HuR-targeted agents: An insight into medicinal chemistry, biophysical, computational studies and pharmacological effects on cancer models

Synthesis and Preliminary Evaluation of Tanshinone Mimic Conjugates for Mechanism of Action Studies

Human antigen R (HuR) is an RNA binding protein (RBP) belonging to the ELAV (Embryonic Lethal Abnormal Vision) family, which stabilizes mRNAs and regulates the expression of multiple genes. Its altered expression or localization is related to pathological features such as cancer or inflammation. Dihydrotanshinone I (DHTS I) is a naturally occurring, tetracyclic ortho-quinone inhibitor of the HuR-mRNA interaction. Our earlier efforts led to the identification of a synthetic Tanshinone Mimic (TM) 2 with improved affinity for HuR. Here we report five new TM probes 3-5 bearing a detection-promoting moiety (either photo affinity probe - PAP or biotin) as a para-substituent on the phenyl-sulphonamide for mechanism of action (MoA) studies. Biological and biochemical assays were used to characterize the novel TM conjugates 3-5. They showed similar toxic activity in HuR-expressing triple-negative breast cancer MDA-MB-231 cells, with micromolar CC50s. REMSAs revealed that photoactivatable groups (4 a and 4 b), but not biotin (5 a and 5 b), prevented conjugates' ability to disrupt rHuR-RNA complexes. Further biochemical studies confirmed that biotinylated probes, in particular 5 a, can be used to isolate rM1 M2 from solutions, taking advantage of streptavidin-coated magnetic beads, thus being the most promising HuR inhibitor to be used for further MoA studies in cell lysates.

Effects of genetic ablation and pharmacological inhibition of HuR on gene expression, iron metabolism, and hormone levels

BACKGROUND

HuR/ELAV1, a ubiquitous RNA-binding protein, belongs to the RNA-binding protein family and is crucial for stabilizing and regulating the translation of various mRNA targets, influencing gene expression. Elevated HuR levels are associated with multiple disorders, including cancer and neurodegenerative diseases. Despite the identification of small molecule inhibitors targeting HuR, their detailed characterization remains limited. Recently, Eltrombopag, an FDA-approved drug for immune thrombocytopenic purpura and chemotherapy-induced thrombocytopenia, emerged as a potential HuR inhibitor. However, the specific molecular pathways influenced by both HuR and Eltrombopag are not fully understood.

RESULTS

Our study demonstrates that Eltrombopag operates via HuR inhibition, affecting gene expression regulation at the posttranscriptional level. We show that both HuR knockout and Eltrombopag treatment modulate iron metabolism by decreasing ferritin heavy chain (FTH1) and light chain (FTL) synthesis while increasing the expression of iron-regulatory protein 2 (IRP2), a key regulator of ferritin translation. Additionally, HuR inhibition reduces the levels of glycoprotein hormones, alpha polypeptide (CGA), a marker associated with hormone-induced tumors, suggesting a potential use of Eltrombopag in treatment of cancers overexpressing CGA. We observed that the main of control is manifested at the level of translation inhibition, with proteasome-mediated regulation also playing an important role.

CONCLUSIONS

These findings uncover novel posttranscriptional mechanisms governed by HuR and its inhibitor, elucidating pathways relevant to HuR-mediated regulation and molecular therapies aimed at targeting this protein.

Structural, biological, and biomedical implications of mRNA interactions with the master regulator HuR

Human antigen R (HuR) is a ubiquitously expressed RNA-binding protein (RBP) that has been implicated in a vast range of biological processes including stress response, angiogenesis, cell proliferation, and differentiation. Dysregulation of HuR has been linked to a number of pathological disorders including vascular disease, inflammation, and cancers such as those of the breast and colon. Like many RBPs, HuR is composed of multiple RNA-recognition motif (RRM) domains; however, HuR and the three other members of the Hu family (HuB, HuC, and HuD) possess a unique structural composition with two RRMs separated from a third C-terminal RRM by a long, unstructured hinge region. While there has been extensive research on the role of HuR in cellular, molecular, and developmental biology, there are fewer structural and biochemical studies of HuR and many questions still remain about the molecular mechanisms of HuR. In this review, we endeavor to synthesize existing HuR research spanning the last three decades in order to define known mechanistic roles of each domain, highlight remaining uncertainties, and provide a backdrop for ongoing research into the chemistry and biology of HuR and similar multi-RRM containing proteins.

