Inhibition of hypoxia-inducible factor prolyl hydroxylase domain oxygen sensors: tricking the body into mounting orchestrated survival and repair responses

Pharmacological regulation of HIF-1α, RGC death, and glaucoma

Hypoxia can regulate oxygen-sensitive pathways that could be neuroprotective to compensate for the detrimental effects of low oxygen. However, prolonged hypoxia can activate neurodegenerative pathways. HIF-1α is upregulated/stabilized in hypoxic conditions, promoting alteration of gene expression, and ultimately leading to cell-death. Therefore, regulation of HIF-1α expression pharmacologically is a vital approach to mitigate cell death. In this review, we provide information showing the role of HIF-1α and its associated pathways in ocular retinopathies. We also discuss the beneficial roles of HIF-1α inhibitor, KC7F2, in ocular pathologies. Finally, we provided our own data demonstrating RGC neuroprotection by KC7F2 in glaucomatous animals.

Daprodustat reduces skeletal muscle ischemia-reperfusion injury in mice

PURPOSE

The purpose of the present work was to assess the specific effects and underlying mechanisms of Daprodustat (GSK1278863) on skeletal muscle injury induced by ischemia reperfusion (I/R).

METHODS

C57BL/6 mice were randomized into the skeletal muscle I/R injury (I/R), Daprodustat (GSK1278863) pretreatment and I/R (I/R + GSK) and sham operation (Sham) groups. The skeletal muscle I/R injury model was established by placing an orthodontic rubber band at the left hip joint for 3 h and releasing it for 3 h. H&E staining, wet weight/dry weight ratio assessment, TUNEL assay, ELISA, qRT-PCR and immunoblot were utilized to assess the effects of Daprodustat.

RESULTS

Daprodustat pretreatment significantly ameliorated apoptosis in skeletal muscle cells, reduced oxidative damage and suppressed inflammatory cytokines. Mechanistically, Daprodustat positively affected NF-κB signaling activation.

CONCLUSION

These data demonstrated that Daprodustat may provide a potential clinical approach for preventing or treating skeletal muscle injury induced by I/R.

Application of Deferoxamine in Tissue Regeneration Attributed to Promoted Angiogenesis

Deferoxamine, an iron chelator used to treat diseases caused by excess iron, has had a Food and Drug Administration-approved status for many years. A large number of studies have confirmed that deferoxamine can reduce inflammatory response and promote angiogenesis. Blood vessels play a crucial role in sustaining vital life by facilitating the delivery of immune cells, oxygen, and nutrients, as well as eliminating waste products generated during cellular metabolism. Dysfunction in blood vessels may contribute significantly to the development of life-threatening diseases. Anti-angiogenesis therapy and pro-angiogenesis/angiogenesis strategies have been frequently recommended for various diseases. Herein, we describe the mechanism by which deferoxamine promotes angiogenesis and summarize its application in chronic wounds, bone repair, and diseases of the respiratory system. Furthermore, we discuss the drug delivery system of deferoxamine for treating various diseases, providing constructive ideas and inspiration for the development of new treatment strategies.

Multimodal Imaging Reveals that Sustained Inhibition of HIF-Prolyl Hydroxylases Induces Opposing Effects on Right and Left Ventricular Function in Healthy Rats

PURPOSE

Hypoxia-inducible factor (HIF) drives transcription of critical hypoxia response genes, increasing the production of red blood cells in low oxygen conditions. In the absence of hypoxia, HIF is degraded by prolyl hydroxylases (HIF-PHs). Pharmacological HIF-PH inhibition stabilizes HIF and is being studied as a treatment for anemia. However, like sustained hypoxia, HIF-PH inhibition may increase pulmonary arterial pressure leading to right ventricular hypertrophy. The aim of this study was to assess the cardiac effects of sustained pharmacological HIF-PH inhibition using multimodal imaging, blood analysis, and histology.

METHODS

Rats were dosed daily with a pan HIF-PH inhibitor or vehicle for 4 weeks followed by a 2-week washout period and underwent longitudinal magnetic resonance imaging (MRI) and echocardiography to simultaneously assess RV and LV function. Blood samples from weeks four and six were analyzed to determine red blood cell composition. Histology was performed on the cardiac tissue from a subset of rats at weeks four and six to assess structural effects.

RESULTS

Imaging revealed that RV ejection fraction was reduced in animals receiving HIF-PH inhibitor and resulted in RV hypertrophy. Interestingly, HIF-PH inhibition had the opposite effect on the left ventricle (LV), increasing contractility measured by LV ejection fraction. LV effects were reversed by week six, while RV effects (functional and structural) were sustained.

CONCLUSION

These opposing cardiac effects of HIF-PH inhibition warrant further study to both understand the potential negative effects on RV structure and function and investigate the therapeutic potential of increased LV contractility for conditions like heart failure.

Plasma phospholipids profiling changes were associated with the therapeutic response to Roxadustat in peritoneal dialysis patients

Background: Elevated Phospholipids (PLs) and sphingolipid (SM) metabolism relates to with poor clinical status and adverse outcome of end-stage kidney disease patients undergoing peritoneal dialysis (PD). Studies have suggested that the use of hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI) (Roxadustat) is associated with altered lipid metabolism. Observing on how PLs and SMs changes after the HIF-PHI treatment in PD patients may help understand the possible effect of HIF-PHI on PD patients besides correcting of anemia. Materials and methods: Stable peritoneal dialysis (PD) patients treated with Roxadustat for over 3 months were included. Phospholipid and sphingolipid metabolism were measured before and after treatment. Results: 25 PD patients were included. Overall, phospholipid and sphingolipid metabolism showed a decreasing trend after HIF-PHI treatment. Levels of LysoPC (20:0), 1,2-dilinoleoyl-sn-glycero-3-phosphocholine [CisPC (DLPC) (18:2)], lysophosphatidylethanolamine (LysoPE) (14:0), and sphingomyelin (d18:1/17:0) (17:0) were significantly decreased (all p < 0.05). Further regression analyses confirmed the significant relationship between the increased of hemoglobin levels and the decrease in egg lyso PC: phosphatidylethanolamines (PE) (16:0-18:1), PE (16:0-18:2), PE (16:0-22:6), PE (18:0-20:4), PE (18:0-18:2), LysoPE (18:0), LysoPE (18:1), and phosphatidylcholine (PC) (18:1-18:0). Conclusion: This study demonstrated that phospholipid and sphingolipid metabolism decreased after administration of HIF-PHI and was associated with improvement of anemia.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Lipoylation is dependent on the ferredoxin FDX1 and dispensable under hypoxia in human cells

Iron-sulfur clusters (ISC) are essential cofactors that participate in electron transfer, environmental sensing, and catalysis. Amongst the most ancient ISC-containing proteins are the ferredoxin (FDX) family of electron carriers. Humans have two FDXs- FDX1 and FDX2, both of which are localized to mitochondria, and the latter of which is itself important for ISC synthesis. We have previously shown that hypoxia can eliminate the requirement for some components of the ISC biosynthetic pathway, but FDXs were not included in that study. Here, we report that FDX1, but not FDX2, is dispensable under 1% O2 in cultured human cells. We find that FDX1 is essential for production of the lipoic acid cofactor, which is synthesized by the ISC-containing enzyme lipoyl synthase. While hypoxia can rescue the growth phenotype of either FDX1 or lipoyl synthase KO cells, lipoylation in these same cells is not rescued, arguing against an alternative biosynthetic route or salvage pathway for lipoate in hypoxia. Our work reveals the divergent roles of FDX1 and FDX2 in mitochondria, identifies a role for FDX1 in lipoate synthesis, and suggests that loss of lipoic acid can be tolerated under low oxygen tensions in cell culture.

