Effects of Photons Irradiation on 18F-FET and 18F-DOPA Uptake by T98G Glioblastoma Cells.

The differential diagnosis between brain tumors recurrence and early neuroinflammation or late radionecrosis is still an unsolved problem. The new emerging magnetic resonance imaging, computed tomography, and positron emission tomography diagnostic modalities still lack sufficient accuracy. In the last years, a great effort has been made to develop radiotracers able to detect specific altered metabolic pathways or tumor receptor markers. Our research project aims to evaluate irradiation effects on radiopharmaceutical uptake and compare the kinetic of the fluorinate tracers. T98G glioblastoma cells were irradiated at doses of 2, 10, and 20 Gy with photons, and 18F-DOPA and 18F-FET tracer uptake was evaluated. Activity and cell viability at different incubation times were measured. 18F-FET and 18F-DOPA are accumulated via the LAT-1 transporter, but 18F-DOPA is further incorporated, whereas 18F-FET is not metabolized. Therefore, time-activity curves (TACs) tend to plateau with 18F-DOPA and to a rapid washout with 18F-FET. After irradiation, 18F-DOPA TAC resembles the 18F-FET pattern. 18F-DOPA activity peak we observed at 20 min might be fictitious, because earlier time points have not been evaluated, and a higher activity peak before 20 min cannot be excluded. In addition, the activity retained in the irradiated cells remains higher in comparison to the sham ones at all time points investigated. This aspect is similar in the 18F-FET TAC but less evident. Therefore, we can hypothesize the presence of a second intracellular compartment in addition to the amino acidic pool one governed by LAT-1, which could explain the progressive accumulation of 18F-DOPA in unirradiated cells.

Evidence of 68Ga-DOTA-NT-20.3 Uptake in Pancreatic Adenocarcinoma AsPC-1 Cell Line - in vitro Study.

BACKGROUND: Neurotensin receptors are overexpressed in several cancer types including pancreatic ductal adenocarcinoma. Three NTR subtypes have been cloned: NTR-1, NTR-2 and NTR-3. The most expressed NTR-1 is not present in normal pancreatic tissue and has a low expression in chronic pancreatitis. OBJECTIVE: Objective of this study was to test in vitro affinity of the new 68Ga labelled neurotensin analogue DOTA-NT-20.3 (fragment 6-13, Ac-Lys(DOTA)-Pro-Arg(N-CH3)-Arg-Pro-Tyr-Tle-Leu) on the human pancreatic ductal adenocarcinoma cell line AsPC-1. METHOD: For the preparation of 68Ga-DOTA-NT-20.3, 68GaCl3 solution (eluted from 68Ge/68Ga generator) and 50 µg of precursor (Iason, Graz, Austria) water dissolved were used in an automatic synthesis module. The labeled compound was added to cell culture flask and incubated at 37°C. At various time points after tracer addition up to 80min, cells were recovered, rinsed and counted for radioactivity. Results were expressed as percent binding normalized to 200000 cells and affinity parameters were calculated. RESULTS: Labeling yield was ≥98 %. The molar ratio between labelled and total peptide was about 1/400. AsPC-1 cell line showed rapid uptake of the tracer including surface and internalized binding, tending to a plateau phase 80 min after tracer addition (11%/200.000 cells). The Kd (7.335 pmol) and Bmax (90.52 kBq) value indicated high tracer affinity for AsPC-1cell line especially if compared with the literature data regarding other malignancies (e.g. colonic cancer cell line). Binding sites were 1.09x106 sites per cell. CONCLUSION: New tracer 68Ga-DOTA-NT-20.3 can be a suitable candidate for the clinical use in patients with pancreatic ductal adenocarcinoma.

Radium-223 and metastatic castration-resistant prostate cancer: All that glitters is not gold.

After being approved by the National Drug Agency in several countries, Radium-223 (Ra-223) is gaining wide acceptance in the treatment of bone metastatic castration resistant prostate cancer. The exact mechanism of action remain unclear: The established model of direct alpha-particle irradiation from the remodelling bone surface, where Ra-223 accumulates, surrounding the tumor foci can explain a lethal effect only on metastatic microdeposits, but not on higher tumor burden. According to the "pre-metastatic niche model", it is likely that Ra-223 targets several non-tumoral cell types of the tumor microenvironment involved in the complex mechanism of cancer bone homing and colonization. A deeper insight into this hypothetical mechanism will lead to a more accurate dosimetric approach and to find optimal sequencing and/or combination with the other therapeutic options.

(99m)Tc-human serum albumin nanocolloids: particle sizing and radioactivity distribution.