Novel, soluble 3-heteroaryl-substituted tanshinone mimics attenuate the inflammatory response in murine macrophages

The RNA binding protein Human Antigen R (HuR) has been identified as a main regulator of the innate immune response and its inhibition can lead to beneficial anti-inflammatory effects. To this aim, we previously synthesized a novel class of small molecules named Tanshinone Mimics (TMs) able to interfere with HuR-RNA binding, and that dampen the LPS-induced immune response. Herein, we present a novel series of TMs, encompassing thiophene 3/TM9 and 4/TM10, furan 5/TM11 and 6/TM12, pyrrole 7b/TM13, and pyrazole 8. The furan-containing 5(TM11) showed the greatest inhibitory effect of the series on HuR-RNA complex formation, as suggested by RNA Electromobility Shift Assay and Time-Resolved FRET. Molecular Dynamics Calculation of HuR - 5/TM11 interaction, quantum mechanics approaches and Surface Plasmon Resonance data, all indicates that, within the novel heteroaryl substituents, the furan ring better recapitulates the chemical features of the RNA bound to HuR. Compound 5/TM11 also showed improved aqueous solubility compared to previously reported TMs. Real-time monitoring of cell growth and flow cytometry analyses showed that 5/TM11 preferentially reduced cell proliferation rather than apoptosis in murine macrophages at immunomodulatory doses. We observed its effects on the innate immune response triggered by lipopolysaccharide (LPS) in macrophages, showing that 5/TM11 significantly reduced the expression of proinflammatory cytokines as Cxcl10 and Il1b.

ELAVL1 regulates glycolysis in nasopharyngeal carcinoma cells through the HMGB3/β-catenin axis

BACKGROUND

The role of ELAVL1 in the progression of various tumors has been demonstrated. Our research aims to investigate how ELAVL1 controls the glycolytic process in nasopharyngeal carcinoma cells through the HMGB3/β-catenin pathway.

METHODS

The expression of ELAVL1 was detected in clinical tumor samples and nasopharyngeal carcinoma cell lines. A subcutaneous tumor model was established in nude mice to investigate the role of ELAVL1 in tumor progression. The relationship between HMGB3 and ELAVL1 was validated by RNA pull down and RIP assays. TOPFlash/FOPFlash reporter assay was used to detect β-catenin activity. Assay kits were utilized to measure glucose consumption, lactate production, and G6PD activity in nasopharyngeal carcinoma cells. Western blot was conducted to detect the expression of glycolysis-related proteins. The glycolytic capacity was analyzed through extracellular acidification rate (ECAR).

RESULTS

In both clinical samples and nasopharyngeal carcinoma cell lines, the expression levels of ELAVL1 mRNA and protein were found to be upregulated. Knockdown of ELAVL1 significantly inhibited the in vivo proliferation of nasopharyngeal carcinoma and suppressed the glycolytic capacity of nasopharyngeal carcinoma cells. ELAVL1 interacts with HMGB3, leading to an increase in the stability of HMGB3 mRNA. Overexpression of HMGB3 elevated the reduced β-catenin activity caused by sh-ELAVL1 and reversed the inhibitory effect of sh-ELAVL1 on cellular glycolytic capacity. Treatment with β-catenin inhibitor (FH535) effectively suppressed the promotion of glycolytic capacity induced by HMGB3 overexpression.

CONCLUSIONS

ELAVL1 promotes glycolysis in nasopharyngeal carcinoma cells by interacting with HMGB3 to stabilize HMGB3 mRNA, thereby activating β-catenin pathway. Therefore, targeting the ELAVL1-HMGB3-β-catenin axis has the potential to be a novel approach for treating nasopharyngeal carcinoma.

Repurposing celecoxib for colorectal cancer targeting via pH-triggered ultra-elastic nanovesicles: Pronounced efficacy through up-regulation of Wnt/β-catenin pathway in DMH-induced tumorigenesis

