Targeting radiation-resistant hypoxic tumour cells through ATR inhibition.
BACKGROUND
Most solid tumours contain regions of sub-optimal oxygen concentration (hypoxia). Hypoxic cancer cells are more resistant to radiotherapy and represent the most aggressive fraction of a tumour. It is therefore essential that strategies continue to be developed to target hypoxic cancer cells. Inhibition of the DNA damage response (DDR) might be an effective way of sensitising hypoxic tumour cells to radiotherapy.


METHODS
Here, we describe the cellular effects of pharmacological inhibition of the apical DDR kinase ATR (Ataxia Telangiectasia and Rad 3 related) with a highly selective inhibitor, VE-821, in hypoxic conditions and its potential as a radiosensitiser.


RESULTS
VE-821 was shown to inhibit ATR-mediated signalling in response to replication arrest induced by severe hypoxia. In these same conditions, VE-821 induced DNA damage and consequently increased Ataxia Telangiectasia Mutated-mediated phosphorylation of H2AX and KAP1. Consistently, ATR inhibition sensitised tumour cell lines to a range of oxygen tensions. Most importantly, VE-821 increased radiation-induced loss of viability in hypoxic conditions. Using this inhibitor we have also demonstrated for the first time a link between ATR and the key regulator of the hypoxic response, HIF-1. HIF-1 stabilisation and transcriptional activity were both decreased in response to ATR inhibition.


CONCLUSIONS
These findings suggest that ATR inhibition represents a novel strategy to target tumour cells in conditions relevant to pathophysiology and enhance the efficacy of radiotherapy.
Department of Oncology, The Gray Institute for Radiation Oncology & Biology, University of Oxford, Oxford OX3 7DQ, UK.
I M
IM
Pires
M M
MM
Olcina
S
S
Anbalagan
J R
JR
Pollard
P M
PM
Reaper
P A
PA
Charlton
W G
WG
McKenna
E M
EM
Hammond
D001260:Ataxia Telangiectasia / Q000235:genetics; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects; D045325:HCT116 Cells; D006367:HeLa Cells; D006657:Histones / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology; D011836:Radiation Tolerance / Q000187:drug effects* / Q000235:genetics; D011878:Radiotherapy / Q000379:methods; D012097:Repressor Proteins / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D013450:Sulfones / Q000494:pharmacology; D000076183:Tripartite Motif-Containing Protein 28
C560580:3-amino-6-(4-(methylsulfonyl)phenyl)-N-phenylpyrazine-2-carboxamide; D018797:Cell Cycle Proteins; C468783:H2AX protein, human; C497442:HIF1A protein, human; D006657:Histones; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011719:Pyrazines; D012097:Repressor Proteins; D013450:Sulfones; C101116:TRIM28 protein, human; D000076183:Tripartite Motif-Containing Protein 28; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases