The stimulator-of-interferon-gene (STING) protein is involved in innate immunity. The drug DMXAA (5,6-dimethylxanthenone-4-acetic acid) proved to be a potent murine-STING (mSTING) agonist but had little effect on human-STING (hSTING). In this paper, we draw upon the comparison of different crystal structures and protein-ligand interaction relationships analysis to venture the hypothesis that the drug design of DMXAA variants has the potential to convert STING agonists to inhibitors. Based on our previous discovery of two DMXAA analogs, 3 and 4 (both could bind to STING), we structurally optimized them and synthesized new derivatives, respectively. In binding assays, we found compounds 11 and 27 to represent STING binders that were superior to the original structures and discussed the structure-activity relationships. All target compounds were inactive in cellular assays for the screening of STING agonistic activity. Gratifyingly, we identified 11 and 27 as STING inhibitors with micromolar activity in both hSTING and mSTING pathways. In addition, 11 and 27 inhibited the induction of interferon and inflammatory cytokines activated by 2′3′-cGAMP without apparent cytotoxicity. These findings break the rigid thinking that DMXAA provides the structural basis specifically for STING agonists and open up more possibilities for developing novel STING agonists or inhibitors.

Due to the resistance of Gram-negative bacteria Pseudomonas aeruginosa PAO1 to most clinically relevant antimicrobials, the use of traditional antibiotic treatments in hospitals is challenging. The formation of biofilms, which is regulated by the quorum-sensing (QS) system of Pseudomonas aeruginosa (PA), is an important cause of drug resistance. There are three main QS systems in P. aeruginosa: the las system, the rhl system, and the pqs system. The inhibitors of the las system are the most studied. Previously, the compound AOZ-1 was found to have a certain inhibitory effect on the las system when screened. In this study, twenty-four compounds were designed and synthesized by modifying the Linker and Rings of AOZ-1. Using C. violaceum CV026 as a reporter strain, this study first assessed the inhibitory effects of new compounds against QS, and their SAR was investigated. Then, based on the SAR analysis of compound AOZ-1 derivatives, the parent core of AOZ-1 was replaced to explore the structural diversity. Then, nine new compounds were designed and synthesized with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one. The compound Y-31 (IC₅₀ = 91.55 ± 3.35 µM) was found to inhibit the QS of C. violaceum CV026. Its inhibitory effect on C. violaceum CV026 was better than that of compound AOZ-1 (IC₅₀ > 200 µM). Furthermore, biofilm formation is one of the important causes of Pseudomonas aeruginosa PAO1 resistance. In this study, it was found that compound Y-31, with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one, had the highest biofilm inhibition rate (40.44%). The compound Y-31 has a certain inhibitory effect on the production of PAO1 virulence factors (pyocyanin, rhamnolipid, and elastase) and swarming. When the concentration of compound Y-31 was 162.5 µM, the inhibition rates of pyocyanin, rhamnolipid, and elastase were 22.48%, 6.13%, and 22.67%, respectively. In vivo, the lifetime of wildtype Caenorhabditis elegans N2 infected with P. aeruginosa PAO1 was markedly extended by the new parent nucleus Y-31. This study also performed cytotoxicity experiments and in vivo pharmacokinetics experiments on the compound Y-31. In conclusion, this study identified a compound, Y-31, with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one, which is a potential agent for treating P. aeruginosa PAO1 that is resistant to antibiotics and offers a way to discover novel antibacterial medications.

Radiotherapy is a vital approach for brain tumor treatment. The standard treatment for glioblastoma (GB) is maximal surgical resection combined with radiotherapy and chemotherapy. However, the non-sensitivity of tumor cells in the hypoxic area of solid tumors to radiotherapy may cause radioresistance. Therefore, radiotherapy sensitizers that increase the oxygen concentration within the tumor are promising for increasing the effectiveness of radiation. Inspired by hemoglobin allosteric oxygen release regulators, a series of novel phenoxyacetic acid analogues were designed and synthesized. A numerical method was applied to determine the activity and safety of newly synthesized compounds. In vitro studies on the evaluation of red blood cells revealed that compounds 19c (∆P₅₀ = 45.50 mmHg) and 19t (∆P₅₀ = 44.38 mmHg) improve the oxygen-releasing property effectively compared to positive control efaproxiral (∆P₅₀ = 36.40 mmHg). Preliminary safety evaluation revealed that 19c exhibited no cytotoxicity towards HEK293 and U87MG cells, while 19t was cytotoxic toward both cells with no selectivity. An in vivo activity assay confirmed that 19c exhibited a radiosensitization effect on orthotopically transplanted GB in mouse brains. Moreover, a pharmacokinetic study in rats showed that 19c was orally available.