Ursane-type pentacyclic triterpenoids as useful platforms to discover anticancer drugs

Recent advances in the chemistry and biology of oleanolic acid and its derivatives

The pentacyclic triterpenes represent a significant class of plant bioactives with a variety of structures and a wide array of biological activities. These are biosynthetically produced via the mevalonate pathway although occasionally mixed pathways may also occur to introduce structural divergence. Oleanolic acid is one of the most explored bioactive from this class of compounds and possesses a broad spectrum of pharmacological and biological activities including liver protection, anti-cancer, atherosclerosis, anti-inflammation, antibacterial, anti-HIV, anti-oxidative, anti-diabetic etc. This review provides an overview of the latest research findings, highlighting the versatile medicinal and biological potential of oleanolic and its future prospects.

Minor Hydroxylated Triterpenoids Produced in Engineered Yeast by the Enzymes OSC and CYP716s from the Plant Enkianthus chinensis and Their Anti-Inflammatory and Hepatoprotective Activities

Triterpenoids are a type of specialized metabolites that exhibit a wide range of biological activities. However, the availability of some minor triterpenoids in nature is limited, which has hindered our understanding of their pharmacological potential. To overcome this limitation, heterologous biosynthesis of triterpenoids in yeast has emerged as a promising and time-efficient production platform for obtaining these minor compounds. In this study, we analyzed the transcriptomic data of Enkianthus chinensis to identify one oxidosqualene cyclase (EcOSC) gene and four CYP716s. Through heterologous expression of these genes in yeast, nine natural pentacyclic triterpenoids, including three skeleton products (1-3) produced by one multifunctional OSC and six minor oxidation products (4-9) catalyzed by CYP716s, were obtained. Of note, we discovered that CYP716E60 could oxidize ursane-type and oleanane-type triterpenoids to produce 6β-OH derivatives, marking the first confirmed C-6β hydroxylation in an ursuane-type triterpenoid. Compound 9 showed moderate inhibitory activity against NO production and dose-dependently reduced IL-1β and IL-6 production at the transcriptional and protein levels. Compounds 1, 2, 8, and 9 exhibited moderate hepatoprotective activity with the survival rates of HepG2 cells from 61% to 68% at 10 μM.

Pentacyclic triterpene-amino acid derivatives induced apoptosis and autophagy in tumor cells, affected the JNK and PI3K/AKT/mTOR pathway

A series of pentacyclic triterpene-amino acid derivatives were synthesized and tested for anti-proliferative activity. The results showed that most of the target compounds had good anti-proliferative activity. 2c did not contain protecting groups and hydrochloride, had excellent cytotoxicity, so it had been selected for further study in the mechanism of action in T24 cells. The data from transcriptome sequencing indicated that 2c was found to be closely related to apoptosis and autophagy. Observation of fluorescence staining and analysis from flow cytometry demonstrated that 2c induced apoptosis and cause cell cycle arrest in S/G2 phase in T24 cells. Molecular mechanism studies exhibited that 2c induced apoptosis in the intrinsic and extrinsic pathways. 2c also induced cellular autophagy in T24 cells. Results from Western Blotting showed that 2c could activate JNK pathway and inhibit PI3K/AKT/mTOR pathway. In conclusion, 2c was deserved further investigation in the field of anti-tumor.

Self-assembled renewable nano-sized pentacyclic triterpenoid maslinic acids in aqueous medium for anti-leukemic, antibacterial and biocompatibility studies: An insight into targeted proteins-compound interactions based mechanistic pathway prediction through molecular docking

Maslinic acid is a naturally occurring dihydroxy, mono-carboxy bioactive triterpenoid. Its bulky structure was the main hindrance in the path of biological activity. Sodium and potassium salts of nano-sized triterpenoid maslinic acid were prepared from maslinic acid and its self-assembly property was studied in aqueous and aqueous-organic binary liquid mixtures. Morphology of the compounds studied by Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), High Resolution Transmission Electron Microscopy (HRTEM), Optical Microscopy, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) revealed vesicular morphology of the self-assemblies. Selective cytotoxicity was performed in leukemic (K-562 and KG-1a) and PBMC cells. Among the three self-assemblies (maslinic acid 1, sodium maslinate 2 and potassium maslinate 3), sodium maslinate 2 showed better antileukemic efficacy. Sodium maslinate 2 induced apoptosis in leukemic cells by elevating ROS levels and disrupting the cellular antioxidant system. From the in-silico studies, it was confirmed that 2 interacted with extrinsic and intrinsic apoptotic proteins of leukemic cells and killed those cells by inducing apoptotic pathways. The compounds 1, 2 and 3 showed significant antibacterial efficacy against E.coli strain through binding with several periplasmic membrane fusion protein (MFP) and limiting the efflux system leading to arrestation of antimicrobial resistance.

