MyD88 Inhibitor Research Articles

Short-term MyD88 inhibition ameliorates cardiac graft rejection and promotes donor-specific hyporesponsiveness of skin grafts in mice.

Recognition of evolutionarily conserved ligands by Toll-like receptors (TLRs) triggers signaling cascades in innate immune cells to amplify adaptive immune responses. Nearly all TLRs require MyD88 to transduce downstream signaling. MyD88 deficiency has been shown to promote the allograft acceptance in mice. However, direct evidence for therapeutic potential of MyD88 inhibitors remains lacking. Herein, we used a MyD88 inhibitor, namely ST2825, to explore its therapeutic potential and mechanisms in fully allogeneic skin and heart transplant models. Phenotypic maturation of dendritic cells stimulated by TLR ligands was alleviated by ST2825 in parallel with reduced T-cell proliferation in vitro. A short-course treatment with ST2825 significantly prolonged cardiac graft survival (mean survival time = 18.5 ± 0.92 days vs. 7.25 ± 0.46 days). ST2825-treated group had significantly reduced proinflammatory cytokines in allografts compared with control group. ST2825 combined with anti-CD154 induced long-term skin allograft acceptance in about one-third of recipients (>100 days). 'Skin-tolerant' recipients showed attenuated donor-specific IFN-γ responses, intact IL-4 responses, and compromised alloantibody responses. We conclude that MyD88 inhibitor ST2825 attenuates acute cardiac rejection and promotes donor-specific hyporesponsiveness in stringent skin transplant models. The direct evidence suggests that pharmacological inhibition of MyD88 hold promising potential for transplant rejection.

Human casein alpha s1 induces proinflammatory cytokine expression in monocytic cells by TLR4 signaling.

Human casein alpha S1 (CSN1S1) is a milk-derived protein, which gives rise to sustained antibody formation after breast feeding in infancy and induces the expression of proinflammatory cytokines. So far, the cellular CSN1S1 receptor is unrecognized. Our objective was to identify the receptor employed by CSN1S1 to induce proinflammatory effects. CSN1S1 concentration and time dependently induced expression of IL-1β, IL-8, and IL-6 in monocytic cells despite addition of polymyxin B, which completely abrogated LPS effects. Coincubation of monocytic cells with a neutralizing antibody to Toll-like receptor 4 (TLR4) but not to TLR2 inhibited CSN1S1-induced effects. In TLR4/MD2/CD14-cotransfected HEK293 cells CSN1S1 increased IL-8 expression, while untransfected cells were completely unresponsive. Furthermore, CSN1S1-induced IL1-β secretion was impeded by inhibition of MyD88 and caspase-1. Flow cytometric in vitro assays confirmed binding of CSN1S1 to TLR4. Phosphorylation of CSN1S1 by casein-kinase 2 completely abolished proinflammatory cytokine induction and binding to TLR4. CSN1S1 is a multifunctional milk protein that exerts proinflammatory properties via TLR4 and the inflammasome pathway in a phosphorylation-dependent manner. The contribution of CSN1S1 in mother milk to the development of a potent immune system in breastfed individuals should be further assessed.

TLR-7 agonist attenuates airway reactivity and inflammation through Nrf2-mediated antioxidant protection in a murine model of allergic asthma

