Cancer pharmacology Flashcards
Definition of apoptosis
Programmed cell death
How is apoptosis and cell proliferation related?
Both occur continuously in the body
Billions of new cells are generated daily from proliferation, with equivalent numbers being removed by apoptosis
Which processes is cell proliferation involved in?
Growth
Repair and healing after injury
Acute and chronic inflammation
Hypertrophy and hyperplasia
Which processes is cell apoptosis involved in?
Embryogenesis
Development of self-tolerance in the immune system
Regression of mammary gland cells after lactation
Shedding of the intestinal lining
Pathophysiology of autoimmune, neurodegenerative and cardiovascular diseases
What triggers the cell cycle?
Growth factor interaction
What controls the cell cycle?
Kinases
How do kinases control the cell cycle?
Act as transcription factors
Enable the transcription of positive and negative regulators of the cell cycle
Example of positive regulators of the cell cycle
Cyclins
Cyclin-dependent kinases
Examples of negative regulators of the cell cycle
p53 proteins
Rb proteins
Cdk inhibitors
How do growth factors control the cell cycle?
Bind to receptor tyrosine kinases
Stimulate the production of kinases
Kinases then stimulate the production of positive and negative regulators of the cell cycle
What is the role of integrins in the control of the cell cycle?
Integrins are transmembrane receptors
These bind to components of the extracellular matrix
Cooperate with GFs in the production of cell cycle transducers
What, apart from the production of regulators of the cell cycle, can GFs stimulate the release of?
Can stimulate the cells to release MMPs
These degrade the local matrix
Make space for increasing cell numbers
During which part of the cell cell cycle do growth factors act on?
G1 phase
What are the 5 phases of the cell cycle?
G0
G1
S
G2
Mitosis
What is the G0 phase?
Resting phase
What is the G1 phase?
Gap between mitosis and S phase
Cell is preparing for DNA synthesis
What is S phase?
Phase of DNA synthesis
During which the DNA is duplicated
What is the G2 phase?
The gap between S phase and mitosis
Cell is duplicating its other constituents
What is M?
Mitosis
Split into metaphase, anaphase and production of daugher phase
The daughter cells can then re-enter G1 or G0
Where does checkpoint 1 target?
Between G1 and S
Which proteins act on checkpoint 1?
The Rb protein acts as a break here, keeping the cell in G1 by inhibiting the genes necessary for entry into S phase
The p53 protein stops the cycle here if there has been DNA damage
Where does checkpoint 2 target?
Between G2 and Mitosis
What is the difference between apoptosis and necrosis?
Apoptosis is a programmed sequence of biochemical processes
Necrosis is disorganised disintegration of damaged cells, resulting in products that trigger the inflammatory response
What is necessary for a cell to survive?
It must constantly be receiving continuous stimulation by survival factors
If this essential signalling by the anti-apoptotic pathway ceases, the cell’s self-destruct machinery is activated
= Death by neglect
Pro-survival factors
Cytokines
Integrins
Hormones
Adhesion factors
What are the two main apoptotic pathways?
Death receptor pathway
Mitochondrial pathway
What is different about the death receptor pathway?
It involves binding of death receptor ligands
So it is a death by design mechanism
Not inhibited by the anti-apoptotic pathway
Which apoptotic pathway is inhibited by the anti-apoptotic pathway?
The mitochondrial pathway
Describe how binding of death receptor ligands triggers apoptosis
- Death receptor ligands bind to receptors
- The receptor dimerises, causing activation of adapter proteins
- Adapter proteins activate Caspase 8
- Caspase 8 activates caspase 3
Example of a death receptor ligand
TNFa
What does activation of caspase 3 result in?
Effector stage activation
- Cleavage and inactivation of enzymes and structural constituents
- Fragmentation of genomic DNA through DNAse activation
Describe the mitochondrial apoptotic pathway
- DNA damage causes the mitochondria to stimulate caspase 9
- Caspase 9 activates caspase 3
How does DNA damage cause the mitochondria to stimulate caspase-9?
