In vitro assessment of 2-fluoro-2-deoxy-D-glucose, L-methionine and thymidine as agents to monitor the early response of a human adenocarcinoma cell line to radiotherapy

The tumor cell uptake of three tracers that can be labeled with isotopes suitable for PET imaging-FDG, L-methionine and thymidine-were examined in vitro in a human ovarian carcinoma cell line (HTB77IP3) at varying times following 30 Gy ⁶⁰Co irradiation and were compared to a nonirradiated control group. FDG, methionine and thymidine uptake per tissue culture well all increased following irradiation when compared to basal values, although to a much lower extent than the increases in uptake seen in a nonirradiated group. This increase in tracer uptake occurred despite a 6.25-fold decline in viable cell numbers. When examined per cell, FDG uptake per cell increased 9.77-fold, methionine 7.82-fold and thymidine 9.48-fold over basal levels from Day 0 to Day 12 following irradiation. Part of these increases may be due to giant cell formation and/or radiation repair processes that require energy, protein and DNA substrates. While the in vitro system differs from in vivo systems due to the absence of a blood supply in vitro, a lack of infiltrating leukocytes and other factors, our data suggest that early assessment of human adenocarcinoma response to radiotherapy by PET with these tracers may be complicated by this normal increase in tracer uptake postirradiation. Clearly, in this human cancer cell line, early radiation- induced cell death is not associated with an early decline in tumor cell uptake of FDG, methionine or thymidine.