Post hoc analysis of the SONAR trial indicates that the endothelin receptor antagonist atrasentan is associated with less pain in patients with type 2 diabetes and chronic kidney disease

Pain is prevalent among patients with diabetes and chronic kidney disease (CKD). The management of chronic pain in these patients is limited by nephrotoxicity of commonly used drugs including non-steroidal anti-inflammatory drugs (NSAIDs) and opioids. Since previous studies implicated endothelin-1 in pain nociception, our post hoc analysis of the SONAR trial assessed the association between the endothelin receptor antagonist atrasentan and pain and prescription of analgesics. SONAR was a randomized, double-blind, placebo-controlled clinical trial that recruited participants with type 2 diabetes and CKD (estimated glomerular filtration rate 25-75 ml/min/1.73 m2; urinary albumin-to-creatinine ratio 300-5000 mg/g). Participants were randomized to receive atrasentan or placebo (1834 each arm). The main outcome was pain-related adverse events (AEs) reported by investigators. We applied Cox regression to assess the effect of atrasentan compared to placebo on the risk of the first reported pain-related AE and, secondly, first prescription of analgesics. We used the Anderson-Gill method to assess effects on all (first and subsequent) pain-related AEs. During 2.2-year median follow-up, 1183 pain-related AEs occurred. Rates for the first pain-related event were 138.2 and 170.2 per 1000 person-years in the atrasentan and placebo group respectively (hazard ratio 0.82 [95% confidence interval 0.72-0.93]). Atrasentan also reduced the rate of all (first and subsequent) pain-related AEs (rate ratio 0.80 [0.70-0.91]). These findings were similar after accounting for competing risk of death (sub-hazard ratio 0.81 [0.71-0.92]). Patients treated with atrasentan initiated fewer analgesics including NSAIDs and opioids compared to placebo during follow-up (hazard ratio = 0.72 [0.60-0.88]). Thus, atrasentan was associated with reduced pain-related events and pain-related use of analgesics in carefully selected patients with type 2 diabetes and CKD.

Endothelin Receptor Antagonists in Kidney Disease

Endothelin (ET) is found to be increased in kidney disease secondary to hyperglycaemia, hypertension, acidosis, and the presence of insulin or proinflammatory cytokines. In this context, ET, via the endothelin receptor type A (ET_A) activation, causes sustained vasoconstriction of the afferent arterioles that produces deleterious effects such as hyperfiltration, podocyte damage, proteinuria and, eventually, GFR decline. Therefore, endothelin receptor antagonists (ERAs) have been proposed as a therapeutic strategy to reduce proteinuria and slow the progression of kidney disease. Preclinical and clinical evidence has revealed that the administration of ERAs reduces kidney fibrosis, inflammation and proteinuria. Currently, the efficacy of many ERAs to treat kidney disease is being tested in randomized controlled trials; however, some of these, such as avosentan and atrasentan, were not commercialized due to the adverse events related to their use. Therefore, to take advantage of the protective properties of the ERAs, the use of ET_A receptor-specific antagonists and/or combining them with sodium-glucose cotransporter 2 inhibitors (SGLT2i) has been proposed to prevent oedemas, the main ERAs-related deleterious effect. The use of a dual angiotensin-II type 1/endothelin receptor blocker (sparsentan) is also being evaluated to treat kidney disease. Here, we reviewed the main ERAs developed and the preclinical and clinical evidence of their kidney-protective effects. Additionally, we provided an overview of new strategies that have been proposed to integrate ERAs in kidney disease treatment.

Increase in BNP in Response to Endothelin-Receptor Antagonist Atrasentan Is Associated With Incident Heart Failure

BACKGROUND

The endothelin receptor antagonist atrasentan reduced the risk of kidney failure in patients with type 2 diabetes mellitus and chronic kidney disease (CKD) in the SONAR (Study of Diabetic Nephropathy with Atrasentan) trial, although with a numerically higher incidence of heart failure (HF) hospitalization.

OBJECTIVES

The purpose of this study was to assess if early changes in B-type natriuretic peptide (BNP) and body weight during atrasentan treatment predict HF risk.

