Reproducible preparation of [^99mTc]TRODAT-1 with high radiochemical purity using simple Sep-Pak purification

Objectives [^99mTc]TRODAT-1 is useful as a potential CNS DAT imaging agent by SPECT and its radiolabeling was improved by the development of kit formulation in a single vial. However, the preparation of [^99mTc]TRODAT-1 was difficult with an efficient radiochemical yield, purity and reproducibility in-house production because of an instability of precursor and side products. In this study, we describe simple synthetic method based on home-made kit type and easily separation with tC18 Sep-Pak for high radiochemical purity.

Methods After the acidic hydrolysis of bisaminebisTrtiol (N₂TrS₂) compound (1 mg) as occasion demands, the obtained precursor was dispensed to eight vials containing the other ingredients. All vials were lyophilized and storaged at -20 ^oC. 1 mL of Na^99mTcO₄ was added to a vial and the labeling reaction proceeded at 100 ^oC for 30 min. To obtain reliably high radiochemical purity, the separation of mixture was performed on HPLC or Sep-Pak cartridge. In tC18 Sep-Pak purification, the solid phase was washed with 20 mL of saline followed by 3 mL of 20% and 30 % ethanol in saline. Finally, the desired product was eluted by 1 mL of 60% ethanol in saline and the collected solution was diluted for 5% ethanol in saline for the clinical research. The radiochemical yields and purity were measured by radio-TLC.

Results The purification of [^99mTc]TRODAT-1 using HPLC was not sufficient to obtain the desired purity compare to the method of Sep-Pak cartridge because of the decomposition of product in the organic mobile phase. [^99mTc]TRODAT-1 was prepared in 48 ± 13.03 % (n = 64) radiochemical yield within 60 min including solid-phase purification, 87 ± 4.14 % (n = 64) radiochemical purity, and good reproducibility.

Conclusions [^99mTc]TRODAT-1 was prepared in high yield and reproducibility using home-made TRODAT-1 kit. Simple purification using tC18 Sep-Pak was acquired more high reliable radiochemical purity of [^99mTc]TRODAT-1 for clinical research studies