Eltrombopag directly inhibits BAX and prevents cell death

Drug repositioning in thyroid cancer: from point mutations to gene fusions

The diagnosis of thyroid cancer (TC) has increased dramatically in recent years. Papillary TC is the most frequent type and has shown a good prognosis. Conventional treatments for TC are surgery, hormonal therapy, radioactive iodine, chemotherapy, and targeted therapy. However, resistance to treatments is well documented in almost 20% of all cases. Genomic sequencing has provided valuable information to help identify variants that hinder the success of chemotherapy as well as to determine which of those represent potentially druggable targets. There is a plethora of targeted therapies for cancer, most of them directed toward point mutations; however, chromosomal rearrangements that generate fusion genes are becoming relevant in cancer but have been less explored in TC. Therefore, it is relevant to identify new potential inhibitors for genes that are recurrent in the formation of gene fusions. In this review, we focus on describing potentially druggable variants and propose both point variants and fusion genes as targets for drug repositioning in TC.

New insights into the anti-apoptotic mechanism of natural polyphenols in complex with Bax protein

Excessive apoptosis can kill normal cells and lead to liver damage, heart failure and neurodegenerative diseases. Polyphenols are secondary metabolites of plants that can interact with proteins to inhibit toxins and disease-related apoptosis. Bax is the major pro-apoptotic protein that disrupts the outer mitochondrial membrane to induce apoptosis, but limited studies have focused on the interaction between polyphenols and Bax and the associated anti-apoptotic mechanisms, especially at the atomic level. In this article, we collected 69 common polyphenols for active ingredient screening targeting Bax. Polyphenols with better and worse molecular docking scores were selected, and their anti-apoptosis effects were compared using the H2O2-induced HepG2 cell model. The interactions between the selected polyphenols and Bax protein were analyzed using molecular dynamics simulation to explore the molecular mechanism underlying the anti-apoptosis effect. Secoisolariciresinol diglucoside (SDG) and Epigallocatechin-3-gallate (EGCG) with the best affinity for Bax (-6.76 and -6.52 kcal/mol) reduced the expression of cytochrome c and caspase 3, decreasing the apoptosis rate from 52 to 11% and 12%. Molecular dynamics simulation results showed that Bim unfolded the α1-α2 loop of Bax, and disrupted the non-bond interactions between the loop (Pro-43, Glu-44 and Leu-45) and surface (Ile-133, Arg-134 and Met-137) residues, with binding free energy changed from -15.0 to 0 kJ/mol. The hydrogen bonds and van der Waals interactions formed between polyphenols and Bax prevented the unfolding of the loop. Taken together, our results proved that polyphenols can inhibit apoptosis by maintaining the unactivated conformation of Bax to reduce outer mitochondrial membrane damage.Communicated by Ramaswamy H. Sarma.

Covalent inhibition of pro-apoptotic BAX

BCL-2-associated X protein (BAX) is a promising therapeutic target for activating or restraining apoptosis in diseases of pathologic cell survival or cell death, respectively. In response to cellular stress, BAX transforms from a quiescent cytosolic monomer into a toxic oligomer that permeabilizes the mitochondria, releasing key apoptogenic factors. The mitochondrial lipid trans-2-hexadecenal (t-2-hex) sensitizes BAX activation by covalent derivatization of cysteine 126 (C126). In this study, we performed a disulfide tethering screen to discover C126-reactive molecules that modulate BAX activity. We identified covalent BAX inhibitor 1 (CBI1) as a compound that selectively derivatizes BAX at C126 and inhibits BAX activation by triggering ligands or point mutagenesis. Biochemical and structural analyses revealed that CBI1 can inhibit BAX by a dual mechanism of action: conformational constraint and competitive blockade of lipidation. These data inform a pharmacologic strategy for suppressing apoptosis in diseases of unwanted cell death by covalent targeting of BAX C126.