METHODS

Participants with type 2 diabetes and CKD entered an open-label enrichment phase to assess response to atrasentan 0.75 mg/day. Participants without substantial fluid retention (>3 kg body weight increase or BNP increase to >300 pg/mL), were randomized to atrasentan 0.75 mg/day or placebo. Cox proportional hazards regression was used to assess the effects of atrasentan vs placebo on the prespecified safety outcome of HF hospitalizations.

RESULTS

Among 3,668 patients, 73 (4.0%) participants in the atrasentan and 51 (2.8%) in the placebo group developed HF (HR: 1.39; 95% CI: 0.97-1.99; P = 0.072). In a multivariable analysis, HF risk was associated with higher baseline BNP (HR: 2.32; 95% CI: 1.81-2.97) and percent increase in BNP during response enrichment (HR: 1.46; 95% CI: 1.08-1.98). Body weight change was not associated with HF. Exclusion of patients with at least 25% BNP increase during enrichment attenuated the risk of HF with atrasentan (HR: 1.02; 95% CI: 0.66-1.56) while retaining nephroprotective effects (HR: 0.58; 95% CI: 0.44-0.78).

CONCLUSIONS

In patients with type 2 diabetes and CKD, baseline BNP and early changes in BNP in response to atrasentan were associated with HF hospitalization, highlighting the importance of natriuretic peptide monitoring upon initiation of atrasentan treatment. (Study Of Diabetic Nephropathy With Atrasentan [SONAR]; NCT01858532).

The Effect of Atrasentan on Kidney and Heart Failure Outcomes by Baseline Albuminuria and Kidney Function: A Post Hoc Analysis of the SONAR Randomized Trial

BACKGROUND AND OBJECTIVES

Atrasentan reduces the risk of kidney failure but increases the risk of edema and, possibly, heart failure. Patients with severe CKD may obtain greater absolute kidney benefits from atrasentan but may also be at higher risk of heart failure. We assessed relative and absolute effects of atrasentan on kidney and heart failure events according to baseline eGFR and urinary albumin-creatinine ratio (UACR) in a post hoc analysis of the Study of Diabetic Nephropathy with Atrasentan (SONAR) trial.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The effect of atrasentan versus placebo in 3668 patients with type 2 diabetes and CKD with elevated albuminuria was examined in the SONAR trial. We used Cox proportional hazards regression analysis to study effects on the primary kidney outcome (composite of doubling of serum creatinine, kidney failure, or kidney death) and heart failure hospitalization across subgroups of eGFR (<30, ≥30-45, and ≥45 ml/min per 1.73 m²) and UACR (<1000, ≥1000-3000, and ≥3000 mg/g).

RESULTS

Atrasentan reduced the relative risk of the primary kidney outcome (hazard ratio, 0.71; 95% confidence interval, 0.58 to 0.88) consistently across all subgroups of baseline eGFR and UACR (all P interaction >0.21). Patients in the highest UACR and lowest eGFR subgroups, in whom rates of the primary kidney outcome were highest, showed the largest absolute benefit (all P interaction <0.01). The risk of heart failure hospitalization was higher in the atrasentan group (hazard ratio, 1.39; 95% confidence interval, 0.97 to 1.99) and was consistent across subgroups, with no evidence that relative or absolute risks differed across eGFR or UACR subgroups (all P interaction >0.09).

CONCLUSIONS

Atrasentan reduced the relative risk of the primary kidney outcome consistently across baseline UACR and eGFR subgroups. The absolute risk reduction was greater among patients in the lowest eGFR and highest albuminuria category who were at highest baseline risk. Conversely, the relative and absolute risks of heart failure hospitalization were similar across baseline UACR and eGFR subgroups.Clinical Trial registry name and registration number: Study of Diabetic Nephropathy with Atrasentan (SONAR), NCT01858532.

