Enniatin A inhibits the chaperone Hsp90 and unleashes the immune system against triple-negative breast cancer

Low response rates and immune-related adverse events limit the remarkable impact of cancer immunotherapy. To improve clinical outcomes, preclinical studies have shown that combining immunotherapies with N-terminal Hsp90 inhibitors resulted in improved efficacy, even though induction of an extensive heat shock response (HSR) and less than optimal dosing of these inhibitors limited their clinical efficacy as monotherapies. We discovered that the natural product Enniatin A (EnnA) targets Hsp90 and destabilizes its client oncoproteins without inducing an HSR. EnnA triggers immunogenic cell death in triple-negative breast cancer (TNBC) syngeneic mouse models and exhibits superior antitumor activity compared to Hsp90 N-terminal inhibitors. EnnA reprograms the tumor microenvironment (TME) to promote CD8+ T cell-dependent antitumor immunity by reducing PD-L1 levels and activating the chemokine receptor CX3CR1 pathway. These findings provide strong evidence for transforming the immunosuppressive TME into a more tumor-hostile milieu by engaging Hsp90 with therapeutic agents involving novel mechanisms of action.

Abstract 2272: Targeting the chaperone Hsp90 to activate the immune system and eradicate the triple negative breast cancer

Low response rates and immune-related adverse events limit the impact of cancer immunotherapy. To improve clinical outcomes, preclinical studies have shown that combining immunotherapies with N-terminal Hsp90 inhibitors resulted in improved efficacy, even though induction of an extensive heat shock response (HSR) with these inhibitors limited their clinical efficacy as monotherapies. We discovered that Enniatin A (EnnA) binds to the interface between the middle domains of the Hsp90 dimer and destabilizes Hsp90 client oncoproteins without inducing an HSR. EnnA induces cancer cell immunogenic cell death in aggressive breast cancer models and exhibits superior anti-tumor activity compared to Hsp90 N-terminal inhibitors. EnnA reprograms the tumor microenvironment in syngeneic mouse models to promote CD8+ T cell-dependent anti-tumor activity mediated through a reduced level of PD-L1 and activation of CX3CR1 pathway. We propose that EnnA is a promising anti-tumor agent with a mechanism of action involving immunogenic cancer cell toxicity and mobilization of CD8+ T cells into the tumor site.

Citation Format: Nada Eisa, Vincent M. Crowley, Asif Elahi, Vamsi K. Kommalapati, Hasan Korkaya, Abdessamad Debbab, Brian Blagg, Ahmed Chadli. Targeting the chaperone Hsp90 to activate the immune system and eradicate the triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2272.

Flavonoid glycosides from Olax mannii: Structure elucidation and effect on the nuclear factor kappa B pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Olax mannii Oliv. (Olacaceae) is among the many medicinal plants used in Nigeria for the ethnomedicinal management of both cancer and inflammation. Such plants represent potential sources of innovative therapeutic agents for the treatment of cancer and other malignant disorders. While the majority of medicinal plants exert their anticancer effects by direct cytotoxicity on tumor cells, it is important that other mechanisms through which these plants can exhibit anticancer effects are investigated. Preliminary studies indicated that Olax mannii leaves are rich sources of novel flavonoid glycosides. The detailed chemistry as well the mechanisms through which these flavonoid constituents may exert their cancer chemo-preventive and therapeutic effects are, however, not yet investigated.

AIM OF THE STUDY

The aim of this study is to carry out a detailed chemical investigation of Olax mannii leaves and the effects of the isolated constituents on the nuclear factor kappa B (NF-κB) pathway.

MATERIALS AND METHODS

A methanol leaf extract was subjected to various chromatographic separations to achieve isolation of flavonoid glycosides and the structures of the isolated compounds were elucidated by a combination of 1D and 2D NMR and high resolution mass spectrometry. Biological activities were assessed by measurement of cellular viability and proliferation using quantitative IncuCyte videomicroscopy, trypan blue staining and by quantification of the number of metabolically active K562 cells based on quantitation of ATP. The effect of the compounds on the inhibition of the NF-κB pathway as well as toxicity towards peripheral blood mononuclear cells to evaluate differential toxicity was also assayed.

RESULTS

Chemical investigation of the methanol leaf extract of the plant material led to the isolation of three new flavonoid triglycosides, kaempferol 3-O-[α-D-apiofuranosyl-(1 → 2)-α-L-arabinofuranoside]-7-O-α-L-rhamnopyranoside (1), kaempferol 3-O-[β-D-glucopyranosyl-(1 → 2)-α-L-arabinofuranoside]-7-O-α-L-rhamnopyranoside (2), kaempferol 3-O-[β-D-arabinopyranosyl-(1→4)-α-L-rhamnopyranoside]-7-O-α-L-rhamnopyranoside (3), in addition to fourteen known flavonoid glycosides (4-17). Of all the tested compounds, only compound 9 (kaempferol 3-O-α-L-rhamnopyranoside) exhibited promising and specific antiproliferative activity on human K562 chronic myelogenous leukemia cells and dose-dependently inhibited NF-κB transactivation.