Oxygen-Sensing Protein Cysteamine Dioxygenase from Mandarin Fish Involved in the Arg/N-Degron Pathway and Siniperca chuatsi Rhabdovirus Infection

Mammalia cysteamine (2-aminoethanethiol) dioxygenase (ADO) controls the stability of the regulator of G protein signaling 4 (RGS4) through the Cys branch of the Arg/N-degron pathway, thereby affecting the response of the body to hypoxia. However, the oxygen-sensing function of ADO remains unknown in teleost fish. Mandarin fish (Siniperca chuatsi) is one of the most important freshwater economic fishes in China. As the scale of the rearing density continues to increase, hypoxia has become an important factor threatening the growth of mandarin fish. Herein, the molecular characterization, the oxygen-sensing enzyme function, and the role in virus infection of ADO from mandarin fish (scADO) were explored. Bioinformation analysis results showed that scADO had all the molecular foundations for achieving thiol dioxygenase function: three histidine residues coordinated with Fe(II), PCO/ADO domain, and a "jelly roll" β-barrel structure. The expression pattern analysis showed that scAdo was highly expressed in the immune-related tissues, liver, and kidneys and responded to hypoxia on the expression level. Protein degradation experiment results revealed that scADO could lead to the degradation of RGS4 protein through the Cys branch of the Arg/N-degron pathway. Furthermore, the expression levels of scADO responded to fish virus infection. scADO could significantly promote the replication of Siniperca chuatsi rhabdovirus, and this was associated with its thiol dioxygenase activity. These findings not only demonstrate scADO as an oxygen-sensing protein in teleost fish, but are also of considerable importance for clarifying the contribution of the mechanism of hypoxia to the outbreaks of fish viruses.

The association between renal accumulation of pancreatic amyloid-forming amylin and renal hypoxia

Chronic kidney disease (CKD) is increasing worldwide and is associated with diabetic states (obesity, prediabetes and type-2 diabetes mellitus). The kidney is intrinsically susceptible to low oxygen (hypoxia) and renal hypoxia plays a vital role in the progression of CKD. Recent studies suggest an association between CKD and renal deposition of amyloid-forming amylin secreted from the pancreas. Renal accumulation of amyloid-forming amylin is associated with hypertension, mitochondrial dysfunction, increased production of reactive oxygen species (ROS) and activation of hypoxia signaling in the kidney. In this review we will discuss potential associations between renal amylin amyloid accumulation, hypertension, and mechanism of hypoxia-induced kidney dysfunction, including activation of hypoxia-inducible factors (HIFs) and mitochondrial dysfunction.

Drug discovery and amyotrophic lateral sclerosis: Emerging challenges and therapeutic opportunities

Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of upper and lower motor neurons (MNs) leading to paralysis and, ultimately, death by respiratory failure 3-5 years after diagnosis. Edaravone and Riluzole, the only drugs currently approved for ALS treatment, only provide mild symptomatic relief to patients. Extraordinary progress in understanding the biology of ALS provided new grounds for drug discovery. Over the last two decades, mitochondria and oxidative stress (OS), iron metabolism and ferroptosis, and the major regulators of hypoxia and inflammation - HIF and NF-κB - emerged as promising targets for ALS therapeutic intervention. In this review, we focused our attention on these targets to outline and discuss current advances in ALS drug development. Based on the challenges and the roadblocks, we believe that the rational design of multi-target ligands able to modulate the complex network of events behind the disease can provide effective therapies in a foreseeable future.

The ribosomal chaperone NACA recruits PHD2 to cotranslationally modify HIF-α

Prolyl hydroxylase domain protein 2 (PHD2)-catalyzed modification of hypoxia-inducible factor (HIF)-α is a key event in oxygen sensing. We previously showed that the zinc finger of PHD2 binds to a Pro-Xaa-Leu-Glu (PXLE) motif. Here, we show that the zinc finger binds to this motif in the ribosomal chaperone nascent polypeptide complex-α (NACA). This recruits PHD2 to the translation machinery to cotranslationally modify HIF-α. Importantly, this cotranslational modification is enhanced by a translational pause sequence in HIF-α. Mice with a knock-in Naca gene mutation that abolishes the PXLE motif display erythrocytosis, a reflection of HIF pathway dysregulation. In addition, human erythrocytosis-associated mutations in the zinc finger of PHD2 ablate interaction with NACA. Tibetans, who have adapted to the hypoxia of high altitude, harbor a PHD2 variant that we previously showed displays a defect in zinc finger binding to p23, a PXLE-containing HSP90 cochaperone. We show here that Tibetan PHD2 maintains interaction with NACA, thereby showing differential interactions with PXLE-containing proteins and providing an explanation for why Tibetans are not predisposed to erythrocytosis.

Improving lipophilicity of 5-(1-acetyl-5-phenylpyrazolidin-3-ylidene)-1,3-dimethylbarbituric acid increases its efficacy to activate hypoxia-inducible factors

Hypoxia-inducible factor (HIF) activators aid the treatment of renal anemia and ischemia. Recently, PyrzA (5-(1-acetyl-5-phenylpyrazolidin-3-ylidene)-1,3-dimethylbarbituric acid), a HIF activator by PHD inhibition without a 2-oxoglutarate moiety was reported. However, PyrzA has low lipophilicity, and it was necessary to improve its solubility by synthesizing derivatives. In this study, we synthesized and evaluated a higher lipophilic derivative of PyrzA and found that it exhibited higher HIF activity and stabilizing ability at low concentrations compared to Roxadustat, a commercially available HIF activator.

Methyltransferase SMYD3 impairs hypoxia tolerance by augmenting hypoxia signaling independent of its enzymatic activity

Hypoxia-inducible factor (HIF)1α, a main transcriptional regulator of the cellular response to hypoxia, also plays important roles in oxygen homeostasis of aerobic organisms, which is regulated by multiple mechanisms. However, the full cellular response to hypoxia has not been elucidated. In this study, we found that expression of SMYD3, a methyltransferase, augments hypoxia signaling independent of its enzymatic activity. We demonstrated SMYD3 binds to and stabilizes HIF1α via co-immunoprecipitation and Western blot assays, leading to the enhancement of HIF1α transcriptional activity under hypoxia conditions. In addition, the stabilization of HIF1α by SMYD3 is independent of HIF1α hydroxylation by prolyl hydroxylases and the intactness of the von Hippel-Lindau ubiquitin ligase complex. Furthermore, we showed SMYD3 induces reactive oxygen species accumulation and promotes hypoxia-induced cell apoptosis. Consistent with these results, we found smyd3-null zebrafish exhibit higher hypoxia tolerance compared to their wildtype siblings. Together, these findings define a novel role of SMYD3 in affecting hypoxia signaling and demonstrate that SMYD3-mediated HIF1α stabilization augments hypoxia signaling, leading to the impairment of hypoxia tolerance.