Endothelin Receptor Antagonists as a Potential Treatment of Diabetic Nephropathy: A Systematic Review

Diabetic nephropathy is becoming a more predominant cause of end-stage renal disease, as the prevalence of diabetes mellitus worldwide is on the rise. In this systematic review, we aimed to define the role of endothelin receptor antagonists, in the prevention and treatment of diabetic nephropathy, in addition to determining their safety. For this review, PubMed, Google Scholar, and Cochrane Library databases, in addition to ClinicalTrials.gov, were searched for publications in the last 20 years. We included 14 studies, seven randomized control trials, and seven post hoc analyses in this paper. Atrasentan decreased albuminuria, reduced blood pressure, and improved lipid profiles with more manageable fluid overload-related adverse events than avosentan and bosentan. Overall, endothelin receptor antagonists, in combination with renin-angiotensin-aldosterone system inhibitors, effectively reduce albuminuria and prevent the progression of diabetic kidney disease. However, more extensive clinical trials still need to be conducted to confirm these relationships and to learn more about the specific factors affecting their efficacy in individual patients.

Beneficial effect on podocyte number in experimental diabetic nephropathy resulting from combined atrasentan and RAAS inhibition therapy

Podocyte loss and proteinuria are both key features of human diabetic nephropathy (DN). The leptin-deficient BTBR mouse strain with the ob/ob mutation develops progressive weight gain, type 2 diabetes, and diabetic nephropathy that has many features of advanced human DN, including increased mesangial matrix, mesangiolysis, podocyte loss, and proteinuria. Selective antagonism of the endothelin-1 type A receptor (ET_AR) by atrasentan treatment in combination with renin-angiotensin-aldosterone system inhibition with losartan has been shown to have the therapeutic benefit of lowering proteinuria in patients with DN, but the underlying mechanism for this benefit is not well understood. Using a similar therapeutic approach in diabetic BTBR ob/ob mice, this treatment regimen significantly increased glomerular podocyte number compared with diabetic BTBR ob/ob controls and suggested that parietal epithelial cells were a source for podocyte restoration. Atrasentan treatment alone also increased podocyte number but to a lesser degree. Mice treated with atrasentan demonstrated a reduction in proteinuria, matching the functional improvement reported in humans. This is a first demonstration that treatment with the highly selective ET_AR antagonist atrasentan can lead to restoration of the diminished podocyte number characteristic of DN in humans and thereby underlies the reduction in proteinuria in patients with diabetes undergoing similar treatment. The benefit of ET_AR antagonism in DN extended to a decrease in mesangial matrix as measured by a reduction in accumulations of collagen type IV in both the atrasentan and atrasentan + losartan-treated groups compared with untreated controls.

Endothelin Receptor Antagonists: Status Quo and Future Perspectives for Targeted Therapy

The endothelin axis, recognized for its vasoconstrictive action, plays a central role in the pathology of pulmonary arterial hypertension (PAH). Treatment with approved endothelin receptor antagonists (ERAs), such as bosentan, ambrisentan, or macitentan, slow down PAH progression and relieves symptoms. Several findings have indicated that endothelin is further involved in the pathogenesis of certain other diseases, making ERAs potentially beneficial in the treatment of various conditions. In addition to PAH, this review summarizes the use and perspectives of ERAs in cancer, renal disease, fibrotic disorders, systemic scleroderma, vasospasm, and pain management. Bosentan has proven to be effective in systemic sclerosis PAH and in decreasing the development of vasospasm-related digital ulcers. The selective ERA clazosentan has been shown to be effective in preventing cerebral vasospasm and delaying ischemic neurological deficits and new infarcts. Furthermore, in the SONAR (Study Of Diabetic Nephropathy With Atrasentan) trial, the selective ERA atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease. These data suggest atrasentan as a new therapy in the treatment of diabetic nephropathy and possibly other renal diseases. Preclinical studies regarding heart failure, cancer, and fibrotic diseases have demonstrated promising effects, but clinical trials have not yet produced measurable results. Nevertheless, the potential benefits of ERAs may not be fully realized.

Renoprotection Provided by Additional Diuretic Treatment in Partially Nephrectomized Ren-2 Transgenic Rats Subjected to the Combined RAS and ETA Blockade

Objective

Our previous study in heterozygous Ren-2 transgenic rats (TGR) demonstrated that long-term treatment with endothelin receptor A (ET_A) blocker atrasentan added to the renin-angiotensin system (RAS) blockade had renoprotective effects in a model of chronic kidney disease (CKD) induced by partial nephrectomy. Since ET_A blockade is known to cause edema, we were interested whether diuretic treatment added to this therapy would be beneficial.

