Helenalin bypasses Bcl-2-mediated cell death resistance by inhibiting NF-κB and promoting reactive oxygen species generation

Sesquiterpene lactones as emerging biomolecules to cease cancer by targeting apoptosis

Apoptosis is a programmed cell death comprising two signaling cascades including the intrinsic and extrinsic pathways. This process has been shown to be involved in the therapy response of different cancer types, making it an effective target for treating cancer. Cancer has been considered a challenging issue in global health. Cancer cells possess six biological characteristics during their developmental process known as cancer hallmarks. Hallmarks of cancer include continuous growth signals, unlimited proliferation, resistance to proliferation inhibitors, apoptosis escaping, active angiogenesis, and metastasis. Sesquiterpene lactones are one of the large and diverse groups of planet-derived phytochemicals that can be used as sources for a variety of drugs. Some sesquiterpene lactones possess many biological activities such as anti-inflammatory, anti-viral, anti-microbial, anti-malarial, anticancer, anti-diabetic, and analgesic. This review article briefly overviews the intrinsic and extrinsic pathways of apoptosis and the interactions between the modulators of both pathways. Also, the present review summarizes the potential effects of sesquiterpene lactones on different modulators of the intrinsic and extrinsic pathways of apoptosis in a variety of cancer cell lines and animal models. The main purpose of the present review is to give a clear picture of the current knowledge about the pro-apoptotic effects of sesquiterpene lactones on various cancers to provide future direction in cancer therapeutics.

Enhancing Ocular Surface in Dry Eye Disease Patients: A Clinical Evaluation of a Topical Formulation Containing Sesquiterpene Lactone Helenalin

The aim of this work was to assess the tolerability, safety, and efficacy of an ophthalmic topical formulation containing helenalin from Arnica montana and hyaluronic acid 0.4% (HA) in patients with mild-to-moderate Dry Eye Disease (DED) exhibiting positive Matrix Metalloproteinase 9 (MMP-9) test results. Tolerability and safety were evaluated in 24 healthy subjects. Participants were instructed to apply one drop of the formulation three times a day in the study eye, for 2 weeks, followed by a clinical follow-up of 21 days. Efficacy was studied in 48 DED patients randomized into Study (Group 1/receiving the studied formulation) or Control (Group 2/Receiving HA 0.4% eye lubricant) groups for 1 month. Assessments included an MMP-9 positivity test, conjunctival impression cytology (CIC), Ocular Surface Disease Index (OSDI), non-invasive film tear breakup time (NIBUT), non-invasive average breakup time (NIAvg-BUT), ocular surface staining, Schirmer's test, and meibomiography. A crossover design with an additional 1-month follow-up was applied to both groups. Healthy subjects receiving the studied formulation exhibited good tolerability and no adverse events. Regarding the efficacy study, Group 1 exhibited a statistically significant reduction in the MMP-9 positivity rate compared to Group 2 (p < 0.001). Both Group 1 and Group 2 exhibited substantial improvements in OSDI and NIBUT scores (p < 0.001). However, Group 1 demonstrated a significant improvement in NI-Avg-BUT and Schirmer's test scores (p < 0.001), whereas Group 2 did not (p > 0.05). Finally, after the crossover, the proportion of MMP-9-positive subjects in Group 1 increased from 25% to 91.6%, while Group 2 showed a significant decrease from 87.5% to 20.8%. Overall, the topical formulation containing sesquiterpene helenalin from Arnica montana and hyaluronic acid was well tolerated and exhibited a favorable safety profile. Our formulation reduces DED symptomatology and modulates the ocular surface inflammatory process; this is evidenced by the enhancement of CIC, the improvement of DED-related tear film status, and the reduction of the MMP-9 positivity rate.

