IRE-1-Targeting Caged Prodrug with Endoplasmic Reticulum Stress-Inducing and XBP-1S-Inhibiting Activities for Cancer Therapy

Ferroptosis contributed to endoplasmic reticulum stress in preterm birth by targeting LHX1 and IRE-1

Preterm birth (PTB) significantly contributed to neonatal mortality, emphasizing the need for a detailed understanding of its pathogenesis. This study aimed to explore the involvement of ferroptosis, an iron-dependent cell death process, in PTB and investigated the possible crosstalk with endoplasmic reticulum stress (ERS). First, we explored the occurrence of ferroptosis in placenta samples from PTB parturients. Then we established a ferroptosis cell model was established by subjecting trophoblast cells to hypoxia/reoxygenation (H/R), and found the ERS was induced in H/R exposed cells and was attenuated by ferroptosis inhibition using Fer-1, suggesting that ferroptosis could induce ERS. Meanwhile, we also induced ERS in trophoblast cells via tunicamycin (TM) treatment. Ferroptosis inhibition with Fer-1 alleviated TM-induced ER stress. TM treatment reduced trophoblast cell viability and migration while promoted apoptosis and autophagy, effects that were reversed by ferroptosis inhibition. Thus, targeting ferroptosis might help mitigate ER stress-related pathophysiological changes in PTB. Mechanically, we found two ERS mediators LIM homeobox 1 (LHX1)/Inositol-requiring enzyme 1 (IRE-1) were also upregulated in H/R treated cells. Silencing LHX1 or IRE-1 was demonstrated to reverse the H/R-induced ferroptosis. Additionally, rescue assays further revealed that LHX1 promoted ferroptosis by regulating IRE-1. In conclusion, ferroptosis contributed to ERS and was critically involved in PTB, highlighting the LHX1/IRE-1 axis as a promising therapeutic target for mitigating ferroptosis-related complications. These findings offered a foundation for innovative interventions in preterm birth.

Fluorogenic, Subsingle-Turnover Monitoring of Enzymatic Reactions Involving NAD(P)H Provides a Generalized Platform for Directed Ultrahigh-Throughput Evolution of Biocatalysts in Microdroplets

Enzyme engineering and discovery are crucial for a sustainable future bioeconomy. Harvesting new biocatalysts from large libraries through directed evolution or functional metagenomics requires accessible, rapid assays. Ultrahigh-throughput screening formats often require optical readouts, leading to the use of model substrates that may misreport target activity and necessitate bespoke synthesis. This is a particular challenge when screening glycosyl hydrolases, which leverage molecular recognition beyond the target glycosidic bond, so that complex chemical synthesis would have to be deployed to build a fluoro- or chromogenic substrate. In contrast, coupled assays represent a modular "plug-and-play" system: any enzyme-substrate pairing can be investigated, provided the reaction can produce a common intermediate which links the catalytic reaction to a detection cascade readout. Here, we establish a detection cascade producing a fluorescent readout in response to NAD(P)H via glutathione reductase and a subsequent thiol-mediated uncaging reaction, with a low nanomolar detection limit in plates. Further scaling down to microfluidic droplet screening is possible: the fluorophore is leakage-free and we report 3 orders of magnitude-improved sensitivity compared to absorbance-based systems, with a resolution of 361,000 product molecules per droplet. Our approach enables the use of nonfluorogenic substrates in droplet-based enrichments, with applicability in screening for glycosyl hydrolases and imine reductases (IREDs). To demonstrate the assay's readiness for combinatorial experiments, one round of directed evolution was performed to select a glycosidase processing a natural substrate, beechwood xylan, with improved kinetic parameters from a pool of >106 mutagenized sequences.

Coumarin-Conjugated Macromolecular Probe for Sequential Stimuli-Mediated Activation

Protein bioconjugation has emerged as one of the most valuable tools for the development of protein-based biochemical assays. Here, we report a fluorescent macromolecular material, RF16_Halo, in which the coumarin derivative RF16 is specifically conjugated onto HaloTag protein to achieve a dual-stimuli-mediated fluorescence response. RF16 is first obtained by installing a H2O2-sensitive boron cage onto the C7 hydroxy moiety of the coumarin fluorophore with a HaloTag ligand attaching to the pH-labile 1,3-dioxane moiety. Upon stimulation, RF16_Halo exhibits a sequential fluorescence response to H2O2/pH at both liquid and solid interfaces. The fluorescence of the RF16_Halo-based protein film increases linearly toward H2O2 with a higher sensitivity when compared with that of RF16. Subsequently, the H2O2-cleaved RF16_Halo presents a pH-dependent fluorescence decrease under acidic conditions. Such a stimulus-responsive fluorescence "off-on-off" multimode enables RF16_Halo to be applied as a sequential logic circuit. In addition, we evaluate the fluorescence labeling ability of RF16 to intracellular IRE1_Halo protein and demonstrate that RF16 containing the HaloTag ligand could be precisely retained in cells to track IRE1_Halo protein. Hence, we provide a unique structural design strategy to construct a fluorescence dual-responsive macromolecular probe for information encryption and protein tracking in cells.

