Monitoring Early Response To Irradiation With¹⁸F-FDG And¹⁸F-FLT In Human Colorectal Cancer Cells In Vitro

Objective To establish a stable method to detect the¹⁸F-FDG and¹⁸F-FLT uptake inhuman colorectal cancer cell lines HCT116in vitro. Investigate the changes of the celluptake to two tracers after exposed to different does of6MV-X ray, then analyses therelationship of the uptake rate to the cell viability and proliferation, evaluate the capabilityof¹⁸F-FDG and¹⁸F-FLT on monitoring and prediction of tumor response to therapy.Methods: Investigate the uptake rate of human colorectal cancer cell lines HCT116to¹⁸F-FDG and¹⁸F-FLT at different cell numbers (1.0×10⁵¹.5×10⁶) and different culturetimes (36h,60h,84h), then select the suitable experimental condition. The uptake rate of¹⁸F-FDG and¹⁸F-FLT ware measured by γ RAI counter after exposed to different does of6MV-X ray (0Gy,2Gy,4Gy,6Gy,8Gy) at different times (after24h,48h,72h). Thencalculate the cell uptake inhibition rate of each group by the formula: cell uptake inhibitionrate=(1-uptake rate of treated group/uptake rate of control group)×100%. The cell growthinhibition rate was calculated by MTT colorimetric assay and use flow cytometry tomeasure cell viability and cell cycle. ANOVA and correlation analysis were applied toanalysis correlation between HCT116cell uptake inhibition rate to¹⁸F-FDG or¹⁸F-FLTand cell viability or proliferation.Results: The uptake rate of¹⁸F-FDG higher than¹⁸F-FLT in HCT116, and the uptakerate positively correlated with the cell numbers and incubation times within a certain range,then saturated and stabilized gradually. The cells proliferation was significantly delayedafter irradiation. As cell proliferation, the¹⁸F-FDG or¹⁸F-FLT uptake ability and apoptosiswas also affected to varying degrees. The¹⁸F-FDG uptake inhibition rate (Δ_FDG) at24hafter different does of irradiation (2,4,6,8Gy) ware (10.11±1.76)%,(14.84±2.25)%,(13.17±3.70)%,(6.77±4.50)%, and48h ware (4.94±1.19)%,(11.15±1.43)%,(13.94±1.22)%,(11.72±2.64)%,72h ware (2.01±1.43)%,(5.66±0.88)%,(8.76±0.91)%,(4.99±0.98)%, respectively. Δ_FDG was positively correlated with the cell growth inhibitionrate at24h,48h,72h,(r=0.471, P=0.036),(r=0.781, P＜0.01),(r=0.809, P＜0.01), respectively. The¹⁸F-FLT uptake inhibition rate (ΔFLT) at24h after different does ofirradiation (2,4,6,8Gy) ware (32.10±0.02)%,(54.46±0.04)%,(62.74±0.04)%,(65.81±4.81)%, and48h ware (26.60±0.02)%,(44.00±0.03)%,(52.76±0.01)%,(60.49±4.65)%,72h ware (19.10±0.03)%,(33.74±0.05)%,(42.22±0.05)%,(49.15±5.80)%,respectively. ΔFLTwas positively correlated with the cell growth inhibition rate at48h,72h,(r=0.902, P＜0.01),(r=0.847,P＜0.01), respectively.Conclusion: The uptake ability to¹⁸F-FDG or¹⁸F-FLT in human colorectal cancercell lines HCT116was decrease obviously within72h after irradiation, and the uptake ratepositively correlated with the cell growth inhibition rate. So¹⁸F-FDG and¹⁸F-FLT couldmonitor response to irradiation in human colorectal cancer cells at early stage in vitro,especially for¹⁸F-FLT. This could provide an experimental basis for the use of¹⁸F-FDG or¹⁸F-FLT imaging to predict the responsibility to preoperative radiotherapy in colorectalcancer patients at an early time.