Determination of Pentacyclic Triterpenoids in Plant Biomass by Porous Graphitic Carbon Liquid Chromatography-Tandem Mass Spectrometry

Pentacyclic triterpenoids (PCTs), which possess a number of bioactive properties, are considered one of the most important classes of secondary plant metabolites. Their chromatographic determination in plant biomass is complicated by the need to separate a large number of structurally similar compounds belonging to several classes that differ greatly in polarity (monools, diols, and triterpenic acids). This study proposes a rapid, sensitive, and low-cost method for the simultaneous quantification of ten PCTs (3β-taraxerol, lupeol, β-amyrin, α-amyrin, betulin, erythrodiol, uvaol, betulinic, oleanolic, and ursolic acids) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) using porous graphitic carbon (Hypercarb) as a stationary phase capable of hydrophobic retention and specific interactions with analytes. Revealing the effects of the mobile phase composition, pH, ionic strength, and column temperature on retention and selection of chromatographic conditions on this basis allowed for the effective separation of all target analytes within 8 min in gradient elution mode and attaining limits of detection in the range of 4-10⁴ µg L^-1. The developed method was fully validated and successfully tested in the determination of PCTs in common haircap (Polytrichum commune) and prairie sphagnum (Sphagnum palustre) mosses, and fireweed (Chamaenerion angustifolium) stems and leaves.

Design, synthesis, and biological evaluation of new arjunolic acid derivatives as anticancer agents

Arjunolic acid (AA) is a pentacyclic triterpenoid with promising anticancer properties. A series of novel AA derivatives containing a pentameric A-ring with an enal moiety, combined with additional modifications at C-28, were designed and prepared. The biological activity on the viability of human cancer and non-tumor cell lines was evaluated in order to identify the most promising derivatives. Additionally, a preliminary study of the structure-activity relationship was carried out. The most active derivative, derivative 26, also showed the best selectivity between malignant cells and non-malignant fibroblasts. For compound 26, the anticancer molecular mechanism of action in PANC-1 cells was further studied and the results showed that this derivative induced a cell-cycle arrest at G0/G1 phase and significantly inhibited the wound closure rate of PANC-1 cancer cells in a concentration-dependent manner. Additionally, compound 26 synergistically increased the cytotoxicity of Gemcitabine, especially at a concentration of 0.24 μM. Moreover, a preliminary pharmacological study indicated that at lower doses this compound did not demonstrate toxicity in vivo. Taken together, these findings suggest that compound 26 may be a valuable compound for the development of new pancreatic anticancer treatment, and further studies are needed to explore its full potential.

Bioactive Usual and Unusual Triterpenoids Derived from Natural Sources Used in Traditional Medicine

Triterpenoids are accessible in several terrestrial plants as well as marine organisms, including sponges, algae, fungi, and sea cucumbers are examples of marine creatures. So far, more than 20,000 natural triterpenoids have exhibited several varied bioactivities, including anticancer, antimalarial, anti-HIV, inhibit HIF-1 activation, antibacterial, chemopreventive, anti-inflammatory, antioxidant, cardioprotective, antiviral, neuroprotective, hepatoprotective, insecticidal, antidiabetic, cytotoxic. Several plants are used in folklore medicine to treat numerous ailments, and the preparation or uses of traditional practices have been scientifically validated. Although various structural diversity has been observed in the triterpenoids, this review presents the sources and uses of those triterpenoids that showed significant biological activities which could be accessible and promoted to familiar people in the form of traditional medicine or for industrial, or pharmaceutical applications.

Pentacyclic Triterpenoids-Based Ionic Compounds: Synthesis, Study of Structure-Antitumor Activity Relationship, Effects on Mitochondria and Activation of Signaling Pathways of Proliferation, Genome Reparation and Early Apoptosis

The present research paper details the synthesis of novel ionic compounds based on triterpene acids (betulinic, oleanolic and ursolic), with these acids acting both as anions and connected through a spacer with various nitrogen-containing compounds (pyridine, piperidine, morpholine, pyrrolidine, triethylamine and dimethylethanolamine) and acting as a cation. Based on the latter, a large number of ionic compounds with various counterions (BF₄-, SbF₆-, PF₆-, CH₃COO-, C₆H₅SO₃-, m-C₆H₄(OH)COO- and CH₃CH(OH)COO-) have been synthesized. We studied the cytotoxicity of the synthesized compounds on the example of various tumor (Jurkat, K562, U937, HL60, A2780) and conditionally normal (HEK293) cell lines. IC50 was determined, and the influence of the structure and nature of the anion and cation on the antitumor activity was specified. Intracellular signaling, apoptosis induction and effects of the most active ionic compounds on the cell cycle and mitochondria have been discussed by applying modern methods of multiparametric enzyme immunoassay and flow cytometry.

Selected plant triterpenoids and their amide derivatives in cancer treatment: A review

Medicinal plants have been used to treat different diseases throughout the human history namely in traditional medicine. Most of the plants mentioned in this review article belong among them, including those that are widely spread in the nature, counted frequently to be food and nutrition plants and producing pharmacologically important secondary metabolites. Triterpenoids represent an important group of plant secondary metabolites displaying emerging pharmacological importance. This review article sheds light on four selected triterpenoids, oleanolic, ursolic, betulinic and platanic acid, and on their amide derivatives as important natural or semisynthetic agents in cancer treatment, and, in part, in pathogenic microbe treatment. A literature search was made in the Web of Science for the given key words covering the required area of secondary plant metabolites and their amide derivatives. The most recently published findings on the biological activity of the selected triterpenoids, and on the structures and biological activity of their relevant amide derivatives have been summarized therein. Mainly anti-cancer effects, and, in part, antimicrobial and other effects of the four selected triterpenoids and their amide derivatives have also been reviewed. A comparison of the effects of the parent plant products and those of their amide derivatives has been made.

