Lecture 12

Question 1

What are the current cancer therapies and cures?

Answer 1

1. Surgery:
   A) Tumor removal (risk of cancer cells being left behind)B) Prophylactic (definition: intend to prevent disease) surgery (breast/ovary removal)
2. Kill diving cells
   A) Radiation therapy

B) DNA replication stress (Drugs that can block replication fork)

3. Block functions of oncogenes as drug targets
   A) Gleevac targeting ABL1 oncogene
4. Synthetic lethal induction
   a) PARPi for BRCA 1/2 LOH
5. ## CAR T-cell Immunotherapy

Question 2

Why is BRCA2 so important?

Answer 2

It is a tumor suppressor gene required for homology-directed repair.
*Cannot survive with BRCA1 and BRCA2 as we need them for DNA repair when dsDNA breaks occur so that they do not accumulate.
- Can also cause cancer in men

Question 3

PARP inhibitors (PARPi)

Answer 3

• These inhibitors can act as a treatment for BRCA-deficient cancer
  
  • So those with mutations in BRCA 1/2 that disrupt homology-directed repair

*NOTE: BRCA 1/2 -/- cells CANNOT repair DSBs and undergo apoptosis

Question 4

What is the inhibitor for the BCL-ABL oncogene?

Answer 4

Imatinib AKA Gleevac targets the BCR-ABL (a fusion of the BCR and ABL proteins forming a constitutive tyrosine kinase)
- Gleevac is the INHIBITOR FOR the tyrosine kinase (BCR-ABL protein fusion)
- Helps to inhibit BCR-ABL from phosphorylating multiple substrates which can lead to oncogenesis.
- Does this by binding to the catalytic pocket to inhibit the enzyme
*Requires ATP binding + hydrolysis!

Question 5

Describe CAR T-cell Therapy

Answer 5

AKA immunotherapy:
This is a type of therapy where T-cells are genetically engineered to bind to specific proteins (specifically, antigens) on cancer cells
- CAR T-cells are made by inserting CAR gene to specific tumor marker
- Car T-cells recognize TAA (Tumor Associated Antigen) and kills the cell

*CAR = Chimeric Antigen Receptor
*Patients with Lupus – an autoimmune disease with dysregulated self-reactive B-cells
- Make autoantibodies against its on body’s cells!

Question 6

How does NHEJ and homology-directed repair lead to DIFFERENT outcomes in BRCA 1/2?

Answer 6

–> For BRCA 1/2, when DSB, 2 pathways can occur:

1) NHEJ, apoptosis, or other error-prone pathway:
- LOH occurs: +/- –> -/-
2) Homology-directed repair:
- use homologous DNA sequence to repair DSB sequence
- BRCA 1/2 -/+

Question 7

What can cause ssDNA breaks to occur?

Answer 7

DNA replication stress due to metabolism or environment which causes a stalled replication fork, resulting in ssDNA breaks.

*ssDNA breaks can turn into DSBs

Question 8

Describe PARPi and their importance

Answer 8

*PARPi = PARP inhibitors:
- REQUIRED to repair ssDNA breaks that occur due to DNA replication stress such as:
a) The environment: X-rays, gamma-rays from outer space can all cause ssDNA breaks
b) Metabolism: free radicals can cause ssDNA breaks

*Importance: used as treatment for BRCA-deficient cancer

Question 9

Explain the difference between the lifespan of a normal vs tumor BRCA 1/2 in terms of a ssDNA break

Answer 9

–> Following a ssDNA in a normal BRCA 1/2 cell:
- Normal BRCA 1/2 cell = +/+ or +/- or -/+
1. PARPi is inhibited from fixing the ssDNA break allowing it to turn into a DSB.
2. Active BRCA1/2 DSB goes through DNA repair allow the cell to survive

–> Following a ssDNA in a tumor BRCA 1/2 cell:
- Tumor BRCA 1/2 cell = -/-
1. The PARPi is inhibited from fixing the ssDNA break which allows it to turn into a DSB.
2. Since there is no functionally active BRCA 1/2 to repair the DSB, the DSBs accumulate –> causing DNA damage and lead to cell death

Question 10

Poly polymerase (ADP-ribose) ?????????

Question 11

Describe Imatinib

Answer 11

Imatinib AKA Gleevac is an inhibitor of the tyrosine kinase protein (The BCR-ABL gene fusion)
- When BCR & ABL genes fused together, they combine to create a protein that has tyrosine kinase activity
- BCR = N-terminal
- ABL = C-terminal
- This protein is constitutive which means that it is always ON
-