2'-C-cyano-2'-deoxy-1-β-d-arabino-pentofuranosylcytosine (
CNDAC) is the active metabolite of the anticancer drug,
sapacitabine.
CNDAC is incorporated into the genome during DNA replication and subsequently undergoes β-elimination that generates single-strand breaks with abnormal 3'-ends. Because
tyrosyl-DNA phosphodiesterase 1 (TDP1) selectively hydrolyzes nonphosphorylated 3'-blocking ends, we tested its role in the repair of
CNDAC-induced DNA damage. We show that cells lacking TDP1 (avian TDP1-/- DT40 cells and human TDP1 KO TSCER2 and HCT116 cells) exhibit marked
hypersensitivity to
CNDAC. We also identified BRCA1, FANCD2, and
PCNA in the DNA repair pathways to
CNDAC. Comparing
CNDAC with the chemically related arabinosyl
nucleoside analog,
cytosine arabinoside (
cytarabine, AraC) and the
topoisomerase I inhibitor camptothecin (
CPT), which both generate 3'-end blocking DNA lesions that are also repaired by TDP1, we found that inactivation of BRCA2 renders cells hypersensitive to
CNDAC and
CPT but not to AraC. By contrast, cells lacking PARP1 were only hypersensitive to
CPT but not to
CNDAC or AraC. Examination of TDP1 expression in the
cancer cell line databases (CCLE, GDSC, NCI-60) and human
cancers (TCGA) revealed a broad range of expression of TDP1, which was correlated with PARP1 expression, TDP1 gene copy number and promoter methylation. Thus, this study identifies the importance of TDP1 as a novel determinant of response to
CNDAC across various
cancer types (especially non-small cell
lung cancers), and demonstrates the differential involvement of BRCA2, PARP1, and TDP1 in the cellular responses to
CNDAC, AraC, and
CPT. Mol
Cancer Ther; 16(11); 2543-51. ©2017 AACR.