Medicinal chemistry strategies towards the development of non-covalent SARS-CoV-2 Mpro inhibitors

The main protease(M^(pro))of SARS-CoV-2 is an attractive target in anti-COVID-19 therapy for its high conservation and major role in the virus life cycle.The covalent M^(pro)inhibitor nirmatrelvir(in combination with ritonavir,a pharmacokinetic enhancer)and the non-covalent inhibitor ensitrelvir have shown efficacy in clinical trials and have been approved for therapeutic use.Effective antiviral drugs are needed to fight the pandemic,while non-covalent M^(pro)inhibitors could be promising alternatives due to their high selectivity and favorable druggability.Numerous non-covalent M^(pro)inhibitors with desirable properties have been developed based on available crystal structures of M^(pro).In this article,we describe medicinal chemistry strategies applied for the discovery and optimization of non-covalent M^(pro)inhibitors,followed by a general overview and critical analysis of the available information.Prospective viewpoints and insights into current strategies for the development of non-covalent M^(pro)inhibitors are also discussed.

Chemotherapy induces breast cancer stem cell enrichment through repression of glutathione S-transferase Mu

Triple-negative breast cancer(TNBC)has aggressive characteristics as exemplified by the high risk of recurrence,metastasis,and patient mortality.1 Cytotoxic chemotherapy may reduce tumor burden initially,but leave behind chemo-resistant breast cancer stem cells(BCSCs)that lead to tumor recurrence and metastasis.2 Chemotherapy induces BCsC enrichment through the activation of glutathione biosynthesis pathways,which increases intracellular glutathione levels and specifies the BCSC phenotype through complicated downstream signaling pathways.3 Glutathione S-transferases(GSTs),a superfamily(which contains seven cytosolic classes:Alpha,Kappa,Mu,Omega,Pi,Theta,and Zeta,and one microsomal class MGSTs)of phase Il enzymes that catalyze the conjugation of glutathione with electrophilic compounds,play a critical role in detoxification and chemotherapy resistance of cancer cells.However,the role of GSTs in the regulation of BCSCs is largely elusive.

Research progress in the mechanism and treatment of osteosarcoma

Osteosarcoma(OS)is the most common primary malignant bone tumor that more commonly occurs in children and adolescents.The most commonly used treatment for OS is surgery combined with chemotherapy,but the treatment outcomes are typically unsatisfactory.High rates of metastasis and post-treatment recurrence rates are major challenges in the treatment of OS.This underlines the need for studying the in-depth characterization of the pathogenetic mechanisms of OS and development of more effective therapeutic modalities.Previous studies have demonstrated the important role of the bone microenvironment and the regulation of signaling pathways in the occurrence and development of OS.In this review,we discussed the available evidence pertaining to the mechanisms of OS development and identified therapeutic targets for OS.We also summarized the available treatment modalities for OS and identified future priorities for therapeutics research.

Targeting hypoxia-induced CBS expression inhibits breast cancer stem cells through the induction of ferroptosis

Triple-negative breast cancer(TNBC)has a poor prognosis because of its aggressive characteristics and lack of targeted therapies.1 Recently,it has been reported that TNBC is sensitiveto ferroptosis,an iron-dependent type of programmed cell death,making it a potential target for the treatment of TNBC.2 Breast cancer stem cells(BCSCs),a small population of cancer cells that possess the infinite proliferative potential and tumor-initiating properties,play important roles in drug resistance.3 The responses of BCsCs to ferroptosis-inducing agents are controversial and remain elusive.

rFliC prolongs allograft survival in association with the activation of recipient Tregs in a TLR5-dependent manner

