Gold Nanorods as Radiopharmaceutical Carriers: Preparation and Preliminary Radiobiological In Vitro Tests.

Low-energy electrons (Auger electrons) can be produced via the interaction of photons with gold atoms in gold nanorods (AuNRs). These electrons are similar to those emitted during the decay of technetium-99m (99mTc), a radioactive nuclide widely used for diagnostics in nuclear medicine. Auger and internal conversion (IC) electron emitters appropriately targeted to the DNA of tumors cells may, therefore, represent a new radiotherapeutic approach. 99mTc radiopharmaceuticals, which are used for diagnosis, could indeed be used in theragnostic fields when loaded on AuNRs and delivered to a tumor site. This work aims to provide a proof of concept (i) to evaluate AuNRs as carriers of 99mTc-based radiopharmaceuticals, and (ii) to evaluate the efficacy of Auger electrons emitted by photon-irradiated AuNRs in inducing radio-induced damage in T98G cells, thus mimicking the effect of Auger electrons emitted during the decay of 99mTc used in clinical settings. Data are presented on AuNRs' chemical characterization (with an aspect ratio of 3.2 and Surface Plasmon Resonance bands at 520 and 680 nm) and the loading of pharmaceuticals (after 99mTc decay) on their surface. Spectroscopic characterizations, such as UV-Vis and synchrotron radiation-induced X-ray photoelectron (SR-XPS) spectroscopies, were performed to investigate the drug-AuNR interaction. Finally, preliminary radiobiological data on cell killing with AuNRs are presented.

Does Heparin Affect 99mTc-MAA In Vitro Stability?

INTRODUCTION: Pulmonary embolism (PE) can be diagnosed by perfusion lung scintigraphy using human albumin macroaggregates labelled 99mTc (99mTc-MAA). When PE is suspected, subcutaneous Low Molecular Weight Heparin (LMWH) should be administered even before the results of the PE diagnostic flowchart. In our study, we aimed to evaluate a possible interaction (in vitro interference) between 99mTc-MAA and LMWH. METHODS: The reconstitution of MAA kit was performed according to the manufacturer's instruction. After labelling, we carried out the following preparations: a standard dose of 99mTc-MAA alone, as control; 99mTc-MAA and enoxaparin at different ratios. According to the manufacturer's instruction, the radiochemical purity was performed and evaluated immediately (T0), after 15 and 30 minutes after incubation (T15 and T30). RESULTS: We compared the radiochemical purity of 99mTc-MAA with: (i) radiochemical purity of 99mTc-MAA and enoxaparin (11 ratio), (ii) radiochemical purity of 99mTc-MAA and enoxaparin (0.5 ratio), and (iii) radiochemical purity of 99mTc-MAA and enoxaparin (ratio 2). No significant differences were found between all the measured parameters at each time point for each ratio. We also tested the stability of 99mTc-MAA in physiological conditions (at 37°C in PBS): the initial radiochemical purity of 99mTc-MAA was 99.78%. The values of 99mTc-MAA radiochemical purity were high in all conditions of possible interaction with LMWH, with values ranging from 98.00% at T0 to 95% at T30. CONCLUSION: We found no statistically significant change in the in vitro stability of 99mTc-MAA in the presence of enoxaparin, excluding a possible direct interference. Future studies will be needed to check the 99mTc-MAA stability under physiological conditions.

90Y-DOTA-Nimotuzumab: Synthesis of a Promising ß- Radiopharmaceutical.

BACKGROUND: Nimotuzumab is a humanized anti-epidermal growth factor receptor (EGFR) monoclonal antibody, nowadays used for tumour immunochemotherapy. This study aimed to label the conjugate DOTA-nimotuzumab with yttrium-90, in order to provide a ß- emitting radioimmunoconjugate (90Y-DOTA-nimotuzumab) potentially useful to assess the feasibility of a new radio-guided surgery approach. METHODS: The synthesis of 90Y-DOTA-nimotuzumab was performed in two days. Nimotuzumab was conjugated with a 50-fold excess of DOTA and then labelled with 90Y3+. The 90Y-DOTA-nimotuzumab preparation was optimized considering several parameters such as pH, temperature and reaction volume. Moreover, the 90Y-DOTA-nimotuzumab stability was evaluated in human plasma. RESULTS: The radioimmunoconjugate 90Y-DOTA-nimotuzumab was obtained with a radiochemical purity greater than 96%, and showed a good stability at 20°C as well as at 37°C in human plasma. CONCLUSIONS: The optimized conditions for a mild and easy preparation of 90Y-DOTA-nimotuzumab joined to a promising stability under physiological conditions suggest to propose this radioimmunoconjugate as a potential diagnostic radiopharmaceutical for ß- radio-guided surgery.

