Uracil-DNA glycosylase expression determines human lung cancer cell sensitivity to pemetrexed.

Abstract

Uracil misincorporation into DNA is a consequence of pemetrexed inhibition of thymidylate synthase. 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 histologic subtypes (small cell and squamous cell carcinoma). Acute pemetrexed exposure induces UNG protein and mRNA, consistent with upregulation 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 upregulation of BER as a feature of acquired pemetrexed resistance. Cotreatment with the BER inhibitor methoxyamine overrides pemetrexed resistance in chronically exposed cells, underscoring the use 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 upregulation 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.

• Authors: Lachelle D Weeks, Pingfu Fu, Stanton L Gerson
• Journal: Molecular cancer therapeutics (Mol Cancer Ther) Vol. 12 Issue 10 Pg. 2248-60 (Oct 2013) ISSN: 1538-8514 [Electronic] United States
• PMID: 23873851 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: ©2013 AACR.

Chemical References

• Glutamates
• RNA, Small Interfering
• Pemetrexed
• Guanine
• Uracil-DNA Glycosidase

Topics

• Cell Line, Tumor
• DNA Breaks, Double-Stranded (drug effects)
• DNA Damage (drug effects)
• DNA Replication (drug effects)
• Drug Resistance, Neoplasm (genetics)
• Gene Expression Regulation, Neoplastic (drug effects)
• Glutamates (administration & dosage)
• Guanine (administration & dosage, analogs & derivatives)
• Humans
• Lung Neoplasms (drug therapy, enzymology, pathology)
• Pemetrexed
• RNA, Small Interfering
• Uracil-DNA Glycosidase (biosynthesis)