A Practical Method for Synthesizing Iptacopan.

Iptacopan, the first orally available small-molecule complement factor B inhibitor, was developed by Novartis AG of Switzerland. Iptacopan for the treatment of PNH was just approved by the FDA in December 2023. Other indications for treatment are still in phase III clinical trials. Iptacopan is a small-molecule inhibitor targeting complement factor B, showing positive therapeutic effects in the treatment of PNH, C3 glomerulonephritis, and other diseases. Although Iptacopan is already on the market, there has been no detailed synthesis process or specific parameter report on the intermediates during the synthesis of its compounds except for the original research patent. In this study, a practical synthesis route for Iptacopan was obtained through incremental improvement while a biosynthesis method for ketoreductase was used for the synthesis of the pivotal intermediate 12. Moreover, by screening the existing enzyme library of our research group on the basis of random as well as site-directed mutagenesis methods, an enzyme (M8) proven to be of high optical purity with a high yield for biocatalectic reduction was obtained. This enzyme was used to prepare the compound benzyl (2S,4S)-4-hydroxy-2-(4-(methoxycarbonyl)-phenyl)-piperidine-1-carboxylate) white powder (36.8 g HPLC purity: 98%, ee value: 99%). In the synthesis of intermediate 15, the reaction was improved from two-step to one-step, which indicated that the risk of chiral allosterism was reduced while the scale was expanded. Finally, Iptacopan was synthesized in a seven-step reaction with a total yield of 29%. Since three chiral intermediate impurities were synthesized directionally, this paper lays a solid foundation for the future of pharmaceutical manufacturing.

Factor B inhibitor iptacopan for the treatment of paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, clonal, complement-mediated hemolytic anemia with a variety of manifestations. Currently, the methods for treating PNH include anti-C5 treatments (eculizumab and ravulizumab) and pegcetacoplan (a targeted C3 inhibitor). On December 5, 2023, the US FDA approved a factor B inhibitor called Fabhalta® (iptacopan), previously known as LNP023, for the treatment of adult patients with PNH, including those who have previously received anti-C5 therapy. The main objective of this review was to elucidate the clinical efficacy and safety of the newly approved factor B inhibitor, iptacopan. Iptacopan plays a proximal role in the alternative complement pathway to control extravascular hemolysis mediated by C3b and intravascular hemolysis mediated by terminal complement. The recommended dosage is 200 mg orally twice daily. The 24-week results of the pivotal phase III open-label trial, APPLY-PNH, demonstrated that among PNH patients who had previously received anti-C5 therapy, 51/60 (estimated percentages 82%) of patients in the iptacopan group showed an increase in hemoglobin of ≥2 g/dL compared to 0/35 (estimated percentages 2%) in the standard treatment group, also, 69% of iptacopan-treated patients achieved hemoglobin levels ≥12 g/dL, while no patients in the standard treatment group reached this level (both p < 0.001). The 48-week results were similar to those observed at 24 weeks. The most common adverse events were headache, infection and diarrhea. There were almost no clinical breakthrough hemolysis. Trials evaluating the long-term safety and efficacy of iptacopan are currently recruiting.

Oral Iptacopan Monotherapy in Paroxysmal Nocturnal Hemoglobinuria.

