SAR-Guided Scaffold Innovation of Selective V₂R Antagonists: Therapeutic Frontiers in ADPKD

Abstract

The vasopressin V₂ receptor (V₂R) is a class A G protein–coupled receptor (GPCR) that plays a pivotal role in the regulation of renal water homeostasis and has been implicated in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD) through sustained activation of cyclic adenosine monophosphate (cAMP) signaling. Pharmacological antagonism of V₂R has emerged as a clinically validated strategy for attenuating cyst growth. However, the therapeutic application of currently available V₂R antagonists remains constrained by safety liability and a relatively narrow chemical space. A recent study employed systematic structure–activity relationship (SAR) analyses to expand existing design paradigms for V₂R antagonists, leading to the identification and synthesis of a series of structurally diverse V₂R antagonist analogues. Supported by multidimensional pharmacological evaluations, these findings provide an important framework for the rational design and optimization of next-generation therapeutics for ADPKD.

Autosomal dominant polycystic kidney disease (ADPKD) is among the most common monogenic kidney disorders and remains a leading cause of end-stage kidney disease. , The ADPKD is driven by the persistent formation and progressive expansion of renal cysts, resulting in marked kidney enlargement and a gradual but irreversible decline in renal function over decades. , Despite its substantial clinical and societal burden, therapeutic management has long been limited to supportive care and complication control. As a result, the development of disease-modifying, targeted therapies for ADPKD represents a critical unmet clinical need. In this context, growing mechanistic insights into the vasopressin-cAMP signaling axis have established the vasopressin V₂ receptor (V₂R) as a central regulator of cystogenesis and a clinically validated molecular target for therapeutic intervention in ADPKD. ,

The V₂R, a G protein-coupled receptor (GPCR) predominantly expressed on the basolateral membrane of renal collecting duct principal cells, is the primary mediator of arginine vasopressin signaling in the kidney. , Converging mechanistic evidence has established sustained V₂R-driven cAMP signaling as a central pathogenic axis in ADPKD, promoting cyst epithelial cell proliferation, dysregulated ion transport, and fluid secretion, thereby driving progressive cyst expansion, kidney enlargement, and functional decline. These insights have positioned V₂R antagonism as a rational and clinically validated strategy for disease modification in ADPKD, exemplified by the approval of the nonpeptidic antagonist tolvaptan. However, the therapeutic potential of V₂R inhibition remains incompletely realized due to limitations of existing agents, including suboptimal selectivity, hepatotoxicity risk, and mechanism-based aquaretic adverse effects, highlighting the need for next-generation V₂R antagonists with improved safety and pharmacological profiles.

Conventional structure–activity relationship (SAR) studies of V₂R antagonists have long assumed that a benzoazacyclic scaffold is indispensable for achieving high potency and receptor selectivity, which confines medicinal chemistry optimization to peripheral modifications and severely restricting the accessible chemical space. A recent study discoverd that high antagonistic activity and V₂R subtype selectivity instead depend on effective occupation of a hydrophobic subpocket formed by three amino acid residues by an aromatic moiety, independent of the benzoazacyclic framework itself. Guided by this revised structure–function insight, the authors used the tolvaptan-derived compound C18 as a starting point to design a series of V₂R antagonists with nontraditional scaffolds.

The nitrogen-containing seven-membered ring of C18 was proposed to facilitate preorganization of the adjacent phenyl ring and orient it toward the hydrophobic subpocket. To expand scaffold diversity and assess whether this conformational constraint could be effectively replaced, the seven-membered ring was substituted with an ethoxy linker. As a result, compound 1 retained V₂R binding affinity to a measurable extent. Subsequent optimization of linker length led to the identification of compound 3, which exhibited improved binding affinity and was therefore selected as the lead scaffold for further optimization. Docking studies combined with SAR analysis suggested that rings a and b adopt relatively constrained and rigid conformations upon binding. Introduction of a para-fluoro substituent on ring a afforded compound 18, which displayed the highest binding affinity, supporting the notion that incorporation of hydrophobic substituents to enhance hydrophobic subpocket occupancy in this region is advantageous. Binding mode analysis further revealed the presence of a positively charged side-chain residue in proximity to ring b, capable of acting as a hydrogen bond donor. Installation of a hydroxyl group at the 3-position of ring b (compound 22) was hypothesized to exploit this potential hydrogen-bonding interaction, resulting in a further enhancement of V₂R binding affinity. Additional binding mode analysis indicated that rings d and e of compound 22 were predominantly solvent-exposed, therefore, modifications at these positions were unlikely to disrupt key binding interactions but provided an opportunity to improve physicochemical properties such as aqueous solubility. Consistent with this rationale, introduction of polar substituents on ring e led to compound 29 (XYDC2050), which exhibited a marked improvement in water solubility while further optimizingV₂R binding affinity (Figure ).

