Targeting the Endothelin A Receptor in IgA Nephropathy

The role of endothelin receptor antagonists in kidney disease

Kidney diseases are among the most prevalent conditions worldwide, impacting over 850 million individuals. They are categorized into acute kidney injury and chronic kidney disease. Current preclinical and clinical trials have demonstrated that endothelin (ET) is linked to the onset and progression of kidney disease. In kidney diseases, pathological conditions such as hyperglycemia, acidosis, insulin resistance, and elevated angiotensin II levels lead to an increase in ET. This elevation activates endothelin receptor type A, resulting in harmful effects like proteinuria and a reduced glomerular filtration rate (GFR). Therefore, to slow the progression of kidney disease, endothelin receptor antagonists (ERAs) have been proposed as promising new therapies. Numerous studies have demonstrated the efficacy of ERAs in significantly reducing proteinuria and improving GFR, thereby slowing the progression of kidney diseases. This review discusses the mechanisms of action of ERAs in treating kidney disease, their efficacy and safety in preclinical and clinical studies, and explores future prospects for ERAs.

Treatment of patients with IgA nephropathy: a call for a new paradigm

IgA nephropathy (IgAN), the world's most common primary glomerular disease, carries a significant lifetime risk for kidney failure as well as an enormous socioeconomic burden. In the past, studies in patients with IgAN largely focused on optimizing so-called supportive care, that is, blockade of the renin-angiotensin system, blood pressure control, and lifestyle modifications. The effectiveness of immunosuppressive measures, particularly high-dose corticosteroid therapy, has been reported variably, but there is considerable evidence for an increase in serious adverse effects with such therapies. This disappointing situation has changed dramatically with a better understanding of the pathogenesis of IgAN, and with regulatory agencies accepting changes in proteinuria and the estimated glomerular filtration rate loss or slope over 2 to 3 years as surrogate outcome markers. A multitude of new therapies are now being evaluated in IgAN, and several drugs, such as sodium-glucose transporter-2 inhibitors, sparsentan (a dual endothelin-1 and angiotensin II receptor blocker), nefecon (a targeted release formulation of budesonide), and iptacopan (a complement factor B inhibitor), have been approved, with more to come in the next few years. In this review, we propose a new treatment paradigm that combines therapies with different mechanisms of action to target the immune components and the chronic kidney disease components of IgAN in parallel to preserve long-term kidney survival.

Alternative Complement Pathway Inhibition with Iptacopan in IgA Nephropathy

BACKGROUND

The alternative complement pathway plays a key role in the pathogenesis of IgA nephropathy. Iptacopan specifically binds to factor B and inhibits the alternative pathway.

METHODS

In this phase 3, double-blind, randomized, placebo-controlled trial, we enrolled adults with biopsy-confirmed IgA nephropathy and proteinuria with a 24-hour urinary protein-to-creatinine ratio of 1 or higher (with protein and creatinine both measured in grams) despite optimized supportive therapy. Patients were randomly assigned, in a 1:1 ratio, to receive oral iptacopan (200 mg) or placebo twice daily for 24 months while continuing to receive supportive therapy. The primary objective of this prespecified interim analysis was to assess the efficacy of iptacopan as compared with that of placebo in reducing proteinuria at month 9; the primary end point was the change from baseline in the 24-hour urinary protein-to-creatinine ratio at month 9. The proportion of patients who had a 24-hour urinary protein-to-creatinine ratio of less than 1 at month 9 without receiving rescue or alternative medication or undergoing kidney-replacement therapy (dialysis or transplantation) was a secondary end point. Safety was also assessed. The effect of iptacopan on kidney function will be assessed at the end of the 2-year double-blind treatment period.

RESULTS

The main trial population included 222 patients in the iptacopan group and 221 in the placebo group. The interim efficacy analysis included the first 250 patients who underwent randomization in the main trial population (125 patients in each group) and who remained in the trial until month 9 or discontinued the trial by month 9. Safety was assessed in all the patients in the main trial population. At month 9, the adjusted geometric mean 24-hour urinary protein-to-creatinine ratio was 38.3% (95% confidence interval, 26.0 to 48.6; two-sided P<0.001) lower with iptacopan than with placebo. The reduction in proteinuria was supported by consistent results in secondary end point analyses. There were no unexpected safety findings with iptacopan. The incidence of adverse events that occurred during the treatment period was similar in the two groups; most events were mild to moderate in severity and reversible. No increased risk of infection was observed.

