Chemical constituents from salt lake-derived Streptomyces sp. QHA10.

Two new alkaloids (1,2) and one new enoic acid (3), together with three known piericidins (4-6), were isolated from the liquid fermentation of the salt lake derived Streptomyces sp. QHA10. The structures of 1-3 were elucidated based on extensive spectroscopic data (NMR, HRESIMS) as well as single-crystal X-ray diffraction. Compound 3 showed potential anti-inflammatory activity by inhibiting the production of nitric oxide (NO) in lipopolysaccharide (LPS)-induced RAW 264.7 mouse macrophages with the IC50 value of 24.5 µM.

Heteroexpression of Aspergillus nidulans laeA in Marine-Derived Fungi Triggers Upregulation of Secondary Metabolite Biosynthetic Genes.

Fungi are a prospective resource of bioactive compounds, but conventional methods of drug discovery are not effective enough to fully explore their metabolic potential. This study aimed to develop an easily attainable method to elicit the metabolic potential of fungi using Aspergillus nidulans laeA as a transcription regulation tool. In this study, functional analysis of Aspergillus nidulans laeA (AnLaeA) and Aspergillus sp. Z5 laeA (Az5LaeA) was done in the fungus Aspergillus sp. Z5. Heterologous AnLaeA-and native Az5LaeA-overexpression exhibited similar phenotypic effects and caused an increase in production of a bioactive compound diorcinol in Aspergillus sp. Z5, which proved the conserved function of this global regulator. In particular, heteroexpression of AnLaeA showed a significant impact on the expression of velvet complex genes, diorcinol synthesis-related genes, and different transcription factors (TFs). Moreover, heteroexpression of AnLaeA influenced the whole genome gene expression of Aspergillus sp. Z5 and triggered the upregulation of many genes. Overall, these findings suggest that heteroexpression of AnLaeA in fungi serves as a simple and easy method to explore their metabolic potential. In relation to this, AnLaeA was overexpressed in the fungus Penicillium sp. LC1-4, which resulted in increased production of quinolactacin A.

Gephyromycin C, a novel small-molecule inhibitor of heat shock protein Hsp90, induces G2/M cell cycle arrest and apoptosis in PC3 cells in vitro.

Gephyromycin C (GC), a natural compound isolated from a marine-derived actinomycete Streptomyces sp. SS13I, which exerts anti-proliferative effect on PC3 cells. However, its underlying mechanism of the anti-cancer effect remains unknown. The results of SRB assays showed that GC inhibited the proliferation of PC3 cells with an IC50 value of 1.79 ± 0.28 µM. GC also induced G2/M cell cycle arrest which was accompanied by declining levels of cyclin proteins. Possible mechanisms were investigated and it was found that GC bound to Hsp90 and caused the degradation of Hsp90 client proteins (AKT, CHK1, P53, CDK4, Raf-b, and Raf-1). The fluorescent polarization assay with FITC-labeled geldanamycin (FITC-GA) demonstrated that GC was able to compete with FITC-GA in binding to wild type Hsp90 with an IC50 of 2.15 µM. Results of a docking study also suggested that GC interacted with the N-terminal domain of Hsp90. Our results showed that GC could bind to Hsp90, which resulted in down-regulation of Hsp90 client proteins and G2/M arrest in PC3 cells. Since the antitumor effects of this kind of angucycline via targeting Hsp90 has not been reported before, our results indicate that GC is a novel inhibitor of Hsp90 from marine resources and worthy of further study.

A new compound from the marine-derived Streptomyces sp. SS13M.

As part of our efforts toward search for structurally new and bioactive natural products from marine-derived microorganisms, one new compound (1) was characterized from a marine-derived actinomycete Streptomyces sp. SS13M. The structure of new compound was elucidated by the analysis of HRESIMS, 1D, and 2D NMR spectroscopic data, and the absolute configuration was determined by ECD calculations.[Formula: see text].

A new medermycin analog from the marine-derived actinomycetes Streptomyces sp. ZS-A45.