Design and Methods

Partial nephrectomy (NX) was performed at the age of 3 months in TGR rats which were subjected to: (i) RAS blockade alone (angiotensin receptor blocker losartan and angiotensin converting enzyme inhibitor trandolapril), (ii) combined RAS (losartan and trandolapril) and ET_A receptor blockade (atrasentan), or (iii) diuretic (hydrochlorothiazide) added to the combined RAS + ET_A blockade for 50 weeks following NX.

Results

At the end of the study systolic blood pressure and cardiac hypertrophy were similarly decreased in all treated groups. Survival was significantly improved by ET_A receptor blockade added to RAS blockade with no further effects of diuretic treatment. However, additional diuretic treatment combined with RAS + ET_A blockade decreased body weight and had beneficial renoprotective effects - reductions of both kidney weight and kidney damage markers. Proteinuria gradually increased in rats treated with RAS blockade alone, while it was substantially lowered by additional ET_A blockade. In rats treated with additional diuretic, proteinuria was progressively reduced throughout the experiment.

Conclusion

A diuretic added to the combined RAS and ET_A blockade has late renoprotective effects in CKD induced by partial nephrectomy in Ren-2 transgenic rats. The diuretic improved: renal function (evaluated as proteinuria and creatinine clearance), renal morphology (kidney mass, glomerular volume), and histological markers of kidney damage (glomerulosclerosis index, tubulointerstitial injury).

Canagliflozin and Renal Events in Diabetes with Established Nephropathy Clinical Evaluation and Study of Diabetic Nephropathy with Atrasentan: what was learned about the treatment of diabetic kidney disease with canagliflozin and atrasentan?

In April 2019, two major Phase 3 randomized clinical trials were published that assessed primary renal outcomes in diabetic kidney disease (DKD) in type 2 diabetes mellitus (T2DM). The Canagliflozin and Renal Events in Diabetes with Established Nephropathy Clinical Evaluation (CREDENCE) tested an already available antidiabetic drug, canagliflozin, and the Study of Diabetic Nephropathy with Atrasentan (SONAR) tested a novel molecule, the endothelin-1 receptor blocker atrasentan, both on top of renin-angiotensin system blockade. Both trials demonstrated significant nephroprotection in patients with overt DKD (albuminuria >300 mg/g urinary creatinine) for combined primary endpoints of end-stage kidney disease (ESKD), doubling of serum creatinine or death from renal or cardiovascular causes in CREDENCE {hazard ratio [HR] 0.70 [95% confidence interval (CI) 0.59-0.82]} and ESKD and doubling of serum creatinine in SONAR [HR 0.65 (95% CI 0.49-0.88)]. Canagliflozin also decreased the secondary renal endpoint ESKD, doubling of serum creatinine or renal death [HR 0.66 (95% CI 0.53-0.81)], which was similar in nature and impact to the primary endpoint in SONAR. In addition, canagliflozin decreased a secondary endpoint of cardiovascular death or hospitalization for heart failure [HR 0.69 (95% CI 0.57-0.83)], whereas atrasentan had no significant impact on a secondary cardiovascular composite endpoint or on hospital admissions for heart failure and, despite restrictive exclusion criteria, there was a non-significant trend towards more frequent episodes of heart failure. Based on these results, canagliflozin will likely be approved for the indication of treating DKD in T2DM and the estimated glomerular filtration rate threshold for prescribing it will be lifted, whereas the future and place of atrasentan in the treatment of DKD remain unclear.

Baseline characteristics and enrichment results from the SONAR trial

AIM

The SONAR trial uses an enrichment design based on the individual response to the selective endothelin receptor antagonist atrasentan on efficacy (the degree of the individual response in the urinary albumin-to-creatinine ratio [UACR]) and safety/tolerability (signs of sodium retention and acute increases in serum creatinine) to assess the effects of this agent on major renal outcomes. The patient population and enrichment results are described here.