Toll-like receptors (TLRs) through innate immune system recognize pathogen associated molecular patterns and play an important role in host defense against bacteria, fungi and viruses. TLR-7 is responsible for sensing single stranded nucleic acids of viruses but its activation has been shown to be protective in mouse models of asthma. The NADPH oxidase (NOX) enzymes family mainly produces reactive oxygen species (ROS) in the lung and is involved in regulation of airway inflammation in response to TLRs activation. However, NOX-4 mediated signaling in response to TLR-7 activation in a mouse model of allergic asthma has not been explored previously. Therefore, this study investigated the role TLR-7 activation and downstream oxidant–antioxidant signaling in a murine model of asthma. Mice were sensitized with ovalbumin (OVA) intraperitoneally and treated with TLR-7 agonist, resiquimod (RSQ) intranasally before each OVA challenge from days 14 to 16. Mice were then assessed for airway reactivity, inflammation, and NOX-4 and nuclear factor E2-related factor 2 (Nrf2) related signaling [inducible nitric oxide synthase (iNOS), nitrotyrosine, lipid peroxides and copper/zinc superoxide dismutase (Cu/Zn SOD)]. Treatment with RSQ reduced allergen induced airway reactivity and inflammation. This was paralleled by a decrease in ROS which was due to induction of Nrf2 and Cu/Zn SOD in RSQ treated group. Inhibition of MyD88 reversed RSQ-mediated protective effects on airway reactivity/inflammation due to reduction in Nrf2 signaling. SOD inhibition produced effects similar to MyD88 inhibition. The current study suggests that TLR-7 agonist is beneficial and may be developed into a therapeutic option in allergic asthma.

Targeting of MyD88 Homodimerization by Novel Synthetic Inhibitor TJ-M2010-5 in Preventing Colitis-Associated Colorectal Cancer.

The TLR/MyD88 signaling pathway is an important driver of inflammation and cancer and is a possible target for antitumor therapy. We generated a MyD88 inhibitor (TJ-M2010-5), which was designed to bind to the TIR domain of MyD88 to interfere with its homodimerization, and the TLR/MyD88 signal pathway. We utilized a mouse model of azoxymethane/dextran sodium sulfate (AOM/DSS)-induced colitis-associated cancer (CAC) in combination with TJ-M2010-5 administration to investigate the anti-inflammation-related cancer effect of MyD88 inhibitor in vivo. Data were analyzed with one-way and repeated measures analysis of variance. Differences in survival between groups were compared using the log rank test. All statistical tests were two-sided. TJ-M2010-5 inhibited MyD88 homodimerization in transfected HEK293 cells in a concentration-dependent manner and suppressed MyD88 signaling in LPS-responsive RAW 264.7 cells in vitro. In a 10-week CAC mouse model (n = 30 per group), TJ-M2010-5 treatment statistically significantly reduced AOM/DSS-induced colitis and completely prevented CAC development with less related body mass loss, resulted in 0% mortality of treated mice (compared with 53% mortality of control mice), decreased cell proliferation, and increased apoptosis in colon tissue. TJ-M2010-5 treatment also inhibited production of inflammatory cytokines and chemokines (TNF-α, IL-6,G-CSF, MIP-1β, TGF-β1, IL-11, IL-17A, IL-22 and IL-23) and infiltration of immune cells (macrophages, dendritic cells, neutropihls and CD(+)4 T cells) in colon tissues of mice. Our findings suggest that TLR/MyD88 signaling may be a therapeutic target for CAC intervention and MyD88 inhibitors may be a promising therapeutic modality for treating patients with colitis or CAC.

Activation of Toll-like receptor 3 inhibits Marek's disease virus infection in chicken embryo fibroblast cells.

Toll-like receptor 3 (TLR3) is a critical component of the innate immune system against viral infection and controls the activation of adaptive immunity. The role of TLR3 in Marek's disease virus (MDV) infection is not clear. In this study, we found that the abundance of TLR3 mRNA was significantly higher in chicken embryo fibroblast cells (CEF) infected with MDV than in a control group. Activated TLR3 signaling via TLR3 ligand stimulation inhibited replication of the RB1B strain of MDV in CEF cells. In contrast, CEF cells transfected with TLR3 siRNA promoted RB1B infection and replication. However, treatment with other TLR ligands, whether stimulatory (LPS, imiquimod and CpG) or inhibitory (TLR2/4 inhibitor and/or MyD88 inhibitor), had little effect on RB1B infection and replication. In addition, we found that the expression trend of TLR3 mRNA in RB1B-infected CEF cells was similar to that of mdv1-mir-M4-5p (a functional ortholog of oncogenic miR-155 encoded by MDV). Inconsistent with this, the TLR3 protein level was sharply reduced in RB1B-infected CEF cells at 96 hpi, while there was an at least 200-fold increase in miR-M4-5p at the same time point. Additionally, CEF cells transfected with an mdv1-mir-M4-5p mimic promoted RB1B infection and replication, while an mdv1-mir-M4-5p inhibitor inhibited RB1B infection and replication. Similar results were observed in CEF cells transfected with a gga-miR-155 mimic or inhibitor. These findings suggest that TLR3 and MDV-encoded miRNAs might be involved in MDV infection.

