Is Tocilizumab An Effective Therapy For Severe Covid-19: A Single Center Study.

Background: The quest for effective therapies in Covid-19 continues. We compared the outcome of severe COVID-19 patients treated with and without Tocilizumab, an IL-6 inhibitor. Methods: This is a prospective cohort study on the clinical characteristics and outcomes of patients with Covid-19 patients admitted at The Indus Hospital and Health Network, Karachi between 24th March and 19th June 2020. Adult patients who received TCZ were compared with respect to mortality and days of hospitalization with those who did not. Results: A total of 88 patients including 41 patients in the TCZ group and 47 in non-TCZ group were recruited. Baseline demographic characteristics were comparable. TCZ group patients presented with worse clinical features including median SpO2 82% vs 88%, p<0.05 and CRP 193 vs 133.9 mg/L, p<0.05. Approximately, 85.4% were admitted in ICU compared to 69.8% in non-TCZ group, p>0.05. Mortality was not different among the groups (46% in TCZ group vs 51.1% in non-TCZ group, p>0.05). Median length of hospital stays, days of intubation, use of inotropic agents, and use of invasive ventilation or in-hospital complications were similar between the groups. Sub-group analysis revealed that mortality within TCZ group was associated with high IL-6 levels (173 vs 69.66 pg/ml, p<0.05), ICU admission (100% vs 72%, p<0.05), need for mechanical ventilation (100% vs 13.6%, p<0.05) and higher incidence of in-hospital complications, p<0.05. Conclusion: TCZ failed to demonstrate any mortality benefit in our patients. Non-survivors within the TCZ group were more critical compared to survivors and developed more in hospital complications.

Concomitant Expression of IL-6 and TGF-ß Cytokines and their Receptors in Peripheral Blood of Patients with Multiple Sclerosis: The Effects of INFß Drugs.

BACKGROUND: Concomitant signals from IL-6 and TGF-ß have a central role in the Th17 cells development and differentiation, and these cells are the main promoters of demyelinating inflammation in the central nervous system (CNS) resulting in multiple sclerosis (MS). OBJECTIVES: To evaluate the simultaneous IL-6 and TGF-ß gene and their receptor protein expression in patients with Relapsing-Remitting (RR)-MS. MATERIALS AND METHODS: IL-6 and TGF-ß mRNA and their receptor expression on the surface of CD4+T cells were evaluated using real-time PCR (RT-PCR) and flow cytometry, respectively. RESULTS: The IL-6 mRNA expression in patients with RRMS was significantly higher than in the controls (p= 0.019). When patients who did not receive any other treatment were compared with the controls, the significant difference was substantial (p=0.006). The TGF-ß mRNA expression in patients was lower than in the controls (p = 0.03). However, in patients receiving IFNß, it increased compared with the other patients (p= 0.036). There was no difference in cytokine receptor expression between patients and the control group. CONCLUSION: Our data conclude an increase and decrease in mRNA expression levels of IL-6 and TGF-ß in patients with RRMS, respectively. Moreover, there were no significant differences in receptor expression of either cytokines. Based on our data the balance of TGF and IL-6 appears to have a positive impact on the disease control.

Augmented glioma-targeted theranostics using multifunctional polymer-coated carbon nanodots.

Overcoming biological barriers to imaging-guided site-specific delivery of therapeutics is the goal of current nanomedicine designs. Here, multifunctional polymer-coated carbon nanodots with an interleukin-6 (IL-6) fragment peptide for receptor-targeting (pCDPI) were prepared for drug delivery. The pCDPI exhibits small hydrodynamic diameters, high water solubility and biocompatibility. In vitro and in vivo results demonstrated that pCDPI can overcome the blood-brain barrier (BBB) and deeply penetrate into orthotopic glioma in mice, to inhibit IL-6-induced cell proliferation and achieve imaging-guided targeted drug delivery. Simultaneously, a pH-sensitive sustained release of doxorubicin (DOX) accompanied with real-time fluorescence monitoring was realized. A distinct synergistic therapeutic outcome could be achieved which suggests the presented nanomedicine having promising potential for future cancer treatments.

Interleukin-6 subfamily cytokines and rheumatoid arthritis: role of antagonists.