Preclinical Characterization of Vadadustat (AKB-6548), an Oral Small Molecule Hypoxia-Inducible Factor Prolyl-4-Hydroxylase Inhibitor, for the Potential Treatment of Renal Anemia

Pharmacological inhibition of prolyl-4-hydroxylase domain (PHD) enzymes stabilizes hypoxia-inducible factors (HIFs), transcription factors that activate target genes that, among others, increase erythropoietin (EPO) synthesis, resulting in the production of new red blood cells (RBCs). Herein, we summarize the preclinical characteristics of the small molecule HIF prolyl-4-hydroxylase inhibitor vadadustat (AKB-6548), which is in development for the treatment of anemia in patients with chronic kidney disease (CKD). Vadadustat inhibits the enzyme activity of all three human PHD isozymes, PHD1, PHD2, and PHD3, with similar low nanomolar inhibitory constant values. PHD enzyme inhibition by vadadustat is competitive with endogenous cofactor 2-oxoglutarate and is insensitive to free iron concentration. In the human hepatocellular carcinoma cell line (Hep 3B) and human umbilical vein endothelial cells, PHD inhibition by vadadustat leads to the time- and concentration-dependent stabilization of HIF-1α and HIF-2α In Hep 3B cells, this in turn results in the synthesis and secretion of EPO; vascular endothelial growth factor is not measured at detectable levels. A single oral dose of vadadustat in rats potently increases circulating levels of EPO, and daily oral dosing for 14 days increases RBC indices in healthy rats and in the 5/6 nephrectomy model of CKD. In mice and dogs, once-daily repeat oral dosing increases hemoglobin and hematocrit. Vadadustat has a relatively short half-life in all nonclinical species evaluated and does not accumulate when administered as a single bolus dose (oral or intravenous) or upon repeat oral dosing. The pharmacological profile of vadadustat supports continued development for treatment of renal anemia. SIGNIFICANCE STATEMENT: Vadadustat (AKB-6548) is an orally bioavailable small molecule prolyl-4-hydroxylase inhibitor in development for anemia of chronic kidney disease. It is an equipotent inhibitor of the three human prolyl-4-hydroxylase domain isoforms, which activates erythropoiesis through stabilization of hypoxia-inducible factor (HIF)-1α and HIF-2α, increasing production of erythropoietin, without detectable stimulation of vascular endothelial growth factor.

Elucidation of clearance mechanism of TP0463518, a novel hypoxia-inducible factor prolyl hydroxylase inhibitor: does a species difference in excretion routes exist between humans and animals?

1. TP0463518, a novel hypoxia-inducible factor prolyl hydroxylase inhibitor, is reportedly excreted predominantly through urinary excretion in an unchanged form in humans, with partial biliary excretion also possible. However, the clearance mechanisms remain unclear. The aim of this study was to investigate the clearance mechanisms in humans and to assess species differences in the excretion routes.2. TP0463518 was not metabolised in rat, dog, or human hepatocytes. TP0463518 is a substrate for human BCRP, OATP1B1, OATP1B3, and OAT3, suggesting that renal uptake by OAT3 is probably the predominant clearance route, with hepatic uptake by OATP1B1 and OATP1B3 contributing partially to clearance in humans.3. A species difference in excretion routes was observed. The unchanged urinary excretion rates in humans, male rats, female rats, dogs, and monkeys were 80.7%, 0.1%, 40.9%, 15.2%, and 72.6%, respectively. Urinary excretion was predominant in humans and monkeys, while only biliary excretion was observed in male rats. Uptake studies using hepatocytes showed that the hepatic uptake clearance in rats was 13.6-fold higher than that in humans. Therefore, not only reabsorption via renal tubules, but also hepatic uptake seems to be involved in the species differences in excretion routes between rats and humans.

Prolyl Hydroxylase Domain Protein Inhibitor Not Harboring a 2-Oxoglutarate Scaffold Protects against Hypoxic Stress

Hypoxia-inducible factor-α (HIF-α) activation has shown promising results in the treatment of ischemia, such as stroke, myocardial infarction, and chronic kidney disease. A number of HIF-α activators have been developed to improve the symptoms of these diseases. Many feature 2-oxoglutarate (2-OG) scaffolds that interact with the active centers of prolyl hydroxylase domain-containing proteins (PHDs), displacing the coenzyme 2-OG. This stabilizes HIF-α. Therefore, the specificity of the 2-OG analogs is not high. Here, we identified 5-(1-acetyl-5-phenylpyrazolidin-3-ylidene)-1,3-dimethylbarbituric acid (PyrzA) among over 10 000 compounds as a novel HIF activator that does not contain a 2-OG scaffold. In cultured cells, PyrzA enhanced HIF-α stability and upregulated the expression of HIF target genes. Interestingly, PyrzA decreased HIF-1α prolyl hydroxylation, suggesting that PyrzA may activate HIF to prevent the degradation of HIF-α. These results indicate that PyrzA stabilizes HIF via a novel mechanism and could be a potential HIF activator candidate.

Tetrahydropyridin-4-ylpicolinoylglycines as novel and orally active prolyl hydroxylase 2 (PHD2) inhibitors for the treatment of renal anemia

Prolyl hydroxylase 2 (PHD2) is a key regulatory enzyme responsible for the degradation of hypoxia-inducible factor-α (HIF-α). Pharmacological inhibition of PHD2 stabilizes HIF-α and induces the production of endogenous erythropoietin (EPO), which is regarded as a promising strategy for the treatment of renal anemia. To date, a series of PHD2 inhibitors have been approved or advanced into clinical studies. In this study, we developed a new type of PHD2 inhibitors with the tetrahydropyridin-4-ylpicolinoylglycine scaffold by using a scaffold hopping strategy. Among them, compound 25 showed potent inhibition toward PHD2 with an IC50 of 6.55 ± 0.41 nM. Furthermore, compound 25 upregulated reticulocytes in C57BL/6 mice. The subacute toxicological assay demonstrated 25 has no obvious toxicity in vivo. Overall, compound 25 is a promising candidate for the treatment of renal anemia.

Mapping the m1A, m5C, m6A and m7G methylation atlas in zebrafish brain under hypoxic conditions by MeRIP-seq

BACKGROUND

The epigenetic modifications play important regulatory roles in tissue development, maintenance of physiological functions and pathological process. RNA methylations, including newly identified m1A, m5C, m6A and m7G, are important epigenetic modifications. However, how these modifications are distributed in the transcriptome of vertebrate brains and whether their abundance is altered under pathological conditions are still poorly understood. In this study, we chose the model animal of zebrafish to conduct a systematic study to investigate the mRNA methylation atlas in the brain.

RESULTS

By performing unbiased analyses of the m1A, m5C, m6A and m7G methylation of mRNA, we found that within the whole brain transcriptome, with the increase of the gene expression levels, the overall level of each of these four modifications on the related genes was also progressively increased. Further bioinformatics analysis indicated that the zebrafish brain has an abundance of m1A modifications. In the hypoxia-treated zebrafish brains, the proportion of m1A is decreased, affecting the RNA splicing and zebrafish endogenous retroviruses.

CONCLUSIONS

Our study presents the first comprehensive atlas of m1A, m5C, m6A and m7G in the epitranscriptome of the zebrafish brain and reveals the distribution of these modifications in mRNA under hypoxic conditions. These data provide an invaluable resource for further research on the involvement of m1A, m5C, m6A and m7G in the regulation of miRNA and repeat elements in vertebrates, and provide new thoughts to study the brain hypoxic injury on the aspect of epitranscriptome.