Media Fill Test for Validation of Non-Radioactive Kit for Radiopharmaceutical Preparations.

INTRODUCTION: The administration of improperly prepared intravenous fluids might determine healthcare-associated infections. Quality and sterility assurance in radiopharmaceutical manufacturing products must be evaluated by media fill tests that simulate the performance of the aseptic manufacturing procedure. The aim of this study is to show a methodological modification of a specific step of media fill tests, giving an overview of economic and organizational advantages that it might bring. MATERIALS AND METHODS: Media fill tests were conducted to ensure that they reproduce as strictly as possible the routine aseptic production process with all the critical steps described in the internal Standard Operating Procedures. We introduced an innovative modification in step 1: instead of using a completely decayed 99Mo/99mTc generator, we used a99Mo/99mTc generator just before its disposal, eluting it with saline solution aspirated in an empty vacuum vial. RESULTS: A total of 47 production runs were performed, and a total of 799 vials were tested for sterility. Thirteen nuclear medicine technicians were assessed. We found contamination in 1% of the total number of vials analyzed. CONCLUSIONS: The modification proposed shows several advantages: reduction of the costs of the media fill tests, the possibility to manage these without referring to external services, and decreased injuries for technicians who perform the tests.

Radiation exposure of the operators in the preparation and administration of yttrium-90 microspheres in the treatment of malignant hepatic lesions: What is the risk?

Liver radioembolization is an emerging treatment against liver primary and secondary tumours. The whole procedure of radioembolization involves different health care specialists with different expertise. During the fractionation and infusion phases, the personnel manipulates high activities of 90Y. In our centre, the number of radioembolization treatments per year is increasing; the aim of this study is to monitor the dose to the operators and to estimate the radiological risk for the operators involved in the RE. At present, two medical devices are approved: Sir-Sphere® and Therasphere™, both loaded with 90Y. The dosimeters used were TLDs placed over the fingertips, for a total of 4 dosimeters for each phase; the selected dose descriptor was Hp0.07. The study concerned 17 patients affected by malignant hepatic lesions, treated from September 2017 to March 2018. We performed 27 procedures: 10 fractionations (with Sir-Sphere®) and 17 infusions to the patients (10 with Sir-Spheres®, 7 with Theraspheres™). For fractionation phase, the average activity of each preparation was 3.34 GBq, the average value of Hp0.07 was 0.50mSv. For infusion phase, the average activity was 1.51 GBq for Sir-Sphere® and 2.10 GBq for Theraspheres™, the average value of Hp0.07 was 0.10mSv. No significant differences were found between senior (Hp0.07 = 0.08mSv) and young operators (Hp0.07 = 0.09mSv), respectively. Similarly, no significant differences were found between the right and left hand, with the same average value of Hp0.07 (0.01mSv). In conclusion, the results are encouraging, since fingertips reported doses very low. The handling of 90Y microspheres and the radioembolization procedure can be carried out under safe conditions.

Radioguided surgery with ß- radiation in pancreatic Neuroendocrine Tumors: a feasibility study.

The possibility to use ß- decaying isotopes for radioguided surgery (RGS) has been recently proposed, and first promising tests on ex-vivo samples of Meningioma and intestinal Neuroendocrine Tumor (NET) have been published. This paper reports a study of the uptake of 68Ga-DOTATOC in pancreatic NETs (pNETs) in order to assess the feasibility of a new RGS approach using 90Y-DOTATOC. Tumor and healthy pancreas uptakes were estimated from 68Ga-DOTATOC PET/CT scans of 30 patients with pNETs. From the obtained SUVs (Standardised Uptake Value) and TNRs (Tumor Non tumor Ratio), an analysis algorithm relying on a Monte Carlo simulation of the detector has been applied to evaluate the performances of the proposed technique. Almost all considered patients resulted to be compatible with the application of ß--RGS assuming to administer 1.5 MBq/kg of activity of 90Y-DOTATOC 24 h before surgery, and a sampling time of few seconds. In just 2 cases the technique would have required a mildly increased amount of activity or of sampling time. Despite a high physiological uptake of 68Ga-DOTATOC in the healthy pancreas, the proposed RGS technique promises to be effective. This approach allows RGS to find application also in pancreatic diseases, where traditional techniques are not viable.