CONCLUSIONS

Among patients with IgA nephropathy, treatment with iptacopan resulted in a significant and clinically meaningful reduction in proteinuria as compared with placebo. (Funded by Novartis; APPLAUSE-IgAN ClinicalTrials.gov number, NCT04578834.).

The road ahead: emerging therapies for primary IgA nephropathy

Primary IgA nephropathy (IgAN) is the most common form of primary glomerulopathy. A slowly progressive disease presenting in the young to middle-aged, most patients with reduced eGFR or proteinuria will progress to end-stage kidney disease (ESKD) in their lifetimes. The pathogenesis involves increased production of galactose-deficient IgA1 (Gd-IgA1) that forms immune complexes that deposit in the glomerulus, eliciting mesangial cell proliferation, inflammation, and complement activation. The backbone of therapy is supportive, including lifestyle modifications, strict blood pressure control, and renin-angiotensin system inhibition targeting proteinuria < 300 mg/day. Sodium-glucose transporter 2 inhibitors are indicated for persisting proteinuria or declining eGFR. Sparsentan is indicated for persisting proteinuria. Immunosuppression should be considered for all patients at risk for progression (persisting proteinuria and/or declining eGFR). To reduce Gd-IgA1 production, targeted-release budesonide is approved. Agents targeting B cell survival factors APRIL or BAFF/APRIL have significantly reduced Gd-IgA1 production and proteinuria in phase 2 trials but await phase 3 data for approval. To reduce inflammation, high-dose steroids are ineffective and toxic in Caucasian patients, although lower-dose regimens may be effective in Chinese patients. Complement inhibition is being actively studied. The factor B inhibitor iptacopan has conditional approval. The terminal pathway inhibitors cemdisiran and ravulizumab show promise in phase 2 studies. Our current approach for those requiring immunosuppression involves combining the reduction of Gd-IgA1 (nefecon) with suppressing the effects of inflammation (iptacopan). The optimal duration of such therapy is uncertain. Clearly, there is more to be learned with many trials underway.

ALIGNing the treatment of IgA nephropathy: Reducing proteinuria with endothelin A receptor inhibition

The ALIGN trial1 demonstrates that atrasentan, an endothelin A (ETA) receptor antagonist, reduces proteinuria in patients with IgA nephropathy (IgAN), a key goal to slow progressive renal disease. These results are consistent with those from sparsentan,2,3 a combined ETA and angiotensin inhibitor, in IgAN, suggesting two-year data will show atrasentan improves renal outcomes.

Study Design and Baseline Characteristics of ALIGN, a Randomized Controlled Study of Atrasentan in Patients With IgA Nephropathy

Introduction

Endothelin A (ETA) receptor activation is a driver of proteinuria, kidney inflammation, and fibrosis in IgA nephropathy (IgAN). Atrasentan, a selective ETA receptor antagonist, has potential to reduce proteinuria and preserve kidney function in IgAN. ALIGN (NCT04573478) is a phase 3, randomized, double-blind, placebo-controlled clinical trial of atrasentan in patients with IgAN at high risk of kidney function loss.

Methods

Eligibility criteria for the ALIGN main stratum included patients with biopsy-proven IgAN, total protein excretion ≥ 1 g/d, estimated glomerular filtration rate (eGFR) ≥ 30 ml/min per 1.73 m2, receiving a maximally tolerated stable dose of a renin-angiotensin system (RAS) inhibitor. An exploratory stratum enrolled participants also receiving a stable dose of sodium glucose cotransporter-2 inhibitors (SGLT2i). Participants were randomized to 0.75 mg atrasentan or placebo orally daily for 132 weeks followed by a 4-week wash-out period. The primary outcome is proteinuria change from baseline (24-hour urine protein-to-creatinine ratio [UPCR]) to week 36 in the main stratum. Key secondary end points include eGFR change from baseline to week 136, safety, and tolerability.