Chemical modulation of cytosolic BAX homodimer potentiates BAX activation and apoptosis

The BCL-2 family protein BAX is a major regulator of physiological and pathological cell death. BAX predominantly resides in the cytosol in a quiescent state and upon stress, it undergoes conformational activation and mitochondrial translocation leading to mitochondrial outer membrane permeabilization, a critical event in apoptosis execution. Previous studies reported two inactive conformations of cytosolic BAX, a monomer and a dimer, however, it remains unclear how they regulate BAX. Here we show that, surprisingly, cancer cell lines express cytosolic inactive BAX dimers and/or monomers. Expression of inactive dimers, results in reduced BAX activation, translocation and apoptosis upon pro-apoptotic drug treatments. Using the inactive BAX dimer structure and a pharmacophore-based drug screen, we identify a small-molecule modulator, BDM19 that binds and activates cytosolic BAX dimers and prompts cells to apoptosis either alone or in combination with BCL-2/BCL-XL inhibitor Navitoclax. Our findings underscore the role of the cytosolic inactive BAX dimer in resistance to apoptosis and demonstrate a strategy to potentiate BAX-mediated apoptosis.

Enhancing nasopharyngeal carcinoma cell radiosensitivity by suppressing AKT/mTOR via CENP-N knockdown

OBJECTIVE

Investigating the impact of centromere protein N (CENP-N) on radiosensitivity of nasopharyngeal carcinoma (NPC) cells.

METHODS

Using immunohistochemistry and immunofluorescence to detect CENP-N expression in tissues from 35 patients with radiosensitive or radioresistant NPC. Assessing the effect of combined CENP-N knockdown and radiotherapy on various cellular processes by CCK-8, colony formation, flow cytometry, and Western blotting. Establishing a NPC xenograft model. When the tumor volume reached 100 mm3, a irradiation dose of 6 Gy was given, and the effects of the combined treatment were evaluated in vivo using immunofluorescence and Western blotting techniques.

RESULTS

The level of CENP-N was significantly reduced in radiosensitive tissues of NPC (p < 0.05). Knockdown of CENP-N enhanced NPC radiosensitivity, resulting in sensitizing enhancement ratios (SER) of 1.44 (5-8 F) and 1.16 (CNE-2Z). The combined treatment showed significantly higher levels of proliferation suppression, apoptosis, and G2/M phase arrest (p < 0.01) compared to either CENP-N knockdown alone or radiotherapy alone. The combined treatment group showed the highest increase in Bax and γH2AX protein levels, whereas the protein Cyclin D1 exhibited the greatest decrease (p < 0.01). However, the above changes were reversed after treatment with AKT activator SC79. In vivo, the mean volume and weight of tumors in the radiotherapy group were 182 ± 54 mm3 and 0.16 ± 0.03 g. The mean tumor volume and weight in the combined treatment group were 84 ± 42 mm3 and 0.04 ± 0.01 g.

CONCLUSION

Knockdown of CENP-N can enhance NPC radiosensitivity by inhibiting AKT/mTOR.

Development of novel cytoprotective small compounds inhibiting mitochondria-dependent cell death

We identified cytoprotective small molecules (CSMs) by a cell-based high-throughput screening of Bax inhibitors. Through a medicinal chemistry program, M109S was developed, which is orally bioactive and penetrates the blood-brain/retina barriers. M109S protected retinal cells in ocular disease mouse models. M109S directly interacted with Bax and inhibited the conformational change and mitochondrial translocation of Bax. M109S inhibited ABT-737-induced apoptosis both in Bax-only and Bak-only mouse embryonic fibroblasts. M109S also inhibited apoptosis induced by staurosporine, etoposide, and obatoclax. M109S decreased maximal mitochondrial oxygen consumption rate and reactive oxygen species production, whereas it increased glycolysis. These effects on cellular metabolism may contribute to the cytoprotective activity of M109S. M109S is a novel small molecule protecting cells from mitochondria-dependent apoptosis both in vitro and in vivo. M109S has the potential to become a research tool for studying cell death mechanisms and to develop therapeutics targeting mitochondria-dependent cell death pathway.