Microbial-Catalyzed Baeyer-Villiger Oxidation for 3,4-seco-Triterpenoids as Potential HMGB1 Inhibitors

Pentacyclic triterpenoids are considered to be the potential HMGB1 inhibitors, but due to the limited number of hydrogen bond donors and the number of rotatable bonds in the rigid skeletons, their further chemical biology research with this target was restricted. To improve these profiles, microbial-catalyzed Baeyer-Villiger oxidation of the primary ursane and oleanane-type triterpenoids including uvaol (1), erythrodiol (2), oleanolic acid (3), and ursolic acid (4) was performed by Streptomyces olivaceus CICC 23628. As a result, ten new and one known A-ring cleaved metabolites were obtained and the possible biogenetic pathways were also discussed based on the HPLC-MS analysis. Furthermore, the direct interactions between compounds 1d, 2b, and HMGB1 were observed by the biolayer interferometry technique. Molecular docking revealed that the newly introduced vicinal diol at C-4, C-24, and the hydroxyl group at C-21 of compound 1d are crucial for binding with HMGB1. The cellular assay showed that co-treatment of 1d could significantly block HMGB1-activated nitric oxide release with an IC₅₀ value of 9.37 μM on RAW 264.7 cells. Altogether, our research provides some insights into 3,4-seco-triterpenes as potential anti-inflammatory candidates for the discovery of novel HMGB1 inhibitors.

Discovery of Natural Ursane-type SENP1 Inhibitors and the Platinum Resistance Reversal Activity Against Human Ovarian Cancer Cells: A Structure-Activity Relationship Study

Platinum-resistant ovarian cancer is one of the most common and refractory gynecologic cancers around the world. The SENP1/JAK2 (small ubiquitin-like modifier-specific protease 1/Janus activating kinase 2) axis activation has been proposed as a critical mechanism in platinum-resistant ovarian cancer, and as such, SENP1 inhibitors become a feasible alternative to reverse platinum resistance. In this work, 29 commercially available natural ursane-type aglycones were tested for their SENP1 inhibitory activities, among which 12 aglycones showed IC₅₀ activity at the concentration below 5 μM. Pomolic acid and tormentic acid were identified as potent SENP1 inhibitors with the IC₅₀ values of 5.1 and 4.3 μM, respectively. The structure-activity relationship (SAR) of ursane-type SENP1 inhibitors was evaluated. A molecular docking model of the SENP1-tormentic acid complex was obtained and applied to describe the SAR. Moreover, the combinations of cisplatin with pomolic acid (IC₅₀ = 3.69 μM, combination index (CI) = 0.23) and tormentic acid (IC₅₀ = 2.40 μM, CI = 0.30) exhibited potent platinum-resistant reversal activities to cisplatin only (IC₅₀ = 28.23 μM) against the human ovarian cancer SKOV3 cells. The data suggested a potential for pomolic acid and tormentic acid to be promising compounds for in vivo studies of platinum-resistant ovarian cancer with SENP1 activation.

A novel, differential mobility spectrometry tandem mass spectrometric method for the in vivo quantitation of ursolic acid

Ursolic acid (UA) is a naturally occurring pentacyclic triterpene widely distributed in fruits and plants. It is pharmacologically active and has the potential to be a useful therapeutic compound. To date, bioanalysis of UA has been limited by biomatrix interference and poor collision induced dissociation (CID) efficiency in tandem mass spectrometry. In this study, we developed a method based on liquid chromatography differential mobility spectrometry tandem mass spectrometry LC-DMS-MS/MS with multiple ion monitoring (MIM) for quantitation of UA in rat plasma. The method involves efficient sample preparation by solid phase extraction and requires only a limited volume of plasma (40 μL) to achieve linearity in the 1-100 ng/mL range with good accuracy and precision. The method was successfully applied to a pharmacokinetic study of orally administered UA in rat. The results indicate that LC-DMS-MS/MS with MIM is a useful strategy for the bioassay of UA suitable for high throughput analysis.

Elesesterpenes A–K: Lupane-type Triterpenoids From the Leaves of Eleutherococcus sessiliflorus

Elesesterpenes A–K (1–11), eleven new lupane-type triterpenoids, triterpenoid glycosides, and nortriterpenoid were isolated from the leaves of Eleutherococcus sessiliflorus. Their structures and relative configurations were completely elucidated by a combination of diverse methods including physical, spectroscopic data. The absolute configuration of elesesterpenes A–B (1–2) was defined by single-crystal X-ray diffraction. Meanwhile, all the isolates were evaluated for anti-inflammatory activities on lipopolysaccharide-induced nitric oxide production in BV2 microglial cells, and antiproliferative activities against human hepatoma (HepG2), human lung adenocarcinoma (A549), and human glioma cells (LN229) in vitro. It was found that some of them exhibited obvious anti-inflammatory activities and potent antiproliferative activities.

