Hypoxia-inducible Factor Prolyl Hydroxylase Domain Research Articles

Safety and Efficacy of Hypoxia-Inducible Factor-Prolyl Hydroxylase Inhibitors vs. Erythropoietin-Stimulating Agents in Treating Anemia in Renal Patients (With or Without Dialysis): A Meta-Analysis and Systematic Review.

Hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) are a novel group of drugs used to treat renal anemia, but their benefits vary among different trials. Our meta-analysis aims to assess the safety and efficacy of HIF-PHI versus erythropoiesis-stimulating agents (ESA) in managing anemia among patients with chronic kidney disease (CKD), regardless of their dialysis status. PubMed, Embase, and Google Scholar were queried to discover eligible randomized controlled trials (RCTs). To quantify the specific effects of HIF-PHI, we estimated pooled mean differences (MDs) and relative risks (RR) with 95% CIs. Our meta-analysis involved 22,151 CKD patients, with 11,234 receiving HIF-PHI and 10,917 receiving ESA from 19 different RCTs. The HIF-PHI used included roxadustat, daprodustat, and vadadustat. HIF-PHI yielded a slight but significant increase in change in mean hemoglobin (Hb) levels (MD: 0.06, 95% CI (0.00, 0.11); p = 0.03), with the maximum significant increase shown in roxadustat followed by daprodustat as compared to ESA. There was a significant decrease in efficacy outcomes such as change in mean iron (MD: -1.54, 95% CI (-3.01, -0.06); p = 0.04), change in mean hepcidin (MD: -21.04, 95% CI (-28.92, -13.17); p < 0.00001), change in mean ferritin (MD: -16.45, 95% CI (-27.17,-5.73); p = 0.03) with roxadustat showing maximum efficacy followed by daprodustat. As for safety, HIF-PHI showed significantly increased incidence in safety outcomes such as diarrhea (MD: 1.3, 95% CI (1.11, 1.51); p = 0.001), adverse events leading to withdrawal (MD: 2.03, 95% CI (1.5, 2.74), p = 0.00001) among 25 various analyzed outcomes. This meta-analysis indicates that HIF-PHIs present a potentially safer and more effective alternative to ESAs, with increased Hb levels and decreased iron usage in CKD patients without significantly increasing adverse events. Therefore, in these patients, we propose HIF-PHI alongside renal anemia treatment.

First evidence of the incorporation of daprodustat and other hypoxia-inducible factor stabilizers into equine hair by passive transfer based on segmental quantitative analysis

Daprodustat is a hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) inhibitor and is used as an erythropoiesis stimulant for the treatment of anemia in humans. In general, administering daprodustat to horses will result in a lifetime ban from both equestrian sports and horseracing by the International Federation of Horseracing Authorities and the Fédération Équestre Internationale, respectively. To control the misuse/abuse of daprodustat, we conducted nasoesophageal administration of daprodustat (100 mg/day for 3 days) to three thoroughbred mares and the post-administration hair samples collected from the three horses over 6 months were analyzed to demonstrate the potential longer-term detection of daprodustat and its metabolites in hair compared with the detection times of daprodustat of 1 and 2 weeks in plasma and urine respectively. The results of the quantitative 2-cm segmental analysis showed that daprodustat was primarily localized in the proximal region (0–2 cm) at 0.375–0.463 pg/mg at 1 month post-administration. These drug bands were gradually spread out along the hair shaft at a rate consistent with the reported growth rate of horse mane hair (approximately 2.5 cm/month) over the following 6 months. In addition, to attain deeper insight into the mechanism of drug incorporation into hair, a total of 11 relevant parameters, including the actual PK parameters and simulated physicochemical and biopharmaceutical parameters for three HIF stabilizers (i.e., daprodustat, vadadustat, and IOX4), were investigated after normalization of the z-scores of all these parameters. Multiple regression analysis indicated that the major factors contributing to the incorporation of the three drugs into hair were their maximum plasma concentrations and lipophilicities, strongly suggesting that the three HIF stabilizers permeated from the bloodstream into the hair bulb via passive transfer with concentration gradients. This work is the first reported evidence showing the incorporation of HIF stabilizers into hair via passive transfer. In addition, cross-species comparison of drug incorporations into hair between daprodustat in horse and roxadustat in human was made in order to have a better understanding of the interactive interpretations about the analysis results obtained from different species. The above findings are not only useful and beneficial for the purpose of doping control but also provide a better understanding of the mechanism of drug incorporation into horse hair.