AIIorejection remains an obstacle for successful organ transplantation. Although different types of immunosuppressive agents are effective for controlling rejection and prolonging graft survival, drug treatment is limited because of side effects and toxicity. Therefore, it is necessary and urgent to identify new candidate drugs for inducing allotolerance. Recently, it has been reported that bacterial flagellin induces the immunosuppressive activity of regulatory T cells （Tregs） in humans in vitro. In the present study, we analyzed the effects of recombinant flagellin （rFliC） on allograft survival and explored the underlying mechanisms associated with the activation of recipient Tregs in a murine skin allotransplantation model. The results showed that rFliC administration （3 mg/kg, once per day for 3 days, i.p.） prolonged allograft survival （mean survival time： 18.4--.1.1 days） compared to the control group （10___0.7 days, P〈O.01）. Additionally, higher positive expression of Toll-like receptor 5 （TLR5） was detected within the allograft administered with rFliC. The frequency of CD4＋CD25＋Foxp3＋ Tregs; the expression of Treg-related factors TLR5, Foxp3, TGF-I^I and IL-IO; and the proliferation and suppression of Tregs were increased following rFliC administration compared to the control. Moreover, the increased expression of tolerance-related molecules and the proliferation of Tregs induced by rFliC were attenuated by an anti-TLR5 blocking antibody both in vivo and in vitro. In conclusion, rFliC administration prolongs the survival of allografts, which is associated with the activation of recipient Tregs in a TLR5-dependent manner, rFliC may be a new candidate for anti-allorejection therapy.

CUL4B orchestrates mesenchymal stem cell commitment by epigenetically repressing KLF4 and C/EBPδ

Dysregulated lineage commitment of mesenchymal stem cells(MSCs)contributes to impaired bone formation and an imbalance between adipogenesis and osteogenesis during skeletal aging and osteoporosis.The intrinsic cellular mechanism that regulates MSC commitment remains unclear.Here,we identified Cullin 4B(CUL4B)as a critical regulator of MSC commitment.CUL4B is expressed in bone marrow MSCs(BMSCs)and downregulated with aging in mice and humans.Conditional knockout of Cul4b in MSCs resulted in impaired postnatal skeletal development with low bone mass and reduced bone formation.Moreover,depletion of CUL4B in MSCs aggravated bone loss and marrow adipose accumulation during natural aging or after ovariectomy.In addition,CUL4B deficiency in MSCs reduced bone strength.Mechanistically,CUL4B promoted osteogenesis and inhibited adipogenesis of MSCs by repressing KLF4 and C/EBPδexpression,respectively.The CUL4B complex directly bound to Klf4 and Cebpd and epigenetically repressed their transcription.Collectively,this study reveals CUL4B-mediated epigenetic regulation of the osteogenic or adipogenic commitment of MSCs,which has therapeutic implications in osteoporosis.

nhibition of Pim2-prolonged skin allograft surviva through the apoptosis regulation pathway

Recently, apoptosis has been considered to be an important regulator for allograft survival. The serine/threonine kinase Pim2 has been implicated in many apoptotic pathways. In a previous study, we found that pim2was highly expressed in CD4＋ T cells in an allograft model. Here, we further investigated the effects of Pim2 on allograft survival and the underlying mechanisms associated with apoptosis. The results showed that pim2 was overexpressed in grafts and spleens, particularly in spleen CD4＋ T cells when acute allorejection occurred, and correlated positively with the extent of rejection. In T cells from the spleens of naive BALB/c mice treated with 5 pM 4a （a specific inhibitor of Pim2） for 24 h, the apoptosis rate increased and the phosphorylation of BAD was decreased. Furthermore, adoptive transfer of CD4＋ T cells treated with 4a in vitroto allografted severe combined immunodeficiency （SCID） mice effectively prolonged allograft survival from 19.5± 1.7 days to 31 ±2.3 days. Moreover, the results demonstrated that the CD4＋CD25- effector T-cell subset was the predominate expresser of the pim2 gene as compared with the CD4＋CD25＋ regulatory T （Treg） cell subset. AIIoantigen-induced CD4＋CD25＋ T cells displayed less Foxp3 expression and a low suppression of apoptosis compared with effector CD4＋CD25- T cells treated with 4a. Collectively, these data revealed that Pim2 facilitated allograft rejection primarily by modulating the apoptosis of effector T cells and the function of Treg cells. These data suggested that Pim2 may be an important target for in vivoanti-rejection therapies and for the ex vivoexpansion of CD4＋CD25＋ T cells.