Apoptotic stress causes mtDNA release during senescence and drives the SASP

Senescent cells drive age-related tissue dysfunction partially through the induction of a chronic senescence-associated secretory phenotype (SASP)1. Mitochondria are major regulators of the SASP; however, the underlying mechanisms have not been elucidated2. Mitochondria are often essential for apoptosis, a cell fate distinct from cellular senescence. During apoptosis, widespread mitochondrial outer membrane permeabilization (MOMP) commits a cell to die3. Here we find that MOMP occurring in a subset of mitochondria is a feature of cellular senescence. This process, called minority MOMP (miMOMP), requires BAX and BAK macropores enabling the release of mitochondrial DNA (mtDNA) into the cytosol. Cytosolic mtDNA in turn activates the cGAS-STING pathway, a major regulator of the SASP. We find that inhibition of MOMP in vivo decreases inflammatory markers and improves healthspan in aged mice. Our results reveal that apoptosis and senescence are regulated by similar mitochondria-dependent mechanisms and that sublethal mitochondrial apoptotic stress is a major driver of the SASP. We provide proof-of-concept that inhibition of miMOMP-induced inflammation may be a therapeutic route to improve healthspan.

Mechanisms of BCL-2 family proteins in mitochondrial apoptosis

The proteins of the BCL-2 family are key regulators of mitochondrial apoptosis, acting as either promoters or inhibitors of cell death. The functional interplay and balance between the opposing BCL-2 family members control permeabilization of the outer mitochondrial membrane, leading to the release of activators of the caspase cascade into the cytosol and ultimately resulting in cell death. Despite considerable research, our knowledge about the mechanisms of the BCL-2 family of proteins remains insufficient, which complicates cell fate predictions and does not allow us to fully exploit these proteins as targets for drug discovery. Detailed understanding of the formation and molecular architecture of the apoptotic pore in the outer mitochondrial membrane remains a holy grail in the field, but new studies allow us to begin constructing a structural model of its arrangement. Recent literature has also revealed unexpected activities for several BCL-2 family members that challenge established concepts of how they regulate mitochondrial permeabilization. In this Review, we revisit the most important advances in the field and integrate them into a new structure-function-based classification of the BCL-2 family members that intends to provide a comprehensive model for BCL-2 action in apoptosis. We close this Review by discussing the potential of drugging the BCL-2 family in diseases characterized by aberrant apoptosis.

Eltrombopag directly activates BAK and induces apoptosis

Small molecule direct BAK activators can potentially be used for the development of anti-cancer drugs or as tools to study BAK activation. The thrombopoietin receptor agonist eltrombopag (Eltro) inhibits BAX activation and BAX-mediated apoptosis. Here we report that, in contrast to its function as a BAX inhibitor, Eltro directly binds BAK but induces its activation in vitro. Moreover, Eltro induces or sensitizes BAK-dependent cell death in mouse embryonic fibroblasts (MEFs) and Jurkat cells. Chemical shift perturbation analysis by NMR indicates that Eltro binds to the BAK α4/α6/α7 groove to initiate BAK activation. Further molecular docking by HADDOCK suggests that several BAK residues, including R156, F157, and H164, play an important role in the interaction with Eltro. The introduction of an R156E mutation in the BAK α4/α6/α7 groove not only decreases Eltro binding and Eltro-induced BAK activation in vitro but also diminishes Eltro-induced apoptosis. Thus, our data suggest that Eltro directly induces BAK activation and BAK-dependent apoptosis, providing a starting point for the future development of more potent and selective direct BAK activators.

Mitochondrial control of inflammation

Numerous mitochondrial constituents and metabolic products can function as damage-associated molecular patterns (DAMPs) and promote inflammation when released into the cytosol or extracellular milieu. Several safeguards are normally in place to prevent mitochondria from eliciting detrimental inflammatory reactions, including the autophagic disposal of permeabilized mitochondria. However, when the homeostatic capacity of such systems is exceeded or when such systems are defective, inflammatory reactions elicited by mitochondria can become pathogenic and contribute to the aetiology of human disorders linked to autoreactivity. In addition, inefficient inflammatory pathways induced by mitochondrial DAMPs can be pathogenic as they enable the establishment or progression of infectious and neoplastic disorders. Here we discuss the molecular mechanisms through which mitochondria control inflammatory responses, the cellular pathways that are in place to control mitochondria-driven inflammation and the pathological consequences of dysregulated inflammatory reactions elicited by mitochondrial DAMPs.

