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

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.

Target identification of anticancer natural products using a chemical proteomics approach

In recent years, there has been a strong demand worldwide for the identification and development of potential anticancer drugs based on natural products. Natural products have been explored for their diverse biological and therapeutic applications from ancient time. In order to enhance the efficacy and selectivity and to minimize the undesired side effects of anti cancer natural products (ANPs), it is essential to understand their target proteins and their mechanistic pathway. Chemical proteomics is one of the most powerful tools to connect ANP target identification and quantification where labeling and non-labeling based approaches have been used. Herein, we have discussed the various strategies to systemically develop selective ANP based chemical probes to characterise their specific and non-specific target proteins using a chemical proteomic approach in various cancer cell lysates.

Aaptamine attenuates the proliferation and progression of non-small cell lung carcinoma

CONTEXT

Aaptamine is a potent ocean-derived non-traditional drug candidate against human cancers. However, the underlying molecular mechanisms governing aaptamine-mediated repression of lung cancer cells remain largely undefined.

OBJECTIVE

To examine the inhibitory effect of aaptamine on proliferation and progression of non-small cell lung carcinoma (NSCLC) and dissect the potential mechanisms involved in its anticancer functions.

MATERIALS AND METHODS

In vitro assays of cell proliferation, cell cycle analysis, clonal formation, apoptosis and migration were performed to examine the inhibitory effects of aaptamine (8, 16 and 32 μg/mL) on NSCLC cells. The expression levels of proteins were analysed using western blotting analysis when cells were treated with a single drug or a combination treatment for 48 h.

RESULTS

Aaptamine significantly inhibited A549 and H1299 cells proliferation with IC₅₀ values of 13.91 and 10.47 μg/mL. At the concentrations of 16 and 32 μg/mL, aaptamine significantly reduced capacities in clonogenicity, enhanced cellular apoptosis and decreased the motile and invasive cellular phenotype. In addition, aaptamine arrested cell cycle at G1 phase via selectively abating cell cycle regulation drivers (CDK2/4 and Cyclin D1/E). Western blotting results showed that aaptamine attenuated the protein expression of MMP-7, MMP-9 and upregulated the expression of cleaved-PARP and cleaved-caspase 3. Moreover, aaptamine inhibited PI3K/AKT/GSK3β signalling cascades through specifically degrading the phosphorylated AKT and GSK3β.

DISCUSSION AND CONCLUSIONS

Aaptamine retarded the proliferation and invasion of NSCLC cells by selectively targeting the pathway PI3K/AKT/GSK3β suggesting it as a potential chemotherapeutic agent for repressing tumorigenesis and progression of NSCLC in humans.

A Review of the Secondary Metabolites From the Marine Sponges of the Genus Aaptos

Marine sponges, which belong to the phylum Porifera (Metazoa), are considered the single best source of marine natural products. Among them, members of the genus Aaptos are attractive targets for marine natural product research owing to their abundant biogenetic ability to produce aaptamine derivatives. Apart from aaptamine alkaloids, there are also reports of other compounds from Aaptos sponges. This work reviews the secondary metabolites isolated from Aaptos species from 1982 to 2020, with 46 citations referring to 62 compounds (47 for aaptamines and 15 for others). The emphasis is placed on the structure of the organic molecules, relevant biological activities, chemical ecology aspects, and biosynthesis studies, which are described in the classifications of aaptamines and other compounds in the order of the published year.

Inspired by Sea Urchins: Warburg Effect Mediated Selectivity of Novel Synthetic Non-Glycoside 1,4-Naphthoquinone-6S-Glucose Conjugates in Prostate Cancer

The phenomenon of high sugar consumption by tumor cells is known as Warburg effect. It results from a high glycolysis rate, used by tumors as preferred metabolic pathway even in aerobic conditions. Targeting the Warburg effect to specifically deliver sugar conjugated cytotoxic compounds into tumor cells is a promising approach to create new selective drugs. We designed, synthesized, and analyzed a library of novel 6-S-(1,4-naphthoquinone-2-yl)-d-glucose chimera molecules (SABs)—novel sugar conjugates of 1,4-naphthoquinone analogs of the sea urchin pigments spinochromes, which have previously shown anticancer properties. A sulfur linker (thioether bond) was used to prevent potential hydrolysis by human glycoside-unspecific enzymes. The synthesized compounds exhibited a Warburg effect mediated selectivity to human prostate cancer cells (including highly drug-resistant cell lines). Mitochondria were identified as a primary cellular target of SABs. The mechanism of action included mitochondria membrane permeabilization, followed by ROS upregulation and release of cytotoxic mitochondrial proteins (AIF and cytochrome C) to the cytoplasm, which led to the consequent caspase-9 and -3 activation, PARP cleavage, and apoptosis-like cell death. These results enable us to further clinically develop these compounds for effective Warburg effect targeting.