DNA damage stimulates pro-apoptotic members of the Bcl-2 family to promote the release from the mitochondria of cytochrome c
Cytochrome c complexes with Apaf-1 (apoptotic protease-activating factor 1)
This complex activates caspase 9
How does the action of caspase 3 lead to phagocytosis of the cell?
The cell is reduced to a cluster of membrane-bound bodies each containing a variety of organelles
These display eat-me signals which are recognised by macrophages
Which proteins normally control the action of caspases?
Inhibitors of apoptosis proteins
What does cancer refer to?
Malignant tumour
What does cancer manifest as?
Uncontrolled proliferation
Invasiveness
Infiltration of normal tissue
Loss of function due to the lack of capacity to differentiate
What are the two main alterations in DNA underlying cancerous change in a cell?
Inactivation of tumour suppressor genes (p53, APC)
Activation in proto-oncogenes (RAS, MYC)
What type of process underlies the development of cancer?
Multistage process
More than one genetic change
Non-genetic factors increasing the likelihood that the mutation will result in cancer
What are the drivers of the cell cycle?
CDK
Cyclins
What happens if you have different amount of CDKs and cyclins than normal?
If too little - not enough cell replication
If too much - a lot of cell replication
How do mutations in RAS (oncogene) lead to cancer?
RAS is a receptor-bound to GF receptors
When GFs bind to their receptors, the RAS protein becomes activated, it induces transcription of cyclins and CDK
Mutations to these RAS proteins leads to uncontrolled transcription CDK and cyclins
Causing uncontrolled cell growth
What is the role of tumour suppressor genes?
Prevents abnormal cells from progressing in the cell cycle
How does p53 suppress cell proliferation?
p53 is a transcription factor controlling the transcription of p21
p21 is tumour suppressing since it inhibits CDK and cyclins for carrying out their functions
What process is required for cancer growth?
Angiogenesis
Allows cell infiltration to nearby tissues and metastasis
What are most anticancer agents like?
Cytotoxic
Antiproliferative
What, regarding cancer, are anticancer agents not able to target?
Invasiveness
Loss of differentiation
Tendency to metastasise
What are the two types of chemotherapy used in disease?
Cancer chemotherapy
Antimicrobial chemotherapy
What was the only option for cancer patients before chemotherapy?
Surgical methods to remove solid tumours
Describe the history of chemotherapy development
Soldiers exposed to mustard gas developed neutropenia
This was interesting, since showed potential for treating WBC cancers
Mehcanism of mustard gas
Alkylating agents
Form covalent bonds with bases in the DNA which induces apoptosis
What was the problem with using mustard gas as a chemotherapy agent?
Toxic
Experiment showing the efficacy of alkylating agents in cancer therapy
1943
Mouse model with lymphoma showed improved survival with nitrogen mustard
Goodman and Gilman then tested the gas on patients with lymphoma = increased survival
How was Cyclophosphamide derived?
Mustard gas was modified through adding sulphate
Mechanism of action of Cyclophosphamide
Pro-drug which actively transports into cells
Once inside cells they are enzymatically converted into active, toxic form = phosphoramide
Forms covalent bonds with bases of DNA, cross-linking the two strands together
This interferes with cell division and triggers apoptosis
Side effects of Cyclophosphamide
Hair loss
GI disturbance
Nausea
Vomiting
Specific side effect of Cyclophosphamide
Hemorrhagic cystitis
Due to urinary excretion of acrolein
Active product of Cyclophosphamide
Phosphoramide mustard
Toxic product of Cyclophosphamide metabolism leading to bladder cystitis
Acrolein
Causes production of free radicals
How do you prevent bladder cystitis following Cyclophosphamide administration?
