Foundations of Pharmacology and Toxicology Notes PDF

Foundations of Pharmacology and Toxicology  Pharmacodynamics: how drugs act on the body organ cell molecular Source: D Young - created in Biorender.com  Learning Outcomes Describe the 4 major drug target classe...

Foundations of Pharmacology and Toxicology  Pharmacodynamics: how drugs act on the body organ cell molecular Source: D Young - created in Biorender.com  Learning Outcomes Describe the 4 major drug target classes Describe the role of receptors, enzymes, ion channels and transporters in drug action Understand how drugs bind to receptors, and define the principles of affinity, efficacy and potency and be aware of the influence of the tissue on these properties Understand the concentration-response curve and what information can be gained from it Differentiate between inverse agonism, agonism, different types of antagonism, allosteric modulators and understand their impact on the concentration response curve  Drug targets Receptors organ cell proteins Ion channels (molecular) Transporters Most drugs produce their effects by binding to proteins - drug targets An important exception is DNA - a target Enzymes for many anti-cancer and antibiotic drugs Acronym: RITE  Receptors Receptors are proteins that recognise and respond to: – Endogenous ligands = neurotransmitters (e.g. glutamate, acetylcholine, GABA), hormones (e.g insulin), inflammatory mediators (e.g TNFa) – Exogenous ligands = drugs e.g paracetamol, clobazam The binding of the ligand to the receptor alters the conformation of the receptor leading to a cell response  Receptor families Four main families: Ligand-gated ion channel receptors (ionotropic receptor) G-protein-coupled receptors Extracellular Receptor tyrosine kinases Intracellular receptors Plasma membrane intracellular  Ligand-gated ion channel receptors Activated in response to binding by endogenous Allows ion passage through ligands impermeable cell membrane See later: agonists, antagonist drug classes Ion conductivity is highly selective e.g -GABA receptors - Cl- ions -Glutamate receptors – Na+ K+ Multi-protein subunit assemblies Mediate fast signalling at synapses (fraction of a millisecond)  Example: GABAA receptors GABA – main inhibitory neurotransmitter GABAA receptors - ligand-gated ion channel receptors Pentameric structure formed from two ⍺, α1 β2 two β and one ɣ subunit but there are 1Cl- multiple subunit isoforms - (⍺1-6), (β1-3) 𝛾2 and (ɣ1-3) β2 Receptor properties (e.g. conductance, α1 chance of opening, ligand affinity, others) dependent on subunit combination GABA binding site formed by peptide loops between an alpha and beta subunit Therapeutic use: Main drug target for benzodiazepines (e.g. diazepam, lorazepam, clobazam Sedation, anxiolytic, seizures (epilepsy) Benzodiazepine binding site is formed between the alpha and gamma subunit  Receptor families Four main families: Ligand-gated ion channel receptors (ionotropic receptor) G-protein-coupled receptors Extracellular Receptor tyrosine kinases Intracellular receptors Plasma membrane intracellular  G-protein-coupled receptors (GPCR) Monomeric proteins with 7 transmembrane domains Coupled to G-proteins: Gi – inhibit adenylate cyclase Gs – stimulate adenylate cyclase Gq – phospholipase C Mediates activation of a downstream signalling cascade that leads to a cell response  Example: muscarinic receptors 5 muscarinic receptor subtypes: M1, M2, M3, M4 or M5 muscarinic receptors Similarities: all activated by acetylcholine (non-selective) Differences: primary structure, distribution in tissue types, pharmacological properties and signal transduction activity M2 M4 M1 M3 M5  Tissue distribution Functional response M1 Autonomic ganglia (including intramural CNS excitation (? improved cognition) ganglia in stomach) Gastric secretion Gastric oxyntic glands (acid secretion) Glands: salivary, lacrimal, etc. Cerebral cortex M2 Heart: atria Cardiac inhibition CNS: widely distributed Neural inhibition Central muscarinic effects (e.g. tremor, hypothermia) M3 Exocrine glands: salivary, etc. Gastric, salivary secretion Smooth muscle: gastrointestinal tract, eye, Gastrointestinal smooth muscle contraction airways, bladder Ocular accommodation Blood vessels: endothelium Vasodilatation M4 CNS Enhanced locomotion M5 CNS: very localised expression in substantia Not known nigra Salivary glands Iris/ciliary muscle Adapted from Rang & Dale: Table 14.2 For a drug to be useful as a therapy, it must act primarily on the intended target cell  Drug specificity and selectivity While we aim for drug specificity (drug acts only at the desired drug target e.g NMDA receptors and not D1 dopamine receptors) in reality, even the best drugs only act selectively (i.e. preferentially) at a drug target. Unwanted effects can occur with increased drug concentration https://www.proteomicsdb.org/proteomicsdb/ #protein/proteinDetails/58336/expression  Tissue distribution Functional response M1 Autonomic ganglia (including intramural CNS excitation (? improved cognition) ganglia in stomach) Gastric secretion Gastric oxyntic glands (acid secretion) Glands: salivary, lacrimal, etc. Cerebral cortex M2 Heart: atria Cardiac inhibition CNS: widely distributed Neural inhibition Central muscarinic effects (e.g. tremor, hypothermia) M3 Exocrine glands: salivary, etc. Gastric, salivary secretion Smooth muscle: