EXAM 4 - Gleevec Case Study Flashcards
What was the first tyrosine kinase inhibitor drug?
Imatinib (2001)
What are the majority of kinase inhibitors used for?
Anticancer treatment
Explain how receptor tyrosine kinases function.
- cell-surface receptors are bound to ligand
- ATP binds in ATP-binding site of intracellular region
- autophosphorylated tyrosine residues
- results in downstream signaling effects –> cell growth
Describe why RTKs can be anticancer targets.
Misregulation of RTKs results in a constitutively active signal cascade.
* increased RTK activity = uncontrolled cell growth
Explain the use of HTS for Protein Kinase C.
Protein Kinase C (PKC) - generic cytoplasmic kinase use to identify inhibitors
* Novartis ran a HTS against PKC to identify kinase inhibitors
* HTS –> inhibit kinase activity
* Intent –> use as a generic scaffold to develop specific kinase inhibitors
What compound did Novartis find as the PKC inhibitor through HTS of PKC?
2-phenylaminopyrimidine (PAP)
* low selectivity and cellular activity
* good drug-like properties
* ATP competitive
Describe what occured at round 1 of general synthesis of Gleevec.
Functionalization at first and last step = fewer modifications of first ring
* pyridine improved PKC inhibition in cells (non-selective for any specific kianse)
* benzamide increased selectivity
Explain the purpose of ‘flag’ methyl group on a compound.
- ortho-methyl group added to phenyl ring
- prevents flexibility of the compound
- increased kinase specificity
Describe the PAP scaffold development.
- 3’-pyridyl –> enhances cellular activity
- amide –> provides selectivity against tyrosine kinases
- ‘flag’ methyl –> eliminates PKC inhibition
- N-methyl piperazine –> increases solubility and oral bioavailability
What was the final compound from the PAP scaffold?
STI571
List what kinases STI571 are active against.
- BCR-ABl
- c-kit
- PDGF
Describe the contribution of “activation loop” region on specific kinase activity.
- all kinases contain activation loop region
- this region controls catalytic activation of kinase by switching on/off
- the active conformation is similar across all known kinases
- the inactive conformation structures are varied based on specific kinases
How does STI571 affect BCR-ABl?
BCR-ABl is a protein kinase
STI571 is a specific PKC inhibitor
* STI571 binds to BCR-ABl and stabilizes the inactive conformation –> no longer will turn into active conformation
Describe Chronic Myelogenous Leukemia (CML).
CML - unregulated growth of myeloid bone marrow cells and their accumulation in the blood.
* orphan disease
* first cancer linked to specific genetic mutation
* Philadelphia chromosome –> encodes BCR-ABl protein with tyrosine kinase activity (active)
During preclinical studies of STI571, what was the effect of STI571 on BCR-ABl+ vs BCR-ABl-?
BCR-ABl+ (tumor cells that require BCR-ABl to grow) –> saw decrease in tumor growth because STI571 was able to act and inhibit BCR-ABl.
BCR-ABl- (tumor cells don’t have/need BCR-ABl to grow) –> saw no change in tumor growth because STI571 couldn’t stabilize inactive conformation of BCR-ABl (not present).
Describe the ways in which CML has formed resistance to Gleevec.
- Amplification of BCR-ABl gene - more difficult to inhibit
- Cellular activation of Src kinases –> Src kinases can continue downstream signaling cascades –> cell proliferation
- BCR-ABl mutations in Gleevec binding site –> can’t bind
- Suboptimal pharmacokinetics –> Gleevec must be influxed by OCT1 protein