BACKGROUND: Persistent hemolytic anemia and a lack of oral treatments are challenges for patients with paroxysmal nocturnal hemoglobinuria who have received anti-C5 therapy or have not received complement inhibitors. Iptacopan, a first-in-class oral factor B inhibitor, has been shown to improve hemoglobin levels in these patients. METHODS: In two phase 3 trials, we assessed iptacopan monotherapy over a 24-week period in patients with hemoglobin levels of less than 10 g per deciliter. In the first, anti-C5-treated patients were randomly assigned to switch to iptacopan or to continue anti-C5 therapy. In the second, single-group trial, patients who had not received complement inhibitors and who had lactate dehydrogenase (LDH) levels more than 1.5 times the upper limit of the normal range received iptacopan. The two primary end points in the first trial were an increase in the hemoglobin level of at least 2 g per deciliter from baseline and a hemoglobin level of at least 12 g per deciliter, each without red-cell transfusion; the primary end point for the second trial was an increase in hemoglobin level of at least 2 g per deciliter from baseline without red-cell transfusion. RESULTS: In the first trial, 51 of the 60 patients who received iptacopan had an increase in the hemoglobin level of at least 2 g per deciliter from baseline, and 42 had a hemoglobin level of at least 12 g per deciliter, each without transfusion; none of the 35 anti-C5-treated patients attained the end-point levels. In the second trial, 31 of 33 patients had an increase in the hemoglobin level of at least 2 g per deciliter from baseline without red-cell transfusion. In the first trial, 59 of the 62 patients who received iptacopan and 14 of the 35 anti-C5-treated patients did not require or receive transfusion; in the second trial, no patients required or received transfusion. Treatment with iptacopan increased hemoglobin levels, reduced fatigue, reduced reticulocyte and bilirubin levels, and resulted in mean LDH levels that were less than 1.5 times the upper limit of the normal range. Headache was the most frequent adverse event with iptacopan. CONCLUSIONS: Iptacopan treatment improved hematologic and clinical outcomes in anti-C5-treated patients with persistent anemia - in whom iptacopan showed superiority to anti-C5 therapy - and in patients who had not received complement inhibitors. (Funded by Novartis; APPLY-PNH ClinicalTrials.gov number, NCT04558918; APPOINT-PNH ClinicalTrials.gov number, NCT04820530.).

SAR443809: a selective inhibitor of the complement alternative pathway, targeting complement factor Bb.

Dysregulated activation of the complement system is implicated in the onset or progression of several diseases. Most clinical-stage complement inhibitors target the inactive complement proteins present at high concentrations in plasma, which increases target-mediated drug disposition and necessitates high drug levels to sustain therapeutic inhibition. Furthermore, many efforts are aimed at inhibiting only terminal pathway activity, which leaves opsonin-mediated effector functions intact. We describe the discovery of SAR443809, a specific inhibitor of the alternative pathway C3/C5 convertase (C3bBb). SAR443809 selectively binds to the activated form of factor B (factor Bb) and inhibits alternative pathway activity by blocking the cleavage of C3, leaving the initiation of classical and lectin complement pathways unaffected. Ex vivo experiments with patient-derived paroxysmal nocturnal hemoglobinuria erythrocytes show that, although terminal pathway inhibition via C5 blockade can effectively inhibit hemolysis, proximal complement inhibition with SAR443809 inhibits both hemolysis and C3b deposition, abrogating the propensity for extravascular hemolysis. Finally, intravenous and subcutaneous administration of the antibody in nonhuman primates demonstrated sustained inhibition of complement activity for several weeks after injection. Overall, SAR443809 shows strong potential for treatment of alternative pathway-mediated disorders.

Complement factor B inhibitor LNP023 improves lupus nephritis in MRL/lpr mice.

