Uracil DNA glycosylase expression determines human lung cancer cell sensitivity to pemetrexed
Menée sur des lignées cellulaires de cancer du poumon, cette étude met en évidence le rôle joué par une glycolase du mécanisme de réparation de l'ADN par excision de base, UNG, dans la résistance au pemetrexed
Uracil misincorporation into DNA is a consequence of pemetrexed inhibition of thymidylate synthetase. The base excision repair (BER) enzyme, uracil DNA glycosylase (UNG) is the major glycosylase responsible for removal of misincorporated uracil. We previously illustrated hypersensitivity to pemetrexed in UNG-/- human colon cancer cells. Here, we examined the relationship between UNG expression and pemetrexed sensitivity in human lung cancer. We observed a spectrum of UNG expression in human lung cancer cells. Higher levels of UNG are associated with pemetrexed resistance and are present in cell lines derived from pemetrexed-resistant histological subtypes (small cell and squamous cell carcinoma). Acute pemetrexed exposure induces UNG protein and mRNA, consistent with up-regulation of uracil-DNA repair machinery. Chronic exposure of H1299 adenocarcinoma cells to increasing pemetrexed concentrations established drug-resistant sublines. Significant induction of UNG protein confirmed up-regulation of BER as a feature of acquired pemetrexed resistance. Co-treatment with the BER inhibitor, methoxyamine (MX) overrides pemetrexed resistance in chronically exposed cells, underscoring the utility of BER directed therapeutics to offset acquired drug resistance. Expression of UNG-directed siRNA and shRNA enhanced sensitivity in A549 and H1975 cells, and in drug-resistant sublines, confirming that UNG up-regulation is protective. In human lung cancer, UNG deficiency is associated with pemetrexed-induced retention of uracil in DNA that destabilizes DNA replication forks resulting in DNA double strand breaks and cell death. Thus, in experimental models, UNG is a critical mediator of pemetrexed sensitivity that warrants evaluation to determine clinical value.
http://mct.aacrjournals.org/content/early/2013/07/19/1535-7163.MCT-13-0172.abstract