Chemical and Physical Characterisation of Human Serum Albumin Nanocolloids: Kinetics, Strength and Specificity of Bonds with 99mTc and 68Ga

Abstract

Nanoparticles of Human Serum Albumin (NC) labelled with 99mTc are widely used in Nuclear Medicine and represent the gold-standard for the intraoperative detection of the sentinel lymph node in many kinds of cancer, mainly breast cancer and melanoma. A significant amount of radionuclides can be incorporated into the HSA particle, due to the multiple binding sites, and HSA-based nanocolloid catabolism is a fast and easy process that results in innocuous degradation products. NCs labelled with different isotopes represent an interesting radiopharmaceutical for extending diagnostic accuracy and surgical outcome, but the knowledge of the chemical bond between NCs and isotopes has not been fully elucidated, including information on its strength and specificity. The aim of this study is to investigate and compare the physicochemical characteristics of the bond between NCs and 99mTc and 68Ga isotopes. Commercial kits of HSA-based nanocolloid particles (NanoAlbumon®) were used. For this purpose, we have primarily studied the kinetic orders of NC radiolabelling. Langmuir isotherms and pH effect on radiolabelling were tested and the stability of the radiometal complex was verified through competition reactions carried out in presence of different ligands. The future goal of our research is the development of inexpensive and instant kits, easily labelled with a wide spectrum of diagnostic and therapeutic isotopes, thus facilitating the availability of versatile and multipurpose radiopharmaceuticals.

Chemical and Physical Characterisation of Macroaggregated Human Serum Albumin: Strength and Specificity of Bonds with 99mTc and 68Ga

“…It was then normalised to the number of human serum albumin molecules forming a single MAA particle, obtaining (8.29(2) 1 × 10 −5 ), which is even lower than that of HSA (about 1 atom/10,000 tightly bound) at SPC condition. A value sharply different from NC (46.4(2)) and from human serum albumin forming a single NC particle (2.1(2)) was observed [23].…”

“…To characterise the bond characteristic between isotopes and MAA, an attempt was made to evaluate the kinetics of radiolabelling of MAA with 99m Tc. The speed of radiolabelling was too rapid to detect the variation of MAA labelled (95% labelling in less than 60 s); it should be noted that the speed increase from HSA to NC [23] to MAA is probably due to the greater reaction surface.…”

“…Instead, if the pH is changed after the bond is created, the binding complex breaks down and fails to reform, due to a series of side reactions that change the state of technetium [32]. The behaviour of MAA is completely opposite to that of NC [23], probably because a multitude of different amino acid side chains are exposed on the MAA surface, which, unlike NC, lead to a nondiscriminatory environment. Therefore, the change of pH can break a previously formed complex but cannot interfere in creating a new complex with different amino acid side chains.…”

An investigation of aspects of radiochemical purity of 99mTc-labelled human serum albumin nanocolloid

“…Smaller, 50–80 nm HSA nanoparticles labelled with 99m Tc provide a diagnostic radiopharmaceutical agent for sentinel lymph nodes scintigraphy (Giammarile et al 2013 ; Sadkin et al 2020 ). Several commercially available kit formulations for preparing [ 99m Tc]Tc-HSA nanocolloid have become available recently and are described in the literature (Nanotop®, Nanoalbumon®, Nanocoll®) (Persico et al 2015 ; Gommans et al 2009 ; Marenco et al 2021 ). Since the radiopharmaceutical is prepared shortly prior to administration, a quality control (QC) must be performed immediately after radiolabelling in order to determine the radiochemical purity (RCP).…”

“…The SPC of Nanoalbumon® (Medi-Radiopharma Ltd, Erd, Hungary) stipulates 85% aqueous methanol mobile phase with iTLC-SG or Whatman No. 1 for determining the RCP (Marenco et al 2021 ). The United States Pharmacopoeia includes a monograph on [ 99m Tc]Tc-albumin colloid injection, giving a method for determining RCP using iTLC-SG with methyl ethyl ketone (United States Pharmacopoeia Convention.…”