1. CYP450

2. CYP families in Humans isozyme CYP3A4 subfamily family
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.
isozyme
CYP3A4
Cytochrome P450은 heme을 prosthetic group으로 가지는 superfamily 효소군으로 대부분의 약물이나 환경물질들 등의 다양한 외인성 물질 또는 스테로이드나 지질 등의 내인성 물질에 대해 산화적 대사 작용을 수행하는 생명체에 필수적인 촉매효소로 알려졌다.
subfamily
family

3. 9%
16%
12%
~75%
~73%
46%

4. 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+
Cytochrome P450들은 heme에 포함되어 있는 철 이온이 환원상태에서 일산화탄소(CO)와 결합시 450 nm의 특이적인 Soret 흡광스펙트럼을 보임으로써 그 이름이 유래되었다

5. Targeting, retention and transport microsomal CYP proteins
Human CYPs are Primarily membrane-associated proteins.(Inner membrane of mitochondria or Endoplasmic reticulum cell)
Curr Opin Drug Devel

6. 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.

7. 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. Binding mode reversible vs irreversible
inhibitor blocks access of the drug to me metabolized to
the active sites of the enzyme
Activated by the enzymes to form a reactive metabolite
that covalently binds to the apoprotein.
Irreversible
Quasi-Irreversible
inhibitor is activated by the enzyme to form an intermediate
That results in the destruction of the prosthetic haem group
(metabolic intermediate complex).
inhibitor is activated by the enzyme to form a reactive
intermediate that covalently binds to the prosthetic
haem group.
DDT

9. in vitro CYP inhibition
Criteria at the Early Stage of drug discovery

10. in vivo CYP inhibition

11. Case Study

12. Structural modification strategy
Isoform Specificity?
Pyridine analogs
Terminal imidazoles
Terminal olefin
Terminal acetylene
Quinolines
Amines
Hydrazines
Hydrazones
Methylene dioxyphenyls etc.
Molecules
Current Drug Metab
Curr Opin Drug Devel

13. Isoform Specificity
DDT 2002, 7(17), 918

14. Isoform Specificity

15. CYP1A2 Substrates
CYP1A2 tends to catalyze the metabolism of planar amines and amides

16. CYP2D6 Substrates

17. 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!

18. CYP2C9 Substrates

19. CYP2C9 Substrates
7.8Å
82o
4.0Å
Cationic 2C9

20. CYP3A4 Substrates r < 2.7Å Iq-180OI <45O
Macrolide immunosuppressant Sirolimus (Rapamycin)
Prophylaxis against graft rejection in kidney transplant patients
in combination with cyclosporine
r < 2.7Å
Iq-180OI <45O
JMC

21. CYP3A4 Substrates
Introduction of Steric Hinderance at 2-, 6- position of N of heterocycles
Electronic substitution (Halogen) to reduce pKa of N

22. Methods

23. Screening methods
DDT 2002, 7(17), 918

24. Assessing DDI
NRDD