Losartán y sus derivados como radiotrazadores del receptor tipo 1 de agiotensina II

El receptor tipo 1 de angiotensina II (AT1R) juega un papel fundamental en las enfermedades cardiovasculares y se ha reconocido, en los últimos diez años, por su activa expresión en varios tipos de células y tejidos tumorales propiciando la progresión del cáncer. Los fármacos antagonistas de este receptor, como el losartán, utilizados para el control de la hipertensión arterial han demostrado un potencial efecto antitumoral al ser capaces de reducir la progresión del tumor, la vascularización y la metastásis. El objetivo de este trabajo es brindar una panorámica sobre los estudios más recientes de los derivados marcados del losartán, destacando su posible utilización como radiotrazadores del AT1R en tumores que lo expresen. Derivados del losartán marcados con tecnecio-99 metaestable, carbono-11 y fluor-18 permiten detectar y cuantificar el AT1Ren algunos órganos como el corazón y los riñones. Se demuestra la relación existente entre el losartán y el cáncer según los resultados de estudios preclínicos, se resumen diferentes vías de obtención de sus derivados marcados y los resultados de su evaluación como radiotrazadores biológicos del AT1R. En las conclusiones se señala que los derivados de losartán marcados con 99mTc, 11C y 18F pudieran ser utilizados como radiotrazadores para detectar y cuantificar el AT1R en células y tejidos tumorales de pacientes utilizando la imagen molecular como técnica no invasiva.  Existe un amplio campo de investigación relacionado con el desarrollo de nuevos radiotrazadores SPECT o PET del AT1R con fines diagnósticos tanto en patologías como la hipertensión y enfermedades cardiovasculares, como en oncología

Nanomicelles of Radium Dichloride [223Ra]RaCl2 Co-Loaded with Radioactive Gold [198Au]Au Nanoparticles for Targeted Alpha–Beta Radionuclide Therapy of Osteosarcoma

Alpha and beta particulate radiation are used for non-treated neoplasia, due to their ability to reach and remain in tumor sites. Radium-223 (223Ra), an alpha emitter, promotes localized cytotoxic effects, while radioactive gold (198Au), beta-type energy, reduces radiation in the surrounding tissues. Nanotechnology, including several radioactive nanoparticles, can be safely and effectively used in cancer treatment. In this context, this study aims to analyze the antitumoral effects of [223Ra]Ra nanomicelles co-loaded with radioactive gold nanoparticles ([198Au]AuNPs). For this, we synthesize and characterize nanomicelles, as well as analyze some parameters, such as particle size, radioactivity emission, dynamic light scattering, and microscopic atomic force. [223Ra]Ra nanomicelles co-loaded with [198Au]AuNPs, with simultaneous alpha and beta emission, showed no instability, a mean particle size of 296 nm, and a PDI of 0.201 (±0.096). Furthermore, nanomicelles were tested in an in vitro cytotoxicity assay. We observed a significant increase in tumor cell death using combined alpha and beta therapy in the same formulation, compared with these components used alone. Together, these results show, for the first time, an efficient association between alpha and beta therapies, which could become a promising tool in the control of tumor progression

Síntese de análogos do losartan marcados com flúor-18 como novos traçadores para imagem do câncer utilizando tomografia por emissão de pósitrons

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.O losartan é um antagonista seletivo do receptor tipo 1 de angiotensina II (AT1R). Vários reportes têm destacado a expressão do AT1R em vários cânceres favorecendo o desenvolvimento tumoral e progressão do câncer. O objetivo desta tese é a síntese e avaliação do [18F]fluoroetil-losartan ([18F]FEtLos) e [18F]amoniometiltrifluoroborato-losartan ([18F]AMBF3Los) como dois novos análogos do losartan para imagem de tumores AT1R-positivos usando a tomografia por emissão de pósitrons (PET). Inicialmente, os compostos padrões FEtLos e AMBF3Los foram sintetizados por reações de alquilação e química click respetivamente, e caraterizados por técnicas espectroscópicas. A seguir, a radiosíntese do 2-[18F]fluoroetil-tosilato foi otimizada do ponto de vista de seguridade radiológica. O [18F]FEtLos foi depois sintetizado por alquilação do losartan utilizando o grupo prostético 2-[18F]fluoroetil-tosilato, com baixa atividade molar, e pureza radioquímica maior do 99%. [18F]AMBF3Los foi facilmente sintetizado com pureza radioquímica maior do 97% por troca isotópica 18F-19F usando baixas e altas atividades de [18F]fluoreto o que providenciou atividades molares entre 2 e 139 GBq/μmol. Ensaios de ligação por competição in vitro mostraram que FEtLos e AMBF3Los têm baixa e alta afinidade de ligação ao AT1R humano respetivamente. A expressão do AT1R foi confirmada em tumores de mama, ovário e gástrico, implantados em camundongos Nude. A pesar da baixa afinidade, o [18F]FEtLos foi específico pelo AT1R renal. Não entanto, [18F]FEtLos não mostrou especificidade pela ligação ao AT1R no tumor. A imagem μPET, autoradiografia, e os estudos de biodistribuição ex vivo mostraram a especificidade do [18F]AMBF3Los pela ligação ao AT1R nos rins e no tumor. O radiotraçador [18F]AMBF3Los não foi capaz de ligar no tumor quando injetado intravenosamente, provavelmente devido ao seu rápido metabolismo e rápida depuração sanguínea. Apesar disso, nossos dados demonstram que os derivados de Bloqueadores do Receptor de Angiotensina II (ARBs) radiomarcados com 18F podem ser potenciais radiofármacos para o imageamento do microambiente tumoral positivo para AT1R, no entanto o perfil farmacocinético dos ARBs radiomarcados ainda precisa ser melhorado

