Red Kale (Brassica oleracea L. ssp. acephala L. var. sabellica) Induces Apoptosis in Human Colorectal Cancer Cells In Vitro

This article presents the results of studies investigating the effect of red kale (Brassica oleracea L. ssp. acephala L. var. sabellica) extract on cancer cells (HT-29). The cytotoxicity of the red kale extract was assessed using MTT and LDH assays, while qRT-PCR was employed to analyze the expression of genes associated with the p53 signaling pathway to elucidate the effect of the extract on cancer cells. Furthermore, HPLC-ESI-QTOF-MS/MS was applied to identify bioactive compounds present in red kale. The obtained results indicated that red kale extract reduced the viability and suppressed the proliferation of HT-29 cells (the IC50 value of 60.8 µg/mL). Additionally, mRNA expression analysis revealed significant upregulation of several genes, i.e., casp9, mapk10, mapk11, fas, kat2 b, and ubd, suggesting the induction of cell apoptosis through the caspase-dependent pathway. Interestingly, the study revealed a decrease in the expression of genes including cdk2 and cdk4 encoding cell cycle-related proteins, which may lead to cell cycle arrest. Furthermore, the study identified certain bioactive compounds, such as sinigrin, spirostanol, hesperetin and usambarensine, which could potentially contribute to the apoptotic effect of red kale extracts. However, further investigations are necessary to elucidate the specific role of these individual compounds in the anti-cancer process.

In Vitro Enzyme Kinetics and NMR-Based Product Elucidation for Glutathione S-Conjugation of the Anticancer Unsymmetrical Bisacridine C-2028 in Liver Microsomes and Cytosol: Major Role of Glutathione S-Transferase M1-1 Isoenzyme

This work is the next step in studying the interplay between C-2028 (anticancer-active unsymmetrical bisacridine developed in our group) and the glutathione S-transferase/glutathione (GST/GSH) system. Here, we analyzed the concentration- and pH-dependent GSH conjugation of C-2028 in rat liver microsomes and cytosol. We also applied three recombinant human GST isoenzymes, which altered expression was found in various tumors. The formation of GSH S-conjugate of C-2028 in liver subfractions followed Michaelis-Menten kinetics. We found that C-2028 was conjugated with GSH preferentially by GSTM1-1, revealing a sigmoidal kinetic model. Using a colorimetric assay (MTT test), we initially assessed the cellular GST/GSH-dependent biotransformation of C-2028 in relation to cytotoxicity against Du-145 human prostate cancer cells in the presence or absence of the modulator of GSH biosynthesis. Pretreatment of cells with buthionine sulfoximine resulted in a cytotoxicity decrease, suggesting a possible GSH-mediated bioactivation process. Altogether, our results confirmed the importance of GSH conjugation in C-2028 metabolism, which humans must consider when planning a treatment strategy. Finally, nuclear magnetic resonance spectroscopy elucidated the structure of the GSH-derived product of C-2028. Hence, synthesizing the compound standard necessary for further advanced biological and bioanalytical investigations will be achievable.

The interactions of monomeric acridines and unsymmetrical bisacridines (UAs) with DNA duplexes: an insight provided by NMR and MD studies

Members of a novel class of anticancer compounds, exhibiting high antitumor activity, i.e. the unsymmetrical bisacridines (UAs), consist of two heteroaromatic ring systems. One of the ring systems is an imidazoacridinone moiety, with the skeleton identical to the structural base of Symadex. The second one is a 1-nitroacridine moiety, hence it may be regarded as Nitracrine's structural basis. These monoacridine units are connected by an aminoalkyl linker, which vary in structure. In theory, these unsymmetrical dimers should act as double-stranded DNA (dsDNA) bis-intercalators, since the monomeric units constituting the UAs were previously reported to exhibit an intercalating mode of binding into dsDNA. On the contrary, our earlier, preliminary studies have suggested that specific and/or structurally well-defined binding of UAs into DNA duplexes might not be the case. In this contribution, we have revisited and carefully examined the dsDNA-binding properties of monoacridines C-1305, C-1311 (Symadex), C-283 (Ledakrin/Nitracrine) and C-1748, as well as bisacridines C-2028, C-2041, C-2045 and C-2053 using advanced NMR techniques, aided by molecular modelling calculations and the analysis of UV-VIS spectra, decomposed by chemometric techniques. These studies allowed us to explain, why the properties of UAs are not a simple sum of the features exhibited by the acridine monomers.

