Potent immunosuppressive principles, dimeric sesquiterpene thioalkaloids, isolated from nupharis rhizoma, the rhizoma of Nuphar pumilum (nymphaeaceae): structure-requirement of nuphar-alkaloid for immunosuppressive activity

Functionalized magnetic particles coupled with LC-MS strategy facilitated discovery of trace thioalkaloids with potent immunosuppressive activity

Trace natural products (TNPs) are still the vital source of drug development. However, the mining of novel TNPs is becoming increasingly challenging due to their low abundance and complex interference. A comprehensive strategy was proposed in which the functionalized magnetic particles integrated with LC-MS for TNPs discovery. Under the guidance of the approach, fifteen trace Nuphar alkaloids including seven new ones, cyanopumiline A sulfoxide (1), cyanopumiline C sulfoxide (8) and cyanopumilines A-E (4-5, 10, 12-13) featuring an undescribed nitrile-containing 6/6/5/6/6 pentacyclic ring system were isolated from the rhizomes of Nuphar pumila. Their structures and absolute configurations were determined on the basis of detailed spectroscopic data analysis and single-crystal X-ray diffraction analysis. Notably, a concise method based on 13C NMR spectroscopy was established to determine the relative configurations of spiroatoms. Biologically, compounds 1-12 exhibited potent immunosuppressive activities with IC50 values ranging from 0.1-12.1 μM against anti-CD3/CD28 induced human peripheral T cell proliferation. Mechanistic studies revealed that 4 could dose-dependently decrease pro-inflammatory cytokines and the expression levels of CD25 and CD71.

The biological activities of quinolizidine alkaloids

Quinolizidine alkaloids isolated from various marine and terrestrial animals and plants are primarily composed of lupinine-, matrine-, and sparteine-type alkaloids. Matrine, phenanthroquinolizidines, bis-quinolizidines, and small molecules from amphibian skins are representative compounds of such alkaloids. Quinolizidine alkaloids harbor anticancer, antibacterial, antiinflammatory, antifibrosis, antiviral, and anti-arrhythmia. In this chapter, we comprehensively outline the biological activity and pharmacological action of quinolizidine alkaloids and discuss new avenues toward the discovery of novel and more efficient drugs based on these naturally occurring compounds. It is urgent for basic research and clinical practice to conduct more targeted comprehensive research based on the lead drugs of quinolizidine alkaloids with significant pharmacological activity.

Inhibition of Cysteine Proteases by 6,6'-Dihydroxythiobinupharidine (DTBN) from Nuphar lutea

The specificity of inhibition by 6,6′-dihydroxythiobinupharidine (DTBN) on cysteine proteases was demonstrated in this work. There were differences in the extent of inhibition, reflecting active site structural-steric and biochemical differences. Cathepsin S (IC₅₀ = 3.2 μM) was most sensitive to inhibition by DTBN compared to Cathepsin B, L and papain (IC₅₀ = 1359.4, 13.2 and 70.4 μM respectively). DTBN is inactive for the inhibition of M^pro of SARS-CoV-2. Docking simulations suggested a mechanism of interaction that was further supported by the biochemical results. In the docking results, it was shown that the cysteine sulphur of Cathepsin S, L and B was in close proximity to the DTBN thiaspirane ring, potentially forming the necessary conditions for a nucleophilic attack to form a disulfide bond. Covalent docking and molecular dynamic simulations were performed to validate disulfide bond formation and to determine the stability of Cathepsins-DTBN complexes, respectively. The lack of reactivity of DTBN against SARS-CoV-2 M^pro was attributed to a mismatch of the binding conformation of DTBN to the catalytic binding site of M^pro. Thus, gradations in reactivity among the tested Cathepsins may be conducive for a mechanism-based search for derivatives of nupharidine against COVID-19. This could be an alternative strategy to the large-scale screening of electrophilic inhibitors.

