A Specific HPLC Method to Determine Residual HEPES in [68Ga]Ga-Radiopharmaceuticals: Development and Validation

Background: Nowadays, in Nuclear Medicine, clinically applied radiopharmaceuticals must meet quality release criteria such as high radiochemical purity and radiochemical yield. Many radiopharmaceuticals do not have marketing authorization and have no dedicated monograph within European Pharmacopeia (Ph. Eur.); therefore, general monographs on quality controls (QCs) have to be applied for clinical application. These criteria require standardization and validation in labeling and preparation, including quality controls measurements, according to well defined standard operation procedures. However, QC measurements are often based on detection techniques that are specific to a certain chromatographic system. Several radiosyntheses of [⁶⁸Ga]Ga-radiopharmaceuticals are more efficient and robust when they are performed with 2-[4-(2-hydroxyethyl)piperazin-1-yl] ethanesulfonic acid (HEPES) buffer, which is considered as an impurity to be assessed in the QC procedure, prior to clinical use. Thus, Ph. Eur. has introduced a thin-layer chromatography (TLC) method to quantify the HEPES amount that is present in [⁶⁸Ga]Ga-radiopharmaceuticals. However, this is only qualitative and has proven to be unreliable. Here we develop and validate a new high-performance liquid chromatography (UV-Radio-HPLC) method to quantify the residual amount of HEPES in ⁶⁸Ga-based radiopharmaceuticals. Method: To validate the proposed UV-Radio-HPLC method, a stepwise approach was used, as defined in the guidance document that was adopted by the European Medicines Agency (CMP/ICH/381/95 2014). The assessed parameters are specificity, linearity, precision (repeatability), accuracy, and limit of quantification. A range of concentrations of HEPES (100, 80, 60, 40, 20, 10, 5, 3 μg/mL) were analyzed. Moreover, to test the validity and pertinence of our new HPLC method, we analyzed samples of [⁶⁸Ga]Ga-DOTATOC; [⁶⁸Ga]Ga-PSMA; [⁶⁸Ga]Ga-DOTATATE; [⁶⁸Ga]Ga-Pentixafor; and [⁶⁸Ga]Ga-NODAGA-Exendin-4 from different batches that were prepared for clinical use. Results: In the assessed samples, HEPES could not be detected by the TLC method that was described in Ph. Eur. within 4 min incubation in an iodine-saturated chamber. Our developed HPLC method showed excellent linearity between 3 and 100 μg/mL for HEPES, with a correlation coefficient (R²) for calibration curves that was equal to 0.999, coefficients of variation (CV%) < 2%, and percent deviation value of bias from 100% to 5%, in accordance with acceptance criteria. The intra-day and inter-day precision of our method was statistically confirmed and the limit-of-quantification (LOQ) was 3 μg/mL, confirming the high sensitivity of the method. The amount of HEPES that was detected with our developed HPLC method in the tested [⁶⁸Ga]Ga-radiopharmaceuticals resulted well below the Ph. Eur. limit, especially for [⁶⁸Ga]Ga-NODAGA-Exendin-4. Conclusions: The TLC method that is described in Ph. Eur. to assess residual HEPES in [⁶⁸Ga]-based radiopharmaceuticals may not be sufficiently sensitive and thus unsuitable for QC release. Our new HPLC method was sensitive, quantitative, reproducible, and rapid for QCs, allowing us to exactly determine the residual HEPES amount in [⁶⁸Ga]Ga-radiopharmaceuticals for safe patient administration.     

Transient dynamics of an adiabatic NEMS

This paper is focused on the transient dynamics of an adiabatic nano‐electromechanical system (NEMS), consisting of a nano‐mechanical oscillator coupled to a quantum dot. By numerically solving the nonlinear stochastic differential equation governing the oscillator, the time evolution of the oscillator position, of the dot occupation number and of the current are studied. Different parameter settings are studied where the system exhibits bi‐stable, tri‐stable or mono‐stable behavior on a finite‐time horizon. It is shown that, after a typically long transient, the system under investigation exhibits no hysteretic behavior and that a unique steady state is reached, independently of the initial conditions. The transient dynamics is marked out by one or two well separated characteristic times, depending on the considered case (i.e., mono‐ or multi‐stable). These times are evaluated for a dot on‐resonance or off‐resonance. It turns out that the characteristic time scales are long in comparison to the period of the uncoupled oscillator, particularly at low bias, suggesting that the predicted transient dynamics may be observed in state‐of‐the‐art experimental setups.

     

First Experimental Quantitative Charge Density Studies of Advanced Intermediate of Vitamin D Analogues

Vitamins D are a group of fat-soluble secosteroids which play a regulatory role in the functioning of most cells. Rational design of new vitamin D analogs, of increased therapeutic potency and lowered calcemic side effects, requires high-resolution initial structures and a deep understanding of interactions with the molecular targets. In this paper, using quantum crystallography, we present the first determination of the experimental quantitative charge density of an advanced intermediate of vitamin D analogues as well as a reconstruction of the theoretical electron density of final vitamin D analogues. Application of these methods allows for topological and electrostatic interaction energy analysis. We showed that the A-ring chair conformation has a significant influence on the topological properties of vitamin D compounds. Moreover, the interactions between the CD-ring and side-chain additionally stabilize the crystal structure. These results are supported by our theoretical calculations and previous biological studies.     

Periodic magnetic geodesics on Heisenberg manifolds

Annals of Global Analysis and Geometry - We study the dynamics of magnetic flows on Heisenberg groups, investigating the extent to which properties of the underlying Riemannian geometry are...     

