Complement Activation by an Anti-Dengue/Zika Antibody with Impaired Fcγ Receptor Binding Provides Strong Efficacy and Abrogates Risk of Antibody-Dependent Enhancement.

To combat infectious diseases, vaccines are considered the best prophylactic strategy for a wide range of the population, but even when vaccines are effective, the administration of therapeutic antibodies against viruses could provide further treatment options, particularly for vulnerable groups whose immunity against the viruses is compromised. Therapeutic antibodies against dengue are ideally engineered to abrogate binding to Fcγ receptors (FcγRs), which can induce antibody-dependent enhancement (ADE). However, the Fc effector functions of neutralizing antibodies against SARS-CoV-2 have recently been reported to improve post-exposure therapy, while they are dispensable when administered as prophylaxis. Hence, in this report, we investigated the influence of Fc engineering on anti-virus efficacy using the anti-dengue/Zika human antibody SIgN-3C and found it affected the viremia clearance efficacy against dengue in a mouse model. Furthermore, we demonstrated that complement activation through antibody binding to C1q could play a role in anti-dengue efficacy. We also generated a novel Fc variant, which displayed the ability for complement activation but showed very low FcγR binding and an undetectable level of the risk of ADE in a cell-based assay. This Fc engineering approach could make effective and safe anti-virus antibodies against dengue, Zika and other viruses.

SKY59, A Novel Recycling Antibody for Complement-mediated Diseases.

BACKGROUND: The complement system usually helps protect against microbial infection, but it could also be involved in the onset of various diseases. Inhibition of complement component 5 (C5) with eculizumab has resulted in a significant reduction of hemolysis, reduction of thromboembolic events, and increased survival in patients with Paroxysmal Nocturnal Hemoglobinuria (PNH). However, eculizumab requires frequent intravenous infusions due to the abundance of C5 in plasma and some patients may still experience breakthrough hemolysis. This review introduces the recent body of knowledge on recycling technology and discusses the likely therapeutic benefits of SKY59, a novel recycling antibody, for PNH and complement-mediated disorders. METHODS: By using recycling technology, we created a novel anti-C5 antibody, SKY59, capable of binding to C5 pH-dependently. RESULTS: In cynomolgus monkeys, SKY59 robustly inhibited C5 and complement activity for significantly longer than a conventional antibody. SKY59 also showed an inhibitory effect on C5 variant p.Arg885His, whereas eculizumab does not suppress complement activity in patients with this type of mutation. CONCLUSION: SKY59 is a promising anti-C5 biologic agent that has significant advantages over current therapies such as long duration of action and efficacy against C5 variants.

Loss of the adhesion G-protein coupled receptor ADGRF5 in mice induces airway inflammation and the expression of CCL2 in lung endothelial cells.

BACKGROUND: Adhesion G-protein coupled receptor F5 (ADGRF5) was recently identified as an essential regulator of pulmonary surfactant homeostasis in alveolar type II cells. We previously showed that in addition to abnormal surfactant accumulation, Adgrf5-deficient (Adgrf5-/-) mice exhibit emphysema-like signs, suggesting a possible role for ADGRF5 in immune regulation. Here, we extended the phenotypic analysis of Adgrf5-/- mice to help understand its biological role in the lung, and especially in immune regulation. METHODS: Histological features of lungs were evaluated by Alcian blue and Masson's trichrome staining. Quantitative real-time PCR (qPCR) and western blot analyses were performed to analyze the differential expression of genes/proteins related to airway inflammation in lungs between wildtype and Adgrf5-/- mice. Acid-base status was assessed by performing blood gas tests and urine pH measurements. Inflammatory cell counting was performed using Giemsa-stained bronchoalveolar lavage cells. Serum IgE concentrations were determined by enzyme-linked immunosorbent assay. The expression of Ccl2, S100a8, S100a9, and Saa3 in primary lung endothelial cells (ECs) was determined by qPCR and/or western blotting. Finally, the effect of administrating RS504393 to 2-week-old Adgrf5-/- mice on gene expression in the lungs was analyzed by qPCR. RESULTS: Adgrf5-/- mice exhibited several features of chronic airway inflammation (mucous cell metaplasia, mucus hyperproduction, subepithelial fibrosis, respiratory acidosis, high serum IgE, mast cell accumulation, and neutrophilia) in parallel with elevated expression of genes involved in mucous cell metaplasia (Muc5ac, Muc5b, Slc26a4, and Clca1), fibrosis (Tgfb1, Col1a1, Fn1, and Tnc), and type 2 immune response (Il4, Il5, Il13, IL-25, and IL-33) at 12 and/or 30 weeks of age. In contrast, mRNA expression of Ccl2, S100a8, and S100a9 was upregulated in embryonic or neonatal Adgrf5-/- lungs as well as in lung ECs of Adgrf5-/- mice at 1 week of age. RS504393 treatment suppressed the upregulation of S100a8, S100a9, Slc26a4, and Il5 in Adgrf5-/- lungs. CONCLUSIONS: Targeted disruption of ADGRF5 results in the development of airway inflammation, which is likely mediated by the type 2 immune response and possibly CCL2-mediated inflammation. ADGRF5 also has a potential role in the regulation of genes encoding CCL2 in lung ECs, thereby maintaining immune homeostasis.