Many cytokines have been implicated in the inflammatory pathways that characterize rheumatoid arthritis (RA) and related inflammatory diseases of the joints. These include members of the interleukin-6 (IL-6) family of cytokines, several of which have been detected in excess in the synovial fluid from RA patients. What makes the IL-6 group of cytokines a family is their common use of the glycoprotein 130 (gp130) receptor subunit, to which they bind with different affinities. Several strategies have been developed to block the pro-inflammatory activities of IL-6 subfamily cytokines. These include the application of monoclonal antibodies, the creation of mutant form(s) of the cytokine with enhanced binding affinity to gp130 receptor and the generation of antagonists by selective mutagenesis of the specific cytokine/gp130 receptor-binding site(s). The rationale for the use of anti-cytokine therapy in inflammatory joint diseases is based on evidence from studies in vitro and in vivo, which implicate major cytokines such as interleukin-1 (IL-1), tumour necrosis factor (TNF)-alpha and IL-6 in RA pathogenesis. In particular, IL-6 subfamily antagonists have a wide range of potential therapeutic and research applications. This review focuses on the role of some of the IL-6 subfamily cytokines in the pathogenesis of the inflammatory diseases of the joints (IJDs), such as RA. In addition, an overview of the recently developed antagonists will be discussed.

Simultaneous inhibition of the constitutively activated nuclear factor kappaB and of the interleukin-6 pathways is necessary and sufficient to completely overcome apoptosis resistance of human U266 myeloma cells.

Elevated Nuclear Factor kappaB (NFkappaB) levels have been reported in multiple myeloma cells derived from patients relapsing after chemotherapy. In the search of an in vitro a model with molecular features similar to relapsing lesions, we focused our attention on an IL-6 autocrine human myeloma cell line (U266), characterized by apoptosis resistance due to upregulation of two constitutive signaling pathways: NFkappaB and STAT-3. NFkappaB activity was inhibited with proteasome inhibitory agents, such as PS-341 and Withaferin A, with an IKK inhibitor (Wedelolactone) or with the adenoviral vector HD IkappaBalphamut-IRES-EGFP encoding a mutant IkappaBalpha protein, resistant to proteasomal degradation. We observed that the NFkappaB intracellular dislocation at the beginning of the treatment affected therapeutic effectiveness of PS-341, Withaferin A and Wedelolactone; interestingly, the adenoviral vector was highly effective in inducing apopotosis even with NFkappaB being predominantly nuclear at the time of infection. We also observed that U266 treated with the Interleukin-6 antagonist Sant7 exhibited reduced STAT3 activity and preferential cytoplasmic NFkappaB location; moreover they became capable of undergoing apoptosis mainly from the G1 phase. Adenoviral vector treated U266 have NFkappaB localized completely in the cytoplasm and also showed downregulation of nuclear phospho STAT-3. Finally, combined targeting of NFkappaB and STAT3 signalling pathways was the most effective treatment in inducing apoptosis. These findings suggest that combined NFkappaB and STAT3 targeting warrants further investigations in other apoptosis resistant MM cell lines as well as in suitable MM animal models.

Interleukin-6 receptor superantagonist Sant7 inhibits TGF-beta-induced proliferation of human lung fibroblasts.

OBJECTIVES: Both interleukin-6 (IL-6) and transforming growth factor-beta (TGF-beta) are crucially involved in fibrotic events that characterize interstitial lung diseases (ILD). Therefore, the aim of this study was to investigate in primary cultures of normal and fibrotic human lung fibroblasts (HLF), exposed to either IL-6 or TGF-beta1, the effects on phosphorylation of mitogen-activated protein kinases (MAPK) and cell growth of IL-6 signalling inhibition, performed by the IL-6 receptor superantagonist Sant7. MATERIALS AND METHODS: MAPK phosphorylation was detected by Western blotting, HLF viability and proliferation were evaluated using the trypan blue staining and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, respectively. RESULTS: Sant7, at a concentration of 1 microg/mL, was capable of significantly inhibiting HLF proliferation and MAPK phosphorylation induced by cell exposure to IL-6 (100 ng/mL) or TGF-beta1 (10 ng/mL), whose actions were more evident in fibrotic cells. CONCLUSIONS: These findings suggest that, in HLFs derived from patients with ILDs, the proliferative mechanisms activated by TGF-beta1 are at least in part mediated by an increased release of IL-6, leading to phosphorylation-dependent MAPK activation. Such preliminary findings may thus open new therapeutic perspectives for fibrogenic ILDs, based on inhibition of signal transduction pathways stimulated by the IL-6 receptor.

Comparative activity of Sant7 and anti-IL-6, IL-6R monoclonal antibodies in a murine model of B-cell lymphoma.

