Molecular Cloning, Heterologous Expression, Purification, and Evaluation of Protein-Ligand Interactions of CYP51 of Candida krusei Azole-Resistant Fungal Strain.

Due to the increasing prevalence of fungal diseases caused by fungi of the genus Candida and the development of pathogen resistance to available drugs, the need to find new effective antifungal agents has increased. Azole antifungals, which are inhibitors of sterol-14α-demethylase or CYP51, have been widely used in the treatment of fungal infections over the past two decades. Of special interest is the study of C. krusei CYP51, since this fungus exhibit resistance not only to azoles, but also to other antifungal drugs and there is no available information about the ligand-binding properties of CYP51 of this pathogen. We expressed recombinant C. krusei CYP51 in E. coli cells and obtained a highly purified protein. Application of the method of spectrophotometric titration allowed us to study the interaction of C. krusei CYP51 with various ligands. In the present work, the interaction of C. krusei CYP51 with azole inhibitors, and natural and synthesized steroid derivatives was evaluated. The obtained data indicate that the resistance of C. krusei to azoles is not due to the structural features of CYP51 of this microorganism, but rather to another mechanism. Promising ligands that demonstrated sufficiently strong binding in the micromolar range to C. krusei CYP51 were identified, including compounds 99 (Kd = 1.02 ± 0.14 µM) and Ch-4 (Kd = 6.95 ± 0.80 µM). The revealed structural features of the interaction of ligands with the active site of C. krusei CYP51 can be taken into account in the further development of new selective modulators of the activity of this enzyme.

Rhizochalinin Exhibits Anticancer Activity and Synergizes with EGFR Inhibitors in Glioblastoma In Vitro Models.

Rhizochalinin (Rhiz) is a recently discovered cytotoxic sphingolipid synthesized from the marine natural compound rhizochalin. Previously, Rhiz demonstrated high in vitro and in vivo efficacy in various cancer models. Here, we report Rhiz to be highly active in human glioblastoma cell lines as well as in patient-derived glioma-stem like neurosphere models. Rhiz counteracted glioblastoma cell proliferation by inducing apoptosis, G2/M-phase cell cycle arrest, and inhibition of autophagy. Proteomic profiling followed by bioinformatic analysis suggested suppression of the Akt pathway as one of the major biological effects of Rhiz. Suppression of Akt as well as IGF-1R and MEK1/2 kinase was confirmed in Rhiz-treated GBM cells. In addition, Rhiz pretreatment resulted in a more pronounced inhibitory effect of γ-irradiation on the growth of patient-derived glioma-spheres, an effect to which the Akt inhibition may also contribute decisively. In contrast, EGFR upregulation, observed in all GBM neurospheres under Rhiz treatment, was postulated to be a possible sign of incipient resistance. In line with this, combinational therapy with EGFR-targeted tyrosine kinase inhibitors synergistically increased the efficacy of Rhiz resulting in dramatic inhibition of GBM cell viability as well as a significant reduction of neurosphere size in the case of combination with lapatinib. Preliminary in vitro data generated using a parallel artificial membrane permeability (PAMPA) assay suggested that Rhiz cannot cross the blood brain barrier and therefore alternative drug delivery methods should be used in the further in vivo studies. In conclusion, Rhiz is a promising new candidate for the treatment of human glioblastoma, which should be further developed in combination with EGFR inhibitors.

Assimiloside A, a Glycolipid with Immunomodulatory Activity from the Northwestern Pacific Marine Sponge Hymeniacidon assimilis.

Assimiloside A (1), an unprecedented marine glycolipid containing a γ-lactone of 4R,16,26R-trihydroxy C28 fatty acid as an aglycon and a trisaccharide carbohydrate moiety, was isolated from the marine sponge Hymeniacidon assimilis. Its structure was elucidated by NMR spectroscopy, mass spectrometry, chemical transformations, and ECD spectroscopy combined with time-dependent density functional theory calculations. Assimiloside A at nontoxic concentrations of 0.01-0.1 µM was shown to present lysosomal activity stimulation and intracellular reactive oxygen species level elevation in RAW 264.7 murine macrophages.