BACKGROUND: Lupus nephritis (LN) is the most common complication of systemic lupus erythematosus (SLE), and the abnormal activation of the alternative complement pathway is associated with the pathogenesis of LN. As an inhibitor of complement factor B (CFB) in the alternative pathway, LNP023 has been used in the treatment of a variety of renal diseases with abnormal complement system involvement, such as paroxysmal nocturnal hemoglobinuria, IgA nephropathy, and membranous nephropathy. The aim of our study was to explore whether LNP023 improved LN in MRL/lpr mice by inhibiting the activation of the alternative complement pathway. METHODS: The mice were divided into a normal control group (Normal group) (n = 6), MRL/lpr model group (n = 6), and LNP023 group (n = 6). The LNP023 group was administered LNP023 for 2 weeks by gavage; the MRL/lpr model group was administered saline for 2 weeks by gavage; and the Normal group was administered saline for 2 weeks by gavage. External signs, renal pathology, renal function, renal immune complex and complement deposition, serum anti-dsDNA, serum ANA concentration, and the expression of core complement factors in the alternative complement pathway were analyzed in the 3 groups of animals. The core targets of LNP023 in the treatment of LN were screened using network pharmacology. The pathogenicity of the core targets in LN was verified by analyzing the mRNA expression of the core targets in the peripheral blood mononuclear cells (PBMCs) of normal individuals, SLE patients, and LN patients. The mRNA and protein expression of core targets in the Normal group, MRL/lpr group, and LNP023 group were analyzed to verify whether LNP023 exerted it LN therapeutic effect through the regulation of core targets. RESULTS: Compared with the MRL/lpr group, the LNP023 group had reduced lupus-like signs, improved renal function, decreased serum anti-dsDNA and ANA concentrations, and reduced renal IgM, IgG, IgG1, C1q, C3, and C4 deposition. Renal pathology showed that LNP023 attenuated pathological damage in the kidneys of MRL/lpr mice. Compared with the MRL/lpr model group, the treatment group had no crescent formation, less immune deposition, no nuclear fragmentation, and less inflammatory cell infiltration. The expression of complement proteins C3, C3b, CR1, CFB, and C5b-9 in kidney tissues and liver was decreased, and the expression of C5 was increased. Network pharmacology screening indicated that AKT, TNF-α, MDM2, UBC, STST3, ESR1, and TP53 were core targets of LNP023 in the treatment of LN. Compared with that in the Normal group, the mRNA expression of the core target in the SLE and LN groups was different; compared with the MRL/lpr group, the LNP023 treatment group showed different mRNA and protein expression levels of AKT, TNF-α, and STST3. CONCLUSION: LNP023 improves LN in MRL/lpr mice. The mechanism is as follows: LNP023 binds to CFB to inhibit the activation of the alternative complement pathway. LNP023 treatment for LN may also play a role in regulating the protein expression of AKT, TNF-α, and STST3.

Addition of iptacopan, an oral factor B inhibitor, to eculizumab in patients with paroxysmal nocturnal haemoglobinuria and active haemolysis: an open-label, single-arm, phase 2, proof-of-concept trial.

BACKGROUND: The haematological benefit of standard-of-care anti-C5 treatment for haemolytic paroxysmal nocturnal haemoglobinuria is limited by residual intravascular haemolysis or emerging C3-mediated extravascular haemolysis. Therefore, the aim of this phase 2 study was to assess the safety, tolerability, pharmacokinetics and pharmacodynamics, and activity of the new complement factor B inhibitor, iptacopan, in patients with paroxysmal nocturnal haemoglobinuria who have active haemolysis despite anti-C5 therapy. METHODS: In this multicentre, open-label, single-arm, phase 2 trial, we enrolled adult patients (aged 18-80 years) with paroxysmal nocturnal haemoglobinuria who showed signs of active haemolysis despite receiving eculizumab treatment. Patients were enrolled at Federico II University Hospital (Naples, Italy), Hôpital Saint-Louis (Paris, France), and University Hospital Essen (Essen, Germany). For enrolment, patients were required to show lactate dehydrogenase more than 1·5-times the upper limit of normal and a paroxysmal nocturnal haemoglobinuria type 3 erythrocyte or granulocyte clone size of 10% or greater. Patients with bone marrow failure, on systemic steroid or immunosuppressive drugs, or with severe comorbidities were excluded from the study. Iptacopan was given orally as an add-on therapy at a dose of 200 mg twice daily. The primary endpoint was the effect of iptacopan on the reduction of chronic residual intravascular haemolysis measured as change in lactate dehydrogenase from baseline value to week 13. At 13 weeks, patients could opt into a long-term study extension (ongoing), allowing for modifications of standard treatment. This trial is registered at ClinicialTrials.gov, NCT03439839. FINDINGS: Between May 31, 2018, and April 9, 2019, ten patients had twice daily 200 mg iptacopan. Iptacopan resulted in marked reduction of lactate dehydrogenase from baseline versus at week 13 (mean 539 IU/L [SD 263] vs 235 IU/L [44], change from baseline -309·2 IU/L [SD 265·5], 90% CI -473·77 to -144·68, p=0·0081), associated with significant improvement of haemoglobin concentrations (mean 97·7 g/L [SD 10·5] vs 129·5 g/L [18·3] change from baseline 31·9 g/L [14·5], 90% CI 23·42-40·28, p<0·0001). All biomarkers of haemolysis improved on iptacopan treatment. Observed haematological benefits were maintained longer than the 13-week study period, throughout the study extension, including seven patients who stopped concomitant standard-of-care treatment and continued iptacopan as monotherapy. There were no deaths or treatment-related serious adverse events during the study period. Of three non-related serious adverse events, two occurred in the same patient (one during run-in and before exposure to iptacopan). INTERPRETATION: Iptacopan at a chronic dose of 200 mg twice daily was well tolerated without any major drug-related safety findings and shows lactate dehydrogenase reduction and haemoglobin normalisation in most patients with paroxysmal nocturnal haemoglobinuria at week 13 and beyond, even in monotherapy. On the basis of these data, iptacopan will be tested as monotherapy in pivotal trials investigating its haematological benefit in a broader paroxysmal nocturnal haemoglobinuria population. FUNDING: Novartis Institutes for Biomedical Research.

