title: Impact of bidentate chelators on lipophilicity, stability, and biodistribution characteristics of cationic 99mTc-nitrido complexes.
abstract: This report describes synthesis and evaluation of novel cationic 99mTc-nitrido complexes, [99mTcN(L)(PNP)](+) (L = ma, ema, tma, etma and mpo; PNP = PNP5, PNP6, and L6), as potential radiotracers for heart imaging. Cationic complexes [99mTcN(L)(PNP)](+) were prepared in two steps. For example, reaction of succinic dihydrazide with 99mTcO4(-) in the presence of excess stannous chloride and PDTA resulted in the [99mTcN(PDTA)n] intermediate, which then reacted Hmpo and PNP6 at 100 degrees C for 10-15 min to give [99mTcN(mpo)(PNP6)](+) in >90% yield. It was found that bidentate chelators have a significant impact on lipophilicity, solution stability, biodistribution, and metabolic stability of cationic 99mTc-nitrido complexes. The fact that [99mTcN(ema)(PNP6)](+) decomposes rapidly in the presence of cysteine (1 mg/mL) while [99mTcN(etma)(PNP6)](+) and [99mTcN(mpo)(PNP6)](+) remain stable for >6 h under the same conditions strongly suggests that thione-S donors in bidentate chelators increase the solution stability of their cationic 99mTc-nitrido complexes. Biodistribution studies were performed on four cationic 99mTc-nitrido complexes in Sprague-Dawley rats. [99mTcN(etma)(PNP5)](+) is of particular interest due to its high initial heart uptake (1.81 +/- 0.35 %ID/g at 5 min postinjection), and long myocardial retention (1.99 +/- 0.47 %ID/g at 120 min postinjection). The heart/liver ratio of [99mTcN(etma)(PNP5)](+) (6.06 +/- 1.48) at 30 min postinjection is almost identical that of 99mTcN-DBODC5 (6.01 +/- 1.45), and is >2 times better than that of 99mTc-sestamibi (2.90 +/- 0.22). Results from metabolism studies show that [99mTcN(etma)(PNP5)](+) has no significant metabolism in the urine, but it does show significant metabolism in feces samples at 120 min postinjection. Planar imaging studies suggest that [99mTcN(etma)(PNP5)](+) might be able to give clinically useful images of the heart as early as 30 min postinjection. [99mTcN(etma)(PNP5)](+) is a very promising candidate for more preclinical evaluations in various animal models.
authors.affiliation: Civil Engineering Building, School of Health Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Young-Seung
authors.initials: YS
authors.lastname: Kim
authors.forename: Zhengjie
authors.initials: Z
authors.lastname: He
authors.forename: Wen-Yuan
authors.initials: WY
authors.lastname: Hsieh
authors.forename: Shuang
authors.initials: S
authors.lastname: Liu
mesh_terms: D000818:Animals; D002412:Cations; D002614:Chelating Agents / Q000737:chemistry; D005243:Feces / Q000737:chemistry; D006321:Heart / Q000000981:diagnostic imaging*; D008099:Liver / Q000000981:diagnostic imaging / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics*; D015609:Organotechnetium Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution; D014556:Urine / Q000737:chemistry
chemical_list: D002412:Cations; D002614:Chelating Agents; D009942:Organometallic Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C522262:nitrido(N-ethoxyethyl-N,N-bis(2-(bis(3-methoxypropyl)phoshino)ethyl)amine)(ethylthiomaltol)technetium(V)