#3715 THE EFFECT OF DAPRODUSTAT ON INTRAVENOUS IRON USE IN PATIENTS WITH CKD-RELATED ANAEMIA ON DIALYSIS IN THE ASCEND TRIALS

Abstract Background and Aims Intravenous (IV) iron is frequently needed in patients with chronic kidney disease (CKD) to ensure sufficient iron is available for erythropoiesis. However high doses of IV iron and erythropoiesis stimulating agents (ESAs) may be associated with risks in these patients [1]. The hypoxia-inducible factor-prolyl hydroxylase domain inhibitor daprodustat was non-inferior to comparator ESAs for the primary endpoint of efficacy (change-in-Hb) in the multicentre, randomised, Phase 3 trials ASCEND-D (NCT02879305) [2] and ASCEND-TD (NCT03400033) [3], also for the safety (major adverse cardiovascular [CV] events) coprimary endpoint in ASCEND-D [2]. This analysis of ASCEND-D and ASCEND-TD compared daprodustat to active ESAs on measures of IV iron use in dialysis patients. Method Daprodustat and ESAs were compared in patients with CKD anaemia on haemodialysis/peritoneal dialysis (ASCEND-D); haemodialysis (ASCEND-TD). ASCEND-D (N = 2,964) was an open-label CV outcome study using daprodustat once daily, while ASCEND-TD (N = 407) was a double-blind, double-dummy, 52-week study investigating three times weekly dosing of daprodustat. In both studies, following randomisation, treatment dosage was titrated to achieve the Hb target range of 10.0–11.0g/dL, with Hb efficacy assessed during the evaluation period (EP), Weeks 28–52. All patients were required to have ferritin &amp;gt;100 ng/mL and/or transferrin saturation (TSAT) &amp;gt;20% at baseline for inclusion. Throughout the study, iron therapy was administered if ferritin was ≤100 ng/mL and/or TSAT was ≤20% so patients would remain iron replete throughout the study. Investigators chose the route and dose of iron administration per patient iron status and clinical judgement. Stopping threshold criteria of 800 ng/mL ferritin + TSAT &amp;gt;20%, or TSAT&amp;gt;40% were implemented to avoid iron overload, but investigators could stop administration of iron at levels below the protocol-defined stopping thresholds. The average monthly IV iron dose (mg)/patient to Week 52 was a principal secondary endpoint, while the proportion of patients who met iron management criteria with a decrease in monthly IV iron dose during the EP relative to baseline and until patients received first transfusion were exploratory endpoints. The baseline monthly IV iron dose was defined as the average monthly IV iron (mg) over the 16 weeks prior to randomisation for ASCEND-D and over the 12 weeks prior to randomisation for ASCEND-TD. Results The proportion of patients with IV iron use at baseline was similar in both treatment arms for ASCEND-D (64%) but lower in the daprodustat group in ASCEND-TD (63% vs 72% in the ESA group). In both studies the proportion of patients receiving IV iron during the EP decreased (ASCEND-D: daprodustat 49%, ESA 52%; ASCEND-TD: daprodustat 38%, ESA 40%). The average monthly IV iron dose during the EP and from Day 1 to Week 52 was lower than monthly IV iron dose at baseline, however daprodustat was not associated with a statistically significant reduction in monthly IV iron per patient to Week 52 vs ESA comparator (Table 1). After a period of IV iron requirements decreasing, based on adjustment to protocol-specified levels, IV iron dosage remained relatively stable for daprodustat and ESA (Figure 1). In ASCEND-D, 3 of 23 pre-defined subgroups (prior ESA dose group, ESA hyporesponders2, history of myocardial infarction) showed a trend towards heterogeneity (interaction p-value &amp;lt;0.1), with differences in monthly IV iron use in the prior ESA dose group receiving ≥7000 U/week (-21.2 mg/month) and in the ESA hyporesponder group (-31.7 mg/month) in favour of daprodustat. Fewer patients met the criteria for stopping iron while on daprodustat vs ESA, whereas the converse was observed in ASCEND-TD (Table 1). Conclusion In ASCEND-D and -TD, no clinically or statistically significant reduction in monthly IV iron use was seen with daprodustat vs ESA comparators, although there was a numerical decrease in the proportion of patients receiving IV iron during the EP for the daprodustat group in both studies.

