Possible binding sites and interactions of propanidid and AZD3043 within the γ-aminobutyric acid type A receptor (GABA_AR)

<p>Propanidid is an intravenous anesthetic with transient action and rapid recovery features, but it is clinically unacceptable due to its side effects. AZD-3043, an analog of propanidid with the methoxy group substituted by the ethoxy group, has become the focus of recent development efforts. Although propanidid and AZD-3043 are known to act by potentiating the γ-aminobutyric acid type A receptors (GABA_ARs), their action sites and binding modes in the recognition of target proteins still remain unclear. In this study, molecular docking and ONIOM calculations were performed to explore the possible binding sites and binding modes of propanidid and AZD-3043 with the GABA_AR. The predicted active region located in the transmembrane domain (TMD) of GABA_AR was identified as the most favorable binding site for propanidid and AZD-3043, with the highest docking score (−39.69 and −39.44 kcal/mol, respectively) and the largest binding energy (−88.478 and −78.439 kcal/mol, respectively). The important role of amino acids Asp245, Asp424, Asp425, Arg428, Phe307, and Ser308 in determining the binding modes of propanidid or AZD-3043 with GABA_AR was revealed. The detailed molecular interactions between propanidid and AZD-3043 and the GABA_AR were revealed for the first time. This could improve our understanding of the action mechanism of general anesthetics and will be helpful for the design of more potential lead-like molecules.</p

β‑Galactosidase-Activated and Red Light-Induced RNA Modification Strategy for Prolonged NIR Fluorescence/PET Bimodality Imaging

Improving the retention of small-molecule-based therapeutic agents in tumors is crucial to achieve precise diagnosis and effective therapy of cancer. Herein, we propose a β-galactosidase (β-Gal)-activated and red light-induced RNA modification (GALIRM) strategy for prolonged tumor imaging. A β-Gal-activatable near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe 68Ga-NOTA-FCG consists of a triaaza triacetic acid chelator NOTA for 68Ga-labeling, a β-Gal-activated photosensitizer CyGal, and a singlet oxygen (1O2)-susceptible furan group for RNA modification. Studies have demonstrated that the probe emits an activated NIR FL signal upon cleavage by endogenous β-Gal overexpressed in the lysosomes, which is combined with the PET imaging signal of 68Ga allowing for highly sensitive imaging of ovarian cancer. Moreover, the capability of 68Ga-NOTA-FCG generating 1O2 under 690 nm illumination could be simultaneously unlocked, which can trigger the covalent cross-linking between furan and nucleotides of cytoplasmic RNAs. The formation of the probe-RNA conjugate can effectively prevent exocytosis and prolong retention of the probe in tumors. We thus believe that this GALIRM strategy may provide entirely new insights into long-term tumor imaging and efficient tumor treatment

The Role of the Hydroxyl Group in Propofol–Protein Target Recognition: Insights from ONIOM Studies

Propofol (PFL, 1-hydroxyl-2,6-diisopropylbenzene) is currently used widely as one of the most well-known intravenous anesthetics to relieve surgical suffering, but its mechanism of action is not yet clear. Previous experimental studies have demonstrated that the hydroxyl group of PFL plays a dominant role in the molecular recognition of PFL with receptors that lead to hypnosis. To further explore the mechanism of anesthesia induced by PFL in the present work, the exact binding features and interaction details of PFL with three important proteins, human serum albumin (HSA), the pH-gated ion channel from <i>Gloeobacter violaceus</i> (GLIC), and horse spleen apoferritin (HSAF), were investigated systematically by using a rigorous three-layer ONIOM (M06-2X/6-31+G*:PM6:AMBER) method. Additionally, to further characterize the possible importance of such hydroxyl interactions, a similar set of calculations was carried out on the anesthetically inactive fropofol (FFL, 1-fluoro-2,6-diisopropylbenzene) in which the fluorine was substituted for the hydroxyl. According to the ONIOM calculations, atoms in molecules (AIM) analyses, and electrostatic potential (ESP) analyses, the significance of hydrogen bond, halogen bond, and hydrophobic interactions in promoting proper molecular recognition was revealed. The binding interaction energies of PFL with different proteins were generally larger than FFL and are a significant determinant of their differential anesthetic efficacies. Interestingly, although the hydrogen-bonding effect of the hydroxyl moiety was prominent in propofol, the substitution of the 1-hydroxyl by a fluorine atom did not prevent FFL from binding to the protein via a halogen-bonding interaction. It therefore became clear that multiple specific interactions rather than just hydrogen or halogen bonds must be taken into account to explain the different anesthesia endpoints caused by PFL and FFL. The contributions of key residues in ligand–receptor binding were also quantified, and the calculated results agreed with many available experimental observations. This work will provide complementary insights into the molecular mechanisms of anesthetic action for PFL from a robust theoretical point of view. This will not only assist in interpreting experimental observations but will also help to develop working hypotheses for further experiments and future drug design