gastrointestinal tract, eye, Gastrointestinal smooth muscle contraction airways, bladder Ocular accommodation Blood vessels: endothelium Vasodilatation M4 CNS Enhanced locomotion M5 CNS: very localised expression in substantia Not known nigra Salivary glands Iris/ciliary muscle Adapted from Rang & Dale: Table 14.2 Selective drug Achieved through drug design e.g. M4 >M1 receptors Could also take advantage of differences in the tissue distribution and abundance of the drug target (e.g receptor) in the body Potential therapeutic uses of mAChR subtype-selective compounds* From: Nature Reviews Drug Discovery 6, 721-733 (2007) doi:10.1038/nrd2379  Other drugs that act through GPCRs β-adrenoceptors – isoprenaline Adenosine receptors – caffeine, theophylline Dopamine receptors – L-dopa, haloperidol Opioid receptors – morphine, codeine Serotonin receptors – buspirone, ondansetron Cannabinoid receptors – cannabis, rimonabant, Sativex  Receptor families Four main families: Ligand-gated ion channel receptors (ionotropic receptor) G-protein-coupled receptors Extracellular Receptor tyrosine kinases Intracellular receptors Plasma membrane intracellular  Receptor tyrosine kinases (RTKs) An extracellular part that the ligand binds to, and an intracellular part that functions as a kinase enzyme RTKs transfer phosphate groups from ATP to a tyrosine amino acid residue on a target protein Phosphorylation can control protein function substrate (i.e. phosphorylation) by changing the activity of an enzyme to an “on” or “off” state, altering its subcellular location or interaction with other proteins (i.e. adaptor proteins, kinases, phosphatases, lipases) Example:Vascular Endothelial Growth Factor Receptors Essential for angiogenesis (i.e. blood vessel formation) during development, pregnancy, wound healing Also associated with pathophysiological conditions e.g. cancer, rheumatoid arthritis, cardiovascular disease Multiple receptors/multiple ligands - we will look briefly at VEGFR2  Ligand-stimulated receptor dimerisation Autophosphorylation of tyrosine residues in cytoplasmic domain Associates with SH2 domain proteins Activation by phosphorylation PLC γ-hydrolyses PIP2 to DAG + IP3 DAG activates PKC PKC activation leads to activation of ERK via Raf and MEK /ERK leading to increased gene transcription 1) Cross et al , Trends in Biochemical Sciences, Volume 28, Issue 9, 2003, Pages 488-494, ISSN 0968-0004, https://doi.org/10.1016/S0968- 0004(03)00193-2. 2) Matsumoto et al., SCIENCE'S STKE, 11 Dec 2001, Vol 2001, Issue 112, DOI: 10.1126/stke.2001.112.re21  VEGFR2 as a drug target Potential therapeutic use: – Angiogenesis inhibitors – block endothelial cell growth in tumours – Angiogenesis stimulators – promote blood vessel growth following ischaemic conditions e.g. heart disease, limb ischemia  Receptor families Four main families: Ligand-gated ion channel receptors (ionotropic receptor) G-protein-coupled receptors Extracellular Receptor tyrosine kinases Intracellular receptors Plasma membrane intracellular Located in the cytosol and nucleus  Nuclear/steroid hormone receptors The hormone (ligand) binds to the receptor before the hormone/receptor dimer translocates to the nucleus to stimulate target gene expression (acts as a transcription factor) https://commons.wikimedia.org/wiki/File:Nuclear_receptor_action.png Summary Ligand-gated GPCR Kinase-linked Nuclear Ion Channels receptor Receptor Location Membrane Membrane Membrane Intracellular Effector Ion channel Channel or Enzyme Gene enzyme Transcription Coupling Direct G-protein Direct Via DNA Examples Nicotinic, Dopamine, Insulin, growth Steroid, GABAa cannabinoid, factor, cytokine thyroid adenosine, hormone muscarinic receptors Structure Oligomeric Monomeric Single Monomeric assembly of structure of 7 transmembrane structure with subunits transmembrane helix linking separate surrounding domains extracellular receptor and pore receptor to DNA binding intracellular domains. kinase domain  2021 – MST question From lecture 2: What is/are the drug targets? What are ligands? Which one is the endogenous one – which is exogenous (drug)? What does “selective” and “non- selective” mean? Adenosine induces airways obstruction in people with asthma, but the adenosine receptor subtype responsible remains unknown. The effect of the non-selective adenosine agonist CPA in the absence or presence of the selective A1 adenosine receptor antagonist 8-CPT (Figure A) or the selective A2B adenosine receptor antagonist PSB-601 (Figure B) on contraction (as shown by an increase in tension) was measured in bronchial ring samples isolated from human lung tissue. Each data point represents mean ± SEM from bronchial preparations from four subjects. (a) Using these data, which adenosine receptor subtype (A1 or A2B) is most likely involved in mediating the bronchial ring contraction in response to CPA? Justify your answer. (6 marks) (b) Adenosine A1 receptor agonists have anticonvulsant effects in mouse models of epilepsy. From the information and data in Q1a), explain whether you would recommend testing an A1 receptor agonist in a clinical trial for refractory epilepsy. (3 marks) (c) The table below shows the Kd values for the ligands at human A1 adenosine receptors. Which ligand has the highest affinity for A1 adenosine receptors? Briefly explain your reasoning in two to three sentences. (2 marks)