Receptor Theory and Phamacodynamics 2011.9.13. Definition and characteristics of receptors Classification of Receptors Receptor activation and signal transduction ·Drug actions Classification of agonists and antagonists Dose-response relationship The Development of Receptor Theory Claude Bernard(1813-1878) A French physiologist,he contributed greatly to the development of experimental medicine.One of his studies was on the arrow poison curare.He asked the question of why the poison was effective when delivered by an arrow,but ineffective when taken by mouth.His work led to the understanding that the ability of a drug to elicit its effects depends on its access to a particular location
Receptor Theory and Phamacodynamics 2011.9.13. • Definition and characteristics of receptors • Classification of Receptors • Receptor activation and signal transduction • Drug actions • Classification of agonists and antagonists • Dose-response relationship The Development of Receptor Theory Claude Bernard (1813 – 1878) A French physiologist, he contributed greatly to the development of experimental medicine. One of his studies was on the arrow poison curare. He asked the question of why the poison was effective when delivered by an arrow, but ineffective when taken by mouth. His work led to the understanding that the ability of a drug to elicit its effects depends on its access to a particular location
The Development of Receptor Theory G.G.Stokes,a physicist at Cambridge,observed in 1864 spectral changes occurred when oxygen was removed from blood or subsequently reintroduced to blood.This finding demonstrated molecular interactions between two substances,implicating a complex between oxygen and hemoglobin. As will be discussed later,one hemoglobin molecule can bind 4 oxygen molecules,and there is a positive cooperativity of binding of molecular oxygen to hemoglobin. The Development of Receptor Theory Paul Erhlich(1854-1915)was a German bacteriologist who attempted to find a 'magic bullet'to cure syphilis and was a pioneer in the study of immunology.One of his findings was made when he incubated toxins with anti-toxins in a test tube.Erhlich found that antigen- antibody interactions are direct chemical encounters and not generalized phenomena as they require an ongoing biological process in the whole body.He also coined the term"chemotherapeutic index",meaning the ratio of the minimal curative dose to the maximal tolerated dose
The Development of Receptor Theory G.G. Stokes, a physicist at Cambridge, observed in 1864 spectral changes occurred when oxygen was removed from blood or subsequently reintroduced to blood. This finding demonstrated molecular interactions between two substances, implicating a complex between oxygen and hemoglobin. As will be discussed later, one hemoglobin molecule can bind 4 oxygen molecules, and there is a positive cooperativity of binding of molecular oxygen to hemoglobin. The Development of Receptor Theory Paul Erhlich (1854-1915) was a German bacteriologist who attempted to find a 'magic bullet' to cure syphilis and was a pioneer in the study of immunology. One of his findings was made when he incubated toxins with anti-toxins in a test tube. Erhlich found that antigenantibody interactions are direct chemical encounters and not generalized phenomena as they require an ongoing biological process in the whole body. He also coined the term “chemotherapeutic index”, meaning the ratio of the minimal curative dose to the maximal tolerated dose
The Development of Receptor Theory John Newport Langley(1852-1926),a British physiologist, first coined the term"receptive substance".His work described curare as a blocker of neuromuscular transmission,as he was able to show that curare also could block chemical stimulation of frog gastrocnemius muscle by nicotine,without motor nerves.Therefore, there is a mutual antagonism between nicotine and curare,and the effect of which depends on the relative concentration of each.He also worked on atropine and pilocarpine,and the work led to the hypothesis that both atropine and pilocarpine could form a complex with a common substance at the nerve end,which we now know are the muscarinic receptors. The Development of Receptor Theory Langley's work also led to the concept that the rate of combination(binding)and the saturable effects are characteristic of drug and receptor interactions.This concept was not readily accepted at that time.For instance,Henry H.Dale(1875-1968)thought that the differential effectiveness of adrenaline analogues in mimicking sympathetic functions in varying tissues does not necessarily imply the existence of specific chemical receptors on target tissues.Eventually, experimental data prove the presence of specific receptors for these (as we know today) pharmacological interactions
