Pharmacodynamy & Receptors

1. Pharmacodynamy& Receptors Dr. M. H. Ghahremani References: 1-B.G.Katzung; Basic & Clinical Pharmacology 2012, Chapter 2, p 15-35. 2-H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2011, Chapter 1 & 2, p7-50. 3-Goodman & Gilman's: The pharmacological basis of therapeutics 2012, Chapter 3, p41-73. Dr. Mohammad H Ghahremani

2. Pharmacodynamy: The study of the biochemical and physiological effects of drugs and their mechanisms of action. The objectives of the study of drug action are: • to delineate the chemical or physical interactions between drug and target cell • to characterize the sequence and scope of actions of each drug. • to understand the pathological condition and discover new targets for therapy.

3. Pharmacodynamy & Receptors The goal of this course is to understand: • The concept of receptor • The Pharmacological effect • Drug-receptor-effect parameters • Types of receptors • Receptor signaling • Receptor regulation

4. The Receptor Concept Ehrich & Langley late 19th – early 20th century The effects of most drugs result from their interaction with macromolecular components of the organism. Receptor: The component of the organism (or cell) interact with the chemicals. Receptor is a translator of hormone (or chemicals) message for the cell or organ. Receptor : 1- binds to the hormone or drug (Ligand) 2- undergoes conformational changes 3- transduces message to the effector

5. The Receptor Concept In Receptor Concept, there is a: • Pharmacologic effect • Quantitative relationship • Selectivity

6. Pharmacologic effect • Drug-receptor interaction • Dose dependency • Multiple or single effect • Signal transduction and effector system • Duration of action • Regulation

7. Ligand Receptor Active Receptor R AR AR* A + Response Agonist Antagonist Ligand Receptor Inactive Receptor R BR + B No Response Drug-Receptor Interaction

8. Agonist & Antagonist Antagonist is a ligand: • binds to a specific receptor • binds to the same or different site as agonist • in a reversible or irreversible fashion • changes receptor conformation • changes receptor to inactive state • produces no response Agonist is a ligand: • binds to a specific receptor on a specific site • in a reversible or irreversible fashion • changes receptor conformation • changes receptor to active state • produces a response

9. H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.9.

10. B A C % Response Log [Agonist] H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.11. Dose-response effect

11. Potency and Efficacy • Potency is defined by the occupancy of the receptor. A more potent ligand will occupy more receptors and produce maximum response in lower concentration • Efficacy is defined by the response elicited by the agonist A more efficient agonist will produce higher maximum response

12. C B A Response Log [Agonist] Potency and Efficiency Potency A>B>C Efficancy C>A=B

13. The receptor quantification: receptor binding H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.10.

14. Competitive antagonism pA2= -Log [KB] = - Log 2.2x10-9 pA2=8.6 H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.16. pA2= negative Log of Antagonist results in 2 fold shift to right

15. Irreversible antagonism

16. Partial agonist; Reverse agonist H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.13.

17. Partial agonist; Reverse agonist H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.14.

18. Therapeutic Index A=lowering BP B=Toxicity The therapeutic index is the ratio of the ED50 of a drug to produce a toxic effect to the ED50 to produce a therapeutic effect. For the drug example above, the ED50 for the beneficial effect of blood pressure lowering is 0.4 nM while the ED50 for toxicity is 40 nM. Therefore, the therapeutic index will be: TI= ED50 (toxic)/ED50 (Therapeutic) TI= 35/0.4=87.5 % Response ED50 Log [Agonist]

19. The Receptor Types Function & coupling 1- membrane voltage change Ion channels 2- change in [Ca++]I Ion channels G-protein coupled Transporter 3- Change in cAMP and IP3 G-protein coupled 4- Proliferation or Apoptosis Tyrosine kinase Matrix protein G-protein coupled Nuclear receptor Enzymes 5-… Location 1- membrane bound Ion channels G-protein coupled Tyrosine kinase Matrix protein 2- Intercellular Enzymes cellular organelles 3- Nuclear Transcription factor Nuclear receptor Enzymes Structure 1- Ion channels 2- G-protein coupled 3- Tyrosine kinase 4- Matrix protein 5- Enzymes 6- Transporters 7- Nuclear receptor

21. Type of Receptor-Drug interactions Receptor: The component of the organism (or cell) interact with the chemicals. H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.23.

22. The receptor-effector linkage

23. The Receptor Types H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, p.27.

24. Ion Channels Gating • Voltage gating • Ligand gating • Multiple subunits making a pore in the middle • In ligand gated two similar subunit  Ligand binding Flow of the current • Inward or outward current of ions Type of Ions • Na+, K+, Ca++, Cl-

25. Ion Channels • Ligand gated : nicotinic receptor, GABA receptor • Voltage gated: Calcium channels ( N, L,T, P type); Sodium channels; Potassium channels (inward rectifier)

26. Ligand Gated Ion Channel

27. Glutamate receptor Domain structure in glutamate receptor ion channels. • Each subunit consists of a bilobed amino-terminal domain (NTD), the two-domain ligand-binding core (D1 D2), an ion channel with three membrane-spanning segments (1–3) and a pore loop (P), and a cytoplasmic domain of variable length. Mayer, Current Opinion in Neurobiology 15, 2005, 282-288.