Targeting the DNA damage response (DDR) by natural compounds

Natural compounds (NC) are an important source of anticancer drugs. The genomic DNA of tumor cells is a major target of conventional anticancer therapeutics (cAT). DNA damage elicits a complex stress response programme termed DNA damage response (DDR), with the PI3-like kinase ATM and ATR being the key regulators. Since the DDR coordinates mechanisms of DNA repair and apoptosis, hence regulating the balance between death and survival, it is an attractive target of novel anticancer strategies. The aim of the study was to identify natural compounds derived from endophytic fungi, lichens, marine sponges or plants that interfere with mechanisms of the DDR. To this end, the cytotoxic and DDR modulating potency of 296 natural compounds, used alone or in combination with the cAT cisplatin (Cis) and doxorubicin (Doxo) was investigated by fluorescence-based analysis of the ATM/ATR-catalyzed S139 phosphorylation of histone 2AX (γH2AX), a surrogate marker of DNA damage-triggered DDR. After initial screening, a total of ten natural compounds were identified that were toxic in pancreatic carcinoma cells and activated the DDR on their own and/or promoted the DDR if used in combination with cAT. Their mode of action was shown to be independent of drug transport mechanisms. Based on their chemical structures, DDR modulatory activity and published data we suggest the marine NC 5-epi-nakijiquinone Q and 5-epi-ilimaquinone as well as the fungal compound secalonic acid F as most promising NC-based drug candidates for future synthesis of DDR-modulating chemical derivatives and their preclinical in vitro and in vivo testing.

5-Azacitidine Exerts Prolonged Pro-Apoptotic Effects and Overcomes Cisplatin-Resistance in Non-Seminomatous Germ Cell Tumor Cells

Despite high cure rates, about 20% of patients with advanced germ cell tumors (GCTs) fail cisplatin-based chemotherapy. High levels of DNA methylation have been identified in GCTs and linked to cisplatin resistance. Here, we examined the effects of DNA hypomethylating 5-azacitidine (5-aza) on two embryonal carcinoma cell lines (NCCIT, 2102Ep) and their cisplatin-resistant isogenic derivatives. Effects on cell viability and cisplatin sensitivity were assessed by the trypan blue exclusion method. Western blotting was used to examine induction of apoptosis 5-aza and results were validated by flow cytometry. Single agent treatment with 5-aza strongly impacted viability and induced apoptosis at low nanomolar concentrations, both in cisplatin-sensitive and -resistant cell lines. 5-aza exerted an immediate apoptotic response, followed by a prolonged inhibitory effect on cell viability and cell-cycle progression. Sequential treatment with 5-aza and cisplatin reduced cellular survival of the cisplatin-resistant sublines already at nanomolar concentrations, suggesting a partial restoration of cisplatin sensitivity by the compound. 5-aza demonstrated anti-tumor activity as a single agent at low nanomolar concentrations in GCT cells, irrespective of cisplatin-sensitivity. 5-aza may also have the potential at least to partially restore cisplatin-sensitivity in non-seminoma cells, supporting the hypothesis that combining DNA demethylating agents with cisplatin-based chemotherapy may be a valid therapeutic approach in patients with refractory GCTs.

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.

Proteomic-based investigations on the mode of action of the marine anticancer compound rhizochalinin

Rhizochalinin (Rhiz) is a novel marine natural sphingolipid-like compound, which shows promising in vitro and in vivo activity in human castration-resistant prostate cancer. In the present study, a global proteome screening approach was applied to investigate molecular targets and biological processes affected by Rhiz in castration-resistant prostate cancer. Bioinformatical analysis of the data predicted an antimigratory effect of Rhiz on cancer cells. Validation of proteins involved in the cancer-associated processes, including cell migration and invasion, revealed downregulation of specific isoforms of stathmin and LASP1, as well as upregulation of Grp75, keratin 81, and precursor IL-1β by Rhiz. Functional analyses confirmed an antimigratory effect of Rhiz in PC-3 cells. Additionally, predicted ERK1/2 activation was confirmed by Western blotting analysis, and revealed prosurvival effects in Rhiz-treated prostate cancer cells indicating a potential mechanism of resistance. A combination of Rhiz with MEK/ERK inhibitors PD98059 (non-ATP competitive MEK1 inhibitor) and FR180204 (ATP-competitive ERK1/2 inhibitor) resulted in synergistic effects. This work provides further insights into the molecular mechanisms underlying Rhiz bioactivity. Furthermore, our research is exemplary for the ability of proteomics to predict drug targets and mode of action of natural anticancer agents.

