretreatment inhibited Cuc B induced DNA damage and G2/M phase arrest. Taken together, these results suggested that Cuc B induces DNA damage in A549 cells mediated by increasing intracellular ROS formation, which lead to G2/M cell phase arrest through ATM-activated Chk1-Cdc25C-Cdk1 and p53-14-3-3-σ parallel branches. These observations provide novel mechanisms and potential targets for better understanding of the anti-cancer mechanisms of cucurbitacins.

Targeting the STAT3 signaling pathway in cancer: role of synthetic and natural inhibitors

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic transcription factors that mediate intracellular signaling that is usually generated at cell surface receptors and thereby transmit it to the nucleus. Numerous studies have demonstrated constitutive activation of STAT3 in a wide variety of human tumors, including hematological malignancies (leukemias, lymphomas, and multiple myeloma) as well as diverse solid tumors (such as head and neck, breast, lung, gastric, hepatocellular, colorectal and prostate cancers). There is strong evidence to suggest that aberrant STAT3 signaling promotes initiation and progression of human cancers by either inhibiting apoptosis or inducing cell proliferation, angiogenesis, invasion, and metastasis. Suppression of STAT3 activation results in the induction of apoptosis in tumor cells, and accordingly its pharmacological modulation by tyrosine kinase inhibitors, antisense oligonucleotides, decoy nucleotides, dominant negative proteins, RNA interference and chemopreventive agents have been employed to suppress the proliferation of various human cancer cells in culture and tumorigenicity in vivo. However, the identification and development of novel drugs that can target deregulated STAT3 activation effectively remains an important scientific and clinical challenge. This review presents the evidence for critical roles of STAT3 in oncogenesis and discusses the potential for development of novel cancer therapies based on mechanistic understanding of STAT3 signaling cascade.

Discovery and antitumor activities of constituents from Cyrtomium fortumei (J.) Smith rhizomes

Background

Cyrtomium fortumei (J.) Smith is an important Chinese herbal medicine because of its biological functions. However, systematic and comprehensive studies on the phytochemicals from Cyrtomium fortumei (J.) Smith and their bioactivity are limited.

Results

Using the bioassay-guided technique, the ethyl acetate and n-BuOH extracts of the rhizomes of Cyrtomium fortumei (J.) Smith were shown to exhibit good antitumor activities, consequently leading to the isolation of 23 compounds. All compounds were isolated from the plant for the first time. The inhibitory activities of these compounds were investigated on tumor cells MGC-803, PC3, and A375 in vitro by MTT (thiazolyl blue tetrazolium bromide) assay, and the results showed that pimpinellin (3) had potent cytotoxic activities against the three cell lines, with the IC₅₀ values of 14.4 ± 0.3 μM, 20.4 ± 0.5 μM, and 29.2 ± 0.6 μM, respectively. The mechanism of the antitumor action indicated that pimpinellin inhibited the growth of MGC-803 cells via the induction of tumor cell apoptosis, with apoptosis ratio of 27.44% after 72 h of treatment at 20 μM.

Conclusions

This study suggests that most of the compounds from the roots of Cyrtomium fortumei (J.) Smith could inhibit the growth of human carcinoma cells. Moreover, pimpinellin inhibited the growth of tumor cells via the induction of tumor cell apoptosis.

The triterpenoid cucurbitacin B augments the antiproliferative activity of chemotherapy in human breast cancer

Despite recent advances in therapy, breast cancer remains the second most common cause of death from malignancy in women. Chemotherapy plays a major role in breast cancer management, and combining chemotherapeutic agents with nonchemotherapeutic agents is of considerable clinical interest. Cucurbitacins are triterpenes compounds found in plants of the Cucurbitaceae family, reported to have anticancer and anti-inflammatory activities. Previously, we have shown antiproliferative activity of cucurbitacin B (CuB) in breast cancer, and we hypothesized that combining CuB with chemotherapeutic agents can augment their antitumor effect. Here, we show that a combination of CuB with either docetaxel (DOC) or gemcitabine (GEM) synergistically inhibited the proliferation of MDA-MB-231 breast cancer cells in vitro. This antiproliferative effect was accompanied by an increase in apoptosis rates. Furthermore, in vivo treatment of human breast cancer orthotopic xenografts in immunodeficient mice with CuB at either low (0.5 mg/kg) or high (1 mg/kg) doses in combination with either DOC (20 mg/kg) or GEM (12.5mg/kg) significantly reduced tumor volume as compared with monotherapy of each drug. Importantly, no significant toxicity was noted with low-dose CuB in combination with either DOC or GEM. In conclusion, combination of CuB at a relatively low concentration with either of the chemotherapeutic agents, DOC or GEM, shows prominent antiproliferative activity against breast cancer cells without increased toxicity. This promising combination should be examined in therapeutic trials of breast cancer.

