Design and Optimization of 1H-1,2,3-Triazole-4-carboxamides as Novel, Potent, and Selective Inverse Agonists and Antagonists of PXR

First-in-Class Small Molecule Degrader of Pregnane X Receptor Enhances Chemotherapy Efficacy

Pregnane X receptor (PXR) is a ligand-activated transcription factor that binds diverse compounds and upregulates drug metabolism machinery in response. PXR activation is detrimental to drug efficacy and safety because it reduces active drug concentrations and increases reactive metabolites, leading to toxicity and/or drug-drug interactions. Thus, effort must be expended in drug development pipelines to assess PXR activation by lead candidates and chemically modify agonists to reduce PXR liabilities while maintaining on-target potencies. Coadministration of drugs with PXR antagonists could prevent PXR-mediated metabolism events, but such compounds are rare and may themselves be converted to agonists by metabolic enzymes or PXR mutations. Here, we report the design, synthesis, optimization, and biological validation of proteolysis targeting chimeras that induce PXR degradation through E3 ubiquitin ligase recruitment. PXR degradation blocks agonist-induced gene expression and enhances anticancer effects of the chemotherapy paclitaxel, a known PXR agonist and substrate of downstream metabolic enzymes.

Chemical manipulation of an activation/inhibition switch in the nuclear receptor PXR

Nuclear receptors are ligand-activated transcription factors that can often be useful drug targets. Unfortunately, ligand promiscuity leads to two-thirds of receptors remaining clinically untargeted. PXR is a nuclear receptor that can be activated by diverse compounds to elevate metabolism, negatively impacting drug efficacy and safety. This presents a barrier to drug development because compounds designed to target other proteins must avoid PXR activation while retaining potency for the desired target. This problem could be avoided by using PXR antagonists, but these compounds are rare, and their molecular mechanisms remain unknown. Here, we report structurally related PXR-selective agonists and antagonists and their corresponding co-crystal structures to describe mechanisms of antagonism and selectivity. Structural and computational approaches show that antagonists induce PXR conformational changes incompatible with transcriptional coactivator recruitment. These results guide the design of compounds with predictable agonist/antagonist activities and bolster efforts to generate antagonists to prevent PXR activation interfering with other drugs.

Regulation of PXR in drug metabolism: chemical and structural perspectives

INTRODUCTION

Pregnane X receptor (PXR) is a master xenobiotic sensor that transcriptionally controls drug metabolism and disposition pathways. PXR activation by pharmaceutical drugs, natural products, environmental toxins, etc. may decrease drug efficacy and increase drug-drug interactions and drug toxicity, indicating a therapeutic value for PXR antagonists. However, PXR's functions in physiological events, such as intestinal inflammation, indicate that PXR activators may be useful in certain disease contexts.

AREAS COVERED

We review the reported roles of PXR in various physiological and pathological processes including drug metabolism, cancer, inflammation, energy metabolism, and endobiotic homeostasis. We then highlight specific cellular and chemical routes that modulate PXR activity and discuss the functional consequences. Databases searched and inclusive dates: PubMed, 1 January 1980 to 10 January 2024.

EXPERT OPINION

Knowledge of PXR's drug metabolism function has helped drug developers produce small molecules without PXR-mediated metabolic liabilities, and further understanding of PXR's cellular functions may offer drug development opportunities in multiple disease settings.