Current Radiopharmaceuticals - Volume 15, Issue 2, 2022

Coronavirus disease 2019 (COVID-19) pandemic, which has emerged in December 2019 in the city of Wuhan, China, has significantly affected healthcare systems and economies within a short timeframe. Treatment strategies offer alleviation of symptoms in the absence of commercially available specific antiviral agents. Within this context, the introduction of innovative therapeutic approaches against the SARS-CoV-2 virus is a critical need that should be addressed urgently. The anti-inflammatory effect of low dose irradiation has been proposed as a potential therapeutic strategy for COVID-19 pneumonia. Consideration of external beam irradiation for management of COVID-19 pneumonia has prompted the investigation of alternative methods of irradiation with potentially improved toxicity profiles. Theoretically, targeted radiotherapy may have several advantages over conventional external beam radiotherapy owing to the capability to deliver effective radiation doses without adverse irradiation effects. Since radionuclides are conjugated to targeting vectors, such as antibodies and cell surface receptor binding peptides, irradiation may be focused on targeted cells with optimal sparing of surrounding normal tissues. In the context of COVID-19 management, targeted irradiation is expected to compromise SARS-CoV-2 extracellular virions. Targeted radiotherapy may offer a viable means of combating against SARS-CoV-2 virus. There is room for improvement with the need for efficacy, feasibility, and toxicity studies. Although targeted radiotherapy itself may not achieve absolute eradication of virus or virus-infected cells, it may at least serve as a supplementary therapeutic strategy that could be utilized in combination with other antiviral treatments. Further investigations focusing on nuclear medicine, radiopharmaceuticals, and targeted radiotherapy strategies may pave the way for the development of efficacious antiviral treatments which may be utilized in the battle against the current COVID-19 pandemic.

Background: The recent approval of radiopharmaceuticals for diagnosis and treatment of cancer is ushering nuclear medicine into a new era of theranostics and alpha therapy using radiopharmaceuticals labeled with ²²⁵Ac shows remarkable results in clinical trials. As such, reliable methods for the synthesis and quality control of ²²⁵Ac-radiopharmaceuticals are needed. Objective: ²²⁵Ac-PSMA-617 is being used for targeted alpha therapy in patients with prostate cancer, and we had cause to synthesize the agent for preclinical use. However, technology transfer proved cumbersome owing to the paucity of information available on synthesizing and analyzing ²²⁵Ac-radiotherapeutics. To address this need, we describe a straightforward synthesis of ²²⁵Ac-PSMA- 617 as well as suitable approaches for quality control analysis using standard equipment in a modern PET Center. Methods: PSMA-617 precursor was dissolved in 25 μL metal-free water (0.67 mg/mL) and combined with 500 μL 0.05M Tris buffer, pH 9. Actinium stock solution (~65 μCi in 15 μL) was added and the reaction was heated at 120°C for 40-50 min. The reaction was cooled and 0.6 mL gentisic acid solution (4 mg/mL in 0.2 M NH4OAc) was added. To formulate the dose for injection, sterile saline, USP (8 mL) was added and the pH was adjusted by the addition of 100 μL 0.05 M Tris buffer (pH 9) to give a final pH of ~7.2. The final solution was filtered using a 0.22 μm GV sterile filter into a sterile dose vial. Radiochemical purity was determined by radio-TLC (eluent: 50mM Sodium Citrate, pH 5), and plates were analyzed using an AR2000 scanner. Results: The method provided ²²⁵Ac-PSMA-617 in high radiochemical yield (57 ± 3 μCi, >99%) and radiochemical purity (98 ± 1%), formulated for preclinical studies (9 mL, pH = 7.2), n=3. Conclusion: A straightforward synthesis of ²²⁵Ac-PSMA-617 is described that will facilitate production for (pre)clinical studies. The approach could also be applicable to the synthesis of other alpha radiotherapeutics incorporating ²²⁵Ac.

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.