Celecoxib (CLX), a selective inhibitor for cyclooxygenase 2 (COX-2), has manifested potential activity against diverse types of cancer. However, low bioavailability and cardiovascular side effects remain the major challenges that limit its exploitation. In this work, we developed ultra-elastic nanovesicles (UENVs) with pH-triggered surface charge reversal traits that could efficiently deliver CLX to colorectal segments for snowballed tumor targeting. CLX-UENVs were fabricated via a thin-film hydration approach. The impact of formulation factors (Span 80, Tween 80, and sonication time) on the nanovesicular features was evaluated using Box-Behnken design, and the optimal formulation was computed. The optimum formulation was positively coated with polyethyleneimine (CLX-PEI-UENVs) and then coated with Eudragit S100 (CLX-ES-PEI-UENVs). The activity of the optimized nano-cargo was explored in 1,2-dimethylhydrazine-induced colorectal cancer in Wistar rats. Levels of COX-2, Wnt-2 and β-catenin were assessed in rats' colon. The diameter of the optimized CLX-ES-PEI-UENVs formulation was 253.62 nm, with a zeta potential of -23.24 mV, 85.64% entrapment, and 87.20% cumulative release (24 h). ES coating hindered the rapid release of CLX under acidic milieu (stomach and early small intestine) and showed extended release in the colon section. In colonic environments, the ES coating layer was removed due to high pH, and the charge on the nanovesicular corona was shifted from negative to positive. Besides, a pharmacokinetics study revealed that CLX-ES-PEI-UENVs had superior oral bioavailability by 2.13-fold compared with CLX suspension. Collectively, these findings implied that CLX-ES-PEI-UENVs could be a promising colorectal-targeted nanoplatform for effective tumor management through up-regulation of the Wnt/β-catenin pathway.

SUMOylation controls Hu antigen R posttranscriptional activity in liver cancer

The posttranslational modification of proteins critically influences many biological processes and is a key mechanism that regulates the function of the RNA-binding protein Hu antigen R (HuR), a hub in liver cancer. Here, we show that HuR is SUMOylated in the tumor sections of patients with hepatocellular carcinoma in contrast to the surrounding tissue, as well as in human cell line and mouse models of the disease. SUMOylation of HuR promotes major cancer hallmarks, namely proliferation and invasion, whereas the absence of HuR SUMOylation results in a senescent phenotype with dysfunctional mitochondria and endoplasmic reticulum. Mechanistically, SUMOylation induces a structural rearrangement of the RNA recognition motifs that modulates HuR binding affinity to its target RNAs, further modifying the transcriptomic profile toward hepatic tumor progression. Overall, SUMOylation constitutes a mechanism of HuR regulation that could be potentially exploited as a therapeutic strategy for liver cancer.

A TRIM21-based bioPROTAC highlights the therapeutic benefit of HuR degradation

Human antigen R (HuR) is a ubiquitously expressed RNA-binding protein, which functions as an RNA regulator. Overexpression of HuR correlates with high grade tumours and poor patient prognosis, implicating it as an attractive therapeutic target. However, an effective small molecule antagonist to HuR for clinical use remains elusive. Here, a single domain antibody (VHH) that binds HuR with low nanomolar affinity was identified and shown to inhibit HuR binding to RNA. This VHH was used to engineer a TRIM21-based biological PROTAC (bioPROTAC) that could degrade endogenous HuR. Significantly, HuR degradation reverses the tumour-promoting properties of cancer cells in vivo by altering the HuR-regulated proteome, highlighting the benefit of HuR degradation and paving the way for the development of HuR-degrading therapeutics. These observations have broader implications for degrading intractable therapeutic targets, with bioPROTACs presenting a unique opportunity to explore targeted-protein degradation through a modular approach.

hucMSCs Treatment Ameliorated Pulmonary Fibrosis via Downregulating the circFOXP1-HuR-EZH2/STAT1/FOXK1 Autophagic Axis

This study was performed to determine the effect of human umbilical cord mesenchymal stem cells (hucMSCs) treatment on pulmonary fibrosis and investigate the circFOXP1-mediated autophagic mechanism of hucMSCs treatment. Pulmonary fibrosis models were established by spraying bleomycin in mice and TGF-β1 treatment of MRC-5 cells. Results showed that hucMSCs were retained in lung and hucMSCs treatment alleviated pulmonary fibrosis. Morphological staining indicated that hucMSCs-treated mice had thinner alveolar walls, effectively improved alveolar structure, significantly reduced alveolar inflammation, and decreased collagen deposition than control mice. Fibrotic proteins, including vimentin, α-SMA, collagens I and III, and the differentiation-related protein S100 calcium-binding protein A4 was reduced considerably in the hucMSCs-treated group. The mechanistic study revealed that the inhibition of hucMSCs treatment on pulmonary fibrogenesis depended on downregulating circFOXP1, in which hucMSCs treatment promoted circFOXP1-mediated autophagy process via blocking the nuclear human antigen R (HuR) translocation and promoting the HuR degradation, leading to a marked decrease in autophagy negative regulators EZH2, STAT1, and FOXK1. In conclusion, hucMSCs treatment significantly improved pulmonary fibrosis by downregulating the circFOXP1-HuR-EZH2/STAT1/FOXK1 autophagic axis. hucMSCs can act as an effective treatment for pulmonary fibrosis.

