Metabolic Stability Lee, Sang-Hwi

-2- 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.

-3- Stability challenges following oral administration. pH or Enzymatic Stability Plasma Stability Nature Reviews Drug Discovery 2003, 2, 192 Gut Stability pH / Enzymatic, Plasma (hydrolysis Rx) Metabolism Liver, Intestinal First pass metabolism Intestinal lumen

동영상

In vivo assessment of diverse stability challenge -5-

-6- Metabolic Stability Effects Clearance t=0.693×Vd/Cl intestinal permeability & solubility 1 Metabolic Stability ∝

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-8- Phase I metabolism Phase I reactions ① Oxidation ② Dealkylation ③ Reduction Enzyme families catalyze : monooxygenases ① Cytochrome P450 (CYP) family : NADPH provides the e - for reducing Fe 3+ to Fe 2+ via a NADPH-CYP450 reductase ② Flavin-containing monooxygenase (FMO) family : NADPH directly reduces the flavine RH + O 2 + NADPH + H + → ROH + H 2 O + NADP +

-9- Cytochrome P450 (CYP) family RH + O 2 + NADPH + H + → ROH + H 2 O + NADP + 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 - Cytochrome P450 Oxidase (CYP2C9)

-10- Mechanism of catalytic cycle for CYP450 reactions. PNAS 2010, 107, NADPH-P450 reductase NADPH-P450 reductase

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-13- 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.

-14- Block Metabolic Site By Adding Fluorine

-15- Block Metabolic Site By Adding Fluori ne Buspirone : 5-HT1A receptor agonist  decrease blood pressure and heart rate or cause hypotension via a central mechanism metabolized in vivo primarily by CYP3A4. BMCL, 2004, 14, 1709

-16- 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%).

-17- Block Metabolic Site By Adding Fluorine antitumor agent JMC, 2002, 45, 744

Block Metabolic Site By Adding Other Blocking Groups -18- anti-HIV activity JMC, 2002, 45, 3143

Steric Hindrance -19- CYP2D6

Remove Labile Functional Group -20- δ opioid receptor agonist (analgesics) 5-Lipoxygenase (5-LO) inhibitor : asthma

Cyclization / Change Ring Size / Change Chirality Reduce Liphophilicity -21- Neurokinon-2(NK 2 ) antagonist

Replace Unstable Groups -22- piperidine : unstable piperazine : stable

-23- Phase II Metabolism Phase II reactions are additions (conjugations) of polar groups to the molecular structure.

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Structure Modification Strategies for Phase II Metabolic Stability -25-

Introduce Electron-Withdrawing Groups and Steric Hindrance -26- Human glucagon receptor (hGluR) antagonist

Change Phenolic Hydroxyl to Cyclic Urea or Thiourea -27- Change Phenolic Hydroxyl to Prodrug

Applications of Metabolic Stability Data ( 중요 ) -28-

-29- Metabolic stability methods

-30- Metabolic stability methods

-31- Metabolic stability methods

-32- Metabolic stability methods