Fresh Gastrodia elata Blume alleviates simulated weightlessness-induced cognitive impairment by regulating inflammatory and apoptosis-related pathways

In aerospace medicine, the influence of microgravity on cognition has always been a risk factor threatening astronauts' health. The traditional medicinal plant and food material Gastrodia elata Blume has been used as a therapeutic drug for neurological diseases for a long time due to its unique neuroprotective effect. To study the effect of fresh Gastrodia elata Blume (FG) on cognitive impairment caused by microgravity, hindlimb unloading (HU) was used to stimulate weightlessness in mice. The fresh Gastrodia elata Blume (0.5 g/kg or 1.0 g/kg) was intragastrically administered daily to mice exposed to HU and behavioral tests were conducted after four weeks to detect the cognitive status of animals. The behavioral tests results showed that fresh Gastrodia elata Blume therapy significantly improved the performance of mice in the object location recognition test, Step-Down test, and Morris Water Maze test, including short-term and long-term spatial memory. According to the biochemical test results, fresh Gastrodia elata Blume administration not only reduced serum factor levels of oxidative stress but also maintained the balance of pro-inflammatory and anti-inflammatory factors in the hippocampus, reversing the abnormal increase of NLRP3 and NF-κB. The apoptosis-related proteins were downregulated which may be related to the activation of the PI3K/AKT/mTOR pathway by fresh Gastrodia elata Blume therapy, and the abnormal changes of synapse-related protein and glutamate neurotransmitter were corrected. These results identify the improvement effect of fresh Gastrodia elata Blume as a new application form of Gastrodia elata Blume on cognitive impairment caused by simulated weightlessness and advance our understanding of the mechanism of fresh Gastrodia elata Blume on the neuroprotective effect.

Targeting protein conformations with small molecules to control protein complexes

Dynamic protein complexes function in all cellular processes, from signaling to transcription, using distinct conformations that regulate their activity. Conformational switching of proteins can turn on or off their activity through protein-protein interactions, catalytic function, cellular localization, or membrane interaction. Recent advances in structural, computational, and chemical methodologies have enabled the discovery of small-molecule activators and inhibitors of conformationally dynamic proteins by using a more rational design than a serendipitous screening approach. Here, we discuss such recent examples, focusing on the mechanism of protein conformational switching and its regulation by small molecules. We emphasize the rational approaches to control protein oligomerization with small molecules that offer exciting opportunities for investigation of novel biological mechanisms and drug discovery.

A multi-targeting natural product, aiphanol, inhibits tumor growth and metastasis

Cancer is one of the main causes of death in humans worldwide, the development of more effective anticancer drugs that can inhibit the malignant progression of cancer cells is of great significance. Aiphanol is a natural product identified from the seeds of Arecaceae and the rhizome of Smilax glabra Roxb. Our preliminary studies revealed that it had potential antiangiogenic and antilymphangiogenic activity by directly targeting VEGFR2/3 and COX2 in endothelial cells. However, the influence of aiphanol on cancer cells per se remains largely undefined. In this study, the effects and related mechanisms of aiphanol on cancer growth and metastasis were evaluated in vitro and in vivo. Acute toxicity assay and pharmacokinetic analysis were utilized to investigate the safety profile and metabolism characteristics of aiphanol. We revealed that aiphanol inhibited the proliferation of various types of cancer cells and the growth of xenograft tumors in mice and zebrafish models. The possible mechanism was associated with the inactivation of multiple kinases, including FAK, AKT and ERK, and the upregulation of BAX and cleaved caspase-3 to promote cancer cell apoptosis. Aiphanol significantly inhibited cancer cell migration and invasion, which was related to the inhibition of epithelial-mesenchymal transition (EMT) and F-actin aggregation. Aiphanol effectively attenuated the metastasis of several types of cancer cells in vivo. In addition, aiphanol exerted no significant toxicity and had fast metabolism. Collectively, we demonstrated the anticancer effects of aiphanol and suggested that aiphanol has potential as a safe and effective therapeutic agent to treat cancer.