The production mechanism and immunosuppression effect of pulmonary surfactant protein D via toll like receptor 4 signaling pathway in human corneal epithelial cells during Aspergillus fumigatus infection

ObjectiveTo observe the production mechanism of surfactant protein D (SP-D) in human corneal epithelial cells (HCECs) when infected by Aspergillus fumigatus (A. fumigatus) hyphae, and explore whether SP-D can inhibit the cell activations through toll-like receptor 4 signaling pathway during fungal infection. MethodsmRNA and protein expressions of SP-D were evaluated in HCECs after stimulation by A. fumigatus, with or without pretreatment of TLR4 inhibitor (CLI-095) by real time PCR and Western blot. The expression levels of inflammatory cytokines IL-1β and IL-8 evaluated when pretreated with SP-D antibody or recombinant human SP-D in fungi-stimulated HCECs by real time PCR and ELISA, IL-1β and IL-8 expressions were also detected in A. fumigatus-stimulated HCECs that pretreated with CLI095 or MyD88 inhibitor (Pepinh-MYD) and recombinant human SP-D. ResultsmRNA and protein levels of SP-D increased after stimulation of A. fumigatus for 16h and 20h respectively. The upregulation of SP-D could be inhibited by CLI-095. mRNA and protein expressions of IL-1β and IL-8 decreased significantly when pretreated HCECs with recombinant human SP-D for 4h before A. fumigatus stimulation, while IL-1β and IL-8 increased when pretreated with SP-D antibody for 1h. Pretreatment of CLI095 or Pepinh-MYD can increase the expressions of IL-1β and IL-8 mRNA and protein in HCECs induced by recombinant human SP-D and A. fumigatus. ConclusionsSP-D can be stimulated by TLR4 during A. fumigatus infection. Recombinant human SP-D can inhibit the expression of inflammatory cytokines through TLR4 signaling pathway.

Dioscin attenuates renal ischemia/reperfusion injury by inhibiting the TLR4/MyD88 signaling pathway via up-regulation of HSP70

We previously reported the effect of dioscin against hepatic ischemia/reperfusion injury (IRI) in rats. However, little is known concerning the role of dioscin in renal IRI. In the present study, rats were subjected to IRI and dioscin was intragastrically administered for seven consecutive days before surgery. In vitro models of hypoxia/reoxygenation were developed in NRK-52E and HK-2 cells, which were prophylacti -cally treated with or without dioscin. The results showed that dioscin significantly decreased serum BUN and Cr levels, and markedly attenuated cell injury. Mechanistic studies showed that dioscin significantly increased HSP70 levels, decreased the levels of TLR4, MyD88, TRAF6, COX-2, JNK, ERK and p38 MAPK phosphorylation, suppressed the nuclear translocation of NF-κB and HMGB1, and subsequently decreased the mRNA levels of IL-1β, IL-6, TNF-α, ICAM-1 and IFN-γ. Moreover, HSP70 siRNA or TLR4 DNA reversed the nephroprotective effects of dioscin, while dioscin still significantly down-regulated the TLR4 signaling pathway. Furthermore, by inhibiting MyD88 with ST2825 (a MyD88 inhibitor), renal IRI was significantly attenuated, suggesting that the effect of dioscin against renal IRI depended on MyD88. Our results suggested that dioscin had a potent effect against renal IRI through suppressing the TLR4/MyD88 signaling pathway by up-regulating HSP70. These data provide new insights for investigating the natural product with the nephroprotective effect against IRI, which should be developed as a new therapeutic agent for the treatment of acute kidney injury in the future.

Toll-like receptor 4 contributes to vascular remodelling and endothelial dysfunction in angiotensin II-induced hypertension.