Introduction: Natural products can be used as radioprotector agents because of containing phenolic compounds and several flavonoids with antioxidant properties. When the normal cells are exposed to ionizing radiation, they generate free radicals and reactive oxygen species that can cause damage in DNA, which leads to cellular dysfunction or even cell death. However, it is necessary to identify new radioprotective agents to protect normal cells. Ferulago angulata (F. angulata), a medicinal plant, can be used as a new radioprotective agent. Purpose: In this study, the radioprotective effect of F. angulata was evaluated against genotoxicity and oxidative stress induced by ionizing radiation in human blood lymphocytes. Methods: The antioxidant activity of F. angulata was assayed using FRAP and DPPH methods. Then, the human blood samples were incubated with F. angulata at different concentrations (25, 50, 100, and 200 μM) and subsequently exposed to IR at a dose of 2Gy. The radioprotective effect of F. angulata on the exposed cells was assessed by the micronucleus (MN) method. Also, biomarkers of oxidative stress in the exposed cells were evaluated by malondialdehyde (MDA) and superoxide dismutase (SOD) methods. Results: Our findings showed that F. angulata reduced the frequency of MN induced by IR in exposed cells. At a 200 μM concentration of F. angulata, the maximum reduction in the frequency of MN (63.11%) was observed that demonstrated a high degree of radioprotection. Afterward, pretreatment at 200 μM concentration of F. angulata inhibited oxidative stress in irradiated lymphocytes, leading to a reduction in MN frequency and MDA levels while SOD activity was enhanced in the exposed cells. Conclusion: F. angulata as a natural radioprotective agent can protect normal cells against reactive oxygen species and genetic damage induced by IR.

Introduction: In myocardial perfusion imaging, reducing the number of photons in images of obese patients causes poor image quality. To solve this problem, we need to inject the tracer according to the patients' weight. Therefore, this study aimed to investigate the relationship between myocardial photon counts with patients' weight, BMI, and gender. Materials and Methods: A total of 129 patients underwent myocardial perfusion imaging in a twoday stress-first protocol, but only rest images were included in this study. Multiplication factor was used to determine the amount of radiopharmaceutical activity injected into the patients. For evaluating the effect of gender, the photon counts of 22 female patients were also assessed when the breast tissue was pulled upward (Breast Up). The total myocardial detector counts in the raw images were calculated from the summation of 32 projections. A multiple linear regression test was used to simultaneously examine the effects of weight, BMI, and gender on photon counts. Results: There was no significant relationship between photon counts and patients' weight (p=0.129) and BMI (0.406), but gender had significant effects on photon counts, and myocardial detector counts were found to be higher in males (p=0.00). There was a statistically significant difference between the images of Breast Up and Non-Breast Up, and myocardial detector counts were higher in the Breast Up imaging method (p=0.00). Conclusion: Using the bodyweight formula, the image quality was comparable in obese and lean patients, but myocardial detector counts were lower in females, and this formula needs to be adjusted according to the patient's gender.

Background: Peptide receptor radionuclide therapy (PRRT) has been recently approved for advanced, metastatic, or progressive neuroendocrine tumors (NETs). Objective: This study reports the adverse events (AEs) observed with patient-tailored administered activity. Methods: Fifty-two PRRT naive patients were treated with 177Lu-DOTATATE. The administered activity ranges between 2.78 and 5.55 GBq/cycle using the patient's unique characteristics (age, symptoms, blood work, and biomarkers). Results: The protocol was well tolerated with the overwhelming majority of participants being forty- six (88%), completing all 4 induction therapy cycles. The median cumulative administered activity was 19.6 GBq (ranged 3.8-22.3 GBq). A total of 42/52 (81%) reported at least one symptom, and 43/52 (83%) had evidence of biochemical abnormality at enrollment that would meet grade 1 or 2 criteria for AEs. These symptoms only slightly increase with treatment to 50/52 (96%) and 51/52 (98%), respectively. The most common symptoms were mild fatigue (62%), shortness of breath (50%), nausea (44%), abdominal pain (38%), and musculoskeletal pain (37%). The most common biomarker abnormalities were mild anemia (81%), reduced estimated glomerular filtration rate (eGFR) (58%), increased alkaline phosphatase (ALP) (50%), and leukopenia (37%). Of critical importance, no 177Lu-DOTATATE related grade 3 or 4 AEs were observed. Conclusion: Tailoring the administered activity of 177Lu-DOTATATE to the individual patient with a variety of NETs is both safe and well-tolerated. No patient developed severe grade 3 or 4 AEs. Most patients exhibit symptoms or biochemical abnormality before treatment and this only slightly worsens following induction therapy.

