Recommendations by the Asian Pacific society of nephrology (APSN) on the appropriate use of HIFPH inhibitors

Renal anaemia is a common and important complication in patients with chronic kidney disease (CKD). The current standard-of-care treatment for renal anaemia in CKD patients involves ensuring adequate iron stores and administration of erythropoietin stimulating agents (ESA). Hypoxia inducible factor (HIF) is a key transcription factor primarily involved in the cellular regulation and efficiency of oxygen delivery. Manipulation of the HIF pathway by the use of HIF-prolyl hydroxylase inhibitors (HIF-PHI) has emerged as a novel approach for renal anaemia management. Despite it being approved for clinical use in various Asia-Pacific countries, its novelty mandates the need for nephrologists and clinicians generally in the region to well understand potential benefits and harms when prescribing this class of drug. The Asian Pacific society of nephrology HIF-PHI Recommendation Committee, formed by a panel of 11 nephrologists from the Asia-Pacific region who have clinical experience or have been investigators in HIF-PHI studies, reviewed and deliberated on the clinical and preclinical data concerning HIF-PHI. This recommendation summarizes the consensus
views of the committee regarding the use of HIF-PHI, taking into account both available data and expert opinion in areas where evidence remains scarce.

## K e y w o r d s
anaemia, Asian Pacific, chronic kidney disease, hypoxia inducible factor, prolyl hydroxylase inhibitor Hypoxia inducible factor (HIF) is a key transcription factor primarily involved in the cellular regulation and efficiency of oxygen delivery.
Its preliminary state comprises a constitutively expressed, nucleusbound -subunit and three isoforms of a cytoplasmic -subunit (HIF-1, HIF-2 and HIF-3). HIF-1 and HIF-2 are master regulators of defensive mechanisms against hypoxia and enhance oxygen delivery by stimulating a variety of genes. Representative target genes are erythropoietin (EPO) and those that optimize iron utilization.
When oxygen availability is normal, the -subunit is sequentially degraded: first by prolyl hydroxylation by HIF-prolyl hydroxylase (HIF-PH), followed by ubiquitination via the Von-Hippel Lindau (VHL) gene and the E3 ubiquitin ligase complex, which facilitates proteosomal degradation. However, prolyl hydroxylation is oxygendependent; hence, during periods of hypoxia HIF-PH loses its activity, resulting in stabilization of the -subunit before it undergoes nuclear translocation and formation of a heterodimer with the -subunit. As the oxygen sensing mechanism and the adaptive response against hypoxia is so important and essential, three great scientists who elucidated this mechanism, Peter Ratcliffe, Gregg Semenza, and William Kaelin Jr., were awarded the Nobel Prize in Physiology and Medicine in 2019.
The current standard-of-care treatments for anaemia in chronic kidney disease (CKD) is intravenous (IV) or subcutaneous (SC) administration of human recombinant EPO or its derivatives, known as erythropoiesis stimulating agents (ESA) which stimulate the haematopoietic system specifically. HIF-PH inhibitors (HIF-PHI) are now approved and available in some countries as an oral drug of a completely new mechanism to treat anaemia in CKD.HIF-PHI work systemically and may exert some effects outside the haematopoietic system. Being a relatively novel therapy that was first approved in various Asia-Pacific countries, it is important for nephrologists and clinicians within the region to well understand the potential benefits and harms when prescribing this class of drug. Physician can consider HIF-PHI as alternatives to ESAs in correcting and maintaining haemoglobin (Hb) for renal anaemia both in dialysis-dependent (DD) and non-dialysis-dependent (NDD) CKD patients based on the new data concerning its efficacy and safety from several recent clinical trials.These trials show that the efficacy and safety of HIF-PHI are comparable to ESAs in treating renal anaemia in the short term, although the long-term risks and benefits of HIF-PHIs in treating renal anaemia remains to be assessed.
Physicians should recognize that HIF-PHI are very different in its mechanism of action of erythropoiesis compared to ESAs. ESAs stimulate erythropoiesis by acting specifically on the erythropoietin receptor that expressed on red blood cell precursors.In clinical studies, HIF-PHIs have been shown to increase blood TIBC with no significant changes in serum iron levels, resulting in reduced TSAT.Treatment with HIF-PHI is also associated with decreased blood ferritin level and hepcidin level.Iron deficiency is associated with thromboembolic events, and clinical trials of roxadustat in Japan have reported increased incidence of thromboembolic events.As treatment with HIF-PHIs may decrease serum iron levels due to increased availability of iron for erythropoiesis, one T A B L E 1 Pharmacologic profiles of HIF-PHIs in phase III development* should pay attention to avoid treatment-induced reduction in serum iron levels. Apart from increasing EPO transcription and inhibiting hepcidin production, HIF also induces transcription of genes relating to neovascularization and tumour growth (specific to tumour type). These include vascular endothelial growth factor (VEGF), nitric oxide, TWIST gene, metalloproteinase and mitogen-activated protein kinase, among others. Importantly, HIF-1 (rather than HIF-2) appears related to tumour gene activity and associated with metastatic spread for breast, prostate, lung, bone and colorectal cancers.Nonetheless, HIF-2 has also been identified in in vitro malignant hepatocellular lines, is involved in the activation of cancer stem cells factor and is strongly associated with various tumour metastases, as well as a poor prognosis.The relevance of HIF activation on the potential for malignancy is evident in conditions such as VHL disease, where the incidence of several tumours, including renal cell carcinoma (RCC) is increased.
Conversely, most RCCs display somatic mutations in the VHL gene, reducing proteolysis of the HIF -subunit and increasing HIF activity.Solid tumours have a poorer prognosis when HIF activity is increasedAt least two agents have been assessed regarding their potential for cancer development in longer-term murine studies: roxadustat and daprodustat.Roxadustat is usually administered to humans at doses up to 1.5 mg/kg daily or thrice-weekly (TIW). At doses of up to 10 (rats) and 60 (mice) mg/kg administered TIW and followed for up to 104 weeks, there was no effect in either animal on survival or on the development of neoplastic lesions.Similarly, daprodustat was administered to a cohort of mice and Sprague-Dawley rats for up to 2 years at 143-fold the predicted maximal human clinical exposure.
Again, no neoplastic changes were observed, although (male) rat lifespan was curtailed due erythrocytosis, aortic thrombosis and/or associated cardiomyopathy.
In summary, from the available animal and short-term human data, so far there is no evidence of tumour risk with the use of PHIs.
Whether the same can be said for humans, and whether there is a difference between primary oncogenesis and enhancing known tumour growth and spread is unclear. Some idea of the relative risk of malignancy will be available following publication of current studies, but since patients with known tumours were unlikely to be enrolled, it is probable such questions will not be fully addressed. Given broad marketing approval ensues, or in Japan maintained, it will be essential to maintain post-marketing surveillance for a substantive period-at least 5 years-given the theoretical and experimental concerns associated with increased HIF activity, as well as the long-term malignancy risk posed by related genetic diseases.

