Evaluation of 18F-FDG and 18F-FLT for monitoring therapeutic responses of colorectal cancer cells to radiotherapy

In order to compare the efficacy of 18F-fluorothymidine (FLT) and 18F-fluorodeoxyglucose (FDG) for monitoring early responses to irradiation, two human colorectal cancer (CRC) cell lines SW480 and SW620, which were derived from the primary lesions and the metastatic lymph node, underwent X-ray irradiation of 0, 10, or 20 Gy and were examined at 0, 24 and 72 h After irradiation, reduced proliferation of both SW480 and SW620 cells was observed in a dose-dependent manner (P < 0.001), G0-G1 arrest was also noted in both cell types after 72 h in the 20 Gy group (P < 0.001). Although increased apoptosis was observed in both cell lines after irradiation (P < 0.001), a greater percentage of SW480 cells underwent apoptosis in response to irradiation than SW620 cells. Increased Hsp27 and decreased integrin β3, Ki67 and VEGFR2 expression was observed over time via immunocytochemistry and Western blot analysis (P < 0.001), however, no significant changes were noted in response to irradiation. Finally, reduced uptake of 18F-FLT by SW480 or SW620 cells was observed at 24-h post-irradiation, however, reduced 18F-FDG uptake was only observed after 72 h. Therefore, we conclude that 18F-FLT is a more suitable positron emission tomography (PET) tracer for monitoring early responses to irradiation in primary and metastatic lymph node CRC cells.