Enhancement of radiation effects by acyclovir.

Acyclovir (ACV), a new antiviral drug, was used to investigate its effect of radiosensitivity in tumors in vivo. In in vivo experiments with Sarcoma-180 transplanted into the ICR mouse and FM3A transplanted into the C3H mouse, ACV enhanced the radiosensitivity of both tumors. In S-180, radiation effects were enhanced by treatment with 100 mg/kg of ACV from 30 min before to 60 min after irradiation. In S-180 treated by 400 mg/kg of ACV, the enhancement ratio was approximately 2.0, as evaluated by the growth delay method. In the FM3A tumor treated by 20 mg/kg of ACV, the enhancement ratio was approximately 1.3, as evaluated by tumor cure (TCD50 assay). ACV is already clinically used as an antiviral drug. Its ability to radiosensitize tumors could therefore have clinical potential when combined with radiotherapy.