Results

Enrolment occurred across 20 countries; 404 patients were randomized: 340 in the main stratum and 64 in the SGLT2i stratum. At baseline in the main stratum, mean age was 44.7 years, 42.4% were female, mean eGFR and median UPCR were 58.9 ml/min per 1.73 m2 and 1.4 g/g, respectively.

Conclusion

The ongoing ALIGN trial evaluates the efficacy and safety of atrasentan in a representative global IgAN population at risk for disease progression despite optimized RAS inhibitor therapy and includes an exploratory stratum evaluating atrasentan use in combination with an SGLT2i.

The pathogenesis of IgA nephropathy and implications for treatment

IgA nephropathy (IgAN) is a common form of primary glomerulonephritis and represents an important cause of chronic kidney disease globally, with observational studies indicating that most patients are at risk of developing kidney failure within their lifetime. Several research advances have provided insights into the underlying disease pathogenesis, framed by a multi-hit model whereby an increase in circulating IgA1 that lacks galactose from its hinge region - probably derived from the mucosal immune system - is followed by binding of specific IgG and IgA antibodies, generating immune complexes that deposit within the glomeruli, which triggers inflammation, complement activation and kidney damage. Although treatment options are currently limited, new therapies are rapidly emerging that target different pathways, cells and mediators involved in the disease pathogenesis, including B cell priming in the gut mucosa, the cytokines APRIL and BAFF, plasma cells, complement activation and endothelin pathway activation. As more treatments become available, there is a realistic possibility of transforming the long-term outlook for many individuals with IgAN.

The Influence of Anti-ETAR and Anti-CXCR3 Antibody Levels on the Course of Specific Glomerulonephritis Types

Background: Anti-ETAR (endothelin A receptor) antibodies and anti-CXCR3 (C-X-C motif chemokine receptor 3) antibodies are types of non-HLA (human leukocyte antigens) antibodies that could have some influence on the course of glomerulonephritis. The authors aimed to study the influence of these antibodies' levels on the course of specific glomerulonephritis types. Methods: We evaluated the anti-ETAR and anti-CXCR3 antibody levels in the serum of patients with membranous nephropathy (n = 18), focal and segmental glomerulosclerosis (FSGS) (n = 25), systemic lupus erythematosus (n = 17), IgA nephropathy (n = 14), mesangiocapillary glomerulonephritis (n = 6), anti-neutrophil cytoplasmic antibodies (c-ANCA) vasculitis (n = 40), and perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) vasculitis (n = 16), and we compared their levels with the control group (n = 22). Next, we observed the patients' clinical parameters (serum creatinine, albumin, total protein) for 2 years and checked the correlation of the clinical course markers with basic receptor antibody level. Results: Our results indicate lower anti-ETAR antibody levels in patients with FSGS and IgA nephropathy compared to the control group. Both types of antibodies correlated with creatinine levels after 2 years of observation in IgA nephropathy. Both types of antibodies seemed to negatively influence the total protein and albumin levels in systemic lupus erythematosus. Conclusions: This prospective observation showed that anti-ETAR and anti-CXCR 3 antibody levels are connected with the course of IgA nephropathy and lupus nephritis.

Emerging perspectives in the management of IgA nephropathy: a comprehensive review

IgA nephropathy (IgAN) is the most prevalent form of primary glomerulonephritis worldwide and a leading cause of chronic kidney disease and renal failure. This disorder is characterized by the deposition of immune complexes containing galactose-deficient forms of IgA and complement C3 in the glomeruli. Until now, disease management relied mainly on optimized supportive care. Systemic corticosteroid therapy is proposed for patients at high risk of disease progression, but the effectiveness and safety of this approach are under debate. A significant proportion of patients do not respond to current therapies and require kidney replacement therapy at a young age, with substantial costs and impact on quality of life. Recently, there have been multiple joint efforts to improve the understanding of IgAN pathophysiology. International collaborations resulted in multiple ongoing clinical trials that are providing new insights toward innovative therapeutic options such as SGLT2 inhibitors, dual endothelin and angiotensin receptor blockers, targeted-release budesonide, B-cell proliferation and differentiation inhibitors, and complement system blockers. Based on this new evidence, revision of the guidelines to manage IgAN is expected to occur in the near future. In addition to the novelty in therapeutic agents, there is also a growing interest in new noninvasive biomarkers for IgAN screening, risk stratification to monitor the course of the disease, and the response to treatment. In this review, we discuss current knowledge on the pathophysiology of IgAN, disease management, and emerging advances in clinical translation of IgAN research.

