Background:
Technetium 99m-n-mpo (tc-99m-n(mpo)(pnp5)) is a cationic tc-99m nitrido complex. the objective of this study is to evaluate its potential as a new radiotracer for myocardial perfusion imaging.
Methods and results:
Biodistribution studies were performed in sprague-dawley rats and guinea pigs to compare the myocardial uptake and excretion kinetics of tc-99m-n-mpo from noncardiac organs, such as the liver and lungs, with those of the known cationic tc-99m radiotracers: tc-99m-n-dbodc5 and tc-99m-sestamibi. planar imaging was performed in sprague-dawley rats to evaluate the utility of tc-99m-n-mpo as a myocardial perfusion imaging agent. metabolism studies were carried out by use of both sprague-dawley rats and guinea pigs. in general, the heart uptake of tc-99m-n-mpo was between that of tc-99m-sestamibi and tc-99m-n-dbodc5 over the 2-hour study period. however, the heart-liver ratio of tc-99m-n-mpo (12.75 +/- 3.34) at 30 minutes after injection was more than twice that of tc-99m-n-dbodc5 (6.01 +/- 1.45) and approximately 4 times higher than that of tc-99m-sestamibi (2.90 +/- 0.22). the heart uptake and heart-liver ratio of tc-99m-n-mpo and tc-99m-sestamibi in guinea pigs were significantly lower than those obtained in sprague-dawley rats. the metabolism studies demonstrated no detectable tc-99m-n-mpo metabolites in the urine and feces samples of the sprague-dawley rats at 120 minutes after injection. in guinea pigs no tc-99m-n-mpo metabolites were detected in the urine at 120 minutes, but only approximately 60% of tc-99m-n-mpo remained intact in the feces samples. in contrast, there was no intact tc-99m-sestamibi detected in urine samples, and less than 15% of tc-99m-sestamibi remained intact in the feces samples. planar imaging studies indicated that clinically useful images of the heart may be obtained as early as 15 minutes after injection of tc-99m-n-mpo.
Conclusion:
The combination of favorable organ biodistribution and myocardial uptake with rapid liver clearance makes tc-99m-n-mpo a very promising myocardial perfusion radiotracer worthy of further evaluation in various preclinical animal models.