Pharmacokinetics and metabolism of LNP023 in rats by liquid chromatography combined with electrospray ionization-tandem mass spectrometry.

In this study, a simple and sensitive LC-tandem mass spectrometric method was developed and validated for the determination of LNP023 in rat plasma. The plasma sample was precipitated with acetonitrile and then separated on an ACQUITY HSS T3 column (50 mm × 2.1 mm, 1.8 µm) using 0.1% formic acid in water and acetonitrile as the mobile phase. The MS detection was performed in positive multiple-reaction monitoring mode with precursor-to-product ion transitions of m/z 423.3 → 174.1 and m/z 435.3 → 367.1 for LNP023 and olaparib (internal standard), respectively. The developed assay was validated in the linear range of 0.1-1000 ng/mL with correlation coefficient (r) greater than 0.9992. The validation parameters were all within the acceptable limits. The validated method has been successfully used to investigate the pharmacokinetics of LNP023 in rat plasma, and our results indicated that LNP023 showed low clearance and high bioavailability (62.2%). Furthermore, four minor metabolites from rat plasma were detected and identified by LC combined with high-resolution mass spectrometry. The metabolic pathways were O-deethylation (M1), hydroxylation (M4), oxidation (M3), and acyl-glucuronidation (M2).

Discovery of 4-((2S,4S)-4-Ethoxy-1-((5-methoxy-7-methyl-1H-indol-4-yl)methyl)piperidin-2-yl)benzoic Acid (LNP023), a Factor B Inhibitor Specifically Designed To Be Applicable to Treating a Diverse Array of Complement Mediated Diseases.

The alternative pathway (AP) of the complement system is a key contributor to the pathogenesis of several human diseases including age-related macular degeneration, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and various glomerular diseases. The serine protease factor B (FB) is a key node in the AP and is integral to the formation of C3 and C5 convertase. Despite the prominent role of FB in the AP, selective orally bioavailable inhibitors, beyond our own efforts, have not been reported previously. Herein we describe in more detail our efforts to identify FB inhibitors by high-throughput screening (HTS) and leveraging insights from several X-ray cocrystal structures during optimization efforts. This work culminated in the discovery of LNP023 (41), which is currently being evaluated clinically in several diverse AP mediated indications.

Failed B cell survival factor trials support the importance of memory B cells in multiple sclerosis.

Clinical trials are probably the most informative experiments to help an understanding of multiple sclerosis (MS) biology. Recent successes with CD20-depleting antibodies have focused attention towards B cell subsets as important mediators in MS. The trial of tabalumab (NTC00882999), which inhibits B cell activation factor (BAFF), is reported and reviewed and this trial is contrasted with the trial on the inhibition of a proliferation-inducing ligand (APRIL) and BAFF using atacicept (NCT00642902). Both tabalumab and atacicept induce depletion of mature B cells and inhibit antibody formation, but they fail to deplete memory B cells and do not inhibit relapsing MS. Atacicept is reported to augment memory B cell responses and may precipitate relapse, suggesting the importance of APRIL. However, BAFF inhibition can enhance peripheral blood memory B cell responses, which was not associated with augmented relapse. Although other interpretations are possible, these data further support the hypothesis that memory B cells may be of central importance in relapsing MS, as they are the major CD20+ B cell subset expressing APRIL receptors. They also suggest that quantitative and/or qualitative differences in B cell responses or other factors, such as an immune-regulatory effect associated with APRIL, may be important in determining whether MS reactivates following neutralization of peripheral B cell maturation and survival factors.

