PCO371 intracellular agonism at the parathyroid hormone 1 receptor produces pan-activation of signalling partners
- 1Coventry University
Abstract
Small-molecule agonists of class B1 G-protein-coupled receptors (GPCRs) remain rare because these receptors typically require large extracellular peptide ligands for activation. PCO371 is a notable exception: an intracellular non-peptide agonist, originally developed for osteoporosis treatment, that activates parathyroid hormone 1 receptor (PTH1R) from the cytoplasmic face of the receptor and is considered Gs-protein biased. In this study, we compared the functional, pharmacological and structural properties of PCO371 with the canonical extracellular peptide agonist PTH 1-34 at the PTH1R to define the molecular mechanisms underlying PCO371's unusual signalling profile. By manipulating receptor reserve, we demonstrate that PCO371 is a partial agonist relative to PTH 1-34, contrary to previous observations. Across Gs, Gi3, Gq, cAMP, and {beta}-arrestin-2 pathways, operational model analysis showed that PCO371 is non-biased, engaging the same transducers as PTH1-34 but with ~1000-fold lower potency. Mechanistic modelling using the Cubic Ternary Complex Activation model revealed that reduced intrinsic efficacy is sufficient to reproduce PCO371's distinct monotonic signalling kinetics, providing a quantitative explanation for its partial agonism. PCO371 binding is {beta}-arrestin-compatible but only drives measurable {beta}-arrestin-2 recruitment when PTH1R is highly expressed. Molecular modelling suggests that PC0371 stable binding needs an intact receptor-G protein complex. Overall, these insights define the mechanistic basis of intracellular agonism at a class B1 GPCR and provide a framework for designing next-generation small-molecule modulators that exploit this emerging pharmacological space.
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BibTeX
@misc{khwaja2026pco371,
title = {{PCO371 intracellular agonism at the parathyroid hormone 1 receptor produces pan-activation of signalling partners}},
author = {F. Napier Khwaja and Z. Mariam and Y. Abdolhay and T. Redfern-Nichols and G. Ladds and D. Poyner and G. Deganutti and M. Wheatley and H. Ayub},
howpublished = {bioRxiv},
year = {2026},
month = may,
doi = {10.64898/2026.05.27.728112},
url = {https://www.biorxiv.org/content/10.64898/2026.05.27.728112v2},
note = {CC BY-ND},
}
RIS
TY - UNPB
TI - PCO371 intracellular agonism at the parathyroid hormone 1 receptor produces pan-activation of signalling partners
AU - F. Napier Khwaja
AU - Z. Mariam
AU - Y. Abdolhay
AU - T. Redfern-Nichols
AU - G. Ladds
AU - D. Poyner
AU - G. Deganutti
AU - M. Wheatley
AU - H. Ayub
PY - 2026
DA - 2026/05/27
PB - bioRxiv
DO - 10.64898/2026.05.27.728112
UR - https://www.biorxiv.org/content/10.64898/2026.05.27.728112v2
AB - Small-molecule agonists of class B1 G-protein-coupled receptors (GPCRs) remain rare because these receptors typically require large extracellular peptide ligands for activation. PCO371 is a notable exception: an intracellular non-peptide agonist, originally developed for osteoporosis treatment, that activates parathyroid hormone 1 receptor (PTH1R) from the cytoplasmic face of the receptor and is considered Gs-protein biased. In this study, we compared the functional, pharmacological and structural properties of PCO371 with the canonical extracellular peptide agonist PTH 1-34 at the PTH1R to define the molecular mechanisms underlying PCO371's unusual signalling profile. By manipulating receptor reserve, we demonstrate that PCO371 is a partial agonist relative to PTH 1-34, contrary to previous observations. Across Gs, Gi3, Gq, cAMP, and {beta}-arrestin-2 pathways, operational model analysis showed that PCO371 is non-biased, engaging the same transducers as PTH1-34 but with ~1000-fold lower potency. Mechanistic modelling using the Cubic Ternary Complex Activation model revealed that reduced intrinsic efficacy is sufficient to reproduce PCO371's distinct monotonic signalling kinetics, providing a quantitative explanation for its partial agonism. PCO371 binding is {beta}-arrestin-compatible but only drives measurable {beta}-arrestin-2 recruitment when PTH1R is highly expressed. Molecular modelling suggests that PC0371 stable binding needs an intact receptor-G protein complex. Overall, these insights define the mechanistic basis of intracellular agonism at a class B1 GPCR and provide a framework for designing next-generation small-molecule modulators that exploit this emerging pharmacological space.
ER -