How do Vinca Alkaloids work?
They bind strongly to tubulin dimers, causing a conformational change and preventing them form binding to the microtubule, and so preventing it from growing
They then condense into paracrystalline aggregates
Vinblastine binds to the (+) microtubule, preventing tubulin dimers from binding also
Using various assays, what was found to be favourable in a PARP-1 inhibitor, and what was found to not matter?
Not Matter --> Polarity of the 3-substituent, H-bonding and size
Favoured --> Electron donating groups, only a bottom substituent on the benzene, presence of an amide and a bulky substituent in the right bottom corner
What is hormone therapy?
Slowing or stopping the production of hormones like progesterone or oestrogen to prevent the growth of hormone-sensitive tumours
So you cant take HRT with a positive tumour as it would ber counteracting the action of the hormone therapy!
Why can inhibiting PARP-1 be useful following ischaic/reperfusion injuries?
Reperfusion after hypoxia will flood the cells with oxygen, which in itself is a diradical and can damage DNA
This causes overactivation of PARP-1, but due to the lack of NAD+ (due to the earlier hypoxia) there is not enough to power the cell and be the substrate for PARP-1.....meaning the enzyme functions but the cell dies due to a lack of energy! This can lead to organ faliure
So inhibiting PARP-1 will ensure that more NAD+ is readily avalaible to the cell
What are the 3 ways that hormone therapy can be used?
Adjuvant (post) treatment --> Prevent reoccureance
In advanced/metastatic breast cancer
As a neoadjuvant (pre) treatment --> To shrink the tumour
How does the Scintillation Counter work?
Beta particles strike the scintillant molecule, which then gives off photons, which can be detected by photomultiplier tubes, which we can use to quantify the amount of radiation that is present
What is positron?
A positively charged electron
When it combines with an electron it produces 2 gamma waves at 180 degree angles from each other
How does Autoradiography work?
Tritium is used to unionise silver, using beta radiation
This will mean that where ionization has occured will show silver spots
How do Bicalutamide and Enzalutamide work?
These are androgen receptors blockers
Bicalutamide --> Binds to the AR, causing internalisation of the complex (but no conformational change), but it cannot get into the nucleus. Has some agonist activity, especially at mutant AR
Enzalutamide --> The same as bicalutamide but has no agonist activity
Name 3 inhibitors of CYP17A1
Why are these good inhibitors?
Ketoconazole --> Non-specific and an antifungal
Abiraterone --> Selectivie inhibitor of CYP17A1
Abiraterone Acetate --> Pro-drug of abiraterone
These are good as they all have a nitrogen with a lone pair of electrons, allowing them to bind to metals (such as the haem needed to bind CYP17A1)
How does PARP-1 help repair DNA?
When DNA damage is detected, Poly(ADPr) binds to PARP-1 and Histone, removing the histone
The removal of the histone allows DNA repair proteins (blue) to be activated
Poly(ADP-Ribose)glycohydrolase (PARG) then removes the Poly(ADPr)s from PARP-1 and Histone, allowing them to return to normal
Why do we want to inhibit PARP-1 when treating cancer?
As it repairs ssDNA!
When giving chemotherapy we want to damage the DNA and cause the cell to die, but PARP-1 will prevent this from occuring
So giving a PARP-1 inhibitor will potentiate chemotherapy when given in combination
Explain the self-potentiation of Gemcitabine
UTP is broken down to dCTP, which inhibits dCK....so low levels of dCTP will activate dCK
dCK inhibits the conversion of Gemcitabine to F2dCMP, which we dont want!
F2dCMP inhibits the conversion of UTP to dCTP, which means that dCK is activated, and so more Gemcitabine can be converted to F2dCMP
How do Colchicine like drugs work?
Eg, Colchicine/Combretastatin A-4
They bind to colchcine binding sites on the beta subunit of tubulin dimers
If they bind to the free tubulin dimers then it prevents the microtubules from growing
If they bind to the microtubules, then it prevents them from breaking down
How does PARP-1 bind using zinc fingers?
And where would the inhibitor Olaparib bind?
The Zn2+ binds to the thiols of 3 Cys residues, and a His imidazole binds to the DNA-binding domain
Olaparib binds to the NAD+ binding domain (at the C-terminus)
How does gamma imaging and positron emmision tomography work?
Gamma Imaging --> Tc is put into the brain and then detected
- Due to its short life it is made on site from Molybdenum
PET --> 18F is used as a glucose mimic, which is taken up into the body and the gamma radiation thay is produced is detected
What is the main problem with inhibiting PARP-1?
They all function by blocking its substrate (NAD+)....but NAD+ is used everywhere! So there are so many side effects across the body
How can we block ovarian function?
Remove the ovaries (oophorectomy) or by using radiation....this is permanent
Use of GnRH/LH-RH agonists such as Goserelin (Zoladex) to supprese ovarian function
Why are microtubules a good cancer target?
As they are resposnible for maintaining structure of the cell and seperating chromosomes during mitosis (cell division)....so interfering with them will inhibit mitosis and so kill the cell
How does 6-MP and 6-TG work?
They are mimics of Hypoxanthine and Guanine respectively, but with a sulfur instead of a carbonyl (as part of the amide group)
This means that the same pathway can occur, but not fully correctly
Why are SSRIs problematic for people taking tamoxifen?
SSRIs inhibit CYP2D6, which is a vital enzyme for breaking down tamoxifen into more active metabolites
What are the 3 regions of PARP-1?
DNA Binding Domain --> Contains 2 zinc fingers that bind to the DNA tightly
Auto-modification centre --> Where it binds to glutamic acid
NAD+ Binding Domain
Explain alpha, beta and gamma decay
Alpha --> Slow moving helium nucleus (very efficient ionisation)
Beta --> High speed electron (also releases gamma radiation)
Gamma --> A photon (inefficient ionisation)
What are antimetabolite drugs?
And what are the 4 classes of drugs?
Drugs that kill cancer cells by inhibiting critical enzymes that are involved in the biosynthesis of DNA
Folate Antagonists --> Methotrexate
Pyrimidine Antagonists --> 5-FU
Pure Antagnoists --> 6-Mercaptopurine
Sugar Modified Nucleosides --> Cytarabine
What is triple negative breast cancer?
And what drug cant be used in this case?
When the tumour is ER -ve, PR -ve and HER2 -ve
Cannot take Herceptin (Trastuzumab) as no HER2 receptors
How do we block oestrogen production?
Using drugs called aromatase inhibitors to block the enzyme aromastase which produces oestrogen in the ovaries
Can only be used in post-menopausal women as pre-menopausal women create too much aromastase to inhibit
Examples --> Anastrozole (temproary), Letrozole (temporary), and Exemestane (permanent)
How does 5-FU inhibit TS?
It's metabolised to dUMP, but with a F present
The F cannot be removed (unlike the H that is normally present) due to its large electronegative charge (so cant be F+) and so the pathway stops dead, so dTMP and DHF cant be made
What was the major problem with Iniparib?
It was a non-specific thiol-reacting compound, ejecting Zn2+ from PARP-1
So it reacted with anything that had zinc fingers
Why can Pemetrexed and Raltitrexed inhibit TS?
They are analogues of 5,10-CH2-tetrahydrofolate but without the CH2, meaning it can bind to the tetrahydrofolate binding site (as a competitive inhibitor), and inhibit TS
How do Taxols work?
Eg, Paclitaxel/Docetaxel (Taxotere)
Bind to taxol binding sites inside of the microtubules, preventing the breakdown of the microtubules by stabilising it
This means that there is less tubulin dimers present, so less microtubules can be built