2'-Epi-uscharin from the latex of Calotropis gigantea with HIF-1 inhibitory activity

HPLC-MS standardization and validation methods for determination of calactin content in dichloromethane fraction of Calotropis gigantea (L.) Dryand. (Niu jiao gua) stem bark and its application in prediction of anticancer activities

Calactin, a doubly-linked cardenolide, is commonly found in Apocynaceae family including Calotropis gigantea (L.) Dryand. (Niu jiao gua, C. gigantea). This phytochemical has gained recognition for its potential as an anticancer agent and a marker for anticancer properties. Our previous reports demonstrated the remarkable anti-liver and anti-colon cancer activities both in vitro and in vivo of the dichloromethane fraction from the stem barks of C. gigantea (CGD). However, quantitative analysis of calactin content in CGD by using a high-performance liquid chromatography (HPLC) - ultraviolet (UV) method was limited. Therefore, this study aimed to develop more sensitive and reliable method for measurement of calactin in CGD by using a HPLC- electrospray ionization mass spectrometry (ESI-MS) for its application on quality control and prediction of anticancer activity of CGD. The study utilized a HPLC-ESI-MS system, negative mode, for standardization and validation. An octadecylsilane column and a mixture of acetonitrile and water containing 0.1 % formic acid in gradient system were used as a stationary phase and a mobile phase, respectively. The method was validated in terms of linearity, accuracy, precision, recovery, limit of detection (LOD), and limit of quantitation (LOQ). The linearity of the developed technique was verified within the calactin concentrations range from 1 to 50 μg/mL, exhibiting a linear coefficient of determination (R2) greater than 0.998. The LOD and LOQ were 0.1 and 1 μg/mL, respectively. The proposed methodology met the acceptance criteria according to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) guideline Q2(R1). Therefore, the method was suitable for the quality control of CGD. Additionally, we suggest applying the established protocol to quantify the calactin contents in CGDs collected over a period of one year (12 months) to investigate the correlation to their cytotoxicities against human cell lines derived from colon cancer (HCT116), human hepatoblastoma (HepG2) and human cell line derived from stomach cancer metastasized to liver (MKN74). This will help in predicting its cytotoxicity against HCT116, HepG2 and MKN74. In summary, the established HPLC-ESI-MS method is suitable for both quality control and predicting of CGD anticancer activities for further utilization.

Research Progress on Plant-Derived Cardenolides (2010-2023)

Cardenolides are a class of steroidal glycoside compounds that are mainly distributed in plants, have significant physiological activity in the heart, and have been used clinically for over 200 years. To provide a reference for further research and development of these compounds, the phytochemical and biological properties of natural cardenolides (295 compounds in total) isolated between 2010 and 2023 from 17 families and hundreds of species belonging to 70-80 genera were reviewed. In vitro and in vivo studies have indicated that antitumor, antibacterial, and antiviral activities are the most commonly reported pharmacological properties of cardenolides. Antitumor activities have been thoroughly studied to understand their structure-activity relationships, revealing numerous potential anticancer molecules that lay the theoretical foundation for further development of traditional Chinese medicinal herbs and the creation of new drugs.

Tapping the potential of Calotropis procera hairy roots for cardiac glycosides production and their identification using UHPLC/QTOF-MS

The present work deals with the establishment of hairy root cultures from different explants of C. procera using Agrobacterium rhizogenes strain A4. A high transformation frequency (95%) was obtained from leaves followed by cotyledons (81.6%) and hypocotyls (38.3%). Genetic transformation of hairy roots was confirmed through PCR by amplifying a 400 bp fragment of the rolB gene. Hairy roots were highly branched, possessed plagiotropic and rapid growth on hormone-free ½ B5 medium. Ten cardiac glycosides, including calotropagenin, calotoxin, frugoside, coroglaucigenin, calotropin, calactin, uzarigenin, asclepin, uscharidin, and uscharin, based on their specific masses and fragmentation properties were identified in ethanolic extracts of hairy roots by ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry UHPLC/QTOF-MS. This protocol could be used as a powerful tool for large-scale in vitro production of highly valued cardiac glycosides and for further transcriptomics or metabolomics studies.