Endothelin Inhibitors in Chronic Kidney Disease: New Treatment Prospects

The endothelin system is reported to play a significant role in glomerular and tubulointerstitial kidney disease. In the kidney, endothelins are produced in mesangial cells and the glomerular basement membrane by the endothelium and podocytes. The endothelin system regulates glomerular function by inducing proliferation, increasing permeability and in effect proteinuria, and stimulating inflammation, tubular fibrosis, and glomerular scarring. Endothelin A receptor antagonists have been proven to delay the progression of chronic kidney disease and play a protective role in immunoglobulin A nephropathy, focal segmental glomerulosclerosis, and diabetic nephropathy. There are several ongoing research studies with ETAR antagonists in nondiabetic nephropathy, Alport disease, vasculitis and scleroderma nephropathy, which results are promising. Some reports suggest that the endothelin system might contribute to ischemia-reperfusion injury, acute graft rejection and deterioration of graft function. Endothelin inhibition in renal transplantation and its influence on graft survival is the future direction needing further research. The most frequent side effects associated with ETAR antagonists is fluid retention. Additionally, it should be considered if selective ETAR antagonists therapy needs to be co-administered with sodium-glucose co-transporter 2 inhibitors, renin-angiotensin-aldosterone inhibitors or diuretics and which patients should be recruited to such treatment to minimize the risk of adverse outcomes.

The role of endothelin receptor antagonists in IgA nephropathy

There is growing evidence of endothelin receptor antagonists (ERAs) in renoprotection in proteinuric kidney disease including IgA nephropathy (IgAN). Here, we review current evidence, including the use of sparsentan, atrasentan and zibotentan in IgAN. Recent trails of combination therapy including SGLT2 inhibitors and ERAs suggest possible benefit in further reduction of proteinuria and reducing ERA fluid-retention side effects although more evidence is needed for clinical applications.

The Rapidly Changing Treatment Landscape of IgA Nephropathy

The past few years have heralded a sea change in the treatment landscape of IgA nephropathy (IgAN). An increasing understanding of its pathogenesis coupled with favorable changes in the regulatory approval pathway has led to an explosion of clinical drug development in this disease. This has directly resulted in the approval of three novel therapies specifically for the treatment of IgAN (nefecon, sparsentan, and iptacopan), and several others are in the late stages of clinical development. In this review, we outline the rationale for new therapies in development for IgAN and emerging clinical trial data and propose a new paradigm for the treatment of this condition.

Contemporary review of IgA nephropathy

IgA nephropathy (IgAN) is considered the most common primary glomerulonephritis worldwide with a predilection for Asian-Pacific populations and relative rarity in those of African descent. Perhaps 20%-50% of patients progress to kidney failure. The pathogenesis is incompletely understood. Mesangial deposition of immune complexes containing galactose-deficient IgA1 complexed with anti-glycan IgG or IgA antibodies results in mesangial cell activation and proliferation, inflammatory cell recruitment, complement activation, and podocyte damage. Diagnosis requires a biopsy interpreted by the Oxford criteria. Additional pathologic features include podocytopathy, thrombotic microangiopathy, and C4d staining. Biomarkers predicting adverse outcomes include proteinuria, reduced GFR, hypertension, and pathology. Acceptable surrogate endpoints for therapeutic trials include ongoing proteinuria and rate of eGFR decline. The significance of persisting hematuria remains uncertain. The mainstay of therapy is supportive, consisting of lifestyle modifications, renin-angiotensin inhibition (if hypertensive or proteinuric), sodium-glucose-transporter 2 inhibition (if GFR reduced or proteinuric), and endothelin-receptor antagonism (if proteinuric). Immunosuppression should be considered for those at high risk after maximal supportive care. Corticosteroids are controversial with the most positive results observed in Chinese. They carry a high risk of serious side effects. Similarly, mycophenolate may be most effective in Chinese. Other immunosuppressants are of uncertain benefit. Tonsillectomy appears efficacious in Japanese. Active areas of investigation include B-cell inhibition with agents targeting the survival factors BAFF and APRIL and complement inhibition with agents targeting the alternate pathway (Factors B and D), the lectin pathway (MASP-2), and the common pathway (C3 and C5). Hopefully soon, the who and the how of immunosuppression will be clarified, and kidney failure can be forestalled.