Interleukin-6 (IL-6) plays a central role in the pathogenesis of several autoimmune and inflammatory diseases as well as B-cell lymphoproliferative disorders. This work describes the effects of the recombinant or adenovirally-delivered IL-6 superantagonist Sant7, anti-IL-6 and IL-6 receptor monoclonal antibodies in a severe murine model of human B-cell lymphoma induced in SCID mice by transplantation of an LCL-41 cell line variant (isotype-switched IgM>IgG). Survival of 60% of the animals treated with anti-gp130 was observed up to day 33, while about 20% of the animals survived with anti-gp80 and Sant7 treatment. No survival was observed with the anti-IL-6 monoclonal antibody treatment. No significant change in serum and peritoneal levels of human IL-6 (hIL-6) and soluble human IL-6 receptor (shIL-6R) was observed in the recombinant Sant7-treated group towards the control group. The anti-gp80 monoclonal antibody induced significant increase of both hIL-6R and hIL-6 in serum and peritoneum. The anti-gp130 monoclonal antibody treatment determined a reduction of the seric shIL-6R and a significant increase of the seric hIL-6. Anti-IL-6 monoclonal antibody administration resulted in a reduction of serum and in an increase of peritoneal hIL-6. Treatment with adenoviral Sant7 was associated with a reduction of circulating shIL-6R, hIgG and mSAP. However, only marginal anti-tumor efficacy of the adenoviral Sant7 was observed. Overall, the present data suggest a potential for anti-hIL-6 therapy in B-cell lymphomas. Less severe animal models might be useful to better evaluate Sant7 efficacy alone or in combination with other anti-IL-6 therapeutics.

Combination therapy with interleukin-6 receptor superantagonist Sant7 and dexamethasone induces antitumor effects in a novel SCID-hu In vivo model of human multiple myeloma.

Interleukin-6 (IL-6) protects multiple myeloma cells against apoptosis induced by glucocorticoids. Here, we investigated whether inhibition of the IL-6 signaling pathway by the IL-6 receptor superantagonist Sant7 enhances the in vivo antitumor effects of dexamethasone on the IL-6-dependent multiple myeloma cell line INA-6. For this purpose, we used a novel murine model of human multiple myeloma in which IL-6-dependent INA-6 multiple myeloma cells were directly injected into human bone marrow implants in severe combined immunodeficient (SCID) mice (SCID-hu). The effect of in vivo drug treatments on multiple myeloma cell growth was monitored by serial determinations of serum levels of soluble IL-6 receptor (shuIL-6R), which is released by INA-6 cells and served as a marker of tumor growth. In SCID-hu mice engrafted with INA-6 cells, treatment with either Sant7 or dexamethasone alone did not induce significant reduction in serum shuIL-6R levels. In contrast, the combination of Sant7 with dexamethasone resulted in a synergistic reduction in serum shuIL-6R levels after 6 consecutive days of treatment. Gene expression profiling of INA-6 cells showed down-regulation of proliferation/maintenance and cell cycle control genes, as well as up-regulation of apoptotic genes in multiple myeloma cells triggered by Sant7 and dexamethasone combination. In vitro colony assays showed inhibition of myeloid and erythroid colonies from normal human CD34(+) progenitors in response to dexamethasone, whereas Sant7 neither inhibited colony growth nor potentiated the inhibitory effect of dexamethasone. Taken together, these results indicate that inhibition of IL-6 signaling by Sant7 significantly potentiates the therapeutic action of dexamethasone against multiple myeloma cells, providing the preclinical rationale for clinical trials of Sant7 in combination with dexamethasone to improve patient outcome in multiple myeloma.

Knocking out IL-6 by vaccination.

Inappropriate expression of IL-6 plays a role in various inflammatory conditions, degenerative diseases, and cancers. Several model systems have been developed that can specifically block IL-6-receptor interactions. Here we present a simple and highly effective approach based on vaccination with a pool of specifically mutated IL-6 analogues to induce a neutralizing IL-6 antibody response in mice. Judged by the ability of the analogues to bind to heterologous anti-IL-6 antibodies and cellular IL-6 receptors the IL-6 analogues seemed to have a three-dimensional structure comparable to that of wild-type IL-6. Injection of them broke self-tolerance and induced an immune response to IL-6, presumably because of the amino acid differences between the analogues and wild-type IL-6. This resulted in a long-lasting anti-IL-6 antibody-mediated IL-6 deficiency that blocked experimentally induced IL-6-mediated pathology.