METHODS

Patients with type 2 diabetes with an estimated glomerular filtration rate (eGFR) within 25 to 75 mL/min/1.73 m² and UACR between 300 and 5000 mg/g were enrolled. After a run-in period, eligible patients received 0.75 mg/d of atrasentan for 6 weeks. A total of 2648 responder patients in whom UACR decreased by ≥30% compared to baseline were enrolled, as were 1020 non-responders with a UACR decrease of <30%. Patients who experienced a weight gain of >3 kg and in whom brain natriuretic peptide exceeded ≥300 pg/mL, or who experienced an increase in serum creatinine >20% (0.5 mg/dL), were not randomized.

RESULTS

Baseline characteristics were similar for atrasentan responders and non-responders. Upon entry to the study, median UACR was 802 mg/g in responders and 920 mg/g in non-responders. After 6 weeks of treatment with atrasentan, the UACR change in responders was -48.8% (95% CI, -49.8% to -47.9%) and in non-responders was -1.2% (95% CI, -6.4% to 3.9%). Changes in other renal risk markers were similar between responders and non-responders except for a marginally greater reduction in systolic blood pressure and eGFR in responders.

CONCLUSIONS

The enrichment period has successfully identified a population with a profound UACR reduction without clinical signs of sodium retention in whom a large atrasentan effect on clinically important renal outcomes is possible. The SONAR trial aims to establish whether atrasentan confers renal protection.

Rationale and protocol of the Study Of diabetic Nephropathy with AtRasentan (SONAR) trial: A clinical trial design novel to diabetic nephropathy

AIMS

Individuals with diabetes and chronic kidney disease (CKD) are at high risk for renal events. Recent trials of novel treatments have been negative, possibly because of variability in response to treatment of the target risk factor. Atrasentan is a selective endothelin A receptor antagonist that reduces urinary albumin-to-creatinine ratio (UACR), with a large variability between patients. We are assessing its effect on renal outcomes in the Study Of diabetic Nephropathy with AtRasentan (SONAR; NCT01858532) with an enrichment design (>30% lowering of albuminuria) to select patients most likely to benefit.

MATERIALS AND METHODS

SONAR is a randomized, double-blind, placebo-controlled trial with approximately 3500 participants who have stage 2-4 CKD and macroalbuminuria and are receiving a maximum tolerated dose of a renin-angiotensin system inhibitor.

RESULTS

After 6 weeks of exposure to atrasentan 0.75 mg once daily (enrichment period), participants with ≥30% UACR decrease and no tolerability issues (responders) were randomly assigned to placebo or atrasentan 0.75 mg/day. The responder group will be used for primary efficacy and safety analyses. Approximately 1000 participants with <30% UACR reduction (non-responders) were also randomized to placebo or atrasentan. The primary endpoint is a composite of a sustained doubling of serum creatinine or end-stage renal disease. The original power calculation indicated that a total of 425 primary renal events in the responder group provides 90% power to detect a 27% reduction in relative risk (alpha level of .05).

CONCLUSION

SONAR aims to determine whether atrasentan added to guideline-recommended therapies safely reduces the risk of CKD progression and delays the onset of end-stage renal disease in patients with type 2 diabetes and nephropathy. SONAR also aims to establish whether the enrichment of patients based on their initial "surrogate" response to atrasentan will deliver a trial design in accord with personalized treatment of diabetic kidney disease.

Prevention of the progression of renal injury in diabetic rodent models with preexisting renal disease with chronic endothelin A receptor blockade

