Radiosynthesis and biological evaluation of 166Ho labeled methoxylated porphyrins as possible therapeutic agents

¹⁶⁶Ho labeled 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrin, and 5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl) porphyrin ([¹⁶⁶Ho]–TDMPP and [¹⁶⁶Ho]–TTMPP respectively) were prepared with acceptable radiochemical purity and specific activities. Stability and partition coefficient of the complexes were determined in the final formulations and biodistribution studies in mouse demonstrated high accumulation of [¹⁶⁶Ho]–TDMPP in the lung and liver and less excretion through the kidney. while [¹⁶⁶Ho]–TTMPP was mostly excreted into intestines and kidneys while lungs were a minor accumulation site. In contrast to other reported radiolanthanide labeled porphyrins these two complexes showed less liver accumulation. Further investigation of their potential therapeutic properties is of interest.     

Development and evaluation of a 166holmium labelled porphyrin complex as a possible therapeutic agent

Porphyrins are interesting derivatives with low toxicity, tumor avidity and rapid wash-out suggested as potential radiopharmaceuticals in radiolabeled form. In this work, [¹⁶⁶Ho] labeled 5,10,15,20-tetrakis(phenyl) porphyrin ([¹⁶⁶Ho]-TPP) was prepared using [¹⁶⁶Ho]HoCl₃ and 5,10,15,20-tetrakis(phenyl)porphyrin (H₂TPP) for 12 h at 50 °C (radiochemical purity: >95 ± 2 % ITLC, >99 ± 0.5 % HPLC, specific activity: 0.9–1.1 GBq/mmol). Stability of the complex was checked in final formulation and human serum for 48 h. The partition coefficient was calculated for the compound (log P = 2.01). The biodistribution of the labeled compound in vital organs of wild-type rats was studied using scarification studies and SPECT. A detailed comparative pharmacokinetic study performed for ¹⁶⁶Ho cation and [¹⁶⁶Ho]-TPP performed up to 24 h. The complex is mostly washed out from the circulation through kidneys and in less extends from the liver. The kidney:blood, kidney:liver and kidney:muscle ratios 4 h post injection were 14, 3.6 and 7.38 respectively.     

Production and quality control of [<Superscript>166</Superscript>Ho]-DOTA-bevacizumab for therapeutic applications

Antiangiogenic monoclonal antibodies in combination with therapeutic radionuclides are potential targeted therapy agents in cancer. In this study, bevacizumab was successively labeled with [¹⁶⁶Ho]HoCl₃ after conjugation with DOTA-NHS-ester with a radiochemical purity of higher than 95% (RTLC). The conjugates were purified by molecular filtration, the average number of DOTA conjugated per mAb was calculated and total concentration was determined by spectrophotometric method and the average chelate to antibody ratio (c/a) for the conjugate used in this study was 5.8:1 and protein integrity experiments (SDS-PAGE). The biodistribution studies in wild-type rats demonstrate a similar pattern to the other radiolabeled anti-vascular endothelial growth factor A (VEGF-A) immunoconjugates. ¹⁶⁶Ho-DOTA-bevacizumab is a potential compound for therapy/imaging of VEGF-A expression in oncology.     

Radiolanthanide-labeled HA particles in the treatment of rheumatoid arthritis: ready-to-use cold kits for rapid formulation in hospital radiopharmacy