Antibiotic-sterol interactions provide insight into the selectivity of natural aromatic analogues of amphotericin B and their photoisomers

Aromatic heptaene macrolides (AHMs) belong to the group of polyene macrolide antifungal antibiotics. Members of this group were the first to be used in the treatment of systemic fungal infections. Amphotericin B (AmB), a non-aromatic representative of heptaene macrolides, is of significant clinical importance in the treatment of internal mycoses. It includes the all-trans heptaene chromophore, whereas the native AHMs contain two cis-type (Z) double bonds within the chromophore system. Lately we have proven that it is possible to obtain AHMs' stable derivatives in the form of all-trans (AmB-type) isomers by photochemical isomerization. Our further studies have shown that such alteration leads to the improvement of their selective toxicity in vitro. Computational experiments carried out so far were only an initial contribution in the investigation of the molecular basis of the mechanism of action of AHMs and did not provide explanation to observed differences in biological activity between the native (cis-trans) and isomeric (all-trans) AHMs. Herein, we presented the results of two-dimensional metadynamics studies upon AmB and its aromatic analogues (AHMs), regarding preferable binary antibiotic/sterol complexes orientation, as well as more detailed research on the behaviour of AHMs' alkyl-aromatic side chain in cholesterol- or ergosterol-enriched lipid bilayers.

Application of the 2-deoxyglucose scaffold as a new chiral probe for elucidation of the absolute configuration of secondary alcohols

Herein, we present the application of 2-deoxy-d-glucose derivatives as chiral probes for elucidation of the absolute configuration of chiral secondary alcohols. The probes are attached to the studied molecules via glycosylation reaction and the resulting products are examined by a set of standard 2D NMR experiments. The absolute configuration of an oxymethine carbon atom binding the probe is established on a basis of a set of diagnostic dipolar couplings (NOEs/ROEs). These correlations may be considered diagnostic due to a pronounced lack of conformational freedom of the formed glycosidic linkage. While the chance for an observation of the diagnostic signals is the highest when the resulting glycoside in an α-anomer. 2-deoxy-d-glucose was selected as a probe of choice since is it known to strongly prefer the formation of α-glycosides

Acid–Base Equilibrium and Self-Association in Relation to High Antitumor Activity of Selected Unsymmetrical Bisacridines Established by Extensive Chemometric Analysis

Unsymmetrical bisacridines (UAs) represent a novel class of anticancer agents previously synthesized by our group. Our recent studies have demonstrated their high antitumor potential against multiple cancer cell lines and human tumor xenografts in nude mice. At the cellular level, these compounds affected 3D cancer spheroid growth and their cellular uptake was selectively modulated by quantum dots. UAs were shown to undergo metabolic transformations in vitro and in tumor cells. However, the physicochemical properties of UAs, which could possibly affect their interactions with molecular targets, remain unknown. Therefore, we selected four highly active UAs for the assessment of physicochemical parameters under various pH conditions. We determined the compounds’ pK_a dissociation constants as well as their potential to self-associate. Both parameters were determined by detailed and complex chemometric analysis of UV-Vis spectra supported by nuclear magnetic resonance (NMR) spectroscopy. The obtained results indicate that general molecular properties of UAs in aqueous media, including their protonation state, self-association ratio, and solubility, are strongly pH-dependent, particularly in the physiological pH range of 6 to 8. In conclusion, we describe the detailed physicochemical characteristics of UAs, which might contribute to their selectivity towards tumour cells as opposed to their effect on normal cells.

Changes in Epigenetic Patterns Related to DNA Replication in Vicia faba Root Meristem Cells under Cadmium-Induced Stress Conditions

Experiments on Vicia faba root meristem cells exposed to 150 µM cadmium chloride (CdCl2) were undertaken to analyse epigenetic changes, mainly with respect to DNA replication stress. Histone modifications examined by means of immunofluorescence labeling included: (1) acetylation of histone H3 on lysine 56 (H3K56Ac), involved in transcription, S phase, and response to DNA damage during DNA biosynthesis; (2) dimethylation of histone H3 on lysine 79 (H3K79Me2), correlated with the replication initiation; (3) phosphorylation of histone H3 on threonine 45 (H3T45Ph), engaged in DNA synthesis and apoptosis. Moreover, immunostaining using specific antibodies against 5-MetC-modified DNA was used to determine the level of DNA methylation. A significant decrease in the level of H3K79Me2, noted in all phases of the CdCl2-treated interphase cell nuclei, was found to correspond with: (1) an increase in the mean number of intranuclear foci of H3K56Ac histones (observed mainly in S-phase), (2) a plethora of nuclear and nucleolar labeling patterns (combined with a general decrease in H3T45Ph), and (3) a decrease in DNA methylation. All these changes correlate well with a general viewpoint that DNA modifications and post-translational histone modifications play an important role in gene expression and plant development under cadmium-induced stress conditions.