Antibody engineering to generate SKY59, a long-acting anti-C5 recycling antibody.

Modulating the complement system is a promising strategy in drug discovery for disorders with uncontrolled complement activation. Although some of these disorders can be effectively treated with an antibody that inhibits complement C5, the high plasma concentration of C5 requires a huge dosage and frequent intravenous administration. Moreover, a conventional anti-C5 antibody can cause C5 to accumulate in plasma by reducing C5 clearance when C5 forms an immune complex (IC) with the antibody, which can be salvaged from endosomal vesicles by neonatal Fc receptor (FcRn)-mediated recycling. In order to neutralize the increased C5, an even higher dosage of the antibody would be required. This antigen accumulation can be suppressed by giving the antibody a pH-dependent C5-binding property so that C5 is released from the antibody in the acidic endosome and then trafficked to the lysosome for degradation, while the C5-free antibody returns back to plasma. We recently demonstrated that a pH-dependent C5-binding antibody, SKY59, exhibited long-lasting neutralization of C5 in cynomolgus monkeys, showing potential for subcutaneous delivery or less frequent administration. Here we report the details of the antibody engineering involved in generating SKY59, from humanizing a rabbit antibody to improving the C5-binding property. Moreover, because the pH-dependent C5-binding antibodies that we first generated still accumulated C5, we hypothesized that the surface charges of the ICs partially contributed to a slow uptake rate of the C5-antibody ICs. This idea motivated us to engineer the surface charges of the antibody. Our surface-charge engineered antibody consequently exhibited a high capacity to sweep C5 and suppressed the C5 accumulation in vivo by accelerating the cycle of sweeping: uptake of ICs into cells, release of C5 from the antibody in endosomes, and salvage of the antigen-free antibody. Thus, our engineered anti-C5 antibody, SKY59, is expected to provide significant benefits for patients with complement-mediated disorders.

Long lasting neutralization of C5 by SKY59, a novel recycling antibody, is a potential therapy for complement-mediated diseases.

Dysregulation of the complement system is linked to the pathogenesis of a variety of hematological disorders. Eculizumab, an anti-complement C5 monoclonal antibody, is the current standard of care for paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). However, because of high levels of C5 in plasma, eculizumab has to be administered biweekly by intravenous infusion. By applying recycling technology through pH-dependent binding to C5, we generated a novel humanized antibody against C5, SKY59, which has long-lasting neutralization of C5. In cynomolgus monkeys, SKY59 suppressed C5 function and complement activity for a significantly longer duration compared to a conventional antibody. Furthermore, epitope mapping by X-ray crystal structure analysis showed that a histidine cluster located on C5 is crucial for the pH-dependent interaction with SKY59. This indicates that the recycling effect of SKY59 is driven by a novel mechanism of interaction with its antigen and is distinct from other known pH-dependent antibodies. Finally, SKY59 showed neutralizing effect on C5 variant p.Arg885His, while eculizumab does not inhibit complement activity in patients carrying this mutation. Collectively, these results suggest that SKY59 is a promising new anti-C5 agent for patients with PNH and other complement-mediated disorders.

Lung surfactant levels are regulated by Ig-Hepta/GPR116 by monitoring surfactant protein D.

