Investigating cellular 2´-deoxyribonucleotide pools as targets for non-small cell lung cancer therapy
thesisposted on 11.09.2017, 12:21 by Hussein Hadi Khairi Abbas
Free 2´-deoxyribonucleotide triphosphates (dNTPs) are vulnerable to oxidation by reactive oxygen species (ROS) formed both as by-products of intracellular metabolism and from other exogenous oxidising agents. NUDT1 hydrolyses oxidised dNTPs to prevent their misincorporation into genomic DNA. Given that oxidative stress is a cancer hallmark, NUDT1 activity was proposed essential for cancer cell growth but non-essential in normal cells. Recently, potent and highly selective NUDT1 small molecule inhibitors have highlighted a new cancer therapeutic approach which could convert oxidative stress into cytotoxic DNA damage with eventual cancer cell death. To assess the potential clinical relevance of NUDT1 inhibition for improving lung cancer cell targeting, this study aimed to test the genotoxic and cytotoxic effects of NUDT1 deficiency (siRNA-mediated knockdown or small-molecule inhibition) on H23, H522 and A549 non-small-cell lung cancer (NSCLC) cells relative to normal MRC-5 lung fibroblasts, and whether NUDT1 knockdown could augment current therapies. The siRNA-mediated NUDT1 knockdown increased oxidatively damaged DNA levels and DNA damage signaling alterations in all lung cancer cell lines but not normal fibroblasts, despite no detectable differences in ROS levels between the lines. Unexpectedly, NUDT1 knockdown did not induce apoptosis in NSCLC cells, or enhance the effect of gemcitabine, cisplatin or radiation in combination treatments. We similarly studied the effects of NUDT1 inhibitors, TH287 and TH588. Inhibitor treatment increased oxidative DNA damage in H23 cells only, but induced apoptosis in H23 and H522 cells, indicating that they kill cells independently of DNA oxidation and seemingly via NUDT1-distinct mechanisms. In conclusion, we show that NUDT1 has a specific role in lung cancer cells for suppressing oxidative DNA damage levels and genomic instability, though surprisingly the basis of this may not be related to ROS levels. However, targeting NUDT1 is not an effective therapeutic strategy; rather it induces non-cytotoxic DNA damage that could promote cancer heterogeneity and evolution.