Acute lung injury is a severe inflammatory disorder characterized by dysregulated immune responses and excessive oxidative stress. It remains a major clinical challenge because therapeutic options are limited; systemic corticosteroids are the most widely used regimen, but their substantial side effects and uncertain efficacy continue to be debated. The researchers set out to develop new agents that could repair damaged lung tissue, mitigate inflammatory responses and offer favorable safety profiles, focusing on the mitogen-activated protein kinase (MAPK) family, a group of serine/threonine kinases that transmit extracellular signals through phosphorylation cascades and play a central role in pulmonary inflammation.

The MAPK network comprises four major subfamilies—ERK1/2, JNK, p38 and ERK5—each implicated in pulmonary disorders including COVID-19, chronic obstructive pulmonary disease, pulmonary fibrosis and acute lung injury or its more severe form, ARDS. During acute lung injury, pathogen-associated molecular patterns such as bacterial lipopolysaccharide (LPS) activate Toll-like receptors, triggering downstream MAPK-dependent NF-κB and AP-1 transcriptional programs that amplify the production of pro-inflammatory cytokines. In parallel, reactive oxygen species generated by hyperoxia or mechanical ventilation further stimulate MAPK cascades and exacerbate tissue injury. Viral infections, including influenza and SARS-CoV-2, also rely on TLR–MAPK signaling to drive hyperinflammatory cytokine responses. Aberrant MAPK activation can additionally worsen lung injury by suppressing autophagy: p38 MAPK, also known as MAPK14, impairs autophagic flux when activated, limiting the clearance of damaged cells. Conversely, pharmacological inhibition of MAPKs has been shown to attenuate inflammatory injury in disease models.

To find new p38 inhibitors, the team first built a pharmacophore model from the crystal structure of the SR-318–p38 complex (PDB: 6SFO), then used pharmacophore-based matching followed by molecular docking to screen an in-house compound library. This workflow identified a chalcone derivative, A1, a synthetic intermediate of the group’s existing p38-targeting lead compounds. Docking analysis suggested that the chalcone carbonyl group forms a hydrogen bond with the amino group of Lys53, while the thioether sulfur atom participates in a polar interaction with the hydroxyl group of Thr106. Cellular assays confirmed that A1 markedly suppresses LPS-induced nitric oxide production in RAW264.7 macrophages, supporting its anti-inflammatory potential. Because chalcone scaffolds are structurally flexible and known to modulate redox balance and cytokine-driven signaling, the researchers retained the two aromatic rings and the α,β-unsaturated carbonyl core and concentrated their optimization on the C-ring.

The target compounds were synthesized through a three-step route: palladium-catalyzed coupling of 4-bromo-2-nitroacetophenone with 2-mercapto-N-methylbenzamide, zinc-mediated reduction of the nitro group, and base-mediated condensation with various aryl aldehydes, yielding thirty-three derivatives in the A, B and C series. Screening began with an MTT viability assay in RAW264.7 macrophages and GES-1 epithelial cells, followed by measurement of nitric oxide release in LPS-stimulated macrophages, a convenient primary screen because p38α regulates LPS-induced nitric oxide production. The initial hit A1 showed moderate activity, inhibiting nitric oxide production with an IC50 of 13.6 ± 3.8 μM, but displayed pronounced cytotoxicity toward both macrophages and epithelial cells.

Three rounds of structural optimization followed. Pyridine analogues A2 and A3 modestly improved nitric oxide suppression but retained unsatisfactory safety profiles. Thiophene analogues A5 and A6 maintained potency and markedly reduced epithelial cytotoxicity, though macrophage toxicity persisted, and methyl substitutions or a methyl-pyrazolyl group partially reduced toxicity at the cost of some activity. In the benzene-core B series, halogenated analogues largely retained potency with low epithelial toxicity, but most remained toxic to macrophages. The breakthrough came with an ortho-isopropyl substituent: compound B15 inhibited nitric oxide production with an IC50 of 2.6 ± 1.4 μM while showing no measurable growth inhibition of either macrophages or epithelial cells at concentrations up to 100 μM. Meta- and para-isopropyl isomers performed worse, and bulky trifluoromethyl or trifluoromethoxy groups either raised macrophage toxicity or abolished activity. Among quinoline derivatives, only the 8-substituted analogue C4 retained meaningful inhibition.