Hydroxyapatite (HA) [Ca₁₀(PO₄)₆(OH)₂] particles radiolabeled with a variety of β^? emitting lanthanide radionuclides and also pseudolanthanide ⁹⁰Y have been proposed for the treatment of arthritis. A ready-to-use cold kit of HA particles (1–10 µm size) was developed for fast and convenient formulation of radiolanthanide-labeled HA particles at hospital radiopharmacy. Six radionuclides namely, ¹⁶⁹Er, ¹⁷⁷Lu, ¹⁵³Sm, ¹⁶⁶Ho, ¹⁴²Pr and ⁹⁰Y, having β^? emissions of a wide range of energy [E_β(max) = 0.34–2.28 MeV] were identified and produced by thermal neutron activation. Clinical doses of HA particles labeled with these radionuclides were prepared in high yield (>97 %) and radiochemical purity (>99 %) using the cold kits. Pre-clinical studies of ¹⁷⁷Lu–HA carried out in Wistar rats bearing arthritis in knee joints revealed no leakage of the activity from the joints. In preliminary clinical investigation using 333 ± 46 MBq doses of the same preparation, significant improvement in the disease conditions was reported in patients with chronic rheumatoid arthritis of knee joints.     

Preparation of <Superscript>166</Superscript>Dy/<Superscript>166</Superscript>Ho-chitosan as an in vivo generator for radiosynovectomy

¹⁶⁶Ho is one of the most effective radionuclides used for radiosynovectomy. One method to deliver this radioisotope to target tissue is via the ¹⁶⁶Dy/¹⁶⁶Ho in vivo generator system. The aim of this work was to prepare ¹⁶⁶Dy/¹⁶⁶Ho-chitosan (¹⁶⁶Dy/¹⁶⁶Ho-CHIT) in vivo generator for radiosynovectomy applications. ¹⁶⁶Dy obtained by the irradiation of natural ¹⁶⁴Dy target. ¹⁶⁶Dy was separated from ¹⁶⁶Ho by extraction chromatographic method (separation yield; 93% and separation factor;1.7). Chitosan labeling was performed in acetic acid with 99.3 ± 0.6% radiochemical purity. Biodistribution studies on intraarticular injected rats demonstrated high retention in the knee joint even 7 days showing no radioactivity leakage from the injection site into other organs as well as any translocation of the daughter nucleus after β^? decay of ¹⁶⁶Dy.     

Radiosynthesis of 10-(2-[18F]fluoroethoxy)-20(S)-camptothecin as a potential positron emission tomography tracer for the imaging of topoisomerase I in cancers

The preparation of 10-(2-[¹⁸F]fluoroethoxy)-20(S)-camptothecin, a potential positron emission tomography tracer for the imaging of topoisomerase I in cancers, is described. 10-(2-[¹⁸F]Fluoroethoxy)-20(S)-camptothecin was synthesized by the [¹⁸F]fluoroalkylation of the corresponding hydroxy precursor molecule with 2-[¹⁸F]fluoroethyl bromide ([¹⁸F]FEtBr) in dimethylsulfoxide (DMSO) at 55 °C for 20 min; this was followed by purification using high performance liquid chromatography (HPLC) with a total preparation time of 60 min. The overall radiochemical yield was approximately 5.4–12 % (uncorrected), and the radiochemical purity was above 96 %.     

Development of 166Ho bleomycin as a possible therapeutic complex

Due to interesting therapeutic properties of ¹⁶⁶Ho and the antineoblastic antibiotic, bleomycin (BLM), ¹⁶⁶Ho-bleomycin (¹⁶⁶Ho-BLM) was developed as a possible therapeutic compound. ¹⁶⁶Ho chloride was obtained by thermal neutron irradiation (1 × 10¹³ n cm^?2 s^?1) of natural Ho(NO₃)₃ samples (specific activity = 3–5 GBq mg^?1), dissolved in acidic media. At optimized conditions (room temperature, 12 h, 0.15–0.3 mg bleomycin for 74 MBq ¹⁶⁶HoCl₃) a radiochemical purity of 94–97% was obtained as shown by ITLC and HPLC (specific activity, 700–740 GBq mmol^?1). Biodistribution studies of ¹⁶⁶Ho chloride and ¹⁶⁶Ho-BLM were performed in wild-type rats. The accumulation of the radiolabeled compound in lungs, liver and spleen demonstrates a similar pattern to the other radiolabeled bleomycins.     

