O-[18F]fluoromethyl- L-tyrosine is a potential tracer for monitoring tumour response to chemotherapy using PET: an initial comparative in vivo study with deoxyglucose and thymidine.

Purpose: To compare the utility of a new artificial amino acid, O-[¹⁸F]fluoromethyl-L-tyrosine ([¹⁸F]FMT), for monitoring cancer chemotherapy with deoxyglucose and thymidine. Methods: [¹⁸F]FMT, [¹⁴C]deoxyglucose ([¹⁴C]DG) and [6-³H]thymidine ([³H]Thd) were applied in this study. A 2.5 mg/kg dose of mitomycin (MMC) was administered to AH272 rat hepatoma-bearing Donryu rats. Tumour uptake of each tracer was measured just before (baseline) and on days 1, 3, 5 and 7 after the MMC administration, 1 h after a mixture of [¹⁸F]FMT, [¹⁴C]DG and [³H]Thd had been injected, and was shown as DURs (% injected dose/gram tissue normalised for the rat body weight). Dual-tracer macroautoradiographs with [¹⁸F]FMT and [¹⁴C]DG were also prepared. Results: The tumour uptake for each tracer decreased earlier than did the tumour size. DURs (mean±SD) at baseline and on days 1, 3, 5 and 7 were as follows: [¹⁸F] FMT: 4.68±0.72, 3.34±0.66, 3.13±0.72, 3.42±0.45, 3.01±0.32; [¹⁴C]DG: 3.26±0.40, 3.09 ±0.55, 3.01±0.97, 2.28±0.35, 1.70±0.72; and [³H]Thd: 2.23±0.46, 1.54±0.45, 1.28±0.37, 1.35±0.20, 0.94±0.12. Decrease in [¹⁸F]FMT uptake compared with baseline was significant from day 1 (p<0.01), and the decrease in [³H]Thd uptake was also significant on day 1 (p<0.05) and days 3-7 (p<0.01). However, decrease in [¹⁴C]DG uptake was only significant from day 5 (p<0.01). Macroautoradiography suggested that the influence of inflammatory cells on the accumulation of [¹⁸F] FMT in tumours is smaller than that on the accumulation of [¹⁴C]DG. Conclusion: [¹⁸F]FMT uptake shows a rapid and sensitive response to chemotherapy, comparable to that of [³H]Thd, suggesting that it may be applied as a powerful tracer for monitoring of proliferative activity after cancer chemotherapy using PET. [ABSTRACT FROM AUTHOR]