Radiosensitizing effects of xanthohumol on human cancer cells

Xanthohumol, the principal flavonoid in hops, was investigated for its radiosensitizing activity on human cancer cells (human breast cancer MCF‐7 and ardiamucin‐resistant MCF‐7 (MCF‐7/ADR) cells, and human colon cancer HT‐29 and HCT116 cells). Cell survival was measured by the MTT assay 2 days after 10 Gy of ionizing radiation. Cells expressing mutant p53 (MCF‐7/ADR and HT29) are more resistant to the ionizing radiation than wild‐type p53 cells (MCF‐7 and HCT116). However, pretreatment of the cells with xanthohumol (10 μM) for 24 h prior to the radiation significantly enhanced radiosensitivity of all the cells, irrespective of p53 status. Some studies showed that there is persistent activation of signal transducer and activator of transcription 3 (STAT3) in a number of human solid tumors including colon cancer. In addition, MCF‐7/ADR showed persistent activation of STAT3. Xanthohumol significantly suppressed the expression of STAT3. In the cells co‐treated with xanthohumol and radiation could have the therapeutic potential as a radiosensitizer in human cancer cells overexpressing STAT3.