Rapid isocratic HPLC investigation of radiochemical purity for <Superscript>90</Superscript>Y-DOTATATE

DOTA-conjugated peptides, such as [DOTA⁰, Tyr³]ocreotide (DOTATOC) and [DOTA⁰, Tyr³]octreotate (DOTATATE) can be labeled with radionuclides such as ⁹⁰Y, ¹⁷⁷Lu and ¹¹¹In at high specific activities. These radiolabelled somatostatin analogues are used for peptide receptor radionuclide therapy (PRRT). Currently, radio-high performance liquid chromatography (radio-HPLC) and radio-thin layer chromatography (radio-TLC) are the methods of choice for the analysis of the labeled compounds. In literature, radiochemical purity of the radiolabelled DOTATATE was investigated using gradient reversed-phase radio-HPLC. However, these studies indicate long retention time of the radiolabelled compound of 14.52 min. In our study, a new simple and rapid reversed-phase isocratic system enables the radiochemical purity of the radiolabelled DOTATATE within a few minutes.     

DOTA-Tyr3-Octreotate: Labeling with β-emitting radionuclides for the preparation of potential therapeutic radiopharmaceuticals

Radiolabeled somatostatin analogues, including octreotate have been used for targeted radiotherapy of neuroendocrine tumors such as lymphoma, breast cancer, small-cell lung cancer and melanoma. In this paper, studies on the optimization of the production of ¹⁷⁷Lu, ¹⁶⁶Ho and ¹⁵³Sm radionuclides in Pakistan Atomic Research Reactor (PARR-I) and the investigations on the labeling of DOTA-Tyr-3 Octreotate with ¹³¹I, ¹⁷⁷Lu, ¹⁶⁶Ho and ¹⁵³Sm have been reported. The labeled DOTA-Tyr3-Octreotate complexes were found to be stable in acetate/ascorbate buffer and saline at room temperature (18–22°C). The biodistribution studies of ¹⁷⁷Lu-DOTA-Tyr-3 Octreotate in rat model indicated that the critical organ for this complex was the pancreas and the excretion route was through kidney.     

Synthesis and evaluation of N-(2-[18F]fluoro-4-nitrobenzoyl)glucosamine: a preliminary report

d-glucosamine at concentration of certain range could kill tumor cells without influencing normal cells. There are also some reports on the antitumor activity of d-glucosamine and its derivatives in murine models. It was therefore postulated that d-glucosamine might have the potential to invade tumor cells. We designed and radiosynthesized a glucosamine derivative, N-(2-[¹⁸F]fluoro-4-nitrobenzoyl)glucosamine ([¹⁸F]FNBG([¹⁸F]7)). Evaluations in vitro and in vivo were performed on tumor bearing mice. Excitingly, the radiochemical purity of [¹⁸F]FNBG([¹⁸F]7) was 99%, and besides the best radiochemical yield was up to 35%. The best T/Bl (Tumor/Blood) and T/M (Tumor/Muscle) ratios of [¹⁸F]FNBG([¹⁸F]7) were 4.40 and 4.84. Although [¹⁸F]FNBG([¹⁸F]7) deserved further studies, the results revealed it might become a potential PET imaging agent for detecting tumors.     

Optimization of the production of [61Cu]Diacetyl-bis(N 4-methylthiosemicarbazone) for PET studies

Summary Copper-61 produced via the ^natZn(p,x)⁶¹Cu nuclear reaction was used for the preparation of [⁶¹Cu]diacetyl-bis(N⁴-methylthiosemicarbazone) ([⁶¹Cu]ATSM) (4) using a house-made ATSM ligand. After a proton irradiation of an electroplated zinc layer by 22 MeV protons at 180 mA for 3.2 hours, ⁶¹Cu was recovered by two-step chromatography using a cation and an anion exchange column. About 222 GBq (6.00 Ci) of ⁶¹Cu²⁺ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of better than 99%. Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The [⁶¹Cu]ATSM production was optimized for reaction conditions (buffer concentration and temperature) with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and a specific activity of about 246 Ci/mmol. The produced [⁶¹Cu]ATSM is a PET radiotracer for hypoxia imaging with an intermediate half life and a satisfactory quality, suitable for future PET studies.     