Marine Sponge Natural Products with Anticancer Potential: An Updated Review

Despite the huge investment into research and the significant effort and advances made in the search for new anticancer drugs in recent decades, cancer cure and treatment continue to be a formidable challenge. Many sources, including plants, animals, and minerals, have been explored in the oncological field because of the possibility of identifying novel molecular therapeutics. Marine sponges are a prolific source of secondary metabolites, a number of which showed intriguing tumor chemopreventive and chemotherapeutic properties. Recently, Food and Drug Administration-approved drugs derived from marine sponges have been shown to reduce metastatic breast cancer, malignant lymphoma, and Hodgkin's disease. The chemopreventive and potential anticancer activity of marine sponge-derived compounds could be explained by multiple cellular and molecular mechanisms, including DNA protection, cell-cycle modulation, apoptosis, and anti-inflammatory activities as well as their ability to chemosensitize cancer cells to traditional antiblastic chemotherapy. The present article aims to depict the multiple mechanisms involved in the chemopreventive and therapeutic effects of marine sponges and critically explore the limitations and challenges associated with the development of marine sponge-based anticancer strategy.

The Inhibitory Activity of Luzonicosides from the Starfish Echinaster luzonicus against Human Melanoma Cells

Malignant melanoma is the most dangerous form of skin cancer, with a rapidly increasing incidence rate. Despite recent advances in melanoma research following the approval of several novel targeted and immuno-therapies, the majority of oncological patients will ultimately perish from the disease. Thus, new effective drugs are still required. Starfish steroid glycosides possess different biological activities, including antitumor activity. The current study focused on the determination of the in vitro inhibitory activity and the mechanism of action of cyclic steroid glycosides isolated from the starfish Echinaster luzonicus-luzonicoside A (LuzA) and luzonicoside D (LuzD)-in human melanoma RPMI-7951 and SK-Mel-28 cell lines. LuzA inhibited proliferation, the formation of colonies, and the migration of SK-Mel-28 cells significantly more than LuzD. Anti-cancer activity has been ascribed to cell cycle regulation and apoptosis induction. The molecular mechanism of action appears to be related to the regulation of the activity of cleaved caspase-3 and poly(ADP-ribose) polymerase (PARP), along with Survivin, Bcl-2, p21 and cyclin D1 level. Overall, our findings support a potential anti-cancer efficacy of luzonicosides A and D on human melanoma cells.

Frondoside A induces AIF-associated caspase-independent apoptosis in Burkitt lymphoma cells

For patients with refractory or relapsed Burkitt lymphoma (BL), no standard therapy is available for second-line treatment to date. Nonfunctional caspases-dependent apoptosis pathways, inactivating p53 mutations and pro-survival autophagy prevent activity of conventional chemotherapy. Thus, new drugs bypassing these mechanisms of resistance are required. Here, we investigated the efficacy of the marine natural compound frondoside A (FrA) in eight BL cell lines. FrA revealed cytotoxic effects in all cell lines tested including the multiresistant CA46 cells. Remarkably, FrA induced caspases- and p53-independent apoptosis, which was characterized by decreased expression of antiapoptotic survivin and Bcl-2, mitochondria targeting (release of cytochrome C, HtrA2/Omi and the apoptosis-inducing factor (AIF), and altered production of ROS) and translocation of AIF to the nuclei. In addition, signs of inhibition of pro-survival autophagy were observed. Thus, FrA is a promising candidate for the treatment of refractory or relapsed BL revealing resistances to standard therapies.

The marine triterpene glycoside frondoside A induces p53-independent apoptosis and inhibits autophagy in urothelial carcinoma cells

Background

Advanced urothelial carcinomas represent a considerable clinical challenge as they are difficult to treat. Platinum-based combination regimens obtain response rates ranging from 40 to 70% in first-line therapy of advanced urothelial carcinoma. In the majority of cases, however, the duration of these responses is limited, and when progression occurs, the outcome is generally poor. Therefore, novel therapeutic strategies are urgently needed. The purpose of the current research is to investigate the anticancer effects and the mode of action of the marine triterpene glycoside frondoside A in p53-wild type and p53-deficient human urothelial carcinoma cells.

Methods

Activity of frondoside A was examined in the human urothelial carcinoma cell lines RT112, RT4, HT-1197, TCC-SUP, T-24, and 486p. Effects of frondoside A on cell viability, either alone or in combination with standard cytotoxic agents were investigated, and synergistic effects were analyzed. Pro-apoptotic activity was assessed by Western blotting and FACS, alone and in combination with a caspases-inhibitor. The impact of functional p53 was investigated by siRNA gene silencing and the p53 inhibitor pifithrin-α. Effects on autophagy were studied using LC3B-I/II and SQSTM/p62 as markers. The unpaired Student’s t-test was used for comparison of the data sets.