In vitro and in vivo anticancer properties of cucurbitacin isolated from Cayaponia racemosa

CONTEXT

Cucurbitacins are a group of triterpenoids that have a cucurbitane skeleton with a wide range of biological activities.

OBJECTIVES

This study evaluated the anticancer properties of one cucurbitacin isolated from Cayaponia racemosa Cong. (Cucurbitaceae), 2β,3β,16α,20(R),25-pentahydroxy-22-oxocucurbita-5-en (1), with in vitro and in vivo models.

MATERIALS AND METHODS

In vitro cytotoxic activity was determined with human leukemia (HL60) and normal blood cells (PBMC). Sarcoma 180 was used as in vivo model.

RESULTS

The cucurbitacin (1) reduced the number of viable cells; however, there was no changed in the number of non-viable cells at 5 µg/mL. Selectivity towards cancer cells was suggested by the absence of activity on normal proliferating lymphocytes at the concentrations tested (IC₅₀ >25 µg/ml). Morphological analysis of compound 1-treated cells showed typical apoptotic features, such as intense deposition of granules in the cytoplasm (eosinophilia), DNA fragmentation and irregularities in the plasma membrane. In addition, the cells treated with compound 1 presented intense vacuolization and disruption of the plasma membrane. Acridine orange/Ethidium bromide staining confirmed these findings, revealing an increased number of apoptotic cells. In the Sarcoma 180 tumor model, compound 1 showed 52 and 62% of antitumor activity, either alone (25 mg/kg/day) or in association with the chemotherapeutic agent 5-FU (10 + 10 mg/kg/day), respectively. Moreover, either alone or associated with 5-FU, treatment with compound 1 caused an increase in spleen weight and morphological alterations related to immunostimulatory properties.

CONCLUSION

These data indicate that these naturally occurring compounds have anticancer potential.

Biological activities and potential molecular targets of cucurbitacins: a focus on cancer

Cucurbitacin and its derivatives (cucurbitacins) are a class of highly oxidized tetracyclic triterpenoids. They are widely distributed in the plant kingdom, where they act as heterologous chemical pheromones that protect plants from external biological insults. Their bioactivities first attracted attention in the 1960s. Documented data demonstrate that cucurbitacins possess strong pharmacological properties, such as antitumor, anti-inflammatory, and hepatoprotective effects, etc. Several molecular targets for cucurbitacins have been discovered, such as fibrous-actin, signal transducer and activator of transcription 3, cyclooxygenase-2, etc. The present study summarizes the achievements of the 50 years of research on cucurbitacins. The aim was to systematically analyze their bioactivities with an emphasis on their anticancer effects. Research and development has shed new insight into the beneficial properties of these compounds.

Cucurbitacin B induces cell cycle arrest, apoptosis and autophagy associated with G actin reduction and persistent activation of cofilin in Jurkat cells

AIM

The present study aimed to explore the antitumor effect and action mechanism of cucurbitacin B (CuB) on human T-cell leukemia Jurkat cells.

METHODS

Cell proliferation was measured by the MTS assay. Cell cycle distribution, mitochondrial membrane potential and annexin V staining were analyzed using flow cytometry. Western blotting was used to determine the levels of apoptosis- and autophagy-related proteins.

RESULTS

CuB inhibited the proliferation of Jurkat cells in a dose-dependent manner and induced G 2 /M phase arrest as well as formation of tetraploid cells. Accompanied with these effects, the actin dynamics was disrupted, and cofilin, a key regulator of actin dynamics, was persistently activated (dephosphorylated). Although CuB induced around 10% cells undergoing apoptosis, most of the cells were alive after CuB treatment for 24 h. Induction of autophagy was also evident by accumulation of LC3-II. CuB-induced autophagy seemed to be a prosurvival response, since suppression of CuB-induced autophagy significantly increased the activation of caspase-3.

CONCLUSION

Our results demonstrated that CuB exhibited antitumor activity in Jurkat cells through induction of cell cycle arrest and apoptosis which was at least partly due to the disruption of actin dynamics.