Drugs That Act On DNA Topoisomerases Flashcards
Describe DNA topoisomerases
Present in all bacterial and eukaryotic cells
Change number of twists in DNA
Untangle DNA molecules
Decatenate
What is the unction of topoisomerases
To unwind DNA that has become overwound ahead of the replication fork in order to allow for replication
What are the 2 classes of topoisomerase enzymes
Type 1 = cuts 1 strand
Type 2 = both strands cut
What is the function of topoisomerase I
DNA replication and txn
Topo I part of txn complexes
K/o in mice = lethal
What is the function of topoisomerase II
A: chromsome segregation, resolves intertwined chromosomes at mitosis
B: neuronal/development and txn initiation
Chromatin condensations and decondensation
How does topoisomerase II work
Is covalently bound to DNA and breaks both strand
Change in conformation allows 2nd DNA strand to pass through
DNA relegates and topo II leaves
Name 2 topoisomerase II poisons
Etoposide
Teniposide
Describe the mechanism of action of Etoposide
Forms a cleavable complex w topo II and DNA
Blocks reaction and stops topo II from opening and closing
Doesn’t allow 2nd strand through
Why is etoposide a poison rather than an inhibitor
Blocks the reaction instead of interacting directly and inhibiting it
How can you detect cleavable complexes formed in cells
Alkaline elation -> TARDIS (trapped in agarose DNA immunostaining)
Describe TARDIS
Liv cells embedded in layer of agarose gel
Cells listed to remove proteins leaving only DBNA
Fluorescent antibodies added that bind to topo protein
Why is TARDIS useful
Allows to look at the effect of drug on topo
Can check if the addition of a second drug will affect the interaction between drugs and topo
Describe anthracyclines
Flat 4 ring structure that can intercalated and distort double helix
Hydroxy radical formed = damage DNA and cell membranes
Name to anthracyclines and their use
Doxorubicin: solid tumours e.g breast, bladder etc
Daunorubicin: leukaemia
Name a topisomerase I poison
Camptothecin
Describe camptothecin
Poorly water soluble
Incredibly potent but too toxic
-> need to change drug structure to change toxicity profile
Name the 2 derivatives of camptothecin
Topotecan
Irinotecan
Overcome the toxicities
Describe the metabolism of irinotecan (CPT-11)
Converted to CES1 and CES2 to SN-38
SN-38 primarily metabolised to inactive glucuronide by UGTs
Produces inactive form excreted in bile
When would someone require a lower does of irniotecan
When have SNPs in CES1 and CES2 that cuase low amounts of glucuronides and high conc on SN38
When does cytotoxicity occur with topoisomerase poisons
Inhibition of enzyme activity and formation of stabilised cleavable complexes
What can happen once DNA damage occurs after topoisomerase poisions
Delay of cell cycle progression and repair/ removal of damage
-> cell survives or mitotic catastrophe or apoptosis triggered by damage
Why are there severe toxic side effects with topo poisons
Not very specific
Why do cytotoxic drugs preferentially attack tumours
Cells more sensitive during DNA replication
Many dividing cells in tumours
What resistance mechanisms do topo poisons have
Less access to target
Altered target or less target
Altered response to DNA damage