Toll-like receptor 4 (TLR4) signalling contributes to inflammatory cardiovascular diseases, but its role in hypertension and the associated vascular damage is not known. We investigated whether TLR4 activation contributed to angiotensin II (AngII)-induced hypertension and the associated vascular structural, mechanical and functional alterations. AngII was infused (1.44 mg · kg(-1) · day(-1), s.c.) for 2 weeks in C57BL6 mice, treated with a neutralizing anti-TLR4 antibody or IgG (1 μg · day(-1); systolic BP (SBP) and aortic cytokine levels were measured. Structural, mechanical and contractile properties of aortic and mesenteric arterial segments were measured with myography and histology. RT-PCR and Western blotting were used to analyse these tissues and cultured vascular smooth muscle cells (VSMC) from hypertensive rats (SHR). Aortic TLR4 mRNA levels were raised by AngII infusion. Anti-TLR4 antibody treatment of AngII-treated mice normalised: (i) increased SBP and TNF-α, IL-6 and CCL2 levels; (ii) vascular structural and mechanical changes; (iii) altered aortic phenylephrine- and ACh-induced responses; (iv) increased NOX-1 mRNA levels, superoxide anion production and NAD(P)H oxidase activity and effects of catalase, apocynin, ML-171 and Mito-TEMPO on vascular responses; and (v) reduced NO release and effects of L-NAME on phenylephrine-induced contraction. In VSMC, the MyD88 inhibitor ST-2825 reduced AngII-induced NAD(P)H oxidase activity. The TLR4 inhibitor CLI-095 reduced AngII-induced increased phospho-JNK1/2 and p65 NF-κB subunit nuclear protein expression. TLR4 up-regulation by AngII contributed to the inflammation, endothelial dysfunction, vascular remodelling and stiffness associated with hypertension by mechanisms involving oxidative stress. MyD88-dependent activation and JNK/NF-κB signalling pathways participated in these alterations.

Adipose stromal cells effects on osteoarthritic synoviocytes are dependent by macrophages

Adipose stromal cells effects on osteoarthritic synoviocytes are dependent by macrophages

Immune effects of R848: Evidences that suggest an essential role of TLR7/8-induced, Myd88- and NF-κB-dependent signaling in the antiviral immunity of Japanese flounder (Paralichthys olivaceus)

The imidazoquinoline compound R848 is a specific agonist of toll-like receptor (TLR) 7/TLR8 that has been used as an immunostimulant in humans against viral diseases. Although R848-induced immune response has been reported in teleost fish, the relevant mechanism is not clear. In this study, we investigated the antiviral potential and the signaling pathway of R848 in a model of Japanese flounder (Paralichthys olivaceus). We found that R848 was able to inhibit the replication of megalocytivirus, stimulated the proliferation of peripheral blood leukocytes (PBL), enhanced the expression of immune genes, and reduced apoptosis of PBL. When endosomal acidification was blocked by chloroquine (CQ), R848-mediated antiviral activity and immune response were significantly reduced. Likewise, inhibition of Myd88 activation markedly impaired the pro-proliferation and anti-apoptosis effect of R848. Cellular study showed that cultured founder cells treated with R848 exhibited augmented NF-κB activity, which, however, was dramatically reduced in the presence of CQ and Myd88 inhibitor. Furthermore, when NF-κB was inactivated, the effect of R848 on cell proliferation and apoptosis was significantly decreased. Taken together, these results indicate that R848 is an immunostimulant with antiviral property in a teleost species, and that the immune response of R848 is mediated by, most likely, TLR7/TLR8 signaling pathway, in which Myd88 and NK-κB play an essential role.