Novel natural product therapeutics targeting both inflammation and cancer

Inflammation is recently recognized as one of the hallmarks of human cancer. Chronic inflammatory response plays a critical role in cancer development, progression, metastasis, and resistance to chemotherapy. Conversely, the oncogenic aberrations also generate an inflammatory microenvironment, enabling the development and progression of cancer. The molecular mechanisms of action that are responsible for inflammatory cancer and cancer-associated inflammation are not fully understood due to the complex crosstalk between oncogenic and pro-inflammatory genes. However, molecular mediators that regulate both inflammation and cancer, such as NF-κB and STAT have been considered as promising targets for preventing and treating these diseases. Recent works have further demonstrated an important role of oncogenes (e.g., NFAT1, MDM2) and tumor suppressor genes (e.g., p53) in cancer-related inflammation. Natural products that target these molecular mediators have shown anticancer and anti-inflammatory activities in preclinical and clinical studies. Sesquiterpenoids (STs), a class of novel plant-derived secondary metabolites have attracted great interest in recent years because of their diversity in chemical structures and pharmacological activities. At present, we and other investigators have found that dimeric sesquiterpenoids (DSTs) may exert enhanced activity and binding affinity to molecular targets due to the increased number of alkylating centers and improved conformational flexibility and lipophilicity. Here, we focus our discussion on the activities and mechanisms of action of STs and DSTs in treating inflammation and cancer as well as their structure-activity relationships.

Total Synthesis of Unsymmetrically Oxidized Nuphar Thioalkaloids via Copper-Catalyzed Thiolane Assembly

An asymmetric total synthesis of (+)-6-hydroxythiobinupharidine (1b) and (-)-6-hydroxythionuphlutine (2b), a set of hemiaminal containing dimeric sesquiterpenes isolated from yellow water lilies of the Nuphar genus, is described. The central bis-spirocyclic tetrahydrothiophene ring was forged through the Stevens rearrangement of a sulfonium ylide, generated in situ from the coupling of a copper-carbene with a spirocyclic thietane. This strategy diverges both from the proposed biosynthesis1 and previous syntheses of this family of alkaloids,2,3 all of which employ dimerization of symmetric monomers to form the aforementioned thiaspirane. The coupling of unsymmetrical monomers allowed access to the unsymmetrically oxidized product 2b for the first time.

Search for Novel Antibacterial Compounds and Targets

Drug-resistant bacteria including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Pseudomonas aeruginosa, and vancomycin-resistant enterococci (VRE) have been spreading; however, the development of new antibacterial drugs has not progressed accordingly. Novel antibacterial drugs or their candidate seeds need to be developed for effective antibiotic therapy. Under these conditions, the search for novel compounds and novel targets is important. In Okayama University, as a part of the Drug Discovery for Intractable Infectious Diseases project, we are proceeding with the development of antibacterial drugs for the treatment of drug-resistant bacterial infections. We found that riccardin C (a natural product of liverwort) and 6,6'-dihydroxythiobinupharidine (from the crude drug Senkotsu) exhibited strong antibacterial activities, particularly against Gram-positive bacteria. We showed that riccardin C induced cell membrane leakage and that 6,6'-dihydroxythiobinupharidine inhibited DNA topoisomerase IV. Moreover, 6,6'-dihydroxythiobinupharidine exerted synergistic effects with already known anti-MRSA drugs as well as with vancomycin for VRE.

Total Syntheses and Biological Evaluation of Both Enantiomers of Several Hydroxylated Dimeric Nuphar Alkaloids

