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

The drug-specific properties of hypoxia-inducible factor-prolyl hydroxylase inhibitors in mice reveal a significant contribution of the kidney compared to the liver to erythropoietin induction

AIMS

Kidney disease often leads to anemia due to a defect in the renal production of the erythroid growth factor erythropoietin (EPO), which is produced under the positive regulation of hypoxia-inducible transcription factors (HIFs). Chemical compounds that inhibit HIF-prolyl hydroxylases (HIF-PHs), which suppress HIFs, have been developed to reactivate renal EPO production in renal anemia patients. Currently, multiple HIF-PH inhibitors, in addition to conventional recombinant EPO reagents, are used for renal anemia treatment. This study aimed to elucidate the therapeutic mechanisms and drug-specific properties of HIF-PH inhibitors.

METHODS AND KEY FINDINGS

Gene expression analyses and mass spectrometry revealed that HIF-PH inhibitors (daprodustat, enarodustat, molidustat, and vadadustat) alter Epo gene expression levels in the kidney and liver in a drug-specific manner, with different pharmacokinetics in the plasma and urine after oral administration to mice. The drug specificity revealed the dominant contribution of EPO induction in the kidneys rather than in the liver to plasma EPO levels after HIF-PH inhibitor administration. We also found that several HIF-PH inhibitors directly induce duodenal gene expression related to iron intake, while these drugs indirectly suppress hepatic hepcidin expression to mobilize stored iron for hemoglobin synthesis through induction of the EPO-erythroferrone axis.

SIGNIFICANCE

Renal EPO induction is the major target of HIF-PH inhibitors for their therapeutic effects on erythropoiesis. Additionally, the drug-specific properties of HIF-PH inhibitors in EPO induction and iron metabolism have been shown in mice, providing useful information for selecting the proper HIF-PH inhibitor for each renal anemia patient.

Targeting hypoxia-inducible factors: therapeutic opportunities and challenges

Hypoxia-inducible factors (HIFs) are highly conserved transcription factors that are crucial for adaptation of metazoans to limited oxygen availability. Recently, HIF activation and inhibition have emerged as therapeutic targets in various human diseases. Pharmacologically desirable effects of HIF activation include erythropoiesis stimulation, cellular metabolism optimization during hypoxia and adaptive responses during ischaemia and inflammation. By contrast, HIF inhibition has been explored as a therapy for various cancers, retinal neovascularization and pulmonary hypertension. This Review discusses the biochemical mechanisms that control HIF stabilization and the molecular strategies that can be exploited pharmacologically to activate or inhibit HIFs. In addition, we examine medical conditions that benefit from targeting HIFs, the potential side effects of HIF activation or inhibition and future challenges in this field.

Molecular medicinal insights into scaffold hopping-based drug discovery success

In both academia and the pharmaceutical industry, innovative hypotheses, methodologies and technologies that can shorten the drug research and development, leading to higher success rates, are vital. In this review, we demonstrate how innovative variations of the scaffold-hopping strategy have been used to create new druggable molecular spaces, drugs, clinical candidates, preclinical candidates, and bioactive agents. We also analyze molecular modulations that enabled improvements of the pharmacodynamic (PD), physiochemical, and pharmacokinetic (PK) properties (P3 properties) of the drugs resulting from these scaffold-hopping strategies.

Mechanistic and Clinical Comparison of the Erythropoietic Effects of SGLT2 Inhibitors and Prolyl Hydroxylase Inhibitors in Patients with Chronic Kidney Disease and Renal Anemia

Renal anemia is treated with erythropoiesis-stimulating agents (ESAs), even though epoetin alfa and darbepoetin increase the risk of cardiovascular death and thromboembolic events, including stroke. Hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) inhibitors have been developed as an alternative to ESAs, producing comparable increases in hemoglobin. However, in advanced chronic kidney disease, HIF-PHD inhibitors can increase the risk of cardiovascular death, heart failure, and thrombotic events to a greater extent than that with ESAs, indicating that there is a compelling need for safer alternatives. Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce the risk of major cardiovascular events, and they increase hemoglobin, an effect that is related to an increase in erythropoietin and an expansion in red blood cell mass. SGLT2 inhibitors increase hemoglobin by ≈0.6-0.7 g/dL, resulting in the alleviation of anemia in many patients. The magnitude of this effect is comparable to that seen with low-to-medium doses of HIF-PHD inhibitors, and it is apparent even in advanced chronic kidney disease. Interestingly, HIF-PHD inhibitors act by interfering with the prolyl hydroxylases that degrade both HIF-1α and HIF-2α, thus enhancing both isoforms. However, HIF-2α is the physiological stimulus to the production of erythropoietin, and upregulation of HIF-1α may be an unnecessary ancillary property of HIF-PHD inhibitors, which may have adverse cardiac and vascular consequences. In contrast, SGLT2 inhibitors act to selectively increase HIF-2α, while downregulating HIF-1α, a distinctive profile that may contribute to their cardiorenal benefits. Intriguingly, for both HIF-PHD and SGLT2 inhibitors, the liver is likely to be an important site of increased erythropoietin production, recapitulating the fetal phenotype. These observations suggest that the use of SGLT2 inhibitors should be seriously evaluated as a therapeutic approach to treat renal anemia, yielding less cardiovascular risk than other therapeutic options.

Assessing the Carcinogenicity of Vadadustat, an Oral Hypoxia-Inducible Factor Prolyl-4-Hydroxylase Inhibitor, in Rodents

Vadadustat is an investigational oral hypoxia-inducible factor (HIF) prolyl-4-hydroxylase inhibitor to treat anemia due to chronic kidney disease (CKD). Some studies suggest that HIF activation promotes tumorigenesis by activating angiogenesis downstream of vascular endothelial growth factor, while other studies suggest that elevated HIF activity may produce an antitumor phenotype. To evaluate the potential carcinogenicity of vadadustat in mice and rats, we dosed CByB6F1/Tg.rasH2 hemizygous (transgenic) mice orally by gavage with 5 to 50 mg/kg/d of vadadustat for 6 months and dosed Sprague-Dawley rats orally by gavage with 2 to 20 mg/kg/d for approximately 85 weeks. Doses were selected based on the maximally tolerated dose established for each species in previous studies. The tumors that were identified in the studies were not considered to be treatment-related for statistical reasons or within the historical control range. There was no carcinogenic effect attributed to vadadustat in mice or rats.