SAR study of 1,2-benzisothiazole dioxide compounds that agonize HIF-2 stabilization and EPO production

Recent progress in the development of hypoxia-inducible factor 2α (HIF-2α) modulators: Inhibitors, agonists, and degraders (2009-2024)

Hypoxia-inducible factor 2α (HIF-2α) is a critical transcription factor that regulates cellular responses under hypoxic conditions. In situations of insufficient oxygen supply or patients with Von Hippel-Lindau (VHL) mutations, HIF-2α accumulates and forms a heterodimeric complex with aryl hydrocarbon receptor nuclear translocator (ARNT, or HIF-β). This complex further binds to coactivator p300 and interacts with hypoxia response elements (HREs) on the DNA of downstream target genes, regulating the transcription of a variety of genes (e.g. VEGFA, CCND1, CXCR4, SLC2A1, etc) involved in various processes like angiogenesis, mitochondrial metabolism, cell proliferation, and metastasis. Targeting HIF-2α holds great promise for effectively addressing solid tumors associated with aberrant oxygen-sensing pathways and hypoxia mechanisms, offering broad application prospects. In this review, we provide an overview of recent advancements (2009-2024) in HIF-2α modulators such as inhibitors, agonists, and degraders for cancer therapy. Additionally, we discuss in detail the challenges and future directions regarding HIF-2α modulators.

A patent review on hypoxia-inducible factor (HIF) modulators (2021-2023)

INTRODUCTION

Hypoxia-inducible factor (HIF) is a central regulatory factor in detecting and adapting to cellular oxygen stress. Dysregulation of HIF is associated with various human diseases. Seven HIF modulators, including six prolyl hydroxylase (PHD) inhibitors and one HIF-2α inhibitor, have already been approved for the treatment of renal anemia and cancer, respectively.

AREAS COVERED

This review summarizes HIF modulators patented in the 2021-2023 period. This review provides an overview of HIF downregulators, including HIF-1α inhibitors, HIF-2α inhibitors, and HIF-2α degraders, as well as HIF upregulators, including PHD, FIH, and VHL inhibitors, and HIF-2α and HIF-3α agonists.

EXPERT OPINION

Efforts should be made to address the adverse clinical effects associated with approved HIF-modulating drugs, including PHD inhibitors and HIF-2α inhibitors. Identification of the specific buried cavity in the HIF-2α and an opened pocket in HIF-3α offer an avenue for designing novel modulators for HIF-2α or HIF-3α. Given the similarities observed in the binding cavities of HIF-2α and HIF-3α, it should be considered whether the approved HIF-2α inhibitors also inhibit HIF-3α. A comprehensive understanding of the HIF signaling pathway biology would lead to the development of novel small-molecule HIF modulators as innovative therapeutic approaches for a wide range of human diseases.

Identification of 3-aryl-5-methyl-isoxazole-4-carboxamide derivatives and analogs as novel HIF-2α agonists through docking-based virtual screening and structural modification

Hypoxia-inducible factor-2 (HIF-2) serves as the pivotal transcription factor in cellular responses to low oxygen levels, particularly concerning the regulation of erythropoietin (EPO) production. A docking-based virtual screening on crystal structures of HIF-2α inhibitors unexpectedly identified 3-phenyl-5-methyl-isoxazole-4-carboxamide derivative v19 as a hit of HIF-2α agonist. Further structural optimizations of compound v19 led to the discovery of a series of HIF-2α agonists with novel scaffolds. The most promising compounds 12g and 14d exhibited potent HIF-2α agonistic activities in vitro with EC50 values of 2.29 μM and 1.78 μM, respectively. Molecular dynamics simulations have revealed their capacity to allosterically enhance HIF-2 dimerization, which shed light on their mechanism of action. Moreover, compound 14d demonstrated a favorable pharmacokinetic (PK) profile, boasting an impressive oral bioavailability value of 68.71 %. These findings strongly suggest that compound 14d is an auspicious lead compound for the treatment of renal anemia.

Decoding Allosteric Control in Hypoxia-Inducible Factors

The mammalian family of basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) transcription factors possess the ability to sense and respond to diverse environmental and physiological cues. These proteins all share a common structural framework, comprising a bHLH domain, two PAS domains, and transcriptional activation or repression domain. To function effectively as transcription factors, members of the family must form dimers, bringing together bHLH segments to create a functional unit that allows for DNA response element binding. The significance of bHLH-PAS family is underscored by their involvement in many major human diseases, offering potential avenues for therapeutic intervention. Notably, the clear identification of ligand-binding cavities within their PAS domains enables the development of targeted small molecules. Two examples are Belzutifan, targeting hypoxia-inducible factor (HIF)-2α, and Tapinarof, targeting the aryl hydrocarbon receptor (AHR), both of which have gained regulatory approval recently. Here, we focus on the HIF subfamily. The crystal structures of all three HIF-α proteins have been elucidated, revealing their bHLH and tandem PAS domains are used to engage their dimerization partner aryl hydrocarbon receptor nuclear translocator (ARNT, also called HIF-1β). A broad range of recent findings point to a shared allosteric modulation mechanism among these proteins, whereby small-molecules at the PAS-B domains exert direct influence over the HIF-α transcriptional functions. As our understanding of the architectural and allosteric mechanisms of bHLH-PAS proteins continues to advance, the possibility of discovering new therapeutic drugs becomes increasingly promising.