CYP450

2014. 2. 21.

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CYP families in Humans

• Major Phase I enzymes: ~90% of Phase I metabolism

[CYP family: Heme-thiolate enzymes]• Involves in Hormone synthesis and metabolism, cholesterol synthesis, Vit. D metabolsim Metabolizes potentially toxic compounds, including drugs and products of endogeneous metabolism such as bilirubin, principally in the liver.

• Humans have 57 genes and more than 59 pseudogenes divided among 18 families of cytochrome P450 genes and 43 subfamilies.

CYP3A4

familysubfamily

isozyme

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~73% ~75% 46%

16%

12%

9%

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Mechanism of CYP450 reactions• Monooxygenase reactions involving TWO-stage reduction of molecular oxygen• Single oxygen atom insertion into substrate molecules• R-H + O2 + NADPH + H+ → R-OH + H2O + NADP+

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Targeting, retention and transport microsomal CYP proteins

Curr Opin Drug Devel 2010 78

• Human CYPs are Primarily membrane-associated proteins.(Inner membrane of mitochondria or Endo-

plasmic reticulum cell)

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Why dose we concern about CYP450?

• Drug-Drug interactions can occur when two drugs are co-administered and compete for the same enzyme.• In CYP inhibition, one drug (perpetrator) binds to the isozyme and the other drug (victim) is excluded from metabolism, thus increasing to a toxic concentration.• Irreversible binding inactivates CYP: Mechanism-based inhibition.• CYP inhibition can cause withdrawal from Clinical use or restrictive labeling for a drug.

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Importance of CYP inhibition

• Terfenadine (Seldane) - Antihistamine - Prodrug completely metabolised to the active form Fexofenadine - Risk of Torsa de Point (QT interval prolongation)

Fexofenadine

-8-DDT 2005 4 825

Binding mode reversible vs irreversible

Reversible Irreversible

Activated by the enzymes to form a reactive metabolitethat covalently binds to the apoprotein.

Irreversible Quasi-Irreversible

inhibitor blocks access of the drug to me metabolized to the active sites of the enzyme

inhibitor is activated by the enzyme to form a reactiveintermediate that covalently binds to the prosthetichaem group.

inhibitor is activated by the enzyme to form an intermediateThat results in the destruction of the prosthetic haem group(metabolic intermediate complex).

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in vitro CYP inhibition

• Criteria at the Early Stage of drug discovery

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in vivo CYP inhibition

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Case Study

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Structural modification strategy

• Pyridine analogs• Terminal imidazoles• Terminal olefin• Terminal acetylene• Quinolines• Amines • Hydrazines• Hydrazones• Methylene dioxyphenyls etc. Current Drug Metab 2000 67

Molecules 2007 1910

Isoform Specificity?

Curr Opin Drug Devel 2010 66

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Isoform Specificity

DDT 2002, 7(17), 918

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Isoform Specificity

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CYP1A2 Substrates

• CYP1A2 tends to catalyze the metabolism of planar amines and amides

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CYP2D6 Substrates

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CYP2D6 Substrates

• A large No. of drugs have basic N atoms CYP2D6 metabolizes ~30% of drugs• Low abundance(~2%) may be saturable and result in a Non-linear increase in drug concentration with dose• Polymophism: 7~10% of white population lacks CYP2D6 Toxicity!

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CYP2C9 Substrates

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CYP2C9 Substrates

7.8Å

4.0Å

Cationic 2C9

82o

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CYP3A4 Substrates

• Macrolide immunosuppressant Sirolimus (Rapamycin)• Prophylaxis against graft rejection in kidney transplant patients in combination with cyclosporine

r < 2.7Å Iq-180OI <45O

JMC 2001 44 2027

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CYP3A4 Substrates

• Introduction of Steric Hinderance at 2-, 6- position of N of heterocycles• Electronic substitution (Halogen) to reduce pKa of N

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Methods

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Screening methods

DDT 2002, 7(17), 918

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Assessing DDI

NRDD 2005 4 825