Lung surfactant is a complex mixture of lipids and proteins, which is secreted from the alveolar type II epithelial cell and coats the surface of alveoli as a thin layer. It plays a crucial role in the prevention of alveolar collapse through its ability to reduce surface tension. Under normal conditions, surfactant homeostasis is maintained by balancing its release and the uptake by the type II cell for recycling and the internalization by alveolar macrophages for degradation. Little is known about how the surfactant pool is monitored and regulated. Here we show, by an analysis of gene-targeted mice exhibiting massive accumulation of surfactant, that Ig-Hepta/GPR116, an orphan receptor, is expressed on the type II cell and sensing the amount of surfactant by monitoring one of its protein components, surfactant protein D, and its deletion results in a pulmonary alveolar proteinosis and emphysema-like pathology. By a coexpression experiment with Sp-D and the extracellular region of Ig-Hepta/GPR116 followed by immunoprecipitation, we identified Sp-D as the ligand of Ig-Hepta/GPR116. Analyses of surfactant metabolism in Ig-Hepta(+/+) and Ig-Hepta(-/-) mice by using radioactive tracers indicated that the Ig-Hepta/GPR116 signaling system exerts attenuating effects on (i) balanced synthesis of surfactant lipids and proteins and (ii) surfactant secretion, and (iii) a stimulating effect on recycling (uptake) in response to elevated levels of Sp-D in alveolar space.

SGLT5 reabsorbs fructose in the kidney but its deficiency paradoxically exacerbates hepatic steatosis induced by fructose.

Although excessive fructose intake is epidemiologically linked with dyslipidemia, obesity, and diabetes, the mechanisms regulating plasma fructose are not well known. Cells transfected with sodium/glucose cotransporter 5 (SGLT5), which is expressed exclusively in the kidney, transport fructose in vitro; however, the physiological role of this transporter in fructose metabolism remains unclear. To determine whether SGLT5 functions as a fructose transporter in vivo, we established a line of mice lacking the gene encoding SGLT5. Sodium-dependent fructose uptake disappeared in renal brush border membrane vesicles from SGLT5-deficient mice, and the increased urinary fructose in SGLT5-deficient mice indicated that SGLT5 was the major fructose reabsorption transporter in the kidney. From this, we hypothesized that urinary fructose excretion induced by SGLT5 deficiency would ameliorate fructose-induced hepatic steatosis. To test this hypothesis we compared SGLT5-deficient mice with wild-type mice under conditions of long-term fructose consumption. Paradoxically, however, fructose-induced hepatic steatosis was exacerbated in the SGLT5-deficient mice, and the massive urinary fructose excretion was accompanied by reduced levels of plasma triglycerides and epididymal fat but fasting hyperinsulinemia compared with fructose-fed wild-type mice. There was no difference in food consumption, water intake, or plasma fructose between the two types of mice. No compensatory effect by other transporters reportedly involved in fructose uptake in the liver and kidney were indicated at the mRNA level. These surprising findings indicated a previously unrecognized link through SGLT5 between renal fructose reabsorption and hepatic lipid metabolism.

Tofogliflozin, a potent and highly specific sodium/glucose cotransporter 2 inhibitor, improves glycemic control in diabetic rats and mice.

Sodium/glucose cotransporter 2 (SGLT2) is the predominant mediator of renal glucose reabsorption and is an emerging molecular target for the treatment of diabetes. We identified a novel potent and selective SGLT2 inhibitor, tofogliflozin (CSG452), and examined its efficacy and pharmacological properties as an antidiabetic drug. Tofogliflozin competitively inhibited SGLT2 in cells overexpressing SGLT2, and K(i) values for human, rat, and mouse SGLT2 inhibition were 2.9, 14.9, and 6.4 nM, respectively. The selectivity of tofogliflozin toward human SGLT2 versus human SGLT1, SGLT6, and sodium/myo-inositol transporter 1 was the highest among the tested SGLT2 inhibitors under clinical development. Furthermore, no interaction with tofogliflozin was observed in any of a battery of tests examining glucose-related physiological processes, such as glucose uptake, glucose oxidation, glycogen synthesis, hepatic glucose production, glucose-stimulated insulin secretion, and glucosidase reactions. A single oral gavage of tofogliflozin increased renal glucose clearance and lowered the blood glucose level in Zucker diabetic fatty rats. Tofogliflozin also improved postprandial glucose excursion in a meal tolerance test with GK rats. In db/db mice, 4-week tofogliflozin treatment reduced glycated hemoglobin and improved glucose tolerance in the oral glucose tolerance test 4 days after the final administration. No blood glucose reduction was observed in normoglycemic SD rats treated with tofogliflozin. These findings demonstrate that tofogliflozin inhibits SGLT2 in a specific manner, lowers blood glucose levels by increasing renal glucose clearance, and improves pathological conditions of type 2 diabetes with a low hypoglycemic potential.

