Uptake evaluation of a new liposomal 99mTc-sestamibi formulation. In vivo and in vitro assays

TESAN F; PORTILLO M; GIAQUINTA ROMERO D; MARTINEL LAMAS D; MARTINEZ SARRASAGUE M; CIMATO A; MEDINA VA; SALGUEIRO MJ; ZUBILLAGA M

Cancún

Congreso; XI Congress of the World Federation of Nuclear Medicine and Biology. XXIV Congress of ALASBIMN. III Congreso de la Federación Mexicana de Medicina Nuclear e Imagen Molecular.; 2014

99mTc-sestamibi is a routinely used radiopharmaceutical predominantly for evaluation of myocardial perfusion. Its use in oncology is also known. Nanoparticles have been postulated as drug delivery systems that could improve tumor targeting by the enhanced permeability and retention effect. Since liposomes are one of the most commonly used nanosystems for drug delivery and some formulations are already commercially available, the objective of this work was to evaluate in vitro and in vivo uptake of a new 99mTc-sestamibi liposomal formulation. Materials and Methods: Sestamibi was radiolabeled according to the manufacturer instructions. Briefly, 60mCi of a pertechnetate solution eluted from a 99Mo?99mTc generator were aseptically added to the 0.5mg freeze-dried sestamibi kit. Saline solution was added to the preparation reaching an activity concentration of 20mCi/mL. Finally, vial was heated for 10min at 100ºC and then left at room temperature for 15min until thermal equilibrium. Phosphatidilcoline liposomes were formed by the lipid-film hydration method with 99mTc-sestamibi solution and sonicated for 30min for particle size reduction. Total lipid concentration was 1mg/mL. Entrapment efficiency was calculated by a exclusion chromatography with Sephadex G-25. For in vitro assays a human melanoma cell line (1205-LU) was cultured in 6 well plates and incubated for 30, 60 and 90 min with either 99mTc-sestamibi or liposomal 99mTc-sestamibi. Cellular uptake percentage was calculated and normalized by cell number. In vivo assays were performed in normal Sprague Dawley rats (250-270g). Animals were administered intravenously with either 99mTc-sestamibi or liposomal 99mTc-sestamibi previously intraperitoneally anesthesized (ketamine/xilazine). Biodistribution was evaluated by gamma camera images acquired at 30, 60 and 90 min post radiopharmaceutical injection. Results: radiochemical purity of 99mTc-sestamibi resulted 96% and the entrapment efficiency was 66%. In vitro assays showed a similar uptake kinetic profile for both formulations with increasing % uptake as a function of time. However at 60 min a slight difference was observed for the %uptake/106cells (2,59 ± 0,07 and 2,95±0,04 for 99mTc-sestamibi and liposomal 99mTc-sestamibi respectively). In vivo imaging analysis showed a similar biodistribution at all time points evaluated for both formulations. Both radiopharmaceuticals accumulated predominantly in the heart, liver, gastrointestinal tract and kidneys while bladder accumulation means there is renal elimination. However a minor increased liver uptake was observed for liposomal 99mTc-sestamibi as expected for particulate radiopharmaceuticals biodistribution. Conclusions: liposomal entrapment of 99mTc-sestamibi could be an interesting strategy to enhance tumor targeting due to improvement in radiopharmaceutical delivery. Further research is needed to evaluate its biodistribution in tumor bearing animals.