New Guanidine Alkaloids Batzelladines O and P from the Marine Sponge Monanchora pulchra Induce Apoptosis and Autophagy in Prostate Cancer Cells.

Two new guanidine alkaloids, batzelladines O (1) and P (2), were isolated from the deep-water marine sponge Monanchora pulchra. The structures of these metabolites were determined by NMR spectroscopy, mass spectrometry, and ECD. The isolated compounds exhibited cytotoxic activity in human prostate cancer cells PC3, PC3-DR, and 22Rv1 at low micromolar concentrations and inhibited colony formation and survival of the cancer cells. Batzelladines O (1) and P (2) induced apoptosis, which was detected by Western blotting as caspase-3 and PARP cleavage. Additionally, induction of pro-survival autophagy indicated as upregulation of LC3B-II and suppression of mTOR was observed in the treated cells. In line with this, the combination with autophagy inhibitor 3-methyladenine synergistically increased the cytotoxic activity of batzelladines O (1) and P (2). Both compounds were equally active in docetaxel-sensitive and docetaxel-resistant prostate cancer cells, despite exhibiting a slight p-glycoprotein substrate-like activity. In combination with docetaxel, an additive effect was observed. In conclusion, the isolated new guanidine alkaloids are promising drug candidates for the treatment of taxane-resistant prostate cancer.

New diterpenes from the marine sponge Spongionella sp. overcome drug resistance in prostate cancer by inhibition of P-glycoprotein.

Spongian diterpenes are a group of marine natural compounds possessing various biological activities. However, their anticancer activity is still poorly studied and understood. We isolated six spongian diterpenes from the marine sponge Spongionella sp., including one new spongionellol A and five previously known molecules. The structures were elucidated using a detailed analysis MS and NMR spectra as well as by comparison with previously reported data. Two of them, namely, spongionellol A and 15,16-dideoxy-15α,17ß-dihydroxy-15,17-oxidospongian-16-carboxylate-15,17-diacetate exhibited high activity and selectivity in human prostate cancer cells, including cells resistant to hormonal therapy and docetaxel. The mechanism of action has been identified as caspase-dependent apoptosis. Remarkably, both compounds were able to suppress expression of androgen receptor (AR) and AR-splice variant 7, as well as AR-dependent signaling. The isolated diterpenes effectively inhibited drug efflux mediated by multidrug-resistance protein 1 (MDR1; p-glycoprotein). Of note, a synergistic effect of the compounds with docetaxel, a substrate of p-glycoprotein, suggests resensitization of p-glycoprotein overexpressing cells to standard chemotherapy. In conclusion, the isolated spongian diterpenes possess high activity and selectivity towards prostate cancer cells combined with the ability to inhibit one of the main drug-resistance mechanism. This makes them promising candidates for combinational anticancer therapy.

Streptocinnamides A and B, Depsipeptides from Streptomyces sp. KMM 9044.

The bacterium Streptomyces sp. KMM 9044 from a sample of marine sediment collected in the northwestern part of the Sea of Japan produces highly chlorinated depsiheptapeptides streptocinnamides A (1) and B (2), representatives of a new structural group of antibiotics. The structures of 1 and 2 were determined using nuclear magnetic resonance and mass spectrometry studies and confirmed by a series of chemical transformations. Streptocinnamide A potently inhibits Micrococcus sp. KMM 1467, Arthrobacter sp. ATCC 21022, and Mycobacterium smegmatis MC2 155.

Toporosides A and B, Cyclopentenyl-Containing ω-Glycosylated Fatty Acid Amides, and Toporosides C and D from the Northwestern Pacific Marine Sponge Stelodoryx toporoki.