Managing Anemia: Point of Convergence for Heart Failure and Chronic Kidney Disease?

The pathologic triangle formed by chronic heart failure (HF), chronic kidney disease (CKD), and anemia carries high morbidity and mortality rates and decreases quality of life. Anemia represents a common condition in patients with advanced HF and CKD, with a total prevalence in cardiorenal syndrome (CRS) ranging from 5% to 55%. Searching for a pragmatic approach for these patients with guided and disease-specific recommendations beyond just targeted hemoglobin therapeutic behavior represents the core of research for ongoing clinical trials. It is well known that the prevalence of anemia increases with the advancement of CKD and HF. The physiopathological mechanisms of anemia, such as the reduction of endogenous erythropoietin and the decrease in oxygen transport, are leading to tissue hypoxia, peripheral vasodilation, stimulating neurohormonal activity, and maintenance of the progressive renal and cardiac dysfunction. Given the challenges with the treatment options for patients with cardiorenal anemia syndrome (CRSA), new therapeutic agents such as hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PH) or hepcidin antagonists are emerging in the light of recent research. This review summarizes the potential therapeutic tools for anemia therapy in the cardiorenal population.

Effects of hypoxia-inducible factor-prolyl hydroxylase inhibitors vs. erythropoiesis-stimulating agents on iron metabolism in non-dialysis-dependent anemic patients with CKD: A network meta-analysis.

To compare the effects of five hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs), two erythropoiesis-stimulating agents (ESAs), and placebo on iron metabolism in renal anemia patients with non-dialysis-dependent chronic kidney disease (NDD-CKD). Five electronic databases were searched for studies. Randomized controlled clinical trials comparing HIF-PHIs, ESAs, and placebo in NDD-CKD patients were selected. The statistical program used for network meta-analysis was Stata/SE 15.1. The main outcomes were the change in hepcidin and hemoglobin (Hb) levels. The merits of intervention measures were predicted by the surface under the cumulative ranking curve method. Of 1,589 original titles screened, data were extracted from 15 trials (3,228 participants). All HIF-PHIs and ESAs showed greater Hb level-raising ability than placebo. Among them, desidustat demonstrated the highest probability of increasing Hb (95.6%). Hepcidin [mean deviation (MD) = -43.42, 95%CI: -47.08 to -39.76], ferritin (MD= -48.56, 95%CI: -55.21 to -41.96), and transferrin saturation (MD = -4.73, 95%CI: -5.52 to -3.94) were decreased, while transferrin (MD = 0.09, 95%CI: 0.01 to 0.18) and total iron-binding capacity (MD = 6.34, 95%CI: 5.71 to 6.96) was increased in HIF-PHIs versus those in ESAs. In addition, this study observed heterogeneity in the ability of HIF-PHIs to decrease hepcidin. Compared with darbepoetin, only daprodustat (MD = -49.09, 95% CI: -98.13 to -0.05) could significantly reduce hepcidin levels. Meanwhile, daprodustat also showed the highest hepcidin-lowering efficacy (84.0%), while placebo was the lowest (8.2%). For NDD-CKD patients, HIF-PHIs could ameliorate functional iron deficiency by promoting iron transport and utilization, which may be achieved by decreasing hepcidin levels. Interestingly, HIF-PHIs had heterogeneous effects on iron metabolism. https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=242777, Identifier CRD42021242777.