Novel PHD2/HDACs hybrid inhibitors protect against cisplatin-induced acute kidney injury

Acute kidney injury (AKI) is associated with high morbidity and mortality. Cisplatin is a common chemotherapeutic, but its nephrotoxicity-driven AKI limits its clinical application. Currently, there are no specific and satisfactory therapies in the clinic for AKI. Inhibitors of hypoxia-inducible factor prolyl hydroxylase 2 (HIF-PHD2) or histone deacetylase (HDACs) had shown renoprotective effects against AKI in preclinical studies. This study aimed to develop a novel therapeutic to prevent AKI progression by targeting PHD2 and HDACs simultaneously. We designed and synthesized a series of PHD2/HDACs hybrid inhibitors. The initial drug activity screening identified a candidate compound 31c, which exhibited potent inhibitory activities against PHD2 and HDAC1/2/6. Cellular analyses further showed that 31c did not affect cisplatin's antitumor activity in cancer cells but strongly protected cisplatin-induced toxicity on HK-2 cells. In vivo studies with the cisplatin-induced AKI mouse model demonstrated that 31c remarkably alleviated kidney dysfunction with suppressed plasma BUN/SCr and increased EPO levels. The potent renoprotective effects of 31c on AKI were confirmed by significant improvements in pathological kidney conditions in the mouse model. These results suggest that the novel PHD2/HDACs hybrid inhibitor, 31c, has a clinical potential as the renoprotective agent for the treatment/prevention of cisplatin-induced AKI for various cancers.

Metabolic resistance to the inhibition of mitochondrial transcription revealed by CRISPR-Cas9 screen

Cancer cells depend on mitochondria to sustain their increased metabolic need and mitochondria therefore constitute possible targets for cancer treatment. We recently developed small-molecule inhibitors of mitochondrial transcription (IMTs) that selectively impair mitochondrial gene expression. IMTs have potent antitumor properties in vitro and in vivo, without affecting normal tissues. Because therapy-induced resistance is a major constraint to successful cancer therapy, we investigated mechanisms conferring resistance to IMTs. We employed a CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats)-(CRISP-associated protein 9) whole-genome screen to determine pathways conferring resistance to acute IMT1 treatment. Loss of genes belonging to von Hippel-Lindau (VHL) and mammalian target of rapamycin complex 1 (mTORC1) pathways caused resistance to acute IMT1 treatment and the relevance of these pathways was confirmed by chemical modulation. We also generated cells resistant to chronic IMT treatment to understand responses to persistent mitochondrial gene expression impairment. We report that IMT1-acquired resistance occurs through a compensatory increase of mitochondrial DNA (mtDNA) expression and cellular metabolites. We found that mitochondrial transcription factor A (TFAM) downregulation and inhibition of mitochondrial translation impaired survival of resistant cells. The identified susceptibility and resistance mechanisms to IMTs may be relevant for different types of mitochondria-targeted therapies.

A small-molecule inhibitor of hypoxia-inducible factor prolyl hydroxylase improves obesity, nephropathy and cardiomyopathy in obese ZSF1 rats

Prolyl hydroxylase (PH) enzymes control the degradation of hypoxia-inducible factor (HIF), a transcription factor known to regulate erythropoiesis, angiogenesis, glucose metabolism, cell proliferation, and apoptosis. HIF-PH inhibitors (HIF-PHIs) correct anemia in patients with renal disease and in animal models of anemia and kidney disease. However, the effects of HIF-PHIs on comorbidities associated with kidney disease remain largely unknown. We evaluated the effects of the HIF-PHI FG-2216 in obese ZSF1 (Ob-ZSF1) rats, an established model of kidney failure with metabolic syndrome. Following unilateral nephrectomy (Nx) at 8 weeks of age, rats were treated with 40 mg/kg FG-2216 or vehicle by oral gavage three times per week for up to 18 weeks. FG-2216 corrected blood hemoglobin levels and improved kidney function and histopathology in Nx-Ob-ZSF1 rats by increasing the glomerular filtration rate, decreasing proteinuria, and reducing peritubular fibrosis, tubular damage, glomerulosclerosis and mesangial expansion. FG-2216 increased renal glucose excretion and decreased body weight, fat pad weight, and serum cholesterol in Nx-Ob-ZSF1 rats. Additionally, FG-2216 corrected hypertension, improved diastolic and systolic heart function, and reduced cardiac hypertrophy and fibrosis. In conclusion, the HIF-PHI FG-2216 improved renal and cardiovascular outcomes, and reduced obesity in a rat model of kidney disease with metabolic syndrome. Thus, in addition to correcting anemia, HIF-PHIs may provide renal and cardiac protection to patients suffering from kidney disease with metabolic syndrome.

A small molecule HIF-1α stabilizer that accelerates diabetic wound healing

Impaired wound healing and ulcer complications are a leading cause of death in diabetic patients. In this study, we report the design and synthesis of a cyclometalated iridium(III) metal complex 1a as a stabilizer of hypoxia-inducible factor-1α (HIF-1α). In vitro biophysical and cellular analyses demonstrate that this compound binds to Von Hippel-Lindau (VHL) and inhibits the VHL-HIF-1α interaction. Furthermore, the compound accumulates HIF-1α levels in cellulo and activates HIF-1α mediated gene expression, including VEGF, GLUT1, and EPO. In in vivo mouse models, the compound significantly accelerates wound closure in both normal and diabetic mice, with a greater effect being observed in the diabetic group. We also demonstrate that HIF-1α driven genes related to wound healing (i.e. HSP-90, VEGFR-1, SDF-1, SCF, and Tie-2) are increased in the wound tissue of 1a-treated diabetic mice (including, db/db, HFD/STZ and STZ models). Our study demonstrates a small molecule stabilizer of HIF-1α as a promising therapeutic agent for wound healing, and, more importantly, validates the feasibility of treating diabetic wounds by blocking the VHL and HIF-1α interaction.

Targeting oxidative stress, a crucial challenge in renal transplantation outcome

Disorders characterized by ischemia/reperfusion (I/R) are the most common causes of debilitating diseases and death in stroke, cardiovascular ischemia, acute kidney injury or organ transplantation. In the latter example the I/R step defines both the amplitude of the damages to the graft and the functional recovery outcome. During transplantation the kidney is subjected to blood flow arrest followed by a sudden increase in oxygen supply at the time of reperfusion. This essential clinical protocol causes massive oxidative stress which is at the basis of cell death and tissue damage. The involvement of both reactive oxygen species (ROS) and nitric oxides (NO) has been shown to be a major cause of these cellular damages. In fact, in non-physiological situations, these species escape endogenous antioxidant control and dangerously accumulate in cells. In recent years, the objective has been to find clinical and pharmacological treatments to reduce or prevent the appearance of oxidative stress in ischemic pathologies. This is very relevant because, due to the increasing success of organ transplantation, clinicians are required to use limit organs, the preservation of which against oxidative stress is crucial for a better outcome. This review highlights the key actors in oxidative stress which could represent new pharmacological targets.