New pentacyclic triterpene from Potentilla atrosanguinea Lodd. as anticancer agent for breast cancer targeting estrogen receptor-α

One new (compound 3) along with two previously known ursane type triterpenoids (compounds 1 and 2) were purified by chromatographic techniques from ethyl acetate extract of aerial parts of Potentilla atrosanguniea and characterized by HRMS, 1 D and 2 D-NMR. Compounds 1 (ursolic acid), 2 (euscaphic acid) and 3 (3α,20α-dihydroxy 2-oxo-urs-12-en-28-oic acid) were tested for their antiproliferative activity along with standard bazedoxifene. Compounds 1 and 3 were found to be of higher activity (3.71 and 6.05 μg/mL) as compared to compound 2 and bazedoxifene (IC₅₀: 24.53 and 17.87 μg/mL). Anti-estrogenic activity of three compounds on breast cancer (BC) were studied in vitro by accessing their antiproliferative activity and binding with estrogen receptor alpha (ER-α). All three compounds have effective binding affinity towards ER-α and decreased cell growth by downregulating the expression of mRNA and its translational protein as tested by semi-qRT-PCR and western blotting. In terms of effectiveness compounds 1 and 3 were found more active due to their antiproliferative, and antiestrogenic activity as compared to standard bazedoxifene.

3-Pyridinylidene Derivatives of Chemically Modified Lupane and Ursane Triterpenes as Promising Anticancer Agents by Targeting Apoptosis

Cancer persists as a global challenge due to the extent to which conventional anticancer therapies pose high risks counterbalanced with their therapeutic benefit. Naturally occurring substances stand as an important safer alternative source for anticancer drug development. In the current study, a series of modified lupane and ursane derivatives was subjected to in vitro screening on the NCI-60 cancer cell line panel. Compounds 6 and 7 have been identified as highly active with GI₅₀ values ranging from 0.03 µM to 5.9 µM (compound 6) and 0.18–1.53 µM (compound 7). Thus, these two compounds were further assessed in detail in order to identify a possible antiproliferative mechanism of action. DAPI (4′,6-diamidino-2-phenylindole) staining revealed that both compounds induced nuclei condensation and overall cell morphological changes consistent with apoptotic cell death. rtPCR analysis showed that both compounds induced upregulation of proapoptotic Bak and Bad genes while downregulating Bcl-XL and Bcl-2 antiapoptotic genes. Molecular docking analysis revealed that both compounds exhibited high scores for Bcl-XL inhibition, while compound 7 showed higher in silico Bcl-XL inhibition potential as compared to the native inhibitor ATB-737, suggesting that compounds may induce apoptotic cell death through targeted antiapoptotic protein inhibition, as well.

Two new cytotoxic ursane triterpenoids from the aerial parts of Salvia urmiensis Bunge

Bioassay-guided fractionation of a dichloromethane extract of the aerial parts of Salvia urmiensis, an endemic plant species of Iran, led to the isolation of two new cytotoxic ursane triterpenoids, Salvurmin A and Salvurmin B. Their structures were elucidated by a combination of 1D and 2D NMR, HR-ESI-MS, IR and UV analysis. Cytotoxicity of the above-mentioned compounds were evaluated against two human cancerous cell lines (SW1116, MCF-7). IC₅₀ values for Salvurmin A and Salvurmin B on colon cancer cell line (SW1116) were 41.6 ± 2.6 and 23.2 ± 0.4 μM respectively, in comparison to cisplatin as control positive. In addition, these two compounds exhibited cytotoxic activity on breast cancer cell line (MCF-7) with an IC₅₀ of 54.2 ± 5.3 and 40.2 ± 3.1 μM for Salvurmin A and Salvurmin B, respectively. The cytotoxic activities of these two compounds present a promising potential for the future investigation on this endemic species of Salvia.

Screening and semi-quantitative determination of pentacyclic triterpenoids in plants by liquid chromatography-tandem mass spectrometry in precursor ion scan mode

INTRODUCTION

Pentacyclic triterpenoids (PCTs) are secondary plant metabolites. They are of exceptional interest as biologically active substances and raw materials for a wide range of medications. Thus, the development of a methodology for rapid screening of PCTs in plant biomass is an important task.

OBJECTIVE

The goal of this work was to develop an approach for simultaneous screening and semi-quantitative determination of PCTs in plant tissues by liquid chromatography-tandem mass spectrometry with a precursor ion scan (PrecIS).

MATERIALS AND METHODS

Pressurised liquid extraction (PLE) with methanol was used for the isolation of PCTs from plant biomass. Screening and semi-quantitative determination of PCTs in the obtained extracts were carried out by reversed phase high-performance liquid chromatography-tandem mass spectrometry in a PrecIS mode.

RESULTS

The product ion at m/z 95 with collision energy of 40 V was used as a diagnostic ion to identify PCTs by the PrecIS mode. In plant materials, 26 PCTs and their derivatives, such as PCTs esters and glycosides, were detected and identified. Calculation of the relative response factor for nine available PCTs showed that using a betulin calibration curve allows us to estimate the semi-quantitative content of PCTs and their derivatives in plant PLE extracts.

CONCLUSION

The developed approach can be applied for simultaneous untargeted screening and semi-quantitative determination of PCTs and their derivatives in various plants at sub-parts per million levels.

