Surfactant protein B labelled with [Tc-99m(CO)(3)(H2O)(3)](+) retains biological activity in vitro

Labelling of the hydrophobic surfactant protein B (SP-B) under non-reducing conditions was achieved with [Tc-99m(CO)(3)(H2O)(3)](+) prepared according to Alberto et al. (JACS, 1998). The binding of radioactivity was protein-s pecific, with an overall radiochemical yield of 50%. Gel electrophoresis an d Westernblot analyses showed no structural changes of SP-B. Spreading prop erties and surface activity of Tc-99m-labelled SP-B in an air/water interfa ce coincided with those of unlabelled SP B. Tc-99m-SP-B seems to be a promi sing agent to observe surfactant spreading under clinical conditions. Background: Therapeutic results for surfactant instillation in clinical tri als are conflicting. The Tc-99m-labelling of surfactant would allow to obse rve its spreading in the lung under clinical conditions. Methods: [Tc-99m(CO)(3)(H2O)(3)](+) was prepared as described by Alberto et al. (JACS, 1998). This carbonyl complex was used for the direct labelling of surfactant protein B (SP-B) under non-reductive conditions by direct inc ubation with SP-B at elevated temperature followed by extraction into CHCl3 /MeOH. Results: The hydrophobic protein SP-B was labelled with [Tc-99m(CO)(3)(H2O) (3)](+). An overall radiochemical yield of about 50% was achieved. HPLC-ana lysis revealed a single radiolabelled species according to UV elution profi le of SP-B, supported by paper and size exclusion chromatography. Gel elect rophoresis confirmed that the dimer structure of SP-B was preserved. Spread ing properties of Tc-99m-labelled SP-B in an air/water interface coincided with those of unlabelled SP-B. Spreading of radioactivity observed in a gla ss trough of 26 cm x 27 cm with a gamma camera was completed during the fir st 7-9 sec after application of Tc-99m-labelled SP-B. The corresponding dec rease of surface tension to 45 mN/m at the peripheral surface tension senso rs took 7 sec +/- 2 sec (MEAN +/- STD; n = 3). Conclusions: Direct and specific Tc-99m-labelling of the hydrophobic surfac tant protein B was achieved using the [Tc-99m(CO)(3)(H2O)(3)](+) precursor. This procedure can easily be used to prepare specifically labelled surfact ant mixtures with spreading properties that coincide with those of unlabell ed surfactant. (C) 2001 Elsevier Science Inc. All rights reserved.