Several parameters affect the biodistribution of administered nanocolloids (NC) for Sentinel Lymph Node (SLN) detection: particle size distribution, number of Tc atoms per particle and specific activity (SA). Relatively few data are available with frequently conflicting results. (99m)Tc-NC-human serum albumin (HSA) Nanocoll®, Nanoalbumon® and Nanotop® were analysed for particles' dimensional and radioactivity distribution, and a mathematical model was elaborated to estimate the number of particles involved. Commercially available kits were reconstituted at maximal SA of 11 MBq/µg HSA. Particles size distribution was evaluated by Dynamic Light Scattering. These data were related to the radioactivity distribution analysis passing labelled NC through three polycarbonate filters (15-30-50-nm pore size) under vacuum. Highest radioactivity was carried by 30-50 nm particles. The smallest ones, even though most numerous, carried only the 10% of (99m)Tc atoms. Nanocoll and Nanotop are not significantly different, while Nanoalbumon is characterized by largest particles (>30 nm) that carried the most of radioactivity (80%). Smallest particles could saturate the clearing capacity of macrophages; therefore, if the tracer is used for SLN detection, more node tiers could be visualized, reducing accuracy of SLN mapping. Manufacturers could implement technical leaflets with particle size distribution and could improve the labelling protocol to provide clinicians useful information.

A sensitive, rapid and inexpensive method to assess aluminium(III) ions in technetium eluates.

The aim of the study was to validate a semiquantitative analytical method to identify the aluminium(III) [Al(III)] concentration in 99Mo/99mTc generator eluates to check the European Pharmacopoeia (Ph. Eur.) requirement (<5 µg/ml). Three different solutions measuring 20 ml - 0.2% 1,10-phenanthroline, 0.05% chrome azurol S and 20% hexamethylenetetramine - were prepared. A cellulose filter paper was subsequently immersed in them, dried overnight at room temperature and cut into rectangles. A volume of 5 µl of first eluates of various 99Mo/99mTc generators was placed onto a reagent paper and the spot colour was compared with a standard aluminium solutions scale (0-100 µg/ml). A cyan/magenta/yellow/key (CMYK) model analysis was adapted to quantify the intensity of colour on the paper, and the presence of aluminium in the eluates was detected by a spectrophotometer. Small changes in standard solution pH (4.1-5.2) and chrome azurol S concentration did not affect the analysis. The cyan channel image analysis was proportional to the Al3+ solution concentration (y=25 019x+1489, R2=0.9554 within 2.5-8 µg/ml). The detection limit for aluminium by the visual test method is about 1 µg/ml, and fading is absent. The cyan channel image analysis method is independent of the observer and is applicable for the evaluation of the chemical purity of 99Mo/99mTc generator eluates. Our colorimetric 'spot test' is advantageous for the visual evaluation of Al pertechnetate concentrations as required by Ph. Eur. showing a sensitivity and a limit of detection superior to that of commercially available spot systems.

Deficiencies in product labelling instructions and quality control directions for 99mTc radiopharmaceuticals.

OBJECTIVE: The aim of the study was to identify deficiencies in product labelling instructions for reconstitution and in the quality control directions detailed in the technical leaflets (TLs) or summary product characteristic (SPC) sheets of commonly used technetium labelling cold kits. MATERIALS AND METHODS: The reconstitution and quality control directions in 25 TLs/SPCs were evaluated to identify deficiencies, incompleteness, restrictions, errors, impracticability, and vagueness. In addition, their congruence with the statements given in the relative European Pharmacopoeia (Ph. Eur. VII ed.) monography and diagnostic reference levels of Directive 97/43/EURATOM was evaluated. RESULTS: Deficiencies in information were scored and classified into five categories: 1, absent or incomplete; 2, restrictive; 3, inconsistent or wrong; 4, impractical; and 5, vague. In the 25 documents analyzed a total of 141 deficiencies were found (corresponding to 40.2% of the total scores assigned), and more frequently they pertained to quality control procedures (70.9%), followed by those related to quantitative composition (14.9%), preparation (8.5%), and particle size (5.7%). Nearly 80% of these deficiencies were classified as type 1 - that is, absent or incomplete information. CONCLUSION: The indications in TLs and SPCs should provide useful information for maintaining the quality and purity of the radiopharmaceutical preparation and ensure the safety level and effectiveness required by law. However, the instructions are often suboptimal or even erroneous, and consequently there are countless failures or difficulties, which represent an impediment to good laboratory practice. We believe that a 'smart' review of radiopharmaceutical documentation would be beneficial in order to align these indications to the real needs of the operators involved in routine in-house nuclear medicine practice.