Background: The testis is one of the most radiosensitive tissues in pelvic radiotherapy, especially in prostate cancer. Febuxostat (FBX), as an inhibitor of xanthine oxidase, has anti-inflammatory, antioxidant, and anti-apoptosis properties. Objectives: The aim of this research was to survey the protective effect of FBX against irradiation (IR)-induced testis damage via the attenuation of oxidative stress. Methods: Male adult mice were randomly assigned into eight groups: control, FBX with three doses of 5, 10, and 15 mg/kg, IR with 6 Gy, IR + FBX (IR + FBX in three doses), respectively. In the IR + FBX groups, FBX was administrated for 8 consecutive days, and then mice were exposed to IR at a dose of 6 Gy on the 9th day. One day after irradiation, biochemical parameters were evaluated in the testis of animals, while histopathological assessment had been performed on 14th day. Results: Irradiation led to the induction of testicular toxicity. FBX significantly protected histopathological alterations and decreased oxidative stress parameters in irradiated testis. Besides, FBX increased the diameter and germinal epithelial thickness of seminiferous tubules and Johnson’s score in irradiated mice. Conclusion: Data showed that FBX markedly protected testicular injury induced by IR by inhibiting oxidative stress and may be considered as an infertility inhibitor in cancer patients, especially prostate cancer.

Background and Objective: Herniarin is a simple coumarin that is found naturally in some plant species. In this study, we aimed to evaluate the protective effect of herniarin against ionizing radiation-induced genotoxicity and cytotoxicity in human peripheral blood lymphocytes. Methods: Herniarin was added to human lymphocytes before irradiation with a dose of 2 Gy of Xrays. The antagonistic potential of herniarin against radiation was measured by MTT [3-(4,5- dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide] assay, micronucleus assay, flow cytometry, and reactive oxygen species (ROS) level analysis. Results: The maximum survival of lymphocytes against radiation was observed at a concentration of 50 μM of herniarin and a treatment time of 1 h. Pretreatment with 50 μM herniarin significantly decreased the micronuclei frequency, the percentage of apoptotic lymphocytes, and the ROS level in irradiated human lymphocytes. Moreover, 50 μM herniarin significantly increased the cytokinesis blocked proliferation index in irradiated lymphocytes. Conclusion: Herniarin could reduce radiation-induced cytotoxicity and genotoxicity in human lymphocytes. To complete the results of this study, it is suggested that in the future, more preclinical studies with larger samples or animal models be performed on herniarin.

Background: Breast cancer Auger electron therapy is a growing field of study in radioimmunotherapy and oncology research. Trastuzumab, a high affinity-binding monoclonal antibody against HER2/neu is which is over-expressed in breast tumors, is used in radiopharmaceutical development. Objectives: In this work, the lethal effects of ¹¹¹In³⁺, ¹¹¹In-DTPA-trastuzumab and ¹¹¹In-trastuzumab coupled-nuclear localizing sequence peptide (¹¹¹In-DTPA-NLS-trastuzumab) on malignant cells were studied in vitro. Methods: DTPA-NLS-trastuzumab was prepared using sulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) conjugation with NLS peptide in the first step, followed by conjugation with diethylenetriaminepentaacetic acid (DTPA). Both DTPA-trastuzumab and DTPA- NLS-trastuzumab were labeled with ¹¹¹In followed by purification and quality control techniques. Sk-Br-3 (a HER2/neu+ cell line), was used in the cell viability assessment assay for ¹¹¹In, ¹¹¹In-DTPA-trastuzumab and ¹¹¹In-DTPA-NLS-trastuzumab (3.7 MBq) at 37 ºC. The cytotoxicity of the three species was studied using MTT and comet assay was utilized DNA damage detection. Results: A significant radiochemical purity for ¹¹¹In-DTPA-NLS-trastuzumab (99.36% ± 0.30%, ITLC) at the DTPA:antibody ratio of 6.90 ± 0.34:1, was obtained. Significant cell viability difference was found for ¹¹¹In-DTPA-NLS-trastuzumab compared to the other treatments at two-time points. In addition, comet assay demonstrated significant DNA damage at 144 h using ¹¹¹In-DTPA- NLS-trastuzumab. Conclusion: The results of cell viability and cell death using MTT assay and comet assay, respectively, demonstrate the NLS-peptide effectively facilitates ¹¹¹In-trastuzumab transport into the HER2/neu positive cancer cell nuclei to impose the radiotherapeutic effects of Auger electrons on DNA leading to cell death.