## | retinopathy <recommendation>
- Retinopathy is a theoretical concern of HIF-PHI in CKD patients.
Early referral for ophthalmologic assessment is warranted in patients who report visual disturbance after drug initiation.
Retinopathy is a sight-threatening condition and remains a serious concern in the use of HIF-stabilizer in CKD patients. Theoretically, activation of the HIF pathway may enhance retinal angiogenesis and predispose patients to retinal complications such as haemorrhage.The overall incidence of retinal adverse events is low. While the cur-

## | liver dysfunction <recommendation>
- Liver dysfunction is relatively uncommon in CKD patients receiving HIF-PHI. Regular monitoring of liver function may facilitate early detection of HIF-PHI -related hepatic dysfunction.
The effect of HIF on liver and hepatic diseases remains elusive.
Animal data suggest that HIF confers protective effect on ischaemic-
reperfusion injury of liver but shows pathogenic roles in the progression of hepatic fibrosis and fatty liver.In an open-label randomized study in dialysis patients, transient elevation of liver biochemistries was noted in two roxadustat-treated patients (3.3%) during the 12-week treatment period and both showed normalization of liver function without drug discontinuation.In a phase 3 study of roxadustat in Chinese patients receiving dialysis, two subjects (1%)
showed liver dysfunction which was mild or moderate in severity.The derangement in liver function test, however, was not observed in another phase 3 study of roxadustat conducted in NDD Chinese CKD patients.Correction of renal anaemia has been shown to reduce incidence of heart failure and improve cardiac function. However, there were a series of reports on reduced cardiac function following sustained activation of HIF or inhibition of prolyl hydroxylase.Studies of HIF deletion in a model of heart failure reported discrepant results.The molecular mechanism of this effect is not clearly defined. Basic science studies suggested that this might be associated with the extent of HIF activation, where over-activation of HIF might lead to defective energy utilisation of the cardiac myocytes.
This highlights the importance of the fine balance between prolyl hydroxylase inhibition to stimulate erythropoiesis for correction of renal anaemia and modest HIF activation at the heart to prevent deterioration of cardiac function. One should also pay attention to the experimental study which showed that HIF-1 directly upregulated BNP, a marker of heart failure.The potential benefits of HIF-PHIs on improving myocardial ischaemia and the potential risks of compromising cardiac function need to be further studied in RCTs.

