C91
Inhibition of ATM mediated DNA repair potentiates the cytotoxicity of DNA damaging ionising radiation in HCC cells
Gary Beale1, Calvin Yu1, Graeme Smith2, Stephen Stewart3, Derek Manas3, Nicola Curtin1, Helen Reeves1
1Newcastle University, Newcastle-upon-Tyne, UK, 2Freeman Hospital, Newcastle-upon-Tyne, UK, 3KuDos Pharmaceuticals Ltd, Cambridge, UK
Background
Liver toxicity and tumour resistance limit the use of cytotoxic chemo and radiotherapy in hepatocellular (HCC). We hypothesized that upregulated DNA repair in response to DNA damage contributes to resistance and that its inhibition would facilitate treatment at doses less toxic to the underlying liver. Our aim was to assess the double strand DNA repair kinase, ATM, in response to irradiation in three HCC cell lines and to determine whether its specific inhibition would enhance radiosensitivity.
Method
The effects of radiation (2Gy) in the presence and absence of ATM inhibitor KU55933 were visualised with a phospho-ATM antibody. The effects of radiation on cell survival with or without KU55933 were assessed by colony forming ability and FACS.
Results
Ionizing radiation induced phospho-ATM was was inhibited by KU55933, as was colony forming ability, with only 50% of cells surviving relative to radiotherapy alone at concentrations (IC50s) of 2.81±0.49µM, 3.67±0.12µM and 3.54±0.07µM in Hep G2, Hep3B and HUH7 cells respectively. Irradiation potentiation at 1Gy was observed - cell survival was reduced from 80% to less than 15% with KU55933(1µM). KU55933 potentiated a G2 arrest in HepG2 cells.
Conclusion
ATM levels and activity were high in HCC cell lines. Specific inhibition of ATM activity potentiated the effect of ionizing radiation, markedly reducing cancer cell survival. Sensitisation of HCC with an inhibitor of DNA repair prior to cytotoxic treatment shows promise as a treatment strategy for HCC.
