Preparation of188Re-lanreotide peptide and its quality control

Preparation, quality control, biological evaluation, and human absorbed dose estimation of 188Re-HYNIC-TOC

In this study, concerning the advantages of rhenium-188 over other therapeutic radionuclides, such as its stock availability from 188W/188Re generator and radiolabeled peptide therapy in the treatment of patients with widespread disease, preparation and quality control of 188Re-HYNIC-TOC were studied. Optimized conditions for radiolabeling of HYNIC-TOC with 188Re were assessed by several experiments. 188Re-HYNIC-TOC was prepared with radiochemical purity >97%. The radiolabelled compound showed high stability both in PBS buffer and in human serum even after 24 h. Biodistribution of the complex in male Wistar rats was examined up to 24 h after intravenous injection and indicated fast blood clearance and significant accumulation in the kidney. The radiation absorbed dose assessment resource (RADAR) method was used to estimate the equivalent and effective absorbed dose of human organs. Kidney received the absorbed dose of 0.72 mSv/MBq, the highest estimated amount, after injection of the complex. The results showed fast preparation, easy quality control, and relatively similar biodistribution of 188Re-HYNIC-TOC to other peptides. This complex can be considered as an agent for the treatment of patients with medium-sized tumors expressing somatostatin receptors. However, more biological studies are still needed.

Development of radiochemistry in Pakistan – 1960 to 2010

With the inception of Pakistan Atomic Energy Commission (PAEC) in 1956, peaceful uses of atomic energy commenced for the benefit of scientific community as well as masses of Pakistan. Radiochemistry played a vital role right from the beginning. The research and development in this field accelerated soon after the criticality of the first research reactor named as Pakistan Research Reactor (PARR- 1) at the Pakistan Institute of Nuclear Science and Technology (PINSTECH), Islamabad. The first radioisotope produced at PARR-1 for application in nuclear medicine was 131I. Later on, many other radioisotopes were prepared and radiopharmaceuticals were synthesised for their use in industry and hospitals. Besides providing pure radioactive tracers for nuclear medicine, radiochemistry also enhanced the detection limit of impurities at all stages of nuclear fuel cycle for power generation. In 1983, research in the field of nuclear data measurement began. The main aim was to identify suitable conditions for the production of radionuclides for cancer diagnostics, treatment and therapy. With the establishment of a second research reactor (PARR-2) at PINSTECH, research in neutron activation analysis, radioisotope production and separation studies gained more momentum and many research articles were published. Solvent extraction, adsorption and ion-exchange were the main routes of separation in those studies. Separation of heavy metals and treatment of waste generated in a nuclear power plant are other important aspects related to environmental restoration and nuclear waste management, where radiochemistry is required. In future, work in radiochemistry will be continued on similar lines to develop novel radiopharmaceuticals, identify indigenous schemes for nuclear waste management and work out intelligent procedures for material characterization for benefit to mankind, especially the people of Pakistan.

Direct labeling studies of octapeptides with rhenium-188

The somatostatin octapeptide lanreotide and octreotide were labeled with rhenium-188 by direct method. The optimization of the labeling, the in vitro stability of the complexes and the biodistribution were evaluated. Labeling efficiency was generally greater than 95. The best time for reaction was 2hours. 188Re-lanreotide gave better radiochemical yields than 188Re-octreotide, and it was stable for a longer time (24 vs. 4 hours), but the mass of lanreotide had to be larger than that for octreotide (350 vs. 250μg), and the required ratio between mass of stannous chloride and peptide was also greater for lanreotide. Use of tartrate/phthalate buffer with 188Re-octreotide gave better radiochemical results and showed more labeling stability than the use of acetate/acetic acid buffer. The results of Cys challenge for 188Re-peptides revealed higher chelation strength for 188Re-octreotide than for 188Re-lanreotide for concentrations of cysteine below 1mM. For a concentration of cysteine of 100mM the rate of transchelation of 188Re to cysteine was the same for both peptides. The CD50 value for 188Re-octreotide was 10mM of cysteine and for 188Re-lanreotide, it was 55mM.188Re-labeled peptides were distributed in the gastrointestinal tract or in the kidneys and rapid blood clearance was observed in the first hour. Results indicated that the products can be obtained with high radiochemical purity, appropriate for in vivo studies to assess their efficacy in radioimmunotherapy.

Water-soluble phosphines for direct labeling of peptides with technetium and rhenium: insights from electrospray mass spectrometry

Direct labeling of salmon calcitonin (sCT) is possible in one step using water-soluble phosphines (sulfonated triphenylphosphines) as the reducing agent both for disulfide and for pertechnetate. Phosphines were the most efficient reducing agent for disulfide bonds among those examined. The phosphines both reduced the pertechnetate to Tc(III), and contributed to the technetium coordination sphere in the labeled product. In contrast, the phosphines did not reduce rhenium below oxidation state V, nor did they participate in the rhenium coordination sphere in the labeled peptide. Instead, the expected oxorhenium(V) moiety was incorporated. Both Tc and Re labeling processes gave rise to dimers with two peptides linked by the metal center, as well as simple monomeric species. Positive mode electrospray mass spectrometry not only revealed the presence of phosphine bound to technetium and oxygen bound to rhenium in the metallopeptides but also revealed the oxidation states of the metals. Electrospray mass spectrometry is proving to be an exceptionally valuable technique for characterizing radiopharmaceuticals. Although the one-step direct labeling method described gives mixed products and poor receptor affinity when applied to the small peptide sCT, it might be readily adapted to monoclonal antibodies.

Syntheses and reactivity of 'sulfur rich' Re(iii) and Tc(iii) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

Reduction-substitution reactions of [M(O)Cl(4)](-)(M=Re, (99)Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS(2))(-) in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M(III)(R-PhCS(3))(2)(R-PhCS(2))(M=Re; Rel--9; M=99)Tc; Tel--9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS(3))(2)(4-Me-PhCS(2)), Re 2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d(4) trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(v) to Re(iii) and oxidation of dithiobenzoate to trithioperoxybenzoate. M2--9 complexes contain a substitution-inert [M(R-PhCS(3))(2)](+) moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M(III)(R-PhCS(3))(2)(Et(2)NCS(2))(M=Re; Re 10--18; M=(99)Tc; Tc--18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS(3))(2)(Et(2)NCS(2)), Re 10 and (99)Tc(PhCS(3))(2)(Et(2)NCS(2)), Tc 10.