Results

Frondoside A shows high cytotoxicity in urothelial carcinoma cells with IC_50s ranging from 0.55 to 2.33 μM while higher concentrations of cisplatin are required for comparable effects (IC₅₀ = 2.03 ~ 5.88 μM). Induction of apoptosis by frondoside A was associated with the regulation of several pro-apoptotic factors, like caspase-3, -8, and -9, PARP, Bax, p21, DNA fragmentation, and externalization of phosphatidylserine. Remarkably, inhibition of p53 by gene silencing or pifithrin-α pretreatment, as well as caspase inhibition, did not suppress apoptotic activity of frondoside A, while cisplatin activity, in contrast, was significantly decreased. Frondoside A inhibited pro-survival autophagy, a known mechanism of drug resistance in urothelial carcinoma and showed synergistic activity with cisplatin and gemcitabine.

Conclusions

A unique combination of properties makes marine compound frondoside A a promising candidate for the treatment of human urothelial carcinomas.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3085-z) contains supplementary material, which is available to authorized users.

Marine compound rhizochalinin shows high in vitro and in vivo efficacy in castration resistant prostate cancer

Development of drug resistance is an inevitable phenomenon in castration-resistant prostate cancer (CRPC) cells requiring novel therapeutic approaches. In this study, efficacy and toxicity of Rhizochalinin (Rhiz) - a novel sphingolipid-like marine compound - was evaluated in prostate cancer models, resistant to currently approved standard therapies. In vitro activity and mechanism of action of Rhiz were examined in the human prostate cancer cell lines PC-3, DU145, LNCaP, 22Rv1, and VCaP. Rhiz significantly reduced cell viability at low micromolar concentrations showing most pronounced effects in enzalutamide and abiraterone resistant AR-V7 positive cells. Caspase-dependent apoptosis, inhibition of pro-survival autophagy, downregulation of AR-V7, PSA and IGF-1 expression as well as inhibition of voltage-gated potassium channels were identified as mechanisms of action. Remarkably, Rhiz re-sensitized AR-V7 positive cells to enzalutamide and increased efficacy of taxanes.In vivo activity and toxicity were evaluated in PC-3 and 22Rv1 NOD SCID mouse xenograft models using i.p. administration. Rhiz significantly reduced growth of PC-3 and 22Rv1 tumor xenografts by 27.0% (p = 0.0156) and 46.8% (p = 0.047) compared with controls with an increased fraction of tumor cells showing apoptosis secondary to Rhiz exposure. In line with the in vitro data, Rhiz was most active in AR-V7 positive xenografts in vivo. In animals, no severe side effects were observed.In conclusion, Rhiz is a promising novel marine-derived compound characterized by a unique combination of anticancer properties. Its further clinical development is of high impact for patients suffering from drug resistant prostate cancer especially those harboring AR-V7 mediated resistance to enzalutamide and abiraterone.

Absolute Configuration and Body Part Distribution of the Alkaloid 6-epi-Monanchorin from the Marine Polychaete Chaetopterus variopedatus

As a result of the first study on secondary metabolites from the cosmopolitan bioluminescent marine tube polychaete Chaetopterus variopedatus, a new bicyclic guanidine alkaloid, 6- epi-monanchorin (1), along with the previously known monanchorin (2) were isolated. The structure of 1 was elucidated by spectroscopic and chemical methods, including a cleavage of the C1–O7 bond to obtain a secondary alcohol (3), which was used to determine the absolute configurations by Mosher's method. It was found that 1 and 2 were mainly accumulated in a secreted mucus special organ of the worm (food net), where green and blue-green microalgae were detected. A biosynthetic pathway to 6- epi-monanchorin and monanchorin from dietary polyenic fatty acid precursors was proposed.

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.

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-1β 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.

Marine alkaloid Monanchocidin a overcomes drug resistance by induction of autophagy and lysosomal membrane permeabilization

Monanchocidin A (MonA) is a novel alkaloid recently isolated from the marine sponge Monanchora pulchra. The compound reveals cytotoxic activity in genitourinary cancers including cisplatin-sensitive and -resistant germ cell tumor (GCT) cell lines, hormone-sensitive and castration-resistant prostate carcinoma cell lines and different bladder carcinoma cell lines. In contrast, non-malignant cells were significantly less sensitive. MonA is highly synergistic with cisplatin in GCT cells. Induction of autophagy at lower and lysosomal membrane permeabilization (LMP) at higher concentrations were identified as the dominating modes of action. Cytotoxicity and protein degradation could be inhibited by 3-methyladenine, an inhibitor of autophagy. LMP was confirmed by loss of acridine orange staining of lysosoms and by release of cathepsin B. In conclusion, MonA exerts cytotoxic activity by mechanisms different from "classical" apoptosis, and could be a promising new compound to overcome resistance to standard therapies in genitourinary malignancies.