Modulation of Intratumoral Fusobacterium nucleatum to Enhance Sonodynamic Therapy for Colorectal Cancer with Reduced Phototoxic Skin Injury

Intratumoral pathogens can contribute to cancer progression and affect therapeutic response. Fusobacterium nucleatum, a core pathogen of colorectal cancer (CRC), is an important cause of low therapeutic efficacy and metastasis. Thus, the modulation of intratumoral pathogens may provide a target for cancer therapy and metastasis inhibition. Herein, we propose an intratumoral F. nucleatum-modulating strategy for enhancing the therapeutic efficacy of CRC and inhibiting lung metastasis by designing an antibacterial nanoplatform (Au@BSA-CuPpIX), which produced reactive oxygen species (ROS) under ultrasound and exhibited strong antibacterial activity. Importantly, Au@BSA-CuPpIX reduced the levels of apoptosis-inhibiting proteins by inhibiting intratumoral F. nucleatum, thereby enhancing ROS-induced apoptosis. In vivo results demonstrated that Au@BSA-CuPpIX effectively eliminated F. nucleatum to enhance the therapeutic efficacy of sonodynamic therapy (SDT) for orthotopic CRC and inhibit lung metastasis. Notably, entrapped gold nanoparticles reduced the phototoxicity of metalloporphyrin accumulated in the skin during tumor treatment, preventing severe inflammation and damage to the skin. Therefore, this study proposes a strategy for the elimination of F. nucleatum in CRC to enhance the therapeutic effect of SDT, thus providing a promising paradigm for improving cancer treatment with fewer toxic side effects and promoting the clinical translational potential of SDT.

Natural Products as Anticancer Agents: Current Status and Future Perspectives

Natural products have been an invaluable and useful source of anticancer agents over the years. Several compounds have been synthesized from natural products by modifying their structures or by using naturally occurring compounds as building blocks in the synthesis of these compounds for various purposes in different fields, such as biology, medicine, and engineering. Multiple modern and costly treatments have been applied to combat cancer and limit its lethality, but the results are not significantly refreshing. Natural products, which are a significant source of new therapeutic drugs, are currently being investigated as potential cytotoxic agents and have shown a positive trend in preclinical research and have prompted numerous innovative strategies in order to combat cancer and expedite the clinical research. Natural products are becoming increasingly important for drug discovery due to their high molecular diversity and novel biofunctionality. Furthermore, natural products can provide superior efficacy and safety due to their unique molecular properties. The objective of the current review is to provide an overview of the emergence of natural products for the treatment and prevention of cancer, such as chemosensitizers, immunotherapeutics, combinatorial therapies with other anticancer drugs, novel formulations of natural products, and the molecular mechanisms underlying their anticancer properties.

Sesquiterpene Lactones as Promising Candidates for Cancer Therapy: Focus on Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease which confers to patients a poor prognosis at short term. PDAC is the fourth leading cause of death among cancers in the Western world. The rate of new cases of pancreatic cancer (incidence) is 10 per 100,000 but present a 5-year survival of less than 10%, highlighting the poor prognosis of this pathology. Furthermore, 90% of advanced PDAC tumor present KRAS mutations impacting in several oncogenic signaling pathways, many of them associated with cell proliferation and tumor progression. Different combinations of chemotherapeutic agents have been tested over the years without an improvement of significance in its treatment. PDAC remains as one the more challenging biomedical topics thus far. The lack of a proper early diagnosis, the notable mortality statistics and the poor outcome with the available therapies urge the entire scientific community to find novel approaches against PDAC with real improvements in patients' survival and life quality. Natural compounds have played an important role in the process of discovery and development of new drugs. Among them, terpenoids, such as sesquiterpene lactones, stand out due to their biological activities and pharmacological potential as antitumor agents. In this review, we will describe the sesquiterpene lactones with in vitro and in vivo activity against pancreatic tumor cells. We will also discuss the mechanism of action of the compounds as well as the signaling pathways associated with their activity.

In vitro metabolism of helenalin and its inhibitory effect on human cytochrome P450 activity

