Drug Targets PDF

Drug Targets Cell Surface Receptors – G protein coupled receptors (GPCRs) – Ion Channels Voltage Gated channels Ligand Gated channels – Enzyme Linked Receptors Enzymes Transporters insulin Nuclear Receptors  Targets of Curr...

Drug Targets Cell Surface Receptors – G protein coupled receptors (GPCRs) – Ion Channels Voltage Gated channels Ligand Gated channels – Enzyme Linked Receptors Enzymes Transporters insulin Nuclear Receptors  Targets of Current Marketed Drugs (Enzymes and Transporters) Santos, R., Ursu, O., Gaulton, A. et al. A comprehensive map of molecular drug targets. Nat Rev Drug Discov 16, 19–34 (2017). https://doi-org.libproxy.temple.edu/10.1038/nrd.2016.230 Ion Channels G Protein Coupled Receptors (GPCRs) Comprise the Largest Group of Drug Targets Ion Channels GPCRs  Class A Example: β-adrenergic Receptor The helices of the membrane-spanning domains form a binding pocket for norepinephrine > membranes Keeping molecule in place through molecular interactions  Major Classes of GPCRs Class A Class A Class C – Most numerous and diverse – ~45 kDa – Relatively short amino terminus – Small molecule binding site in a lipophillic Class B pocket Binding within in the 7 TM region Class B – Longer amino terminus that sometimes is involved in binding ligand – Ligands bind predominantly to extracellular loops – Peptides, small proteins are typical ligands Class C – ~80 kDa – Very large amino terminus – Forms functional heterodimers – Agonists binding occurs in the amino terminus However, ligands binding sites can occur all over the receptor molecule Culhane et al (2015) Frontiers in Pharmacology. 6. 10.3389/fphar.2015.00264.  Class B Example: PAR-1 (Protease Activated Receptor) “Tethered ligand” mechanism of activation The N-terminus of PAR-1, contains a protease cleavage site that, once cleaved by thrombin, results in a new N-terminus. The new N-terminal sequence, SFLLRN, acts as a tethered ligand and binds intramolecularly to the heptahelical body of the receptor to effect transmembrane signaling and G protein activation.  Class C Example: Sweet and Umami Tastant Receptors Sweet taste receptor is a heterodimer composed of two full-length GPCR monomers The long amino terminus can form a “venus flytrap” binding pocket Sanematsu et al (2014) Curr Pharm Biotechnol. 2014;15(10):951-61. doi: 10.2174/1389201015666140922105911.  Guanosine Tri- and Di-phosphates Nucleotides in the G protein activation cycle GTP 3P GDP 2P GPCRs Can Initiate a Signal Transduction Cascade G protein must be activated, GTp to GDp will inactivate nearby G proteins, but when attached to GTP it is activated. A B C D E  Phospholipase C in an Enzyme “Hydrolyzes” a Phospholipid in the Plasma Membrane to Yield IP3 * PLC takes pieces from phospholipid, searching for PIP to cleave A phosphate group , creating IP3 and DAG, IP3 is a against for cell inside cell which is on surface of ER called IP3R ( ion channel), opening up the channel, CA2+ will exit into cytoplasm IP3 Causes Release of Calcium form Intracellular Stores Endoplasmic Reticulum (ER) and Sarcoplasmic Reticulum (SR) Palmer et al (1996) Am J Physiol. 271(1 Pt 1):C43-53. Quiet cells Microinjection of IP3 in neuroepithelioma cells evokes intracellular release of calcium Buffer and subsequent paracrine calcium signaling IP3 microinjection Red cells mean Ca 2+ have gone out into cytoplasm Time Recovery following washout Adenylyl Cyclase is an Enzyme in the Plasma Membrane that Converts Cytosolic ATP to cAMP Creates CAMP ✗ inhibort Takes ATP Caffeine Sildenafil Theophylline inhibitor reverse back to AMP Down-regulation of Receptors Leads to Desensitization β-Arrestins orchestrate GPCR internalization in clathrin-coated pits Following agonist binding (1), GRKs are activated, which phosphorylate agonist-bound receptor (2). The phosphorylated C- terminus of the GPCR then serves to recruit β-arrestins (B-ARR) to the cell membrane (3 and 4), which in turn bind and polymerize clathrin protein into cages that stabilize the receptor complex during the subsequent engulfment of the cell membrane. The engulfed receptor, now sequestered within an endocytic vesicle, may be shuttled further into the cell for degradation within lysosomes, or it may be recycled back to the cell membrane (5). Ahmadzai et al (2017) Advances in Immunology, Volume 136, Pages 279-313 Up-regulation of Receptors can Lead to Sensitization Multiple mechanisms Prolonged exposure to antagonist (pool of ready-for-duty receptors Chronically low levels of intrinsic neurotransmitter or hormone agonist Pathological factors that impact gene regulation and protein expression  Nuclear Receptors Nuclear receptors are transcription factors – Directly bind to DNA to regulate the expression of specific genes General structure – Ligand biding domain – DNA binding domain Examples of agonists for nuclear receptors – Steroid hormones Estradiol Testosterone Cortisol Aldosterone – Retinoic aid (metabolite of vitamin A) Glucocorticoid Receptor and Dexamethasone – Calcitriol (active form of vitamin D) – Triiodothyronine (thyroid hormone T3) Educational portal of the Protein Data Bank: https://pdb101.rcsb.org/motm/258  Nuclear Receptor Mechanism of Action binds to Class I Nuclear Receptor ① 2 ligand detailing dimer Androgen receptor Estrogen receptor Done b²ydimerization Progesterone receptor created Glucocorticoid receptor Translocates inside nucleus transcription binds to Receptor located in the cytosol bound to Heat Shock Protein (HSP) Ligand diffuses across membrane, binds to receptor Ligand-Receptor (LR) complex dissociates from HSP LR complex translocate to nucleus LR complex binds Hormone Response Element (HRE) sequence on DNA LR complex recruits additional proteins to form a transcription initiation complex Transcription of DNA to RNA By Boghog2 - Made by Boghog2, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2375278  Nuclear Receptor Mechanism of Action Class II Nuclear Receptor 'created Thyroid hormone receptor Retinoic acid receptor t Vitamin D receptor transcription PPARα receptor ¢ Unoccupied receptor already located in the nucleus bound to DNA Unoccupied receptor is bound to a corepressor protein Ligand binding to thyroid hormone receptor (TR) causes dissociation of corepressor and recruitment of coactivator protein, polymerase