anti-cancer drugs

• what is EGFR?

  The epidermal growth factor receptor. It is a receptor tyrosine kinase that is expressed on the surface of many types of cells. It is a trans-membrane protein, the intracellular portion is a kinase and the extracellular portion binds a small protein called Epidermal Growth Factor.
• EGF binding to receptors leads to what?

  Leads to the dimerisation of the receptor. This causes the kinase to assume an active conformation leading to further signalling inside the cell.
• what are kinases?

  Enzymes that catalyse the transfer of a phosphate group from ATP onto a target molecule (substrate). The target can be proteins, lipids, nucleotides etc. They often sit in an inactive form become activated following phosphorylation by other specific kinases.
• EGFR will phosphorylate other kinases and that phosphorylation will cause those kinases to become activated. They will phosphorylate downstream kinases. Leading to signal amplification and converts extracellular message into an intracellular message.
• Why is EGFR an important cancer target?

  Signalling through EGFR can drive many 'carcinogenic' aspects of cancer. Such as survival, cell proliferation and angiogenesis. If the signalling becomes dysregulated, cells can become more proliferative, avoid apoptosis and more likely to migrate.
• The up-regulation (expression) of the EDFR receptor is seen in a larger proportion of tumours, particularly in lung cancer.
• what happens when mutation of the EGFR kinase domain is activated?

  This leads to the enzyme (kinase) being constitutively active. So active in the absence of EGFR binding. Which means auto-phosphorylation and dimerisation. Cells will become addicted to the EGFR signalling.
• cells with the EGFR activating mutation are more likely to what?

  To become cancerous as they receive uncontrolled 'growth' signals through the EGFR signalling pathways.
• what is IC50?

  The concentration of the drug required to achieve 50% inhibition of an enzyme. Lower numbers = more potent so more active compound. A lower concentration of the drug is needed to inhibit the target.
• Cancer cells with activating mutants are ~10 x more sensitive and can be killed at doses that have a limited effect on healthy cells.
• 1st generation of inhibitors for EGFR mutations - erlotinib and gefitinib
• why was there a need to develop a second generation of EGFR mutation inhibitors?

  Resistance. Development of a second mutation in the kinase. The T790M mutation increased the affinity of ATP and decreased the binding of drug molecules.
• what mutation occurred with the T790M mutation?

  The mutation of the threonine to a methionine which is larger. This meant that it caused a clash with the ligand when binding but didn't with ATP.
• what was different about the second generation of EGFRR inhibitors?

  Designed to form a covalent bond with a residue present in EGFR = Irreversible binding/inhibition. This overcomes the increased ATP affinity in the T790M mutated protein.
• 2nd generation EGFR inhibitors - Over time you can pull all of the EGFR into its inhibited form, but the rate at which it will do so depends on the degree of occupancy of the drug.
• 2nd generation irreversible inhibitors of EGFR (e.g. afatinib) are more potent vs T790M but were too active against WT EGFR (normal protein) to allow sufficient exposure to benefit T790M patients.

  • They are less active in the double mutant form (compared to the traditional drugs) than in the wild-type
  • And so you would get toxicity before efficacy so drugs don’t work.
• Lipophilicity and how it affects physical properties...

  A) potency

  B) solubility

  C) metabolism

  D) toxicity

  E) solubility

  F) permeability

  G) potency

  
• increase in log D;

  • More lipophilic = you are likely to increase their potency (more active)
  • Fatty molecules like to bind to proteins because water doesn’t like them.
  • But less likely to be soluble, maybe more permeable, likely to be highly metabolised (poor pharmacokinetics), might have non-specific binding to albumin/other proteins that are likely to cause toxicity
  • So in drug discovery projects, high lipophilicity is always an enemy.
• challenge when considering lipophilicity of a drug;

  need to be able to find a way to reduce lipophilicity but also maintain or increase potency and permeability.
• example of changes that alter properties of compounds (dependable);

  • adding an amine base - makes the compound more likely to be ionised so in an aqueous solution it becomes ionised lowering log D = favouring solubility
  • Adding extra nitrogen to the ring system compound makes a compound more hydrophilic.
• what is hERG activity known to cause?

  Cause heart problems in patients and IGF1R inhibition which likely causes hyperglycemia.
• changes:

  A) H

  B) log D

  C) potency

  D) position

  E) potency

  
• AZD9291 is well tolerated and demonstrates significant and prolonged target inhibition with significant tumour reduction in vivo.