Total synthesis and biological evaluation of methylgerambullone

First total synthesis of methylgerambullone (MGB, 1) isolated from Glycosmis angustifolia was completed via a convergent route. The effect of MGB on the contractile responses of the isolated guinea-pig ileum induced by acetylcholine was investigated. As a result, it showed a potent relaxation rate (78.66 ± 4.30% at 100 mg/L) in a concentration-dependent manner on longitudinal smooth muscle contraction of isolated guinea-pig ileum induced by 1 μM acetylcholine.     

DNA damage and senescence in osteoprogenitors expressing Osx1 may cause their decrease with age

Age‐related bone loss in mice results from a decrease in bone formation and an increase in cortical bone resorption. The former is accounted by a decrease in the number of postmitotic osteoblasts which synthesize the bone matrix and is thought to be the consequence of age‐dependent changes in mesenchymal osteoblast progenitors. However, there are no specific markers for these progenitors, and conclusions rely on results from in vitro cultures of mixed cell populations. Moreover, the culprits of such changes remain unknown. Here, we have used Osx1‐Cre;TdRFP mice in which osteoprogenitors express the TdRFP fluorescent protein. We report that the number of TdRFP‐Osx1 cells, freshly isolated from the bone marrow, declines by more than 50% between 6 and 24 months of age in both female and male mice. Moreover, TdRFP‐Osx1 cells from old mice exhibited markers of DNA damage and senescence, such as γH2AX foci, G1 cell cycle arrest, phosphorylation of p53, increased p21^CIP1 levels, as well as increased levels of GATA4 and activation of NF‐κB – two major stimulators of the senescence‐associated secretory phenotype (SASP). Bone marrow stromal cells from old mice also exhibited elevated expression of SASP genes, including several pro‐osteoclastogenic cytokines, and increased capacity to support osteoclast formation. These changes were greatly attenuated by the senolytic drug ABT263. Together, these findings suggest that the decline in bone mass with age is the result of intrinsic defects in osteoprogenitor cells, leading to decreased osteoblast numbers and increased support of osteoclast formation.     

Perspectives on immune checkpoint ligands: expression,regulation, and clinical implications

In the tumor microenvironment, immune checkpoint ligands (ICLs) must be expressed in order to trigger the inhibitory signal via immune checkpoint receptors (ICRs). Although ICL expression frequently occurs in a manner intrinsic to tumor cells, extrinsic factors derived from the tumor microenvironment can fine-tune ICL expression by tumor cells or prompt non-tumor cells, including immune cells. Considering the extensive interaction between T cells and other immune cells within the tumor microenvironment, ICL expression on immune cells can be as significant as that of ICLs on tumor cells in promoting anti-tumor immune responses. Here, we introduce various regulators known to induce or suppress ICL expression in either tumor cells or immune cells, and concise mechanisms relevant to their induction. Finally, we focus on the clinical significance of understanding the mechanisms of ICLs for an optimized immunotherapy for individual cancer patients.     

Activity of novel inhibitors of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> biofilms

Staphylococcus aureus is one of the most important pathogens causing chronic biofilm infections. These are becoming more difficult to treat owing to drug resistance, particularly because S. aureus biofilms limit the efficacy of antimicrobial agents, leading to high morbidity and mortality. In the present study, we screened for inhibitors of S. aureus biofilm formation using a natural product library from the Korea Chemical Bank (KCB). Screening by crystal violet-based biomass staining assay identified hit compounds. Further examination of antibiofilm properties of these compounds was conducted and led to the identification of celastrol and telithromycin. In vitro, both celastrol and telithromycin were toxic to planktonic S. aureus and also active against a clinical methicillin-resistant S. aureus (MRSA) isolate. The effect of the compounds on preformed biofilms of clinical MRSA isolates was evaluated by confocal laser scanning microscopy (CLSM), which revealed the absence of typical biofilm architecture. In addition, celastrol and telithromycin inhibited the production of extracellular protein at selected sub-MIC concentrations, which revealed the reduced extracellular polymeric substance (EPS) secretion. Celastrol exhibited greater cytotoxicity than telithromycin. These data suggest that the hit compounds, especially telithromycin, could be considered novel inhibitors of S. aureus biofilm. Although the mechanisms of the effects on S. aureus biofilms are not fully understood, our data suggest that telithromycin could be a useful adjuvant therapeutic agent for S. aureus biofilm-related infections.