Normonanchocidins A, B and D, New Pentacyclic Guanidine Alkaloids from the Far-Eastern Marine Sponge Monanchora pulchra

New pentacyclic guanidine alkaloids, normonanchocidins A, B and D (1–3) along with the earlier known monanchocidin A were isolated from the Far-Eastern marine sponge Monanchora pulchra. Structures of 1–3 were elucidated using 1D- and 2D-NMR spectroscopic and mass spectrometric data. Compound 1 and a mixture of 2 and 3 (1:1) exhibited cytotoxic activities against human leukemia THP-1 cells with IC50 values of 2.1 μM and 3.7 μM, respectively, and against cervix epithelial carcinoma HeLa cells with IC50 of 3.8 μM and 6.8 μM, respectively.

Identification and validation of potential new biomarkers for prostate cancer diagnosis and prognosis using 2D-DIGE and MS

This study was designed to identify and validate potential new biomarkers for prostate cancer and to distinguish patients with and without biochemical relapse. Prostate tissue samples analyzed by 2D-DIGE (two-dimensional difference in gel electrophoresis) and mass spectrometry (MS) revealed downregulation of secernin-1 (P < 0.044) in prostate cancer, while vinculin showed significant upregulation (P < 0.001). Secernin-1 overexpression in prostate tissue was validated using Western blot and immunohistochemistry while vinculin expression was validated using immunohistochemistry. These findings indicate that secernin-1 and vinculin are potential new tissue biomarkers for prostate cancer diagnosis and prognosis, respectively. For validation, protein levels in urine were also examined by Western blot analysis. Urinary vinculin levels in prostate cancer patients were significantly higher than in urine from nontumor patients (P = 0.006). Using multiple reaction monitoring-MS (MRM-MS) analysis, prostatic acid phosphatase (PAP) showed significant higher levels in the urine of prostate cancer patients compared to controls (P = 0.012), while galectin-3 showed significant lower levels in the urine of prostate cancer patients with biochemical relapse, compared to those without relapse (P = 0.017). Three proteins were successfully differentiated between patients with and without prostate cancer and patients with and without relapse by using MRM. Thus, this technique shows promise for implementation as a noninvasive clinical diagnostic technique.

Sargassopenillines A-G, 6,6-spiroketals from the alga-derived fungi Penicillium thomii and Penicillium lividum

Seven new 6,6-spiroketals, sargassopenillines A-G (1-7) were isolated from the alga-derived fungi Penicillium thomii KMM 4645 and Penicillium lividum KMM 4663. The structures of these metabolites were determined by HR-MS and 1D and 2D NMR. The absolute configurations of compounds 1, 5 and 6 were assigned by the modified Mosher's method and by CD data. Sargassopenilline C (3) inhibited the transcriptional activity of the oncogenic nuclear factor AP-1 with an IC50 value of 15 µM.

Anti-photoaging effect of aaptamine in UVB-irradiated human dermal fibroblasts and epidermal keratinocytes

Chronic exposure to ultraviolet (UV) irradiation causes sunburn, inflammatory responses, skin cancer, and photoaging. Photoaging, in particular, generates reactive oxygen species (ROS) that stimulate mitogen-activated protein kinase (MAPK) signaling and transcription factors. UV irradiation also activates matrix metalloproteinases (MMPs) expression and inactivates collagen synthesis. Aaptamine, a marine alkaloid isolated from the marine sponge, has been reported to have antitumor, antimicrobial, antiviral, and antioxidant activities. However, the photo-protective effects of aaptamine have not been elucidated. In this study, our data demonstrated that aaptamine deactivated UVB-induced MAPK and activator protein-1 signaling by suppressing ROS, resulting in attenuating the expression of MMPs in UVB-irradiated human dermal fibroblasts. Aaptamine also decreased proinflammatory cytokines such as cyclooxygenase-2, tumor necrosis factor-α, interleukin-1β, and nuclear factor-kappa B subunits in UVB-irradiated human keratinocytes. In conclusion, we suggest that aaptamine represents a novel and effective strategy for treatment and prevention of photoaging.

A novel mouse model for inhibition of DOHH-mediated hypusine modification reveals a crucial function in embryonic development, proliferation and oncogenic transformation

The central importance of translational control by post-translational modification has spurred major interest in regulatory pathways that control translation. One such pathway uniquely adds hypusine to eukaryotic initiation factor 5A (eIF5A), and thereby affects protein synthesis and, subsequently, cellular proliferation through an unknown mechanism. Using a novel conditional knockout mouse model and a Caenorhabditis elegans knockout model, we found an evolutionarily conserved role for the DOHH-mediated second step of hypusine synthesis in early embryonic development. At the cellular level, we observed reduced proliferation and induction of senescence in 3T3 Dohh-/- cells as well as reduced capability for malignant transformation. Furthermore, mass spectrometry showed that deletion of DOHH results in an unexpected complete loss of hypusine modification. Our results provide new biological insight into the physiological roles of the second step of the hypusination of eIF5A. Moreover, the conditional mouse model presented here provides a powerful tool for manipulating hypusine modification in a temporal and spatial manner, to analyse both how this unique modification normally functions in vivo as well as how it contributes to different pathological conditions.