Natural Product-Derived Phytochemicals for Influenza A Virus (H1N1) Prevention and Treatment

Influenza A (H1N1) viruses are prone to antigenic mutations and are more variable than other influenza viruses. Therefore, they have caused continuous harm to human public health since the pandemic in 2009 and in recent times. Influenza A (H1N1) can be prevented and treated in various ways, such as direct inhibition of the virus and regulation of human immunity. Among antiviral drugs, the use of natural products in treating influenza has a long history, and natural medicine has been widely considered the focus of development programs for new, safe anti-influenza drugs. In this paper, we focus on influenza A (H1N1) and summarize the natural product-derived phytochemicals for influenza A virus (H1N1) prevention and treatment, including marine natural products, flavonoids, alkaloids, terpenoids and their derivatives, phenols and their derivatives, polysaccharides, and derivatives of natural products for prevention and treatment of influenza A (H1N1) virus. We further discuss the toxicity and antiviral mechanism against influenza A (H1N1) as well as the druggability of natural products. We hope that this review will facilitate the study of the role of natural products against influenza A (H1N1) activity and provide a promising alternative for further anti-influenza A drug development.

Combination of ethyl acetate fraction from Calotropis gigantea stem bark and sorafenib induces apoptosis in HepG2 cells

The cytotoxicity of the ethyl acetate fraction of the Calotropis gigantea (L.) Dryand. (C. gigantea) stem bark extract (CGEtOAc) has been demonstrated in many types of cancers. This study examined the improved cancer therapeutic activity of sorafenib when combined with CGEtOAc in HepG2 cells. The cell viability and cell migration assays were applied in HepG2 cells treated with varying concentrations of CGEtOAc, sorafenib, and their combination. Flow cytometry was used to determine apoptosis, which corresponded with a decline in mitochondrial membrane potential and activation of DNA fragmentation. Reactive oxygen species (ROS) levels were assessed in combination with the expression of the phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (Akt)/ mammalian target of rapamycin (mTOR) pathway, which was suggested for association with ROS-induced apoptosis. Combining CGEtOAc at 400 μg/mL with sorafenib at 4 μM, which were their respective half-IC50 concentrations, significantly inhibited HepG2 viability upon 24 h of exposure in comparison with the vehicle and each single treatment. Consequently, CGEtOAc when combined with sorafenib significantly diminished HepG2 migration and induced apoptosis through a mitochondrial-correlation mechanism. ROS production was speculated to be the primary mechanism of stimulating apoptosis in HepG2 cells after exposure to a combination of CGEtOAc and sorafenib, in association with PI3K/Akt/mTOR pathway suppression. Our results present valuable knowledge to support the development of anticancer regimens derived from the CGEtOAc with the chemotherapeutic agent sorafenib, both of which were administered at half-IC50, which may minimize the toxic implications of cancer treatments while improving the therapeutic effectiveness toward future medical applications.

Cryptolepine suppresses breast adenocarcinoma via inhibition of HIF-1 mediated glycolysis

As a characteristic transcription factor in solid tumors, hypoxia inducible factor-1 (HIF-1) acts as a master regulator in breast cancer progression. Cryptolepine, as a natural alkaloid, noticeably inhibited HIF-1 transcriptional activity and decreased the protein expression of hypoxia-induced HIF-1α in breast cancer cells. Further study showed that cryptolepine blocked HIF-1-mediated glycolysis and suppressed the expression of multiple glycolysis enzymes, resulting in a decrease in ATP production in hypoxic T47D and 4T1 cells. Meanwhile, cryptolepine displayed potent suppressive effect on tumor growth in a dose-dependent manner. In 4T1 tumor xenografts, cryptolepine reduced HIF-1α protein expression, and thus decreased the levels of both lactate acid and ATP productions. The mechanistic study revealed that cryptolepine could effectively suppress the process of HIF-1α mRNA translation rather than transcription, which was attributed to the inhibition on the phosphorylation of eIF4E regulated by both MAPK and mTOR signaling pathways. Collectively, current findings suggested that cryptolepine possesses the potential to treat breast cancers by modulating HIF-1 both in vitro and in vivo.