Discovery of neuroprotective agents that inhibit human prolyl hydroxylase PHD2

Prolyl hydroxylase (PHD) enzymes play a critical role in the cellular responses to hypoxia through their regulation of the hypoxia inducible factor α (HIF-α) transcription factors. PHD inhibitors show promise for the treatment of diseases including anaemia, cardiovascular disease and stroke. In this work, a pharmacophore-based virtual high throughput screen was used to identify novel potential inhibitors of human PHD2. Two moderately potent new inhibitors were discovered, with IC50 values of 4 μM and 23 μM respectively. Cell-based studies demonstrate that these compounds exhibit protective activity in neuroblastoma cells, suggesting that they have the potential to be developed into clinically useful neuroprotective agents.

In silico identification of prolyl hydroxylase inhibitor by per-residue energy decomposition-based pharmacophore approach

Hypoxia is an effective preconditioning stimulus and many cellular responses to hypoxia are mediated through a transcription control complex termed the hypoxia-inducible factor (HIF). The stability and activation of HIF are governed by HIF prolyl-4-hydroxylases 2 (PHD2). Hence, the development of a small molecule inhibitor for prolyl hydroxylase has been suggested as a potentially useful therapeutic strategy for the treatment of oxidative/ischemic stress conditions. Thus, to unveil a novel human PHD2 inhibitor, a custom-based virtual screening was carried out to identify the potential inhibitors against PHD2 based on; (1) the per-residue energy decomposition (PRED)-based pharmacophore model, (2) molecular docking, and (3) MD approaches. The PRED analysis was performed to identify the common interaction pattern of HIF fragment (5L9B) and crystallized ligand (4JZR) to develop a relevant accurate allosteric pharmacophore model. The custom pharmacophore model (AAARR) was developed and further used to screen multiple databases. The docking was performed as a secondary strategy for screening the pharmacophore hits. Furthermore, the docked complexes were screened by molecular dynamics (MD) simulation and molecular mechanics/generalized Born surface area (MM-GBSA) based binding free energy calculations to determine the binding energy of the inhibitors and to identify crucial interaction energy fingerprint. One hit has demonstrated good binding free energy and a better binding affinity for PHD2 compared to the other four selected ligands. Thus, the results obtained from pharmacophore, docking, and MD simulations depicted that linker length and metal binding in the scaffold could be effectively used as a potent inhibitor toward human PHD2 in AD therapeutics.

Frontiers in PROTACs

Targeting protein-protein interactions (PPI) is a key focus in the development of new and emerging small-molecule therapeutics. Shallow interacting surfaces can render PPI targeting notoriously difficult. This leaves many therapeutically captivating targets 'undruggable'. Despite these challenges, there has been extraordinary progress circumventing this issue by hijacking the ubiquitin proteasome system (UPS) to target selected substrates for destruction using target-based degradation (TBD) strategies, including bifunctional molecules known as proteolysis-targeting chimeras (PROTACs). In this review, we discuss some of the most recent innovative concepts emerging from PROTAC research and related technologies.

Development of a colorimetric α-ketoglutarate detection assay for prolyl hydroxylase domain (PHD) proteins

Since the discovery of the prolyl hydroxylases domain (PHD) proteins and their canonical hypoxia-inducible factor (HIF) substrate two decades ago, a number of in vitro hydroxylation (IVH) assays for PHD activity have been developed to measure the PHD-HIF interaction. However, most of these assays either require complex proteomics mass spectrometry methods that rely on the specific PHD-HIF interaction or require the handling of radioactive material, as seen in the most commonly used assay measuring [¹⁴C]O₂ release from labeled [¹⁴C]α-ketoglutarate. Here, we report an alternative rapid, cost-effective assay in which the consumption of α-ketoglutarate is monitored by its derivatization with 2,4-dinitrophenylhydrazine (2,4-DNPH) followed by treatment with concentrated base. We extensively optimized this 2,4-DNPH α-ketoglutarate assay to maximize the signal-to-noise ratio and demonstrated that it is robust enough to obtain kinetic parameters of the well-characterized PHD2 isoform comparable with those in published literature. We further showed that it is also sensitive enough to detect and measure the IC₅₀ values of pan-PHD inhibitors and several PHD2 inhibitors in clinical trials for chronic kidney disease (CKD)-induced anemia. Given the efficiency of this assay coupled with its multiwell format, the 2,4-DNPH α-KG assay may be adaptable to explore non-HIF substrates of PHDs and potentially to high-throughput assays.

Whether Prolyl Hydroxylase Blocker-Roxadustat-In the Treatment of Anemia in Patients with Chronic Kidney Disease Is the Future?

In patients with chronic kidney disease (CKD), anemia develops gradually, which is primarily due to an inadequate synthesis of erythropoietin by the kidneys, as well as to iron disorders in the body, blood loss, shortened erythrocyte survival and inflammation. The currently accepted treatment employs iron, vitamin B12, folic acid supplementation and the use of erythropoiesis stimulants, which are administered only parenterally. Research is currently underway on the new erythropoiesis drugs that can be orally administered, i.e., hypoxia-inducible factor-propyl hydroxylase inhibitor (HIF-PHI) inhibitors which temporarily block propyl hydroxylase [PHD] catalysis and promote a transient increase in the expression of genes regulated by HIF, including kidney and liver erythropoietin [EPO]. Roxadustat is the first oral drug in this class and a potent HIF-PHD inhibitor, exerted to treat anemia in patients with CKD. In phase 1, 2 and 3 studies with CKD-affected patients, roxadustat was more effective to stimulate erythropoiesis for anemia correction than previously used drugs. Roxadustat can be orally given, unlike other erythropoiesis drugs with parenteral administration only, which grants roxadustat a considerable advantage. Our paper presents the results of studies with roxadustat applied for the treatment of anemia in CKD patients with or without dialysis. We are currently not yet able to know the exact role of roxadustat in the treatment of anemia in patients with CKD, but time will tell. It is possible that roxadustat has benefits an iron metabolism and cardiovascular risk.

Efficacy and Safety of Daprodustat for Anemia Therapy in Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis

Objective: Daprodustat is a novel oral agent in treating anemia of chronic kidney disease (CKD), and several clinical trials have been conducted to compare daprodustat with recombinant human erythropoietin (rhEPO) or placebo. Our systematic review aimed to investigate the efficacy and safety of daprodustat for anemia treatment in both dialysis-dependent (DD) and non-dialysis-dependent (NDD) patients.

Methods: Six databases were searched for randomized controlled trials (RCTs) reporting daprodustat vs. rhEPO or placebo for anemia patients in CKD. The outcome indicators were focused on hemoglobin (Hb), ferritin, transferrin saturation (TSAT), total iron-binding capacity (TIBC), vascular endothelial growth factor (VEGF), and serious adverse events (SAEs).

Results: Eight eligible studies with 1,516 participants were included. For both NDD and DD patients, changes in Hb levels from baseline were significantly higher in daprodustat group than that in the placebo (mean difference (MD) = 1.73, [95% confidence interval (CI), 0.34 to 3.12], p = 0.01; MD = 1.88, [95% CI, 0.68 to 3.09], p = 0.002; respectively), and there was no significant difference between daprodustat and rhEPO group (MD = 0.05, [95% CI, −0.49 to 0.59], p = 0.86; MD = 0.12, [95% CI, −0.28 to 0.52], p = 0.55; respectively). The indexes of iron metabolism were improved significantly in the daprodustat group compared to placebo- or rhEPO-treated patients, while there was no similar change in terms of TSAT for DD patients. Furthermore, no trend of increasing plasma VEGF was observed in daprodustat-treated subjects. As for safety, there was no significant difference in the incidence of SAEs between daprodustat and placebo treatment, while the incidence of SAEs in the daprodustat group was significantly lower than that in the rhEPO group.

