The radiosensitizing effect of 5-aminolevulinic acid (5-ALA) has been demonstrated in glioma and melanoma in a number of studies. Enhancing the radiosensitivity of colorectal cancer may improve survival rates and lessen adverse effects. The present study assessed the radiosensitizing effect of 5-ALA in colorectal cancer using the human colon cancer cell line HT29 in vitro and in vivo. In vitro, cells were pretreated with 5-ALA and exposed to ionizing radiation. Cells pretreated with or without 5-ALA were compared using a colony formation assay. In vivo, HT29 cells were implanted into mice subcutaneously and subsequently exposed to ionizing radiation. 5-ALA was administrated by intraperitoneal injection. Subcutaneous tumors treated with or without 5-ALA were compared. Single-dose and multi-dose irradiations were applied both in vitro and in vivo. Cells exposed to multi-dose irradiation and pretreated with 5-ALA in vitro had a significantly lower surviving fraction compared with cells without 5-ALA pretreatment. Following multi-dose irradiation in vivo, the volume of the subcutaneous tumors treated with 5-ALA was significantly lower compared with that of tumors without treatment. These results suggest that radiotherapy with 5-ALA may enhance the therapeutic effect in colon cancer.
Keywords: 5-aminolevulinic acid; colorectal cancer; protoporphyrin IX; radiosensitivity; radiosensitizing effect; radiotherapy.