Radiosensitization of human tumor cells with levamisole

Levamisole in combination with radiation and chemotherapeutic agents is being studied in clinical trials. The mechanism of interaction of levamisole with these modalities is unknown. In order to determine if there is direct interaction between radiation and levamisole, a series of colony-formation assays was performed with the use of two human tumor cell lines. Cells were exposed to 0-10 Gy of radiation, with or without the addition of 0-1000 microM levamisole. Exposure to levamisole alone had no effect on cell survival; however, the combination of continuous exposure to levamisole at concentrations approaching 1000 microM and radiation revealed a potentiation of radiation-induced cell killing.