miR-325-3p Reduces Proliferation and Promotes Apoptosis of Gastric Cancer Cells by Inhibiting Human Antigen R

Human antigen R (HuR), also known as ELAVL1, is a widely expressed RNA-binding protein (RBP) that has a significant impact on the development and advancement of tumors. Our previous study found that 5-fluorouracil (5-FU) may impede the proliferation and increase apoptosis in gastric cancer cells by reducing the nucleocytoplasmic shuttling of HuR. However, how posttranscriptional regulation influences HuR functions in gastric cancer remains to be elucidated. Here, we demonstrated that miR-325-3p has the potential to regulate the expression level of HuR by directly binding to its 3'UTR, which in turn led to a significant reduction in proliferation and an increase in apoptosis in gastric cancer cells. In addition, xenograft experiment showed that knockdown of HuR or overexpression of miR-325-3p group exhibited smaller tumor sizes after transplant of gastric cancer cells into zebrafish larvae. Thus, our findings offer new insights into the pathogenesis of gastric cancer and may potentially assist in identifying novel targets for drug therapy.

LncRNA RMRP aggravates LPS-induced HK-2 cell injury and AKI mice kidney injury by upregulating COX2 protein via targeting ELAVL1

OBJECTIVES

There is emerging evidence that long non-coding RNA component of mitochondrial RNA processing endoribonuclease (lncRNA RMRP) is involved in acute kidney injury (AKI) progression, but the specific mechanism of action still requires further investigation.

METHODS

The lipopolysaccharide (LPS)-treated HK-2 cells were transfected with pcDNA-RMRP or si-RMRP, or transfected with pcDNA-ELAV like RNA binding protein 1 (ELAVL1) or si-ELAVL1, and cell viability, apoptosis, inflammatory factor secretion and oxidative stress were detected. The LPS-treated HK-2 cells were transfected with si-RMRP alone or together with pcDNA-ELAVL1, and cell behaviors were examined. The LPS-treated HK-2 cells were transfected with si-ELAVL1 alone or together with pcDNA- cyclooxygenase-2 (COX2), and the cellular changes were observed. The LPS-treated HK-2 cells were transfected with si-RMRP alone or together with pcDNA-ELAVL1, or together with pcDNA-ELAVL1 and si-COX2, and cell behaviors were examined. A mouse model of AKI was constructed using male C57BL/6 mice by the method of cecal ligation and puncture and intraperitoneal injection of LPS to explore the effect of RMRP silencing on renal injury in vivo.

RESULTS

RMRP and ELAVL1 was upregulated in LPS-treated HK-2 cells, and RMRP or ELAVL1 overexpression inhibited cell viability and promoted cell apoptosis, inflammatory factor secretion and oxidative stress, and RMRP knockdown showed the opposite effects. ELAVL1 upregulated COX2 protein expression and overexpression of COX2 reversed the promoting effects of RMRP knockdown on cell viability, as well as the inhibitory effects on cell apoptosis, inflammatory factor secretion and oxidative stress. Mechanistic findings suggested that RMRP aggravates LPS induced cell injury by activating prostaglandin E (PGE)/janus kinase-2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. We observed that knockdown of RMRP expression significantly alleviated renal tissue apoptosis, inflammatory factor secretion, and oxidative stress with AKI mice.

CONCLUSIONS

Our findings may provide a new reference for the treatment of AKI.

Small Molecules Targeting the RNA-Binding Protein HuR Inhibit Tumor Growth in Xenografts

The RNA-binding protein Hu antigen R (HuR) is a post-transcriptional regulator critical in several types of diseases, including cancer, making it a promising therapeutic target. We have identified small-molecule inhibitors of HuR through a screening approach used in combination with fragment analysis. A total of 36 new compounds originating from fragment linking or structural optimization were studied to establish structure-activity relationships in the set. Two top inhibitors, 1c and 7c, were further validated by binding assays and cellular functional assays. Both block HuR function by directly binding to the RNA-binding pocket, inhibit cancer cell growth dependence of HuR, and suppress cancer cell invasion. Intraperitoneal administration of inhibitor 1c inhibits tumor growth as a single agent and shows a synergistic effect in combination with chemotherapy docetaxel in breast cancer xenograft models. Mechanistically, 1c interferes with the HuR-TGFB/THBS1 axis.