Quest for the Molecular Basis of Improved Selective Toxicity of All-Trans Isomers of Aromatic Heptaene Macrolide Antifungal Antibiotics

Three aromatic heptaene macrolide antifungal antibiotics, Candicidin D, Partricin A (Gedamycin) and Partricin B (Vacidin) were subjected to controlled cis-trans→ all trans photochemical isomerization. The obtained all-trans isomers demonstrated substantially improved in vitro selective toxicity in the Candida albicans cells: human erythrocytes model. This effect was mainly due to the diminished hemotoxicity. The molecular modeling studies on interactions between original antibiotics and their photoisomers with ergosterol and cholesterol revealed some difference in free energy profiles of formation of binary antibiotic/sterol complexes in respective membrane environments. Moreover, different geometries of heptaene: sterol complexes and variations in polyene macrolide molecule alignment in cholesterol-and ergosterol-containing membranes were found. None of these effects are of the crucial importance for the observed improvement of selective toxicity of aromatic heptaene antifungals but each seems to provide a partial contribution.

Iso-Partricin, an Aromatic Analogue of Amphotericin B: How Shining Light on Old Drugs Might Help Create New Ones

Partricin is a heptaene macrolide antibiotic complex that exhibits exceptional antifungal activity, yet poor selective toxicity, in the pathogen/host system. It consists of two compounds, namely partricin A and B, and both of these molecules incorporate two cis-type bonds within their heptaenic chromophores: 28Z and 30Z. In this contribution, we have proven that partricins are susceptible to a chromophore-straightening photoisomerization process. The occurring 28Z→28E and 30Z→30E switches are irreversible in given conditions, and they are the only structural changes observed during the experiment. The obtained all-trans partricin's derivatives, namely iso-partricins A and B, exhibit very promising features, potentially resulting in the improvement of their selective toxicity.

A strong preference for the TA/TA dinucleotide step discovered for an acridine-based, potent antitumor dsDNA intercalator, C-1305: NMR-driven structural and sequence-specificity studies

Triazoloacridinone C-1305, a potent antitumor agent recommended for Phase I clinical trials, exhibits high activity towards a wide range of experimental colon carcinomas, in many cases associated with complete tumor regression. C-1305 is a well-established dsDNA intercalator, yet no information on its mode of binding into DNA is available to date. Herein, we present the NMR-driven and MD-refined reconstruction of the 3D structures of the d(CGATATCG)₂:C-1305 and d(CCCTAGGG)₂:C-1305 non-covalent adducts. In both cases, the ligand intercalates at the TA/TA site, forming well-defined dsDNA:drug 1:1 mol/mol complexes. Orientation of the ligand within the binding site was unambiguously established by the DNA/ligand proton-proton NOE contacts. A subsequent, NMR-driven study of the sequence-specificity of C-1305 using a series of DNA duplexes, allowed us to confirm a strong preference towards TA/TA dinucleotide steps, followed by the TG/CA steps. Interestingly, no interaction at all was observed with duplexes containing exclusively the AT/AT, GG/CC and GA/TC steps.

The complete stereochemistry of the antibiotic candicidin A3 (syn. ascosin A3, levorin A3)

Herein, the stereostructure of the aromatic heptaene macrolide (AHM) antifungal antibiotic candicidin A3 (syn. ascosin A3, levorin A3) has been established upon the 2D NMR studies, consisting of DQF-COSY, TOCSY, ROESY, HSQC and HMBC experiments, as well as upon extensive molecular dynamics simulations. The geometry of the heptaenic chromophore was defined as: (22E, 24E, 26Z, 28Z, 30E, 32E, 34E). The previously unreported absolute configuration of the chiral centres of candicidin A3 was established as: (3R, 9R, 11S, 13S, 15R, 17S, 18R, 19S, 21R, 36S, 37R, 38S, 40S, 41S).

