Transcript TTR
Disease: Hypothyroidis m Reasons: • • Not enough iodine Autoimmune (eg Hashimoto's thyroiditis) • Radioactive Iodine • Surgery/injury Treatment • liothyroxine (synthetic T3) as hormonal replacement • There is no direct way of increasing thyroid hormone secretion by the thyroid gland Sample Presentation Slide 2 Targets: thyroid hormone carriers • In human plasma, T3 & T4 are >99% bound to carrier proteins • Reference range in normal adult blood: – Free (only free hormone is active) • T3: 3-8 pmol/L • T4: 10-20 pmol/L – Total T3/T4: 1-2.5 nmol/L (~ 100-fold higher than free) • 70% bound to thyroxine-binding globulin, TBG • 10-15% to transthyretin, TTR (same as thyroxine-binding prealbumin, TBPA) • 15-20% to albumin TBG TTR Albumin Sample Presentation Slide 3 Targets: Additional role of TH carriers in drugdrug interactions for other drugs • Because >99% of T3/T4 are proteinbound in plasma, carrier protein disregulation may lead to large variations in free T3/T4 • Factors that may change TBG concentration: – pregnancy, estrogen-containing medication (TBG) – infectious hepatitis (TBG) – nephrosis, acromegaly (TBG) – androgen or corticosteroid therapy (TBG) TBG • T3/T4 binding by TTR is inhibited by salicylates. TTR Sample Presentation Slide 4 Target: Human Thyroid Hormone Receptor • Two main types ( and ), each having 2 isoforms THR • Length: 410-490 AA THR • MW ~ 46.8-54.8 kDa THR THR • Tissues: multiple • Cellular localization: nucleus Transactivation domain DNA binding domain Ligand-binding domain 1 53 127 190 410 1 53 127 190 107 181 244 461 122 196 259 476 1 2 1 1 2 1 370 490 Hormone or agonist therapeutic Cell Nucleus Type II Nuclear Hormone Receptor (e.g. THR) Unbound or antagonist-bound (inactive) Agonist-bound (initiates gene transcription) = Co-repressor Co-activator + RNA polymerase DNA HRE target gene HRE target gene Ligand-binding domain of THR 1 in complex with T3, PDB 3gws Sample Presentation Slide 5 Drugs: Liothyronine and Levothyroxine Chemical structure(s) Synthetic L-isomer of triiodothyronine (T3) Synthetic L-isomer of thyroxine (T4) Stereo-isomers MW ~ 650 g/mol MW ~ 775 g/mol Molecular weight Amino-acid: acidic pKa = 2.13, basic pKa = 8.27 Amino-acid: acidic pKa = 2.12, basic pKa = 8.27 Ionization states/species Administered as sodium salt; orally available Administered as sodium salt; orally available Formulations Most active, but short-lived form of TH Pro-hormone (3-4 times less active) and a reservoir for T3. T4 to T3 conversion is catalyzed by cellular iodothyronine deiodinases Nature 2.5 days (free T3) 1 week (free T4) Half-life Cytomel, Tertroxin, etc. Levoxyl, Synthroid, etc. Marketing status + • • • Thyroid hormones (TH) and their synthetic analogs increase oxidative metabolism of carbohydrates, lipids and proteins by the mitochondria. They also increase the number of catecholamine (e.g. adrenaline) receptors on target cells, thereby increasing catecholamine sensitivity – may aggravate heart conditions; acute overdose may lead to heart failure Indications: hormone replacement therapy for hypothyroidism and myxedema Sample Presentation Slide 5a Liothyronine and Levothyroxine: ionization, dissolution, and phase partitioning Graph from: Acidic pKa = 2.13 Basic pKa = 8.27 Zwitterion at pH = 7, base at pH = 2, acid at pH = 9 Acidic pKa = 2.12, Basic pKa = 8.27 Zwitterion at pH = 7, base at pH = 2, acid at pH = 9 Solubility Free form: 3.96 mg/L ~ 6 uM, logS = -5.22 Sodium salt: «poorly soluble» – MCD increases solubility Free form: 0.105 ml/L ~ 0.14 uM, logS = -6.87 Sodium salt: 770 uM, logS = -3.11 More soluble at pH < 2 and pH > 8 MCD increases solubility Phase partitioning LogP = 3.9 (lipophilic, but within reasonable range) LogD = 1.3 (ionization decreases lipophilicity) LogP = 4.7 (more lipophilic) LogD = 1.7 (ionization decreases lipophilicity) MCD Sample Presentation Slide 6 Liothyronine and Levothyroxine: Target binding Constants and Energies Chemical structure(s) Full agonist Not so potent agonist (~ 10% of potency in cell culture) Mode of action Thyroid hormone receptor A (THA) pKd = 9.6 Kd = 0.25 nM Gbind = -13.4 kcal/mol - Equilibrium dissociation constant for primary and secondary targets Thyroid hormone receptor B (THB) pKd = 10.39 Kd = 0.04 nM Gbind = -14.4 kcal/mol Kd ~ 2 nM Gbind ~ -12 kcal/mol (30-50 fold lower affinity than T3) Equilibrium dissociation constant for primary and secondary targets •https://www.ebi.ac.uk/chembldb/ •Sandler B, et al. Thyroxine-thyroid hormone receptor interactions. J Biol Chem. 2004; 279(53):55801-8 Sample Presentation Slide 7 Liothyronine and THR Molecular basis of drug-target interaction Van der Waals interactions: • Perfect steric fit between the ligand and the pocket many VW contacts Electrostatics: • The three Arg in the bottom of the pocket create a strong positive charge interacting with the negatively charged carboxyl group of the drug. Sample Presentation Slide 8 Liothyronine and THR Molecular basis of drug-target interaction Hydrogen bonds: • Three residues make HBs with the ligand: Arg-282, Asn-331, and His-435 near the pocket entrance. The ligand has no unsatisfied hydrogen bond donors/acceptors. Other types of interactions are not observed: • Two aromatic residues in the pocket, none of them makes a Piinteraction. • No metal ions • Non-covalent interaction Sample Presentation Slide 9 Liothyronine: LogP, PSA and lipophilicity • The surface of Liothyronine molecule is mostly non-polar • LogP = 3.9 Liothyronine is lipophilic • Levothyroxine has an additional iodine atom: LogP = 4.7, more lipophilic • PSA is 98A2 , good permeability ( < 140). • Has 4 freely rotatable and 3 restricted bonds Polar atoms Non-polar atoms Introduction and conclusion • Interesting aspects of pharmacodynamics and pharmacokinetics resulting from the drug properties described above. Bioavailability? Protein binding? Half life? Drug interactions? • Past and future of the drug(s). Market and competition. Stage? OR: Discontinued? Why? OR: To become a generic in 1.5 yrs? • Provide good illustrations, key references and acknowledgements. • Make it fun and special