Aaptamines from the marine sponge Aaptos sp. display anticancer activities in human cancer cell lines and modulate AP-1-, NF-κB-, and p53-dependent transcriptional activity in mouse JB6 Cl41 cells

Aaptamine (8,9-dimethoxy-1H-benzo[de][1,6]naphthyridine) is a marine natural compound possessing antioxidative, antimicrobial, antifungal, and antiretroviral activity. Earlier, we have found that aaptamine and its derivatives demonstrate equal anticancer effects against the human germ cell cancer cell lines NT2 and NT2-R and cause some changes in the proteome of these cells. In order to explore further the mechanism of action of aaptamine and its derivatives, we studied the effects of aaptamine (1), demethyl(oxy)aaptamine (2), and isoaaptamine (3) on human cancer cell lines and on AP-1-, NF-κB-, and p53-dependent transcriptional activity in murine JB6 Cl41 cells. We showed that compounds 1–3 demonstrate anticancer activity in THP-1, HeLa, SNU-C4, SK-MEL-28, and MDA-MB-231 human cancer cell lines. Additionally, all compounds were found to prevent EGF-induced neoplastic transformation of murine JB6 Cl41 cells. Nuclear factors AP-1, NF-κB, and p53 are involved in the cellular response to high and nontoxic concentrations of aaptamine alkaloids 1–3. Furthermore, inhibition of EGF-induced JB6 cell transformation, which is exerted by the compounds 1–3 at low nontoxic concentrations of 0.7–2.1 μM, cannot be explained by activation of AP-1 and NF-κB.

Oxirapentyns F-K from the marine-sediment-derived fungus Isaria felina KMM 4639

Six new highly oxygenated chromene derivatives, oxirapentyns F-K (2-7), one new polyketide (8), one new benzofurane (9), and two known cyclodepsipeptides, isoisariin B and isaridin E, were isolated from the lipophilic extract of the marine-derived fungus Isaria felina KMM 4639. The structures of compounds 2-9 were determined using spectroscopic methods. The relative configurations of compounds 2-7 were established through a combination of NOE data and spin coupling constants, and these results were confirmed by X-ray crystallographic analysis of 4. The absolute structures of all oxirapentyns were assumed based on their biogenetic relationship and confirmed using the modified Mosher's method on 2 and 7. Isariketide (8) showed moderate cytotoxicity toward HL-60 cells.

Meroterpenoids from the alga-derived fungi Penicillium thomii Maire and Penicillium lividum Westling

Ten new austalide meroterpenoids (1-10) were isolated from the alga-derived fungi Penicillium thomii KMM 4645 and Penicillium lividum KMM 4663. Their structures were elucidated by extensive spectroscopic analysis and by comparison with related known compounds. The absolute configurations of some of the metabolites were assigned by the modified Mosher's method and CD data. Compounds 1, 2, 8, and 9 were able to inhibit AP-1-dependent transcriptional activity in JB6 Cl41 cell lines at noncytotoxic concentrations. Austalides 1-5, 8, and 9 exhibited significant inhibitory activity against endo-1,3-β-D-glucanase from a crystalline stalk of the marine mollusk Pseudocardium sachalinensis.

Quinone-carbohydrate nonglucoside conjugates as a new type of cytotoxic agents: synthesis and determination of in vitro activity

We have found that 2-methoxy-1,4-naphthoquinones easily react with primary alcohols to produce the corresponding 2-alkoxyderivatives. Using this reaction, we synthesized methyl-6-O-(naphthalene-1,4-dione-2-yl)-α-D-glucopyranosides, a new type of water soluble quinone-carbohydrate nonglucoside conjugates. The resulting conjugates induced apoptosis in human cancer HeLa and normal mouse JB6 P(+) Cl41 cells with simultaneous inhibition of p53-dependant transcriptional activity, suggesting that the observed cell death was p53-independent. Furthermore, we analyzed structure-activity relationship and bioactivity of 2-hydroxy- and 2-methoxy-1,4-naphthoquinones as well as carbohydrate nonglucoside conjugates. All compounds containing a quinone moiety were able to inhibit p53-dependant transcriptional activity and exerted moderate inhibitory effects on HeLa cell colony formation. Investigations of structure-activity relationships revealed that cytotoxicity depended on the type of substituent at C-2 of the quinone moiety, decreasing in the following order: methoxyderivatives > carbohydrate nonglucoside conjugates > hydroxyderivatives. Furthermore, cytotoxicity depended on the position of the hydroxy substituent in the quinone moiety in all derivatives and decreased in the following order: 8- > 5- > 5,8-derivatives. In conclusion, this is the first report on synthesis and biological structure-activity relationships of the new class of quinone-carbohydrate nonglucoside conjugates.