Conjugation of the dangerous metablite Acrolein with Mesna
Mesna is a sulfhydryl donor
Acts as an antioxidant and neutralises the damaging effect of Acrolein
Name another newer alkylating agent
Cisplatin
Describe how Cisplatin was discovered
Barnett Rosemberg wanted to check whether electrical stimulation could kill cancer cells
He observed that an electrical field caused bacteria to grow 300 times the length
This was because corrosion of the platinum electrodes formed a compound (Cisplatin) that inhibited DNA replication
Why did Cisplatin cause prokaryotic cells to grow?
There is no apoptotic mechanism in prokaryotic cells
Therefore, Cisplatin cause the bacteria to grow due to its inhibition of cell division
In eukaryotic cells, Cisplatin causes apoptosis due to its effect on DNA replication
What are antimetabolites?
Interfere with DNA synthesis
Describe the history behind antimetabolites
Studying vitamin deficiencies
Folate is important in cell replication
Folate deficiency = megaloblastic (very large cells) anaemia and increases the rate of spina bifida
Why is folate important in cell replication?
Without folate there is a build-up of uracil and little thymidine
Inhibiting this cycle through mimicking the mechanisms in spina bifida could help the replication of cells in cancer
How can nucleotide synthesis be targeted in cancer therapy?
Folate antagonists
Purine analogues
How do we make thymidine from uracil?
Methylation
Using Thymidylate synthase
Describe how folate is used in the production of thymidine
Folate is converted into dihydrofolate
Dihydrofolate reductase converts DHF into tetrahydrofolate
Tetrahydrofolate forms methyl-THF
Methyl-THF and Thymidylate synthase work together to convert uracil into thymidine
How do purine analogues interfere with cancer replication?
Cause destruction of the enzymes of the elongating chain of DNA due to the explosive nature of the elements attached to the nucleotides
Example of pyramidine/purine analogues used in cancer therapy
5-fluorouracil
Cytarabine
Fludarabine
Example of a folate antagonist
Methotrexate
Mechanims of action of Methotrexate
Blocks Dihydrofolate reductase
Why do antimetabolites have fewer side effects?
More selective to cancer cells, since these are replicating more often and therefore use more nucleotides
Where in nature have new cytotoxic agents been found?
Bacterial cytotoxic agents (-icin)
Plant derived cytotoxic agents
Examples of antibacterial cytotoxic agents
Doxorubicin
Bleomycin
Mechanism of action of Doxorubicin
Inhibits progression of topoisomerase II
What is the function of topoisomerase II?
Essential in the separation of entangles daughter strands during replication
Twisting tension builds up and at some point you can not separate two chains and a supercoil is formed
Topoisomerase relaxes these supercoils
What is the specific side effect of Doxorubicin?
Cardiomyopathy
What is the speicific side effect of Bleomycin?
Cardiomyopathy
Mechanism of action of Belomycin
Cause DNA fragmentation
Example of plant derived cytotoxic agents
Paclitaxel - Yews plant
Vincristine - Rose periwinkle
Mechanism of action of plant derived cytotoxic agents
Suppress microtubule formation
Suppress cell stabilisation
This induces apoptosis
Other pharmacoloical treatments for neoplastic disorders
Radioactive iodine
Hormone sensitive tumours
Monoclonal antibodies
Mechanism of action of radioactive iodine
Thyroid cells have unique abilities to take up iodine
I-131 is taken up and kills surrounding thyroid cells
Example of therapies given to hormone sensitive tumours
Prostate cancer - androgen antagonists
Estrogen positive breast cancer - oestrogen antagonists
Lymphoid cancer - glucocorticoids
Why are glucocorticoids effective treatments for lymphoid cancers?
Glucocorticoids inhibit lymphoid cell proliferation
Mechanism of action behind hormone antagonists
Hormone induces proliferation and survival of cancer cells
Antagonists blocks this survival signal
Leads to cell death
Example of an anti-oestrogen drug
Tamoxifen
Example of monoclonal antibodies used in cancer therapy
Her2+ in breast cancer
Anti-EGFR
Example of anti-EGFR monoclonal antibody therapies
Herceptin
Trastuzumab
Examples of antineoplastic resistance
Altered membrane transport
Enhanced enzymatic deactivation
Apoptotic pathway defects
Enhanced DNA repair mechanisms
What is a way to reduce resistance in cancer cells?