Evaluation of the enantiomeric selectivity in the chiral ligand-exchange chromatography of amino acids by a computational model

The chromatographic resolution of enantiomeric amino acids is accomplished on a reversed phase column using aqueous mobile phase containing the chiral reagent N,N-dimethyl-S-phenylalanine-Cu(II). The separation is a result of the whole interaction between the diastereomeric complex surface and the mixed stationary phase realized by the dynamic coating of the RP-18 carbon chains layer. The elution order seems to be related to the different water coordination capability on copper ion in the formation of the mixed ternary complexes.     

A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites

Some lichens were recently reported to modify the surface state of asbestos. Here we report some new insight on the physico-chemical modifications induced by natural chelators (lichen metabolites) on two asbestos samples collected in two different locations. A biomimetic approach was followed by reproducing in the laboratory the weathering effect of lichen metabolites. Norstictic, pulvinic and oxalic acid (0.005, 0.5 and 50 mM) were put in contact with chrysotile fibres, either in pure form (A) or intergrown with balangeroite, an iron-rich asbestiform phase (B). Mg and Si removal, measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), reveals an incongruent dissolution for pure chrysotile (A), with Mg removal always exceeding that of Si, while chrysotile-balangeroite (B) follows a congruent dissolution pattern in all cases except in the presence of 50 mM oxalic acid. A much larger removal of Mg than Si in the solutions of 0.5 and 50 mM oxalic acid with chrysotile (A) suggests a structural collapse, which in the case of chrysotile-balangeroite (B) only occurs with 50 mM oxalic acid; in these cases both samples are converted into amorphous silica (as detected by X-ray diffraction (XRD)). Subsequent to incubation, some new phases (Fe(2)O(3), CaMg(CO(3))(2), Ca(C(2)O(4)) x H(2)O and Mg(C(2)O(4))2 x H(2)O), similar to those observed in the field, were detected by XRD and micro-Raman spectroscopy. The leaching effect of lichen metabolites also modifies the Fenton activity, a process widely correlated with asbestos pathogenicity: pure chrysotile (A) activity is reduced by 50 mM oxalic acid, while all lichen metabolites reduce the activity of chrysotile-balangeroite (B). The selective removal of poorly coordinated, highly reactive iron ions, evidenced by NO adsorption, accounts for the loss in Fenton activity. Such fibres were chemically close to the ones observed in the field. Chrysotile-rich rocks, colonised by lichens, could be exposed to a natural bioattenuation and considered as a transient environmental hazard.     

Surface-activated chemical ionization ion trap mass spectrometry for the analysis of cocaine and benzoylecgonine in hair after extraction and sample dilution

Surface-activated chemical ionization (SACI) was employed for the analysis of cocaine and its metabolite, benzoylecgonine, extracted from hair. Following decontamination and acid hydrolysis procedures on the hair sample, the sample solution was diluted (1:10) and directly analyzed by liquid chromatography/surface-activated chemical ionization multiple collisional stage single reaction monitoring mass spectrometry (LC/SACI-MS(3)-SRM) without solid-phase extraction (SPE) pre-purification and concentration procedures. To increase the selectivity of the method, MS(3) was chosen instead of the less selective MS/MS. This data was compared with that achieved using gas chromatography/mass spectrometry (GC/MS), the reference method used by the Italian Government Institute of Health protocol. The limits of detection (LODs) were 0.003 ng/(mg hair) for cocaine and 0.02 ng/(mg hair) for benzoylecgonine and the limits of quantitation (LOQs) were 0.01 ng/(mg hair) for cocaine and 0.04 ng/(mg hair) for benzoylecgonine. The squared correlation coefficient (R(2)) of the calibration curve was 0.9887-0.9980 for cocaine and 0.9987-0.9997 for benzoylecgonine. The percent accuracy error was 2-5% for both cocaine and benzoylecgonine using the LC/SACI-MS(3)-SRM approach, whereas it was higher for benzoylecgonine (20-25%) using the LC/SACI-MS/MS-SRM approach compared with the GC/MS data due to hair matrix contamination. In both cases, high precision was achieved (1-3% precision error), which confirmed the stability of the developed methods.     

Nisin production utilizing skimmed milk aiming to reduce process cost

Nisin is a natural additive for conservation of food, pharmaceutical, and dental products and can be used as a therapeutic agent. Nisin inhibits the outgrowth of spores, the growth of a variety of gram-positive and gram-negative bacteria. This study was performed to optimize large-scale nisin production in skimmed milk and subproducts aiming at low-costs process and stimulating its utilization. Lactococcus lactis American Type Culture Collection (ATCC) 11454 was developed in a rotary shaker (30 degrees C/36 h/100 rpm) in diluted skimmed milk and nisin activity, growth parameters, and media components were also studied. Nisin activity in growth media was expressed in arbitrary units (AU/mL) and converted to standard nisin concentration (Nisaplin, 25 mg of pure nisin is 1.0x10(6) AU/mL). Nisin activity in skimmed milk 2.27 g(total solids) was up to threefold higher than transfers in skimmed milk 4.54 g(total solids) and was up to 85-fold higher than transfers in skimmed milk 1.14 g(total solids). L. lactis was assayed in a New Brunswick fermentor with 1.5 L of diluted skimmed milk (2.27 g(total solids)) and airflow of 1.5 mL/min (30 degrees C/36/200 rpm), without pH control. In this condition nisin activity was observed after 4 h (45.07 AU/mL) and in the end of 36 h process (3312.07 AU/mL). This work shows the utilization of a low-cost growth medium (diluted skimmed milk) to nisin production with wide applications. Furthermore, milk subproducts (milk whey) can be exploited in nisin production, because in Brazil 50% of milk whey is disposed with no treatment in rivers and because of high organic matter concentrations it is considered an important pollutant. In this particular case an optimized production of an antimicrobial would be lined up with industrial disposal recycling.