Sesquiterpene lactone helenalin is used as an antiphlogistic in European and Chinese folk medicine. The pharmacological activities of helenalin have been extensively investigated, yet insufficient information exists about its metabolic properties. The objectives of the present study were (1) to investigate the in vitro NADPH-dependent metabolism of helenalin (5 and 100 µM) using human and rat liver microsomes and liver cytosol, (2) to elucidate the role of human cytochrome P450 (CYP) enzymes in its oxidative metabolism, and (3) to study the inhibition of human CYPs by helenalin. Five oxidative metabolites were detected in NADPH-dependent human and rat liver microsomal incubations, while two reduced metabolites were detected only in NADPH-dependent human microsomal and cytosolic incubations. In human liver microsomes, the main oxidative metabolite was 14-hydroxyhelenalin, and in rat liver microsomes 9-hydroxyhelenalin. The overall oxidation of helenalin was several times more efficient in rat than in human liver microsomes. In humans, CYP3A4 and CYP3A5 followed by CYP2B6 were the main enzymes responsible for the hepatic metabolism of helenalin. The extrahepatic CYP2A13 oxidized helenalin most efficiently among CYP enzymes, possessing the K_m value of 0.6 µM. Helenalin inhibited CYP3A4 (IC₅₀ = 18.7 µM) and CYP3A5 (IC₅₀ = 62.6 µM), and acted as a mechanism-based inhibitor of CYP2A13 (IC₅₀ = 1.1 µM, K_I = 6.7 µM, and k_inact = 0.58 ln(%)/min). It may be concluded that the metabolism of helenalin differs between rats and humans, in the latter its oxidation is catalyzed by hepatic CYP2B6, CYP3A4, CYP3A5, and CYP3A7, and extrahepatic CYP2A13.

Mechanism of Action of the Sesquiterpene Compound Helenalin in Rhabdomyosarcoma Cells

Rhabdomyosarcoma (RMS) is the most frequent soft tissue sarcoma in paediatric patients. Relapsed or refractory RMS shows very low 5-year survival rates, which urgently necessitates new chemotherapy agents. Herein, the sesquiterpene lactone, helenalin, was investigated as a new potential therapeutic agent against the embryonal RMS (eRMS) and alveolar RMS (aRMS) cells. We have evaluated in vitro antiproliferative efficacy of helenalin on RMS cells by the MTT and wound healing assay, and estimated several cell death pathways by flow cytometry, confocal microscopy and immunoblotting. It was shown that helenalin was able to increase reactive oxygen species levels, decrease mitochondrial membrane potential, trigger endoplasmic reticulum stress and deactivate the NF-κB pathway. Confirmation was obtained through the use of antagonistic compounds which alleviated the effects of helenalin in the corresponding pathways. Our findings demonstrate that oxidative stress is the pivotal mechanism of action of helenalin in promoting RMS cell death in vitro.

Recent Patents on Anti-Cancer Potential of Helenalin

BACKGROUND

Arnica montana, containing helenalin as its principal active constituent, is the most widely used plant to treat various ailments. Recent studies indicate that Arnica and helenalin provide significant health benefits, including anti-inflammatory, neuroprotective, antioxidant, cholesterol-lowering, immunomodulatory, and most important, anti-cancer properties.

OBJECTIVE

The objective of the present study is to overview the recent patents of Arnica and its principal constituent helenalin, including new methods of isolation, and their use in the prevention of cancer and other ailments.

METHODS

Current prose and patents emphasizing the anti-cancer potential of helenalin and Arnica, incorporated as anti-inflammary agents in anti-cancer preparations, have been identified and reviewed with particular emphasis on their scientific impact and novelty.

RESULTS

Helenalin has shown its anti-cancer potential to treat multiple types of tumors, both in vitro and in vivo. It has also portrayed synergistic effects when given in combination with other anti- cancer drugs or natural compounds. New purification/isolation techniques are also developing with novel helenalin formulations and its synthetic derivatives have been developed to increase its solubility and bioavailability.

CONCLUSION

The promising anti-cancer potential of helenalin in various preclinical studies may open new avenues for therapeutic interventions in different tumors. Thus clinical trials validating its tumor suppressing and chemopreventive activities, particularly in conjunction with standard therapies, are immediately required.

Helenalin Facilitates Reactive Oxygen Species-Mediated Apoptosis and Cell Cycle Arrest by Targeting Thioredoxin Reductase-1 in Human Prostate Cancer Cells

Background

Helenalin is a pseudoguaianolide natural product with anti-cancer activities. This study investigated the underlying mechanism of the anti-prostate cancer effects of helenalin in vitro.

