Transcript Metabolic stability methods

Metabolic Stability
2013. 12. 20.
Lee, Sang-Hwi
Overview
 Metabolism is the enzymatic modification of compounds
to increase clearance.
 It is a determinant of oral bioavailability, clearance, and
half-life in vivo.
 Metabolism occurs predominantly in the liver, and some may
occur in the intestine.
 Metabolic stability is increased by structure modifications that
block or sterically interfere with metabolic sites or
withdraw electrons.
-2-
Stability challenges following oral administration.
 Stability
Intestinal lumen
Gut
pH / Enzymatic, Plasma (hydrolysis Rx)
 Metabolism
Liver, Intestinal
pH or
Enzymatic
Stability
Plasma
Stability
First pass metabolism
Nature Reviews Drug Discovery 2003, 2, 192
-3-
동영상
http://www.dnatube.com/video/9334/Absorption-Oral-Medications
http://www.dnatube.com/video/4871/Drug-Metabolism
-4-
In vivo assessment of diverse stability challenge
-5-
Metabolic Stability Effects
intestinal permeability & solubility
t=0.693×Vd/Cl
Metabolic Stability
∝
1
Clearance
-6-
-7-
Phase I metabolism
 Phase I reactions
① Oxidation
② Dealkylation
③ Reduction
RH + O2 + NADPH + H+ → ROH + H2O + NADP+
 Enzyme families catalyze : monooxygenases
① Cytochrome P450 (CYP) family : NADPH provides the e- for reducing Fe3+to Fe2+ via a
NADPH-CYP450 reductase
② Flavin-containing monooxygenase (FMO) family : NADPH directly reduces the flavine
-8-
Cytochrome P450 (CYP) family
RH + O2 + NADPH + H+ → ROH + H2O + NADP+
- Cytochrome P450 Oxidase (CYP2C9)
 Metabolic switching
If metabolism of a drug at one enzyme is blocked by substrate saturation of the enzyme or by structural
modification, then metabolism at another enzyme with weaker binding or lower reactivity may become
a more favorable route.
 Drug–drug interactions
can occur if two or more drugs are co-administered, and one drug inhibits the metabolism of
a second drug at a particular isozyme, leading to toxic effect
-9-
Mechanism of catalytic cycle for CYP450 reactions.
NADPH-P450 reductase
NADPH-P450 reductase
PNAS 2010, 107, 18783
-10-
-11-
-12-
Structure Modification Strategies for Phase I Metabolic Stability
The modifications for phase I metabolism are based on two key characteristics of
metabolic reactions :
(a) binding of the compound to the metabolic enzyme
(b) reactivity of the site on the molecule that is adjacent to the reactive heme of CYP
or reactive site of another metabolic enzyme.
-13-
Block Metabolic Site By Adding Fluorine
-14-
Block Metabolic Site By Adding Fluorine
BMCL, 2004, 14, 1709
 Buspirone : 5-HT1A receptor agonist
 decrease blood pressure and heart rate or cause hypotension via a central mechanism
 metabolized in vivo primarily by CYP3A4.
-15-
Ibutilide
Class III antiarrhythmic drugs
(항부정맥 치료제)

















Absorption
Ibutilide is intravenously administered.
It has a high first-pass metabolism, which results in a poor BA when taken orally.
Individual pharmacokinetic properties are highly viable during the clinical trial.
Distribution
Ibutilide has a relatively large volume of distribution among individual subjects, which is about 11 L/kg.
Approximately 40% of the drug is bound with plasma albumin of healthy volunteers in a trial.
This is also approximately close to patients with atrial fibrillation and flutter.
Metabolism
Ibutilide has a high systemic plasma clearance that closes to the hepatic blood flow (29 mL/min/kg).
Its metabolic pathway is via liver’s cytochrome P450 system by isoenzymes other than CYP3A4 and CYP2D6 by which the heptyl side
chain of ibutilide is oxidized.
With eight metabolites are detected in the urine, however, only one is an active metabolite that shares the similar electrophysiologic
property of the Class III antiarrhythmic agents.
The plasma concentration of this metabolite is only less than 10% of ibutilide.
Excretion
After administration of ibutilide, it is quickly excreted by renal pathway with a half-life of approximately 6 hours.
Approximately 82% of a 0.01 mg/kg dose is excreted in the urine during the trial.
Among those, around 7% is excreted as unchanged drug. The reminder of the drug is excreted in feces (about 19%).
-16-
Block Metabolic Site By Adding Fluorine
antitumor agent
JMC, 2002, 45, 744
-17-
Block Metabolic Site By Adding Other Blocking Groups
anti-HIV activity
JMC, 2002, 45, 3143
-18-
Steric Hindrance
CYP2D6
-19-
Remove Labile Functional Group
δ opioid receptor agonist (analgesics)
5-Lipoxygenase (5-LO) inhibitor : asthma
-20-
Cyclization / Change Ring Size / Change Chirality
Reduce Liphophilicity
Neurokinon-2(NK2) antagonist
-21-
Replace Unstable Groups
piperazine : stable
piperidine : unstable
-22-
Phase II Metabolism
Phase II reactions are additions (conjugations) of polar groups to the
molecular structure.
-23-
-24-
Structure Modification Strategies for Phase II
Metabolic Stability
-25-
Introduce Electron-Withdrawing Groups and
Steric Hindrance
Human glucagon receptor (hGluR) antagonist
-26-
Change Phenolic Hydroxyl to Cyclic Urea or
Thiourea
Change Phenolic Hydroxyl to Prodrug
-27-
Applications of Metabolic Stability Data (중요)
-28-
Metabolic stability methods
-29-
Metabolic stability methods
-30-
Metabolic stability methods
-31-
Metabolic stability methods
-32-