The Development of Receptor Theory John Newport Langley (1852-1926), a British physiologist, first coined the term “receptive substance”. His work described curare as a blocker of neuromuscular transmission, as he was able to show that curare also could block chemical stimulation of frog gastrocnemius muscle by nicotine, without motor nerves. Therefore, there is a mutual antagonism between nicotine and curare, and the effect of which depends on the relative concentration of each. He also worked on atropine and pilocarpine, and the work led to the hypothesis that both atropine and pilocarpine could form a complex with a common substance at the nerve end, which we now know are the muscarinic receptors. The Development of Receptor Theory Langley’s work also led to the concept that the rate of combination (binding) and the saturable effects are characteristic of drug and receptor interactions. This concept was not readily accepted at that time. For instance, Henry H. Dale (1875-1968) thought that the differential effectiveness of adrenaline analogues in mimicking sympathetic functions in varying tissues does not necessarily imply the existence of specific chemical receptors on target tissues. Eventually, experimental data prove the presence of specific receptors for these (as we know today) pharmacological interactions
Receptors cinProtein-Coupled Receptor Systems 5HTa serotonin R G protein- Cell Surface Multisubunit Ligand-gated lon channels GTP GDP Catalytic Activities: G Proteins: Effectors atawth factor tecentors Defined by Regulated by Cytoplasm a Subunits: composition TGFB-rec 1 adenyly cycase.t Ca2.currents guanylin recepto Nat exchange Cvtosoli Nucleus regulated by 所subunits: phospholipase CB Figure 2-1.Structural motifs of physiologice and their relationships to signaling pathways. Basic qualifications for a receptor For a molecule to qualify as a receptor,it must meet at least 3 criteria: 1.In a given sample,there is finite number of receptors (saturation of binding and effect) 2.Ligand binding is specific and can be competed off by a ligand of the same or similar structure(e.g., agonists and antagonists) 3.Binding kinetics is consistent with biological effect (concentration-and time-dependency)
Basic qualifications for a receptor For a molecule to qualify as a receptor, it must meet at least 3 criteria: 1. In a given sample, there is finite number of receptors (saturation of binding and effect) 2. Ligand binding is specific and can be competed off by a ligand of the same or similar structure (e.g., agonists and antagonists) 3. Binding kinetics is consistent with biological effect (concentration- and time-dependency)
Other qualifications for a receptor High affinity:Most endogenous ligands bind to their cognate receptors with high affinities(usually in the range of nmol/L) Reversibility:In most cases,the bound ligand can be dissociated from the receptor,or replaced by another ligand that also bind to the same receptor Subtypes and subunits:Many receptors have subtypes, which are structurally and functionally similar receptors (but functions could be different).Some receptors are composed of multiple subunits Classification of receptors(by location) Cell surface receptors:Most receptors are present on cell surface,which is the boundary between intracellular environment and extracellular environment Cytoplasmic receptors:Usually participate in the transport of ligands and/or their signaling Nuclear receptors:Usually involved in transcriptional regulation
Other qualifications for a receptor • High affinity: Most endogenous ligands bind to their cognate receptors with high affinities (usually in the range of nmol/L) • Reversibility: In most cases, the bound ligand can be dissociated from the receptor, or replaced by another ligand that also bind to the same receptor • Subtypes and subunits: Many receptors have subtypes, which are structurally and functionally similar receptors (but functions could be different). Some receptors are composed of multiple subunits • Cell surface receptors: Most receptors are present on cell surface, which is the boundary between intracellular environment and extracellular environment • Cytoplasmic receptors: Usually participate in the transport of ligands and/or their signaling • Nuclear receptors: Usually involved in transcriptional regulation Classification of receptors (by location)
Receptors chinRProten-Coupled Receptor Systems 5HTa serotonin R Cell Surface Multisubunit Ligand-gated lon channels GTP GDP Catalytic Activities: G Proteins: Effectors atawth factor tecentors Defined by Regulated by Cytoplasm a Subunits composition TGFB-rec I adenytyl cycase.Ca.cuments Nat exchange Nucleus regulated by 所subunits: phospholipase CB Figure 2-1.Structural motifs of physiologi and their relationships to signaling pathways. Classification of receptors(by structure and mode of action) 1)lon channel receptors:Include ligand-gated ion channels and voltage-gated ion channels 2)G protein-coupled receptors:Largest cell surface receptor family (or "superfamily").Also termed 7-TM (transmembrane domain)receptors 3)Kinase-linked receptors:These receptors have an extracellular ligand-binding domain and an intracellular kinase domain 4)Nuclear receptors:These receptors are named not just for their locations,but also for their mode of activation
1) Ion channel receptors: Include ligand‐gated ion channels and voltage‐gated ion channels 2) G protein‐coupled receptors: Largest cell surface receptor family (or “superfamily”). Also termed 7‐TM (transmembrane domain) receptors 3) Kinase‐linked receptors: These receptors have an extracellular ligand‐binding domain and an intracellular kinase domain 4) Nuclear receptors: These receptors are named not just for their locations, but also for their mode of activation. Classification of receptors (by structure and mode of action)
