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.

1-O-Alkylglycerol Ethers from the Marine Sponge Guitarra abbotti and Their Cytotoxic Activity.

The cytotoxicity-bioassay-guided fractionation of the ethanol extract from the marine sponge Guitarra abbotti, whose 1-O-alkyl-sn-glycerol ethers (AGEs) have not been investigated so far, led to the isolation of a complex lipid fraction containing, along with previously known compounds, six new lipids of the AGE type. The composition of the AGE fraction as well as the structures of 6 new and 22 previously known compounds were established using 1H and 13C NMR, GC/MS, and chemical conversion methods. The new AGEs were identified as: 1-O-(Z-docos-15-enyl)-sn-glycerol (1), 1-O-(Z-docos-17-enyl)-sn-glycerol (2), 1-O-(Z-tricos-15-enyl)-sn-glycerol (3), 1-O-(Z-tricos-16-enyl)-sn-glycerol (4), 1-O-(Z-tricos-17-enyl)-sn-glycerol (5), and 1-O-(Z-tetracos-15-enyl)-sn-glycerol (6). The isolated AGEs show weak cytotoxic activity in THP-1, HL-60, HeLa, DLD-1, SNU C4, SK-MEL-28, and MDA-MB-231 human cancer cells. A further cytotoxicity analysis in JB6 P+ Cl41 cells bearing mutated MAP kinase genes revealed that ERK2 and JNK1 play a cytoprotective role in the cellular response to the AGE-induced cytotoxic effects.

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.

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.

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.

Anti-migratory activity of marine alkaloid monanchocidin A - proteomics-based discovery and confirmation.

Monanchocidin A (MonA) is a novel marine alkaloid with promising anti-cancer properties. We recently demonstrated its high efficacy in human urogenital cancers including germ cell tumors. Here, we applied a global proteome screening approach to investigate molecular targets and biological processes affected by MonA in the human cisplatin-resistant germ cell cancer cell line NCCIT-R. Bioinformatical analysis of the proteomics data predicted an effect of MonA on cancer cell migration. Thus, proteins known to be involved in cancer cell migration and invasion were chosen for further validation. The protein alterations identified by proteomics resulted from both, regulation of the total protein expression and post-transcriptional modifications. Among others, regulation of an isoform of vimentin, up-regulation of multiple apolipoprotein E isoforms, and inhibition of hypusination of eukaryotic translation initiation factor 5A-1 were found upon treatment with MonA. Further functional analyses were performed and revealed decreased cell migration and colony formation of cancer cells treated with MonA at non-cytotoxic and non-antiproliferative concentrations. This work provides further insights into the molecular mechanisms behind MonA bioactivity. Furthermore, our research is exemplary for the ability of proteomics to predict drug targets and mode of action of natural anti-cancer agents.

The marine triterpene glycoside frondoside A exhibits activity in vitro and in vivo in prostate cancer.

Despite recent advances in the treatment of metastatic castration-resistant prostate cancer (CRPC), outcome of patients remains poor due to the development of drug resistance. Thus, new drugs are urgently needed. We investigated efficacy, toxicity and mechanism of action of marine triterpene glycoside frondoside A (FrA) using CRPC cell lines in vitro and in vivo. FrA revealed high efficacy in human prostate cancer cells, while non-malignant cells were less sensitive. Remarkably, proliferation and colony formation of cells resistant to enzalutamide and abiraterone (due to the androgen receptor splice variant AR-V7) were also significantly inhibited by FrA. The marine compound caused cell type specific cell cycle arrest and induction of caspase-dependent or -independent apoptosis. Up-regulation or induction of several pro-apoptotic proteins (Bax, Bad, PTEN), cleavage of PARP and caspase-3 and down-regulation of anti-apoptotic proteins (survivin and Bcl-2) were detected in treated cells. Global proteome analysis revealed regulation of proteins involved in formation of metastases, tumor cell invasion, and apoptosis, like keratin 81, CrkII, IL-1ß and cathepsin B. Inhibition of pro-survival autophagy was observed following FrA exposure. In vivo, FrA inhibited tumor growth of PC-3 and DU145 cells with a notable reduction of lung metastasis, as well as circulating tumor cells in the peripheral blood. Increased lymphocyte counts of treated animals might indicate an immune modulating effect of FrA. In conclusion, our results suggest that FrA is a promising new drug for the treatment of mCRPC. Induction of apoptosis, inhibition of pro-survival autophagy, and immune modulatory effects are suspected modes of actions.

Guanidine Alkaloids from the Marine Sponge Monanchora pulchra Show Cytotoxic Properties and Prevent EGF-Induced Neoplastic Transformation in Vitro.

Guanidine alkaloids from sponges Monanchora spp. represent diverse bioactive compounds, however, the mechanisms underlying bioactivity are very poorly understood. Here, we report results of studies on cytotoxic action, the ability to inhibit EGF-induced neoplastic transformation, and the effects on MAPK/AP-1 signaling of eight rare guanidine alkaloids, recently isolated from the marine sponge Monanchora pulchra, namely: monanchocidin A (1), monanchocidin B (2), monanchomycalin C (3), ptilomycalin A (4), monanchomycalin B (5), normonanchocidin D (6), urupocidin A (7), and pulchranin A (8). All of the compounds induced cell cycle arrest (apart from 8) and programmed death of cancer cells. Ptilomycalin A-like compounds 1-6 activated JNK1/2 and ERK1/2, following AP-1 activation and caused p53-independent programmed cell death. Compound 7 induced p53-independent cell death without activation of AP-1 or caspase-3/7, and the observed JNK1/2 activation did not contribute to the cytotoxic effect of the compound. Alkaloid 8 induced JNK1/2 (but not ERK1/2) activation leading to p53-independent cell death and strong suppression of AP-1 activity. Alkaloids 1-4, 7, and 8 were able to inhibit the EGF-induced neoplastic transformation of JB6 P⁺ Cl41 cells. Our results suggest that investigated guanidine marine alkaloids hold potential to eliminate human cancer cells and prevent cancer cell formation and spreading.