Roxadustat and its failure: A comparative dynamic study

Roxadustat, a small-molecule inhibitor of hypoxia-inducible factor prolyl hydroxylase domain 2 (HIF-PHD2) has been recently overruled by the American Food and Drug Administration (FDA) in Phase 3 clinical trials. This study provides insights into the dynamics of Roxadustat with PHD2 and proposes two FDA-approved drugs; Pemetrexed and Valrubicin to treat chronic kidney disease (CKD). Role of chemical scaffolds such as synthetic pyrimidine-based antifolate is found critical for PHD2 inhibitory activity, which is concurrent with the experimental findings for stimulating Endogenous erythropoietin (EPO) gene expression. Furthermore, Fe+2 and Mn+2 in solution are essential for imparting structural stability to the screened carboxylic and non-carboxylic acid drugs. Comparative analysis of FDA-approved drugs namely, Roxadustat, two-hit carboxylic, and non-carboxylic-acid type compounds (Pemetrexed and Valrubicin), as well as the control ligands (KU1 and 4JR), unveil structural dynamics of Roxadustat and its failure. However, the proposed FDA compounds, Pemetrexed and Valrubicin, used to treat mesothelioma, non-small cell lung cancer, and bladder cancer should be subjected to in vitro analysis for renal anemia.

Pleotropic effects of hypoxia-inducible factor-prolyl hydroxylase domain inhibitors: are they clinically relevant?

Anemia is common in patients with chronic kidney disease (CKD) and is mainly caused by insufficient production of erythropoietin from fibrotic kidney. Because anemia impairs quality of life and overall prognosis, recombinant human erythropoietin-related products (erythropoiesis-stimulating agents, ESAs) have been developed to increase hemoglobin level for decades. However, many safety concerns have been announced regarding the use of ESAs, including an increased occurrence of cardiovascular events, vascular access thrombosis, cancer progression, and recurrence. Hypoxia-inducible factor (HIF) is crucial to erythropoietin production, as a result, prolyl hydroxylase domain (PHD) enzyme inhibitors have been new therapeutic agents for the treatment of anemia in CKD. They can be administered orally, which is a preferred route for patients not undergoing hemodialysis. In clinical trials, PHD inhibitor could induce noninferior effect on erythropoiesis and improve functional iron deficiency compared with ESAs. Although no serious adverse events were reported, safety is still a concern because HIF stabilization induced by PHD inhibitor has pleotropic effects, such as angiogenesis, metabolic change, and cell survival, which might lead to unwanted deleterious effects, including fibrosis, inflammation, cardiovascular risk, and tumor growth. More molecular mechanisms of PHD inhibition and long-term clinical trials are needed to observe these pleotropic effects for the confirmation of safety and efficacy of PHD inhibitors.

Evolving Strategies in the Treatment of Anaemia in Chronic Kidney Disease: The HIF-Prolyl Hydroxylase Inhibitors.

Chronic kidney disease (CKD) affects approximately 10% of the worldwide population; anaemia is a frequent complication. Inadequate erythropoietin production and absolute or functional iron deficiency are the major causes. Accordingly, the current treatment is based on iron and erythropoiesis stimulating agents (ESAs). Available therapy has dramatically improved the management of anaemia and the quality of life. However, safety concerns were raised over ESA use, especially when aiming to reach near-to-normal haemoglobin levels with high doses. Moreover, many patients show hypo-responsiveness to ESA. Hypoxia-inducible factor (HIF) prolyl hydroxylase domain (PHD) inhibitors (HIF-PHIs) were developed for the oral treatment of anaemia in CKD to overcome these concerns. They simulate the body's exposure to moderate hypoxia, stimulating the production of endogenous erythropoietin. Some molecules are already approved for clinical use in some countries. Data from clinical trials showed non-inferiority in anaemia correction compared to ESA or superiority for placebo. Hypoxia-inducible factor-prolyl hydroxylase domain inhibitors may also have additional advantages in inflamed patients, improving iron utilisation and mobilisation and decreasing LDL-cholesterol. Overall, non-inferiority was also shown in major cardiovascular events, except for one molecule in the non-dialysis population. This was an unexpected finding, considering the lower erythropoietin levels reached using these drugs due to their peculiar mechanism of action. More data and longer follow-ups are necessary to better clarifying safety issues and further investigate the variety of pathways activated by HIF, which could have either positive or negative effects and could differentiate HIF-PHIs from ESAs.