Inhibition of IL-6+IL-6 soluble receptor-stimulated aromatase activity by the IL-6 antagonist, Sant 7, in breast tissue-derived fibroblasts.

Interleukin 6 (IL-6) and its soluble receptor (IL-6sR) can markedly stimulate aromatase activity in cultured fibroblasts derived from normal or malignant breast tissues. IL-6 acts by binding to a low-affinity membrane-spanning receptor (IL-6R), which must associate with a high-affinity receptor (gp130) for signal transduction to occur. Sant 7 is a mutated form of IL-6 that can bind to the IL-6R, but inhibits its ability to interact with the gp130 signal transducing protein. In this study, we have used Sant 7 to examine its ability to inhibit IL-6+IL-6 soluble receptor (IL-6sR)-stimulated aromatase activity in breast tissue-derived fibroblasts. As previously observed, IL-6+IL-6sR markedly stimulated aromatase activity (7.7-20.8-fold) in fibroblasts derived from reduction mammoplasty tissue, tissue proximal to tumours and breast tumours. Sant 7 inhibited basal aromatase activity in some fibroblasts by 25-30% that had a high basal activity, but almost completely blocked the ability of IL-6+IL-6sR to stimulate aromatase activity. The IC(50) for the inhibition of IL-6+IL-6sR-stimulated aromatase activity by Sant 7 was 60 ng ml(-1). A comparison of the effects of prostaglandin E(2) (PGE(2)), which can also regulate aromatase activity, and IL-6+IL-6sR revealed a greater degree of aromatase stimulation by IL-6+IL-6sR. Sant 7, however, inhibited PGE(2)-stimulated aromatase activity by 70% suggesting that PGE(2) acts, in part, by stimulating IL-6 production. Much of the IL-6 and IL-6sR available to stimulate breast tumour aromatase activity may originate from infiltrating macrophages and lymphocytes. The ability to block aromatase stimulation by these factors may offer a novel therapeutic strategy for reducing oestrogen synthesis in breast tumours.

In the presence of bone marrow stromal cells human multiple myeloma cells become independent of the IL-6/gp130/STAT3 pathway.

The interleukin 6/glycoprotein 130/signal transducer and activator of transcription 3 (IL-6/gp130/STAT3) pathway has been reported to play an important role in the pathogenesis of multiple myeloma (MM) and for survival of MM cells. However, most data concerning the role of IL-6 and IL-6-triggered signaling pathways were obtained from experiments performed with MM cell lines and without considering the bone marrow microenvironment. Thus, the precise role of IL-6 and its intracellular signaling pathways for survival of human MM cells is still unclear. Here we show that treatment of human MM cells (IL-6-dependent MM cell line INA-6 and primary MM cells) with the IL-6 receptor antagonist Sant7 or with an anti-gp130 monoclonal antibody (mAb) induced apoptosis if the cells were cultured in the absence of bone marrow stromal cells (BMSCs). In contrast, apoptosis could not be observed if the MM cells were cocultured with BMSCs. The analysis of intracellular pathways revealed that Sant7 and anti-gp130 mAb were effectively inhibiting the phosphorylation of gp130 and STAT3 in the absence and presence of BMSCs, whereas ERK1 and ERK2 (ERK1,2) phosphorylation was only slightly affected. In contrast, treatment with the farnesyl transferase inhibitor, FPT III, induced apoptosis in MM cells in the absence or presence of BMSCs and led to a complete inhibition of the Ras/mitogen-activated protein kinase pathway. These observations indicate that the IL-6/gp130/STAT3 pathway is not essential for survival of human myeloma cells if they are grown in the presence of cells from the bone marrow microenvironment. Furthermore, we provide evidence that farnesyl transferase inhibitors might be useful for the development of novel therapeutic strategies for the treatment of MM.

The IL-6 receptor super-antagonist Sant7 enhances antiproliferative and apoptotic effects induced by dexamethasone and zoledronic acid on multiple myeloma cells.

Interleukin-6 (IL-6) is the major growth and survival factor for multiple myeloma (MM), and has been shown to protect MM cells from apoptosis induced by a variety of agents. IL-6 receptor antagonists, which prevent the assembly of functional IL-6 receptor complexes, inhibit cell proliferation and induce apoptosis in MM cells. We have investigated whether the IL-6 receptor super-antagonist Sant7 might enhance the antiproliferative and apoptotic effects induced by the combination of dexamethasone (Dex) and zoledronic acid (Zln) on human MM cell lines and primary cells from MM patients. Here we show that each of these compounds individually induced detectable antiproliferative effects on MM cells. Sant7 significantly enhanced growth inhibition and apoptosis induced by Dex and Zln on both MM cell lines and primary MM cells. These results indicate that overcoming IL-6 mediated cell resistance by Sant7 potentiates the effect of glucocorticoides and bisphosphonates on MM cell growth and survival, providing a rationale for therapies including IL-6 antagonists in MM.

