Measurement Of Radiochemical Purity Research Articles

Optimised quality control method for determination of the radiochemical purity of [99mTc]Tc-mebrofenin and [99mTc]Tc-etifenin in a clinical context

ObjectivesIn the context of a supply disruption of mebrofenin (Cholediam)-based kits for radiolabelling with technetium-99m [99mTc], the medicine agencies allowed the importation of a back-up radiopharmaceutical diagnostic agent, etifenin (Techida),...

A suitable time point for quantifying the radiochemical purity of 225Ac-labeled radiopharmaceuticals

BackgroundAs 225Ac-labeled radiopharmaceuticals continue to show promise as targeted alpha therapeutics, there is a growing need to standardize quality control (QC) testing procedures. The determination of radiochemical purity (RCP) is an essential QC test. A significant obstacle to RCP testing is the disruption of the secular equilibrium between actinium-225 and its daughter radionuclides during labeling and QC testing. In order to accelerate translation of actinium-225 targeted alpha therapy, we aimed to determine the earliest time point at which the RCP of an 225Ac-labeled radiopharmaceutical can be accurately quantified.ResultsSix ligands were conjugated to macrocyclic metal chelators and labeled with actinium-225 under conditions designed to generate diverse incorporation yields. RCP was determined by radio thin layer chromatography (radioTLC) followed by exposure of the TLC plate on a phosphor screen either 0.5, 2, 3.5, 5, 6.5, or 26 h after the plate was developed. The dataset was used to create models for predicting the true RCP for any pre-equilibrium measurement taken at an early time point. The 585 TLC measurements span RCP values of 1.8–99.5%. The statistical model created from these data predicted an independent data set with high accuracy. Predictions made at 0.5 h are more uncertain than predictions made at later time points. This is primarily due to the decay of bismuth-213. A measurement of RCP > 90% at 2 h predicts a true RCP > 97% and guarantees that RCP will exceed 90% after secular equilibrium is reached. These findings were independently validated using NaI(Tl) scintillation counting and high resolution gamma spectroscopy on a smaller set of samples with 10% ≤ RCP ≤ 100%.ConclusionsRCP of 225Ac-labeled radiopharmaceuticals can be quantified with acceptable accuracy at least 2 h after radioTLC using various methods of quantifying particle emissions. This time point best balances the need to accurately quantify RCP with the need to safely release the batch as quickly as possible.

Visualization and Quantification of Radiochemical Purity by Cerenkov Luminescence Imaging.

Determination of radiochemical purity is essential for characterization of all radioactive compounds, including clinical radiopharmaceuticals. Radio-thin layer chromatography (radio-TLC) has been used as the gold standard for measurement of radiochemical purity; however, this method has several limitations in terms of sensitivity, spatial resolution, two-dimensional scanning, and quantification accuracy. Here, we report a new analytical technique for determination of radiochemical purity based on Cerenkov luminescence imaging (CLI), whereby entire TLC plates are visualized by detection of Cerenkov radiation. Sixteen routinely used TLC plates were tested in combination with three different radioisotopes (131I, 124I, and 32P). All TLC plates doped with a fluorescent indicator showed excellent detection sensitivity with scanning times of less than 1 min. The new CLI method was superior to the traditional radio-TLC scanning method in terms of sensitivity, scanning time, spatial resolution, and two-dimensional scanning. The CLI method also showed better quantification features across a wider range of radioactivity values compared with radio-TLC and classical zonal analysis, especially for β--emitters such as 131I and 32P.

Study of the peak splitting in an alternative method for the radiochemical purity measurement of 99mTechnetium-sestamibi

One of the alternative methods for the measurement of radiochemical purity (RCP) of Technetium-sestamibi uses Whatman 3MM paper as the stationary phase and ethyl acetate as the mobile phase. However, alternative method shows peak splitting and shouldering of the radiopharmaceutical. This could be because of higher levels of analyte. We aimed to assess the effect of sample dilution (1 : 1) on this method and to compare these RCP values with the reference method. The diluted samples showed a unique peak in the radiopharmaceutical zone, but the RCP values were significantly different (P<0.05) and correlated poorly with the reference method.