The endothelin (ET) system has emerged as a therapeutic target for the treatment of diabetic nephropathy (DN). The present study examined whether chronic endothelin A (ET_A) receptor blockade with atrasentan prevents the progression of renal injury in two models of DN with preexisting renal disease that exhibit an increased renal ET-1 system compared with nondiabetic rats: streptozotocin-treated Dahl salt-sensitive (STZ-SS) and type 2 diabetic nephropathy (T2DN) rats. Nine week-old SS rats were treated with (STZ; 50 mg/kg ip) to induce diabetes. After 3 wk of diabetes, proteinuria increased to 353 ± 34 mg/day. The rats were then separated into two groups: 1) vehicle and 2) atrasentan (5 mg·kg^-1·day^-1) via drinking water. After 6 wk of treatment with atrasentan, mean arterial pressure (MAP) and proteinuria decreased by 12 and 40%, respectively, in STZ-SS rats. The degree of glomerulosclerosis and renal fibrosis was significantly reduced in the kidneys of atrasentan-treated STZ-SS rats compared with vehicle STZ-SS rats. Interestingly, treatment with atrasentan did not affect GFR but significantly increased renal blood flow by 33% and prevented the elevations in filtration fraction and renal vascular resistance by 23 and 20%, respectively, in STZ-SS rats. In contrast to the STZ-SS study, atrasentan had no effect on MAP or proteinuria in T2DN rats. However, treatment with atrasentan significantly decreased glomerular injury and renal fibrosis and prevented the decline in renal function in T2DN rats. These data indicate that chronic ET_A blockade produces advantageous changes in renal hemodynamics that slow the progression of renal disease and also reduces renal histopathology in the absence of reducing arterial pressure and proteinuria.

Relationship Between Atrasentan Concentrations and Urinary Albumin to Creatinine Ratio in Western and Japanese Patients With Diabetic Nephropathy

PURPOSE

The objective of the current analyses was to characterize the pharmacokinetic properties of atrasentan and the exposure-response relationships for the efficacy end point, urinary albumin to creatinine ratio (UACR), and the treatment-emergent adverse event, peripheral edema, during 8 or 12 weeks of treatment.

METHODS

Results from 3 Phase II, randomized, double-blind, placebo-controlled studies (N = 257) were used for the population pharmacokinetic and exposure-response models. Concentration-time and response data for efficacy and tolerability were analyzed using a nonlinear mixed-effects population analysis and logistic regression approaches.

FINDINGS

The pharmacokinetic data were adequately described by a 2-compartment model with first-order absorption and elimination. After weight was accounted for, no clinically meaningful differences were found in CL/F or V_d/F of the central compartment between Western and Japanese patients. Exposure-response analyses confirmed the efficacy of atrasentan in reducing UACR, with an estimated decrease in UACR of ≥37% when the atrasentan dose was 0.75 mg or higher. No significant association between atrasentan exposure and the rate of edema was identified at atrasentan doses of 0.5, 0.75, and 1.25 mg. The rates of peripheral edema were comparable in patients receiving active treatment and placebo.

IMPLICATIONS

The exposure-response relationships for efficacy and tolerability were consistent between Western and Japanese patients. On the basis of these analyses, a dose of 0.75 mg/d was selected for the Phase III trial. ClinicalTrials.gov identifiers: NCT01356849, NCT01399580, and NCT01424319.

Atrasentan for the treatment of diabetic nephropathy

INTRODUCTION

Endothelin-1 (ET-1) is the most potent vasoconstrictor, and is involved in the renal regulation of salt and water homeostasis. When produced in excess in the kidney, ET-1 promotes proteinuria and tubulointerstitial injury. There is great interest in the clinical use of endothelin receptor antagonists (ERAs) in chronic kidney disease (CKD), mainly in diabetic nephropathy (DN). Areas covered: Physiopathological actions of ET-1 on the kidney. Both dual ETAR/ET_BR (bosentan) or ET_AR specific endothelin antagonists (avosentan and atrasentan, among others), which have progressed to early clinical development, with particular emphasis on atrasentan. Expert opinion: Different phase I and II clinical trials with ERAs in DN, mostly with atrasentan, have shown that these drugs have a marked anti-proteinuric effect on residual proteinuria when administered as add-on therapy in addition to ACEi or ARAII treatment. In the past few years, a series of randomized controlled trials investigating new approaches to DN have provided negative or inconclusive data, or even were terminated due to safety concerns or lack of efficacy. Therefore, we eagerly but cautiously await the results of the ongoing SONAR trial with atrasentan in more than 4,000 patients including assessment of renal and cardiovascular hard-end points (estimated primary completion date, July 2018).