1.

SAR optimization of compound C18. ^a Data are mean ± SEM from 3 independent experiments with K _i values determined via fluorescent ligand displacement experiments. ^b The IC₅₀ values are determined from dose–response curves The data was adapted from ref . Copyright 2025 American Chemical Society.

Functional evaluation using cAMP assays identified that compound 29 potently inhibited vasopressin-induced cAMP accumulation, confirming its pronounced functional antagonism toward the V₂R. Subtype selectivity profiling revealed that compound 29 exhibited a high degree of selectivity for V₂R over V₁aR, with a selectivity margin of 162-fold, which under the conditions of this study exceeded that of the clinically approved V₂R antagonist tolvaptan (Figure , A). Pharmacokinetic characterization further indicated that compound 29 possessed a moderate elimination half-life and achieved peak plasma concentrations rapidly following administration, accompanied by a high maximum concentration and favorable systemic exposure, which provides adequate pharmacokinetic support for subsequent in vitro and in vivo pharmacodynamic investigations (Figure , B). In disease-relevant models, compound 29 markedly suppressed cyst growth in a dose-dependent manner in the Madin–Darby canine kidney (MDCK) cyst model (Figure , C). Consistent results were obtained in an ex vivo embryonic kidney model, further substantiating its inhibitory effects on cystogenesis (Figure , D). Moreover, in vivo evaluation in an ADPKD mice model revealed that treatment with compound 29 significantly reduced kidney enlargement relative to vehicle-treated controls (Figure , E). Given the known hepatotoxicity liabilities associated with tolvaptan, an additional safety assessment was conducted in wild-type C57BL/6 mice following 1 week of repeated dosing, which revealed no evidence of overt hepatotoxicity under the experimental conditions employed (Figure , F).

2.

A. Receptor binding affinity and subtype selectivity of compound 29; B. Key pharmacokinetic parameters of compound 29. C. Dose-dependent suppression of cyst growth in an in vitro MDCK cyst model. D. Inhibition of cystogenesis in an ex vivo embryonic kidney model. E. Reduction of kidney enlargement in an ADPKD mouse model. F. Liver toxicity assessment of compound 29. The data was adapted from ref . Copyright 2025 American Chemical Society.

Future Outlook

Building on systematic scaffold optimization and extensive SAR investigations of V₂R antagonists, compound 29 (XYCD2050) emerged from a series of analogues owing to its potent functional antagonism and high receptor affinity. Future studies should place more emphasis on long-term safety evaluations, complemented by comprehensive assessments of renal function parameters, to more rigorously validate its therapeutic potential in chronic settings. In addition, the development of radiolabeled V₂R-targeting agents derived from compound 29 may enable positron emission tomography (PET)-based molecular imaging approaches for the noninvasive interrogation of V₂R expression and regulatory dynamics during disease progression, , thereby facilitating early monitoring of disease evolution and therapeutic response. Such imaging probes could allow quantitative assessment of in vivo target engagement, providing a powerful framework for refining dose–exposure–response relationships and optimizing dosing regimens. ,

Glossary

Abbreviations

V₂R

V₂ receptor

GPCR

G protein-coupled receptor

ADPKD

Autosomal dominant polycystic kidney disease

cAMP

Cyclic adenosine monophosphate

SAR

Structure–activity relationship

SEM

Standard error of the mean

MDCK

Madin–Darby canine kidney

PET

Positron emission tomography.

No unexpected or unusually high safety hazards were encountered

The authors declare no competing financial interest.