A new medermycin analog (1) was isolated from the marine-derived actinomycetes Streptomyces sp. ZS-A45. The structure elucidation of compound 1 was determined by the HRESIMS and extensive NMR analysis. And compound 1 exhibited significant cytotoxicity against PC3 cell lines with IC50 values of 0.81 ± 0.42 µm.

Bioactive staurosporine derivatives from the Streptomyces sp. NB-A13.

Six new (1-6) and nine known (7-15) staurosporine derivatives were isolated from the rice solid fermentation of the marine-derived Streptomyces sp. NB-A13. The structures of the new staurosporine derivatives were established by extensive spectroscopic data interpretation. The absolute configurations of 1 and 2 were assigned by quantum chemical calculations of the electronic circular dichroism (ECD) spectra. All of these compounds were screened for their cytotoxic activities against PC-3 and SW-620 cell lines. Compound 7 exhibited stronger inhibitory activity against SW-620 cell lines than the positive control staurosporine (25.10 nM), with IC50 values of 9.99 nM. Moreover, compounds 1-5, 8-13 and 15 also showed significant cytotoxicities with IC50 values ranging from 0.02 to 16.60 µM, while 6 exhibited no cytotoxic potency. Additionally, compounds 1-7 were also tested for enzyme inhibition activities of Protein kinase C theta (PKC-θ), and showed activity with IC50 values ranging from 0.06 to 9.43 µM except for compound 6, which has no inhibition activity.

Medermycin-Type Naphthoquinones from the Marine-Derived Streptomyces sp. XMA39.

Four new medermycin-type naphthoquinones, strepoxepinmycins A-D (1-4), and one known compound, medermycin (5), were identified from Streptomyces sp. XMA39. Their structures were elucidated by analysis of HRESIMS, 1D and 2D NMR spectroscopic data, and ECD calculations. Among these compounds, strepoxepinmycin A (1) represents a rare 5,10-oxepindione ring system typically formed by a Baeyer-Villiger oxidation, and strepoxepinmycin B (2) is an isolation artifact derived from 1. Bioactivity evaluations of these compounds showed that compounds 3 and 4 exhibited cytotoxicity against HCT-116 and PC-3 cancer cell lines and 4 exhibited moderate inhibition of ROCK 2 protein kinase. In addition, all of the new compounds showed antibacterial activity against Escherichia coli and methicillin-resistant Staphylococcus aureus and antifungal activity against Candida albicans.

Bioactive Indolocarbazoles from the Marine-Derived Streptomyces sp. DT-A61.

Nine new indolocarbazoles (1-9) were isolated from the marine-derived Streptomyces sp. DT-A61. Among them compounds 1-8 featured a hydroxy group at the C-3 or C-9 position. All purified compounds were identified by 1D and 2D NMR and HRESIMS data. The absolute configurations of 4-6, 8, and 9 were determined by electronic circular dichroism spectroscopic data. Compound 7 exhibited significant activity against human prostate PC-3 cancer cells with an IC50 value of 0.16 µM. Compounds 1, 5, 6, and 9 showed moderate inhibition against the same cell line with IC50 values of 8.0, 3.6, 3.1, and 5.6 µM. Compound 2 displayed a notable inhibitory effect against Rho-associated protein kinase (ROCK2) with an IC50 value of 5.7 nM, which was similar to the positive control staurosporine (IC50 7.8 nM).

Cyclizidine-Type Alkaloids from Streptomyces sp. HNA39.

Eight new cyclizidine-type alkaloids (1-8) and one known alkaloid (9) were identified from the chemical investigations of a marine-derived actinomycete, Streptomyces sp. HNA39. Among these alkaloids, compounds 3, 7, and 8 contain a chlorine atom, and the known alkaloid, (+)-ent-cyclizidine (9), is now first reported as a natural product. Their structures were elucidated by extensive NMR-spectroscopic analysis and HRESIMS data. The absolute configurations of all of the compounds were established by ECD calculations. Cytotoxicity evaluations of all of the compounds showed that compound 2 exhibited significant activity against the PC3 and HCT116 human-cancer-cell lines with IC50 values of 0.52 ± 0.03 and 8.3 ± 0.1 µM, respectively. Interestingly, compounds 2, 5, 7, and 8 exhibited moderate inhibition against the ROCK2 protein kinase with IC50 values from 7.0 ± 0.8 to 42 ± 3 µM.

