Spectroscopic Characterization and Tissue Imaging Using Site-Selective Polyazacyclic Terbium(III) Chelates

Abstract

Polyazamacrocyclic chelates of terbium are shown to be useful in diagnostic medical imaging as tissue site-selective markers. Spectroscopic properties and biodistribution are studied for three terbium(III) species: 3,6,9-tris(methylene phosphonic acid n-butyl ester)-3,6,9,15-tetraaza-bicyclo[9.3.1]pentadeca-1(15),11,13-triene (abbreviated as PCTMB); 3,6,9-tris(methylene phosphonic acid)-3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(13),11,13-triene (abbreviated as PCTMP); and N,N'-bis(methylene phosphonic acid)-2,11-diaza [3.3]-(2,6)pyridinophane (abbreviated as BP2P). The respective aqueous molar absorptivities are found to be 3424, 2513, and 3281/2210 L mole⁻¹ cm⁻¹. Fluorescence quantum efficiency is determined against rhodamine 19 in basic ethanol and rhodamine 6G in ethanol. These values are 0.48, 0.21, and 0.40 for Tb-PCTMB, Tb-PCTMP, and Tb-BP2P, respectively. Biodistribution studies performed in Sprague–Dawley rats indicate tissue site-selectivity. Fluorescence images of bone tissues are presented and demonstrate the potential for using the lanthanide chelates to perform site-directed in vivo imaging for the early identification of abnormal tissue.