Combination therapy
Why does combination therapy reduce chances of developing resistance?
The possibility for cell to be resistant for one treatment = 1 in 1 000 000
The possibility for cell to be resistant to 3 treatments = 1 in 1 000 000 ^ 3
What is important in cancer therapy administration?
The way it is administered is specific to allow for the best effect on patients
Features of chemotherapy administration
Given in cycles
Given as a combination
Targeted therapy is only given after chemotherapy
Why is chemotherapy given in cycles rather than one administration?
Reduce toxicity
Target all the cancer cells
How does giving chemotherapy in cycles reduce the drugs’ toxicity?
Chemotherapy kills cells other than the cancer that are also dividing rapidly
Cycles means that the chemotherapy is given with days in between to allow for the normal cells to get back to their normal levels
Since chemotherapy affects cancer cells more than normal cells, loss of cancer cells is cumulative, whereas normal cell count goes back to normal
How does giving chemotherapy in cycles allow all cells to be targeted?
Chemotherapy targets dividing cells
Not all cells are dividing at one time
Giving the chemotherapy in cycles increases the possibility for targeting dividing cells
Are all cells killed by chemotherapy?
No
Maintaining the immune system healthy will make them deal with the cancer cells
What does giving chemotherapy in combination mean?
Less chance for resistance
Allows the dose of each individual drug to be lower
Why is giving smaller concentrations of each chemotherapeutic agent beneficial?
Less fewer side-effects
Doxorubicin - myopathy
Cyclophosphamide - bladder cystitis
Why must the targeted therapy only be given after the chemotherapy?
Chemotherapy targets specifically replicating cells.
Targeted treatments target specific cells and make them dormant.
Therefore, if you were to give the targeted treatment with chemotherapy, you would increase the number of dormant cells and therefore decrease the effect of the chemotherapy on the cancer cells.
Side effects of EGFR antagonists
Mental disturbances
Increased cholesterol
Problems with fertility
Why is there interest in targeting EGFR upstream?
Lots of side-effects in EGFR antagonists
What are alternatives to EGFR antagonists?
Drugs that target oestrogen before it is produced
Androgens become aromatised to produce oestrogen
Aromatase inhibitors prevent this and so are effective oestrogen receptors
Non-specific side-effects of chemotherapy
Hair loss
Nausea
GI problems
Anaemia
GI problems induced by chemotherapy agents
Ulcers
What causes vomiting upon chemotherapy administration?
Gastric damage
Chemoreceptor trigger zone
How does gastric damage cause vomiting?
Epithelial cells of the gastric lining become targeted by chemotherapy agents
Neurons innervating the GI sense the damage and release substance P
Substane P activates afferent neurons which send signals to the vomiting center
Where is the vomiting center found?
In the brainstem
Where is the chemoreceptor trigger zone found?
Outside the BBB
On the area postrema
What does the Area Postrema control?
Controls blood osmolarity
What does the CTZ get activated by?
Poisons
What happens when the CTZ becomes activated?
Serotonin and dopamine is released
What are the targets of anti-emetics?
Substance P
5HT3 - causing serotonin release
Dopamine
When does anaemia develop?
2 months after chemotherapy
Due to the lifespan of RBCs
Ways to treat ulcers
H2 antagonists
Proton pump inhibitors
Carbonate tablets
Ways to treat neutropenia
Injection of cytokines involved in bone marrow cell proliferation
CM-CSF
Why is IL-10 not a good target to treat neutropenia?
Causes sickness behaviour
When are cytokines given to treat neutropenia?
After chemotherapy
Giving them before will increase cell proliferation
As chemotherapy agents target rapidly dividing cells, this will worsen the neutropenia
How do EGFR antagonists increase cholesterol levels?
EGFR is important in controlling HDL levels
Blocking these reduces the concentration of HDL in the blood