Threshold of Serum Ferritin to Discriminate against Those at Greater Risk of Platelet Increase during Treatment with Hypoxia-Inducible Factor Prolyl Hydroxylase Domain Inhibitor

Introduction: Hypoxia-inducible factor prolyl hydroxylase domain inhibitors (HIF-PHI) are a new treatment for renal anemia. HIF-PHI is believed to increase iron usage to improve availability of iron for erythropoiesis. Therefore, there is concern that HIF-PHI might be prone to iron deficiency and that thrombosis might be induced by increased platelet and transferrin levels due to this iron deficiency. Methods: Relationship of iron-related factors with platelet count (PLT) and total iron-binding capacity (TIBC; which reflects the transferrin level) were examined in 29 patients who were treated with darbepoetin alfa (DA) and then switched to roxadustat (Rox). To determine how changes in PLT and TIBC related to changes in iron-related factors, univariable and multivariable linear regression models were applied. To examine what iron-related factors on Day 0 influenced change in PLT, we used receiver operating characteristic (ROC) curves and logistic regression analysis for a rate of change in PLT ≤0% as the endpoint. Logistic regression analysis was performed with the reference group having serum ferritin (s-ft) or Transferrin saturation below the corresponding cutoff value (low vs. high). Results: Multivariable analysis showed significant positive correlations between the rate of change in PLT and the change in s-ft and red blood cells (RBC) count {β-coefficients; 0.40 [95% confidence interval (CI): 0.17–0.62], p = 0.001} (β-coefficients; 30.45 [95% CI: 10.90–50.00], p = 0.004). The rate of change in TIBC was significantly positively correlated with only the change in RBC count. The ROC showed a significant cutoff value for s-ft of 77.2 ng/mL (sensitivity 63.6%, specificity 83.3%, area under the curve 0.76, 95% CI 0.55–0.96). Multivariable logistic regression also showed that only high s-ft was significantly elevated (9.46, 95% CI 1.42–63.30, p = 0.020). Conclusions: This study showed that changes in PLT were correlated with s-ft and amount of hematopoiesis. This suggests that an increase in PLT due to iron levels is less likely when s-ft is 77.2 ng/mL or higher at the time of switching from DA to Rox. In contrast, TIBC was only related to hematopoiesis in these patients. Control of s-ft before initiation of HIF-PHI treatment and gradual hematopoiesis might reduce the risk of thrombosis when switching from erythropoiesis-stimulating agents to HIF-PHI.

Therapeutic Effect of Extracellular Vesicles Derived from HIF Prolyl Hydroxylase Domain Enzyme Inhibitor-Treated Cells on Renal Ischemia/Reperfusion Injury

Introduction: Acute kidney injury (AKI) is a major public health problem worldwide. However, there is no definitive therapies to treat established AKI. In this study, we used FG-4592 to induce hypoxia inducible factor (HIF) expression in cells and then explored whether the extracellular vesicles (EVs) secreted by HIF-upregulated cells could alleviate ischemia/reperfusion injury (IRI)-induced AKI. Methods: FG-4592/HK2-EVs and FG-4592/HEK293-EVs were prepared by treating HK2 or HEK293 cells with FG-4592 for 24 h, respectively. HK2 cells under hypoxia were treated with FG-4592/HK2-EVs or FG-4592/HEK293-EVs to observe the therapeutic effect of EVs on H/R-induced apoptosis and inflammation. Mice were treated with FG-4592/HEK293-EVs after IRI to observe whether FG-4592/HEK293-EVs treatment could alleviate ischemic AKI. Results: The expression of HIF was induced by FG-4592 in a dose-dependent manner in HK2 and HEK293 cells under normoxia. In vitro, FG-4592/HK2-EVs and FG-4592/HEK293-EVs inhibited apoptosis and inflammation induced by H/R. In vivo, treatment with FG-4592/HEK293-EVs significantly ameliorated renal tubular injury and inflammation caused by IRI. In addition, the expression of HIF-1α in cells and kidneys was significantly downregulated by FG-4592/HK2-EVs and FG-4592/HEK293-EVs treatment. Conclusion: This study demonstrated that EVs derived from HK2 or HEK293 cells after FG-4592 treatment could alleviate renal tubular injury and inflammation, suggesting a novel therapeutic role of FG-4592/EVs in the treatment of AKI.

Hypoxia-inducible factor prolyl hydroxylase domain inhibitor may maintain hemoglobin synthesis at lower serum ferritin and transferrin saturation levels than darbepoetin alfa.