Mechanism of protective actions of sparsentan in the kidney: lessons from studies in models of chronic kidney disease

Simultaneous inhibition of angiotensin II AT1 and endothelin ETA receptors has emerged as a promising approach for treatment of chronic progressive kidney disease. This therapeutic approach has been advanced by the introduction of sparsentan, the first dual AT1 and ETA receptor antagonist. Sparsentan is a single molecule with high affinity for both receptors. It is US Food and Drug Administration approved for immunoglobulin A nephropathy (IgAN) and is currently being developed as a treatment for rare kidney diseases, such as focal segmental glomerulosclerosis. Clinical studies have demonstrated the efficacy and safety of sparsentan in these conditions. In parallel with clinical development, studies have been conducted to elucidate the mechanisms of action of sparsentan and its position in the context of published evidence characterizing the nephroprotective effects of dual ETA and AT1 receptor inhibition. This review summarizes this evidence, documenting beneficial anti-inflammatory, antifibrotic, and hemodynamic actions of sparsentan in the kidney and protective actions in glomerular endothelial cells, mesangial cells, the tubulointerstitium, and podocytes, thus providing the rationale for the use of sparsentan as therapy for focal segmental glomerulosclerosis and IgAN and suggesting potential benefits in other renal diseases, such as Alport syndrome.

Is endothelin targeting finally ready for prime time?

The endothelin family of peptides has long been recognized as a physiological regulator of diverse biological functions and mechanistically involved in various disease states, encompassing, among others, the cardiovascular system, the kidney, and the nervous system. Pharmacological blockade of the endothelin system, however, has encountered strong obstacles in its entry into the clinical mainstream, having obtained only a few proven indications until recently. This translational gap has been attributable predominantly to the relevant side effects associated with endothelin receptor antagonism (ERA), particularly fluid retention. Of recent, however, an expanding understanding of the pathophysiological processes involving endothelin, in conjunction with the development of new antagonists of endothelin receptors or adjustment of their doses, has driven a flourish of new clinical trials. The favorable results of some of them have extended the proven indications for ET targeting to a variety of clinical conditions, including resistant arterial hypertension and glomerulopathies. In addition, on the ground of strong preclinical evidence, other studies are ongoing to test the potential benefits of ERA in combination with other treatments, such as sodium-glucose co-transporter 2 inhibition in fluid retentive states or anti-cancer therapies in solid tumors. Furthermore, antibodies providing long-term blockade of endothelin receptors are under testing to overcome the short half-life of most small molecule endothelin antagonists. These efforts may yet bring new life to the translation of endothelin targeting strategies in clinical practice.

Drugs in Development to Treat IgA Nephropathy

IgA nephropathy is a common glomerulonephritis consequent to the autoimmune response to aberrant glycosylated immunoglobulin (Ig) A antibodies. Although it has historically been considered a benign disease, it has since become clear that a substantial percentage of patients reach end-stage kidney failure over the years. Several therapeutic attempts have been proposed, with systemic steroids being the most prevalent, albeit burdened by possible serious adverse events. Thanks to the more in-depth knowledge of the pathogenesis of IgA nephropathy, new treatment targets have been identified and new drugs developed. In this narrative review, we summarise the molecules under clinical development for the treatment of IgA nephropathy. As a search strategy, we used PubMed, Google, ClinicalTrials.gov and abstracts from recent international congresses. TRF budesonide and sparsentan are the two molecules at a more advanced stage, just entering the market. Other promising agents are undergoing phase III clinical development. These include anti-APRIL and anti-BLyS/BAFF antibodies and some complement inhibitors. Other new possible strategies include spleen tyrosine kinase inhibitors, anti-CD40 ligands and anti-CD38 antibodies. In an era increasingly characterised by 'personalised medicine' and 'precision therapy' approaches and considering that the potential therapeutic armamentarium for IgA nephropathy will be very broad in the near future, the identification of biomarkers capable of helping the nephrologist to select the right drug for the right patient should be the focus of future studies.