Marine low molecular weight natural products as potential cancer preventive compounds

Due to taxonomic positions and special living environments, marine organisms produce secondary metabolites that possess unique structures and biological activities. This review is devoted to recently isolated and/or earlier described marine compounds with potential or established cancer preventive activities, their biological sources, molecular mechanisms of their action, and their associations with human health and nutrition. The review covers literature published in 2003–2013 years and focuses on findings of the last 2 years.

Activity of aaptamine and two derivatives, demethyloxyaaptamine and isoaaptamine, in cisplatin-resistant germ cell cancer

We analyzed the effects of all three marine alkaloids aaptamine, demethyloxyaaptamine and isoaaptamine in NT2-R, a cisplatin-resistant subline of the human embryonal carcinoma cell line NT2. All aaptamines were found to be equally effective in both cell lines, excluding cross-resistance between aaptamines and cisplatin in vitro. At the inhibitory concentration (IC50), aaptamine exerted an antiproliferative effect, whereas demethyloxyaaptamine and isoaaptamine were strong inducers of apoptosis. We analyzed the changes in the proteome of NT2-R cells treated with these compounds. 16-22 proteins were found to be significantly altered, of which several were validated by Western blotting and two-dimensional Western blotting analysis. Changes in the proteome pattern frequently resulted from post-transcriptional protein modifications, i.e. phosphorylation or hypusination in the case of eIF5A. Although the lists of altered proteins were heterogeneous and compound-specific, gene ontology analyses identified rather similar profiles regarding the affected molecular functions. Ingenuity pathway analysis by IPA put the following factors in a central position of the hypothetical networks: myc and p53 for aaptamine; tumor necrosis factor (TNF) for demethyloxyaaptamine; and all three, myc, p53, and TNF for isoaaptamine. Our results represent an important step towards a better understanding of the molecular basis underlying the observed bioactivity of these promising marine compounds.

BIOLOGICAL SIGNIFICANCE

We characterized the mode of action of three aaptamines, marine natural compound with anti-tumor activity, using a functional proteomics approach and the cisplatin-resistant pluripotent human embryonal carcinoma cell line NT2-R. The manuscript is of particular scientific interest, as we could reveal the similarities and differences of the modes of action. Furthermore, we were able to identify several new targets of these promising compounds. We found hypusination of eIF5A to be a prominent feature exclusively of aaptamine treatment, as this was not observed upon treatment with demethyloxyaaptamine or isoaaptamine. Our results are a step towards unraveling the mode of action of these interesting compounds.

Monanchomycalin C, a New Pentacyclic Guanidine Alkaloid from the Far-Eastern Marine Sponge Monanchora Pulchra

A new pentacyclic guanidine alkaloid, monanchomycalin C (1), along with the earlier known ptilomycalin A (2), were isolated from the Far-Eastern marine sponge Monanchora pulchra. The structure of 1 was elucidated using 1D and 2D NMR spectroscopic and mass spectrometric data. Compounds 1 and 2 exhibited cytotoxic activities against human breast cancer MDA-MB-231 cells with IC50 values of 8.2 μM and 4.3 μM, respectively.

Isolation, structures, and biological activities of triterpenoids from a Penares sp. marine sponge

Six new triterpenoids (1-6) and the previously known penasterone, acetylpenasterol, and ergosta-4,24(28)-dien-3-one were isolated from a Penares sp. sponge collected from Vietnamese waters. Structures of the obtained compounds were established by extensive 1D and 2D NMR spectroscopy and mass spectrometry. Configurations of the triterpene epoxy lactones (1-4) were determined on the basis of NOESY and CD data and calculation of spin coupling constants and confirmed by X-ray crystallographic analysis of compound 2. The isolated triterpenoid 6 was cytotoxic against human leukemia HL-60 cells (IC₅₀ = 9.7 μM).

Chemical profiling of deoxyhypusine hydroxylase inhibitors for antimalarial therapy