Oxygenated pentacyclic triterpenoids from the stems and branches of Enkianthus chinensis

Thirty new pentacyclic triterpenoids, including five oleanane-type (1-5), twenty-three ursane-type (9-23, 26-33) and two taraxerane-type (24 and 25), along with fourteen known triterpenoids, were isolated from the stems and branches of Enkianthus chinensis. Their structures were elucidated by extensive spectroscopic analyses, X-ray crystallographic data and electronic circular dichroism (ECD) techniques. Sixteen compounds (1-5, 9-13, 20, 22, 32, 34-36) bearing a gem-hydroxymethyl group at C-4 represent rare examples of pentacyclic triterpenoids. In the in vitro biological activity evaluation, compounds 8, 9, 12-14, 17, 24, and 44 exhibited potent hepatoprotective effects at 10 μM. Moreover, compound 25 showed latent activity against HSV-1 with an IC₅₀ value of 6.4 μM.

Natural Compounds in Sex Hormone-Dependent Cancers: The Role of Triterpenes as Therapeutic Agents

Sex hormone-dependent cancers currently contribute to the high number of cancer-related deaths worldwide. The study and elucidation of the molecular mechanisms underlying the progression of these tumors was a double-edged sword, leading to the expansion and development of new treatment options, with the cost of triggering more aggressive, therapy resistant relapses. The interaction of androgen, estrogen and progesterone hormones with specific receptors (AR, ER, PR) has emerged as a key player in the development and progression of breast, ovarian, prostate and endometrium cancers. Sex hormone-dependent cancers share a common and rather unique carcinogenesis mechanism involving the active role of endogenous and exogenous sex hormones to maintain high mitotic rates and increased cell proliferation thus increasing the probability of aberrant gene occurrence and accumulation highly correlated with abnormal cell division and the occurrence of malignant phenotypes. Cancer related hormone therapy has evolved, currently being associated with the blockade of other signaling pathways often associated with carcinogenesis and tumor progression in cancers, with promising results. However, despite the established developments, there are still several shortcomings to be addressed. Triterpenes are natural occurring secondary metabolites biosynthesized by various pathways starting from squalene cyclization. Due to their versatile therapeutic potential, including the extensively researched antiproliferative effect, these compounds are most definitely a cornerstone in the research and development of new natural/semisynthetic anticancer therapies. The present work thoroughly describes the ongoing research related to the antitumor activity of triterpenes in sex hormone-dependent cancers. Also, the current review highlights both the biological activity of various triterpenoid compounds and their featured mechanisms of action correlated with important chemical structural features.

Novel bioactive properties of low-polarity fractions from sea-buckthorn extracts (Elaeagnus rhamnoides (L.) A. Nelson) - (in vitro)

Due to the richness of bioactive substances and easy accessibility, sea-buckthorn can be an ingredient of currently popular functional food supporting anti-cancer therapy. Low-polarity fractions from fruit (OL), twigs (GL) and leaves (LL) were investigated. Compared to the previous scientific reports a more detailed analysis of the chemical composition of individual fractions was performed. Cytotoxicity of low-polarity fractions has been investigated and activity compared in human tumor and normal cells cultured in vitro. The genotoxicity and pro-apoptotic properties of low-polarity fractions were also followed on selected cell lines that had proved to be the most sensitive. In the proposed research model being tested, low-polarity fractions act cytotoxically, even 3 times more strongly in cancer cells than normal ones. Measurement of caspase 3/7 activity indicated that cell death occurs through apoptosis. Furthermore, high concentrations of low-polarity fractions have moderate genotoxic properties. Data obtained on the biological properties of low-polarity fractions from sea-buckthorn show that these fractions can potentially support cancer cells elimination. Phytotochemical analysis indicates the key role of the triterpenoids in this process.

Hydroxylated Ethacrylic and Tiglic Acid Derivatives from the Stems and Branches of Enkianthus chinensis and Their Potential Anti-inflammatory Activities

Two new hydroxylated ethacrylic acid derivatives (compounds 1 and 2) and 11 new hydroxylated tiglic acid derivatives (compounds 3-13), together with one known compound (compound 14), were isolated from the stems and branches of Enkianthus chinensis. Their structures were established by extensive spectroscopic analyses, while their absolute configurations were determined by X-ray crystallographic methods (compounds 1 and 2), Mo₂(OAc)₄-induced electronic circular dichroism experiments (compounds 3 and 4), and chemical methods (compounds 5-11). This study is the first investigation on the secondary metabolites of this species. The anti-inflammatory activities of all isolated compounds were evaluated in an LPS-induced mouse peritoneal macrophage model. Notably, compounds 3 and 12 both exerted potent inhibitory effects on NO production with IC₅₀ values of 2.9 and 1.2 μM, respectively.

Design, Synthesis, and Biological Evaluation of Two Series of Novel A-Ring Fused Steroidal Pyrazines as Potential Anticancer Agents

BACKGROUND

Increasingly, different heterocyclic systems have been introduced into the steroid nucleus to significantly enhance the antitumor activities of steroid molecules. However, in this study, few literature precedents describing the pyrazine heterocyclic-condensed modification to an A-ring of steroid monomers were found, although the pyrazine group is thought to be essential for the potent anticancer activity of clinically relevant drugs and natural steroid dimers.