New analogues of brefeldin A from sediment-derived fungus Penicillium sp. DT-F29.

Four new analogues of brefeldin A named 7, 7-dimethoxybrefeldin C (3), 6ß-hydroxybrefeldin C (4), 4-epi-15-epi-brefeldin A (5), 4-epi-8α-hydroxy-15-epi-brefeldin C (6), together with four known analogues (1, 7-9) were isolated from a fermentation of the sediment-derived fungus Penicillium sp. DT-F29. The structures of these compounds were elucidated on the basis of extensive spectroscopic and chemical methods. In the bioactivity assays, only compounds 1 and 8 showed significant inhibitory activities against human lung adenocarcinoma cell. In addition, compound 1 was first reported for the potent ability to reactivate latent HIV with EC50 value of 0.03 µM.

Unprecedent aminophysalin from Physalis angulata.

The 95% ethanol extract of the whole plant of Physalis angulata Linn. afforded one new skeletal physalin named aminophysalin A (1) and one new naturally occurring 5ß-hydroxy-6a-chloro-5,6-dihydrophysalin B (2), together with five known physalins (3-7). Their structures were elucidated through MS, IR, NMR spectroscopy analyses and X-ray crystallography. Aminophysalin A (1) had an absolutely unusual structural feature in the chemistry of physalins with a nitrogen atom. Compounds 1-7 were evaluated for quinone reductase activities in hepa 1c1c7 cells. Physalin H (6) showed strong quinone reductase induction activity with IR (Induction ratio, QR induction activity) value of 3.74±0.02, using 4-bromoflavone as a positive control substance (2.17±0.01, 10 µg/mL), while compounds 1, 2, 3, 5 showed weak quinone reductase induction activity.

Upregulating Noxa by ER stress, celastrol exerts synergistic anti-cancer activity in combination with ABT-737 in human hepatocellular carcinoma cells.

The human hepatocellular carcinoma (HCC) represents biologically aggressive and chemo-resistant cancers. Owing to the low affinity with the apoptotic factor Mcl-1, the BH3 mimetic drug ABT-737 failed to exert potent cancer-killing activities in variety of cancer models including HCC. The current study demonstrated that combining ABT-737 and Celastrol synergistically suppressed HCC cell proliferation, and induced apoptosis which was accompanied with the activation of caspase cascade and release of cytochrome c from mitochondria. Further study revealed that the enhanced Noxa caused by Celastrol was the key factor for the synergy, since small interfering RNA-mediated knockdown of Noxa expression in HCC cells resulted in decreased apoptosis and attenuated anti-proliferative effects of the combination. In addition, our study unraveled that, upon Celastrol exposure, the activation of endoplasmic reticulum (ER) stress, specifically, the eIF2α-ATF4 pathway played indispensable roles in the activation of Noxa, which was validated by the observation that depletion of ATF4 significantly abrogated the Noxa elevation by Celastrol. Our findings highlight a novel signaling pathway through which Celastrol increase Noxa expression, and suggest the potential use of ATF4-mediated regulation of Noxa as a promising strategy to improve the anti-cancer activities of ABT-737.

GDC-0941 sensitizes breast cancer to ABT-737 in vitro and in vivo through promoting the degradation of Mcl-1.

The present study showed that GDC-0941 potently sensitized breast cancer to ABT-737 in vitro and in vivo. ABT-737 exhibited limited lethality in breast cancer cells; however, when combined with GDC-0941, it displayed strong synergistic cytotoxicity and enhanced caspase-mediated apoptosis. GDC-0941 promoted proteasomal degradation of Mcl-1, of which the overexpression has been validated to confer ABT-737 resistance, thereby enhanced the anticancer efficacy of ABT-737. Furthermore, the combination of GDC-0941 and ABT-737 exerted increased anti-tumor efficacy on MDA-MB-231 xenograft models. Overall, our data described unprecedentedly the promising therapeutic potential and underlying mechanisms of combining GDC-0941 with ABT-737 in treating breast cancer.