Characterization of cellular immune response and innate immune signaling in human and nonhuman primate primary mononuclear cells exposed to Burkholderia mallei

Burkholderia pseudomallei infection causes melioidosis and is often characterized by severe sepsis. Although rare in humans, Burkholderia mallei has caused infections in laboratory workers, and the early innate cellular response to B. mallei in human and nonhuman primates has not been characterized. In this study, we examined the primary cellular immune response to B. mallei in PBMC cultures of non-human primates (NHPs), Chlorocebus aethiops (African Green Monkeys), Macaca fascicularis (Cynomolgus macaque), and Macaca mulatta (Rhesus macaque) and humans. Our results demonstrated that B. mallei elicited strong primary pro-inflammatory cytokines (IFN-γ, TNF-α, IL-1β, and IL-6) equivalent to the levels of B. pseudomallei in primary PBMC cultures of NHPs and humans. When we examined IL-1β and other cytokine responses by comparison to Escherichia coli LPS, African Green Monkeys appears to be most responsive to B. mallei than Cynomolgus or Rhesus. Characterization of the immune signaling mechanism for cellular response was conducted by using a ligand induced cell-based reporter assay, and our results demonstrated that MyD88 mediated signaling contributed to the B. mallei and B. pseudomallei induced pro-inflammatory responses. Notably, the induced reporter activity with B. mallei, B. pseudomallei, or purified LPS from these pathogens was inhibited and cytokine production was attenuated by a MyD88 inhibitor. Together, these results show that in the scenario of severe hyper-inflammatory responses to B. mallei infection, MyD88 targeted therapeutic intervention may be a successful strategy for therapy.

Human cathelicidin antimicrobial protein 18 (hCAP18/LL-37) is increased in foetal membranes and myometrium after spontaneous labour and delivery

Infection and/or inflammation are most commonly associated with preterm birth. Studies have shown that antimicrobial peptides can modulate the inflammatory response in non-gestational tissues; the human cathelicidin hCAP18 (and its active component LL-37) has such anti-microbial and immunomodulatory properties. The aim of this study was to determine the effect of human labour on hCAP18 expression in foetal membranes and myometrium, and to determine the effect of the synthetic LL-37 peptide on pro-inflammatory and pro-labour mediators in foetal membranes and myometrium. The localisation and expression of hCAP18 in non-labouring and labouring tissues was determined by immunohistochemistry and Western blot, respectively. Tissue explants were used to determine the effect of LL-37 on pro-labour mediators. hCAP18 was localised to the amnion epithelium, cytotrophoblasts and decidua in the foetal membranes, and in the longitudinal and transverse muscle fibres of the myometrium. Additional hCAP18 staining was present in leukocytes. In foetal membranes and myometrium, human labour was associated with significantly higher hCAP18 protein expression. Treatment of foetal membranes and myometrium with LL-37 significantly induced the expression and secretion of the pro-inflammatory cytokines IL-6 and TNF-α, and the chemokines IL-8 and MCP-1. LL-37 also induced expression of MMP-9 mRNA and pro MMP-9 expression in foetal membranes. Co-treatment with BAY 11-7082 was associated with a decrease in LL-37-induced pro-inflammatory cytokine expression. Moreover, inhibition of MyD88 in myometrial cells decreased LL-37-induced pro-inflammatory cytokine expression and release. LL-37 also significantly increased NF-κB transcriptional activity. In conclusion, hCAP18/LL-37 induces pro-inflammatory and pro-labour mediators, via the MyD88/NF-κB pathway.

CXCR4 WHIM-like frameshift and nonsense mutations promote ibrutinib resistance but do not supplant MYD88(L265P) -directed survival signalling in Waldenström macroglobulinaemia cells.