Background: The development of less expensive and pivotal methodologies capable of supporting the researchers in the radiopharmaceutical pre-clinical investigations could provide a crucial incentive for conducting biomedical research involved in the realization of tailored target therapies. Objective: The aim of this pilot study was to evaluate the capability of a digital autoradiography system equipped with a laser scanning device to perform [¹⁸F] choline biodistribution evaluation in a xenograft mouse model of prostate cancer. Methods: PC3 prostate cancer cells were used to develop NOD/SCID mice xenografts. The biodistribution of the radiopharmaceuticals was evaluated at 30, 60, and 120 min after injecting in excised organs by using a digital autoradiography system equipped with a super-resolution laser screen. Histological and immunohistochemical analyses were performed to correlate the [¹⁸F] choline uptake with morphological and molecular tumours characteristics. Results: The reported data clearly indicate the possibility of performing accurate biodistribution studies using the digital autoradiographic system equipped with a super-resolution screen. Specifically, a significant increase in the [¹⁸F] choline inhibitor uptake in PC3 tumours compared to heart, bowel, liver, and kidney at both 30 and 60 min was observed. More importantly, the digital autoradiographic system showed signal uptake almost exclusively in the PC3 tumors at 60 min post-injection. Noteworthy, immunohistochemical analysis demonstrated a strong overlapping between the [¹⁸F] choline uptake and the proliferation index (Ki67 expression). Conclusion: The use of an autoradiography system in pre-clinical investigations could shed new light on the molecular mechanisms that orchestrate the tissues damage induced by therapeutical radiopharmaceuticals.

Background: ¹⁷⁷Lu-Dotatate is used in the treatment of somatostatin-receptor-positive inoperable progressive gastroenteropancreatic neuroendocrine tumors. A co-infusion of amino acids (AAs) is administered to prevent renal toxicity. Objective: This study aimed to quantify the impact of two types of AA cocktails on the pharmacokinetics and toxicity of ¹⁷⁷Lu-Dotatate. Methods: Four injections of 7400 MBq ¹⁷⁷Lu-Dotatate were given per patient with administration of either Primene® 10% (containing a cocktail of 20 AAs with 22g of Lysine and 16.8 g of Arginine) or Lysakare® (containing 25 g of Lysine and 25 g of Arginine). Nine blood samples were collected at each cycle. Radioactivity-time data were analyzed according to a population-based model using NONMEM (version 7.4.1). Renal and hematological toxicity was evaluated after each cycle. Results: 1,678 ¹⁷⁷Lu-Dotatate plasma concentrations versus time were analyzed from 83 consecutive patients with Primene® (n= 45 pts) or Lysakare® (n= 36 pts). Population pharmacokinetic analysis showed that Primene® significantly increased the elimination rate constant of ¹⁷⁷Lu-Dotatate as opposed to Lysakare®. Primene® also significantly lowered Lutathera® plasma exposure (AUC) by 34%, whereas Lysakare® increased AUC by 7%. There was no renal toxicity in either case. Lymphopenia significantly correlated with AUC (p=0.021) with a trend towards higher toxicity with Lysakare®. Conclusion: Unlike Primene®, Lysakare® does not increase ¹⁷⁷Lu-Dotatate elimination. This difference is associated with a significant impact on AUC. The latter parameter has a high interpatient variability but a low intrapatient variability, which could have important clinical implications for treatment tailoring.