Blocking Complement Factor B Activation Reduces Renal Injury and Inflammation in a Rat Brain Death Model.

Introduction: The majority of kidneys used for transplantation are retrieved from brain-dead organ donors. In brain death, the irreversible loss of brain functions results in hemodynamic instability, hormonal changes and immunological activation. Recently, brain death has been shown to cause activation of the complement system, which is adversely associated with renal allograft outcome in recipients. Modulation of the complement system in the brain-dead donor might be a promising strategy to improve organ quality before transplantation. This study investigated the effect of an inhibitory antibody against complement factor B on brain death-induced renal inflammation and injury. Method: Brain death was induced in male Fischer rats by inflating a balloon catheter in the epidural space. Anti-factor B (anti-FB) or saline was administered intravenously 20 min before the induction of brain death (n = 8/group). Sham-operated rats served as controls (n = 4). After 4 h of brain death, renal function, renal injury, and inflammation were assessed. Results: Pretreatment with anti-FB resulted in significantly less systemic and local complement activation than in saline-treated rats after brain death. Moreover, anti-FB treatment preserved renal function, reflected by significantly reduced serum creatinine levels compared to saline-treated rats after 4 h of brain death. Furthermore, anti-FB significantly attenuated histological injury, as seen by reduced tubular injury scores, lower renal gene expression levels (>75%) and renal deposition of kidney injury marker-1. In addition, anti-FB treatment significantly prevented renal macrophage influx and reduced systemic IL-6 levels compared to saline-treated rats after brain death. Lastly, renal gene expression of IL-6, MCP-1, and VCAM-1 were significantly reduced in rats treated with anti-FB. Conclusion: This study shows that donor pretreatment with anti-FB preserved renal function, reduced renal damage and inflammation prior to transplantation. Therefore, inhibition of factor B in organ donors might be a promising strategy to reduce brain death-induced renal injury and inflammation.

Small-molecule factor B inhibitor for the treatment of complement-mediated diseases.

Dysregulation of the alternative complement pathway (AP) predisposes individuals to a number of diseases including paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, and C3 glomerulopathy. Moreover, glomerular Ig deposits can lead to complement-driven nephropathies. Here we describe the discovery of a highly potent, reversible, and selective small-molecule inhibitor of factor B, a serine protease that drives the central amplification loop of the AP. Oral administration of the inhibitor prevents KRN-induced arthritis in mice and is effective upon prophylactic and therapeutic dosing in an experimental model of membranous nephropathy in rats. In addition, inhibition of factor B prevents complement activation in sera from C3 glomerulopathy patients and the hemolysis of human PNH erythrocytes. These data demonstrate the potential therapeutic value of using a factor B inhibitor for systemic treatment of complement-mediated diseases and provide a basis for its clinical development.

Neutralizing antichlamydial activity of complement by chlamydia-secreted protease CPAF.

Ascending infection by sexually transmitted Chlamydia trachomatis is required for chlamydial induction of tubal pathology. To achieve ascension, the C. trachomatis organisms may have to spread from cell to cell, which inevitably exposes the organisms to extracellular mucosal effectors such as complement factors that are known to possess strong antichlamydial activities. Here, we report that the chlamydia-secreted protease CPAF efficiently neutralized complement factor C3-dependent antichlamydial activity. The neutralization was dependent on the proteolytic activity of CPAF and correlated with the CPAF-mediated degradation of complement factor C3 and factor B. As a result, CPAF preferentially inhibited the alternative complement activation pathway. The significance and limitation of these observations were discussed.

Autoantibodies to complement components in C3 glomerulopathy and atypical hemolytic uremic syndrome.

The alternative pathway of complement is implicated in the pathogenesis of several renal diseases, such as atypical hemolytic uremic syndrome, dense deposit disease and other forms of C3 glomerulopathy. The underlying complement defects include genetic and/or acquired factors, the latter in the form of autoantibodies. Because the autoimmune forms require a specific treatment, in part different from that of the genetic forms, it is important to detect the autoantibodies as soon as possible and understand their characteristics. In this overview, we summarize the types of anti-complement autoantibodies detected in such diseases, i.e. autoantibodies to factor H, factor I, C3b, factor B and those against the C3 convertases (C3 nephritic factor and C4 nephritic factor). We draw attention to newly described autoantibodies and their characteristics, and highlight similarities and differences in the autoimmune forms of these diseases.