BackgroundHypoxia-inducible factor (HIF) prolyl hydroxylase domain inhibitors, which have recently become clinically available for treating renal anemia, are attracting attention for their novel mechanisms of action.MethodsRelationships of reticulocyte hemoglobin content (CHr), which reflects recent Hb synthesis, with serum ferritin (s-ft) and transferrin saturation (TSAT) were examined in 30 patients on hemodialysis after switching from darbepoetin alfa (DA) to roxadustat (Rox). Iron deficiency was defined as CHr < 32.0 pg. Cutoff values of s-ft and TSAT were determined using receiver operating characteristic curves for the endpoint CHr ≥ 32.0 pg. Logistic analysis was performed with the reference group having s-ft or TSAT below the corresponding cutoff value (low vs high).ResultsWith the endpoint CHr ≥ 32.0 pg on Day 0, cutoff values for s-ft and TSAT were respectively 49.7 ng/mL and 21.6% on Day 0 and 35.5 ng/mL and 16.2% on Day 28. With the endpoint CHr ≥ 32.0 pg on Day 28, cutoff values for s-ft and TSAT on Day 0 were 81.6 ng/mL and 23.9%, respectively. According to multivariable logistic analysis, the odds ratios of CHr ≥ 32.0 pg on Day 0 were significantly higher for high TSAT on Day 0 [34.7 (95% CI 2.42–131.0), p<0.003] and Day 28 [24.8 (95% CI 2.75–224.0), p = 0.004]. There were no significant differences by s-ft. Odd ratios of CHr ≥ 32.0 pg on Day 28 were also significantly higher for high s-ft on Day 0 [16.0 (95% CI 1.57–163.0), p = 0.019] and high TSAT on Day 0 [13.5 (95% CI 1.24–147.0), p<0.033].ConclusionsOur results suggest Hb synthesis was maintained with lower TSAT and s-ft during Rox therapy compared with DA therapy. To avoid iron deficiency during the 4 weeks after switching DA to Rox, ideal s-ft and TSAT levels before the switch are 81.6 ng/mL and 23.9%, respectively.

Novel roles of HIF-PHIs in chronic kidney disease: the link between iron metabolism, kidney function, and FGF23

Hanudel etal. investigated the effects of hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) on iron metabolism in a chronic kidney disease (CKD) mouse model and showed that vadadustat, an HIF-PHI, exerted beneficial effects on anemia and iron disorders independently of erythroferrone. Vadadustat also inhibited the progression of CKD and the CKD-associated increase of plasma fibroblast growth factor 23 in CKD mice. This study provides new insights into the action of HIF-PIHs in CKD.

Hypoxia-inducible factor prolyl hydroxylase domain (PHD) inhibition after contusive spinal cord injury does not improve locomotor recovery

Traumatic spinal cord injury (SCI) is a devastating neurological condition that involves both primary and secondary tissue loss. Various cytotoxic events including hypoxia, hemorrhage and blood lysis, bioenergetic failure, oxidative stress, endoplasmic reticulum (ER) stress, and neuroinflammation contribute to secondary injury. The HIF prolyl hydroxylase domain (PHD/EGLN) family of proteins are iron-dependent, oxygen-sensing enzymes that regulate the stability of hypoxia inducible factor-1α (HIF-1α) and also mediate oxidative stress caused by free iron liberated from the lysis of blood. PHD inhibition improves outcome after experimental intracerebral hemorrhage (ICH) by reducing activating transcription factor 4 (ATF4)-driven neuronal death. As the ATF4-CHOP (CCAAT-enhancer-binding protein homologous protein) pathway plays a role in the pathogenesis of contusive SCI, we examined the effects of PHD inhibition in a mouse model of moderate T9 contusive SCI in which white matter damage is the primary driver of locomotor dysfunction. Pharmacological inhibition of PHDs using adaptaquin (AQ) moderately lowers acute induction of Atf4 and Chop mRNAs and prevents the acute decline of oligodendrocyte (OL) lineage mRNAs, but does not improve long-term recovery of hindlimb locomotion or increase chronic white matter sparing. Conditional genetic ablation of all three PHD isoenzymes in OLs did not affect Atf4, Chop or OL mRNAs expression levels, locomotor recovery, and white matter sparing after SCI. Hence, PHDs may not be suitable targets to improve outcomes in traumatic CNS pathologies that involve acute white matter injury.