Multiple processing of Ig-Hepta/GPR116, a G protein-coupled receptor with immunoglobulin (Ig)-like repeats, and generation of EGF2-like fragment.

Ig-Hepta/GPR116 is a member of the LNB-TM7 subfamily of G protein-coupled receptors (GPCRs), also termed the adhesion GPCRs, whose members have EGF, cadherin, lectin, thrombospondin, or Ig repeats in their long N-terminus. In this study, we established that Ig-Hepta is processed at multiple sites yielding the following four fragments: (i) presequence (amino acid residues 1-24), (ii) proEGF2 (25-223, alpha-fragment), (iii) Ig repeats (224-993, beta-chain), and (iv) TM7 (994-1349, gamma-chain). The proEGF2 region is converted to EGF2 (52-223) by the processing enzyme furin and remains attached to the beta- and gamma-chains. Expression of some mRNA species was affected by the presence of alpha-fragment. These results suggest that the furin-processed alpha-fragment is involved in cellular signaling.

[Heterogeneity of G protein-coupled receptor generated by post-translational mechanisms and its clinical meanings].

G protein-coupled receptors (GPCRs) are the most famous target proteins for medicinal drugs. So far, heterogeneity of GPCRs is mainly focused on genetic variation. However, it has been reported that the structure and function of GPCRs are modified by several mechanisms after translation. RNA editing introduces the amino acid different from that encoded in genome by changing the nucleotide. Dimer formation is another example of how heterogeneity is produced. Many receptors form homo- or hetero-dimers, and obtain different function from original receptors. Receptors are regulated by several means to modulate stimulation strength. Receptor subtype is often differentially regulated by receptor kinases and/or second messenger-regulated kinases. There is a new type of receptor that shows a novel structural feature, a long amino terminal region belonging to class B seven transmembrane receptors. The physiological function of this class of receptor is assumed to play a role in cell-cell communication. This novel structural feature may directly link GPCR to the cytoskeleton. These mechanisms to produce functional and structural heterogeneity may explain how cells evoke different responses in different tissues or cells upon the same stimulation. Thus, the post-translational mechanism to produce heterogeneity provides additional flexibility when cells respond to one extracellular stimulus.

Cleavage of Ig-Hepta at a "SEA" module and at a conserved G protein-coupled receptor proteolytic site.

Ig-Hepta is a member of a new subfamily of the heptahelical receptors and has an unusually long N terminus extending toward the extracellular side of the plasma membrane. Pulse-chase experiments in 293T cells using antisera specifically recognizing its N- and C-terminal regions demonstrated that Ig-Hepta is core-glycosylated cotranslationally and proteolytically processed into a two-chain form in the endoplasmic reticulum, followed by maturation of oligosaccharide chains and dimerization. The cleavage occurs at two highly conserved sites: one in a "SEA" module (a module first identified in sperm protein, enterokinase, and agrin) near the N terminus and the other in the stalk region preceding the first transmembrane span, generating approximately 20-, 130-, and 32-kDa fragments. The latter two remain tightly associated non-covalently even after cleavage as revealed by immunoprecipitation of native and myc-tagged Ig-Hepta constructs that were transiently expressed in 293T cells. The dimer consisting of four chains, (130 kDa + 32 kDa)(2), is linked by disulfide bonds. A fusion protein of the extracellular domain of Ig-Hepta and the Fc domain of immunoglobulin was found to be a good substrate of the processing enzymes and used for determining the exact cleavage sites in the SEA module and juxtamembrane stalk region.