Material/Methods

CCK-8 assay was performed to detect the optimal concentrations of helenalin in DU145 and PC-3 cells. After exposure to helenalin and/or reactive oxygen species (ROS) inhibitor, ROS production was assessed by DCFH-DA staining. Thioredoxin reductase-1 (TrxR1) expression was detected by RT-qPCR and western blot. Moreover, apoptosis and cell cycle were evaluated by flow cytometry. Following TrxR1 knockdown or overexpression, TrxR1 expression, ROS generation, apoptosis, cell cycle, migration, and invasion were examined in cells co-treated with helenalin.

Results

Helenalin distinctly repressed the viability of prostate cancer cells in a concentration-dependent manner. We chose 8 μM and 4 μM as the optimal concentrations of helenalin for DU145 and PC-3 cells, respectively. Helenalin treatment markedly triggered ROS production and lowered TrxR1 expression, which was ameliorated by ROS inhibitor. Exposure to helenalin facilitated apoptosis as well as G0/G1 cell cycle arrest, which was reversed by ROS inhibitor. Helenalin relieved the inhibitory effect of TrxR1 on ROS production. Furthermore, helenalin ameliorated the decrease in apoptosis rate and the shortening of G0/G1 phase as well as the increase in migration and invasion induced by TrxR1 overexpression.

Conclusions

Our findings revealed that helenalin accelerated ROS-mediated apoptosis and cell cycle arrest via targeting TrxR1 in human prostate cancer cells.

Biological Activity of Flavonoids and Rare Sesquiterpene Lactones Isolated From Centaurea ragusina L

The endemic Croatian species Centaurea ragusina L., like other species from the genus Centaurea, has been traditionally used in Croatia as an antibacterial agent and for the treatment of gastrointestinal and urogenital disorders. In several chromatographic steps, three flavonoids and three sesquiterpene lactones (STLs) were isolated and identified from the most active fractions of the ethanol extract. Two STLs, one for which we created the trivial name ragusinin, and hemistepsin A are here reported for the first time as constituents of the genus Centaurea. All six compounds were screened for their effect on several tumor and one normal cell lines. Among them, ragusinin showed the best bioactivity and high specificity to affect tumor murine SCCVII, human HeLa and Caco-2 cell lines, but not the viability of normal V79 fibroblasts. Due to these characteristics the action of ragusinin was investigated in more detail. Since DNA is the primary target for many drugs with antibacterial and anticancer activity, we studied its interaction with ragusinin. Rather moderate binding affinity to DNA excluded it as the primary target of ragusinin. Due to the possibility of STL interaction with glutathione (GSH), the ubiquitous peptide that traps reactive compounds and other xenobiotics to prevent damage to vital proteins and nucleic acids, its role in deactivation of ragusinin was evaluated. Addition of the GSH precursor N-acetyl-cysteine potentiated the viability of HeLa cells, while the addition of GSH inhibitor L-buthionine sulfoximine decreased it. Moreover, pre-treatment of HeLa cells with the inhibitor of glutathione-S-transferase decreased their viability indicating the detoxifying role of GSH in ragusinin treated cells. Cell death, derived by an accumulation of cells in a G2 phase of the cell cylce, was shown to be independent of poly (ADP-ribose) polymerase and caspase-3 cleavage pointing toward an alternative cell death pathway.

Development of Anticancer Agents from Plant-Derived Sesquiterpene Lactones

Sesquiterpene lactones are of considerable interest due to their potent bioactivities, including cancer cell cytotoxicity and antineoplastic efficacy in in vivo studies. Among these compounds, artesunate, dimethylaminoparthenolide, and L12ADT peptide prodrug, a derivative of thapsigargin, are being evaluated in the current cancer clinical or preclinical trials. Based on the structures of several antitumor sesquiterpene lactones, a number of analogues showing greater potency have been either isolated as natural products or partially synthesized, and some potential anticancer agents that have emerged from this group of lead compounds have been investigated extensively. The present review focuses on artemisinin, parthenolide, thapsigargin, and their naturally occurring or synthetic analogues showing potential anticancer activity. This provides an overview of the advances in the development of these types of sesquiterpene lactones as potential anticancer agents, including their structural characterization, synthesis and synthetic modification, and antitumor potential, with the mechanism of action and structure-activity relationships also discussed. It is hoped that this will be helpful in stimulating the further interest in developing sesquiterpene lactones and their derivatives as new anticancer agents.