Comparison of exposure response relationship of atrasentan between North American and Asian populations

AIMS

The selective endothelin (ET) A receptor antagonist atrasentan has been shown to lower albuminuria in North American and Asian patients with type 2 diabetes and nephropathy. As drug responses to many drugs may differ between North American and Asian populations, we assessed the influence of geographical region on the albuminuria and fluid retention response to atrasentan.

MATERIALS AND METHODS

Two 12-week double-blind randomised controlled trials were performed with atrasentan 0.75 or 1.25 mg/d vs placebo in patients with type 2 diabetes and nephropathy. The efficacy endpoint was the percentage change in albuminuria. Bodyweight change, a proxy of fluid retention, was used as a safety endpoint. Pharmacodynamics were determined in Asians (N = 77) and North Americans (N = 134). Atrasentan plasma concentration was measured in 161 atrasentan-treated patients.

RESULTS

Mean albuminuria reduction in Asian, compared to North American, patients was, respectively, -34.4% vs -26.3% for 0.75 mg/d ( P  = .44) and -48.0% vs -28.9% for 1.25 mg/d ( P  = .035). Bodyweight gain did not differ between North American and Asian populations. Atrasentan plasma concentrations were higher in Asians compared to North Americans and correlated with albuminuria response (7.2% albuminuria reduction per doubling atrasentan concentration; P  = .024). Body surface area (β = -1.09 per m² ; P  < .001) and bilirubin, as a marker of hepatic organic anion transporter activity, (β = 0.69 per mg/dL increment; P  = .010) were independent determinants of atrasentan plasma concentration; correction by body surface area and bilirubin left no significant difference in plasma concentration between Asian and North American populations.

CONCLUSION

The higher exposure and albuminuria reduction of atrasentan in Asian patients is not associated with more fluid retention, suggesting that Asian patients are less sensitive to atrasentan-induced sodium retention.

Prediction of the effect of atrasentan on renal and heart failure outcomes based on short-term changes in multiple risk markers

BACKGROUND

A recent phase II clinical trial (Reducing Residual Albuminuria in Subjects with Diabetes and Nephropathy with AtRasentan trial and an identical trial in Japan (RADAR/JAPAN)) showed that the endothelin A receptor antagonist atrasentan lowers albuminuria, blood pressure, cholesterol, hemoglobin, and increases body weight in patients with type 2 diabetes and nephropathy. We previously developed an algorithm, the Parameter Response Efficacy (PRE) score, which translates short-term drug effects into predictions of long-term effects on clinical outcomes.

DESIGN

We used the PRE score on data from the RADAR/JAPAN study to predict the effect of atrasentan on renal and heart failure outcomes.

METHODS

We performed a post-hoc analysis of the RADAR/JAPAN randomized clinical trials in which 211 patients with type-2 diabetes and nephropathy were randomly assigned to atrasentan 0.75 mg/day, 1.25 mg/day, or placebo. A PRE score was developed in a background set of completed clinical trials using multivariate Cox models. The score was applied to baseline and week-12 risk marker levels of RADAR/JAPAN participants, to predict atrasentan effects on clinical outcomes. Outcomes were defined as doubling serum creatinine or end-stage renal disease and hospitalization for heart failure.

RESULTS

The PRE score predicted renal risk changes of -23% and -30% for atrasentan 0.75 and 1.25 mg/day, respectively. PRE scores also predicted a small non-significant increase in heart failure risk for atrasentan 0.75 and 1.25 mg/day (+2% vs. +7%). Selecting patients with >30% albuminuria reduction from baseline (responders) improved renal outcome to almost 50% risk reduction, whereas non-responders showed no renal benefit.

CONCLUSIONS

Based on the RADAR/JAPAN study, with short-term changes in risk markers, atrasentan is expected to decrease renal risk without increased risk of heart failure. Within this population albuminuria responders appear to contribute to the predicted improvements, whereas non-responders showed no benefit. The ongoing hard outcome trial (SONAR) in type 2 diabetic patients with >30% albuminuria reduction to atrasentan will allow us to assess the validity of these predictions.

