Synthesis of 5,9- and 5,8-Diaminoalkoxy Substituted Benzophenanthridinone Analogues as Tyrosyl-DNA Phosphodiesterase 1 Inhibitors and Their Radiosensitizing Activity

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a potential target for cancer chemotherapy and radiotherapy. There are a few reports on TDP1 inhibitors used in chemotherapy, but no report on their use in radiotherapy. Herein, we designed and synthesized a series of titled analogues. Twelve analogues showed high TDP1 inhibitory activity. Among them, <b>18</b> (IC₅₀ = 6.9 μM) showed strong radiosensitization in colorectal cancer cells, and could suppress tumor growth in the HCT116 xenograft animal model combined with X-ray radiation, and exhibited low acute toxicity with good pharmacokinetic (PK) parameters, implying that <b>18</b> is worth further clinical research. Further studies indicated that <b>18</b> could target cellular TDP1 and suppress NHEJ repair activity for radiation-induced DNA damage, resulting in cancer cell death. Additionally, <b>18</b> could also increase the expression of PIG3, resulting in an enhancement of radiation-induced cellular ROS and mitochondrial dysfunction. Our studies provide a novel cancer treatment strategy combining TDP1 inhibitors and radiotherapy.