A first approach to discover new antimalarials has been recently performed in a combined approach with data from GlaxoSmithKline Tres Cantos Antimalarial Set, Novartis-GNF Malaria Box Data set and St. Jude Children's Research Hospital. These data are assembled in the Malaria Box. In a first phenotypic forward chemical genetic approach, 400 chemicals were employed to eradicate the parasite in the erythrocytic stages. The advantage of phenotypic screens for the identification of novel chemotypes is that no a priori assumptions are made concerning a fixed target and that active compounds inherently have cellular bioavailability. In a first screen 40 mostly heterocyclic, highly active compounds (in nmol range of growth inhibition) were identified with EC50 values ≤2 μM against chloroquine-resistant Plasmodium falciparum strains and a therapeutic window ≥10 against two mammalian cell lines. 78 % of the compounds had no violations with the Lipinski Rule of 5 and only 1 % of the compounds showed cytotoxicity when applied at concentrations of 10 μM. This pre-selective step of parasitic eradication will be used further for a test of the Malaria Box with a potential in iron chelating capacity to inhibit deoxyhypusine hydroxylase (DOHH) from P. falciparum and vivax. DOHH, a metalloprotein which consists of ferrous iron and catalyzes the second step of the posttranslational modification at a specific lysine in eukaryotic initiation factor 5A (EIF-5A) to hypusine. Hypusine is a novel, non-proteinogenic amino acid, which is essential in eukaryotes and for parasitic proliferation. DOHH seems to be a "druggable" target, since it has only 26 % amino acid identity to its human orthologue. For a High-throughput Screening (HTS) of DOOH inhibitors, rapid and robust analytical tools are a prerequisite. A proteomic platform for the detection of hypusine metabolites is currently established. Ultra performance Liquid Chromatography enables the detection of hypusine metabolites with retention times of 7.4 min for deoxyhypusine and 7.3 min for hypusine. Alternatively, the analytes can be detected by their masses with gas chromatography/mass spectrometry or one-dimensional chromatography coupled to mass spectrometry. Moreover, the identified hits will be tracked further to test their efficacy in novel "in vitro assays". Subsequently in vivo inhibition in a humanized mouse model will be tested.

Synthesis and pharmacology of proteasome inhibitors

Shortly after the discovery of the proteasome it was proposed that inhibitors could stabilize proteins which ultimately would trigger apoptosis in tumor cells. The essential questions were whether small molecules would be able to inhibit the proteasome without generating prohibitive side effects and how one would derive these compounds. Fortunately, "Mother Nature" has generated a wide variety of natural products that provide distinct selectivities and specificities. The chemical synthesis of these natural products finally provided access to analogues and optimized drugs of which two different classes have been approved for the treatment of malignancies. Despite these achievements, additional lead structures derived from nature are under investigation and will be discussed with regard to their biological potential and chemical challenges.

Combination of a proteomics approach and reengineering of meso scale network models for prediction of mode-of-action for tyrosine kinase inhibitors

In drug discovery, the characterisation of the precise modes of action (MoA) and of unwanted off-target effects of novel molecularly targeted compounds is of highest relevance. Recent approaches for identification of MoA have employed various techniques for modeling of well defined signaling pathways including structural information, changes in phenotypic behavior of cells and gene expression patterns after drug treatment. However, efficient approaches focusing on proteome wide data for the identification of MoA including interference with mutations are underrepresented. As mutations are key drivers of drug resistance in molecularly targeted tumor therapies, efficient analysis and modeling of downstream effects of mutations on drug MoA is a key to efficient development of improved targeted anti-cancer drugs. Here we present a combination of a global proteome analysis, reengineering of network models and integration of apoptosis data used to infer the mode-of-action of various tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) cell lines expressing wild type as well as TKI resistance conferring mutants of BCR-ABL. The inferred network models provide a tool to predict the main MoA of drugs as well as to grouping of drugs with known similar kinase inhibitory activity patterns in comparison to drugs with an additional MoA. We believe that our direct network reconstruction approach, demonstrated on proteomics data, can provide a complementary method to the established network reconstruction approaches for the preclinical modeling of the MoA of various types of targeted drugs in cancer treatment. Hence it may contribute to the more precise prediction of clinically relevant on- and off-target effects of TKIs.

Protein-protein-interaction network organization of the hypusine modification system

Hypusine modification of eukaryotic initiation factor 5A (eIF-5A) represents a unique and highly specific post-translational modification with regulatory functions in cancer, diabetes, and infectious diseases. However, the specific cellular pathways that are influenced by the hypusine modification remain largely unknown. To globally characterize eIF-5A and hypusine-dependent pathways, we used an approach that combines large-scale bioreactor cell culture with tandem affinity purification and mass spectrometry: "bioreactor-TAP-MS/MS." By applying this approach systematically to all four components of the hypusine modification system (eIF-5A1, eIF-5A2, DHS, and DOHH), we identified 248 interacting proteins as components of the cellular hypusine network, with diverse functions including regulation of translation, mRNA processing, DNA replication, and cell cycle regulation. Network analysis of this data set enabled us to provide a comprehensive overview of the protein-protein interaction landscape of the hypusine modification system. In addition, we validated the interaction of eIF-5A with some of the newly identified associated proteins in more detail. Our analysis has revealed numerous novel interactions, and thus provides a valuable resource for understanding how this crucial homeostatic signaling pathway affects different cellular functions.

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.