Cyanidin-3-O-β-glucoside protects primary mouse hepatocytes against high glucose-induced apoptosis by modulating mitochondrial dysfunction and the PI3K/Akt pathway

Apoptosis is an early event of steatohepatitis in non-alcoholic fatty liver disease (NAFLD), and an increase in oxidative stress induced by hyperglycemia has been linked to an acceleration of apoptosis in hepatocytes. Cyanidin-3-O-β-glucoside (C3G), a classic anthocyanin, has been reported to reduce oxidative stress and attenuate non-alcoholic steatohepatitis in mice. In this study, we evaluated the toxicity of high glucose in primary hepatocytes of mice fed with a high fat diet and amelioration of this toxicity by C3G. Incubation of hepatocytes with 35mM glucose for 12h resulted in a significant decrease in cell viability and increase in apoptotic cell death. Furthermore, hyperglycemia-induced mitochondrial depolarization was accompanied by the release of cytochrome c and altered expression of Bax and Bcl-2, suggesting a mitochondria-mediated apoptotic mode of cell death. Pre-incubation with 50μM C3G induced changes associated with better cell survival and function, including a reduction in reactive species generation, improvement of mitochondrial membrane potential, inactivation of caspase-3 and -9, and down-regulation of the pro-apoptotic Bax protein. We further investigated the role of the phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinases (MAPKs) pathways with respect to the anti-apoptotic action of C3G, and our results showed that C3G could activate Akt. Additionally, C3G inactivated c-Jun N-terminal protein kinase (JNK), but not extracellular signal-regulated kinase or p38 MAPK, in glucose-stressed cells. Interestingly, JNK inhibitor enhanced the protective effect of C3G on cell survival. Our results suggest that anthocyanin C3G may exhibit hepatoprotective potential against NAFLD by promoting functional integrity and survival of hepatocytes.

High-throughput screen of natural product libraries for hsp90 inhibitors

Hsp90 has become the target of intensive investigation, as inhibition of its function has the ability to simultaneously incapacitate proteins that function in pathways that represent the six hallmarks of cancer. While a number of Hsp90 inhibitors have made it into clinical trials, a number of short-comings have been noted, such that the search continues for novel Hsp90 inhibitors with superior pharmacological properties. To identify new potential Hsp90 inhibitors, we have utilized a high-throughput assay based on measuring Hsp90-dependent refolding of thermally denatured luciferase to screen natural compound libraries. Over 4,000 compounds were screen with over 100 hits. Data mining of the literature indicated that 51 compounds had physiological effects that Hsp90 inhibitors also exhibit, and/or the ability to downregulate the expression levels of Hsp90-dependent proteins. Of these 51 compounds, seven were previously characterized as Hsp90 inhibitors. Four compounds, anthothecol, garcinol, piplartine, and rottlerin, were further characterized, and the ability of these compounds to inhibit the refolding of luciferase, and reduce the rate of growth of MCF7 breast cancer cells, correlated with their ability to suppress the Hsp90-dependent maturation of the heme-regulated eIF2α kinase, and deplete cultured cells of Hsp90-dependent client proteins. Thus, this screen has identified an additional 44 compounds with known beneficial pharmacological properties, but with unknown mechanisms of action as possible new inhibitors of the Hsp90 chaperone machine.

Sesquiterpene lactones as drugs with multiple targets in cancer treatment: focus on parthenolide

Sesquiterpene lactones (SLs) constitute a large and diverse group of biologically active plant compounds that possess anti-inflammatory and antitumor activity. The subclass germacranolides is one of the major groups of SLs. It includes parthenolide, a highly cytotoxic SL that is being tested in clinical trials as an anti-cancer agent. In this review, we focus on SL antitumor activity related to cell-cycle arrest, differentiation, apoptosis induction through the intrinsic pathway, and sensitization of the extrinsic pathway. We also address the regression of tumors in response to cotreatment with conventional chemotherapeutics. We review the nuclear factor-κB-targeted anti-inflammatory activity in vitro and in vivo and relate it to the SL structural features involved in the molecular mechanisms. It is obvious that SLs are emerging as promising anticancer agents, but more investigations are required to fully understand the molecular mechanisms of known SLs in different cell death modalities and how these mechanisms contribute toward the potent antitumor and anti-inflammatory activities of SLs.

