Actinopyrone D, a new downregulator of the molecular chaperone GRP78 from Streptomyces sp

Mechanism and Role of Endoplasmic Reticulum Stress in Osteosarcoma

Osteosarcoma is the most common malignant bone tumor, often occurring in children and adolescents. The etiology of most patients is unclear, and the current conventional treatment methods are chemotherapy, radiotherapy, and surgical resection. However, the sensitivity of osteosarcoma to radiotherapy and chemotherapy is low, and the prognosis is poor. The development of new and useful treatment strategies for improving patient survival is an urgent need. It has been found that endoplasmic reticulum (ER) stress (ERS) affects tumor angiogenesis, invasion, etc. By summarizing the literature related to osteosarcoma and ERS, we found that the unfolded protein response (UPR) pathway activated by ERS has a regulatory role in osteosarcoma proliferation, apoptosis, and chemoresistance. In osteosarcoma, the UPR pathway plays an important role by crosstalk with autophagy, oxidative stress, and other pathways. Overall, this article focuses on the relationship between ERS and osteosarcoma and reviews the potential of drugs or gene targets associated with ERS for the treatment of osteosarcoma.

Discovery, Structure Correction, and Biosynthesis of Actinopyrones, Cytotoxic Polyketides from the Deep-Sea Hydrothermal-Vent-Derived Streptomyces sp. SCSIO ZS0520

Three new actinopyrone derivatives, actinopyrones E-G (1, 3, and 4), together with three known analogues, PM050463 (2), actinopyrone D (5), and PM050511 (6), were isolated from Streptomyces sp. SCSIO ZS0520 derived from a deep-sea hydrothermal vent. Their structures, complete with absolute configurations, were elucidated using extensive spectroscopic analyses combined with Mosher's method, ECD calculations, and bioinformatics analyses. These findings corrected the absolute configurations of previously reported actinopyrone analogues 2, 5, and 6 at C-3, C-9, and C-10. Notably, compound 6 displayed notable cytotoxicity against six human cell lines with IC₅₀ values of 0.26-2.22 μM. A likely biosynthetic pathway and annotations of protein function are proposed on the basis of bioinformatics analyses. Genes coding for methyltransferase and glycosyltransferase tailoring chemistries needed to generate final structures were notably absent from the biosynthetic gene cluster. Taken together, these results enable further bioengineering of the actinopyrones and related congeners as potential antitumor agents.

Two new α-Methoxy-γ-Pyrones From the Mangrove Sediment-Derived Streptomyces psammoticus SCSIO NS126

Two new α-methoxy- γ-pyrone analogs, 2-methoxy-3-methyl-5,6-diethyl- γ-pyrone (2) and 2-methoxy-3,5-dimethyl-6-propyl- γ-pyrone (3), together with 2-methoxy-3,5-dimethyl-6-ethyl- γ-pyrone (1), firstly isolated from natural sources, were obtained from the EtOAc-solube extract of the mangrove sediment-derived actinomycete strain Streptomyces psammoticus SCSIO NS126, under the optimized fermentation conditions. Their structures were elucidated by detailed spectroscopic analysis and by comparison of their spectroscopic data with those reported in the literature. Those α-methoxy-γ-pyrones were evaluated for their acetylcholinesterase inhibitory activity; however, none of them exhibited obvious activity. Moreover, their biosynthetic relationship with piericidins was also discussed.

Identification and enhancing production of a novel macrolide compound in engineered Streptomyces peucetius

Streptomyces peucetius produces doxorubicin and daunorubicin, which are important anticancer drugs. In this study, we activate peucemycin, a new antibacterial compound, using an OSMAC strategy. In general, bioactive compounds are produced in a higher amount at room temperature; however, in this study, we have demonstrated that a bioactive novel compound was successfully activated at a low temperature (18 °C) in S. peucetius DM07. Through LC-MS/MS, IR spectroscopy, and NMR analysis, we identified the structure of this compound as a γ-pyrone macrolide. This compound was found to be novel, thus named peucemycin. It is an unusual 14-membered macrocyclic γ-pyrone ring with cyclization. Also, peucemycin exhibits potential antibacterial activity and a suppressive effect on the viability of various cancer cell lines.

Activation of peucemycin in S. peucetius DM07 by the OSMAC strategy.

