Chemical synthesis of L-[75Se]selenomethionine in a high-activity scale

Isolation of high purity 73Se using solid phase extraction after selective 4,5-[73Se]benzopiazselenol formation with aminonaphthalene

A fast and efficient process for the production of the PET radionuclide 73Se was developed using 75Se as a surrogate. 75Se was separated from proton irradiated arsenic trioxide by reaction with 2,3-diaminonaphthalene to 4,5-[75Se]benzopiazelenol. This compound was purified using SPE column chromatography and subsequently decomposed with hydrogen peroxide. For further chemical conversions [75Se]selenite was reduced to elemental [75Se]selenium by either using thiosulfate or sulfur dioxide. The recovery yield of 75Se from the target amounted to 43%. The utility of the isolated 75Se for radiosyntheses was demonstrated by the successful preparation of [75Se]selenomethionine. The methodology developed using 75Se was successfully transformed to 73Se.

Evaluation of radioselenium labeled selenomethionine, a potential tracer for brain protein synthesis by PET

The blood-brain transfer, protein incorporation and metabolism of L-[75Se]selenomethionine (SeMet) of relatively high specific activity (> 400 GBq mmol) were studied in male Wistar rats. The highest uptake was found in the pancreas, followed by the tumor, kidney, liver, brain and muscle. In addition, plasma and brain samples of rats were analyzed for labeled fractions of free SeMet, metabolites, and SeMet bound to t-RNA and proteins. For example, free SeMet represented more than 80% of brain radioactivity at 1.5 min while it was less than 15% at 360 min. A concomitant increase was observed for protein bound SeMet in brain. A three-compartment model was applied to calculate the blood-brain transfer constant (K1 (0.15 +/- 0.070 mL g-1 min-1) and the rate constant of SeMet incorporation into proteins (k3 = 0.026 +/- 0.008 min-1). The apparent incorporation of methionine into proteins was estimated to be about 0.73 nmol g-1 min-1. From the studies it is concluded that the use of L-[75Se]selenomethionine may be appropriate to measure brain protein incorporation in humans with PET.