Herein, we describe the first total syntheses of five members of the dimeric nuphar alkaloids: (+)-6,6'-dihydroxythiobinupharidine (+)-1 a, (+)-6-hydroxythiobinupharidine (+)-1 b, (-)-6,6'-dihydroxythionuphlutine (-)-2 a, (-)-6,6'-dihydroxyneothiobinupharidine (-)-3 a, and (+)-6,6'-dihydroxyneothionuphlutine (+)-4 a. The latter two have not been found in nature. We have also made each of their enantiomers (-)-1 a-b, (+)-2 a, (+)-3 a, and (-)-4 a. The key step in these syntheses was the dimerization of an α-aminonitrile (a hydrolytically stable surrogate for its corresponding hemiaminal) with chiral Lewis acid complexes. We have also reassigned the literature structures of (+)-1 a-1 b—for those instances in which the NMR spectra were obtained in CD3OD—to their corresponding CD3O-adducts. Our efforts provide for the first time apoptosis data for (-)-3 a, (+)-4 a, and all five non-natural enantiomers prepared. The data indicate high apoptotic activity regardless of the enantiomer or relative stereochemical configuration at C7 and C7'.

Action mechanism of 6, 6'-dihydroxythiobinupharidine from Nuphar japonicum, which showed anti-MRSA and anti-VRE activities

BACKGROUND

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE), cause serious infections at clinical sites, for which the development of new drugs is necessary. We screened candidates for new antibiotics and investigated its action mechanism.

METHODS

An antimicrobial compound was isolated from an extract of Nuphar japonicum. Its chemical structure was determined by NMR, MS, and optical rotation. We measured its minimum inhibitory concentration (MIC) using the microdilution method. The effects of the compound on DNA gyrase and DNA topoisomerase IV were investigated with DNA supercoiling, decatenation, and cleavage assay.

RESULTS

We isolated and identified 6,6'-dihydroxythiobinupharidine as the antimicrobial compound. The MIC of this compound was 1-4 μg/mL against various MRSA and VRE strains. We also demonstrated that this compound inhibited DNA topoisomerase IV (IC50 was 10-15 μM), but not DNA gyrase in S. aureus, both of which are known to be the targets of quinolone antibiotics and necessary for DNA replication. However, this compound only exhibited slight cross-resistance to norfloxacin-resistant S. aureus, which indicated that DTBN might inhibit other targets besides topoisomerase IV. These results suggest that 6,6'-dihydroxythiobinupharidine may be a potent candidate or seed for novel antibacterial agents.

CONCLUSIONS

DTBN from N. japonicum showed anti-MRSA and anti-VRE activities. DTBN might be involved in the inhibition of DNA topoisomerase IV.

GENERAL SIGNIFICANCE

DTBN might be useful as a seed compound. The information on the inhibition mechanism of DTBN will be useful for the modification of DTBN towards developing novel anti-MRSA and anti-VRE drug.

Immunosuppressive Activity of Semen Persicae Ethanol Extract on Specific Antibody and Cellular Response to Ovalbumin in Mice

The immunosuppressive activity of the ethanol extract of Semen Persicae (EESP) was studied with respect to specific antibody and cellular response to ovalbumin (OVA) in mice. The effects of EESP on mice splenocyte proliferation in vitro were measured. EESP significantly suppressed concanavalin A (ConA)- and lipopolysaccharide (LPS)-stimulated splenocyte proliferation in vitro in a concentration-dependent manner. Furthermore, the effects of EESP at three dose levels on the humoral and cellular immune responses in the OVA-immunized mice were examined. ICR Mice were immunized subcutaneously with OVA on day 0 and 14. Starting on the day of immunization, the mice were administered intraperitoneally with EESP at a single dose of 0.25, 0.5, and 1.0 mg, and cyclosporin A (CsA, positive drug) at a single dose of 0.1 mg at intervals of 7 days. On day 28, mitogen- and OVA-induced splenocyte proliferation and OVA-specific antibody level in serum were measured. EESP significantly decreased ConA-, LPS-, and OVA-induced splenocyte proliferation in the OVA-immunized mice at the dose of 1.0 mg. Meanwhile, the OVA-specific serum IgG, IgG1, and IgG2b antibody levels in the OVA-immunized mice were markedly reduced by EESP in a dose-dependent manner. The results suggest that EESP could suppress the cellular and humoral immune response in mice, and deserve further research to be developed as immunosuppressant.