Effects of IL-6 variants in multiple myeloma: growth inhibition and induction of apoptosis in primary cells.

Interleukin-6 (IL-6) plays a pathogenetic role in B-cell malignancies and is a growth factor for multiple myeloma (MM) cells. Elevated serum IL-6 levels and a higher proliferative activity of bone marrow plasma cells are poor prognostic factors in MM patients. In addition to clinical trials with anti-IL-6 monoclonal antibodies, an alternative therapeutic approach based on the use of IL-6 receptor (R) super-antagonists (Sants) has been proposed. Sants are variants of the native cytokine characterized by a wild type affinity for the ligand-specific receptor chain IL-6R alpha and by a reduced ability to bind and/or dimerize the signaling chain gp-130. We report the in vitro effects of four different Sants on cell kinetic modulation and induction of apoptosis of primary cells from MM patients. Ten MM samples were cultured in the presence of four different Sants and heterogeneous effects in terms of reduction of proliferation and induction of apoptosis could be observed. A decrease of the S phase cells (> or = 25%) coupled with the induction of apoptosis was obtained in 4/10 samples: three of these samples had a diploid DNA stem line and an inferior initial percentage of S phase cells. Serum IL-6 concentrations did not correlate with the anti-proliferative activities of the Sants. Cell growth inhibition was observed especially in samples with soluble IL-6R serum concentrations > 200 ng/ml. We conclude that Sants can exert antiproliferative effects on selected MM samples. Such effects may depend on the availability of large amounts of soluble IL-6R. Further studies should aim at defining the conditions necessary for optimal antiproliferative activity.

The IL-6 receptor antagonist SANT-7 overcomes bone marrow stromal cell-mediated drug resistance of multiple myeloma cells.

The bone marrow micro-environment produces a number of different survival factors that are important for the malignant growth and drug resistance of multiple myeloma (MM) cells. One of the main factors reported to be essential for survival and growth of MM cells in some experimental systems is IL-6. Therefore, the development and testing of substances that interfere with IL-6 or IL-6 receptor (IL-6R) function might have therapeutic value for the treatment of MM. We analyzed the effect of the IL-6R antagonist SANT-7 on growth and survival of the IL-6--dependent MM cell lines INA-6 and XG-1 as well as primary MM cells from 7 patients co-cultured with bone marrow stromal cells (BMSCs). In particular, we were interested in whether SANT-7 enhances the growth-inhibitory effects of dexamethasone (Dex) and all-trans-retinoic acid (ATRA). None of the drugs when tested as a single substance, including SANT-7, induced major growth inhibition if MM cells were co-cultured with primary human BMSCs. However, when Dex and ATRA were given in combination with SANT-7, strong growth inhibition was achieved in cell lines and primary MM cells. This effect was due to cell-cycle arrest and induction of apoptosis.

Inhibition of apolipoprotein B secretion by IL-6 is mediated by EGF or an EGF-like molecule in CaCo-2 cells.

Small intestinal mucosal inflammation observed in celiac disease is associated with the local release of growth factors and various cytokines. In a previous study, we investigated the effect of various cytokines on triacylglycerol and apoB secretion by CaCo-2 cells and observed that TNF-alpha, IL-1 beta, and particularly IL-6, decreased apolipoprotein (apo) B and triacylglycerol secretion. In this study, we explored possible mechanisms to explain the inhibitory effect of IL-6 on apoB secretion. IL-6, 10 ng/mL, added to the basolateral medium of CaCo-2 cells grown on semi-permeable filters, decreased apoB secretion by 42%. Adding a blocking monoclonal antibody (mAb 528) to the EGF receptor completely prevented this effect. IL-6 decreased the amount of EGF receptor protein and the binding of iodinated EGF to its receptor by 50% and 30%, respectively. Incubation of cells with various ligands to the EGF receptor, such as EGF, TGF-alpha, HB-EGF, and amphiregulin, also decreased apoB secretion. Inhibition of apoB secretion by EGF was prevented by the mAb 528 or an EGF neutralizing antibody. In a dose-dependent manner, the neutralizing antibody to EGF prevented the decrease in secretion of apoB, triacylglycerol mass, and cell-surface binding of labeled EGF caused by IL-6. Similar to the effects of IL-6, EGF decreased the secretion of triacylglycerol mass and the synthesis and secretion on newly synthesized apoB. The results suggest that, in CaCo-2 cells, IL-6 causes the release of EGF or an EGF-like molecule. By binding to cell surface EGF receptors, the molecule then causes a decrease in triacylglycerol and apoB secretion.