CONCLUSION

The presence of this flavonoid glycoside and derivatives may account for the reported efficacy of Olax mannii leaf extract in the ethnomedicinal management of cancer and inflammation.

Anti-inflammatory sesquiterpenes from the medicinal herb Tanacetum sinaicum

New sesquiterpenes tanacetolide A–C (1–3) were isolated from aTanacetum sinaicumextract together with known compounds (4–10).

Bioactive metabolites from Chaetomium aureum: structure elucidation and inhibition of the Hsp90 machine chaperoning activity

Chemical investigation of the EtOAc extract of the fungus Chaetomium aureum, an endophyte of the Moroccan medicinal plant Thymelaea lythroides, afforded one new resorcinol derivative named chaetorcinol, together with five known metabolites. The structures of the isolated compounds were determined on the basis of one- and two-dimensional NMR spectroscopy and high-resolution mass spectrometry as well as by comparison with the literature. All compounds were tested for their activity towards the Hsp90 chaperoning machine in vitro using the progesterone receptor (PR) and rabbit reticulocyte lysate (RRL). Among the isolated compounds, only sclerotiorin efficiently inhibited the Hsp90 machine chaperoning activity. However, sclerotiorin showed no cytotoxic effect on breast cancer Hs578T, MDA-MB-231 and prostate cancer LNCaP cell lines. Interestingly, deacetylation of sclerotiorin increased its cytotoxicity toward the tested cell lines over a period of 48 h.

Optimization of Enniatin Production by Solid-Phase Fermentation of Fusarium tricinctum

Enniatins are cyclic depsipeptides produced by fungi of the genus Fusarium that are of interest due to their pronounced biological activities; especially enniatins A, A1, B, and B1 possess anticarcinogenic and anti-HIV properties. In the present study, F. tricinctum was grown on seven solid media and in one liquid growth medium with or without addition of peptone or of amino acid precursors in order to identify favourable media with simple cultivation conditions for maximum enniatin production. Additionally, the optimal duration of growth was investigated for the highest yields of enniatins. From the different media analysed, white beans (Phaseolus vulgaris, solid medium) induced the highest accumulation of enniatins A, A1, B, and B1, that reached a maximum of 1,365 mg total enniatins in 1 L growth medium after 18 days of fermentation. Fermentation of F. tricinctum on white beans gave the highest yield of enniatins compared to all other media analysed in this study.

A New Tetrahydrofuran Derivative from the Endophytic Fungus Chaetomium sp. Isolated from Otanthus maritimus

A hitherto unidentified endophytic strain of the genus Chaetomium, isolated from the medicinal plant Otanthus maritimus, yielded a new tetrahydrofuran derivative, aureonitolic acid (), along with 5 known natural products, 2 - 6. The structure of 1 was determined by extensive spectroscopic analysis and comparison with reported data. Extracts of the fungus, grown either in liquid culture or on solid rice media, exhibited considerable cytotoxic activity when tested in vitro against L5178Y mouse lymphoma cells. Compounds 2 and 6 showed significant growth inhibition against L5178Y cells with EC50 values of 7.0 and 2.7 μg/mL, respectively, whereas 1 was inactive

Protein kinase and HDAC inhibitors from the endophytic fungus Epicoccum nigrum

A chemical investigation of the endophytic fungus Epicoccum nigrum isolated from leaves of Mentha suaveolens collected in Morocco resulted in the isolation of five new polyketides, epicocconigrones A and B (1 and 2), 3-methoxyepicoccone B (3), 3-methoxyepicoccone (4), and 2,3,4-trihydroxy-6-(methoxymethyl)-5-methylbenzaldehyde (5), together with five known compounds (6-10). The structures of the new compounds were unambiguously determined by extensive analysis of the 1D and 2D NMR and mass spectroscopic data. Compounds 1 and 10 showed potent inhibition of at least 15 protein kinases with IC50 values ranging from 0.07 to 9.00 μM. Moreover, compounds 1 and 10 inhibited histone deacetylase (HDAC) activities with IC50 values of 9.8 and 14.2 μM, respectively. A preliminary structure-activity relationship is discussed. Interestingly, compounds 1 and 10 exert mainly cytostatic effects in human lymphoma RAJI and U-937 cell lines.

Fungal endophytes - secret producers of bioactive plant metabolites

The potential of endophytic fungi as promising sources of bioactive natural products continues to attract broad attention. Endophytic fungi are defined as fungi that live asymptomatically within the tissues of higher plants. This overview will highlight the uniqueness of endophytic fungi as alternative sources of pharmaceutically valuable compounds originally isolated from higher plants, e.g. paclitaxel, camptothecin and podophyllotoxin. In addition, it will shed light on the fungal biosynthesis of plant associated metabolites as well as new approaches developed to improve the production of commercially important plant derived compounds with the involvement of endophytic fungi.

