Inhibition of translesion DNA synthesis as a novel therapeutic strategy to treat brain cancer

Temozolomide is a DNA-alkylating agent used to treat brain tumors, but resistance to this drug is common. In this study, we provide evidence that efficacious responses to this drug can be heightenedsignificantlybycoadministrationofanartificialnucle-oside (5-nitroindolyl-20-deoxyriboside, 5-NIdR) that efficiently and selectively inhibits the replication of DNA lesions generated by temozolomide. Conversion of this compound to the corresponding nucleoside triphosphate, 5-nitroindolyl-20-deoxyribo-side triphosphate, in vivo creates a potent inhibitor of several human DNA polymerases that can replicate damaged DNA. Accordingly, 5-NIdR synergized with temozolomide to increase apoptosis of tumor cells. In a murine xenograft model of glioblastoma, whereas temozolomide only delayed tumor growth, its coadministration with 5-NIdR caused complete tumor regression. Exploratory toxicology investigations showed that high doses of 5-NIdR did not produce the side effects commonly seen with conventional nucleoside analogs. Collectively, our results offer a preclinical pharmacologic proof of concept for the coordinate inhibition of translesion DNA synthesis as a strategy to improve chemotherapeutic responses in aggressive brain tumors.