CXCR4(WHIM) frameshift and nonsense mutations follow MYD88(L265P) as the most common somatic variants in Waldenström Macroglobulinaemia (WM), and impact clinical presentation and ibrutinib response. While the nonsense (CXCR4(S338X) ) mutation has been investigated, little is known about CXCR4 frameshift (CXCR4(FS) ) mutations. We engineered WM cells to express CXCR4(FS) mutations present in patients, and compared their CXCL12 (SDF-1a) induced signalling and ibrutinib sensitivity to CXCR4(wild-type (WT)) and CXCR4(S338X) cells. Following CXCL12 stimulation, CXCR4(FS) and CXCR4(S338X) WM cells showed impaired CXCR4 receptor internalization, and enhanced AKT1 (also termed AKT) and MAPK1 (also termed ERK) activation versus CXCR(WT) cells (P < 0·05), though MAPK1 activation was more prolonged in CXCR4(S338X) cells (P < 0·05). CXCR4(FS) and CXCR4(S338X) cells, but not CXCR4(WT) cells, were rescued from ibrutinib-triggered apoptosis by CXCL12 that was reversed by AKT1, MAPK1 or CXCR4 antagonists. Treatment with an inhibitor that blocks MYD88(L265P) signalling triggered similar levels of apoptosis that was not abrogated by CXCL12 treatment in CXCR4(WT) and CXCR4(WHIM) cells. These studies show a functional role for CXCR4(FS) mutations in WM, and provide a framework for the investigation of CXCR4 antagonists with ibrutinib in CXCR4(WHIM) -mutated WM patients. Direct inhibition of MYD88(L265P) signalling overcomes CXCL12 triggered survival effects in CXCR4(WHIM) -mutated cells supporting a primary role for this survival pathway in WM.

Macrophage-activating lipopeptide-2 requires Mal and PI3K for efficient induction of heme oxygenase-1.

AimsThis study is to investigate the mechanisms by which macrophage-activating lipopeptide-2 (MALP-2) induces heme oxygenase (HO)-1, a cytoprotective enzyme that catalyzes the degradation of heme, in human monocytes.MethodsHuman monocytic THP-1 cells were cultured for transient transfection with plasmids and stimulation with MALP-2 for indicative time intervals. After incubation with MALP-2, cells were collected and disrupted, before being tested for promoter activity using luciferase assay. For analysis of proteins, immunoreactive bands were detected using an enhanced chemiluminescence Western blotting system, and the band intensity was measured by densitometryic analysis. For the detection of co-immunoprecipitation, SDS-PAGE was performed and the membranes were probed using respective antibodies. To investigate the cellular localization of NF-E2-related factor 2 (Nrf2), cells underwent immunofluorescence staining and confocal microscopy, and were analyzed using electrophoretic mobility shift assay.ResultsMALP-2-induced HO-1 expression and promoter activity were abrogated by transfection with dominant negative (DN) plasmids of TLR2 and TLR6, or their neutralizing antibodies. However, inhibition of MyD88 or transfection with the DN-MyD88 was insufficient to attenuate HO-1 expression. In contrast, mutation or silencing of MyD88 adapter-like (Mal) by DN-Mal or siRNA almost completely blocked HO-1 induction. Btk, c-Src and PI3K were also involved in MALP-2-induced HO-1 expression, as revealed by specific inhibitors LFM-A13, PP1 and LY294002, or by transfection with siRNA of c-Src. MALP-2-induced activation of PI3K was attenuated by transfection with DN mutant of Mal, and by pretreatment with LFM-A13 or PP1. Furthermore, MALP-2 stimulated the translocation of Nrf2 from the cytosol to the nucleus and Nrf2 binding to the ARE site in the HO-1 promoter, which could also be inhibited by pretreatment with a PI3K inhibitor, LY294002.ConclusionsThese results indicated that MALP-2 required TLR2/6, Btk, Mal and c-Src to activate PI3K, which in turn initiated the activation of Nrf2 for efficient HO-1 induction.

Pharmacological Inhibition of Myd88 Prevents Dendritic Cell Maturation and Synergizes With CTLA4-Ig to Promote Transplant Survival.