Optimization of enniatin production by solid-phase fermentation of Fusarium tricinctum

Enniatins are cyclic depsipeptides produced by fungi of the genus Fusarium that are of interest due to their pronounced biological activities; especially enniatins A, A1, B, and B1 possess anticarcinogenic and anti-HIV properties. In the present study, F. tricinctum was grown on seven solid media and in one liquid growth medium with or without addition of peptone or of amino acid precursors in order to identify favourable media with simple cultivation conditions for maximum enniatin production. Additionally, the optimal duration of growth was investigated for the highest yields of enniatins. From the different media analysed, white beans (Phaseolus vulgaris, solid medium) induced the highest accumulation of enniatins A, A1, B, and B1, that reached a maximum of 1,365 mg total enniatins in 1 L growth medium after 18 days of fermentation. Fermentation of F. tricinctum on white beans gave the highest yield of enniatins compared to all other media analysed in this study.

Atropisomeric dihydroanthracenones as inhibitors of multiresistant Staphylococcus aureus

Two bisdihydroanthracenone atropodiastereomeric pairs, including homodimeric flavomannin A (1) and the previously unreported flavomannin B (2), two new unsymmetrical dimers (3 and 4), and two new mixed dihydroanthracenone/anthraquinone dimers (5 and 6) were isolated from Talaromyces wortmannii , an endophyte of Aloe vera . The structures of 2-6 were elucidated by extensive NMR and mass spectrometric analyses. The axial chirality of the biaryls was determined using TDDFT ECD and VCD calculations, the combination of which however did not allow the assignment of the central chirality elements of 1. The compounds exhibited antibacterial activity against Staphylococcus aureus , including (multi)drug-resistant clinical isolates. Reporter gene analyses indicated induction of the SOS response for some of the derivatives, suggesting interference with DNA structure or metabolism. Fluorescence microscopy demonstrated defective segregation of the bacterial chromosome and DNA degradation. Notably, the compounds showed no cytotoxic activity, encouraging their further evaluation as potential starting points for antibacterial drug development.

Fungal endophytes: unique plant inhabitants with great promises

Fungal endophytes residing in the internal tissues of living plants occur in almost every plant on earth from the arctic to the tropics. The endophyte-host relationship is described as a balanced symbiotic continuum ranging from mutualism through commensalism to parasitism. This overview will highlight selected aspects of endophyte diversity, host specificity, endophyte-host interaction and communication as well as regulation of secondary metabolite production with emphasis on advanced genomic methods and their role in improving our current knowledge of endophytic associations. Furthermore, the chemical potential of endophytic fungi for drug discovery will be discussed with focus on the detection of pharmaceutically valuable plant constituents as products of fungal biosynthesis. In addition, selected examples of bioactive metabolites reported in recent years (2008-2010) from fungal endophytes residing in terrestrial plants are presented grouped according to their reported biological activities.

Bioactive compounds from marine bacteria and fungi

Marine bacteria and fungi are of considerable importance as new promising sources of a huge number of biologically active products. Some of these marine species live in a stressful habitat, under cold, lightless and high pressure conditions. Surprisingly, a large number of species with high diversity survive under such conditions and produce fascinating and structurally complex natural products. Up till now, only a small number of microorganisms have been investigated for bioactive metabolites, yet a huge number of active substances with some of them featuring unique structural skeletons have been isolated. This review covers new biologically active natural products published recently (2007-09) and highlights the chemical potential of marine microorganisms, with focus on bioactive products as well as on their mechanisms of action.

Bioactive metabolites from the endophytic fungus Stemphylium globuliferum isolated from Mentha pulegium

The endophytic fungus Stemphylium globuliferum was isolated from stem tissues of the Moroccan medicinal plant Mentha pulegium. Extracts of the fungus, which was grown on solid rice medium, exhibited considerable cytotoxicity when tested in vitro against L5178Y cells. Chemical investigation yielded five new secondary metabolites, alterporriol G (4) and its atropisomer alterporriol H (5), altersolanol K (11), altersolanol L (12), stemphypyrone (13), and the known compounds 6-O-methylalaternin (1), macrosporin (2), altersolanol A (3), alterporriol E (6), alterporriol D (7), alterporriol A (8), alterporriol B (9), and altersolanol J (10). The structures were determined on the basis of one- and two-dimensional NMR spectroscopy and mass spectrometry. Among the alterporriol-type anthranoid dimers, the mixture of alterporriols G and H (4/5) exhibited considerable cytotoxicity against L5178Y cells with an EC(50) value of 2.7 microg/mL, whereas the other congeners showed only modest activity. The compounds were also tested for kinase inhibitory activity in an assay involving 24 different kinases. Compounds 1, 2, 3, and the mixture of 4 and 5 were the most potent inhibitors, displaying EC(50) values between 0.64 and 1.4 microg/mL toward individual kinases.