Immunosuppressive Activity of the Ethanol Extract ofSiegesbeckia orientalis on the Immune Responses to Ovalbumin in Mice

The in vitro and in vivo immunosuppressive activity of the ethanol extract of Siegesbeckia orientalis (EESO) was studied on the immune responses in mice. EESO significantly suppressed concanavalin A (Con A)- and lipopolysaccharide (LPS)-stimulated splenocyte proliferation in vitro in a concentration-dependent manner. ICR Mice were immunized subcutaneously with ovalbumin (OVA) on days 0 and 14. Beginning on the day of immunization, the mice were administered intraperitoneally with EESO at a single dose of 0.25, 0.5, and 1.0 mg at intervals of 7 days. On day 28, OVA-specific antibodies in serum, and mitogen- and OVA-induced splenocyte proliferation were measured. EESO significantly suppressed Con A-, LPS- and OVA-induced splenocyte proliferation in the OVA-immunized mice in a dose-dependent manner. The OVA-specific serum IgG, IgG1, and IgG2b levels in the OVA-immunized mice were also significantly reduced by EESO. Moreover, reducing effect on the IgG1 antibody of EESO at the dose of 1.0 mg was more significant than that of cyclosporin A (CsA; positive drug). The results suggest that EESO could suppress the cellular and humoral response to ovalbumin in mice, and deserve further investigations to be developed as immunosuppressant.

Nuphar alkaloids with immediately apoptosis-inducing activity from Nuphar pumilum and their structural requirements for the activity

The methanolic extract and its alkaloid fraction from the rhizomes of Nuphar pumilum showed cytotoxic effects on human leukemia cell (U937), mouse melanoma cell (B16F10), and human fibroblast (HT1080). Dimeric sesquiterpene thioalkaloids with the 6-hydroxyl group (6-hydroxythiobinupharidine, 6,6'-dihydroxythiobinupharidine, 6-hydroxythionuphlutine B) showed substantial cytotoxic activity at a concentration of 10 microM, but dimeric sesquiterpene thioalkaloids lacking the 6-hydroxyl group (thiobinupharidine, thionuphlutine B, 6'-hydroxythionuphlutine B, neothiobinupharidine, thionuphlutine B beta-sulfoxide, and neothiobinupharidine beta-sulfoxide) and monomeric sesquiterpene alkaloids (nupharidine, 7-epideoxynupharidine, and nupharolutine) showed weak activity. Next, apoptosis-inducing activity of a principal active constituent, 6-hydroxythiobinupharidine, on U937 was examined using morphological observation and DNA fragmentation assay (TUNEL method). Apoptosis of U937 was immediately observed within 1 h after treatment of 6-hydroxythiobinupharidine at 2.5-10 microM.

Immunosuppressive activity of Pollen Typhae ethanol extract on the immune responses in mice

The immunosuppressive activity of the ethanol extract of Pollen Typhae (EEPT) consisting of a mixture of flavonoids, steroids and volatile oils was studied on the immune responses in mice. EEPT significantly suppressed concanavalin A (Con A)- and lipopolysaccharide (LPS)-stimulated splenocyte proliferation in vitro in a concentration-dependent manner. ICR mice were immunized subcutaneously with OVA on days 0 and 14. Beginning on the day of immunization, the mice were administered intraperitoneally with EEPT at a single dose of 0.25, 0.5, and 1.0 mg at intervals of 7 days for a total of five doses. On day 28, antigen-specific antibodies in serum, and mitogen- and OVA-induced splenocyte proliferation were measured. EEPT significantly suppressed Con A-, LPS- and OVA-induced splenocyte proliferation in the OVA-immunized mice in a dose-dependent manner. Moreover, the OVA-specific total IgG, IgG1 and IgG2b levels in the OVA-immunized mice were significantly reduced by EEPT. The results suggest that EEPT could suppress the cellular and humoral response in mice, and deserve further researches to be developed as immunosuppressant.