Utilization of (p, 4n) reaction for <Superscript>86</Superscript>Zr production with medium energy protons and development of a <Superscript>86</Superscript>Zr → <Superscript>86</Superscript>Y radionuclide generator

Utilization of (p, 4n) reaction channel for the production of medical radionuclides became very attractive with commercial availability of medium energy cyclotrons. Significantly higher yields and radionuclidic purity may open new perspectives for several novel and some of the radionuclides previously have not been considered due to production difficulties. In present work, we show the proof-of-principle study on the production of ⁸⁶Y for Positron Emission Tomography imaging via radionuclide generator ⁸⁶Zr → ⁸⁶Y. Production suitability of ⁸⁶Zr from natural yttrium target and radiochemical separation strategies were tested. In addition, two generator systems were proposed and evaluated.     

Preparation of titania colloids by thermal hydrolysis of urea and densification behavior of the collid-derived monolithic titania gels

Hydrous titania colloids with different sizes and shapes were prepared from urea-containing TiCl₄ solutions by controlled thermal hydrolysis of urea. Very small colloidal particles (Sw=280–290 m²/g) with anatase structure were precipitated from aqueous HCl solutions of [TiCl₄] <1.0 mol/dm³ and [urea] >16.6 mol/dm³. Sols containing such colloids could be converted to translucent monolithic gels. A decrease in urea concentration ([urea]=8.3 mol/dm³) caused the production of aggregated rutile-type particles with a large aspect ratio, from which only titania powder was obtained. Heating of a monolithic gel above 500°C resulted in the accelerated densification of the gel. A highly densified titania with 96% of theoretical density was produced from the monolithic gel after heating at 700°C for 6 h.     

Chemical speciation of radionuclides migrating in groundwaters

In order to more accurately predict the rates and mechanisms of radionuclide migration from lowlevel waste disposal facilities via groundwater transport, ongoing studies are being conducted at field sites at Chalk River Laboratories to identify and characterize the chemical speciation of mobile, long-lived radionuclides migrating in groundwaters. Large-volume water sampling techniques are being utilized to separate and concentrate radionuclides into particulate, cationic, anionic, and nonionic chemical forms. Most radionuclides are migrating as soluble, anionic species which appear to be predominately organoradionuclide complexes. Laboratory studies utilizing anion exchange chromatography have separated several anionically complexed radionuclides, e.g.,⁶⁰Co and¹⁰⁶Ru, into a number of specific compounds or groups of compounds. Large-volume ultra-filtration experiments have shown that significant fractions of the radionuclides are being transported in these groundwaters in the form of macromolecules having molecular weights ranging from less than 3,000 to 100,000.     

Preliminary synthesis of 2-[18F]-FDG using18F produced in the TRIGA MARK III nuclear reactor of Mexico

The use of¹⁸F radionuclide in the preparation of 2-[¹⁸F]-FDG is reported.     

An improved method for the preparation of [<Superscript>14</Superscript>C]thiourea of high radiochemical purity

Summary An improved method for the preparation of [¹⁴C]thiourea of high radiochemical purity is described. [¹⁴C]thiourea is prepared by the barium cyanamide route and is purified by vacuum-sublimation. The labeled product showed ammonium [¹⁴C]thiocyanate as a radiochemical impurity in the range of 2-4%. This was further purified by silica-gel column chromatography to get the product having more than 99% radiochemical purity.     

Radiochemical determination of Mo in pure tungsten

A radiochemical neutron activation technique for Mo determination in high purity tungsten, based on some specific properties of Mo and W radionuclides has been developed. Al₂O₃ powder has been used as a sorbent. An estimation of the Mo content was carried out via the selectively separated^99mTc daughter radionuclide. Limit of detection was 10 ng g^–1.     