PURPOSE: TLRs (which signal via MyD88) induced maturation of dendritic cells (DC) together with consequent accumulation of inflammatory cytokines are important contributors to alloreactive T cell activation. We aimed to characterize two new small molecule Myd88-specific inhibitors, EM-163 (EM) and T923 (T9), and determine their synergism with CTLA4-Ig in a mouse skin transplant model. METHODS: The effect of inhibitors on DC was assessed by incubating the cells with inhibitors for 6 hrs followed by overnight exposure to LPS and determining the upregulation of maturation markers via flow cytometry and the secretion of IL-6 in supernatant by ELISA. In vivo assessment of T9 protective effect was determined via fully mismatched skin transplantation (BALB/c to B6). RESULTS: Both EM and T9 reduced upregulation of CD40, CD80, and CD86 on maturing DC and significantly reduced the accumulation of IL-6 in supernatants, though the inhibition was stronger with T9 at equimolar level. Interestingly, both inhibitors promoted MHC II expression - a favorable scenario for delivery of “Signal 1” with low “Signal 2-3” that could promote induction of T cell tolerance. In vivo analysis showed that transient administration of T9 (d0-10) combined with CTLA4-Ig doubled skin allograft survival (MST untreated: 9.5d, CTLA4-Ig only: 13d, CTLA4+T9: 19d). CONCLUSION: Our results demonstrate that pharmacological inhibition of MyD88 is possible, and substantiate previous observations in knockout models that targeting Myd88 potentiates the protective effect of costimulation blockade. Further elucidation of the mechanisms underlying this synergism and optimization of the protocol in multiple transplant models are underway. These encouraging results suggest the possibility of using pharmacological inhibition of Myd88, in place of CD154 blockade, in protocols of costimualtion blockade to promote long term transplant acceptance.

A New Tolerogenic Strategy to Attenuate Acute GVHD By a Neoteric MyD88 Inhibitor in Mice.

A New Tolerogenic Strategy to Attenuate Acute GVHD By a Neoteric MyD88 Inhibitor in Mice.

Pharmacological inhibition of MyD88 prevents dendritic cell maturation and synergizes with CTLA4-Ig to promote transplant survival (TRAN3P.918)

Abstract TLRs-induced maturation of dendritic cells (DC) and accumulation of inflammatory cytokines are important contributors to alloreactive T cell activation. We aimed to characterize two new MyD88-specific small molecule inhibitors, EM-163 (EM) and T923 (T9), and determine their synergism with CTLA4-Ig in a mouse skin transplant model. Both EM and T9 reduced upregulation of costimulatory molecules on DC in response to LPS. They also reduced the accumulation of IL-6 in supernatants, though the inhibition was stronger with T9 at equimolar level. Interestingly, both inhibitors promoted high MHC II expression - a favorable scenario for delivery of “Signal 1” with low “Signal 2-3” that could promote induction of T cell tolerance. In vivo analysis in a fully mismatched skin transplantation mouse model (BALB/c to B6) showed that transient administration of T9 (d0-10) combined with CTLA4-Ig doubled skin allograft survival (MST untreated: 9.5d, CTLA4-Ig only: 13d, CTLA4+T9: 19d). Overall, our results demonstrate that pharmacological inhibition of MyD88 is possible and potentiates the protective effect of costimulation blockade. Further elucidation of the mechanisms underlying this synergism and optimization of the protocol in multiple transplant models are underway. These encouraging results also suggest the use of pharmacological inhibition of MyD88 as replacement of CD154 blockade in protocols of costimualtion blockade to promote long term transplant acceptance.

Phospholipase D1 is required for lipopolysaccharide-induced tumor necrosis factor-α expression and production through S6K1/JNK/c-Jun pathway in Raw 264.7 cells

The purpose of this study was to identify the role of phospholipase D1 (PLD1) in lipopolysaccharide (LPS)-induced tumor necrosis factor-α (TNF-α) expression and production. LPS-induced TNF-α expression and production were TLR4 (Toll-like receptor 4)/Myd88 dependent in Raw 264.7 cells. LPS enhanced PLD activation, which was attenuated by TLR4 inhibitor (Polymixin B) or knockdown of Myd88 with siRNA treatment. To investigate the role of PLD in LPS-induced TNF-α expression and production, we transfected PLD1 and PLD2 siRNAs to Raw 264.7 cells, respectively. Interestingly, only knockdown of PLD1 decreased TNF-α expression but not PLD2. Next, we investigated the S6K1-JNK-c-Jun signaling pathway in LPS-induced TNF-α expression mechanism. Knockdown of PLD1 also decreased phosphorylation of S6K1, JNK and c-Jun induced by LPS. Furthermore, we found that activated c-Jun63/73 bound to TNF-α promoter and turned on TNF-α expression. Taken together, our results demonstrate that PLD1 is activated by LPS/TLR4/Myd88 pathway and regulates TNF-α expression and production through S6K1/JNK/c-Jun in Raw 264.7 cells.