Blockade of Tim-3 Pathway Ameliorates Interferon-γ Production from Hepatic CD8^+ T Cells in a Mouse Model of Hepatitis B Virus Infection

T cell immunoglobulin- and mucin-domain-containing molecule-3 （Tim-3） has been reported to participate in the pathogenesis of inflammatory diseases. However, whether Tim-3 is involved in hepatitis B virus （HBV） infection remains unknown. Here, we studied the expression and function of Tim-3 in a hydrodynamics-based mouse model of HBV infection. A significant increase of Tim-3 expression on hepatic T lymphocytes, especially on CD8^＋ T cells, was demonstrated in HBV model mice from day 7 to day 18. After Tim-3 knockdown by specific shRNAs, significantly increased IFN-γ production from hepatic CD8^＋ T cells in HBV model mice was observed. Very interestingly, we found Tim-3 expression on CD8^＋ T cells was higher in HBV model mice with higher serum anti-HBs production. Moreover, Tim-3 knockdown influenced anti-HBs production in vivo. Collectively, our data suggested that Tim-3 might act as a potent regulator of antiviral T-cell responses in HBV infection. Cellular ＆ Molecular Immunology.

Features of a Chinese family with cerebral cavernous malformation induced by a novel CCM1 gene mutation

Background Familial cerebral cavernous malformations （CCMs）, characterized by hemorrhagic stroke, recurrent headache and epilepsy, are congenital vascular anomalies of the central nervous system. Familial CCMs is an autosomal dominant inherited disorder and three CCM genes have been identified. We report a Chinese family with CCMs and intend to explore clinical, pathological, magnetic resonance imaging （MRI） features and pathogenic gene mutation of this family. Methods Totally 25 family members underwent brain MRI examination and clinical check. Two patients with surgical indications had surgical treatment and the specimens were subjected to histopathological and microstructural examination. In addition, polymerase chain reaction （PCR） and direct sequencing were performed with genomic DNA extracted from 25 family members＇ blood samples for mutation detection. Results Brain MRI identified abnormal results in seven family members. All of them had multiple intracranial lesions and four cases had skin cavernous hemangioma. T2-weighted sequence showed that the lesions were typically characterized by an area of mixed signal intensity. Gradient-echo （GRE） sequence was more sensitive to find micro- cavernous hemangiomas. There was a wide range in the clinical manifestations as well as the age of onset in the family. The youngest patient was an 8-year-old boy with least intracranial lesions. Histopathological and microstructural examination showed that CCMs were typically discrete multi-sublobes of berry-like lesions, with hemorrhage in various stages of illness evolution. They were formed by abnormally enlarged sinusoids and the thin basement membranes. A novel T deletion mutation in exon 14 of CCM1 gene was identified by mutation detection in the seven patients. But unaffected members and healthy controls did not carry this mutation. Conclusions The clinical manifestations were heterogenic within this family. We identified a novel mutation （c.1396delT） was the disease-causing mutation for this family and extended the mutational spectrum of CCMs.