METHODS AND RESULTS

Two series of novel A-ring fused steroidal pyrazines were designed and efficiently synthesized from commercially available progesterone via key α-ketoenol intermediates. Through a cell counting kit-8 cytotoxic assay of 36 derivatives for three tumor cells, 14 compounds displayed significant antiproliferative activity compared to 5-fluorouracil, especially for human prostatic tumor cells (PC-3) in vitro. Further mechanistic studies indicated that the most active compound, 12n (IC₅₀, 0.93 μM; SI, 28.71), could induce the cell apoptosis of PC-3 cells in a dose-dependent manner and cause cell cycle arrest in the G2/M phase. The molecular docking study suggested that compound 12n fitted the active sites of cytochrome P450 17A1 (6CIZ) well.

CONCLUSIONS

12n might serve as a promising lead compound for the development of novel anticancer drugs. This facile ring-closing strategy may provide a novel and promising avenue for the cycloaddition reaction of the steroidal skeleton through α-ketoenol intermediates.

Synthesis and biological evaluation of triterpenoid thiazoles derived from betulonic acid, dihydrobetulonic acid, and ursonic acid

In this work, 35 new derivatives of betulonic, dihydrobetulonic and ursonic acid were prepared including 30 aminothiazoles and all of them were tested for their in vitro cytotoxic activity in eight cancer cell lines and two non-cancer fibroblasts. Compounds with the IC₅₀ below 5 μM in CCRF-CEM cells and low toxicity in non-cancer fibroblasts (4m, 5c, 5m, 6c, 6m, 7b, and 7c) were further subjected to tests of pharmacological parameters yielding the final set for advanced biological evaluation (4m, 5m, 6m, and 7b). It was proved by several methods, that all of them trigger apoptosis via the intrinsic pathway and derivatives 5m and 7b are the most effective (IC₅₀ 2.4 μM and 3.6 μM). They are the best candidates to become potentially new anticancer drugs and will be subjected to in vivo tests in mice. In addition, compounds 6b and 6c deserve more attention because their activity is not limited only to chemosensitive CCRF-CEM cell line. Specifically, compound 6b is highly active against K562 leukemic cell line (0.7 μM) and its IC₅₀ activity in colon cancer HCT116 cell line is 1.0 μM. Compound 6c is active in both normal K562 and resistant K562-TAX cell lines (IC₅₀ 3.4 μM and 5.4 μM) and both colon cancer cell lines (HCT116 and HCT116p53^-/-, IC₅₀ 3.5 μM and 3.4 μM).

Loading AKBA on surface of silver nanoparticles to improve their sedative-hypnotic and anti-inflammatory efficacies

Aim: Acetyl-11-keto-β-boswellic acid (AKBA) is a potent anti-inflammatory compound limited by its low water solubility and bioavailability. To load AKBA on silver nanoparticles (AgNPs) to improve bioavailability and water solubility of the compound. Materials & methods: AKBA-AgNPs were chemically synthesized and characterized by UV-Vis spectrophotometry, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. AKBA and AKBA-Ag were studied for their sedative-hypnotic and anti-inflammatory efficacies. Results: Pretreatment with AKBA or AKBA-Ag caused significant dose-dependent sedative-hypnotic effects at 5 and 10 mg/kg intraperitoneal. The effects of AKBA-loaded AgNPs caused pronounced changes in mice compared with those of AKBA, and the AKBA-AgNPs demonstrated anti-inflammatory effects that were superior to those of AKBA. Conclusion: The loading of AKBA on nanoparticles improved its pharmacokinetic effects, and capacity for drug delivery.

Deep insights into the response of human cervical carcinoma cells to a new cyano enone-bearing triterpenoid soloxolone methyl: a transcriptome analysis

Semisynthetic triterpenoids, bearing cyano enone functionality in ring A, are considered now as novel promising anti-tumor agents. However, despite the large-scale studies, their effects on cervical carcinoma cells and, moreover, mechanisms underlying cell death activation by such compounds in this cell type have not been fully elucidated. In this work, we attempted to reconstitute the key pathways and master regulators involved in the response of human cervical carcinoma KB-3-1 cells to the novel glycyrrhetinic acid derivative soloxolone methyl (SM) by a transcriptomic approach. Functional annotation of differentially expressed genes, analysis of their cis^- regulatory sequences and protein-protein interaction network clearly indicated that stress of endoplasmic reticulum (ER) is the central event triggered by SM in the cells. A range of key ER stress sensors and transcription factor AP-1 were identified as upstream transcriptional regulators, controlling the response of the cells to SM. Additionally, by using Gene Expression Omnibus data, we showed the ability of SM to modulate the expression of key genes involved in regulation of the high proliferative rate of cervical carcinoma cells. Further Connectivity Map analysis revealed similarity of SM's effects with known ER stress inducers thapsigargin and geldanamycin, targeting SERCA and Grp94, respectively. According to the molecular docking study, SM could snugly fit into the active sites of these proteins in the positions very close to that of both inhibitors. Taken together, our findings provide a basis for the better understanding of the intracellular processes in tumor cells switched on in response to cyano enone-bearing triterpenoids.