Toporosides A-D (1-4), new ω-glycosylated fatty acid amides, were isolated from the sponge Stelodoryx toporoki. The structures of these compounds, including absolute configurations of stereogenic centers, were established using analysis of 1D and 2D NMR, ECD, and HR mass spectra as well as chemical transformations. Toporosides A (1) and B (2) are the first lipids containing a cyclopentenyl α,ß-unsaturated carbonyl moiety in the polymethylene chain. Toporoside C (3) is likely a precursor, which undergoes intramolecular aldol condensation to produce 1 and 2. Toporosides A, C, and D showed protective effects against TNF-α-induced injury in H9c2 cardiomyocytes.

Novel GSK-3ß Inhibitor Neopetroside A Protects Against Murine Myocardial Ischemia/Reperfusion Injury.

Recent trends suggest novel natural compounds as promising treatments for cardiovascular disease. The authors examined how neopetroside A, a natural pyridine nucleoside containing an α-glycoside bond, regulates mitochondrial metabolism and heart function and investigated its cardioprotective role against ischemia/reperfusion injury. Neopetroside A treatment maintained cardiac hemodynamic status and mitochondrial respiration capacity and significantly prevented cardiac fibrosis in murine models. These effects can be attributed to preserved cellular and mitochondrial function caused by the inhibition of glycogen synthase kinase-3 beta, which regulates the ratio of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced, through activation of the nuclear factor erythroid 2-related factor 2/NAD(P)H quinone oxidoreductase 1 axis in a phosphorylation-independent manner.

Oceanalin B, a Hybrid α,ω-Bifunctionalized Sphingoid Tetrahydroisoquinoline ß-Glycoside from the Marine Sponge Oceanapia sp.

Oceanalin B (1), an α,ω-bipolar natural product belonging to a rare family of sphingoid tetrahydoisoquinoline ß-glycosides, was isolated from the EtOH extract of the lyophilized marine sponge Oceanapia sp. as the second member of the series after oceanalin A (2) from the same animal. The compounds are of particular interest due to their biogenetically unexpected structures as well as their biological activities. The structure and absolute stereochemistry of 1 as a α,ω-bifunctionalized sphingoid tetrahydroisoquinoline ß-glycoside was elucidated using NMR, CD and MS spectral analysis and chemical degradation. Oceanalin B exhibited in vitro antifungal activity against Candidaglabrata with a MIC of 25 µg/mL.

Gracilosulfates A-G, Monosulfated Polyoxygenated Steroids from the Marine Sponge Haliclona gracilis.

Seven new polyoxygenated steroids belonging to a new structural group of sponge steroids, gracilosulfates A-G (1-7), possessing 3ß-O-sulfonato, 5ß,6ß epoxy (or 5(6)-dehydro), and 4ß,23-dihydroxy substitution patterns as a common structural motif, were isolated from the marine sponge Haliclona gracilis. Their structures were determined by NMR and MS methods. The compounds 1, 2, 4, 6, and 7 inhibited the expression of prostate-specific antigen (PSA) in 22Rv1 tumor cells.

Marine alkaloid monanchoxymycalin C: a new specific activator of JNK1/2 kinase with anticancer properties.

Monanchoxymycalin C (MomC) is a new marine pentacyclic guanidine alkaloid, recently isolated from marine sponge Monanchora pulchra by us. Here, anticancer activity and mechanism of action was investigated for the first time using a human prostate cancer (PCa) model. MomC was active in all PCa cell lines at low micromolar concentrations and induced an unusual caspase-independent, non-apoptotic cell death. Kinase activity screening identified activation of mitogen-activated protein kinase (MAPK) c-Jun N-terminal protein kinase (JNK1/2) to be one of the primary molecular mechanism of MomC anticancer activity. Functional assays demonstrated a specific and selective JNK1/2 activation prior to the induction of other cell death related processes. Inhibition of JNK1/2 by pretreatment with the JNK-inhibitor SP600125 antagonized cytotoxic activity of the marine compound. MomC caused an upregulation of cytotoxic ROS. However, in contrast to other ROS-inducing agents, co-treatment with PARP-inhibitor olaparib revealed antagonistic effects indicating an active PARP to be necessary for MomC activity. Interestingly, although no direct regulation of p38 and ERK1/2 were detected, active p38 kinase was required for MomC efficacy, while the inhibition of ERK1/2 increased its cytotoxicity. In conclusion, MomC shows promising activity against PCa, which is exerted via JNK1/2 activation and non-apoptotic cell death.