Hypoxia-inducible factor–prolyl hydroxylase inhibitors in the treatment of anemia of chronic kidney disease

Hypoxia-inducible factor-prolyl hydroxylase domain inhibitors (HIF-PHIs) are a promising new class of orally administered drugs currently in late-stage global clinical development for the treatment of anemia of chronic kidney disease (CKD). HIF-PHIs activate the HIF oxygen-sensing pathway and are efficacious in correcting and maintaining hemoglobin levels in patients with non-dialysis- and dialysis-dependent CKD. In addition to promoting erythropoiesis through the increase in endogenous erythropoietin production, HIF-PHIs reduce hepcidin levels and modulate iron metabolism, providing increases in total iron binding capacity and transferrin levels, and potentially reducing the need for i.v. iron supplementation. Furthermore, HIF-activating drugs are predicted to have effects that extend beyond erythropoiesis. This review summarizes clinical data from current HIF-PHI trials in patients with anemia of CKD, discusses mechanisms of action and pharmacologic properties of HIF-PHIs, and deliberates over safety concerns and potential impact on anemia management in patients with CKD.

Pyrazolo[4,3-d]pyrimidine Derivatives as a Novel Hypoxia-Inducible Factor Prolyl Hydroxylase Domain Inhibitor for the Treatment of Anemia.

Inhibition of hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) promotes erythropoietin (EPO) production by stabilizing the HIFα subunit. Thieno[2,3-d]pyrimidine 8 identified based on X-ray crystal structure analysis was optimized to lead to the discovery of pyrazolo[4,3-d]pyrimidine 13 as the lead compound of orally bioavailable HIF-PHD inhibitors. Conversion of the benzyl moiety in 13 gave pyrazolopyrimidine 19 with high solubility and bioavailability, which increased hemoglobin levels in anemic model rats after repeated oral administration. It was shown that pyrazolo[4,3-d]pyrimidine derivatives are promising therapeutic agents for renal anemia through the inhibition of HIF-PHD.

Got glycogen? An energy resource in HIF-mediated prevention of ischemic kidney injury

Hypoxia-inducible factor activation reprograms glucose metabolism and leads to glycogen accumulation in multiple cell types. In this issue of Kidney International, Ito and colleagues demonstrate that pharmacologic inhibition of hypoxia-inducible factor-prolyl hydroxylase domain oxygen sensors in renal epithelial cells enhances glycogen synthesis and protects from subsequent hypoxia and glucose deprivation. Invivo studies advance the concept that renal glycogen metabolism contributes to cytoprotection afforded by pre-ischemic hypoxia-inducible factor-prolyl hydroxylase domain inhibition.

Hypoxia Pathway Proteins in Normal and Malignant Hematopoiesis.

The regulation of oxygen (O2) levels is crucial in embryogenesis and adult life, as O2 controls a multitude of key cellular functions. Low oxygen levels (hypoxia) are relevant for tissue physiology as they are integral to adequate metabolism regulation and cell fate. Hence, the hypoxia response is of utmost importance for cell, organ and organism function and is dependent on the hypoxia-inducible factor (HIF) pathway. HIF pathway activity is strictly regulated by the family of oxygen-sensitive HIF prolyl hydroxylase domain (PHD) proteins. Physiologic hypoxia is a hallmark of the hematopoietic stem cell (HSC) niche in the bone marrow. This niche facilitates HSC quiescence and survival. The present review focuses on current knowledge and the many open questions regarding the impact of PHDs/HIFs and other proteins of the hypoxia pathway on the HSC niche and on normal and malignant hematopoiesis.

Hypoxia-Inducible Factor-Prolyl Hydroxylase Domain Inhibitors to Treat Anemia in Chronic Kidney Disease.