Efficacy and safety of sparsentan versus irbesartan in patients with IgA nephropathy (PROTECT): 2-year results from a randomised, active-controlled, phase 3 trial

BACKGROUND

Sparsentan, a novel, non-immunosuppressive, single-molecule, dual endothelin angiotensin receptor antagonist, significantly reduced proteinuria versus irbesartan, an angiotensin II receptor blocker, at 36 weeks (primary endpoint) in patients with immunoglobulin A nephropathy in the phase 3 PROTECT trial's previously reported interim analysis. Here, we report kidney function and outcomes over 110 weeks from the double-blind final analysis.

METHODS

PROTECT, a double-blind, randomised, active-controlled, phase 3 study, was done across 134 clinical practice sites in 18 countries throughout the Americas, Asia, and Europe. Patients aged 18 years or older with biopsy-proven primary IgA nephropathy and proteinuria of at least 1·0 g per day despite maximised renin-angiotensin system inhibition for at least 12 weeks were randomly assigned (1:1) to receive sparsentan (target dose 400 mg oral sparsentan once daily) or irbesartan (target dose 300 mg oral irbesartan once daily) based on a permuted-block randomisation method. The primary endpoint was proteinuria change between treatment groups at 36 weeks. Secondary endpoints included rate of change (slope) of the estimated glomerular filtration rate (eGFR), changes in proteinuria, a composite of kidney failure (confirmed 40% eGFR reduction, end-stage kidney disease, or all-cause mortality), and safety and tolerability up to 110 weeks from randomisation. Secondary efficacy outcomes were assessed in the full analysis set and safety was assessed in the safety set, both of which were defined as all patients who were randomly assigned and received at least one dose of randomly assigned study drug. This trial is registered with ClinicalTrials.gov, NCT03762850.

FINDINGS

Between Dec 20, 2018, and May 26, 2021, 203 patients were randomly assigned to the sparsentan group and 203 to the irbesartan group. One patient from each group did not receive the study drug and was excluded from the efficacy and safety analyses (282 [70%] of 404 included patients were male and 272 [67%] were White) . Patients in the sparsentan group had a slower rate of eGFR decline than those in the irbesartan group. eGFR chronic 2-year slope (weeks 6-110) was -2·7 mL/min per 1·73 m2 per year versus -3·8 mL/min per 1·73 m2 per year (difference 1·1 mL/min per 1·73 m2 per year, 95% CI 0·1 to 2·1; p=0·037); total 2-year slope (day 1-week 110) was -2·9 mL/min per 1·73 m2 per year versus -3·9 mL/min per 1·73 m2 per year (difference 1·0 mL/min per 1·73 m2 per year, 95% CI -0·03 to 1·94; p=0·058). The significant reduction in proteinuria at 36 weeks with sparsentan was maintained throughout the study period; at 110 weeks, proteinuria, as determined by the change from baseline in urine protein-to-creatinine ratio, was 40% lower in the sparsentan group than in the irbesartan group (-42·8%, 95% CI -49·8 to -35·0, with sparsentan versus -4·4%, -15·8 to 8·7, with irbesartan; geometric least-squares mean ratio 0·60, 95% CI 0·50 to 0·72). The composite kidney failure endpoint was reached by 18 (9%) of 202 patients in the sparsentan group versus 26 (13%) of 202 patients in the irbesartan group (relative risk 0·7, 95% CI 0·4 to 1·2). Treatment-emergent adverse events were well balanced between sparsentan and irbesartan, with no new safety signals.

INTERPRETATION

Over 110 weeks, treatment with sparsentan versus maximally titrated irbesartan in patients with IgA nephropathy resulted in significant reductions in proteinuria and preservation of kidney function.

FUNDING

Travere Therapeutics.