Solvent paramagnetic relaxation enhancement as a versatile method for studying structure and dynamics of biomolecular systems

Solvent paramagnetic relaxation enhancement (sPRE) is a versatile nuclear magnetic resonance (NMR)-based method that allows characterization of the structure and dynamics of biomolecular systems through providing quantitative experimental information on solvent accessibility of NMR-active nuclei. Addition of soluble paramagnetic probes to the solution of a biomolecule leads to paramagnetic relaxation enhancement in a concentration-dependent manner. Here we review recent progress in the sPRE-based characterization of structural and dynamic properties of biomolecules and their complexes, and aim to deliver a comprehensive illustration of a growing number of applications of the method to various biological systems. We discuss the physical principles of sPRE measurements and provide an overview of available co-solute paramagnetic probes. We then explore how sPRE, in combination with complementary biophysical techniques, can further advance biomolecular structure determination, identification of interaction surfaces within protein complexes, and probing of conformational changes and low-population transient states, as well as deliver insights into weak, nonspecific, and transient interactions between proteins and co-solutes. In addition, we present examples of how the incorporation of solvent paramagnetic probes can improve the sensitivity of NMR experiments and discuss the prospects of applying sPRE to NMR metabolomics, drug discovery, and the study of intrinsically disordered proteins.

Eltrombopag binds SDC4 directly and enhances MAPK signaling and macropinocytosis in cancer cells

Syndecan-4 (SDC4) is a single-pass transmembrane glycoprotein implicated in a variety of oncogenic signaling pathways. It is also an intrinsically disordered protein and considered "undruggable". In the present study, we confirmed that knocking out SDC4 in pancreatic cancer cells markedly impaired macropinocytosis, colony formation, as well as xenograft tumor initiation and growth. Quantitative proteomic profiling of Sdc4 knockout (KO) cells revealed significant changes in cell metabolic pathways. In a cellular protein-based ligand interaction screening, we identified that Eltrombopag (ETBP), an FDA-approved agonist of the thrombopoietin receptor (TPOR) for immune thrombocytopenia, could directly bind to SDC4 with a Kd value of ~2 µM. We showed that the transmembrane motif was essential for SDC4 binding to ETBP. Unexpectedly, ETBP not only increased SDC4 abundance, but also enhanced SDC4-associated MAPK signaling pathway and macropinocytosis in cancer cells. Our results indicate that ETBP is a potential agonist of SDC4 in a fashion similar to its original target TPOR, and that caution should be taken when using ETBP for chemotherapy-induced thrombocytopenia in cancer patients.

Exploring the Potential of Eltrombopag: Room for More?

Since its introduction in clinical practice, eltrombopag (ELT) has demonstrated efficacy in heterogeneous clinical contexts, encompassing both benign and malignant diseases, thus leading researchers to make a more in-depth study of its mechanism of action. As a result, a growing body of evidence demonstrates that ELT displays many effects ranging from native thrombopoietin agonism to immunomodulation, anti-inflammatory, and metabolic properties. These features collectively explain ELT effectiveness in a broad spectrum of indications; moreover, they suggest that ELT could be effective in different, challenging clinical scenarios. We reviewed the extended ELT mechanism of action in various diseases, with the aim of further exploring its full potential and hypothesize new, fascinating indications.

Scutellaria barbata D.Don (SBD) extracts suppressed tumor growth, metastasis and angiogenesis in Prostate cancer via PI3K/Akt pathway

Background

Scutellaria barbata D.Don (SBD) is derived from the dried whole plant of Labiate which has been widely used to treat patients with multiple cancer. It was previously reported that the ethanol extract of SBD is able to promote apoptosis, and inhibit cell proliferation and angiogenesis in cancer.

Materials and methods

CCK8, Edu assays and colony formation assay were performed to assess the effect of SBD on PCa cell growth. Effect of SBD on apoptosis and cell cycle was detected by flow cytometry. Transwell and wounding healing assay were conducted to detect the invasion and migration activities of PCa cells. Western blot was employed to detect the protein expression. 2RRV1 mouse xenograft model was established to detect the effect of SBD on prostate cancer. Angiogenesis was analysed by coculturing PCa cell lines and HUVECs.

