How do Platinum drugs work?
The 2 Cls create a complex with water which is positively charged, so can be attacked by DNA....usually by guanine at N7
This can create both inter and intra-strand breaks
How do mustard drugs work?
The postiviely charged nitrogen that is formed can be attacked by DNA (which is nucleophillic), which causes strand breaks
This DNA alkylation normally occurs at Guanine N7/3 and Adenine N7/3
How does Mitomycin C work?
It reacts with both the N2/7 sites on guanines in the minor groove of DNA
It is attacked by DNA twice, with the first being called the alpha, and the second, beta
The beta reaction will only occur with the correct isomer of Mitomycin C
Known as a conjugate-addition reaction
Explain Base Excision Repair (BER)
The removal of either a single (SP) or multiple damaged (LP) DNA base(s)
The N-glycosydic bond of the damaged base is broken by a DNA glycosylase, creating a abasic (empty) site
The sugar-phosphate backbone of the abasic site is then cleaved
The gap is then filled via a short patch (SP) or a long patch (LP), with PARP being involed in LPs
DNA ligases then fix the backbone via the 5' end
What is Bleomycin?
A mixture of glycopeptides that differ in their terminal amine substituent
They are freely soluble in water
They can bind transition metals (eg, Fe/Cu) and oxygen, allowing them to cause ss and ds strand breaks
Explain Nucleotide Excision Repair (NER)
DNA damage is removed by removing 27-30 bases in which the damage is located
XPC-R23 detects damage and creates a bubble by recruting other proteins that promote DNA unwinding, which creates 2 junctions
2 different DNA endonucleases then cut the DNA at the junctions to remove the damage
The remaining strand is used as a template to synthesize the other complementory strand, which reduces the chance for error
What is the structure of Bleomycins?
Metal Binding Domain --> This is what cuts DNA
What are the 3 ways in which resistance can occur against platinum drugs outside of the nucleus?
The copper transporter CTR1 can be mutated or removed in tumours, meaning drugs cant get into the cell
Glutathione and Metallothioein are upregulated in tumours, which can bind to the platinums and so remove them
Copper exporters (ATP7A/B) and glutathione-drug conjugate exporters are upregulated in cancer, causing the platinums to be pumped out of the cell
What is a Guanine Tetraplex?
4 guanine residues around a single cation (normally K+) which stabilises the complex
Form at the end of DNA strands, stabilising them. They become more stabilised when drugs bind. The increased stability means that DNA polymerase and telomerase cant bind, so DNA can't replicate.
Drugs can only bind to the top or bottom of the stacks, never in-between
Why kind of damage is done by topoisomerase II targetting drugs like doxorubcin?
Double strand DNA breaks
What is the main difference between Adozelesin and Bizelesin (CPIs)?
Adozelesin--> Can form both Watson/Crick base pairing and Hoogsteen base pairing, which makes DNA repair much harder
Bizelesin --> Binds via the A-Track that is formed between the DNA strands. The A-track bends the DNA, making Bizelesin more likely to bind
How does Pluramycin function?
Binds to the TATA-Binding Protein (TBP) -TATA box complex
Alkylation is enhanced by this, meaning that TBP becomes immobilised in the DNA
How did Cyclopropapyrroloindoles (CPIs) cause delayed lethality before they were changed?
Their Ethano bridges cause DNA to overwind, and so eventually cause damage and cell death (these were later removed due to this)
Stereochemistry is vital, especially when it comes to dimerising the drugs, which will increase the potency
What are DNA minor groove binders?
Drugs that have planar poly-aromatic structures and so have a natural twist, allowing them to bind into the DNA minor groove
This causes the DNA and drug to get closer, so DNA alkylation is more likely
How does Temozolomide work?
And how can we reverse this?
It is broken down to methyldiazonium ions, which are a DNA methylating species....which will cause DNA damage
This can be reversed by using a glutahione like molecule called AGT, which guanine at the O6 position, looking for DNA alkylation. If present it removes the methyl group (via its sulphur) and returns the base back to the normal guanine
For CPIs, where does the DNA attack occur?
At the N3 of adenine (the only place thay it will occur)
What are the main concepts currently being considered to prevent platinum resistance?
Increased delivery to the tumour (eg, liposomes)
Resistance Modulators (eg, drugs that will deactivate glutathione)
Targeting Agents (eg, mAbs with the platinum payload)
Drugs that target the resistance mechanims (eg, oxaliplatin/picoplatin/satraplatin)
How do PBDs work?
A reversible aminal bond between the exo-cyclic NH2 of guanine (the only base it will bind with) and the C11 of the PBD
If the PBD has been duplexed, then it can obviously bind to twice as many guanines
What are the methods of resistance to platinums after DNA has bound?
Loss of DNA mismatch repair
Bypassing of adducts by polymerase B and (n)
Down-regulation of apoptopic pathways
Increased removal from the DNA via more NER occuring
What is the function of telomerase in cancer?
An enzyme that adds tandem repeats (TTAGGG) onto the 3' end of chromosomes (telomere region) to stop them from dying naturally, and as allow them to continue causeing cell division
These are always present in cancer cells, so cells never die! As when the telomere repeat sequences are almost fully degraded, the telomerase just adds some more....whereas in healthy cells they would just die off
What are the following....
DACH --> Gives increased resistance to cells producing more glutathione
Aroplatin --> A liposomal formulation of cisplatin-like agents
ProLindac --> A cisplatin-drug that is conjugated to a water-soluble biocompatible co-polymer. This enhances permeability and retention (EPR) effects of macromolecules in tumours
How does Doxorubicin (an anthroycycline) intercalate DNA?
Follow the neighbour exclusion rule, so cant bind next to each other
Do bind symetrically, with pie stacking stabilising the structure
Its tails hang down and bind into the minor grooves
It binds to Topoisomoerase II-DNA complex (Cleavable complex), stabilising it....and so making the repair of the DNA damage that it has caused much harder
How do Bleomycins work?
It makes a cut in the DNA
The bithiazole tail then rotates around to the other side, activating the metal-binding region...creating a second break
These can create both flat and staggered DNA breaks
What is SN-38?
And what did it evolve from?
A topoisomerase I targetter
Evolved from Camptothesin, whcih had low water solubility and several ADRs
What kind of DNA crosslinking can PBDs do?
Inter and Intra-stand
This makes repair much harder
How does Double Strand DNA Repair (DSB) work?
Peel the ends back at the break (can be flat or staggered) to create single stranded tails. This creates a bubble which allows DNA repair to occur
Recombination is the only way of doing this that is inherently error free
Explain the development of platinum based drugs
Cisplatin --> First one (1971)
Safety increased to Carboplatin (1982) before development into the first oral drug of Satraplatin (1993)
Picoplantin/Oxaliplatin --> Broader spectrum of activity (1997/1986 respectively)