Cytochrome P450 Enzymes Overview

Drug Development Process

• The drug development process from lead identification to clinical trials takes >10 years and ~$2 billion USD on average, with a >95% failure rate.
• The process consists of:
  • Discovery (1–∞ years)
  • Preclinical research (~5 years)
  • Clinical development (>5 years)
  • Review (~1 year)
  • Market approval and launch
  • Post-market monitoring (phase IV)

Clinical Development

• Clinical development consists of three stages:
  • Safety (~50 healthy patients, ~1 year)
  • Proof of concept (~250 target patients, ~2 years)
  • Regulatory evidence (>1000 target patients, >2 years)

In Silico Methods

• In silico methods can accelerate the drug development process in terms of time, labor, and cost.
• Applications of in silico methods include:
  • Hit identification
  • Target identification
  • Lead optimization
  • ADMET predictions
  • Virtual patient modeling

Cytochrome P450 Enzymes

• CYP enzymes are majorly found in the endoplasmic reticulum of the liver.
• There are over 7000 CYP proteins, with 57 known CYPs encoded by the human genome.
• CYPs are categorized into families (>40% sequence identity) and subfamilies (>55% sequence identity).
• CYPs contain a haem group, responsible for activating molecular oxygen, along with an electron from CYP reductase.
• CYPs are responsible for making compounds more hydrophilic.

CYP Reactions

• CYP reactions include:
  • Aromatic hydroxylation
  • Deamination
  • N-dealkylation
  • O-dealkylation
  • Aliphatic hydroxylation
  • N-oxidation
  • Sulfoxidation

CYPs and Drug Metabolism

• CYPs are responsible for the metabolism of >80% of drugs.
• Xenobiotics do not exclusively comprise clinical drugs.
• The main CYPs involved in xenobiotic metabolism are:
  • CYPs 1A1/2, 2A6, 2B6, 2C8/9, 2C18/19, 2D6, 2E1, and 3A4/5
• CYPs are a major consideration in drug development.
• Drugs can be substrates, inducers, and/or inhibitors of CYP enzymes.

Clinical Importance

• Genetic differences can lead to individual CYP profiles.
• Environmental factors, age, and disease can also alter CYP profile.
• Drug–drug and drug–herb interactions can lead to unexpected effects as a function of altered CYP activity.
• Therapeutic index: efficacy, safety in terms of dose and window.

Molecular Modelling

• Molecular modelling can be used to predict CYP inhibition.
• The CYP1 family is involved in the metabolism of polycyclic aromatic hydrocarbons (PAHs).
• CYP1 enzymes are overexpressed in some cancers (e.g., lung).
• CYP1 inhibition can play a role in chemoprevention.

Research Question

• Can the activities of CYP1 enzymes be selectively blocked using natural products to prevent cancer?
• One commonly used plant is Petiveria alliacea (guinea hen weed), which potently inhibits the growth of several tumours.
• The key active ingredient is dibenzyl trisulfide (DTS), a moderate inhibitor of a wide range of CYP enzymes, including carcinogen-activating members of the CYP1 family.