RNA binding proteins (RBPs) and their role in DNA damage and radiation response in cancer

Traditionally majority of eukaryotic gene expression is influenced by transcriptional and post-transcriptional events. Alterations in the expression of proteins that act post-transcriptionally can affect cellular signaling and homeostasis. RNA binding proteins (RBPs) are a family of proteins that specifically bind to RNAs and are involved in post-transcriptional regulation of gene expression and important cellular processes such as cell differentiation and metabolism. Deregulation of RNA-RBP interactions and any changes in RBP expression or function can lead to various diseases including cancer. In cancer cells, RBPs play an important role in regulating the expression of tumor suppressors and oncoproteins involved in various cell-signaling pathways. Several RBPs such as HuR, AUF1, RBM38, LIN28, RBM24, tristetrapolin family and Musashi play critical roles in various types of cancers and their aberrant expression in cancer cells makes them an attractive therapeutic target for cancer treatment. In this review we provide an overview of i). RBPs involved in cancer progression and their mechanism of action ii). the role of RBPs, including HuR, in breast cancer progression and DNA damage response and iii). explore RBPs with emphasis on HuR as therapeutic target for breast cancer therapy.

lncNALT knockdown ameliorates hypertensive retinopathy via PTEN/PI3K/AKT pathway

This study aimed to explore the role of the long non-coding RNA NOTCH1-associated lncRNA in T cell acute lymphoblastic leukemia (lncNALT) in the pathogenesis of hypertensive retinopathy (HR). LncNALT expression levels were determined using reverse transcription-quantitative polymerase chain reaction. The effects of lncNALT knockdown on the viability, proliferation, migration, and invasion of human retinal microvascular endothelial cells (RMECs) were determined via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, 5-ethynyl-2'-deoxyuridine staining, and Transwell assays. Protein expression levels were determined using western blotting. We found that lncNALT expression levels were increased in RMECs treated with hydrogen peroxide (H₂O₂), while the knockdown of lncNALT rescued the viability, proliferation, migration, and invasion of RMECs treated with H₂O₂. Moreover, lncNALT interacted with ELAV like RNA binding protein 1 to affect the phosphatase and tensin homolog (PTEN) expression. Knockdown of lncNALT enhanced the viability, proliferation, migration, and invasion of RMECs via the PTEN/phosphoinositide 3-kinase (PI3K)/serine-threonine kinase (AKT) pathway. Taken together, knockdown of lncNALT enhanced the viability, proliferation, migration, and invasion of RMECs via the PTEN/PI3K/AKT pathway, suggesting that lncNALT could be a potential therapeutic target for patients with HR.

Identification and Characterization of an RRM-Containing, RNA Binding Protein in Acinetobacter baumannii

Acinetobacter baumannii is a Gram-negative pathogen, known to acquire resistance to antibiotics used in the clinic. The RNA-binding proteome of this bacterium is poorly characterized, in particular for what concerns the proteins containing RNA Recognition Motif (RRM). Here, we browsed the A. baumannii proteome for homologous proteins to the human HuR(ELAVL1), an RNA binding protein containing three RRMs. We identified a unique locus that we called AB-Elavl, coding for a protein with a single RRM with an average of 34% identity to the first HuR RRM. We also widen the research to the genomes of all the bacteria, finding 227 entries in 12 bacterial phyla. Notably we observed a partial evolutionary divergence between the RNP1 and RNP2 conserved regions present in the prokaryotes in comparison to the metazoan consensus sequence. We checked the expression at the transcript and protein level, cloned the gene and expressed the recombinant protein. The X-ray and NMR structural characterization of the recombinant AB-Elavl revealed that the protein maintained the typical β₁α₁β₂β₃α₂β₄ and three-dimensional organization of eukaryotic RRMs. The biochemical analyses showed that, although the RNP1 and RNP2 show differences, it can bind to AU-rich regions like the human HuR, but with less specificity and lower affinity. Therefore, we identified an RRM-containing RNA-binding protein actually expressed in A. baumannii.