Results

The results showed that SBD induced a significant decrease in cell viability and clonogenic growth in a dose-dependent manner. SBD induced cell apoptosis and cell cycle G2/M phase arrest by inactivating PI3K/AKT signalling pathway. Treatment with SBD also significantly decreased the cell migration and invasion via phenotypic inversion of EMT that was characterized by the increased expression of E-cadherin and Vimentin, and decreased expression of N-cadherin, which could be partially attributed to inhibiting PI3K/AKT signalling pathway. Subsequently, using AKT inhibitor MK2206, we concluded that PI3K/AKT are also involved in cell apoptosis and metastasis of PCa cells stimulated by SBD. Apart from its direct effects on PCa cells, SBD also exhibited anti-angiogenic properties. SBD alone or conditioned media from SBD-treated PCa cells reduced HUVEC tube formation on Matrigel without affecting HUVEC viability. Furthermore, 22RV1 xenograft C57BL/6 mice treated with SBD in vivo showed a significant inhibitory in tumour size and tumour weight without toxicity. In addition, administration with medium- or high-dose of SBD significantly inhibited the cell proliferation and enhanced the damage to tumour tissues.

Conclusions

Collectively, our in vitro and in vivo findings suggest that SBD has the potential to develop into a safe and potent alternative therapy for PCa patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03587-0.

Physiological and pharmacological modulation of BAX

Bcl-2-associated X protein (BAX) is a critical executioner of mitochondrial regulated cell death through its lethal activity of permeabilizing the mitochondrial outer membrane (MOM). While the physiological function of BAX ensures tissue homeostasis, dysregulation of BAX leads to aberrant cell death. Despite BAX being a promising therapeutic target for human diseases, historically the development of drugs has focused on antiapoptotic BCL-2 proteins, due to challenges in elucidating the mechanism of BAX activation and identifying druggable surfaces of BAX. Here, we discuss recent studies that have provided structure-function insights and identified regulatory surfaces that control BAX activation. Moreover, we emphasize the development of small molecule orthosteric, allosteric, and oligomerization modulators that provide novel opportunities for biological investigation and progress towards drugging BAX.

Assessing Mitochondrial DNA Release into the Cytosol and Subsequent Activation of Innate Immune-related Pathways in Mammalian Cells

Mitochondria have emerged as key drivers of mammalian innate immune responses, functioning as signaling hubs to trigger inflammation and orchestrating metabolic switches required for phagocyte activation. Mitochondria also contain damage-associated molecular patterns (DAMPs), molecules that share similarity with pathogen-associated molecular patterns (PAMPs) and can engage innate immune sensors to drive inflammation. The aberrant release of mitochondrial DAMPs during cellular stress and injury is an increasingly recognized trigger of inflammatory responses in human diseases. Mitochondrial DNA (mtDNA) is a particularly potent DAMP that engages multiple innate immune sensors, although mounting evidence suggests that cytosolic mtDNA is primarily detected via the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. cGAS and STING are widely expressed in mammalian cells and serve as key regulators of type I interferon and cytokine expression in both infectious and inflammatory diseases. Despite growing roles for the mtDNA-cGAS-STING axis in human disease, assays to quantify mtDNA release into the cytosol and approaches to link mtDNA to cGAS-STING signaling are not standardized, which increases the possibility for experimental artifacts and misinterpretation of data. Here, we present a series of protocols for assaying the release of mtDNA into the cytosol and subsequent activation of innate immune signaling in mammalian cells. We highlight genetic and pharmacological approaches to induce and inhibit mtDNA release from mitochondria. We also describe immunofluorescence microscopy and cellular fractionation assays to visualize morphological changes in mtDNA and quantify mtDNA accumulation in the cytosol. Finally, we include protocols to examine mtDNA-dependent cGAS-STING activation by RT-qPCR and western blotting. These methods can be performed with standard laboratory equipment and are highly adaptable to a wide range of mammalian cell types. They will permit researchers working across the spectrum of biological and biomedical sciences to accurately and reproducibly measure cytosolic mtDNA release and resulting innate immune responses. © 2022 Wiley Periodicals LLC. Basic Protocol 1: siRNA-mediated knockdown of TFAM to induce mtDNA instability, cytosolic release, and activation of the cGAS-STING pathway Alternate Protocol: Pharmacological induction of mtDNA release and cGAS-STING activation using ABT-737 and Q-VD-OPH Basic Protocol 2: Isolation and quantitation of DNA from cytosolic, mitochondrial, and nuclear fractions Basic Protocol 3: Pharmacological inhibition of mtDNA replication and release.

