Characterization, optimization, and in vitro evaluation of Technetium-99m-labeled niosomes

Background and purpose: Niosomes are nonionic surfactant-based vesicles that exhibit certain unique features which make them favorable nanocarriers for sustained drug delivery in cancer therapy. Biodistribution studies are critical in assessing if a nanocarrier system has preferential accumulation in a tumor by enhanced permeability and retention effect. Radiolabeling of nanocarriers with radioisotopes such as Technetium-99m (Tc-99m) will allow for the tracking of the nanocarrier noninvasively via nuclear imaging. The purpose of this study was to formulate, characterize, and optimize Tc-99m-labeled niosomes. Methods: Niosomes were prepared from a mixture of sorbitan monostearate 60, cholesterol, and synthesized D-alpha-tocopherol polyethylene glycol 1000 succinate-diethylenetriaminepentaacetic acid (synthesis confirmed by H-1 and C-13 nuclear magnetic resonance spectroscopy). Niosomes were radiolabeled by surface chelation with reduced Tc-99m. Parameters affecting the radiolabeling efficiency such as concentration of stannous chloride (SnCl2 center dot H2O), pH, and incubation time were evaluated. In vitro stability of radiolabeled niosomes was studied in 0.9% saline and human serum at 37 degrees C for up to 8 hours. Results: Niosomes had an average particle size of 110.2 +/- 0.7 nm, polydispersity index of 0.229 +/- 0.008, and zeta potential of -64.8 +/- 1.2 mV. Experimental data revealed that 30 mu g/mL of SnCl2 center dot H2O was the optimal concentration of reducing agent required for the radiolabeling process. The pH and incubation time required to obtain high radiolabeling efficiency was pH 5 and 15 minutes, respectively. Tc-99m-labeled niosomes exhibited high radiolabeling efficiency (> 90%) and showed good in vitro stability for up to 8 hours. Conclusion: To our knowledge, this is the first study published on the surface chelation of niosomes with Tc-99m. The formulated Tc-99m-labeled niosomes possessed high radiolabeling efficacy, good stability in vitro, and show good promise for potential use in nuclear imaging in the future.