Effect of Androgen on Normal Biodistribution of [18F]-2-Fluoro-5-methyl-1-beta-D-arabinofuranosyluracil (18F-FMAU) in Athymic Non-tumor-bearing Male Mice

Aim: We assessed the association between the presence and absence of androgen on the normal biodistribution of the positron emission tomography (PET) cellular proliferation imaging biomarker, [¹⁸F]-2'-Fluoro-5-methyl-1-beta-D-arabinofuranosyluracil (¹⁸F-FMAU), in mice. Materials and Methods: Non-castrated (n=4) and castrated (n=4) athymic non-tumor-bearing male mice served as models for presence and absence, respectively, of androgen. MicroPET-CT scans were performed 1 h following tail vein administration of 200 uCi of ¹⁸F-FMAU. Imaging was performed at baseline and then at 7-day intervals longitudinally for 35 days only in castrated mice following subcutaneous introduction of a 12.5 mg, 21-day release, dihydrotestosterone pellet. Mean standardized uptake values (SUV_mean) were obtained for liver, heart, and muscle. Several two-group comparisons of average of SUV_mean were performed. Results: Pre-pellet baseline average SUV_mean (±s.d.) values in castrated mice were significantly lower than baseline non-castrated values, increased on day 15 and reached peak values on day 28, at which time they were significantly higher than corresponding baseline levels in both non-castrated and pre-pellet castrated mice. The peak values decreased significantly following dihydrotestosterone withdrawal. Conclusion: There is a significant modulatory effect of androgen on normal ¹⁸F-FMAU uptake levels in mice liver, heart and muscle tissues.

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