Hypoxia-inducible factor (HIF) stabilizers, also known as inhibitors of HIF prolyl hydroxylase domain (PHD) inhibitors enzymes, are novel small-molecule agents to treat renal anemia. They increase endogenous erythropoietin (EPO) production by stabilizing HIF. This review focuses on the mechanisms by which PHD inhibitors ameliorate anemia in chronic kidney disease (CKD) and summarizes the current clinical experience with and prospects for these drugs. Anemia is a serious complication of CKD and is an independent risk factor for congestive heart failure. Appropriate treatment of anemia is important in the management of advanced stage CKD, as it might help to extend life expectancy and improve the physical function of patients with CKD. However, at present, adverse effects of treatment, such as thromboembolic events, as well as high therapeutic cost have a negative impact on society. PHD inhibitors stabilize the transcription factor HIF, increasing the expression of downstream target genes, including EPO and enzymes involved in iron metabolism, resulting in increased EPO production and improved iron utilization. Key Messages: The potential advantages of PHD inhibitors over conventional EPO-based therapies include a more physiologic response to renal anemia, noninvasive oral administration, and lower cost. Phase III trials of more than 5 PHD inhibitors are ongoing, with overall demonstration of success in increasing hemoglobin levels. In this review, we focus on the mechanisms of PHD inhibitors in improving renal anemia in CKD and summarize the current clinical findings regarding these drugs.

Clinical Trial of Vadadustat in Patients with Anemia Secondary to Stage 3 or 4 Chronic Kidney Disease

Background: Therapeutic options for the treatment of anemia secondary to chronic kidney disease (CKD) remain limited. Vadadustat (AKB-6548) is an oral hypoxia-inducible factor prolyl-hydroxylase domain (HIF-PHD) inhibitor that is being investigated for the treatment of anemia secondary to CKD. Methods: A phase 2a, multicenter, randomized, double-blind, placebo-controlled, dose-ranging trial (NCT01381094) was undertaken in adults with anemia secondary to CKD stage 3 or 4. Eligible subjects were evenly randomized to 5 groups: 240, 370, 500, or 630 mg of once-daily oral vadadustat or placebo for 6 weeks. All subjects received low-dose supplemental oral iron (50 mg daily). The primary endpoint was the mean absolute change in hemoglobin (Hb) from baseline to the end of treatment. Secondary endpoints included iron indices, safety, and tolerability. Results: Ninety-three subjects were randomized. Compared with placebo, vadadustat significantly increased Hb after 6 weeks in a dose-dependent manner (analysis of variance; p < 0.0001). Vadadustat increased the total iron-binding capacity and decreased concentrations of ferritin and hepcidin. The proportion of subjects with at least 1 treatment-emergent adverse event was similar between vadadustat- and placebo-treated groups. No significant changes in blood pressure, vascular endothelial growth factor, C-reactive protein, or total cholesterol were observed. Limitations of this study included its small sample size and short treatment duration. Conclusions: Vadadustat increased Hb levels and improved biomarkers of iron mobilization and utilization in patients with anemia secondary to stage 3 or 4 CKD. Global multicenter, randomized phase 3 trials are ongoing in non-dialysis-dependent and dialysis-dependent patients.

Therapeutic targeting of oxygen-sensing prolyl hydroxylases abrogates ATF4-dependent neuronal death and improves outcomes after brain hemorrhage in several rodent models.

Disability or death due to intracerebral hemorrhage (ICH) is attributed to blood lysis, liberation of iron, and consequent oxidative stress. Iron chelators bind to free iron and prevent neuronal death induced by oxidative stress and disability due to ICH, but the mechanisms for this effect remain unclear. We show that the hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) family of iron-dependent, oxygen-sensing enzymes are effectors of iron chelation. Molecular reduction of the three HIF-PHD enzyme isoforms in the mouse striatum improved functional recovery after ICH. A low-molecular-weight hydroxyquinoline inhibitor of the HIF-PHD enzymes, adaptaquin, reduced neuronal death and behavioral deficits after ICH in several rodent models without affecting total iron or zinc distribution in the brain. Unexpectedly, protection from oxidative death in vitro or from ICH in vivo by adaptaquin was associated with suppression of activity of the prodeath factor ATF4 rather than activation of an HIF-dependent prosurvival pathway. Together, these findings demonstrate that brain-specific inactivation of the HIF-PHD metalloenzymes with the blood-brain barrier-permeable inhibitor adaptaquin can improve functional outcomes after ICH in several rodent models.