The use of Whatman-31ET paper for an efficient method for radiochemical purity test of 131I-Hippuran

Current chromatography methods used for radiochemical purity test of 131I-Hippuran is time consuming. Therefore, in this study we explored several static and mobile phases in order to have a chromatography method which is accurate and efficient or less time consuming. In this study, stationary phases (Whatman-1, 31ET, and 3MM papers) and several mobile phases were explored to separate 131I-Hippuran from its impurity (131I iodide ion). The results of this study showed that the most efficient chromatography system for measurement of radiochemical purity of 131I-Hippuran was by using Whatman-31ET paper and n-butanol: acetic acid: water (4:1:1) as a static phase and mobile phase respectively. Developing time for this method was of approximately 75.7 ± 2.7 minutes. The result of radiochemical purity (%RCP) of 131I-Hippuran measured with this chromatography system either using Whatman-1 or Whatman-31ET paper strips was 98.7%. The short size of Whatman-31ET paper strip (1 x 8 cm) was found to have shorter developing time compared to that of long size paper. This system showed a good separation of 131I-Hippuran from its impurities and gave %RCP of 98.1% ± 0.04% with developing time approximately 44.3 ± 9.4 minutes. The short size of Whatman-31ET paper strips was found to be more efficient compared to that of Whatman-1 and Whatman-3MM paper strips in term of developing time.

The strange case of the [13N]NH3: validation of the production process for human use.

PET radiopharmaceuticals are often injected in patients before all quality controls are performed and before sterility results are available. We propose a process validation to produce very safe and pure [N]NH3 for human use. [N]NH3 was produced in the cyclotron target. Online purification was performed by anionic exchange resin. All the production steps were subjected to a sterility test. Some additional controls were added to those required by the monograph. The radiochemical yield of the syntheses was 26.3 and 61.5% corrected for decay, with a radiochemical purity of 100%. In addition to quality controls requested by the European Pharmacopeia monograph, we carefully analyzed the product for the presence of possible contaminants. Some elements, mainly metals, were found in very low amounts at concentrations in the range of ppb. The radionuclidic purity was verified. The achievement of the parameters of osmolality, by addition of saline solution to the preparation, made the analysis of chemical purity difficult and worsened the measurement of radiochemical purity by high performance liquid chromatography. Only pH control is necessary before administration to patients and therefore a safe production process was set up to prevent microbiological contamination. All phases were carefully standardized, starting from in-target production of [N]NH3, to final splitting in the syringes. Sterility tests showed no bacterial growth, indicating the safety of the production process. All our syntheses followed the monograph indications and were optimal to obtain PET imaging of a patient's myocardium.

Gamma-scanner for control of radiochemical purity of medical isotopes

A gamma-scanner for measurement of radiochemical purity of medical isotopes was designed and tested. The measurements of radiochemical purity of sodium pertechnetate were conducted. The results of measurements confirmed the possibility of using the device for production of medical isotopes.

A new method for the radiochemical purity measurement of 111In-pentetreotide

The recommended method for the measurement of radiochemical purity (RCP) of ¹¹¹In-labelled pentetreotide is thin-layer chromatography with a silica gel as the stationary phase and a 0.1 N sodium citrate solution (pH 5) as the mobile phase. According to the supplier's instructions, the mobile phase must be prepared before the test is carried out, and the recommended stationary phase is off-market. We propose a new method for RCP measurement in which the mobile phase is acid citrate dextrose, solution A, which does not need to be prepared beforehand, and thin-layer chromatography is performed with a silica gel-impregnated glass fibre sheet as the stationary phase. We used both methods to measure the percentages of radiopharmaceutical and impurities. The range of RCP values obtained was 98.0-99.9% (mean=99.3%) by the standard method and 98.1-99.9% (mean=99.2%) by the new method. We observed no differences between the RCP values of both methods (P=0.070). The proposed method is suitable for RCP testing because it yields results that are in good agreement with those of the standard method and because it is easier to perform as the mobile-phase solution need not be prepared in advance.

Noninvasive Visualization of RNA Delivery with 99mTc-Radiolabeled Small-Interference RNA in Tumor Xenografts

Small-interference RNAs (siRNAs) are short, double-strand RNA molecules that target specific messenger RNAs for degradation via the process termed RNA interference. The efficacy of RNA interference depends greatly on effective delivery of siRNA, which calls for noninvasive methods for tracing siRNA in vivo. The purpose of this work was to develop a novel (99m)Tc-radiolabeled method to visualize siRNA targeting of a tumor biomarker of human telomerase reverse transcriptase (hTERT) in HepG2 tumor xenografts. After conjugation with S-acetyl N-hydroxysuccinimide-mercaptoacetyltriglycine (NHS-MAG3), antisense RNA with 2'-O-methyl modification was annealed with sense strand to form a duplex and then radiolabeled with (99m)Tc. (99m)Tc-siRNAs were tested for stability in serum by measurement of radiochemical purity and for inhibitory activity by reverse-transcriptase polymerase chain reaction and Western blotting. In vitro cellular uptake was evaluated in HepG2 cells. Biodistribution studies and static imaging were performed in HepG2 tumor-bearing mice. Radiochemical purity remained highly stable in saline and fresh human serum at room temperature and 37 degrees C. Radiolabeled siRNA demonstrated strong inhibitory effects similar to those of unlabeled siRNA on both hTERT messenger RNA and protein in vitro. (99m)Tc-hTERT siRNA showed more uptake than did control siRNA in HepG2 cells after 1 h of incubation. After administration in HepG2 tumor-bearing mice, (99m)Tc-hTERT siRNA had significantly higher accumulation in tumors and a higher tumor-to-blood ratio than did control siRNA (P < 0.05). Scintigraphy of (99m)Tc-hTERT siRNA showed clear tumor images at 0.5, 1, 3, and 6 h after injection. In contrast, (99m)Tc-control siRNA failed to visualize the tumor. Ratios of uptake in tumor to uptake in contralateral region of hTERT-targeted siRNA were significantly higher than those of control siRNA (P < 0.05) at each time point. The (99m)Tc radiolabeling method with NHS-MAG3 chelator can be used successfully in siRNA radiolabeling, allowing for the noninvasive visualization of siRNA delivery in vivo.