28. Voltage sensor Segments S1–S4 : S1, white; S2, pink; S3, red; S4, light blue; S5–S6 pore region, green. (a) The paddle model as presented by Jiang et al.[9]. In this model the S1 and S2 segments are embedded in the bilayer and the S4 charges (dark blue circles) are pointing into the bilayer. (b) Topology as proposed by Cuello et al.[8]. S1 and S2 segments are transmembrane and S1 is surrounded by the rest of the protein. The S4 segment is located in the periphery but its charges are pointing away from the bilayer and into the protein core, with the most extracellular charge exposed to the transition region of the lipid bilayer. Because most of the charges are covered by the S4 segment, only the first and fourth charges are shown.

29. N-Terminal III IV V VI VII I II C1 C3 C2 C-Terminal G protein coupled receptor

30. G protein coupled receptor • Seven transmembrane domain; Intracellular and extracellular loops • Couples to G protein (α and  subunit) • Active receptor activates G protein and dissociates α subunit from  subunit • GPCR couples to multiple effectors • Inactivation of G protein changes the receptor into inactive state

32. a a a GTP bg bg G protein cycle AC PLC Ligand + GDP GDP

33.  subunit: • 23 distinct subtype • Divided into 4 family 1-Gs consists of s and olf 2-Gi consists of i, o, t and z 3-Gq consists of q, 11/14 and 15/16 4-G12/13 consists of 12 and 13 • GTPase domain • One large  helix  Subunits • Functionally one subunit • Six  subunits and 12  subunits 1  1 and 2 2  2 but not 1

34. N-Terminal III IV V VI VII I II C1 C3 C2 C-Terminal

35. GPCR Baldwin model(Top View) Inactive state Active state Current Opinion in Cell Biology 1997, 9:134–142

36. THE JOURNAL OF BIOLOGICAL CHEMISTRY. Vol. 273, (2), pp. 669–672, 1998

37. G protein coupling • Gαs couples to AC and  cAMP • Gαs can be activated by cholera toxin (CTX) • 2-adrenergic, D1 dopaminergic, PGE2 receptor • Gαi couples to AC and  cAMP • Gαi can be inhibited by pertussis toxin (PTX) • 2-adrenergic, M2 muscarinic, 5-HT1 serotonergic • Gαo couples to K+ channel and hyperpolarizes the cell • Gαo can be inhibited by pertussis toxin (PTX) • M2 muscarinic, 5-HT1 serotonergic

38. G protein coupling • Gαt couples to Ca++ channels and closes the channel • Retinal receptors • Gαq couples to PLC and  DAG and Ca++ • M1 muscarinic, 5-HT2 serotonergic • G couples to PLC, AC2,6, IRK channel and PI3Kinase

40. Pharmacodynamy& Receptors Dr. M. H. Ghahremani References: 1-B.G.Katzung; Basic & Clinical Pharmacology 2001, Chapter 2, p 9-34. 2-H.P. Rang, M.M. Dale & J.M. Ritter, Pharmacology 2003, Chapter 1 & 2, p7-50. 3-Goodman & Gilman's: The pharmacological basis of therapeutics 2006, Chapter 1, p1-40. Dr. Mohammad H Ghahremani

41. Receptor Protein-Tyrosine Kinases

42. Tyrosine kinase receptor Dimerization and Autophosphorylation of Receptor Protein-Tyrosine Kinases

43. Association of Downstream Signaling Molecules with Receptor Protein-Tyrosine

44. Ras Activation Downstream of Receptor Protein-Tyrosine Kinases

45. Activation of the ERK/MAPKinases

46. Tyrosine kinase receptor Signaling • These receptors directly link to their intracellular enzyme targets • Commonly associated with polypeptide growth and differentiation signals. • The basic structure consists of an N-terminal ligand binding domain, a single transmembrane α helix and a cytosolic C-terminal domain that has the protein-tyrosine kinase activity. • Can be a monomer or a dimer • Following ligand binding these receptors form dimers and then autophosphorylate at tyrosine residues in the C-terminus • The phosphorylation stimulates the kinase activity of the receptor and creates binding site for additional intracellular signals • They can then activate target molecules through kinase activity or protein binding and subsequent activation

47. Signaling from Cytokine Receptors

48. Tyrosine kinase receptor Signaling

49. Nuclear Receptors • Ligand easily passes the membrane • A ligand binding and a DNA binding domain • Activates transcription :Directly or indirectly • Gene activation is dependent on the cell type • Thyroid receptor, Steroid receptor, Vitamin D

50. Estrogen Action