CYP450 2014. 2. 21.
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
9% 16% 12% ~75% ~73% 46%
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
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 2010 78
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.
Importance of CYP inhibition Terfenadine (Seldane) - Antihistamine - Prodrug completely metabolised to the active form Fexofenadine - Risk of Torsa de Point (QT interval prolongation) Fexofenadine
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 2005 4 825
in vitro CYP inhibition Criteria at the Early Stage of drug discovery
in vivo CYP inhibition
Case Study
Structural modification strategy Isoform Specificity? Pyridine analogs Terminal imidazoles Terminal olefin Terminal acetylene Quinolines Amines Hydrazines Hydrazones Methylene dioxyphenyls etc. Molecules 2007 1910 Current Drug Metab 2000 67 Curr Opin Drug Devel 2010 66
Isoform Specificity DDT 2002, 7(17), 918
Isoform Specificity
CYP1A2 Substrates CYP1A2 tends to catalyze the metabolism of planar amines and amides
CYP2D6 Substrates
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!
CYP2C9 Substrates
CYP2C9 Substrates 7.8Å 82o 4.0Å Cationic 2C9
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 2001 44 2027
CYP3A4 Substrates Introduction of Steric Hinderance at 2-, 6- position of N of heterocycles Electronic substitution (Halogen) to reduce pKa of N
Methods
Screening methods DDT 2002, 7(17), 918
Assessing DDI NRDD 2005 4 825