Up-regulation of death receptor 4 and 5 by celastrol enhances the anti-cancer activity of TRAIL/Apo-2L.

Our previous study demonstrated that celastrol combined with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L) exhibited significant synergistic anti-cancer activities, thus we were promoted to investigate the molecular mechanism of this synergy. Here in this study, we show that celastrol up-regulates death receptor 4 (DR4) and 5 (DR5) expression at mRNA, total protein and cell surface levels, and the specific knockdown using DR4- or DR5-targeting siRNA transfection attenuates the PARP cleavage caused by the combination of celastrol and TRAIL/Apo-2L, denoting the critical roles of DR induction in this sensitization. Of note is that although celastrol activates p38 mitogen activated protein kinases (p38 MAPK), SB203580, one specific inhibitor of p38, fails to interrupt celastrol-induced DR4 expression and the enhanced apoptosis caused by celastrol plus TRAIL/Apo-2L. In addition, the protein expression of Mcl-1 and FLIP, two critical antiapoptotic factors, is not decreased upon celastrol treatment under our experimental conditions. Taken together, the present study demonstrates that the enhanced mRNA and protein expression of DR4 and DR5 play prominent roles in the sensitization of celastrol to TRAIL/Apo-2L-induced apoptosis, in a p38 MAPK-independent manner.

HIF-1α-dependent autophagy protects HeLa cells from fenretinide (4-HPR)-induced apoptosis in hypoxia.

Novel therapeutic strategies are needed to address and to solve the emerging problem of hypoxia-induced resistance to anticancer drugs. N-(4-Hydroxyphenyl)retinamide (4-HPR) exhibits potent anticancer and chemopreventive activities, but its inefficiency under hypoxia, through undetermined mechanisms, may contribute to its lack of activity in clinical trials. In this study, we showed that under normoxia, 4-HPR resulted in apoptosis and ultimate cell death; in contrast, under hypoxia, autophagy was preferentially induced by 4-HPR at an equivalent concentration, accompanied by microtubule associated protein light-chain 3 (LC3) conversion and acidic vesicular organelle formation. Under hypoxia, autophagy inhibition by 3-methyladenine or chloroquine significantly enhanced apoptosis and decreased cell viability in 4-HPR-exposed cells, indicating that autophagy prevents cancer cell death and presumably leads to hypoxia-induced resistance to 4-HPR. Importantly, knockdown of hypoxia-inducible factor-1α (HIF-1α) inhibited autophagy but promoted 4-HPR-induced apoptosis under hypoxia, demonstrating its critical role as a mediator of this protective autophagy. The present study provides the first evidence supporting the hypothesis that autophagy and apoptosis can be differentially induced by 4-HPR under different oxygen conditions; mediated by HIF-1α, 4-HPR-induced autophagy under hypoxia confers a survival advantage to HeLa cells, protects them from 4-HPR-induced death signals, and thus contributes to their hypoxia-induced resistance to this agent. Our data suggest that autophagy inhibition is a potential alternative strategy to overcome hypoxia-induced resistance to 4-HPR and enhance the anticancer activities of this agent.

Synergistic anti-cancer activity by the combination of TRAIL/APO-2L and celastrol.

The present study demonstrates that the combination of TRAIL/APO-2L and celastrol exerts strong synergistic antiproliferative effect against human cancer cells including ovary cancer OVCAR-8, colon cancer SW620, and lung cancer 95-D, with the combination indices below 0.8. Moreover, the in vivo antitumor efficacy of TRAIL/APO-2L was dramatically increased by celastrol. These enhanced anticancer activities were accompanied by the prompt onset of caspase-mediated apoptosis. Taken together, our data firstly demonstrate the synergistic anticancer capabilities achieved by combining TRAIL/APO-2L and celastrol, and moreover, open new opportunities to enhance the effectiveness of future treatment regimens using TRAIL/APO-2L.