Lecture 14 - Intercalation and new targets Flashcards
1
Q
What is TOP-2?
A
- Topoisomerase II
- Target of important classes of anticancer drugs
- a DNA processing enzyme
- make dsDNA break, to remove twists and knots in duplex DNA molecules
- Promising target in chemo
2
Q
What drug targets TOP-2 and what is this type of drug?
A
- Doxorubicin
- Intercalator
3
Q
What is a side effect of doxorubicin?
A
- formation of secondary malignancies that arise from drug-induced translocations
4
Q
General overview of how intercalators fit into DNA
A
- Slot into the gaps in DNA through base pairs
- Via the neighbourhood exclusion rule where they fill every other gap
5
Q
What is the structure of Doxorubicin?
A
- large aromatic core normally 3 rings fused together forming flat planar mass
- Sugars (multifunctional rings)
- stacks between the base pairs of DNA
- stacking of pi systems within the drug and the two base pairs either side
- very stable, cause a stabilisation of the duplex
6
Q
What do DNA intercalators prefer to associate with on DNA?
A
- Protein DNA complexes rather than naked DNA
7
Q
What do the sugars (multifunctional rings) of doxorubicin do?
A
- bind into the major groove of DNA
- form non-covalent interactions with the phosphate backbone of DNA stabilising the complex
- Important for increasing the potency
8
Q
What increases potency of doxorubicin?
A
Stronger binding
9
Q
Mechanism of action of doxorubicin
A
- TOP-2 complex is a dimer, with 2 binding pockets
- A kink in DNA forms for drug to be dropped into
- Drug slots into the two pockets, which are specific to the binding site
- Results in stabilisation
- Then get covalent modification by the protein of the DNA rather than the drug stuck to the DNA
- The TOP-2 protein stuck covalently, representing big challenge to DNA repair mechanism and thus DNA breaks
10
Q
What intercalator targets TOP-1?
A
- SN-38 complex
- similar way to TOP-2
- interact with the complex TOP-1 and DNA
- single specific binding socket which opens up and drug fits in and binds tightly
- lock the complex of TOP-1 with DNA
11
Q
What is pluramycin and what does it do?
A
- Intercalator/alkylator
- Binding of TBP to the TATA box facilitates intercalation of pluramycin
12
Q
Overview of how doxorubicin works?
A
- stabilisation of a complex with eventual alkylation via a protein forming strand breaks at that site
13
Q
How is SN-38 formed from natural products?
A
- Natural product camptothesin
- formed via hydrolysis of Irinotecan by carboxylesterases and metabolized via glucuronidation at the phenol
14
Q
More than just alkylating DNA - principle of intercalators…
A
- Intercalators –> large molecule in the minor groove of DNA stabilises it, making it difficult for enzymes to pull apart and get into the DNA to repair it
- once complex formed itself may change the DNA
- Can form dimers with drugs, as they get bigger though they become less stable
- Secondary structures are also important within DNA
15
Q
What do telomerases do?
A
- Take DNA and create a repeat end at the end of DNA to form telomeres
- adds DNA sequence repeats, “TTAGGG” to the 3’ end of DNA strands in the telomere regions