Determination of Total Radiochemical Purity of [18F]FDG and [18F]FET by High-Performance Liquid Chromatography Avoiding TLC Method

The goal of this work was to present two high-performance liquid chromatography (HPLC) method that could be applied for the determination of the total radioactive purity of 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) and O-(2-[¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET). The separation of [¹⁸F]fluoride ions, [¹⁸F]FET and [¹⁸F]FET intermediate was accomplished on LiChrosper RP-18, 250?×?4 mm, 5 µm (Merck) analytical column. For mobile phase 10 mM potassium dihydrogen phosphate buffer at pH7 (A) and acetonitrile (B) was used: 0–2 min: 15% B; 2–12 min: 85% B; 12–15 min: 15% B, respectively. Analysis of [¹⁸F]FDG was performed using LiChrosper 100 NH₂, 250?×?4.5 mm, 5 µm (Merck) analytical column. The initial mobile phase composition was 10 mM KH₂PO₄ buffer (pH7) and acetonitrile (15:85, v/v) and the acetonitrile ratio was decreased to 15% at 2 min after the sample injection and held for 5 min. Complete elution of [¹⁸F]fluoride ions from stationary phases could be achieved by adding 10 mg/mL K[¹⁹F]F to radioactive samples in a ratio 1:1 during the sample preparation. Recovery of [¹⁸F]fluoride ions ranged from 99.5 to 100.6%. The validation of the developed methods showed good results for linearity (r²?=?0.9981–0.9996), specificity (R_S?=?3.7–10.2), repeatability (%Area RSD_%?=?1.2–4.3%) and limit of quantitation (LOQ?=?1.6–4.5 kBq). During the cross-validation similar radiochemical purity values were obtained by the novel HPLC methods and thin layer chromatography performed according to the recommendations of the Ph. Eur. monographs.

     

Optimized production,quality control and biodistribution assessment of <Superscript>166</Superscript>Ho–DOTATOC: a novel radiolabelled somatostatin analog

Nowadays, peptide receptor radionuclide therapy is used to treat a specific type of cancer called neuroendocrine tumors. In this research, the optimized conditions for ¹⁶⁶Ho-DOTATOC production are presented. The radiolabeled compound was prepared with the specific activity of 11.1 TBq/mmol and radiochemical purity of more than 99% (using ITLC and HPLC). Stability tests of the complex were investigated in room temperature and in human serum at 37 °C. Biodistribution studies in Syrian rats showed considerable accumulation in pancreas as the somatostatin receptor-positive tissue. ¹⁶⁶Ho-DOTATOC can be considered as a novel agent for treatment of somatostatin receptor-positive tumors.     

(S)-2-((S)-2-(4-(3-[18F]fluoropropyl)benzamido)-3-phenylpropanamido)pentanedioic acid labeled with 18F

As degradation product of Antineoplaston A10 in vivo, phenylacetyl glutamine showed antitumor activities. According to literatures, we designed and radiosynthesized a phenylacetyl glutamine derivative, which was achieved under a mild reaction condition. Evaluations in vitro and in vivo were performed on tumor bearing mice. Excitingly, the radiochemical purity of (S)-2-((S)-2-(4-(3-fluoropropyl)benzamido)-3-phenylpropanamido)pentanedioic acid ([¹⁸F]FBPPA) was 98%, and besides the best radiochemical yield was up to 46%. T/Bl (Tumor/Blood) and T/M (Tumor/Muscle) ratios of [¹⁸F]FBPPA at 60 min post injection were 2.33 and 3.51. Meanwhile, it showed satisfied stability in vitro and in vivo, compared with 2-[¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG). Although [¹⁸F]FBPPA deserved further studies to make optimizations on its structure, the results revealed it might become a potential PET imaging agent for detecting tumors.