Radioguided surgery with ß radiation: a novel application with Ga68.

Radio Guided Surgery is a technique helping the surgeon in the resection of tumors: a radiolabeled tracer is administered to the patient before surgery and then the surgeon evaluates the completeness of the resection with a handheld detector sensitive to emitted radiation. Established methods rely on γ emitting tracers coupled with γ detecting probes. The efficacy of this technique is however hindered by the high penetration of γ radiation, limiting its applicability to low background conditions. To overtake such limitations, a novel approach to RGS has been proposed, relying on ß- emitting isotopes together with a dedicated ß probe. This technique has been proved to be effective in first ex-vivo trials. We discuss in this paper the possibility to extend its application cases to 68Ga, a ß+ emitting isotope widely used today in nuclear medicine. To this aim, a retrospective study on 45 prostatic cancer patients was performed, analysing their 68Ga-PSMA PET images to asses if the molecule uptake is enough to apply this technique. Despite the expected variability both in terms of SUV (median 4.1, IQR 3.0-6.1) and TNR (median 9.4, IQR 5.2-14.6), the majority of cases have been found to be compatible with ß-RGS with reasonable injected activity and probing time (5 s).

Mass spectrometry characterization of DOTA-Nimotuzumab conjugate as precursor of an innovative ß- tracer suitable in radio-guided surgery.

The aim of the present work has been the mass spectrometry characterization of the Nimotuzumab (NIM) antibody chemically modified with the bifunctional chelating agent para-S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza cyclododecanetetraacetic acid (p-SCN-Bn-DOTA). The conjugate, upon labeling with the pure ß--emitter 90Y3+, could represent a promising candidate as radiotracer for an innovative radio-guided surgery (RGS) technique, developed and patented by researchers of our group, which uses a probe system for intraoperative detection of tumor residues exploiting the selective uptake of ß--emitting tracers. The results reported in this study show that multiple DOTA molecules bind to lysine residues of both light and heavy chains of the antibody and, probably, some of them are linked to the variable region of antibody. Moreover, the new mass spectrometric analysis highlights the presence of unreacted NIM in the final product. The information obtained by this work is of fundamental importance in the perspective to utilize this conjugate as a radiocompound after its labeling with 90Y3+ radioisotope. Indeed, the conjugation efficiency and the presence of unreacted NIM affect the specific activity of the final radiotracer which binds specific receptor.

Feasibility of beta-particle radioguided surgery for a variety of "nuclear medicine" radionuclides.

PURPOSE: Beta-particle radioguided tumor resection may potentially overcome the limitations of conventional gamma-ray guided surgery by eliminating, or at least minimizing, the confounding effect of counts contributed by activity in adjacent normal tissues. The current study evaluates the clinical feasibility of this approach for a variety of radionuclides. Nowadays, the only ß- radioisotope suited to radioguided surgery is 90Y. Here, we study the ß- probe prototype capability to different radionuclides chosen among those used in nuclear medicine. METHODS: The counting efficiency of our probe prototype was evaluated for sources of electrons and photons of different energies. Such measurements were used to benchmark the Monte Carlo (MC) simulation of the probe behavior, especially the parameters related to the simulation of the optical photon propagation in the scintillation crystal. Then, the MC simulation was used to derive the signal and the background we would measure from a small tumor embedded in the patient body if one of the selected radionuclides is used. RESULTS: Based on the criterion of detectability of a 0.1 ml tumor for a counting interval of 1 s and an administered activity of 3 MBq/kg, the current probe yields a detectable signal over a wide range of Standard Uptake Values (SUVs) and tumor-to-non-tumor activity-concentration ratios (TNRs) for 31Si, 32P, 97Zr, and 188Re. Although efficient counting of 83Br, 133I, and 153Sm proved somewhat more problematic, the foregoing criterion can be satisfied for these isotopes as well for sufficiently high SUVs and TNRs.