The fluoropyrimidine polymer CF10 synergizes with 5-ethynyl-2'-deoxyuridine by promoting telomere attrition and mitotic catastrophe

Fluoropyrimidine (FP) drugs, including 5-fluorouracil (5FU), are widely used to treat colorectal Cancer (CRC) and target de novo thymidine biosynthesis, resulting in DNA damage and cell death. 5-ethynyl-2'-deoxyuridine (EdU) is a thymidine analog that also causes DNA damage. We investigated synergy between FPs and EdU potentially due to increased EdU incorporation into DNA under thymine-less conditions. Using the highest single agent model, strong synergy was observed between a 2nd-generation FP polymer, CF10, and EdU over a wide range of concentrations. In contrast, only additivity was observed for EdU + 5FU. CRC cells treated with synergistic EdU + CF10 combinations showed increased EdU incorporation into DNA, increased double-strand breaks (DSBs), and S-G2/M cell-cycle arrest. Phosphorylated histone H3 (pH3), a marker of highly condensed chromatin associated with Mitosis, was detected in S- and G2/M-phase cells. Telomere staining was significantly reduced in CRC cells treated with EdU + CF10 combinations, and mitotic cells from these treatments showed mono- and multi-polar mitotic structures consistent with mitotic catastrophe. Our results are consistent with CF10 enhancing EdU incorporation into genomic DNA, causing DSBs but not extending telomeres, leading to telomere attrition and inducing mitotic catastrophe in CRC cells. This unique synergistic mechanism could lead to use of EdU + CF10 as a more effective CRC treatment.