Protein arginine deiminase 4 (PAD4) plays an important role in cancer progression by participating in gene regulation, protein modification, and neutrophil extracellular trap (NET) formation. Many reversible and irreversible PAD4 inhibitors have been reported recently. In this review, we summarize the structure–activity relationships of newly investigated PAD4 inhibitors to bring researchers up to speed by guiding and describing new scaffolds as optimization and development leads for new effective, safe, and selective cancer treatments. In addition, some recent reports have shown evidence that PAD4 inhibitors are expected to trigger antitumor immune responses, regulate immune cells and related immune factors, enhance the effects of immune checkpoint inhibitors, and enhance their antitumor efficacy. Therefore, PAD4 inhibitors may potentially change tumor immunotherapy and provide an excellent direction for the development and clinical application of immunotherapy strategies for related diseases.

Background: Diabetic wound healing is hampered by persistent inflammation and excessive neutrophil extracellular traps (NET) formation. Peptidylarginine deiminase 4 (PAD4) is a key enzyme driving this pathology. This study developed a thermosensitive chitosan/β-glycerophosphate hydrogel for the local delivery of a novel PAD4 inhibitor, YJ-2, to promote diabetic wound repair. Methods: A YJ-2-loaded hydrogel (CGY) was synthesized and characterized. In vitro studies used HaCaT cells and macrophages to assess proliferation, migration, NETs (via H3cit), and polarization. Efficacy was evaluated in diabetic C57 mouse wound models. Results: CGY exhibited temperature-sensitive gelation and sustained YJ-2 release. In vitro, YJ-2 inhibited NETs formation, reduced pro-inflammatory markers, promoted HaCaT migration, and induced M2 macrophage polarization. In vivo, CGY treatment significantly accelerated wound closure. Conclusions: Local hydrogel delivery of the PAD4 inhibitor YJ-2 effectively mitigates inflammation and NETs, promoting healing in diabetic wounds. This strategy represents a promising targeted therapy for diabetic wounds.

Purpose: Due to the lack of effective local therapeutic strategies for oral squamous cell carcinoma (OSCC), this study aimed to develop a novel gelatin/lignin hydrogel loaded with mesenchymal stem cell (MSC)-derived exosomes enriched in microRNA-185 (miR-185 EV) for intraoral delivery, followed by systematic evaluation of its therapeutic efficacy and underlying molecular mechanisms. Materials and Methods: The gelatin/lignin hydrogel was prepared and subsequently loaded with miR-185 EV. The physicochemical properties of the hydrogel, including microstructure, swelling behavior, chemical composition, and rheological characteristics, were systematically evaluated. Next, the stability, viscosity, biocompatibility, and exosome release kinetics of the hydrogel were further assessed. A 4-nitroquinoline-1-oxide (4NQO)-induced mouse tongue carcinogenesis model was established to assess the in vivo antitumor activity of the hydrogel via intraoral administration. Moreover, a proteomic analysis was conducted to investigate the molecular mechanisms of miR-185 EV on OSCC. Results: The miR-185 EV-loaded gelatin/lignin hydrogel exhibited favorable physicochemical properties, stability, and biocompatibility while prolonging the tissue retention time of miR-185 EV. In vivo antitumor efficacy experiments showed that the miR-185 EV-loaded hydrogel significantly inhibited tumor occurrence and alleviated epithelial dysplasia. Immunohistochemical analyses revealed significant suppression of tumor proliferation and epithelial–mesenchymal transition (EMT) of the hydrogel. Proteomic analysis indicated that miR-185 EV suppressed OSCC progression by downregulating interleukin-1β (IL-1β), consequently inhibiting the NF-κB signaling pathway. Conclusion: The findings demonstrate the successful development of the miR-185 EV-loaded gelatin/lignin hydrogel that represents an effective nanomedicine platform for intraoral drug delivery, providing a promising strategy for the clinical treatment of OSCC.

Aims: To evaluate the neuroprotective potential of YJ‐2, a novel peptidylarginine deiminase 4 (PAD4) inhibitor, against ischemia/reperfusion brain injury by targeting neutrophil extracellular trap (NET) formation. Methods: In vitro, a NETs‐induced injury model was established using SH‐SY5Y and bEnd.3 cells. YJ‐2's effects on viability, apoptosis, oxidative stress, and barrier permeability were assessed via CCK‐8, flow cytometry, and FITC‐dextran assays. In vivo, a rat middle cerebral artery occlusion/reperfusion (MCAO/R) model received YJ‐2 (10 μmol/kg) intravenously. Outcomes included infarct volume (TTC staining), neurological score, neuronal apoptosis (TUNEL), and oxidative markers (ELISA). PAD4 activity and histone H3 citrullination (H3cit) were examined by western blot and immunofluorescence. Results: YJ‐2 reduced NET‐mediated neuronal death and oxidative stress in vitro, and improved endothelial barrier integrity. In MCAO/R rats, YJ‐2 significantly lowered infarct volume (44.2% → 30.6%), improved neurological function, and suppressed apoptosis. It also decreased PAD4 and H3cit expression in ischemic brain tissue, confirming target engagement. Conclusion: YJ‐2, by preserving blood–brain barrier (BBB) integrity and reducing neuronal apoptosis, highlights its therapeutic potential for ischemic stroke.

Background: Brain disorders, such as glioblastoma, Alzheimer’s disease and ischemic stroke, represent formidable challenges due to the highly restrictive blood–brain barrier (BBB) and the complex pathophysiological microenvironment, which severely compromise drug delivery and therapeutic outcomes. Metal–phenolic networks (MPNs), as a class of novel hybrid materials, hold great promise for overcoming brain delivery bottlenecks and enabling precise synergistic therapy by leveraging their unique physicochemical properties. However, a comprehensive synthesis of MPN designs tailored specifically to the distinct pathological mechanisms underlying brain disorders is currently lacking. Methods: In this review, we systematically outline the foundational building blocks of MPNs and their diverse nanostructure engineering strategies. Building on this, we closely align MPN customization with the four core pathological pillars of brain diseases, thoroughly summarizing advanced design strategies and synergistic therapeutic mechanisms. Additionally, we prospectively discuss emerging innovative approaches, including the targeting of neutrophil extracellular traps (NETs) to modulate the immunosuppressive tumor microenvironment. Outlook: Finally, we critically examine the pivotal obstacles hindering the clinical translation of MPNs, particularly concerning uncertainties in long-term biosafety and in vivo metabolism, metal-specific neurotoxicity and coordination-stability-governed metal release kinetics, challenges in quality control during scalable production, and the unpredictable interference of the protein corona. Conclusions: In this review, we provide a robust theoretical foundation for the rational design of mechanism-driven MPNs, while offering forward-looking perspectives to accelerate their clinical translation from bench to bedside for the precise management of brain diseases.