MARTHA SAHYLI ORTEGA PIJIEIRA
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Artigo IPEN-doc 29044 A closer look at the synthesis of 2‑[18F] fluoroethyl tosylate to minimize the formation of volatile side‑products2022 - PIJEIRA, MARTHA S.O.; SANTOS, SOFIA N. dos; ARAUJO, YASNIEL B.; LAPOLLI, ANDRE L.; WANDERMUREN, MARCIO N.; RIERA, ZALUA R.; CARVALHO, IVONE; ELSINGA, PHILIP H.; BERNARDES, EMERSON S.Background: 2-[18F]Fluoroethyltosylate ([18F]FEtOTs) is a well-known 18F-fluoroalkylating agent widely used to synthesize radiotracers for positron emission tomography. The widespread use of [18F]FEtOTs is due in part to its low volatility when compared to other halide and sulfonate building blocks. In this work, the radioactive volatile side-products formed during the synthesis of [18F]FEtOTs were identified and characterized for the first time, and an optimization of the reaction conditions to minimize their formation was proposed. Results: In order to characterize the volatiles produced during [18F]FEtOTs synthesis, the reaction mixtures of both cold FEtOTs and [18F]FEtOTs were co-injected onto the HPLC system. The radioactive peaks corresponding to the volatile compounds were collected, analyzed through headspace gas chromatography mass spectrometry sampler (HS-GC–MS) and identified as vinyl fluoride ([19F]VF) and 2-fluoroethanol ([19F]FEOH). By using a rotatable central composite design with a two-level full factorial core of two factors (22), it was determined that temperature and time are independent variables which affect the generation of [18F]VF and [18F]FEOH during the radiosynthesis of [18F]FEtOTs. In addition, in order to reduce the formation of the volatiles ([18F]VF and [18F]FEOH) and increase the yield of [18F]FEtOTs, it was demonstrated that the molar ratio of base to precursor must also be considered. Conclusion: [18F]VF and [18F]FEOH are volatile side-products formed during the radiosynthesis of [18F]FEtOTs, whose yields depend on the reaction time, temperature, and the molar ratio of base to precursor. Therefore, special care should be taken during the radiosynthesis and subsequent reactions using [18F]FEOTs in order to avoid environmental contamination and to improve the yield of the desired products.Resumo IPEN-doc 27749 Radiochemistry and pharmacokinetics of Pectin (MCP)2020 - SILVA, FABIO F.A. da; SANTOS, SOFIA N. dos; PIJEIRA, MARTHA S.O.; BERNARDES, EMERSON S.Artigo IPEN-doc 27181 Synthesis and evaluation of [18F]FEtLos and [18F]AMBF3Los as novel 18F-labelled losartan derivatives for molecular imaging of angiotensin II type 1 receptors2020 - PIJEIRA, MARTHA S.O.; NUNES, PAULO S.G.; SANTOS, SOFIA N. dos; ZHANG, ZHENGXING; NARIO, ARIAN P.; PERINI, EFRAIN A.; TURATO, WALTER M.; RIERA, ZALUA R.; CHAMMAS, ROGER; ELSINGA, PHILIP H.; LIN, KUO-SHYAN; CARVALHO, IVONE; BERNARDES, EMERSON S.Losartan is widely used in clinics to treat cardiovascular related diseases by selectively blocking the angiotensin II type 1 receptors (AT1Rs), which regulate the renin-angiotensin system (RAS). Therefore, monitoring the physiological and pathological biodistribution of AT1R using positron emission tomography (PET) might be a valuable tool to assess the functionality of RAS. Herein, we describe the synthesis and characterization of two novel losartan derivatives PET tracers, [18F]fluoroethyl-losartan ([18F]FEtLos) and [18F]ammoniomethyltrifluoroborate-losartan ([18F]AMBF3Los). [18F]FEtLos was radiolabeled by 18F-fluoroalkylation of losartan potassium using the prosthetic group 2-[18F]fluoroethyl tosylate; whereas [18F]AMBF3Los was prepared following an one-step 18F-19F isotopic exchange reaction, in an overall yield of 2.7 ± 0.9% and 11 ± 4%, respectively, with high radiochemical purity (>95%). Binding competition assays in AT1R-expressing membranes showed that AMBF3Los presented an almost equivalent binding affinity (Ki 7.9 nM) as the cold reference Losartan (Ki 1.5 nM), unlike FEtLos (Ki 2000 nM). In vitro and in vivo assays showed that [18F]AMBF3Los displayed a good binding affinity for AT1R-overexpressing CHO cells and was able to specifically bind to renal AT1R. Hence, our data demonstrate [18F]AMBF3Los as a new tool for PET imaging of AT1R with possible applications for the diagnosis of cardiovascular, inflammatory and cancer diseases.Artigo IPEN-doc 26227 Synthesis of a 2-nitroimidazole glycopeptide radiolabeled with (68)Ga for positron emission tomography (PET) imaging of tumor hypoxia2019 - NARIO, ARIAN P.; PIJIEIRA, MARTHA S.O.; SANTOS, SOFIA N. dos; CAMPOS, VANESSSA L.; BERNARDES, EMERSON S.Hypoxia is a pathological condition characterized by a reduction of oxygen supply to a specific tissue or cell. About 60% of solid tumors in an advanced stage present areas of hypoxia. Tumor-associated hypoxia has been correlated to: 1) tumor aggressiveness; 2) resistance to chemotherapy and radiotherapy; 3) poor prognosis. Thus, the use of non-invasive methods dedicated to assess tumor hypoxic areas are of extremely importance for the treatment of several types of cancers, allowing the use of individualized therapeutic strategies. Here, we developed a new 68Ga-labeled radiopharmaceutical for positron emission tomography (PET) imaging of tumor hypoxia. The 68Ga-labelled 2-nitroimidazole derivative was successfully obtained by linking the 2- nitroimidazole acetic acid derivative with a glycopeptide obtained by solid phase synthesis and further conjugated to DOTA-NHS and its identity was confirmed by mass spectrometry. The radiolabeling procedure of 68Ga-Glycopeptide was optimized regarding the amount of glycopeptide, temperature and time, and was obtained with a high radiochemical purity (96.6± 0.4%). Compared to the standard hypoxic radiopharmaceutical 18 68 F-FAZA, Cancer is a chronic degenerative process that culminates in the loss of mechanisms that regulate cell cycle and death. In addition, it is considered a public health problem worldwide and its incidence has grown by 20% in the last decade. In Brazil, it is the second cause of death due to illness and the National Cancer Institute estimate is approximately 600 thousand Ga-Glycopeptide was obtained in a faster way and high radiochemical purity was achieved after radiolabeling procedures. Our new 68Ga-Glycopeptide may be promising candidate for further evaluation as a potential hypoxia imaging agent. Moreover, the use of 68Ga as an alternative to 18F in the development of new tracers for PET imaging is still an advantage because of the use of radionuclide generators instead of costly cyclotron equipment. Additionally, the use of a glycopeptide may allow the development of a kit-type setup that will ease the preparation of the 68Ga-based agent.Tese IPEN-doc 25695 Synthesis of fluorine-18-labeled losartan analogs as novel positron emission tomography tracers for cancer imaging2019 - PIJEIRA, MARTHA S.O.Losartan is a selective antagonist of the angiotensin II type 1 receptor (AT1R). Several reports have highlighted the AT1R expression in several cancers enhancing tumor development and cancer progression. The aim of this thesis is the synthesis and evaluation of [18F]fluoroethyl-losartan ([18F]FEtLos) and [18F]ammoniomethyltrifluoroborate-losartan ([18F]AMBF3Los) as two novel losartan analogs to image AT1R-positive tumors using the positron emission tomography (PET). Initially, the cold compounds FEtLos and AMBF3Los were synthetized by alkylation and click chemistry reactions respectively, and characterized by spectroscopic techniques. Then, radiosynthesis of 2-[18F]fluoroethyl-tosylate was optimized from a radiation safety point of view. Next, [18F]FEtLos was manually synthetized by [18F]fluoroethylation of losartan with low molar activity and greater than 99% radiochemical purity. [18F]AMBF3Los was easily synthetized with greater than 97% radiochemical purity by one step 18F-19F isotopic exchange approach using low and high activities of [18F]fluoride that afforded molar activities ranging from 2 to 139 GBq/μmol. In vitro competition binding assays showed that FEtLos and AMBF3Los have low and high binding affinity to human AT1R, respectively. AT1R expression was confirmed in breast, ovarian and gastric derived-tumors implanted on Nude mice. In spite of the low affinity, [18F]FEtLos was specific for renal AT1R. However, [18F]FEtLos did not showed specificity for tumor AT1R binding. μPET imaging, autoradiography and ex vivo biodistribution studies showed the specificity of [18F]AMBF3Los for both kidney and tumor AT1R binding. However, [18F]AMBF3Los was not able to reach the tumor site once injected intravenously probably because of its rapid metabolism and very fast clearance. Nonetheless our results demonstrate that 18F-Angiotensin II Receptor Blockers (ARBs) derivatives could be suitable tracers to cancer imaging AT1R-expressing tumor microenvironment, however, radiolabeled ARBs that possess better pharmacokinetics profile may be required.