Complex of the soluble IL-11 receptor and IL-11 acts as IL-6-type cytokine in hepatic and nonhepatic cells.

The signaling functions of the membrane and soluble form of the mouse IL-11 receptor (mIL-11R) were compared in rat and human hepatoma cells, which have a low endogenous IL-11 response. The expression vectors encoding either the full length or a secretory form of the ligand binding subunit of mIL-11R together with IL-6-responsive reporter gene constructs were transiently transfected into the H-35 and HepG2 cells. An IL-11-specific stimulation of transcription was detected that was qualitatively similar to that mediated by the endogenous IL-6R. HepG2 cells were noted to synthesize constitutively IL-11, resulting in an autocrine stimulation of gene expression. Addition of COS cell-derived soluble mIL-11R to the hepatoma cell cultures prominently enhanced IL-11 regulation of transfected reporter gene constructs and expression of endogenous acute phase plasma protein genes. Similarly, the complex of soluble mIL-11R and IL-11 was capable of mediating an IL-6-type signaling in cells that are naturally deficient in IL-11 response as shown by the activation of STAT1 and STAT3 in mouse embryonal carcinoma cells and human T cells. The results indicate that the IL-11R can serve as a substitute to IL-6R in activating gene expression in target cells that are devoid of the appropriate ligand-binding receptor subunits.

Human interleukin-6 receptor super-antagonists with high potency and wide spectrum on multiple myeloma cells.

Interleukin-6 (IL-6) is the major growth factor for myeloma cells and is believed to participate in the pathogenesis of chronic autoimmune diseases and postmenopausal osteoporosis. IL-6 has been recently shown to possess three topologically distinct receptor binding sites: site 1 for binding to the subunit specific chain IL-6R alpha and sites 2 and 3 for the interaction with two subunits of the signaling chain gp130. We have generated a set of IL-6 variants that behave as potent cytokine receptor super-antagonists carrying substitutions that abolish interaction with gp130 at either site 2 alone (site 2 antagonist) or at both sites 2 and 3 (site 2 + 3 antagonist). In addition, substitutions have been introduced in site 1 that lead to variable increases in binding for IL-6R alpha up to 70-fold. IL-6 super-antagonists inhibit wild-type cytokine activity with efficacy proportional to the increase in receptor binding on a variety of human call lines of different origin, and the most potent molecules display full antagonism at low molar excess to wild-type IL-6. When tested on a representative set of IL-6-dependent human myeloma cell lines, although site 2 super-antagonists were in general quite effective, only the site 2 + 3 antagonist Sant7 showed antagonism on the full spectrum of cells tested. In conclusion, IL-6 super-antagonists are a useful tool for the study of myeloma in vitro and might constitute, in particular Sant7, effective IL-6 blocking agents in vivo.

Rational design of a receptor super-antagonist of human interleukin-6.

Interleukin-6 (IL-6) is a differentiation and growth factor for a variety of cell types and its excessive production plays a major role in the pathogenesis of multiple myeloma and post-menopausal osteoporosis. IL-6, a four-helix bundle cytokine, is believed to interact sequentially with two transmembrane receptors, the low-affinity IL-6 receptor (IL-6R alpha) and the signal transducer gp130, via distinct binding sites. In this paper we show that combined mutations in the predicted A and C helices, previously suggested to establish contacts with gp130, give rise to variants with no bioactivity but unimpaired binding to IL-6R alpha. These mutants behave as full and selective IL-6 receptor antagonists on a variety of human cell lines. Furthermore, a bifacial mutant was generated (called IL-6 super-antagonist) in which the antagonist mutations were combined with amino acid substitutions in the predicted D helix that increase binding for IL-6R alpha. The IL-6 super-antagonist has no bioactivity, but improved first receptor occupancy and, therefore, fully inhibits the wild-type cytokine at low dosage. The demonstration of functionally independent receptor binding sites on IL-6 suggests that it could be possible to design super-antagonists of other helical cytokines which drive the assembly of structurally related multisubunit receptor complexes.