Nitro-substituted ruthenium( ii ) polypyridyl complexes synergise with ATR inhibitors to enhance replication stress in cancer cells

-substituted nitro derivative (complex 3) induces the strongest DNA damage response (DDR) and was therefore investigated in combination with the ATR inhibitors (ATRi) berzosertib and ceralasertib. Strong synergism is observed across multiple cancer cell lines, with combination treatment suppressing clonogenic survival and enhancing DNA damage signalling and apoptotic cell death. Mechanistic analyses reveal that DNA intercalation and ROS generation cooperatively elevate replication stress, thereby sensitising cells to ATR inhibition. Comparable ATRi synergism was also observed for the parent complex Ru-PIP, indicating that DSB pathway activation is not a requirement for the observed synergy. This study demonstrates that nitro substitution offers a means to fine-tune DNA-binding behaviour and the resulting cellular DNA damage response to RPCs, and supports the potential of employing Ru(II) metallointercalators in combination with ATR inhibitors as an anti-cancer strategy.