Harmine suppresses homologous recombination repair and inhibits proliferation of hepatoma cells

To avoid cell cycle arrest or apoptosis, rapidly proliferating cancer cells have to promote DNA double strand break (DSB) repair to fix replication stress induced DSBs. Therefore, developing drugs blocking homologous recombination (HR) and nonhomologous end joining (NHEJ) - 2 major DSB repair pathways - holds great potential for cancer therapy. Over the last few decades, much attention has been paid to explore drugs targeting DSB repair pathways for cancer therapy. Here, using 2 well-established reporters for analyzing HR and NHEJ efficiency, we found that both HR and NHEJ are elevated in hepatoma cell lines Hep3B and HuH7 compared with normal liver cell lines Chang liver and QSG-7701. Our further study found that Harmine, a natural compound, negatively regulates HR but not NHEJ by interfering Rad51 recruitment, resulting in severe cytotoxicity in hepatoma cells. Furthermore, NHEJ inhibitor Nu7441 markedly sensitizes Hep3B cells to the anti-proliferative effects of Harmine. Taken together, our study suggested that Harmine holds great promise as an oncologic drug and combination of Harmine with a NHEJ inhibitor might be an effective strategy for anti-cancer treatment.