Development of PARP inhibitors Flashcards
What is PAR?
The third nucleic acid in the mammalian cell. It is built from ADP ribose units derived from NAD+. It is usually built onto Glu side chains in targets proteins. The MW varies with PARP isoform.
They can be linear or branched
PARPs interact with DNA, put PAR chains on itself, DNA binding by two zinc fingers.
How does PARPs use NAD+ as a substrate?
The binding site is involved around the carbonyl oxygen, they are a hydrogen bond acceptor. It is important for binding. When nicotinamide is released there is an active species which is stabilised by glutamate by the negative charge.
It reacts with alcohol and attacks a carbon, there can be branching systems.
What is the role of PARP1 in repair of damaged DNA?
PARP1 repairs DNA, PARP1 is recruited to the site of damage, PARP1 puts PAR chains onto the histone. Histone gets removed from the DNA due to this, this allows repair enzymes to repair DNA.
What is the potentiation of radiotherapy and cytotoxic chemotherapy of cancer in relation to PARP?
Radiotherapy causses DNA strand breaks. Electrophilic cytotoxic drugs cause DNA damage. Inhibitors of topoisomerase II cause DNA single strand breaks by inhibiting strand joining step. If the tumour cells can repair the DNA before it is required, then cells survive. Inhibition of PARP1 inhibits DNA repair. Inhibition of PARP1 potentiates radiotherapy and DNA targeted chemotherapy.
What is the role of PARP1 in reduction of organ damage following reperfusion injury?
When the supply of blood to an organ is interrupted, the cells become hypoxic. Reperfusion with blood causes rapid resupply of O2 to hypoxic cells. O2 is an oxidising diradical which damages DNA. PARP1 is over activated and cells are depleted of NAD+ so cells die and there is organ failure.
How does PARP1 recognise DNA?
Through Zn fingers. The NAD+ binding domain at the C terminal of the protein. The thiols of the three Cys and the imidazole of one His in the DNA binding domain of PARP2 bind to Zn2+, fixing the conformation of the protein.
What is the major issue in design of selective PARP1 inhibitors?
There is a lack of selectivity
What are the different types of DNA damaging therapies?
Radiotherapy – radiation, belomycin
Mono-alkylators – alkylsulfonates, nitrosoureas, temozolomide
Cross linkers – N-mustards, mitomycin C, platinum drugs
Topoisomerase inhibitors – camptothecins, etoposide
Replication inhibitors – aphidicolin, hydroxyurea