## | concerns from basic studies
Basic studies have shown that HIF pathway is associated with thrombosis and plaque stability. In this context, hypoxia and HIF target and also increase in plasminogen activator inhibitor 1, which in turn inhibits fibrinolysis.Plaque stability is related to the expression of HIF within the plaque, specifically its expression in vascular smooth muscle cells (VSMCs), endothelial cells (ECs) and more importantly foam cells. HIF can also stimulate destabilised angiogenesis occurring in the ischaemic and necrotic atherosclerotic lesion. HIF and HIFinduced genes, especially VEGF, can enhance the haemodynamic instability and fragility of the plaque, thus allows further infiltration of inflammatory cells.Basic studies have also shown that HIF pathway may be associ- and 4B.In DD patients, the incidence of CV events was low (42/1741 [2.4%]).
HIF-PH inhibitors were associated with higher incidence of all-cause mortality, hyperkalemia and CV events . In NDD patients, the incidence of CV events was even lower (21/1871 [1.1%]). HIF-PHI were associated with insignificantly higher incidence of all-cause mortality, hyperkalaemia and CV events ( This is mainly due to regional hypoxia as a consequence of compression by enlarged cysts and a mismatch between expanding cysts and the vascularization of cyst walls, but not the genetic defects.Data from animal models further support this idea. Tissue PO 2 in cortical surface of Lewis polycystic kidney rats is approximately half of that in control rats. Moreover, renal blood flow and oxygen delivery in the polycystic rats are 60% and 80% lower than control rats.Overproduction of EPO by increased HIF-2 in chronic hypoxia may explain why patients with autosomal dominant polycystic kidney disease (ADPKD) present with less severe anaemia than patients with other end-stage kidney disease (ESKD).Indeed, serum levels of EPO in ESKD patients due to ADPKD are on average 2-fold higher than in ESKD of other causes.However, the stabilization of HIF in the polycystic disease confers not only such beneficial outcome but also deleterious effects in cyst enlargement. Recent study with mouse ADPKD models in combination with genetic and pharmacological approaches clearly demonstrated that increased levels of HIF-1 due to chronic hypoxia promote cyst progression.HIF-1-dependent apical Ca2 + -activated Cl  secretion is known as a major driving force for cyst fluid secretion.This study also identified the Ca 2+ -activated Clchannel 'anoctamin 1' and the purinergic receptor 'P2Y2R' as 2 major molecular players in the HIF-1-mediated cyst growth.Although the erythropoietic dosage of a HIF-PHI for CKD patients might be different from that used for the animal experiments, undesirable action of HIF-1 on cyst expansion should be taken into consideration in long-term administration of HIF-PHI to treat anaemia in ADPKD patients.

## | seizure or neurological complications <recommendation>
- Clinical studies have no signals that suggest seizure or neurological complications as an adverse event by HIF-PHI.
HIF is involved in transcriptional responses to hypoxia of many genes, and hence its systemic effect on the cerebrovascular system is of potential concern. In theory, HIF-PHI may increase thromboem- (0.9%) occurred after 19 weeks of roxadustat in ESKD patients receiving maintenance HD, and such adverse events were not observed in the epoetin alfa group.Cerebral infarction (0.7%) was also reported in a study of Japanese population after 24 weeks treatment with roxadustat compared to none in the darbopoietin alfa group.One study reported that vadadustat treatment in NDD CKD patients was associated with slightly higher incidence of headache and dizziness compared with placebo during the 20 weeks of treatment.Headache was also more common in NDD CKD patients treated with daprodustat for 1 month compared with placebo,although adverse cerebrovascular event did not occur in another study where NDD patients had received 4 weeks of daprodustat.There was no cerebrovascular adverse events or stroke reported In CKD stage 3 to 5 NDD patients treated with molidustat for 16 weeks. 88,89

## | potential benefits in addition to improvement of anaemia
One potential benefits of HIF-PHI is that HIF-PHI may stimulate erythropoiesis by an increase in circulating EPO levels within a physiological range. However, many clinical studies did not employ time points at which circulating EPO levels reach the peak by administration of HIF-PHI.
As hypoxia is a final common pathway to ESKD, HIF-PHI may preserve kidney function in CKD patients.In addition, HIF is a master regulator of defensive mechanisms against hypoxia, HIF-PHI may provide protection against ischaemic diseases such as ischemic heart disease, stroke, peripheral arterial disease and acute kidney injury.However, there is no solid clinical evidence to support these expectations, and clinical studies to clarify these issues are awaited.
Previous clinical trials showed a decrease in lipids after HIF-PHI treatment. However, treatment with HIF-PHI decreased both LDLcholesterol and HDL-cholesterol in these trials. In addition, while some HIF-PHI showed lipid-lowering effects, others did not. Therefore, this effect may be agent specific, and long-term consequences of metabolic changes induced by HIF-PHI remain to be elucidated.