PI3K/AKT Pathway Is Activated By MYD88 L265P and Use Of PI3K-Delta Inhibitors Induces Robust Tumor Cell Killing In Waldenstrom's Macroglobulinemia

BackgroundMYD88 L265P is a somatic mutation present in >90% of Waldenstrom's Macroglobulinemia (WM) patients. The downstream signaling pathways that promote malignant cell growth and survival remain to be fully clarified but include IRAK 1/4 and BTK (Treon et al, NEJM 2012; Yang et al, Blood 2013). MethodsTo further clarify the downstream signaling associated with MYD88 L265P in WM cells, we employed Phospho Explorer Antibody Arrays in MYD88 L265P expressing BCWM.1 and MCWL-1 WM cells following lentiviral mediated knockdown of MYD88, or over-expression of MYD88 wild type or L265P; or the use of MYD88 homodimerization inhibitor that block MYD88 signaling. Arrays were scanned by Axon GenePix Microarray Scanner and data analyzed by Ingenuity Pathway Analysis. Western blot analysis was performed using total and phospho-specific antibodies in WM cells. CellTiter-Glo® Luminescent cell viability assay (Promega) was used to assess cell survival following treatment with the PI3K-delta inhibitors, CAL101 and PIK-294 (Selleck Chemicals). ResultsIngenuity pathway analysis demonstrated significant enrichment for B-Cell Receptor, PI3K/AKT, LPS-stimulated MAPK and ERK/MAPK signaling following MYD88 modulation in both BCWM.1 and MWCL-1 WM cells. Signal proteins that demonstrated the greatest changes in phosphorylation following MYD88 modulation are shown in Table 1. Western blot analysis confirmed the activation of ATK as downstream of PI3K in WM cells. Use of a MYD88 inhibitor significantly decreased phosphorylation of ATK-pS473 and AKT-pY308 in both BCWM.1 and MCWL-1 WM cells. Cell viability analysis demonstrated robust tumor cell killing (EC50 30-50nM) in BCWM.1 and MWCL-1 WM cells following treatment with both PI3K-delta inhibitors (CAL-101 and PIK-294). ConclusionIn addition to activation of NF-kB through IRAK and BTK signaling, MYD88 L265P promotes survival of WM cells by activation of PI3K/AKT signaling. Inhibition of PI3K-delta is associated with robust killing of WM cells. These studies provide the framework for the investigation of PI3K-delta inhibitors in WM. Disclosures:No relevant conflicts of interest to declare.

Overexpression of the Toll-Like Receptor (TLR) Signaling Adaptor MYD88, but Lack of Genetic Mutation, in Myelodysplastic Syndromes

MYD88 is a key mediator of Toll-like receptor innate immunity signaling. Oncogenically active MYD88 mutations have recently been reported in lymphoid malignancies, but has not been described in MDS. To characterize MYD88 in MDS, we sequenced the coding region of the MYD88 gene in 40 MDS patients. No MYD88 mutation was detected. We next characterized MYD88 expression in bone marrow CD34+ cells (N = 64). Increased MYD88 RNA was detected in 40% of patients. Patients with higher MYD88 expression in CD34+ cells had a tendency for shorter survival compared to the ones with lower MYD88, which was significant when controlled for IPSS and age. We then evaluated effect of MYD88 blockade in the CD34+ cells of patients with lower-risk MDS. Colony formation assays indicated that MYD88 blockade using a MYD88 inhibitor resulted in increased erythroid colony formation. MYD88 blockade also negatively regulated the secretion of interleukin-8. Treatment of MDS CD34+ cells with an IL-8 antibody also increased formation of erythroid colonies. These results indicate that MYD88 plays a role in the pathobiology of MDS and may have prognostic and therapeutic value in the management of patients with this disease.