Targeted modulation of the neuroinflammatory response after spinal cord injury: the ongoing quest for the "holy grail".

This Commentary discusses the role of inflammation after spinal cord injury.

Structure-activity relationships for substrate-based inhibitors of human complement factor B.

Human complement is a cascading network of plasma proteins important in immune defense, cooperatively effecting recognition, opsonization, destruction, and removal of pathogens and infected/damaged cells. Overstimulated or unregulated complement activation can result in immunoinflammatory diseases. Key serine proteases in this cascade are difficult to study due to their multiprotein composition, short lifetimes, formation on membranes, or serum circulation as inactive zymogens. Factor B is inactive at pH 7, but a catalytically active serine protease under alkaline conditions, enabling structure-activity relationship studies for 63 substrate-based peptide inhibitors with 4-7 residues and a C-terminal aldehyde. A potent factor B inhibitor was hexpeptide Ac-RLTbaLAR-H (IC(50) 250 nM, pH 9.5), which at pH 7 also blocked formation of membrane attack complex via the "alternative pathway" of complement activation and inhibited human complement mediated lysis of rabbit erythrocytes. Inhibitors of factor B may be valuable probes and drug leads for complement mediated immunity and disease.

Resistance of the Echinococcus granulosus cyst wall to complement activation: analysis of the role of InsP6 deposits.

The larva of the cestode Echinococcus granulosus (hydatid cyst) is protected by the acellular laminated layer (LL). The mechanisms that make this thick coat a poor activator of host complement are incompletely understood. The structure binds, through unknown motifs, the host regulator of the alternative complement pathway (ACP), factor H. A second potential mechanism of ACP regulation, the inhibition of factor B activation, was detected in assays employing purified components (Immunopharmacology 42 : 91). The inhibitor was subsequently identified as myo-inositol hexakisphosphate (InsP(6)), which in the form of nano-deposits is a major component of the LL (Biochem J 362 : 297; J Cell Biochem 93 : 1272; FEBS J 273 : 3192). In this report we show that colloidal InsP(6 )solids inhibit factor B activation, through adsorption and associated impairment of C3b binding. However, this interaction is not relevant in the presence of serum proteins. In serum, InsP(6) deposits instead bind C1q, and initiate complement activation. This activation is curtailed through efficient C3b inactivation, previously shown to be entirely factor H-dependent, and now observed to be independent of the InsP(6) deposits. Therefore the complement resistance of the LL must be based on functional factor H binding sites present on the mucin-based meshwork that is its other major constituent.

Profiling the enzymatic properties and inhibition of human complement factor B.

Human complement factor B is the crucial catalytic component of the C3 convertase enzyme that activates the alternative pathway of complement-mediated immunity. Although a serine protease in its own right, factor B circulates in human serum as an inactive zymogen and there is a crystal structure only for the inactive state of factor B and various fragments. To provide greater insight to the catalytic function and properties of factor B, we have used short para-nitroanilide derivatives of 4- to 15-residue peptides as substrates to profile the catalytic properties of factor B. Among factors found to influence catalytic activity of factor B was an unusual dependence on pH. Non-physiological alkaline conditions strongly promoted substrate cleavage by factor B, consistent with a pH-accessible conformation of the enzyme that may be critical for catalytic function. Small N-terminal extensions to conventional hexapeptide para-nitroanilide substrates significantly increased catalytic activity of factor B, which was more selective for its cleavage site than trypsin. The new chromogenic assay enabled optimization of catalysis conditions, the profiling of different substrate sequences, and the development of the first reversible and competitive substrate-based inhibitor of factor B. The inhibitor was also shown to prevent in vitro formation of C3a from C3 by factor B, by synthetic and by natural C3 convertase of the alternative complement activation pathway, and to block formation of membrane attack complex. The availability of a reversible substrate-based inhibitor that could stabilize the active conformation of factor B, in conjunction with a pH-promoted higher processing activity, may offer a new avenue to obtain crystal structures of factor B and C3 convertase in an active conformation.