A closer look at the synthesis of 2-[18F]fluoroethyl tosylate to minimize the formation of volatile side-products

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

Evaluating Hydroxyapatite, Gold Nanoparticles, and Graphene-Copper as Bimodal Agents for X-ray and Computed Tomography

A global need exists for new and more effective contrast agents for computed tomography and traditional X-ray modalities. Among the few options available nowadays, limitations imposed by industrial production, performance, and efficacy restrict the use and reduce the potential of both imaging techniques. The use of nanomaterials as new contrast agents for X-ray and computed tomography is an innovative and viable way to increase the options and enhance performance. In this study, we evaluated eight nanomaterials: hydroxyapatite doped with zinc (Zn-HA 10%); hydroxyapatite doped with strontium (Sr-HA 10%); hydroxyapatite without thermal treatment (HA 282 STT); thermally treated hydroxyapatite (HA 212 500 °C and HA 01.256 CTT 1000 °C); hydroxyapatite microspheres (HA microspheres); gold nanoparticles (AuNP); and graphene oxide doped with copper (Cu-GO). The results showed that for both imaging modalities; HA microspheres were the best option, followed by hydroxyapatite thermally treated at 1000 °C. The nanomaterials with the worst results were hydroxyapatite doped with zinc (Zn-HA 10%), and hydroxyapatite doped with strontium (Sr-HA 10%). Our data demonstrated the potential of using nanomaterials, especially HA microspheres, and hydroxyapatite with thermal treatment (HA 01.256 CTT 1000 °C) as contrast agents for X-ray and computed tomography

Ultrastructural Analysis of Cancer Cells Treated with the Radiopharmaceutical Radium Dichloride ([²²³Ra]RaCl₂): Understanding the Effect on Cell Structure

The use of alpha-particle (α-particle) radionuclides, especially [223Ra]RaCl2 (radium dichloride), for targeted alpha therapy is steadily increasing. Despite the positive clinical outcomes of this therapy, very little data are available about the effect on the ultrastructure of cells. The purpose of this study was to evaluate the nanomechanical and ultrastructure effect of [223Ra] RaCl2 on cancer cells. To analyze the effect of [223Ra]RaCl2 on tumor cells, human breast cancer cells (lineage MDA-MB-231) were cultured and treated with the radiopharmaceutical at doses of 2 µCi and 0.9 µCi. The effect was evaluated using atomic force microscopy (AFM) and transmission electron microscopy (TEM) combined with Raman spectroscopy. The results showed massive destruction of the cell membrane but preservation of the nucleus membrane. No evidence of DNA alteration was observed. The data demonstrated the formation of lysosomes and phagosomes. These findings help elucidate the main mechanism involved in cell death during α-particle therapy

Additional file 1 of A closer look at the synthesis of 2-[18F]fluoroethyl tosylate to minimize the formation of volatile side-products

Additional file 1: Figure S1. Results of the HPLC and HS-GC-MS analyses of the [18F]FEtOTs crude mixture co-injected with commercially available 2-fluoroethanol (at m/z 64 according to our HS-GC-MS results) after heating at 130oC for 15 min and using 2 mg of K2CO3

Nanomicelles of Radium Dichloride [223Ra]RaCl2 Co-Loaded with Radioactive Gold [198Au]Au Nanoparticles for Targeted Alpha–Beta Radionuclide Therapy of Osteosarcoma

Alpha and beta particulate radiation are used for non-treated neoplasia, due to their ability to reach and remain in tumor sites. Radium-223 (223Ra), an alpha emitter, promotes localized cytotoxic effects, while radioactive gold (198Au), beta-type energy, reduces radiation in the surrounding tissues. Nanotechnology, including several radioactive nanoparticles, can be safely and effectively used in cancer treatment. In this context, this study aims to analyze the antitumoral effects of [223Ra]Ra nanomicelles co-loaded with radioactive gold nanoparticles ([198Au]AuNPs). For this, we synthesize and characterize nanomicelles, as well as analyze some parameters, such as particle size, radioactivity emission, dynamic light scattering, and microscopic atomic force. [223Ra]Ra nanomicelles co-loaded with [198Au]AuNPs, with simultaneous alpha and beta emission, showed no instability, a mean particle size of 296 nm, and a PDI of 0.201 (±0.096). Furthermore, nanomicelles were tested in an in vitro cytotoxicity assay. We observed a significant increase in tumor cell death using combined alpha and beta therapy in the same formulation, compared with these components used alone. Together, these results show, for the first time, an efficient association between alpha and beta therapies, which could become a promising tool in the control of tumor progression