Download 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»
–
MCD 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
MCD 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)
MCD
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 