Recombinant Metallothionein-Conjugated Streptavidin Labeled with 188Re and 99mTc

Abstract

Consideration is now being given to the use of avidin (or streptavidin) and biotin for radiotherapy of tumor. Accordingly, the goal of this study was to radiolabel a mouse metallothionein-streptavidin fusion protein with 188Re and to compare its properties to those of the same fusion protein radiolabeled with 99mTc. A recombinant metallothionein-streptavidin fusion protein was radiolabeled by transchelation with 99mTc- and 188Re-glucoheptonate. Labeling efficiency, which was not optimized for either radionuclide, was approximately 60% for 99mTc and 20% for 188Re. Radiochemical purity was demonstrated by size exclusion HPLC both by nearly quantitative shifts of the 188Re label to higher molecular weight upon the addition of biotinylated antibody and by the absence of a shift with biotinsaturated 188Re-metallothionein-streptavidin. Stability of the labels in 37 degrees C serum was evaluated by comparing the HPLC radiochromatograms of serum samples both before and after the addition of biotinylated antibody. The 188Re label behaved like 99mTc in that the same peaks were evident, including one prominent peak due to labeled cysteine. Recoveries during HPLC analysis of serum samples showed that oxidation rates to perrhenate and pertechnetate were identical. However, instability to cysteine challenge was greater for 188Re; for example, the loss of label to cysteine after 24 h under one set of conditions was 41% for 188Re and 22% with 99mTc. Analysis by HPLC of liver and kidney homogenates from mice administered the labeled antibodies were qualitatively and, in large measure, quantitatively independent of label. Biodistributions at 5 h in normal mice were statistically identical between the two labels in blood and in most tissues. In conclusion, streptavidin may be radiolabeled with radiorhenium using recombinant mouse metallothionein as a bifunctional chelator, and under one set of labeling conditions at least, 188Re showed similar in vitro and in vivo behavior to that of 99mTc labeled to the same fusion protein.

Genetic Incorporation of Human Metallothionein into the Adenovirus Protein IX for Non-Invasive SPECT Imaging

“…The heavy metals that can be bound by MT include Ag, Au, Bi, Cd, Co, Cu, Fe, Hg, Ni, Pb, Sn, Tc, and Zn, [32], as well as Re [33]. To determine the specificity of 99m Tc binding, we performed a metal competition assay using increasing concentrations of CdCl 2 , CoCl 2 , CuCl 2 , or ZnCl 2 .…”

“…Likewise, next-generation SPECT systems have dramatically increased sensitivity. In addition to evaluation of biodistribution by initially in vitro 99m Tc radiolabeled replication deficient Ads, we expect virions containing the pIX-metallothionein fusion proteins can also be potentially labeled using 188 Re [33]. This method could offer the advantage of dual-functional SPECT imaging and radionuclide therapy [43], [44], [45].…”

Construction and Radiolabeling of Adenovirus Variants that Incorporate Human Metallothionein into Protein IX for Analysis of Biodistribution

“…Nonetheless, SPECT radiotracers are cheaper and more widely available, without the need for an adjacent cyclotron for production of short-lived PET radiotracers. MT has also been demonstrated to bind isotopes of rhenium 55 (ie, 188 Re or 186 Re), which are capable of combined SPECT imaging and radionuclide therapy. 56,57…”

Rhenium and technetium tricarbonyl, {M(CO)3}+ (M = Tc, Re), binding to mammalian metallothioneins: new insights into chemical and radiopharmaceutical implications

“…Studies of MTs with technetium are scarce; most of them were performed around the 90s and are usually based on the metal-binding capability of MTs and the possible conjugation of the protein to a biomolecule. It allows that MTs can act as bifunctional chelating agents linking the radionuclide to biomolecules [15][16][17][18][19]. As far as we know, only two of those works are essentially devoted to the study of the binding ability of MTs to technetium [20,21].…”