LAUSR

MCM8 and MCM9 participate in homologous recombination with long‐tract gene conversion to repair double‐strand breaks caused by replication stress, which is generally higher in cancer cells than in normal cells. MCM8 is highly expressed in certain cancer cells, where it is necessary for maintaining cell growth, migration, and invasion, although the molecular mechanisms remain unclear. Knockdown with siRNAs or knockout of MCM8 or MCM9 selectively sensitizes cancer cells to cisplatin. Thus, drugs inhibiting MCM8 or MCM9 could serve as novel anti‐neoplastic agents and/or chemosensitizers that selectively sensitize cancer cells to platinum compounds. The present study describes the development of an amido‐bridged nucleic acid (AmNA)‐modified gapmer antisense oligonucleotide (ASO) targeting MCM8, called ASO 8–3419. In vitro, ASO 8–3419 inhibited MCM8 expression in several human cell lines and selectively sensitized cancer cells to cisplatin. Moreover, ASO 8–3419 modestly suppressed the growth of several cancer cell lines whose proliferation has been reported to depend on MCM8. In vivo, ASO 8–3419 inhibited the expression of MCM8 in xenografted tumors of colon cancer‐derived HCT116 cells in nude mice and increased tumor sensitivity to cisplatin with minimal toxicity. These findings suggest that AmNA‐modified, MCM8‐specific ASOs hold promise as novel anti‐cancer agents.