Potent anti-metastatic activity of dimeric sesquiterpene thioalkaloids from the rhizome of Nuphar pumilum

The methanolic extract and its alkaloid fraction from the rhizomes of Nuphar pumilum inhibited invasion of B16 melanoma cells across collagen-coated filters in vitro. Dimeric sesquiterpene thioalkaloids with the 6-hydroxyl group, 6-hydroxythiobinupharidine, 6,6'-dihydroxythiobinupharidine, and 6-hydroxythionuphlutine B, showed potent activity with IC(50) values of 0.029, 0.087, and 0.36 microM, respectively, but dimeric sesquiterpene thioalkaloids lacking the 6-hydroxyl group (thiobinupharidine, neothiobinupharidine, syn-thiobinupharidine sulfoxide, thionuphultine B beta-sulfoxide, and neothiobinupharidine beta-sulfoxide) and monomeric sesquiterpene alkaloids (nupharidine, deoxynupharidine, 7-epideoxynupharidine, and nupharolutine) showed weak activity. The alkaloid fraction (20 mg/kg/d, po) and the principal dimeric sesquiterpene thioalkaloid 6-hydroxythiobinupharidine (5 mg/kg/d, po) significantly inhibited lung tumor formation by more than 90% 10 days after injection of B16 melanoma cells in mice.

Structure-activity relationships of 6-fluoroquinazolines: dual-acting compounds with inhibitory activities toward both TNF-alpha production and T cell proliferation

We synthesized various 6-fluoro-7-(1-piperazino)quinazolines based on the structure of 1 and evaluated their inhibitory activities toward both TNF-alpha production and T cell proliferation responses. Among these compounds, 7a, having the 3,4-(methylenedioxy)phenyl moiety at the C(4)-position of the quinazoline ring, showed both inhibitory activities. Furthermore, the oral treatment with 7a exhibited an anti-inflammatory effect in rats with adjuvant arthritis as well as an inhibitory activity toward LPS-induced TNF-alpha production.

Structure-activity relationships of 6-nitroquinazolines: dual-acting compounds with inhibitory activities toward both TNF-alpha production and T cell proliferation

We synthesized various 6-nitroquinazolines by modifying the structure of compound 1 and evaluated their inhibitory activities toward both TNF-alpha production and T cell proliferation responses. The presence of the unsubstituted piperazine ring at the C(7)-position was required for both inhibitory activities. In this series of compounds, 5d and 5f, containing the 4-fluorophenyl and 3,4-difluorophenyl moiety, respectively, at the C(4)-position, showed the suppressing effects toward both responses with low cell growth inhibition. Furthermore, the oral administration of these compounds mentioned above at doses of 30 and 100 mg/kg also resulted in significant inhibition of TNF-alpha production induced by LPS in vivo.

Structure-activity relationships of quinazoline derivatives: dual-acting compounds with inhibitory activities toward both TNF-alpha production and T cell proliferation

We synthesized 4-chlorophenethylaminoquinazoline derivatives and evaluated their inhibitory activities toward both TNF-alpha production and T cell proliferation responses. Compound 2f, containing a piperazine ring at the C(7)-position of the quinazoline ring, exhibited more potent inhibitory activities toward both than the lead compound la. A smaller N-substituent in the piperazine ring was required for inhibition of TNF-alpha production.

Immunomodulatory activity of thunberginol A and related compounds isolated from Hydrangeae Dulcis Folium on splenocyte proliferation activated by mitogens

We investigated the immunomodulatory effects of antiallergic constituents from Hydrangeae Dulcis Folium, the processed leaves of Hydrangea macrophylla SERINGE var. thunbergii MAKINO, on splenocyte proliferation in mice. Thunberginol A and hydrangenol significantly suppressed T lymphocyte proliferation induced by concanavalin A. Thunberginol A also suppressed B lymphocyte proliferation induced by lipopolysaccharide, but other constituents induced significant increases. These inhibitory effects of thunberginol A on splenocyte proliferation seemed to contribute to the suppressive effect on type IV allergy.