Design and synthesis of pentacyclic triterpene conjugates and their use in medicinal research

Triterpenoids are natural products from plants and many other organisms that have various biological activities, such as antitumor, antiviral, antimicrobial, and protective activities. This review covers the synthesis and biological evaluation of pentacyclic triterpene (PT) conjugates with other molecules that have been found to increase the IC₅₀ or improve the pharmacological profile of the parent PT. Some of these molecules are designed to target specific proteins or cellular organelles, which has resulted in highly selective lead structures for drug development. Other PT conjugates are useful for investigating their mechanism of action. This concept has been very successful: 1) Many compounds, especially mitochondria-targeting PT conjugates, have reached a selective cytotoxicity at low nanomolar concentrations in cancer cells. 2) A number of PT conjugates have had high activity against HIV or the influenza virus. 3) Fluorescent PT conjugates have been able to visualize the PT in living cells, which has allowed quantification of the uptake and distribution of the PT within the cell. 4) Biotinylated PT conjugates have been used to identify target proteins, which may help to show their mechanism of action. 5) A large number of PT conjugates with polyethylene glycol (PEG), polyamines, etc. form nanometer-sized micelles that have a much better pharmacological profile than the PT alone. In summary, the connection of a PT to an appropriate modifying molecule has resulted in extremely useful semisynthetic compounds with a high potential to treat cancer or viral infections or compounds that are useful for the study of the mechanism of action of PTs at the molecular level.

Madecassic Acid Derivatives as Potential Anticancer Agents: Synthesis and Cytotoxic Evaluation

A series of novel madecassic acid (1) derivatives was synthesized, and their cytotoxicity was evaluated against the NCI-60 panel of cancer cell lines. Several analogues exhibited broad-spectrum cytotoxic activities over all nine tumor types represented in the panel, with more potent antiproliferative activities observed against selected cancer cell lines, including multidrug-resistant phenotypes. Among them, compound 29 showed GI50 (50% growth inhibition) values ranging from 0.3 to 0.9 μM against 26 different tumor cell lines and selectivity for one colon (COLO 205) and two melanoma (SK-MEL-5 and UACC-257) cell lines at the TGI (total growth inhibition) level. The mode of action of 29 was predicted by CellMiner bioinformatic analysis and confirmed by biochemical and cell-based experiments to involve inhibition of the DNA replication process, particularly the initiation of replication, and disruption of mitochondrial membrane potential. The present findings suggest this novel madecassic acid derivative may have potential as an anticancer therapeutic lead for both solid and hematological tumors.

Synthesis and Antiproliferative Activity of Novel A-Ring Cleaved Glycyrrhetinic Acid Derivatives

A series of new glycyrrhetinic acid derivatives was synthesized via the opening of its ring A along with the coupling of an amino acid. The antiproliferative activity of the derivatives was evaluated against a panel of nine human cancer cell lines. Compound 17 was the most active compound, with an IC50 of 6.1 µM on Jurkat cells, which is 17-fold more potent than that of glycyrrhetinic acid, and was up to 10 times more selective toward that cancer cell line. Further biological investigation in Jurkat cells showed that the antiproliferative activity of compound 17 was due to cell cycle arrest at the S phase and induction of apoptosis.

Lupeol, a Dietary Triterpene, Enhances Wound Healing in Streptozotocin-Induced Hyperglycemic Rats with Modulatory Effects on Inflammation, Oxidative Stress, and Angiogenesis

Impaired wound healing is a debilitating complication of diabetes that leads to significant morbidity, particularly foot ulcers. Natural products have shown to be effective in treating skin wounds. Lupeol is known to stimulate angiogenesis, fibroblast proliferation, and expressions of cytokines and growth factors involved in wound healing. The study is performed to evaluate the wound healing activity of lupeol in streptozotocin-induced hyperglycemic rats by macroscopical, histological, immunohistochemical, immunoenzymatic, and molecular methods. Percentage of wound closure and contraction was increased in the lupeol-treated group when compared to the Lanette group. Histopathological observation revealed decreased inflammatory cell infiltration and increased proliferation of fibroblasts, vascularization, and deposition of collagen fibers after lupeol treatment. Immunohistochemical analyses showed decreased intensity of NF-κB and increased intensity of FGF-2, TGF-β1, and collagen III. ELISA results revealed downregulated IL-6 levels and upregulated IL-10 levels in response to lupeol. The mRNA expression levels of Hif-1α, Sod-2, and Ho-1 were significantly increased in response to lupeol as compared to Lanette whereas Nf-κb and Vegf-A levels were decreased in relation to insulin and lupeol treatment. These findings indicate that lupeol possesses wound healing potential in hyperglycemic conditions and may be useful as a treatment for chronic wounds in diabetic patients.