Pyridine Nucleosides Neopetrosides A and B from a Marine Neopetrosia sp. Sponge. Synthesis of Neopetroside A and Its ß-Riboside Analogue.

Neopetrosides A (1) and B (2), new naturally occurring ribosides of nicotinic acid with extremely rare α-N-glycoside linkages and residues of p-hydroxybenzoic and pyrrole-2-carboxylic acids attached to C-5', were isolated from a marine Neopetrosia sp. sponge. Structures 1 and 2 were determined by NMR and MS methods and confirmed by the synthesis of 1 and its ß-riboside analogue (3). Neopetroside A (1) upregulates mitochondrial functions in cardiomyocytes.

Proteomic profiling of germ cell cancer cells treated with aaptamine, a marine alkaloid with antiproliferative activity.

Aaptamine is a marine compound isolated from the sponge Aaptos aaptos showing antiproliferative properties via an undefined mode of action. We analyzed the effects of aaptamine treatment on the proliferation and protein expression of the pluripotent human embryonal carcinoma cell line NT2. Effects on proliferation, cell cycle distribution, and induction of apoptosis were analyzed. At lower concentrations, including the IC50 of 50 µM, aaptamine treatment resulted in a G2/M phase cell cycle arrest, whereas at higher concentrations, induction of apoptosis was seen. Differentially expressed proteins were assessed by 2D-PAGE and mass spectrometry, followed by verification and analysis of protein modifications of the most significantly up- and down-regulated proteins. Aaptamine treatment at the IC50 for 48 h resulted in alteration of 10 proteins, of which five each showed up- and down-regulation. Changes in the 2D map were frequently noticed as a result of post-transcriptional modifications, e.g., of the hypusine modification of the eukaryotic initiation factor 5A (eIF5A). Observed alterations such as increased expression of CRABP2 and hypusination of eIF5A have previously been identified during differentiation of pluripotent cells. For the first time, we describe changes in protein expression caused by aaptamine, providing valuable information regarding the mode of action of this compound.

Mycalamide A shows cytotoxic properties and prevents EGF-induced neoplastic transformation through inhibition of nuclear factors.

Mycalamide A, a marine natural compound previously isolated from sponges, is known as a protein synthesis inhibitor with potent antitumor activity. However, the ability of this compound to prevent malignant transformation of cells has never been examined before. Here, for the first time, we report the isolation of mycalamide A from ascidian Polysincraton sp. as well as investigation of its cancer preventive properties. In murine JB6 Cl41 P(+) cells, mycalamide A inhibited epidermal growth factor (EGF)-induced neoplastic transformation, and induced apoptosis at subnanomolar or nanomolar concentrations. The compound inhibited transcriptional activity of the oncogenic nuclear factors AP-1 and NF-κB, a potential mechanism of its cancer preventive properties. Induction of phosphorylation of the kinases MAPK p38, JNK, and ERK was also observed at high concentrations of mycalamide A. The drug shows promising potential for both cancer-prevention and cytotoxic therapy and should be further developed.

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.

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.

Monanchocidins B-E: polycyclic guanidine alkaloids with potent antileukemic activities from the sponge Monanchora pulchra.

New unusual polycyclic guanidine alkaloids monanchocidins B-E (2-5) along with monanchocidin A (1), which we recently described, were isolated from the Far-Eastern marine sponge Monanchora pulchra. Their structures were established using spectroscopic data and chemical transformations. Compounds 1-5 show potent cytotoxic activities against HL-60 human leukemia cells with IC50 values of 540, 200, 110, 830, and 650 nM, respectively.

The anticancer activity of 3- and 10-bromofascaplysins is mediated by caspase-8, -9, -3-dependent apoptosis.

3- and 10-Bromofascaplysins was previously found to possess cytotoxic activity. In this study, we investigated their cancer preventive and proapoptotic properties. These effects were tested on mouse skin epidermal JB6 P(+) Cl41 cell line, its stable transfectants, and human tumor HL-60, THP-1, SNU-C4, SK-MEL-28, DLD-1, MDA-MB-231, and HeLa cells using a variety of assessments, including a cell viability (MTS) assay, flow cytometry, anchorage-independent soft agar assay, luciferase assay, mitochondrial permeability assay, and Western blotting. 3- and 10-Bromofascaplysins were effective at submicromolar concentrations as the anticancer agents, which exerted their action, at least in part, through the induction of caspase-8, -9, -3-dependent apoptosis.

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.

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.

Dactylone inhibits epidermal growth factor-induced transformation and phenotype expression of human cancer cells and induces G1-S arrest and apoptosis.

The marine natural chamigrane-type sesquiterpenoid, dactylone, is closely related to secondary metabolites of some edible species of red algae. In the present study, the effect of dactylone was tested on the mouse skin epidermal JB6 P+ Cl41 cell line and its stable transfectants as well as on several human tumor cell lines, including lung (H460), colon (HCT-116), and skin melanomas (SK-MEL-5 and SK-MEL-28). This natural product was effective at nontoxic doses as a cancer-preventive agent, which exerted its actions, at least in part, through the inhibition of cyclin D3 and Cdk4 expression and retinoblastoma tumor suppressor protein (Rb) phosphorylation. The inhibition of these cell cycle components was followed by cell cycle arrest at the G1-S transition with subsequent p53-independent apoptosis. Therefore, these data showed that application of dactylone and related compounds may lead to decreased malignant cell transformation and/or decreased tumor cell proliferation.