The Diels-Alder reaction, which forms a six-membered ring from an alkene (dienophile) and a 1,3-diene, is synthetically very useful for construction of cyclic products with high regio- and stereoselectivity under mild conditions. It has been applied to the synthesis of complex pharmaceutical and biologically active compounds. Although evidence on natural Diels-Alderases has been accumulated in the biosynthesis of secondary metabolites, there has been no report on the structural details of the natural Diels-Alderases. The function and catalytic mechanism of the natural Diels-Alderase are of great interest owing to the diversity of molecular skeletons in natural Diels-Alder adducts. Here we present the 1.70 A resolution crystal structure of the natural Diels-Alderase, fungal macrophomate synthase (MPS), in complex with pyruvate. The active site of the enzyme is large and hydrophobic, contributing amino acid residues that can hydrogen-bond to the substrate 2-pyrone. These data provide information on the catalytic mechanism of MPS, and suggest that the reaction proceeds via a large-scale structural reorganization of the product.

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1 Di erences in the acetylcholine (ACh)-induced endothelium-dependent relaxation and hyperpolarization of the mesenteric arteries of Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. 2 Relaxation was impaired in preparations from SHRSP and tendency to reverse the relaxation was observed at high concentrations of ACh in these preparations. 3 Relaxation was partly blocked by N G -nitro-L-arginine (L-NOARG, 100 mM) and, in the presence of L-NOARG, tendency to reverse the relaxation was observed in response to higher concentrations of ACh, even in preparations from WKY. The relaxation remaining in the presence of L-NOARG was also smaller in preparations from SHRSP. 4 The tendency to reverse the relaxation observed at higher concentrations of ACh in preparations from SHRSP or WKY in the presence of L-NOARG were abolished by indomethacin (10 mM). 5 Elevating the K + concentration of the incubation medium decreased relaxation in the presence of both indomethacin and L-NOARG. 6 Relaxation in the presence of L-NOARG and indomethacin was reduced by the application of both apamin (5 mM) and charybdotoxin (0.1 mM). This suggests that the relaxation induced by ACh is brought about by both endothelium-derived relaxing factor (EDRF, nitric oxide (NO)) and hyperpolarizing factor (EDHF), which activates Ca 2+ -sensitive K + channels. 7 Electrophysiological measurement revealed that ACh induced endothelium-dependent hyperpolarization of the smooth muscle of both preparations in the presence of L-NOARG and indomethacin; the hyperpolarization being smaller in the preparation from SHRSP than that from WKY. 8 These results suggest that the release of both NO and EDHF is reduced in preparations from SHRSP. In addition, indomethacin-sensitive endothelium-derived contracting factor (EDCF) is released from both preparations; the release being increased in preparations from SHRSP.

Introduction Immune checkpoint inhibitors (ICIs) have demonstrated long survival for the treatment of advanced non-small cell lung cancer (NSCLC). However, the effect and safety of ICI rechallenge have not been fully evaluated. The aim of this study was to investigate the efficacy and safety of ICI rechallenge in NSCLC patients. Methods We defined ‘rechallenge’ as re-administration of ICIs for patients who were previously treated with ICIs and discontinued treatment for any reason, and received subsequent chemotherapy. We retrospectively analyzed the histories of 434 patients with advanced NSCLC who received ICIs from December 2015 to December 2017 at seven centers. Results A total of 317 patients discontinued the ICI treatment, and 14 patients (4.4%) received ICI rechallenge. All 14 patients discontinued the first ICI due to disease progression. Eight patients received the same kind of ICIs, and six patients received different ICIs. Median progression-free survival and overall survival were 1.5 months [95% confidence interval (CI): 0.8–2.6] and 6.5 months [95% CI: 1.4–19.0], respectively. The objective response rate was 7.1%, and the disease control rate was 21.4%. Two of three patients who achieved at least a stable disease, received radiotherapy between the first and second ICIs. Adverse events were not significantly different compared with the first ICIs. Conclusions In this study, the effect of ICI rechallenge was limited. Careful consideration of the administration of ICI rechallenge is necessary. This report involved a small number of cases, so further large prospective studies are warranted to confirm the efficacy of ICI rechallenge and to investigate predictive markers to identify a patient population in which ICI rechallenge is effective.