Structure-based design of a chemical probe set for the 5-HT5A serotonin receptor

ABSTRACTThe 5-HT5A receptor (5-HT5AR), for which no selective agonists and only a few antagonists exist, remains the least understood serotonin (5-HT) receptor. A single commercial antagonist (SB-699551) has been widely used to investigate central nervous system (CNS) 5-HT5AR function in neurological disorders, including pain. However, because SB-699551 has affinity for many 5-HTRs, lacks inactive property-matched controls, and has assay interference concerns, it has liabilities as a chemical probe. To better illuminate 5-HT5AR function, we developed a probe set through iterative rounds of molecular docking, pharmacological testing, and optimization. Docking over six million lead-like molecules against a 5-HT5AR homology model identified five mid-μM ligand starting points with unique scaffolds. Over multiple rounds of structure-based design and testing, a new quinoline scaffold with high affinity and enhanced selectivity for the 5-HT5AR was developed, leading to UCSF678, a 42 nM arrestin-biased partial agonist at the 5-HT5AR with a much more restricted off-target profile and decreased assay liabilities vs. SB-699551. Site-directed mutagenesis supported the docked pose of UCSF678, which was also consistent with recent published 5-HTR structures. Surprisingly, property-matched analogs of UCSF678 that were either inactive across 5-HTRs or retained affinity for UCSF678’s off-targets revealed that 5-HT5AR engagement is nonessential for alleviating pain in a mouse model, contrary to previous studies using less-selective ligands. Relative to SB-699551, these molecules constitute a well-characterized and more selective probe set with which to study the function of the 5-HT5A receptor. Table of Contents Graphic

Which Properties Allow Ligands to Open and Bind to the Transient Binding Pocket of Human Aldose Reductase?

The transient specificity pocket of aldose reductase only opens in response to specific ligands. This pocket may offer an advantage for the development of novel, more selective ligands for proteins with similar topology that lack such an adaptive pocket. Our aim was to elucidate which properties allow an inhibitor to bind in the specificity pocket. A series of inhibitors that share the same parent scaffold but differ in their attached aromatic substituents were screened using ITC and X-ray crystallography for their ability to occupy the pocket. Additionally, we investigated the electrostatic potentials and charge distribution across the attached terminal aromatic groups with respect to their potential to bind to the transient pocket of the enzyme using ESP calculations. These methods allowed us to confirm the previously established hypothesis that an electron-deficient aromatic group is an important prerequisite for opening and occupying the specificity pocket. We also demonstrated from our crystal structures that a pH shift between 5 and 8 does not affect the binding position of the ligand in the specificity pocket. This allows for a comparison between thermodynamic and crystallographic data collected at different pH values.

G4-Selective Ligand Induced Autophagy

G-quadruplex (G4) structures have emerged as singular therapeutic targets for cancer and neurodegeneration. Autophagy is a housekeeping cellular homeostatic mechanism and deregulation of autophagy is common in cancer and in neurodegenerative diseases. In this study, we identified the presence of 46 putative G4 sequences in the MTOR gene by use of QGRS mapper tool. We sought to connect these putative G4 sequences to a functional context by leveraging G4-targeting ligands. A G4-selective dimeric carbocyanine dye Bis-4,3 and the porphyrin TMPyP4 were used to affect the replication, transcription and translation of the MTOR gene. The ligand-induced induction of autophagic pathway via MTOR gene regulation was monitored upon treatment of HeLa and SHSY-5Y cells with G4-targeting ligands. The use of Bis-4,3 was compared with the known G4-stabilizing activity of TMPyP4. Our results show that treatment with G4-selective ligands downregulates mTOR activity and leads to the induction of excessive autophagy. This is first report on effect of G4-selective ligands on MTOR regulation and mTOR expression. mTOR being the key negative regulator of autophagy, the current work suggests potential of G4 stabilizing ligands towards induction of autophagy through the downregulation of mTOR.

Activation of T cell checkpoint pathways during beta-cell antigen presentation by engineered dendritic cells promotes protection of non-obese diabetic mice from type 1 diabetes

Defective immune regulation has been recognized in type 1 diabetes (T1D). Immune regulatory T cell check-point receptors, which are generally upregulated on activated T cells, have been the molecules of attention as therapeutic targets for enhancing immune response in tumor therapy. We reported that dendritic cells (DCs) that are engineered to express selective ligands for checkpoint receptors can induce effective T cell tolerance in antigen-immunization models. Here, we show that, compared to engineered control-DCs, pancreatic beta-cell antigen (BcAg) presentation by engineered tolerogenic-DCs (tDCs) that express CTLA4 selective ligand (B7.1wa) or a combination of CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively; multiligand-DCs) causes an increase in regulatory cytokine and T cell (Treg) responses and suppression of the effector T cell function. Non-obese diabetic (NOD) mice treated with BcAg-pulsed CTLA4-ligand-DCs and multiligand-DCs at pre-diabetic and early-hyperglycemic stages showed significantly lower degree of insulitis, higher frequencies of insulin-positive islets, profound delay in, and reversal of, hyperglycemia for a significant duration. Immune cells from the tDC treated mice not only produced lower amounts of IFNgamma; and higher amounts of IL10 and TGF-beta1 upon BcAg challenge, but also failed to induce hyperglycemia upon adoptive transfer. While both CTLA4-ligand-DCs and multiligand-DCs were effective in producing a tolerogenic effect, multiligand-DC treatment produced an overall higher modulatory effect on effector T cell function and disease outcome. Overall, these studies show that enhanced engagement of T cell checkpoint receptors during BcAg presentation can effectively prevent and suppress autoimmunity in T1D.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α1-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α2-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α1-AR subtypes (α1A, α1B, α1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.