Leptogorgins A-C, Humulane Sesquiterpenoids from the Vietnamese Gorgonian Leptogorgia sp.

Leptogorgins A-C (1-3), new humulane sesquiterpenoids, and leptogorgoid A (4), a new dihydroxyketosteroid, were isolated from the gorgonian Leptogorgia sp. collected from the South China Sea. The structures were established using MS and NMR data. The absolute configuration of 1 was confirmed by a modification of Mosher's method. Configurations of double bonds followed from NMR data, including NOE correlations. This is the first report of humulane-type sesquiterpenoids from marine invertebrates. Sesquiterpenoids leptogorgins A (1) and B (2) exhibited a moderate cytotoxicity and some selectivity against human drug-resistant prostate cancer cells 22Rv1.

Urupocidin C: a new marine guanidine alkaloid which selectively kills prostate cancer cells via mitochondria targeting.

New bicyclic guanidine alkaloid, urupocidin C (Ur-C) along with the previously known urupocidin A (Ur-A) were isolated from the rare deep-sea marine sponge Monanchora pulchra, harvested in Northwestern Pacific waters. The unique structure of Ur-C was elucidated using 1D and 2D NMR spectroscopy as well as mass spectra. We discovered a promising selectivity of both alkaloids for human prostate cancer (PCa) cells, including highly drug-resistant lines, compared to non-malignant cells. In cancer cells, marine derived compounds were able to induce G1- and S-cell cycle arrest as well as caspase-mediated cell death. For the first time we have identified mitochondrial targeting as a central mechanism of anticancer action for these and similar molecules. Thus, treatment with the isolated alkaloids resulted in mitochondrial membrane permeabilization consequently leading to the release of cytotoxic mitochondrial proteins to cellular cytoplasm, ROS upregulation, consequent activation of caspase-9 and -3, followed by PARP cleavage, DNA fragmentation, and apoptosis. Moreover, synergistic effects were observed when Ur-A and Ur-C were combined with clinically approved PARP inhibitor olaparib. Finally, these alkaloids exhibited additive effects in combination with docetaxel and androgen receptor inhibitor enzalutamide, both applied in PCa therapy. In conclusion, urupocidin-like compounds are promising lead molecules for the development of new drugs for the treatment of advanced PCa.

Application of Oxidative and Reductive Transformations in the Structure Determination of Marine Natural Products.

This review highlights the application of oxidative and reductive chemical transformations in the structure determination of complex marine natural products, including their absolute configurations. Workability of the Baeyer-Villiger reaction, ozonolysis, periodate oxidation, hydrogenolysis, and reductive amination, as well as other related chemical transformations, are discussed.

Cyclobutastellettolides A and B, C19 Norterpenoids from a Stelletta sp. Marine Sponge.

Two novel C19 terpenoids (1, 2) with an unprecedented carbon skeleton (A) were isolated from a Stelletta sp. sponge collected from Vietnamese waters. Their structures and absolute configurations were established by extensive NMR, MS, and ECD analyses together with quantum chemical modeling and biogenetic considerations. The probable pathways of biogenesis of 1 and 2 from isomalabaricane triterpenoids are discussed. Compounds 1 and 2 significantly increase the production of reactive oxygen species in murine peritoneal macrophages.

New Trisulfated Steroids from the Vietnamese Marine Sponge Halichondria vansoesti and Their PSA Expression and Glucose Uptake Inhibitory Activities.