Predictors of Atrasentan-Associated Fluid Retention and Change in Albuminuria in Patients with Diabetic Nephropathy

BACKGROUND AND OBJECTIVES

Endothelin A receptor antagonists (ERAs) decrease residual albuminuria in patients with diabetic kidney disease; however, their clinical utility may be limited by fluid retention. Consequently, the primary objective of this study was to identify predictors for ERA-induced fluid retention among patients with type 2 diabetes and CKD. A secondary objective was to determine if the degree of fluid retention necessarily correlated with the magnitude of albuminuria reduction in those patients receiving ERAs.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A post hoc analysis was conducted of the phase IIb atrasentan trials assessing albuminuria reduction in 211 patients with type 2 diabetes, urine albumin/creatinine ratios of 300-3500 mg/g, and eGFRs of 30-75 ml/min per 1.73 m(2) who were randomly assigned to receive placebo (n=50) or atrasentan 0.75 mg/d (n=78) or 1.25 mg/d (n=83) for 12 weeks. Changes in body weight and hemoglobin (Hb) after 2 weeks of treatment were used as surrogate markers of fluid retention.

RESULTS

Baseline predictors of weight gain after 2 weeks of atrasentan treatment were higher atrasentan dose, lower eGFR, higher glycated hemoglobin, higher systolic BP, and lower homeostatic metabolic assessment product. Higher atrasentan dose and lower eGFR also predicted decreases in Hb. There were no changes in B-type natriuretic peptide. There was no correlation between reduction in albuminuria after 2 weeks of atrasentan treatment and changes in body weight or Hb.

CONCLUSIONS

In the Reducing Residual Albuminuria in Subjects With Diabetes and Nephropathy With Atrasentan/JAPAN trials, atrasentan-associated fluid retention was more likely in patients with diabetes and nephropathy who had lower eGFR or received a higher dose of atrasentan. Finding that albuminuria reduction was not associated with changes in body weight and Hb suggests that the albuminuria-reducing efficacy of atrasentan is not impaired by fluid retention.

Endothelin receptor A blockade enhances taxane effects in prostate cancer

Endothelin (ET) 1 is important in the growth of prostate cancer cells through the activation of the endothelin A (ET(A)) receptor. ET receptor blockade is a new therapeutic target in treating advanced prostate cancer. This study investigates the impact of the combination of the ET(A) antagonist atrasentan (ABT-627) and taxane chemotherapy on prostate cancer cell survival in vitro and on the delay of prostate cancer in a xenograft mouse model. In vitro, PPC-1 cells transfected with an ET(A)-overexpressing vector were treated with ABT-627, paclitaxel/docetaxel, or both. Clonogenic viability and cell death assays were used to determine cell survival and apoptosis, respectively. ABT-627 and docetaxel combination treatment was used in vivo to treat mice with established ET(A)-overexpressing PPC-1 xenograft tumors, and tumor growth rates were assessed. Cell proliferation and vascularity were determined with Ki-67 and CD31 staining, respectively. Cells treated with combination therapy had significantly fewer viable cells and more programmed cell death than cells given monotherapy. Xenograft tumor growth rates were significantly lower in mice treated with combination therapy than in animals given a single agent. Ki-67 immunostaining demonstrated significantly fewer proliferative cells following combination therapy than following monotherapy. This study demonstrates ABT-627 to have additive antitumor effects when used in combination with taxane drugs both in vitro and in vivo.

Hormone-refractory prostate cancer: new horizons

The eighth session of the 13th International Prostate Cancer Update focused on the mechanisms of androgen-independent cancer growth and on new therapeutic approaches to the treatment of androgen-independent prostate cancer. Three possible mechanisms that might account for the development of hormone resistance are reviewed here. These are: changes in antigen receptor expression, changes in androgen receptor structure, and changes in androgen receptor function. Therapeutic approaches discussed include the endothelin receptor antagonist astrasentan; PS-341, a boronic acid dipeptide that is highly selective for proteosome inhibition; the microtubule-stabilizing agent epothilone B; and exisulind, a selective apoptotic antineoplastic drug. The cooperative cancer study groups will move these treatments from their preliminary phase 1 and 2 studies to comparison against the standard of care for hormone-refractory prostate cancer.