Conclusion: Daprodustat was efficacious and well tolerated for anemia in both NDD and DD patients in the short term based on current RCTs. And daprodustat may become an effective alternative for treatment of anemia with CKD. Since the application of daprodustat is still under exploration, future researches should consider the limitations of our study to evaluate the value of daprodustat.

A small-molecule probe for monitoring binding to prolyl hydroxylase domain 2 by fluorescence polarisation

Inhibition of the dioxygen sensing hypoxia-inducible factor prolyl hydroxylases has potential therapeutic benefit for treatment of diseases, including anaemia. We describe the discovery of a small-molecule probe useful for monitoring binding to human prolyl hydroxylase domain 2 (PHD2) via fluorescence polarisation. The assay is suitable for high-throughput screening of PHD inhibitors with both weak and strong affinities, as shown by work with clinically used inhibitors and naturally occurring PHD inhibitors.

Smart strategies to overcome tumor hypoxia toward the enhancement of cancer therapy

Hypoxia, as a typical factor in a tumor microenvironment, plays a vital role in tumor treatment resistance, tumor invasion and migration. Hypoxia inducible factor (HIF), as the vital response element of hypoxia, mediates these untoward effects through a series of downstream reactions. Cancer treatments such as photodynamic therapy (PDT), radiotherapy (RT) and chemotherapy are severely hindered by hypoxia and HIF, back, however, could be intelligently manipulated through nanocomposite materials for their great potentiality to combine different functions. Herein, we reviewed the smart strategies in emerging research studies to overcome hypoxia toward the enhancement of tumor therapy.

Downregulation of CYP1A2, CYP2B6, and CYP3A4 in Human Hepatocytes by Prolyl Hydroxylase Domain 2 Inhibitors via Hypoxia-Inducible Factor-α Stabilization

Hypoxia-inducible factor (HIF) is associated with the expression of CYP, but the underlying mechanism remains uncertain. In this study, we investigated the effect of HIF-α stabilization caused by novel prolyl hydroxylase domain (PHD) 2 inhibitors, which are HIF-α stabilizers that mimic hypoxia, on the expressions of CYP1A2, CYP2B6, and CYP3A4 in human hepatocytes. An mRNA expression analysis of human hepatocytes treated with PHD2 inhibitors for 72 hours showed the downregulation of genes encoding CYP1A2, CYP2B6, and CYP3A4. The mRNA repressions were accompanied with an increase in erythropoietin protein, a marker of HIF-α stabilization, indicating that HIF-α stabilization was involved in the downregulation of the CYP isoforms. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors [aryl hydrocarbon receptor (AhR), AhR nuclear translocator (ARNT), constitutive androstane receptor (CAR), pregnane X receptor (PXR), and retinoid X receptor (RXR)] in human hepatocytes treated with the HIF-α stabilizers. As a result, the mRNA level of AhR did not decrease, although ARNT expression was repressed. On the other hand, the mRNA expression levels of CAR, PXR, and RXR were repressed and closely associated with those of CYP2B6 and CYP3A4. Although the underlying mechanism of the downregulation for CYP1A2 remains unclear, the presently reported results suggest that the downregulation of CYP2B6 and CYP3A4 via HIF-α stabilization is caused by a decrease in the expressions of CAR, PXR, and RXR. SIGNIFICANCE STATEMENT: We showed that hypoxia-inducible factor (HIF)-α stabilization downregulates CYP1A2, CYP2B6, and CYP3A4 using prolyl hydroxylase domain 2 inhibitors, which are HIF-α stabilizers, as a new tool to mimic hypoxia in human hepatocytes. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors. Our findings would contribute to a better understanding of the hypoxia-triggered regulatory mechanism of drug-metabolizing enzymes in human hepatocytes.

Hypoxia-Inducible Factor and Oxygen Biology in the Kidney

Kidney tissue hypoxia is detected in various kidney diseases and is considered to play an important role in the pathophysiology of both AKI and CKD. Because of the characteristic vascular architecture and high energy demand to drive tubular solute transport, the renal medulla is especially prone to hypoxia. Injured kidneys often present capillary rarefaction, inflammation, and fibrosis, which contribute to sustained kidney hypoxia, forming a vicious cycle promoting progressive CKD. Hypoxia-inducible factor (HIF), a transcription factor responsible for cellular adaptation to hypoxia, is generally considered to protect against AKI. On the contrary, consequences of sustained HIF activation in CKD may be either protective, neutral, or detrimental. The kidney outcomes seem to be affected by various factors, such as cell types in which HIF is activated/inhibited, disease models, balance between two HIF isoforms, and time and methods of intervention. This suggests multifaceted functions of HIF and highlights the importance of understanding its role within each specific context. Prolyl-hydroxylase domain (PHD) inhibitors, which act as HIF stabilizers, have been developed to treat anemia of CKD. Although many preclinical studies demonstrated renoprotective effects of PHD inhibitors in CKD models, there may be some situations in which they lead to deleterious effects. Further studies are needed to identify patients who would gain additional benefits from PHD inhibitors and those who may need to avoid them.

Rank Order of Small Molecule Induced Hypoxiamimesis to Prevent Retinopathy of Prematurity

Here we rank order small molecule inhibitors of hypoxia inducible factor (HIF) prolyl hydroxylases (PHDs) using severity of oxygen induced retinopathy (OIR) as an outcome measure. Dose response analyses in cell cultures of hepatoma (Hep3B), retinal Müller cells (MIO-M1) and primary retinal endothelial cells were conducted to evaluate potency by comparing dose to HIF-1,2 protein levels by western blotting. In vivo dose response was determined using the luciferase-transgene HIF reporter (luc-ODD). Each compound was placed in rank order by their ability to reduce neovascularization and capillary drop out in the OIR mouse model. An Epas1 KO confined to retinal Müller cells was used to determine whether successful protection by HIF stabilization requires HIF-2. Two candidate small molecules can prevent OIR by stabilizing HIF-1 to prevent oxygen induced growth attenuation and vascular obliteration. Müller cell HIF-2, the mediator of pathologic retinal angiogenesis, is not required for protection. The lack of dependence on Müller cell HIF-2 predicts that inhibition of HIF PHD will not drive pathological angiogenesis.

Hypoxia-inducible factor prolyl hydroxylase inhibitors: a paradigm shift for treatment of anemia in chronic kidney disease?

INTRODUCTION

The hypoxia-inducible factor prolyl hydroxylase (HIF-PH) pathway is responsible for regulating the biosynthesis of erythropoietin (EPO) and maintaining iron homeostasis. Investigational drugs that target the HIF-PH pathway are promising alternatives for treating anemia in Chronic Kidney Disease (CKD).

AREAS COVERED

This review summarizes recent advances focused on the clinical development of HIF-PH inhibitors (HIF-PHIs) as potentially novel therapies in the treatment of anemia in CKD based on publications available on PubMed and restricted Google searches. We provide a comparison between HIF-PHIs regarding their pharmacokinetics, dosing regimens and safety concerns, structure-activity relationships, and alterations in key laboratory parameters observed in animal models and clinical trials.

