3 research outputs found
Mechanistic Insights into the Allosteric Modulation of Opioid Receptors by Sodium Ions
The idea of sodium ions altering
G-protein-coupled receptor (GPCR)
ligand binding and signaling was first suggested for opioid receptors
(ORs) in the 1970s and subsequently extended to other GPCRs. Recently
published ultra-high-resolution crystal structures of GPCRs, including
that of the δ-OR subtype, have started to shed light on the
mechanism underlying sodium control in GPCR signaling by revealing
details of the sodium binding site. Whether sodium accesses different
receptor subtypes from the extra- or intracellular sides, following
similar or different pathways, is still an open question. Earlier
experiments in brain homogenates suggested a differential sodium regulation
of ligand binding to the three major OR subtypes, in spite of their
high degree of sequence similarity. Intrigued by this possibility,
we explored the dynamic nature of sodium binding to δ-OR, μ-OR,
and κ-OR by means of microsecond-scale, all-atom molecular dynamics
(MD) simulations. Rapid sodium permeation was observed exclusively
from the extracellular milieu, and following similar binding pathways
in all three ligand-free OR systems, notwithstanding extra densities
of sodium observed near nonconserved residues of κ-OR and δ-OR,
but not in μ-OR. We speculate that these differences may be
responsible for the differential increase in antagonist binding affinity
of μ-OR by sodium resulting from specific ligand binding experiments
in transfected cells. On the other hand, sodium reduced the level
of binding of subtype-specific agonists to all OR subtypes. Additional
biased and unbiased MD simulations were conducted using the δ-OR
ultra-high-resolution crystal structure as a model system to provide
a mechanistic explanation for this experimental observation
Ligand-Based Discovery of a New Scaffold for Allosteric Modulation of the μ‑Opioid Receptor
With
the hope of discovering effective analgesics with fewer side
effects, attention has recently shifted to allosteric modulators of
the opioid receptors. In the past two years, the first chemotypes
of positive or silent allosteric modulators (PAMs or SAMs, respectively)
of μ- and δ-opioid receptor types have been reported in
the literature. During a structure-guided lead optimization campaign
with μ-PAMs BMS-986121 and BMS-986122 as starting compounds,
we discovered a new chemotype that was confirmed to display μ-PAM
or μ-SAM activity depending on the specific substitutions as
assessed by endomorphin-1-stimulated β-arrestin2 recruitment
assays in Chinese Hamster Ovary (CHO)-μ PathHunter cells. The
most active μ-PAM of this series was analyzed further in competition
binding and G-protein activation assays to understand its effects
on ligand binding and to investigate the nature of its probe dependence
Versatility of the Curcumin Scaffold: Discovery of Potent and Balanced Dual BACE‑1 and GSK-3β Inhibitors
The multitarget approach has gained
increasing acceptance as a
useful tool to address complex and multifactorial maladies such as
Alzheimer’s disease (AD). The concurrent inhibition of the
validated AD targets β-secretase (BACE-1) and glycogen synthase
kinase-3β (GSK-3β) by attacking both β-amyloid and
tau protein cascades has been identified as a promising AD therapeutic
strategy. In our study, curcumin was identified as a lead compound
for the simultaneous inhibition of both targets; therefore, synthetic
efforts were dedicated to obtaining a small library of novel curcumin-based
analogues, and a number of potent and balanced dual-target inhibitors
were obtained. In particular, <b>2</b>, <b>6</b>, and <b>7</b> emerged as promising drug candidates endowed with neuroprotective
potential and brain permeability. Notably, for some new compounds
the symmetrical diketo and the β-keto–enol tautomeric
forms were purposely isolated and tested <i>in vitro</i>, allowing us to gain insight into the key requirements for BACE-1
and GSK-3β inhibition