Seven new unusual polysulfated steroids-topsentiasterol sulfate G (1), topsentiasterol sulfate I (2), topsentiasterol sulfate H (3), bromotopsentiasterol sulfate D (4), dichlorotopsentiasterol sulfate D (8), bromochlorotopsentiasterol sulfate D (9), and 4ß-hydroxyhalistanol sulfate C (10), as well as three previously described-topsentiasterol sulfate D (7), chlorotopsentiasterol sulfate D (5) and iodotopsentiasterol sulfate D (6) have been isolated from the marine sponge Halichondria vansoesti. Structures of these compounds were determined by detailed analysis of 1D- and 2D-NMR and HRESIMS data, as well as chemical transformations. The effects of the compounds on human prostate cancer cells PC-3 and 22Rv1 were investigated.

Guitarrins A-E and Aluminumguitarrin A: 5-Azaindoles from the Northwestern Pacific Marine Sponge Guitarra fimbriata.

Guitarrins A-E (1-5), the first natural 5-azaindoles, and aluminumguitarrin A (1a), the first aluminum-containing compound from marine invertebrates, were isolated from the sponge Guitarra fimbriata. The structures of these compounds were established using detailed analysis of 1D and 2D NMR data, mass spectra, and X-ray analysis of 1 and 1a. Compound 3 was proved to be a natural inhibitor of alkaline phosphatase.

Melonoside B and Melonosins A and B, Lipids Containing Multifunctionalized ω-Hydroxy Fatty Acid Amides from the Far Eastern Marine Sponge Melonanchora kobjakovae.

Melonoside B (1) and melonosins B (2) and A (3), new lipids based on polyoxygenated fatty acid amides, and known melonoside A (4) were isolated from two different collections of the marine sponge Melonanchora kobjakovae. The structures of these compounds, including their absolute configurations, were established using detailed analysis of 1D and 2D NMR, ECD, and mass spectra as well as chemical transformations. Melonosins 2 and 3 inhibit AP-1- and NF-kB-dependent transcriptional activities in JB6 Cl41 cells at noncytotoxic concentrations, demonstrating potential cancer preventive activity.

Synthesis and anticancer activity of the derivatives of marine compound rhizochalin in castration resistant prostate cancer.

Development of resistance to standard therapies complicates treatment of advanced prostate cancer. Alternative splicing variants of the androgen receptor (AR), e.g. AR-V7 can mediate resistance to AR-targeting substances abiraterone and enzalutamide. Semi-synthetic marine natural compound rhizochalinin decreases the expression of AR-V7 in human castration-resistant prostate cancer cells and thus resensitizes cells to enzalutamide. In the current study, we modified the structure of rhizochalin in order to determine structure-activity relationships (SAR) and optimize anticancer properties. Thus, we synthesized new 18-hydroxy- and 18-aminorhizochalins and its aglycones. All compounds exhibited anticancer properties in human castration-resistant prostate cancer cells, induced apoptosis and G2/M cell cycle arrest, and were capable of autophagy inhibition. SAR analysis showed an increase of pro-apoptotic activity in the row 18-amino < 18-hydroxy < 18-keto derivatives. In general, aglycones were more cytotoxic compared to glycosides. The sugar elimination was critical for the ability to suppress AR-signaling. Rhizochalinin (2) and 18-hydroxyrhizochalinin (4) were identified as the most promising derivatives and are promoted for further development.

Absolute Configuration of the Cytotoxic Marine Alkaloid Monanchocidin A.

The absolute configuration of the cytotoxic guanidine alkaloid monanchocidin A with 11 stereogenic centers from the marine sponge Monanchora pulchra was determined as 5 R, 8 S, 10 S, 13 R, 14 S, 15 R, 19 R, 23 R, 37 S, 42 S, 43 R after extensive reductive degradation and conversion of the resulting alcohols to MTPA derivatives.