EXPERT OPINION

HIF-PHIs may be advantageous in some aspects compared to the conventional erythropoiesis-stimulating agents (ESAs). While ESAs could increase the risk of cardiovascular events due to rapid rises in ESA blood levels, HIF-PHIs have been reported to maintain EPO concentrations at levels that are closer to the normal physiological ranges. Although HIF-PHIs have been demonstrated to be relatively safe and effective in clinical trials, long-term safety data are needed in order to establish whether these therapeutic agents will lead to a major paradigm change in the treatment of anemia of CKD.

Kinetic parameters of human aspartate/asparagine-β-hydroxylase suggest that it has a possible function in oxygen sensing

Human aspartate/asparagine-β-hydroxylase (AspH) is a 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the post-translational hydroxylation of Asp and Asn residues in epidermal growth factor-like domains (EGFDs). Despite its biomedical significance, studies on AspH have long been limited by a lack of assays for its isolated form. Recent structural work has revealed that AspH accepts substrates with a noncanonical EGFD disulfide connectivity (i.e. the Cys 1-2, 3-4, 5-6 disulfide pattern). We developed stable cyclic thioether analogues of the noncanonical EGFD AspH substrates to avoid disulfide shuffling. We monitored their hydroxylation by solid-phase extraction coupled to MS. The extent of recombinant AspH-catalyzed cyclic peptide hydroxylation appears to reflect levels of EGFD hydroxylation observed in vivo, which vary considerably. We applied the assay to determine the kinetic parameters of human AspH with respect to 2OG, Fe(II), l-ascorbic acid, and substrate and found that these parameters are in the typical ranges for 2OG oxygenases. Of note, a relatively high Km for O2 suggested that O2 availability may regulate AspH activity in a biologically relevant manner. We anticipate that the assay will enable the development of selective small-molecule inhibitors for AspH and other human 2OG oxygenases.

Quantitative MS-Based Proteomics: Comparing the MCF-7 Cellular Response to Hypoxia and a 2-Oxoglutarate Analogue

The hypoxia-inducible factors (HIFs) are key transcription factors in determining cellular responses involving alterations in protein levels in response to limited oxygen availability in animal cells. 2-Oxoglutarate-dependent oxygenases play key roles in regulating levels of HIF and its transcriptional activity. We describe MS-based proteomics studies in which we compared the results of subjecting human breast cancer MCF-7 cells to hypoxia or treating them with a cell-penetrating derivative (dimethyl N-oxalylglycine; DMOG) of the stable 2OG analogue N-oxalylglycine. The proteomic results are consistent with reported transcriptomic analyses and support the proposed key roles of 2OG-dependent HIF prolyl- and asparaginyl-hydroxylases in the hypoxic response. Differences between the data sets for hypoxia and DMOG might reflect context-dependent effects or HIF-independent effects of DMOG.

Aspartate/asparagine-β-hydroxylase: a high-throughput mass spectrometric assay for discovery of small molecule inhibitors

The human 2-oxoglutarate dependent oxygenase aspartate/asparagine-β-hydroxylase (AspH) catalyses the hydroxylation of Asp/Asn-residues in epidermal growth factor-like domains (EGFDs). AspH is upregulated on the surface of malign cancer cells; increased AspH levels correlate with tumour invasiveness. Due to a lack of efficient assays to monitor the activity of isolated AspH, there are few reports of studies aimed at identifying small-molecule AspH inhibitors. Recently, it was reported that AspH substrates have a non-canonical EGFD disulfide pattern. Here we report that a stable synthetic thioether mimic of AspH substrates can be employed in solid phase extraction mass spectrometry based high-throughput AspH inhibition assays which are of excellent robustness, as indicated by high Z'-factors and good signal-to-noise/background ratios. The AspH inhibition assay was applied to screen approximately 1500 bioactive small-molecules, including natural products and active pharmaceutical ingredients of approved human therapeutics. Potent AspH inhibitors were identified from both compound classes. Our AspH inhibition assay should enable the development of potent and selective small-molecule AspH inhibitors and contribute towards the development of safer inhibitors for other 2OG oxygenases, e.g. screens of the hypoxia-inducible factor prolyl-hydroxylase inhibitors revealed that vadadustat inhibits AspH with moderate potency.

Synthesis of Novel Pyridine-Carboxylates as Small-Molecule Inhibitors of Human Aspartate/Asparagine-β-Hydroxylase

The human 2‐oxoglutarate (2OG)‐dependent oxygenase aspartate/asparagine‐β‐hydroxylase (AspH) is a potential medicinal chemistry target for anticancer therapy. AspH is present on the cell surface of invasive cancer cells and accepts epidermal growth factor‐like domain (EGFD) substrates with a noncanonical (i. e., Cys 1–2, 3–4, 5–6) disulfide pattern. We report a concise synthesis of C‐3‐substituted derivatives of pyridine‐2,4‐dicarboxylic acid (2,4‐PDCA) as 2OG competitors for use in SAR studies on AspH inhibition. AspH inhibition was assayed by using a mass spectrometry‐based assay with a stable thioether analogue of a natural EGFD AspH substrate. Certain C‐3‐substituted 2,4‐PDCA derivatives were potent AspH inhibitors, manifesting selectivity over some, but not all, other tested human 2OG oxygenases. The results raise questions about the use of pyridine‐carboxylate‐related 2OG analogues as selective functional probes for specific 2OG oxygenases, and should aid in the development of AspH inhibitors suitable for in vivo use.

The prolyl hydroxylase inhibitor roxadustat: Paradigm in drug discovery and prospects for clinical application beyond anemia

Prolyl hydroxylase (PHD) inhibitors, such as roxadustat, can stabilize hypoxia-inducible factor (HIF)-2α and induce erythropoietin (EPO) production under normal conditions. Roxadustat was recently approved as a first-in-class orally active drug for the treatment of renal anemia. In addition, it has garnered growing therapeutic interest for use against various diseases, such as carcinoma, neurological diseases, ocular diseases, and tissue and organ injuries. In this review, we systemically review target validation, hit identification, and further key clinical trials of roxadustat. The prospective clinical applications of PHD inhibitors are then discussed based on this marketed drug.

Hypoxia sensing by hepatic stellate cells leads to VEGF-dependent angiogenesis and may contribute to accelerated liver regeneration

Portal vein ligation (PVL) induces liver growth prior to resection. Associating liver partition and portal vein ligation (PVL plus transection=ALPPS) or the addition of the prolyl-hydroxylase inhibitor dimethyloxalylglycine (DMOG) to PVL both accelerate growth via stabilization of HIF-α subunits. This study aims at clarifying the crosstalk of hepatocytes (HC), hepatic stellate cells (HSC) and liver sinusoidal endothelial cells (LSEC) in accelerated liver growth. In vivo, liver volume, HC proliferation, vascular density and HSC activation were assessed in PVL, ALPPS, PVL+DMOG and DMOG alone. Proliferation of HC, HSC and LSEC was determined under DMOG in vitro. Conditioned media experiments of DMOG-exposed cells were performed. ALPPS and PVL+DMOG accelerated liver growth and HC proliferation in comparison to PVL. DMOG alone did not induce HC proliferation, but led to increased vascular density, which was also observed in ALPPS and PVL+DMOG. Activated HSC were detected in ALPPS, PVL+DMOG and DMOG, again not in PVL. In vitro, DMOG had no proliferative effect on HC, but conditioned supernatant of DMOG-treated HSC induced VEGF-dependent proliferation of LSEC. Transcriptome analysis confirmed activation of proangiogenic factors in hypoxic HSC. Hypoxia signaling in HSC induces VEGF-dependent angiogenesis. HSC play a crucial role in the cellular crosstalk of rapid liver regeneration.