Light-Induced Transformation of the Aromatic Heptaene Antifungal Antibiotic Candicidin D into Its All-Trans Isomer

Illumination of the aromatic heptaene macrolide antifungal antibiotic candicicin D with UV light results in an isomerization of the molecule. The product formed after irradiation of the candicidin complex with UV light (λ = 365 nm), namely, iso-candicidin D, was isolated and subjected to 2D NMR studies, consisting of DQF-COSY, ROESY, TOCSY, HSQC, and HMBC experiments. The obtained spectral data unambiguously evidenced that iso-candicidin D was the all-trans isomer of the native antibiotic, and straightening of the heptaenic chromophore was the only light-induced structural change that occurred. Hence, iso-candicidin D was proclaimed to be a prototype of a novel class of polyene macrolide antifungal antibiotics: the all-trans aromatic heptaenes, containing a macrolide ring similar to that of amphotericin B.

Analytical studies on ascosin, candicidin and levorin multicomponent antifungal antibiotic complexes. The stereostructure of ascosin A2

In the class of polyene macrolides, there is a subgroup of aromatic heptaenes, which exhibit the highest antifungal activity within this type of antibiotics. Yet, due to their complex nature, aromatic heptaenes were not extensively studied and their potential as drugs is currently underexploited. Moreover, there are many inconsistencies in the literature regarding the composition and the structures of the individual components of the aromatic heptaene complexes. Inspired by one of such cases, herein we conducted the analytical studies on ascosin, candicidin and levorin using HPLC-DAD-(ESI)Q-TOF techniques. The resulting chromatograms and the molecular masses of the individual components of these three complexes strongly indicated that the major components of ascosin, candicidin and levorin are structurally identical. In order to validate these results, the main component of previously structurally uncharacterized ascosin was derivatized, isolated and subjected to 2D NMR studies. The resulting structure of the ascosin's main component, herein named ascosin A2, was shown to be identical with the earlier reported structures of the main components of candicidin and levorin complexes: candicidin D and levorin A2. In the end, all the structural knowledge regarding these three antibiotic complexes was gathered, systematized and completed, and the new nomenclature was proposed.

Intramolecular transformation of an antifungal antibiotic nystatin A1 into its isomer, iso-nystatin A1 - structural and molecular modeling studies

Nystatin A₁ , a polyene macrolide antifungal antibiotic, in a slightly basic or acidic solution undergoes an intramolecular transformation, yielding a structural isomer, the translactonization product, iso-nystatin A₁ with lactone ring diminished by two carbon atoms. Structural evidence is provided by advanced NMR and Mass Spectrometry (MS) studies. Molecular dynamics simulations and quantum mechanics calculations gave the insight into the course and mechanism of the transformation and its effect on the conformation of the subject molecule. Copyright © 2016 John Wiley & Sons, Ltd.

Monosaccharides as Potential Chiral Probes for the Determination of the Absolute Configuration of Secondary Alcohols

Herein, a new method for the elucidation of the absolute configuration of chiral secondary alcohols is proposed. This method is an alternative for a widely used approach reported by Mosher and Dale and similar methods that are based on the ¹H NMR shift (δ) changes of protons that are attached to the substituents of the oxymethine carbon atom. The presented method is not based on tracking the chemical shift changes and utilizes stereochemically defined monosaccharides as chiral probes. A secondary alcohol is glycosylated, and the resulting glycoside is subjected to NMR studies. The observation of dipolar couplings between the protons of the monosaccharide moiety and the protons of the secondary alcohol moiety via the NOESY/ROESY spectra enables the determination of the absolute configuration of the oxymethine carbon atom.

Stereostructure of mycoheptin A(2)

The absolute configurations of all the stereogenic centers of the antibiotic mycoheptin A(2) were established upon previously elaborated general procedure, consisting of DQF-COSY, NOESY, ROESY, HSQC and HMBC experiments as major tools. The structure of mycoheptin A(2) without stereochemistry of its aglycone has been reported before.

Absolute configurations of C34 and C35 of antibiotic niphimycin A

The relative configurations of four stereogenic centers of the C33-C42 fragment of niphimycin A were assigned as 2S*, 3R*, 4S* and 6S*, based upon (1)H NMR analysis with double-quantum filtered COSY and nuclear Overhauser spectroscopy experiments. These data were then correlated with absolute configurations at C36 and C38 of niphimycin A, which were declared previously as 36S and 38S [3]. This allowed for the assignment of the absolute configurations at C34 and C35 of niphimycin A as 34S and 35R.