Perturbed Angular Correlation as a Tool to Study Precursors for Radiopharmaceuticals

Abstract

One of the key components of radiopharmaceuticals for targeting imaging and therapy is a stable bifunctional chelating system to attach radionuclides to selective delivery systems. After-effects of radioactive decay can cause the release of a radioactive isotope from its chelation agent. Perturbed angular correlation (PAC) of γ-rays has become a unique technique to study the behavior of complexes formed between a chelating agent and radionuclide in vivo (in real time) over a relevant range of concentrations (10 −12 M). In the present work, four radionuclides, 111 In, 111m Cd, and 152, 154 Eu, were investigated with diethylenetriaminepentaacetic acid (DTPA) at different pH values to determine the stability constants of the complexes as well as the effects of post-decay processes, which play a major role in determining the suitability of these complexes for application as radiopharmaceuticals (e.g., in vivo generators). The study provides a convenient parameter for the characterization of radionuclide−chelator systems using the PAC method. PAC is proven to be a suitable tool to study novel chelators and radiopharmaceutical precursors attached to radiometals.

Separation of 44mSc/44gSc Nuclear Isomers Based on After-Effects

“…The authors gave a number of 36 ± 2% for the 212 Bi release, while the total conversion was 37.3%. The same case was recorded for [ 152 Eu]­Eu-DTPA investigated by PAC; its daughter 152 Sm was fully released from the initial complex . Bhardwaj et al reported the design of a 177m Lu/ 177g Lu radionuclide generator based on after-effects, , with a yield of 95 ± 4% .…”

“…The trend of the percent of the daughter release (*per the portion of conversion, in the cases of IT and β decay, or per the portion of EC) depending on the Z -number of the daughter for 212 Bi, 177g Lu, 152 Sm, 166 Ho, 140 Pr, 111 Cd, − and 44g Sc. The black curve includes the data on 44g Sc-DOTATOC shown in this work, and the red curve includes the data on 44g Sc-DOTATATE reported by Huclier-Markai et al, which are in agreement with our data.…”

“…The same case was recorded for [ 152 Eu]Eu-DTPA investigated by PAC; its daughter 152 Sm was fully released from the initial complex. 15 Bhardwaj et al reported the design of a 177m Lu/ 177g Lu radionuclide generator based on after-effects, 10,24 with a yield of 95 ± 4%. 10 A similar case was noted with the 140 Nd/ 140 Pr pair, whereby the daughter 140 Pr was released from the initial complex with DOTATOC with a 93 ± 5% release.…”

“…Mossbauer spectroscopy is a useful technique for the investigation of the after-effects in a homogeneous solid-phase medium, while perturbed angular correlation (PAC) is suitable for liquid-phase studies. − The PAC technique measures the hyperfine interaction between the electric and magnetic moments of the nucleus and the external electric and magnetic fields at the nuclear site and is sensitive to the local environment of the probe nucleus. − However, these two methods allow for the study of “the fate” of the daughter radionuclide no earlier than 1 ns after radioactive decay, and the measured parameter is still a microparameter, although it has a statistic “detached” ensemble. These two methods can describe the distribution of the daughter radionuclides’ forms after 1–10 ns after decay.…”