Prolyl Hydroxylase Domain Inhibitor Protects against Metabolic Disorders and Associated Kidney Disease in Obese Type 2 Diabetic Mice

BACKGROUND

Prolyl hydroxylase domain (PHD) inhibitors, which stimulate erythropoietin production through the activation of hypoxia-inducible factor (HIF), are novel therapeutic agents used for treating renal anemia. Several PHD inhibitors, including enarodustat, are currently undergoing phase 2 or phase 3 clinical trials. Because HIF regulates a broad spectrum of genes, PHD inhibitors are expected to have other effects in addition to erythropoiesis, such as protection against metabolic disorders. However, whether such beneficial effects would extend to metabolic disorder-related kidney disease is largely unknown.

METHODS

We administered enarodustat or vehicle without enarodustat in feed to diabetic black and tan brachyury (BTBR) ob/ob mice from 4 to 22 weeks of age. To elucidate molecular changes induced by enarodustat, we performed transcriptome analysis of isolated glomeruli and in vitro experiments using murine mesangial cells.

RESULTS

Compared with BTBR ob/ob mice that received only vehicle, BTBR ob/ob mice treated with enarodustat displayed lower body weight, reduced blood glucose levels with improved insulin sensitivity, lower total cholesterol levels, higher adiponectin levels, and less adipose tissue, as well as a tendency for lower macrophage infiltration. Enarodustat-treated mice also exhibited reduced albuminuria and amelioration of glomerular epithelial and endothelial damage. Transcriptome analysis of isolated glomeruli revealed reduced expression of C-C motif chemokine ligand 2/monocyte chemoattractant protein-1 (CCL2/MCP-1) in enarodustat-treated mice compared with the vehicle-only group, accompanied by reduced glomerular macrophage infiltration. In vitro experiments demonstrated that both local HIF-1 activation and restoration of adiponectin by enarodustat contributed to CCL2/MCP-1 reduction in mesangial cells.

CONCLUSIONS

These results indicate that the PHD inhibitor enarodustat has potential renoprotective effects in addition to its potential to protect against metabolic disorders.

Treatment of Renal Anemia with Roxadustat: Advantages and Achievement

Background

Although renal anemia has attracted widespread attention, a large proportion of chronic kidney disease (CKD) patients with anemia still do not meet the hemoglobin (Hb) targets. The discovery of prolyl hydroxylase domain (PHD) enzymes as regulators of hypoxia-inducible factor (HIF)-dependent erythropoiesis has led to the development of novel therapeutic agents for renal anemia. Roxadustat, the first small-molecule HIF-PHD inhibitor, has completed the phase 3 trials. There are currently more than 15 phase 3 clinical trials worldwide assessing the efficacy and safety of roxadustat in CKD patients with anemia. This review will summarize recent findings of roxadustat in the treatment of renal anemia.

Summary

Although the administration of erythropoiesis-stimulating agents (ESAs) and iron supplementation are a well-established and highly effective therapeutic approach for renal anemia, there are several safety concerns. Current findings from phase 2 and 3 trials suggest that roxadustat is clinically effective and well tolerated. On the one hand, roxadustat could increase endogenous erythropoietin (EPO) levels within or near physiological range in a titratable manner by inducing HIF pathway activation transiently. On the other hand, roxadustat also improves iron metabolism by decreasing serum hepcidin and increasing intestinal iron absorption, which is beneficial to functional iron deficiency and absolute iron deficiency. More importantly, the erythropoietic response of roxadustat is independent of baseline inflammatory state of CKD patients. Thus, the discovery of roxadustat will revolutionize the treatment strategy for renal anemia.

Key Messages

Roxadustat is an emerging and promising therapeutic approach against anemia in CKD patients, which differs from those of conventional ESAs. Roxadustat corrects anemia of CKD patients through multiple pathways, beyond elevating EPO levels within physiological range, and also by handling iron metabolism (particularly decreasing the hepcidin levels). Furthermore, the Hb response of roxadustat is independent of the inflammatory microenvironment.

Discovery of prolyl hydroxylase 2 inhibitors with new chemical scaffolds as in vivo active erythropoietin inducers through a combined virtual screening strategy

Hypoxia-inducible factor (HIF) is identified to be a promising target to mediate the response to hypoxia. Its stability and activation are negatively controlled by prolyl hydroxylase 2 (PHD2). Thus, PHD2 inhibition has been perceived as a promising anti-anemia therapy. In this study, we carried out a structure-based virtual screening followed by in vitro and in vivo biological validation, with the goal to identify novel PHD2 inhibitors. As a result, a set of hits with new chemical scaffolds were revealed to be active in vitro for PHD2 inhibition. Compounds 2 and 3 were revealed to be capable of stabilizing HIF-α and stimulating erythropoietin (EPO) expression in cell-based assays. Notably, further in vivo assays revealed that 2 was capable of elevating the EPO plasma levels in C57BL/6 mice model. These findings provide new chemical scaffolds for further development of PHD2 inhibitors.

Ischemia-reperfusion injury in renal transplantation: 3 key signaling pathways in tubular epithelial cells

Renal ischemia-reperfusion injury (IRI) is a significant clinical challenge faced by clinicians perioperatively in kidney transplantation. Recent work has demonstrated the key importance of transmembrane receptors in the injured tubular epithelial cell, most notably Toll-like receptors, activated by exogenous and endogenous ligands in response to external and internal stresses. Through sequential protein-protein interactions, the signal is relayed deep into the core physiological machinery of the cell, having numerous effects from upregulation of pro-inflammatory gene products through to modulating mitochondrial respiration. Inter-pathway cross talk facilitates a co-ordinated response at an individual cellular level, as well as modulating the surrounding tissue's microenvironment through close interactions with the endothelium and circulating leukocytes. Defining the underlying cellular cascades involved in IRI will assist the identification of novel interventional targets to attenuate IRI with the potential to improve transplantation outcomes. We present a focused review of 3 key cellular signalling pathways in the injured tubular epithelial cell that have been the focus of much research over the past 2 decades: toll-like receptors, sphingosine-1-phosphate receptors and hypoxia inducible factors. We provide a unique perspective on the potential clinical translations of this recent work in the transplant setting. This is particularly timely with the recent completion of phase I and ongoing phase 2 clinical trials of inhibitors targeting specific components of these signaling cascades.

Hypoxia-Inducible Factor Activators in Renal Anemia: Current Clinical Experience

Prolyl hydroxylase domain oxygen sensors are dioxygenases that regulate the activity of hypoxia-inducible factor (HIF), which controls renal and hepatic erythropoietin production and coordinates erythropoiesis with iron metabolism. Small molecule inhibitors of prolyl hydroxylase domain dioxygenases (HIF-PHI [prolyl hydroxylase inhibitor]) stimulate the production of endogenous erythropoietin and improve iron metabolism resulting in efficacious anemia management in patients with CKD. Three oral HIF-PHIs-daprodustat, roxadustat, and vadadustat-have now advanced to global phase III clinical development culminating in the recent licensing of roxadustat for oral anemia therapy in China. Here, we survey current clinical experience with HIF-PHIs, discuss potential therapeutic advantages, and deliberate over safety concerns regarding long-term administration in patients with renal anemia.