99mTc-labeled antimicrobial peptides for detection of bacterial and Candida albicans infections.

UNLABELLED: This study compared the possibilities and limitations of 99mTc-labeled synthetic peptides derived from two human antimicrobial peptides, namely, ubiquicidin (UBI) and lactoferrin (hLF), for the scintigraphic detection of bacterial and fungal infections in mice and rabbits. The rationale of our approach was that selected peptides accumulate in infected areas but not in sterile inflammatory lesions, because they bind preferentially to microorganisms. 99mTc-labeled human neutrophil peptides (defensins), ciprofloxacin, and human polyclonal IgG were included as control agents. METHODS: 99mTc-labeled peptides and control agents were injected intravenously into animals that had been injected intramuscularly 18 h earlier with multidrug-resistant Staphylococcus aureus, Klebsiella pneumoniae, or fluconazole-resistant Candida albicans. Sterile inflammatory sites were induced by the injection of heat-killed microorganisms or lipopolysaccharide (LPS) into the thigh muscle. Up to 4 h after injection, the accumulation of 99mTc-labeled compounds in the infected/inflamed thigh muscles was determined using scintigraphic techniques and radioactivity counts in dissected tissues. RESULTS: Scintigraphy revealed that 99mTc-labeled peptides UBI 29-41, UBI 18-35, UBI 31-38, hLF 1-11, and defensins, which showed preferential in vitro binding to microorganisms in a former study, accumulated at a significantly higher rate (P < 0.01) in bacterial and C. albicans infections in mice and rabbits than in inflamed tissues induced by heat-killed microorganisms or by LPS. No significant difference in the accumulation of 99mTc-labeled ciprofloxacin was observed between infected and sterile inflamed thigh muscles in mice. CONCLUSION: 99mTc-labeled antimicrobial peptides UBI 29-41, UBI 18-35, UBI 31-38, hLF 1-11, and defensins accumulate significantly in tissues infected with gram-positive and gram-negative bacteria and C. albicans. Significantly lower (P < 0.01) accumulation of these peptides occurs in sterile inflamed tissues. These data indicate that the peptides preferentially tag microorganisms at the site of infection, which is in agreement with their preferential binding to the microorganisms in vitro and in vivo. 99mTc-labeled ciprofloxacin does not distinguish between infections and sterile inflammatory lesions, which implies that its specificity for the detection of bacterial infections is not warranted.

Labelling, control and radiopharmacological evaluation of 99mTc-adenosine 5'-diphosphate (99mTc-ADP) as tumour seeking agent.

A study of 99mTc-adenosine-5'-diphosphate (99mTc-ADP) as a radiopharmaceutical for tumour diagnosis is presented. Two different labelling methods, using SnCl2 in alkaline solution and Zn as reducing agents, were developed. Reduction with Sn(II) alkaline solution was the selected method because a lower concentration of ADP (0.5 mg/mL) could be used and a higher radiochemical yield was achieved. A labelled molecule with a radiochemical purity higher than 95%, in vitro stability of at least 6 hours and an over all negative charge was obtained Biodistribution studies carried out in normal mice and rats revealed rapid urinary excretion and no specific accumulation of activity in any other particular organ. This behaviour was similar to that reported for 99mTc-adenosine-5'-triphosphate (99mTc-ATP). Rapid blood clearance, that could be fitted to a bicompartimental model, was also verified. No evidence of in vivo instability was observed. Studies in mice and rats bearing spontaneous mammary adenocarcinomas were performed and the results were compared to those from the 99mTc-ATP studies. Although the tumour models used were not the same, the incorporation of both labelled compounds was very similar. Radioactivity uptake in the tumour and the tumour-to-blood ratio were not notably high. However, a significant increment was observed in the tumour-to-muscle ratio (1.0 +/- 0.2 at 30 minutes to 2.7 +/- 0.4 at 240 minutes). Whole-body autoradiography enabled tumour visualization. Further investigations, including scintigraphic imaging, must be carried to complete the clinical evaluation of 99mTc-ADP as a tumour seeking agent.

99mTc-ADP: a potential agent for in vivo tumor detection.

The possibility of using 99mTc-labelled nucleotides as tumour seeking agents has been proposed by different research groups. We have recently reported the preparation of a 99mTc-ADP complex with a high radiochemical purity (> 95%), good in vitro and in vivo stability and promising biodistribution results when injected in mice bearing spontaneous mammary adenocarcinomas. Here we report the results of further investigations in animals with spontaneous neoplastic processes, including whole-body autoradiography in mice (20 minutes and 60 minutes post injection) and gamma-camera imaging studies in Wistar rats. Dynamic studies (up to 45 minutes) and static images (up to 18 hours) were acquired to determine the pharmacokinetics of 99mTc-ADP and the tumour/muscle and tumour/blood ratios. Blood-pool studies were also performed as a control. Tumours were visualized by autoradiography as was to be expected from the biodistribution studies. Dynamic studies showed a rapid blood clearance and a behaviour that fitted to a tricompartimental model. Radioactivity was rapidly taken up by the kidneys and excreted in the urine. No evidence of in vivo instability of the complex was observed. Tumour uptake reached the maximum values after 20 minutes post-injection. Tumour/blood and tumour/muscle ratios improved over time, enhancing tumour visualization. The best images were obtained after 3 hours post injection. In summary, our studies suggest that 99mTc-ADP is a promising radiopharmaceutical for tumour diagnosis.

Influence of the emulsion sign in phenytoin bioavailability.

To study the influence of the emulsion sign in phenytoin bioavailability, two emulsions (w/o and o/w) were prepared. Bioavailability studies were carried out with both emulsions in Wistar male rats. The study was of a randomized two-way cross over design. A radiotracer technique was chosen as analytical procedure, due to the small blood sample collected. 14C-phenytoin was synthesized with a high yield and suitable radiochemical purity. It is concluded, from a biopharmaceutic point of view, that the emulsion sign does not seem to affect the amount of phenytoin absorbed, as it is shown through the comparison of the areas under curve up to 24 h. An emulsion with oil as an external phase is responsible of a longer absorption, taking into account the apparent elimination constant rates.