Lecture 4 - Molecular Targeting and Leukaemia Flashcards
What is the initiator mutation?
First mutation acquired by the cell
At what stage do progressive or driver mutations occur and what do these cause?
After initiator mutations
Cause metastasises
Is it easier to target overexpression or loss of function?
Overexpression
How do you identify leukaemia?
Take blood sample, if milky then leukaemia
What is leukaemia?
Unregulated proliferation of a clone of immature white blood cells, resulting in crowding normal cells out of the bone marrow
- loss of function of normal cells
How is leukaemia classified?
Acute or chronic
Myeloid or Lymphoid
Mutations in which cell type are the start of leukemia?
Haemopoietic stem cells (progenitor cells)
What are the 3 clinical stages of leukaemia?
- Chronic for 4 years approx (not as serious)
- Accelerated phase
- Then acute stage after 4 years and more mutations, very few functional white blood cells
What are symptoms of leukaemia?
Fatigue, Anaemia, swelling of spleen and liver
In Chronic Myeloid Leukaemia what occurs in 95% of cases?
Reciprocal translocation between the chromosome 9 and 22
Why is the reciprocal translocation an issue causing cancer?
As different chromosomes have different gene transcriptions, therefore if you move an oncogene to a chromosome with high transcription from low transcription this will contribute to cancer
What is the example of reciprocal translocation which occurs in CML?
- Part of the gene for BCL-2 moved from a region of low to high transcription. This is an antiapoptotic pro-survival molecule.
- Placed next to a promotor region
- Formed a fusion protein BRC-ABL
Why does the fusion protein BCR-ABL in CML cause cancer?
- swapping of the genes means the kinase domain is constantly active as protein cannot fold over
- this constantly signals for cell growth
What class is c-ABL and its normal function?
Protein tyrosine kinase in the Src family
Normally has a cytoplasmic localisation and is protective
Upon stress what occurs to c-Abl?
- translocates into the nucleus and engages with tumour suppressor proteins
- Complexes with P53 to induce cell cycle arrest and DNA repair
- complexes with P73 to induce apoptosis
- bound by pRb inducing cell cycle arrest
How does the fusion BCR-Abl protein stop the normal function of c-Abl?
- Locks in the cytoplasm so cannot go to the nucleus to interact with tumour suppressors
- In cytoplasm activates signalling pathways such as Ras-MAPK which signals for cell growth and is pro survival
Small molecule inhibitors for leukaemias with BCR-Abl
Imatinib
Dasatinib
Nilotinib
What are the 4 names of Imatinib?
Imatinib, STI 571, Glivec, Gleevec
What does imatinib work for?
- Inhibits proliferation of human CML-derived cell lines
- Blocks activity of Abl tyrosine kinase
- Also blocks PDGFbR and c-kit tyrosine kinases
What were the responses like for CML patients receiving imatinib?
Nearly all had normal white cell count within 4 weeks
Over half had cytogenic response
How does resistance build against Glivec in CML?
- Loss of sensitivity maybe due to BCR-ABL gene being amplified
- Mutations acquired over time
- clone population from the start with these resistant mutations
What pathway can imatinib upregulate which causes resistance?
Imatinib upregulates Wnt pathway increasing
activation of pro-tumorigenic TCF7 TF which confers resistance
Names of next generation 2nd and 3rd drugs made after imatinib for treatment of leukemia
2nd Dasatinib, Nilotinib
3rd Tozasertib
Fusion protein associated with chronic myelomonocytic leukaemia (CMML)?
TEL-PDGFbeta receptor fusion
What occurs to form TEL-PDGFbeta receptor fusion protein?
Translocation between chromosomes 5 and 12:
- amino terminal region of TEL (transcription factor)
- tyrosine kinase domain of the PDGF receptor
- Tyrosine kinase always active
Which drug can be used to target TEL-PDGFbeta receptor fusion in chronic myelomonocytic leukaemia (CMML)?
Imatinib also
What is the most important thing to do before treating cancers to know what to treat with?
Profile the patient
What is GIST?
Gastro Intestinal Stromal Tumours
What can be used to treat GIST?
Glivec (imatinib)
Where is c-kit found?
- In gastrointestinal tract peristalsis coordinated by interstitial cells of cajal (ICCs)
- In the ICC membrane is c-kit
What is c-kit?
A receptor tyrosine kinase
What ligand binds c-kit and under normal conditions what does this cause?
Stem cell factor
- dimerization of c-kit receptor
- phosphorylation of downstream targets
- leading to proliferation and survival signals
What happens in mutated c-kit?
- Membrane domain disrupted and constitutive activation of c-kit
- constant signalling for proliferation and cell survival
- formation of GISTs
How does Glivec (imatinib) inhibit c-kit?
- GIST have consituitive c-kit activity
- can be inhibited by Glivec (tyrosine kinase inhibitor) which competitively binds to ATP binding pocket of c-Kit in both active and inactive receptors
- inhibiting downstream signalling inducing apoptosis in GIST cells or quiescence
