B179
DNA polymerase beta modulates sensitivity and resistance of colon cancer cells to oxaliplatin via DNA damage repair
Jian Yang1, Jason Parsons1, Christopher F. Harrington2, Patrick G. Johnston3, W. Gillies McKenna1, Grigory L. Dianov1, Ricky A. Sharma1
1University of Oxford, Oxford, UK, 2Nottingham School of Science and Technology, Nottingham, UK, 3Queen's University, Belfast, UK
A significant proportion of cancers overexpress the base excision repair (BER) protein, DNA polymerase beta (PolB). PolB participates in low fidelity repair and translesion DNA synthesis.
We have discovered that oxaliplatin treatment of HCT116 colon cancer cells induces a significant amount of DNA damage which is repaired by a pathway involving stabilisation of PolB on chromatin for 48 h post-treatment. Oxaliplatin (10mM, 24 h treatment) caused a 3-fold increase in PolB protein levels, with no significant effect on the transcription of PolB mRNA. Compared to parent cells, isogenic oxaliplatin-resistant HCT116 cells had higher constitutive levels of PolB protein and exhibited more rapid repair of DNA damage induced by oxaliplatin (P < 0.005 at 24 and 48 h post-treatment). Notably, RNA-interference depletion of PolB protein in oxaliplatin-resistant cells delayed repair and decreased clonogenic survival following oxaliplatin treatment. In a separate model system, PolB-deficient fibroblasts were significantly less able than isogenic PolB-expressing cells to repair DNA damage detected by alkaline comet assay and 1,2-GG oxaliplatin adducts measured by LC-ICP-MS. PolB null cells were 12-fold more susceptible to the clonogenic killing effects of oxaliplatin than isogenic PolB-expressing cells. Translational studies are ongoing comparing PolB levels in histopathology samples and oxaliplatin sensitivity of cells derived from the same tumours.
These data are the first to link oxaliplatin sensitivity, repair of 1,2-GG adducts and PolB. The data provide compelling evidence that PolB plays a role in the sensitivity of cancer cells to oxaliplatin, and suggest that PolB is a target for circumventing drug resistance.