Calotropis gigantea stem bark extract induced apoptosis related to ROS and ATP production in colon cancer cells

Conventional chemotherapeutic agents for colorectal cancer (CRC) cause systemic side effects and eventually become less efficacious owing to the development of drug resistance in cancer cells. Therefore, new therapeutic regimens have focused on the use of natural products. The anticancer activity of several parts of Calotropis gigantea has been reported; however, the effects of its stem bark extract on inhibition of cancer cell proliferation have not yet been examined. In this study, the anticancer activity of C. gigantea stem bark extract, both alone and in combination with 5-fluorouracil (5-FU), was evaluated. A crude ethanolic extract was prepared from dry, powdered C. gigantea barks using 95% ethanol. This was then partitioned to obtain dichloromethane (CGDCM), ethyl acetate, and water fractions. Quantitative analysis of the constituent secondary metabolites and calotropin was performed. These fractions exhibited cytotoxicity in HCT116 and HT-29 cells, with CGDCM showing the highest potency in both the cell lines. A combination of CGDCM and 5-FU significantly enhanced the cytotoxic effect. Moreover, the resistance of normal fibroblast, HFF-1, cells to this combination demonstrated its safety in normal cells. The combination significantly enhanced apoptosis through the mitochondria-dependent pathway. Additionally, the combination reduced adenosine triphosphate production and increased the production of reactive oxygen species, demonstrating the mechanisms involved in the induction of apoptosis. Our results suggest that CGDCM is a promising anti-cancer agent and may enhance apoptosis induction by 5-FU in the treatment of CRC, while minimizing toxicity toward healthy cells.

Non-classical cardenolides from Calotropis gigantea exhibit anticancer effect as HIF-1 inhibitors

Six new non-classical cardenolides (1-6), and seventeen known ones (7-23) were isolated from Calotropis gigantea. All cardenolides showed inhibitory effect on hypoxia inducible factor-1 (HIF-1) transcriptional activity with IC₅₀ of 8.85 nM-16.69 µM except 5 and 7. The novel 19-dihydrocalotoxin (1) exhibited a comparable HIF-1 inhibitory activity (IC₅₀ of 139.57 nM) to digoxin (IC₅₀ of 145.77 nM), a well-studied HIF-1 inhibitor, and 11, 12, 14, 16 and 19 presented 1.4-15.4 folds stronger HIF-1 inhibition than digoxin. 1 and 11 showed a dose-dependent inhibition on HIF-1α protein, which led to their HIF-1 suppressing effects. Compared with LO2 and H9c2 normal cell lines, both 1 and 11 showed selective cytotoxicity against various cancer cell lines including HCT116, HeLa, HepG2, A549, MCF-7, A2780 and MDA-MB-231. Moreover, a comprehensive structure-activity relationship was concluded for these non-classical cardenolides as HIF-1 inhibitors, which may shed some light on the rational design and development of cardenolide-based anticancer drugs.

Deubiquitylase OTUD6B Governs pVHL Stability in an Enzyme-Independent Manner and Suppresses Hepatocellular Carcinoma Metastasis

Hypoxia inducible factors (HIFs) are the key transcription factors that allow cancer cells to survive hypoxia. HIF's stability is mainly controlled by von Hippel-Lindau (pVHL)-mediated ubiquitylation. Unlike sporadic clear-cell renal carcinomas, VHL mutation is rarely observed in hepatocellular carcinoma (HCC) and the regulatory mechanisms of pVHL-HIF signaling remain elusive. Here, it is shown that deubiquitylase ovarian tumor domain-containing 6B (OTUD6B) suppresses HCC metastasis through inhibiting the HIF activity. OTUD6B directly interacts with pVHL, decreases its ubiquitylation and proteasomal degradation to reduce HIF-1α accumulation in HCC cells under hypoxia. Surprisingly, OTUD6B limits the ubiquitylation of pVHL independent of its deubiquitylase activity. OTUD6B couples pVHL and elongin B/C to form more CBCVHL ligase complex, which protects pVHL from proteasomal degradation. Depletion of OTUD6B results in the dissociation of CBCVHL complex and the degradation of pVHL by Trp Asp repeat and suppressors of cytokine signaling box-containing protein 1 (WSB1). In human HCC tissues, the protein level of OTUD6B is positively correlated with pVHL, but negatively with HIF-1α and vascular endothelial growth factor. Low expression of OTUD6B predicts poor patient survival. Furthermore, OTUD6B gene is a direct transcriptional target of HIF-1α and upregulated upon hypoxia. These results indicate a previously unrecognized feedback loop consisting of OTUD6B, pVHL, and HIF-1α, and provide insights into the targeted hypoxic microenvironment for HCC therapy.

SENP1 promotes hypoxia-induced cancer stemness by HIF-1α deSUMOylation and SENP1/HIF-1α positive feedback loop

OBJECTIVE

We investigated the effect and mechanism of hypoxic microenvironment and hypoxia-inducible factors (HIFs) on hepatocellular carcinoma (HCC) cancer stemness.