With B15 selected for biological evaluation, the team verified its molecular target. Surface plasmon resonance showed that B15 binds recombinant p38α protein directly with an equilibrium dissociation constant of 372.1 nM. A cellular thermal shift assay in RAW264.7 macrophages corroborated the binding: B15 treatment enhanced the thermal stability of endogenous p38, and at 53 °C it prevented the heat-induced degradation of the protein that was nearly complete in vehicle-treated controls, while the negative control protein GAPDH showed no stabilization. Functional assays then demonstrated that B15 concentration-dependently reduced LPS-elevated mRNA levels of tumor necrosis factor-α and interleukin-6, lowered intracellular reactive oxygen species, and suppressed the LPS-induced phosphorylation of JNK, p38 and ERK in western blots, with potency comparable to the positive control L-NMMA.

Safety testing preceded the efficacy studies. In an acute toxicity study, mice received a single oral dose of 2000 mg/kg B15 and were monitored for fourteen days. Body weights did not differ significantly from vehicle controls, and histopathological examination of hematoxylin and eosin-stained sections of heart, liver, spleen, lungs and kidneys revealed no obvious structural damage or pathological lesions, indicating the compound is well tolerated at the tested dose.

The protective effect was then tested in female C57BL/6J mice given intratracheal LPS to induce acute lung injury, with B15 administered orally at 10, 20 and 40 mg/kg for four days before challenge. Immunoblot analysis of lung tissue showed that B15 significantly suppressed MAPK pathway activation, reflected in decreased phosphorylation ratios of p38, ERK and JNK. Histological staining revealed marked amelioration of LPS-induced damage, including alveolar collapse, interstitial edema and neutrophil infiltration. Consistent with the cell studies, B15 dose-dependently reduced lung tissue mRNA of TNF-α and IL-6, reversed oxidative stress as shown by decreased malondialdehyde content and increased superoxide dismutase activity, and restored LPS-elevated phosphorylated p38 MAPK and IL-6 protein in lung sections to near-normal levels on immunohistochemistry.

The authors conclude that B15 is a promising therapeutic candidate for acute lung injury, exerting protective effects mainly through targeting p38 MAPK, and that the work provides a molecular basis for developing new agents against the condition. The findings rest on cell culture and mouse models, and the study was conducted in accordance with institutional animal ethics guidelines; translation to human patients would require further preclinical and clinical development. Nevertheless, the combination of direct target engagement, concentration-dependent suppression of cytokine transcription and oxidative stress, a clean acute toxicity profile at a high oral dose, and demonstrable lung protection in vivo makes the phenylthioether chalcone scaffold a noteworthy addition to the search for alternatives to corticosteroids in inflammatory lung disease.

Subject of Research: Development of phenylthioether chalcone p38 MAPK inhibitors as candidate therapeutics for acute lung injury

Article Title: Phenylthioether chalcone derivatives attenuate acute lung injury via suppression of p38 MAPK (MAPK14)-mediated inflammatory signaling

Article References: Yi, Q.-L., Zhou, X.-J., Wu, Z.-F., Jiang, J.-X., Liu, X.-H., Liu, M.-M., & Shi, J.-B. (2026). Phenylthioether chalcone derivatives attenuate acute lung injury via suppression of p38 MAPK (MAPK14)-mediated inflammatory signaling. Results in Chemistry, 31, Article 103976. https://doi.org/10.1016/j.rechem.2026.103976

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DOI: 10.1016/j.rechem.2026.103976

Keywords: acute lung injury, p38 MAPK, chalcone derivatives, drug design, inflammation, oxidative stress, MAPK signaling, macrophages, LPS model, preclinical study, medicinal chemistry, cytokines