CUL4B facilitates HBV replication by promoting HBx stabilization

Objective:Hepatitis B virus(HBV)infection is a major public health problem worldwide.However,the regulatory mechanisms underlying HBV replication remain unclear.Cullin 4 B-RING ubiquitin E3 ligase(CRL4 B)is involved in regulating diverse physiological and pathophysiological processes.In our study,we aimed to explain the role of CUL4 B in HBV infection.Methods:Cul4 b transgenic mice or conditional knockout mice,as well as liver cell lines with CUL4 B overexpression or knockdown,were used to assess the role of CUL4 B in HBV replication.Immunoprecipitation assays and immunofluorescence staining were performed to study the interaction between CUL4 B and HBx.Cycloheximide chase assays and in vivo ubiquitination assays were performed to evaluate the half-life and the ubiquitination status of HBx.Results:The hydrodynamics-based hepatitis B model in Cul4 b transgenic or conditional knockout mice indicated that CUL4 B promoted HBV replication(P<0.05).Moreover,the overexpression or knockdown system in human liver cell lines validated that CUL4 B increased HBV replication in an HBx-dependent manner.Importantly,immunoprecipitation assays and immunofluorescence staining showed an interaction between CUL4 B and HBx.Furthermore,CUL4 B upregulated HBx protein levels by inhibiting HBx ubiquitination and proteasomal degradation(P<0.05).Finally,a positive correlation between CUL4 B expression and HBV pg RNA level was observed in liver tissues from HBV-positive patients and HBV transgenic mice.Conclusions:CUL4 B enhances HBV replication by interacting with HBx and disrupting its ubiquitin-dependent proteasomal degradation.CUL4 B may therefore be a potential target for anti-HBV therapy.

Structural basis of signaling of cannabinoids receptors:paving a way for rational drug design in controling mutiple neurological and immune diseases

Cannabinoids(CBs),analgesic drugs used for thousands of years,were first found in Cannabis sativa,and the multiple CBs used medicinally,such as tetrahydrocannabinol(THC),cannabidiol(CBD)and dozens more,have complex structures.In addition to their production by plants,CBs are naturally present in the nerves and immune systems of humans and animals.Both exogenous and endogenous CBs carry out a variety of physiological functions by engaging with two CB receptors,the CB1 and CB2 receptors,in the human endocannabinoid system(ECS).Both CB1 and CB2 are G protein-coupled receptors that share a 7-transmembrane(7TM)topology.CB1,known as the central CB receptor,is mainly distributed in the brain,spinal cord,and peripheral nervous system.CB1 activation in the human body typically promotes the release of neurotransmitters,controls pain and memory learning,and regulates metabolism and the cardiovascular system.Clinically,CB1 is a direct drug target for drug addiction,neurodegenerative diseases,pain,epilepsy,and obesity.Unlike the exclusive expression of CB1 in the nervous system,CB2 is mainly distributed in peripheral immune cells.Selective CB2 agonists would have therapeutic potential in the treatment of inflammation and pain and avoid side effects caused by currently used clinical drugs.Although significant progress has been made in developing agonists toward CB receptors,efficient clinical drugs targeting CB receptors remain lacking due to their complex signaling mechanisms.The recent structural elucidation of CB receptors has greatly aided our understanding of the activation and signal transduction mechanisms of CB receptors.

Ribosomal protein S26 serves as a checkpoint of T-cell survival and homeostasis in a p53-dependent manner

Ribosomal proteins(RPs),which play critical roles in ribosome assembly and protein translation,have been proven to be associated with important physiological and pathological processes,including the regulation of T-cell development and immune-related diseases.1,2,3 A recent study reported that ribosomal protein S26(Rps26),which is a Diamond–Blackfan anemia-associated RP located in the 40S subunit that controls oocyte growth,4,5 may influence multiple different immune phenotypes.6 Moreover,a SNP in the 5′UTR of the Rps26 gene in CD4^(+)and CD8+T cells was implicated in several autoimmune diseases.7 However,the function of Rps26 in T lymphocytes remains unknown.Here,we found that Rps26 was highly expressed in T lymphocytes.We examined a T-cell-specific Rps26 knockout mouse model and reported for the first time that ablation of Rps26 in T cells not only impairs peripheral T-cell homeostasis but also leads to T-cell developmental arrest in the thymus.Mechanistically,Rps26 critically regulates T-cell survival in a p53-dependent manner.These findings reveal the indispensable role of the Rps26-p53 axis in T-cell development and homeostasis.

