[ 99m Tc]duramycin for cell death imaging: Impact of kit formulation, purification and species difference.

INTRODUCTION: [99m Tc]duramycin is a SPECT tracer for cell death imaging. We evaluated the impact of kit formulation, purification and species difference on the pharmacokinetic profile and cell death targeting properties of [99m Tc]duramycin in order to define the optimal conditions for (pre-)clinical use.

METHODS: Three kits were prepared (A: traditional formulation, B: containing 1/3 of ingredients, C: containing HYNIC-PEG12 -duramycin). Following labeling, the kits were used without purification, or with SPE or HPLC purification. The pharmacokinetic profile was evaluated in mice and rats at 24 h post tracer injection (p.i.). Non-specific accumulation of [99m Tc]duramcyin was studied by μSPECT imaging in chemotherapy treated COLO205 tumor bearing mice pre-treated with cold duramycin (0.01-50 μg). Cell death targeting ability of the kits displaying the best pharmacokinetic profile was compared in a treatment response study in COLO205 tumor bearing mice treated with conatumumab (anti-DR5 antibody).

RESULTS: HPLC purification of kit prepared [99m Tc]duramycin and reducing the amount of kit ingredients resulted in the best pharmacokinetic profile with low accumulation in liver, spleen and kidneys. The use of PEGylated [99m Tc]duramycin required longer circulation times (> 4 h pi) to obtain good imaging characteristics. Pre-treatment with duramycin significantly decreased tracer uptake in chemotherapy treated tumors in a dose-dependent manner. A blocking dose of 50 μg significantly increased non-specific accumulation in liver and spleen. Non-specific accumulation of [99m Tc]duramycin was however demonstrated to be species dependent. HPLC purified kit A (5.21±1.71 %ID/cc) and non-purified kit B (1.68±0.46 %ID/cc) demonstrated a significant increase in tumor uptake compared to baseline following conatumumab treatment.

CONCLUSIONS: To obtain [99m Tc]duramycin with favorable imaging characteristics for cell death imaging in mice [99m Tc]duramycin needs to be prepared with high specific activity by applying HPLC purification. The need for HPLC purification appears to be a species dependent phenomenon and might therefore not be required for clinical translation.