The Antioxidant from Ethanolic Extract of Rosa cymosa Fruits Activates Phosphatase and Tensin Homolog In Vitro and In Vivo: A New Insight on Its Antileukemic Effect

Rosa cymosa Tratt is a Chinese herbal remedy that is used in the treatment of diarrhea, burns, rheumatoid arthritis, and hemorrhage. Despite its use in Asian folk medicine, there are limited reports on the biological activity of R. cymosa fruits. This study focused on the investigation of the antitumor effect of the antioxidative ethanolic extract of R. cymosa fruits (RCE) along with its underlying mechanism of action. RCE showed a potent cytotoxic effect against Sup-T1 and Molt-4 lymphoblastic leukemia cells. In the xenograft animal model, the tumor size was significantly reduced to about 59.42% in the RCE-treated group in comparison with the control group. The use of RCE (37.5, 75, or 150 μg/mL) triggered apoptosis by 26.52–83.49%, disrupted mitochondrial membrane potential (MMP) by 10.44–58.60%, and promoted calcium release by 1.29-, 1.44-, and 1.71-fold compared with the control group. The extract induced redox oxygen species (ROS) generation through the elimination of Nrf2/Keap1/P62-mediated oxidative stress response. The loss of phosphatase and tensin homolog (PTEN) activation by RCE impaired PI3K/Akt/Foxo and Jak/Stat activation pathways, which contributed to tumorigenesis. These multiple targets of R. cymosa against hematologic cancer cells suggested its potential application as an antileukemic dietary supplement.

Oxidosqualene cyclase and CYP716 enzymes contribute to triterpene structural diversity in the medicinal tree banaba

Pentacyclic triterpenes (PCTs) represent a major class of bioactive metabolites in banaba (Lagerstroemia speciosa) leaves; however, biosynthetic enzymes and their involvement in the temporal accumulation of PCTs remain to be studied. We use an integrated approach involving transcriptomics, metabolomics and gene function analysis to identify oxidosqualene cyclases (OSCs) and cytochrome P450 monooxygenases (P450s) that catalyzed sequential cyclization and oxidative reactions towards PCT scaffold diversification. Four monofunctional OSCs (LsOSC1,3-5) converted the triterpene precursor 2,3-oxidosqualene to either lupeol, β-amyrin or cycloartenol, and a multifunctional LsOSC2 formed α-amyrin as a major product along with β-amyrin. Two CYP716 family P450s (CYP716A265, CYP716A266) catalyzed C-28 oxidation of α-amyrin, β-amyrin and lupeol to form ursolic acid, oleanolic acid and betulinic acid, respectively. However, CYP716C55 catalyzed C-2α hydroxylation of ursolic acid and oleanolic acid to produce corosolic acid and maslinic acid, respectively. Besides, combined transcript and metabolite analysis suggested major roles for the LsOSC2, CYP716A265 and CYP716C55 in determining leaf ursane and oleanane profiles. Combinatorial expression of OSCs and CYP716s in Saccharomyces cerevisiae and Nicotiana benthamiana led to PCT pathway reconstruction, signifying the utility of banaba enzymes for bioactive PCT production in alternate plant/microbial hosts that are more easily tractable than the tree species.

Ursolic Acid Induces Apoptotic Cell Death Through AIF and Endo G Release Through a Mitochondria-dependent Pathway in NCI-H292 Human Lung Cancer Cells In Vitro

BACKGROUND/AIM

Ursolic acid (UA), a triterpene compound present in natural plants, has been shown to induce cytotoxic effects on many human cancer cells through induction of cell-cycle arrest and apoptosis. This study investigated the effects of UA on human lung cancer NCI-H292 cells in vitro.

MATERIALS AND METHODS

Flow cytometric assay was used to measure the percentage of cell viability, apoptotic cell death by double staining of annexin V and propidium iodide (PI), production of reactive oxygen species (ROS) and Ca2+, and mitochondriaI membrane potential (Ψm). UA-induced chromatin condensation and DNA fragmentation were examined by 4',6-diamidino-2-phenylindole staining and DNA gel electrophoresis, respectively. Western blotting was used to examine the changes of apoptosis-associated protein expression in NCI-H292 cells.

RESULTS

UA reduced cell viability and induced apoptotic cell death. UA increased Ca2+ production, reduced Ψm, but did not affect ROS production in NCI-H292 cells. UA increased apoptosis-inducing factor (AIF) and endonuclease G in NCI-H292 cells.

CONCLUSION

Based on these observations, we suggest UA induces apoptotic cell death via AIF and Endo G release through a mitochondria-dependent pathway in NCI-H292 cells.

Synthesis and Antiproliferative Activity of Novel Heterocyclic Glycyrrhetinic Acid Derivatives

A new series of glycyrrhetinic acid derivatives has been synthesized via the introduction of different heterocyclic rings conjugated with an α,β-unsaturated ketone in its ring A. These new compounds were screened for their antiproliferative activity in a panel of nine human cancer cell lines. Compound 10 was the most active derivative, with an IC₅₀ of 1.1 µM on Jurkat cells, which is 96-fold more potent than that of glycyrrhetinic acid, and was 4-fold more selective toward that cancer cell line. Further biological studies performed in Jurkat cells showed that compound 10 is a potent inducer of apoptosis that activates both the intrinsic and extrinsic pathways.

Non-volatile natural products in plant glandular trichomes: chemistry, biological activities and biosynthesis

The investigation methods, chemistry, bioactivities, and biosynthesis of non-volatile natural products involving 489 compounds in plant glandular trichomes are reviewed.