Wk 15: Tyrosine kinase inhibitors Flashcards
What was the first generation drug?
- Imatinib
- Inhibit: Bcr-abl, C-kit, PDGF-R, ABL2 + DDR1 tyrosine kinase
What are the different resistance that can happen against protein kinase inhibitors?
Target dependent resistance:
- Target point mutation
- Target amplification/overexpression
Target independent resistance:
- Dec drug uptake
- Inc drug efflux
- Upreg of alternate pathway
What are the 4 mutations that account for 60% of resistant mutants?
- Thr-315-Ile (gatekeeper mutation)
- Tyr-253-Phe (changes in VDW)
- Glu-255-Lys/Val (inside ATP binding pocket)
- Met-351-Thr (aE-helix of C-lobe)
What interactions can occur that may inhibit response?
- Caution w/ food/med impacting CYP3A4, if can’t avoid dec dose
- Drugs that raise gastric pH (PPI, antacids): agent = pH dependent solubility, oral + bioavailability compromised due to inc gastric pH
What are the targets of protein kinase?
- Linked to phenotype
- Upstream MAP-kinase pathway
- Single kinase (mono-specific)
- Multiple kinase (polyspecific)
What are protein kinase?
- Phosphorylated residues on protein (serine/threonine)
- Exists in multicellular organisms
What form are protein kinase usually in?
Inactive:
- Blocked by intrasteric control/pseudo substrates
- Turned on by interaction w/ messenger or phosphorylation
What is the DFG-in conformation?
- Conserved DFG motif (Mg positioning loop)
- Asp200 coordinates Mg at active site
- Phe201 packs into hydrophobic pocket creating hydrophobic regulatory spine
What is DFG-out conformation?
- Inactivation occurs when Phe201 moves out hydrophobic pocket
- Disrupts orientation of Asp200 + sterically blocks ATP binding site
- Asp200 no longer coordinates Mg
What are the different types of protein kinase inhibitors?
- Type 1: Competitive inhibitor, active, DFG in
- Type 1 1/2: Competitive inhibitor, inactive, DFG in
- Type 2: Competitive inhibitor, inactive, DFG out
- Type 3: Allosteric inhibitor near ATP
- Type 4: Allosteric inhibitor away from ATP
What are the structure-activity relationship of type 1 + 2 inhibitors?
- Heteroaromatic ring competes at adenine-binding domain of hinge region
- Lipophilic + H bonding occupy allosteric + hydrophobic pockets adjacent to adenine binding domain
- Polar groups extend into phosphate binding region
What are the structure-activity relationship of type 3 inhibitors?
- Bind in allosteric pocket adjacent adenine-binding site
- Don’t compete w/ ATP
- Hydrophobic, pie stacking + H bond groups = affinity + potency
- Electrostatic interaction btw inhibitor + ATP terminal phosphate of bound ATP + charged residue in catalytic site
What are the structure-activity relationship of type 4 inhibitors?
- Electrophilic
- Contain michael acceptor forming irreversible covalent bond w/ Cys797 flanking ATP binding site
What is the MOA of tyrosine kinase?
- ATP binds to kinase active site
- Prod ADP + phosphate unit
- Activate residue
Why is introduction of a phosphate able to cause change in conformation?
- OH of residue is less able to form H bonds
- Phosphate ionised at pH 7.4 + introduces ionic interactions
What are the components of the tyrosine kinase receptor?
- Extracellular domain
- Transmembrane domain
- Cytoplasmic domain (contains tyrosine kinase function triggering intracellular response)
What activates the tyrosine kinase receptor?
- Dimers
- Once it binds, extracellular component moves across membrane surface + docks w/ 2nd monomeric receptor
In the absence of a ligand, how does the tyrosine kinase receptor exists as?
Monomeric receptor
What happens in receptor-ligand binding?
- Receptor dimerisation
- Leads to reorganisation of intracellular domain, results in activation of tyrosine kinase
What is the key component of dimerisation?
Dimerisation arm - β-hairpin in EGFR extracellular domain - makes extensive contacts w/ binding region in other EGFR of dimer
What do mAbs target?
GF + GFr outside cell membrane
What do nibs target?
Target intracellular process:
- RTK phosphorylation
- Secondary messenger pathway
Which 4 approved monoclonal antibodies target members of the Erb-B family?
- EGFR: cetuximab
- EGFR: panitumumab
- HER2: pertuzumab
- HER2: trastuzumab
What is the mechanism of action of trastuzumab?
- Activation of antibody-dependent cellular cytotoxicity: bind to HER2 flag cells for destruction + attracts lymphocytes inducing apoptosis
- Prevention of HER2 formation: juxtamembrane region prone to proteolytic cleavage resulting in p95HER2
- Bond to extracellular domain preventing down stream activation that induces proliferation + angiogenesis - activates p27
What is the structure of trastuzumab emtansine?
- Trastuzumab w/ DM1 (cytotoxic maytansinoid)
- Each trastuzumab linked to 0-8 DM1 molecule via lysine
What is the mechanism of action of cetuximab?
- Chimeric mAb
- Binds to extracellular EGFR + turns off RAS
- Competitively blocks receptor associated tyrosine kinase activity
What is the mechanism of action of irreversible protein kinase inhibitors?
- Form covalent bond to cysteine residue in kinase active site
- Use a,b-unsaturated Michael acceptor functionality
What are the examples of irreversible protein kinase inhibitors?
Afatinib + ibrutinib