Stability of the mixture of technetium-99m human serum albumin and lidocaine hydrochloride for clinical application

To evaluate the stability of the mixture of technetium-99m (99mTc) human serum albumin (HSA) with the local anesthetic lidocaine hydrochloride. We assessed three preparations of the radiotracer, 99mTc-HSA, filtered 99mTc-HSA, and a mixture of 99mTc-HSA with lidocaine hydrochloride and then filtered. Time sequence evaluation was performed on all the specimens (n= 10) at 0, 30, 60, 90, 120, 150, and 180 min after preparation. Measurements of radiochemical purity as labeling stability and pH value change were conducted for each group of specimens. We found no definite difference in the stability before and after the filtering procedure for 99mTc-HSA. However, we showed a decline of stability in the mixture of 99mTc-HSA with lidocaine. The filtered specimens showed a relatively higher pH value, towards a more neutral status, as compared with the unfiltered specimens. Though pain relief for the patient receiving sentinel lymph node mapping is important, a preparation of a mixture of 99mTc-HSA and lidocaine may cause radiolabeling instability. Furthermore, compared with the filtered 99mTc-sulfur colloid, a filtering procedure does not change the labeling stability of the 99mTc-HSA. On the contrary, the filtered preparation was neutralized closer to the physiologic condition. For lymphoscintigraphic studies,our results suggested that pretreatment with local anesthesia followed by subdermal injection of a filtered 99mTc-HSA rather than a pre-mixture with lidocaine is appropriate for clinical application.

Artefacts in the thin-layer chromatographic analysis of 99Tcm-tetrofosmin injections.

In an evaluation of techniques for dispensing 99Tcm-tetrofosmin injections, variability in radiochemical purity measured by the recommended 'cut-and-count' thin-layer chromatographic (TLC) analytical technique was observed. This was due to inconsistency in the position of the 99Tcm-tetrofosmin on the chromatography plate. An investigation was therefore undertaken to identify the factors which influence the Rf value of 99Tcm-tetrofosmin and the subsequent effect on the values obtained in the measurement of radiochemical purity. TLC was performed on an ITLC/SG stationary phase with a mobile phase of dichloromethane:acetone (65:35). On a satisfactory chromatogram, the main peak had an Rf of approximately 0.5 and the radiochemical purity was measured at > 90%. The Rf of the main peak and the measured radiochemical purity were found to increase as the size of the sample applied to the plate was increased. Force-drying the sample spot after application to the TLC plate gave a single peak with an Rf of 0. The dimensions of the tank and the time allowed for mobile phase saturation did not affect the outcome of the analysis. Small variations in the composition of the mobile phase affected the Rf of the main peak but not the measured radiochemical purity. TLC plates that were dried at 11 degrees C before use were found to give distorted chromatograms and unreliable measurements of radiochemical purity. In conclusion, when using TLC to measure the radiochemical purity of 99Tcm-tetrofosmin, the following precautions should be observed: (1) the sample spot applied to the TLC plate should be in the range 10-20 microliters; (2) the spot should not be force-dried with air; and (3) ITLC/SG plates should not be dried before use.

Determination of radiochemical purity of technetium-99m-labelled complexes by TLC

Simple TLC systems capable of separating the most important fractions of the radiopharmaceuticals 99mTcMAG3, 99mTcMDP, 99mTcDPD and 99mTcHM-PAO were developed for measurements of radiochemical purity. Silica gel or cellulose layers were used for chromatography and the radioactivity distribution in the developed radiochromatograms was obtained with a TLC linear analyser. The chromatographic procedures proposed are suitable also for studies of kinetic instability.