DESIGN

HCC cancer stemness was analysed by self-renewal ability, chemoresistance, expression of stemness-related genes and cancer stem cell (CSC) marker-positive cell population. Specific small ubiquitin-like modifier (SUMO) proteases 1 (SENP1) mRNA level was examined with quantitative PCR in human paired HCCs. Immunoprecipitation was used to examine the binding of proteins and chromatin immunoprecipitation assay to detect the binding of HIFs with hypoxia response element sequence. In vivo characterisation was performed in immunocompromised mice and stem cell frequency was analysed.

RESULTS

We showed that hypoxia enhanced the stemness of HCC cells and hepatocarcinogenesis through enhancing HIF-1α deSUMOylation by SENP1 and increasing stabilisation and transcriptional activity of HIF-1α. Furthermore, we demonstrated that SENP1 is a direct target of HIF-1/2α and a previously unrecognised positive feedback loop exists between SENP1 and HIF-1α.

CONCLUSIONS

Taken together, our findings suggest the significance of this positive feedback loop between HIF-1α and SENP1 in contributing to the increased cancer stemness in HCC and hepatocarcinogenesis under hypoxia. Drugs that specifically target SENP1 may offer a potential novel therapeutic approach for HCC.

Cardenolides from Calotropis gigantea as potent inhibitors of hypoxia-inducible factor-1 transcriptional activity

ETHNOPHARMACOLOGICAL RELEVANCE

Calotropis gigantea (L.) Dryand (Apocynaceae) is a medicinal plant native to southern China, India and Southeast Asia. It has been traditionally used for the treatment of several diseases including cancers in these countries.

AIM OF THE STUDY

This study aimed to isolate bioactive cardenolides from C. gigantea, to screen their hypoxia-inducible factor (HIF-) 1 inhibitory activity, and to analyze the structure-activity relationship (SAR).

MATERIALS AND METHODS

Isolation and purification of cardenolides from the latex and the fruits of C. gigantea were performed by using a series of separation techniques. Their structures were fully characterized by elucidating their NMR and HRMS data. The HIF-1 inhibitory activities of cardenolides were evaluated by using a T47D cell-based dual-luciferase reporter assay. The potent cardenolides were selected to further evaluate their dose-response manner. Cytotoxic effects of selected cardenolides were also examined against breast cancer cell line (MCF-7) and normal mammary epithelial cell line (MCF-10A) by MTT assay.

RESULTS

Among twenty isolated cardenolides, compounds 1, 3, 4, 6-8, 14 and 17 exhibited stronger HIF-1 inhibitory activities than that of digoxin, a well-known HIF-1 inhibitor (P<0.001). These eight cardenolides inhibited HIF-1 transcriptional activity in a dose-dependent manner with IC₅₀ values in nanomolar potency (21.8-64.9nM). An analysis of SAR revealed the great contributions of a β-configuration of the substituents at positions of C-2' and C-3', an aldehydic moiety on C-19, and the dioxane moiety between the aglycone and sugar parts of cardenolides to the HIF-1 inhibitory activity. In contrast, a hydroxyl group at any positions of C-15, C-16 and C-4' of cardenolides showed negative effects on suppressing HIF-1 transcriptional activity. In addition, these eight cardenolides also exhibited potent cytotoxic effects against human breast cancer cell MCF-7 (IC₅₀ values ranged from 30.5 to 68.8nM), but less toxic effects to human normal mammary epithelial cell MCF-10A (IC₅₀ values >20µM).

CONCLUSIONS

This is the first report of a comprehensive study of SAR on cardenolides from C. gigantea as HIF-1 inhibitors. Eight cardenolides (1, 3, 4, 6-8, 14 and 17) showed both potent HIF-1 inhibitory activity and strong cytotoxic effect against MCF-7 cancer cells in nanomolar level. The findings of these cardenolides provided important insights into the development of these potent HIF-1 inhibitors as anticancer drug.

Inhibition of IKK-β by epidioxysterols from the flowers of Calotropis gigantea (Niu jiao gua)

Background

Calotropis gigantea (Asclepiadaceae) (Niu jiao gua) has been used as a poultice in Chinese medicine for treating inflammatory skin diseases, e.g., neurodermatitis. This study aims to isolate the epidioxysterols from the flowers of C. gigantea, elucidate their structures and evaluate their possible inhibitory effects on the NF-κB pathway.