Repurposing Eltrombopag as an Antimicrobial Agent Against Methicillin-Resistant Staphylococcus aureus

Because of the excessive use of antibiotics, methicillin-resistant Staphylococcus aureus (MRSA) has become prevalent worldwide. Moreover, the formation of S. aureus biofilms often cause persistence and relapse of infections. Thus, the discovery of antibiotics with excellent antimicrobial and anti-biofilm activities is urgently needed. In the present study, eltrombopag (EP), a classic thrombopoietin receptor agonist, exhibited potential antimicrobial activity against S. aureus and its biofilms. Through our mechanistic studies, EP was found to interfere with proton motive force in S. aureus. The in vivo anti-infective efficacy of EP was further confirmed in the wound infection model, thigh infection model and peritonitis model by MRSA infection. In addition, the cytotoxicity of EP against mammalian cells and the in vivo toxicity of EP in animal models were not observed at the tested concentrations. Collectively, these results indicate that EP could be considered a potential novel antimicrobial agent against recalcitrant infections caused by MRSA.

The conformational stability of pro-apoptotic BAX is dictated by discrete residues of the protein core

BAX is a pro-apoptotic member of the BCL-2 family, which regulates the balance between cellular life and death. During homeostasis, BAX predominantly resides in the cytosol as a latent monomer but, in response to stress, transforms into an oligomeric protein that permeabilizes the mitochondria, leading to apoptosis. Because renegade BAX activation poses a grave risk to the cell, the architecture of BAX must ensure monomeric stability yet enable conformational change upon stress signaling. The specific structural features that afford both stability and dynamic flexibility remain ill-defined and represent a critical control point of BAX regulation. We identify a nexus of interactions involving four residues of the BAX core α5 helix that are individually essential to maintaining the structure and latency of monomeric BAX and are collectively required for dimeric assembly. The dual yet distinct roles of these residues reveals the intricacy of BAX conformational regulation and opportunities for therapeutic modulation.

Elucidating the Mechanism of Action of the Attributed Immunomodulatory Role of Eltrombopag in Primary Immune Thrombocytopenia: An In Silico Approach

Eltrombopag is a thrombopoietin receptor (MPL) agonist approved for the treatment of primary immune thrombocytopenia (ITP). Recent evidence shows that some patients may sustain platelet counts following eltrombopag discontinuation. The systemic immunomodulatory response that resolves ITP in some patients could result from an increase in platelet mass, caused either by the direct action of eltrombopag on megakaryocytes through MPL stimulation, or potential MPL-independent actions on other cell types. To uncover the possible mechanisms of action of eltrombopag, in silico analyses were performed, including a systems biology-based approach, a therapeutic performance mapping system, and structural analyses. Through manual curation of the available bibliography, 56 key proteins were identified and integrated into the ITP interactome analysis. Mathematical models (94.92% mean accuracy) were obtained to elucidate potential MPL-dependent pathways in non-megakaryocytic cell subtypes. In addition to the effects on megakaryocytes and platelet numbers, the results were consistent with MPL-mediated effects on other cells, which could involve interferon-gamma, transforming growth factor-beta, peroxisome proliferator-activated receptor-gamma, and forkhead box protein P3 pathways. Structural analyses indicated that effects on three apoptosis-related proteins (BCL2L1, BCL2, BAX) from the Bcl-2 family may be off-target effects of eltrombopag. In conclusion, this study proposes new hypotheses regarding the immunomodulatory functions of eltrombopag in patients with ITP.

Too much death can kill you: inhibiting intrinsic apoptosis to treat disease

Apoptotic cell death is implicated in both physiological and pathological processes. Since many types of cancerous cells intrinsically evade apoptotic elimination, induction of apoptosis has become an attractive and often necessary cancer therapeutic approach. Conversely, some cells are extremely sensitive to apoptotic stimuli leading to neurodegenerative disease and immune pathologies. However, due to several challenges, pharmacological inhibition of apoptosis is still only a recently emerging strategy to combat pathological cell loss. Here, we describe several key steps in the intrinsic (mitochondrial) apoptosis pathway that represent potential targets for inhibitors in disease contexts. We also discuss the mechanisms of action, advantages and limitations of small-molecule and peptide-based inhibitors that have been developed to date. These inhibitors serve as important research tools to dissect apoptotic signalling and may foster new treatments to reduce unwanted cell loss.