Construction of Coumarin-Based Bioorthogonal Macromolecular Probes for Photoactivation

Photoactivatable fluorescence imaging is one of the most valuable methods for visualizing protein localization, trafficking, and interactions. Here, we designed four bioorthogonal fluorescent probes K1-K4 by installing photoactive cages and HaloTag ligands onto the different positions of the coumarin fluorophore. Although K1-K4 all exhibited rapid photostimulated responses in aqueous solution, only K3 was found to have an obvious aggregation-induced emission (AIE). Next, macromolecular fluorescent probes Kn=1/2/3/4_POIs were obtained by covalently attaching K1-K4 to HaloTag-fused proteins of interest (POIs). Kn=3/4_POIs exhibited a higher fluorescence increase than that of Kn=1/2_POIs upon photoactivation in both liquid and solid phases. Moreover, K3_GFP_Halo and K4_GFP_Halo presented the fluorescence resonance energy transfer (FRET) from photocleaved K3 and K4 to GFP in the protein complex. We further examined the fluorescence labeling ability of K1-K4 to intracellular IRE1_Halo protein and found that K3 and K4 containing the HaloTag ligand on the C4 position of coumarin could be retained in cells for long-term tracking of the IRE1_Halo protein. Hence, we established a platform of novel bioorthogonal fluorescent probes conjugating onto Halo-tagged POIs for rapid photoactivation in vitro and in cells.

Coumarin-Based Fluorescent Inhibitors for Photocontrollable Bioactivation

Activation of the IRE-1/XBP-1 pathway is related to many human diseases. Coumarin-based derivatives acting as both IRE-1 inhibitors and bright fluorophores are highly desirable to establish an integrated fluorescent inhibitor system. Here, we take insights into the aqueous stability of a photocaged IRE-1 inhibitor PC-D-F07 through a structure activity relationship. The substituent effects indicate that the electron-withdrawing -NO₂ moiety in the photocage combined with the tricyclic coumarin fluorophore contribute to the structural stability of PC-D-F07. To optimize the photocage of PC-D-F07, we incorporate a 1-ethyl-2-nitrobenzyl or 2-nitrobenzyl photolabile moiety on the hydroxyl group of the IRE-1 inhibitor to generate RF-7 and RF-8. Upon photoactivation, both RF-7 and RF-8 present an increased fluorescence response, sequentially enabling the unlocking of the ortho-1,3-dioxane acetal for the release of active IRE-1 inhibitors. Moreover, RF-7 exhibits a high repolarization ratio of converting M2-type tumor-associated macrophages (M2-TAMs) to M1-type immune-responsive macrophages. This provides a novel prodrug strategy of modulating druggable fluorophore backbones to achieve spatiotemporally controllable drug release for precise cancer treatment.

Tumor-intrinsic IRE1α signaling controls protective immunity in lung cancer

IRE1α-XBP1 signaling is emerging as a central orchestrator of malignant progression and immunosuppression in various cancer types. Employing a computational XBP1s detection method applied to TCGA datasets, we demonstrate that expression of the XBP1s mRNA isoform predicts poor survival in non-small cell lung cancer (NSCLC) patients. Ablation of IRE1α in malignant cells delays tumor progression and extends survival in mouse models of NSCLC. This protective effect is accompanied by alterations in intratumoral immune cell subsets eliciting durable adaptive anti-cancer immunity. Mechanistically, cancer cell-intrinsic IRE1α activation sustains mPGES-1 expression, enabling production of the immunosuppressive lipid mediator prostaglandin E2. Accordingly, restoring mPGES-1 expression in IRE1αKO cancer cells rescues normal tumor progression. We have developed an IRE1α gene signature that predicts immune cell infiltration and overall survival in human NSCLC. Our study unveils an immunoregulatory role for cancer cell-intrinsic IRE1α activation and suggests that targeting this pathway may help enhance anti-tumor immunity in NSCLC.