Methods

The two epidioxysterols 9,11-dehydroergosterol peroxide (1) and ergosterol peroxide (2) were isolated from the powdered flowers of C. gigantea by ultrasonic-assisted extraction, followed by the purification of the crude extract by column chromatography (i.e., silica gel and MCI-gel CHP 20P open columns). The chemical structures of these compounds were identified through a comparison of their HRMS, ¹H and ¹³C NMR data with those in the literature. The in vitro IKK-β inhibitory activities of compounds 1 and 2 (1–100 µM) were evaluated using an IKK α and β Assay/Inhibitor Screening Kit, which is a single-site, semi-quantitative immunoassay. Berberine was used as a positive control. The IKK-β inhibitory activities between compounds 1 and 2 were compared by a two-tailed Student’s t test to summarize the structure activity relationship.

Results

Compounds 1 and 2 exhibited a dose-dependent inhibitory activity towards IKK-β in a similar manner to that of berberine. The IKK-β inhibitory activities of these two epidioxysterols were significantly stronger (P = 0.001 for compound 1 and P = 0.028 for compound 2) than that of berberine at the concentration of 100 µM. Furthermore, at the same concentration the suppressive effect of compound 1 towards IKK-β was greater than that of compound 2 (P = 0.041), while their activities at 10 and 50 µM were comparable. The difference in the results at 100 µM therefore suggested that the double bond between C-9 and C-11 in compound 1 could be responsible for its higher inhibitory activity towards IKK-β at this concentration.

Conclusions

9,11-dehydroergosterol peroxide (1) and ergosterol peroxide (2) were isolated from the flowers of C. gigantea and exhibited in vitro inhibitory activities towards IKK-β.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-016-0081-1) contains supplementary material, which is available to authorized users.

Bioactivity guided isolation of oxypregnane-oligoglycosides (calotroposides) from the root bark of Calotropis gigantea as potent anticancer agents

Bioactivity guided isolation of oxypregnane-oligoglycosides (calotroposides) from the ethanolic extract of root bark of Calotropis gigantea (L.) Dryand. with purple flowers has been performed and isolated pure compounds has been evaluated for anticancer activity.

Phenanthroindolizidine alkaloids from Tylophora atrofolliculata with hypoxia-inducible factor-1 (HIF-1) inhibitory activity

Phenanthroindolizidine alkaloids from T. atrofolliculata with potent HIF-1 inhibitory effects.

In vitro anti-influenza virus activities of a new lignan glycoside from the latex of Calotropis gigantea

A new lignan glycoside, (+)-pinoresinol 4-O-[6″-O-vanilloyl]-β-d-glucopyranoside (1) and two known phenolic compounds, 6′-O-vanilloyltachioside (2) and 6′-O-vanilloylisotachioside (3) were isolated from the latex of Calotropis gigantea (Asclepiadaceae). The structure of the new compound was elucidated by using spectroscopic and chemical methods. Three isolates (1–3) and one authentic compound, (+)-pinoresinol 4-O-β-d-glucopyranoside, were screened for A/PR/8/34 (H1N1) inhibitory activity by cytopathic effect (CPE) inhibition assay on MDCK cells. Compound 1 showed inhibitory activity against A/PR/8/34 (H1N1). In sharp contrast, the other three compounds (2, 3 and (+)-pinoresinol 4-O-β-d-glucopyranoside) did not show such activity. An analysis of structure-activity relationship between 1 and (+)-pinoresinol 4-O-β-d-glucopyranoside revealed that the presence of a vanilloyl group in the sugar moiety of 1 is crucial for its anti-influenza virus activity. Compound 1 was further evaluated for in vitro inhibitory activities against a panel of human and avian influenza viruses by CPE inhibition assay. It showed inhibitory effect against human influenza viruses in both subtypes A and B (IC₅₀ values around 13.4–39.8 µM with SI values of 3.7–11.4), while had no effect on avian influenza viruses. Its antiviral activity against human influenza viruses subtype A was further confirmed by plaque reduction assay. The time course assay indicated that 1 exerts its antiviral activity at the early stage of viral replication. A mechanistic study showed that 1 efficiently inhibited influenza virus-induced activation of NF-κB pathway in a dose-dependent manner, but had no effect on virus-induced activation of Raf/MEK/ERK pathway. Further studies demonstrated that nuclear translocation of transcription factor NF-κB induced by influenza virus was significantly blocked by 1, meanwhile, nuclear export of viral ribonucleoproteins was also effectively inhibited. These findings suggest that this new lignan glycoside from Calotropis gigantea, may have therapeutic potential in influenza virus infection through inhibition of NF-κB pathway and viral ribonucleoproteins nuclear export.