Helenalin-induced apoptosis is dependent on production of reactive oxygen species and independent of induction of endoplasmic reticulum stress in renal cell carcinoma

Helenalin, a sesquiterpene lactone, exhibits anti-inflammatory and anti-tumor activities. Here, we investigated whether helenalin could induce apoptosis in human renal carcinoma Caki cells. Helenalin increased apoptosis in dose dependent manner in Caki cells, and also induced apoptosis in other carcinoma cells, such as human renal carcinoma ACHN cells, human colon carcinoma HT29 and HCT116 cells. We found that helenalin markedly induced endoplasmic reticulum (ER) stress-related genes, such as regulated in development and DNA damage responses (REDD) 1, activating transcription factor-4 (ATF4) and/or the CCAAT enhancer-binding protein-homologous protein (CHOP). However, down-regulation of ATF4 and/or CHOP expression by siRNA had no effect on helenalin-induced apoptosis in Caki and HCT116 cells. Helenalin increased production of intracellular reactive oxygen species (ROS). Furthermore, ROS scavengers, N-acetylcystine (NAC), and glutathione ethyl ester (GEE), reduced helenalin-induced apoptosis. Taken together, helenalin induced apoptosis via ROS generation in human renal carcinoma Caki cells.

NF-κB p65 repression by the sesquiterpene lactone, Helenalin, contributes to the induction of autophagy cell death

Background

Numerous studies have demonstrated that autophagy plays a vital role in maintaining cellular homeostasis. Interestingly, several anticancer agents were found to exert their anticancer effects by triggering autophagy. Emerging data suggest that autophagy represents a novel mechanism that can be exploited for therapeutic benefit. Pharmacologically active natural compounds such as those from marine, terrestrial plants and animals represent a promising resource for novel anticancer drugs. There are several prominent examples from the past proving the success of natural products and derivatives exhibiting anticancer activity. Helenalin, a sesquiterpene lactone has been demonstrated to have potent anti-inflammatory and antitumor activity. Albeit previous studies demonstrating helenalin’s multi modal action on cellular proliferative and apoptosis, the mechanisms underlying its action are largely unexplained.

Methods

To deduce the mechanistic action of helenalin, cancer cells were treated with the drug at various concentrations and time intervals. Using western blot, FACS analysis, overexpression and knockdown studies, cellular signaling pathways were interrogated focusing on apoptosis and autophagy markers.

Results

We show here that helenalin induces sub-G1 arrest, apoptosis, caspase cleavage and increases the levels of the autophagic markers. Suppression of caspase cleavage by the pan caspase inhibitor, Z-VAD-fmk, suppressed induction of LC3-B and Atg12 and reduced autophagic cell death, indicating caspase activity was essential for autophagic cell death induced by helenalin. Additionally, helenalin suppressed NF-κB p65 expression in a dose and time dependent manner. Exogenous overexpression of p65 was accompanied by reduced levels of cell death whereas siRNA mediated suppression led to augmented levels of caspase cleavage, autophagic cell death markers and increased cell death.

Conclusions

Taken together, these results show that helenalin mediated autophagic cell death entails inhibition of NF-κB p65, thus providing a promising approach for the treatment of cancers with aberrant activation of the NF-κB pathway.

Fluorinated amino-derivatives of the sesquiterpene lactone, parthenolide, as (19)f NMR probes in deuterium-free environments

The design, synthesis, and biological activity of fluorinated amino-derivatives of the sesquiterpene lactone, parthenolide, are described. A fluorinated aminoparthenolide analogue with biological activity similar to the parent natural product was discovered, and its X-ray structure was obtained. This lead compound was then studied using (19)F NMR in the presence and absence of glutathione to obtain additional mechanism of action data, and it was found that the aminoparthenolide eliminates amine faster in the presence of glutathione than in the absence of glutathione. The exact changes in concentrations of fluorinated compound and amine were quantified by a concentration-reference method using (19)F NMR; a major benefit of applying this strategy is that no deuterated solvents or internal standards are required to obtain accurate concentrations. These mechanistic data with glutathione may contribute to the conversion of the amino-derivative to parthenolide, the active pharmacological agent, in glutathione-rich cancer cells.