NPRC deletion mitigated atherosclerosis by inhibiting oxidative stress, inflammation and apoptosis in ApoE knockout mice

Previous studies suggested a beneficial effect of natriuretic peptides in animal models of cardiovascular disease,but the role of natriuretic peptide receptor C(NPRC)in the pathogenesis of atherosclerosis(AS)remains unknown.This study was designed to test the hypothesis that NPRC may promote AS lesion formation and instability by enhancing oxidative stress,inflammation,and apoptosis via protein kinase A(PKA)signaling.ApoE^(−/−)mice were fed chow or Western diet for 12 weeks and NPRC expression was significantly increased in the aortic tissues of Western diet-fed mice.Systemic NPRC knockout mice were crossed with ApoE^(−/−)mice to generate ApoE^(−/−)NPRC^(−/−)mice,and NPRC deletion resulted in a significant decrease in the size and instability of aortic atherosclerotic lesions in ApoE^(−/−)NPRC^(−/−)versus ApoE^(−/−)mice.In addition,endothelial cell-specific NPRC knockout attenuated atherosclerotic lesions in mice.In contrast,endothelial cell overexpression of NPRC aggravated the size and instability of atherosclerotic aortic lesions in mice.Experiments in vitro showed that NPRC knockdown in human aortic endothelial cells(HAECs)inhibited ROS production,pro-inflammatory cytokine expression and endothelial cell apoptosis,and increased eNOS expression.Furthermore,NPRC knockdown in HAECs suppressed macrophage migration,cytokine expression,and phagocytosis via its effects on endothelial cells.On the contrary,NPRC overexpression in endothelial cells resulted in opposite effects.Mechanistically,the anti-inflammation and anti-atherosclerosis effects of NPRC deletion involved activation of cAMP/PKA pathway,leading to downstream upregulated AKT1 pathway and downregulated NF-κB pathway.In conclusion,NPRC deletion reduced the size and instability of atherosclerotic lesions in ApoE^(−/−)mice via attenuating inflammation and endothelial cell apoptosis and increasing eNOS expression by modulating cAMP/PKA-AKT1 and NF-κB pathways.Thus,targeting NPRC may provide a promising approach to the prevention and treatment of atherosclerosis.

Cullin 4B-RING E3 ligase complex in immune cell differentiation and function

CUL4B,which encodes the scaffold protein in the CRL4B complex,is a commonly mutated gene in X-linked intellectual disability[10,11].In addition to intellectual disability,patients with CUL4B mutations present with an elevated number of monocytes in peripheral blood[10],implying a role for CUL4B in regulating monocytes/macrophages.Monocytes/macrophages are critical players in innate immunity.Hung et al.found that depletion of CUL4B in myeloid cells aggravated lipopolysaccharide(LPS)-induced acute peritonitis[3].They further showed that after LPS stimulation,Cul4b-deficient macrophages secreted more chemokines than control macrophages,which might have accounted for the elevated infiltration of immune cells into the peritoneum[3].Our previous work demonstrated that myeloid-specific Cul4b-knockout mice exhibited reduced survival after LPS injection or Salmonella typhimurium infection compared to control mice[6].In contrast to work from Hung et al.,which showed that Cul4b-deficient macrophages secreted less TNFαand IL-6 after LPS stimulation[3],our works showed that deletion of CUL4B in macrophages increased the production of proinflammatory cytokines and decreased the expression of the anti-inflammatory cytokine IL-10 in response to the activation of Toll-like receptor(TLR).CUL4B regulation of macrophages relies on the ubiquitination activity of the CRL4B complex.The CRL4B complex catalyzes monoubiquitination of H2AK119 at the promoter of Pten,resulting in the repression of Pten transcription and subsequent activation of AKT and AKT-dependent inhibition of GSK3β,which suppresses TLR-triggered proinflammatory responses(Fig.1B)[6].