Receptor topography and classification Cell surface receptors (shown as enzyme-linked receptor with intrinsic enzymatic activity） 市 3 TRE Nuclear receptors Gene (ligand-dependent transcriptional ↑or↓Gene expression regulators) Receptor topography and classification EGF receptor Nicotinic AchR o(outside) i(inside) Transferrin IAP(CD47). receptor(CD71) and GPCRs S.J.Singer(1990.Ann Rev Cell Biol 6:247)
Nuclear receptors (ligand-dependent transcriptional regulators) Cell surface receptors (shown as enzyme-linked receptor with intrinsic enzymatic activity) Receptor topography and classification (outside) (inside) EGF receptor Transferrin receptor (CD71) IAP (CD47), and GPCRs Nicotinic AchR S.J. Singer (1990, Ann Rev Cell Biol 6:247) Receptor topography and classification
Receptor topography and classification Type V is cell surface molecule anchored to plasma membrane through a glycosyl-phosphatidyl inositol (GPI)anchor.The two examples shown are neural GPI cell adhesion molecules(GPI-CAMs). Other examples include CD16,also called FcyRIll, CD14.which is associated with Toll-like receptor 4 for signaling.and uPA receptor(uPAR,also called CD87). GPIlinkage A Some GPl-linked receptors are capable of trans- membrane signaling.The mechanism has not yet been fully elucidated. GPI linkage B L 品 Receptor-mediated signaling RTK:receptor tyrosine kinase (e.g.,receptors for EGF,PDGF) Shc:proto-oncogene,adaptor Grb2:adaptor protein MEK Sos:Ras exchange factor ERK Ras:Small GTPase Mnk CYTOPLASM Raf,MEK,ERK:kinases Elk-1:transcription factor NUCLEUS Mnk:a MAPKAPK
Type V is cell surface molecule anchored to plasma membrane through a glycosyl-phosphatidyl inositol (GPI) anchor. The two examples shown are neural GPI cell adhesion molecules (GPI-CAMs). Other examples include CD16, also called FcγRIII, CD14, which is associated with Toll-like receptor 4 for signaling, and uPA receptor (uPAR, also called CD87). Some GPI-linked receptors are capable of transmembrane signaling. The mechanism has not yet been fully elucidated. Receptor topography and classification Receptor‐mediated signaling RTK: receptor tyrosine kinase (e.g., receptors for EGF, PDGF) Shc: proto-oncogene, adaptor Grb2: adaptor protein Sos: Ras exchange factor Ras: Small GTPase Raf, MEK, ERK: kinases Elk-1: transcription factor Mnk: a MAPKAPK
G protein signaling (in phagocytes) Signal amplification GEF Downstream effectors Ga-GDP GaGTP PLC-B PI-3 kinase Sre GAP MAPK Ca2 Signal integration CAMP Nuclear Membrane Small Cytoskeleton Phoaphatase translocation Phosphorylation translocation GTPase reorganization Suppression NF-xB,AP-1 NADPH Granule Cell shape change oxidase release Adhesion Cytokine production Bacterial killing Chemotaxis Binding of one ligand to two receptors Ligand-gated ion (Na)channel found in autonomic ganglions,adrenal medulla. neuromuscular junction. Binds both acetylcholine and nicotine Pentameric receptor comprised of 4 different subunits:a(2),B,y,8 M2 G protein-coupled receptor with typical "cardiac" 7-membrane span structure The acetylcholine effect is mimicked by muscarine M1 and M3 couple to Gaq:M2 couples to Gai Gi
G protein signaling (in phagocytes) Gα•GDP GAP GEF Gα•GTP βγ βγ Pi Downstream effectors PLC-β PI-3 kinase Src MAPK Ca2+ Signal amplification Signal integration Small GTPase Cytoskeleton reorganization Membrane translocation cAMP Phoaphatase Phosphorylation Nuclear translocation Cell shape change Chemotaxis Adhesion Cytokine production Bacterial killing NF-κB, AP-1 Granule release NADPH oxidase Suppression • G protein-coupled receptor with typical 7-membrane span structure • The acetylcholine effect is mimicked by muscarine • M1 and M3 couple to Gαq; M2 couples to Gαi M2 “cardiac” Gi • Ligand-gated ion (Na+) channel found in autonomic ganglions, adrenal medulla, neuromuscular junction. • Binds both acetylcholine and nicotine • Pentameric receptor comprised of 4 different subunits: α(2), β, γ, δ Binding of one ligand to two receptors
Ligand-receptor interaction Rate of reaction is driven by the mass of reactants on each side of the equation 0R岩R Initial association rate=kI[D][R] Initial dissociation rate=k2 [DR] [D]=concentration of free radioligand [R]=concentration of unbound receptor [DR]=concentration of ligand receptor complex [DR]+[R]=[RHTOT Ligand-receptor interaction At equilibrium,the rate of association equals to the rate of dissociation,and therefore k [DIIR]=k [DR] The rate of bound drug to the reactants is: [DR] -=molar 0阿 KA=association constant at equilibrium Kp.or dissociation constant at equilibrium,is more often used for its unit being molar rather than reciprocal molar: [DIg-是-Kmolar D风 The smaller the value of Kp.the higher the affinity
• Rate of reaction is driven by the mass of reactants on each side of the equation Initial association rate = k1 [D][R] D + R k2 k1 DR Initial dissociation rate = k2 [DR] [D] = concentration of free radioligand [R] = concentration of unbound receptor [DR] = concentration of ligand receptor complex [DR] + [R] = [R]TOT Ligand‐receptor interaction At equilibrium, the rate of association equals to the rate of dissociation, and therefore k1 [D][R] = k2 [DR] The rate of bound drug to the reactants is: [D] [R] [DR] = = k1 k2 KA, molar -1 KA = association constant at equilibrium KD, or dissociation constant at equilibrium, is more often used for its unit being molar rather than reciprocal molar: [D][R] [DR] = = k2 k1 KD, molar The smaller the value of KD, the higher the affinity Ligand‐receptor interaction