Natural Polypropionates in 1999-2020: An Overview of Chemical and Biological Diversity

Natural polypropionates (PPs) are a large subgroup of polyketides with diverse structural features and bioactivities. Most of the PPs are discovered from marine organisms including mollusks, fungi and actinomycetes, while some of them are also isolated from terrestrial resources. An increasing number of studies about PPs have been carried out in the past two decades and an updated review is needed. In this current review, we summarize the chemical structures and biological activities of 164 natural PPs reported in 67 research papers from 1999 to 2020. The isolation, structural features and bioactivities of these PPs are discussed in detail. The chemical diversity, bioactive diversity, biodiversity and the relationship between chemical classes and the bioactivities are also concluded.

GRP78 and next generation cancer hallmarks: An underexplored molecular target in cancer chemoprevention research

Glucose regulated protein 78 (GRP 78), a master regulator of endoplasmic reticulum stress has been reported to be up regulated in various cancers and remains a crucial link between tumor glycolysis and tumor microenvironment. Overexpressed GRP78 has also shown to induce immune suppressive molecules and thereby tumor immune evasion. On the other hand emerging reports indicates that the next generation hallmarks viz., metabolic reprogramming and immune evasion, the two distinct processes are suggested to be fundamentally linked which is yet to be explored. Our concern is, if GRP78 is considered as a connecting link between these two different processes then targeting this triangle would be a promising approach in anticancer drug discovery. Lack of sufficient literature on this aspect represents GRP78 as an under explored target in anti-cancer research. The objective of this review is to provide a concise and integrated information on GRP78 and its association with tumor glycolysis and immune evasion which will revive and draw attention of the researchers to consider GRP78 as a potential drug target for cancer intervention and it also highlights few potential natural products investigated so far as GRP78 inhibitors.

Pharmacological effectors of GRP78 chaperone in cancers

The protein chaperone GRP78 is a master regulator of endoplasmic reticulum (ER) functions and is frequently over-expressed at the surface of cancer cells where it contributes to chemo-resistance. It represents a well-studied ER stress marker but an under-explored target for new drug development. This review aims to untangle the structural and functional diversity of GRP78 modulators, covering over 130 natural products, synthetic molecules, specific peptides and monoclonal antibodies that target GRP78. Several approaches to promote or to incapacitate GRP78 are presented, including the use of oligonucleotides and specific cell-delivery peptides often conjugated to cytotoxic payloads to design GRP78-targeted therapeutics. A repertoire of drugs that turn on/off GRP78 is exposed, including molecules which bind directly to GRP78, principally to its ATP site. There exist many options to regulate positively or negatively the expression of the chaperone, or to interfere with its cellular trafficking. This review provides a molecular cartography of GRP78 pharmacological effectors and adds weight to the notion that GRP78 repressors could represent promising anticancer therapeutics, notably as regards limiting chemo-resistance of cancer cells. The potential of GRP78-targeting drugs in other therapeutic modalities is also evoked.

Brucella suis Vaccine Strain 2 Induces Endoplasmic Reticulum Stress that Affects Intracellular Replication in Goat Trophoblast Cells In vitro

Brucella has been reported to impair placental trophoblasts, a cellular target where Brucella efficiently replicates in association with the endoplasmic reticulum (ER), and ultimately trigger abortion in pregnant animals. However, the precise effects of Brucella on trophoblast cells remain unclear. Here, we describe the infection and replication of Brucella suis vaccine strain 2 (B.suis.S2) in goat trophoblast cells (GTCs) and the cellular and molecular responses induced in vitro. Our studies demonstrated that B.suis.S2 was able to infect and proliferate to high titers, hamper the proliferation of GTCs and induce apoptosis due to ER stress. Tunicamycin (Tm), a pharmacological chaperone that strongly mounts ER stress-induced apoptosis, inhibited B.suis.S2 replication in GTCs. In addition, 4 phenyl butyric acid (4-PBA), a pharmacological chaperone that alleviates ER stress-induced apoptosis, significantly enhanced B.suis.S2 replication in GTCs. The Unfolded Protein Response (UPR) chaperone molecule GRP78 also promoted B.suis.S2 proliferation in GTCs by inhibiting ER stress-induced apoptosis. We also discovered that the IRE1 pathway, but not the PERK or ATF6 pathway, was activated in the process. However, decreasing the expression of phosphoIRE1α and IRE1α proteins with Irestatin 9389 (IRE1 antagonist) in GTCs did not affect the proliferation of B.suis.S2. Although GTC implantation was not affected upon B.suis.S2 infection, progesterone secretion was suppressed, and prolactin and estrogen secretion increased; these effects were accompanied by changes in the expression of genes encoding key steroidogenic enzymes. This study systematically explored the mechanisms of abortion in Brucella infection from the viewpoint of pathogen invasion, ER stress and reproductive endocrinology. Our findings may provide new insight for understanding the mechanisms involved in goat abortions caused by Brucella infection.