The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology.

Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.

Design and development of 6-hydrazinonicotinyl-fatty acid-mimetic 99mTc-complex as a potential myocardial imaging agent

Abstract The goal of this work is to identify new fatty acid-mimetic 99mTc-complexes to be used as myocardial imaging agents that allow studying heart abnormalities in high-risk patients. In this sense, we designed a fatty acid-mimetic substructure including an amide moiety that, among other properties, could improve myocardial residence time. A diamide with a chain length of 15 atoms and porting a 6-hydrazinonicotinyl (HYNIC) chelator, and an analog with a short carbon-chain, were prepared with convergent organic synthetic procedures and radiolabeled with 99mTc using tricine as the sole coligand. The in vivo proofs of concept were performed using healthy mice. The new 99mTc-complexes were obtained with adequate radiochemical purity. The lipophilicities were in agreement with the length of the chains. While both 99mTc-complexes showed uptake in the myocardial muscle, the designed radiopharmaceutical with the longest chain length had preferential target-uptake and target-retention compared to other complexes described in the bibliography. Further studies, involving imaging assays, synthetic modifications, and assay of new coligands for 99mTc-HYNIC complexes, are currently ongoing.

Optimization of the 2-arylquinazoline-4(3H)one scaffold for a selective and potent antitrypanosomal agent: modulation of the mechanism of action through chemical functionalization.

We sought to identify a potent and selective antitrypanosomal agent through modulation of the mechanism of action of a 2-arylquinazoline scaffold as an antitrypanosomal agent via chemical functionalization at the 4-position. We wished to use the: (i) susceptibility of trypanosomatids towards nitric oxide (NO) and reactive oxygen species (ROS); (ii) capacity of the 4-substituted quinazoline system to act as an antifolate agent. Three quinazolin-based moieties that differed from each other by having at the 4-position key pharmacophores targeting the induction of NO and ROS production were evaluated in vitro against Leishmania infantum and Trypanosoma cruzi parasites and their modes of action were explored. Replacement of an oxygen moiety at the 4-position of the antifolate 2-arylquinazolin-4(3H)one by hydrazinyl and 5-nitrofuryl-hydrazinyl pharmacophores enhanced antitrypanosomatid activity significantly due to promotion of an additional mechanism beyond the antifolate response such as NO or ROS production, respectively. Among the three types of chemical functionalization, the 5-nitrofuryl-hydrazinyl moiety generated the most potent compounds. Compound 3b was a potential candidate thanks to its sub-micromolar response against the promastigotes/amastigotes of L. infantum and epimastigote of T. cruzi, moderate toxicity on macrophages (J774.1), good selectivity index (∼15.1-17.6) and, importantly, non-mutagenic effects. 2-Arylquinazoline could be an attractive platform to design new anti-trypanosomatid agents with the use of key pharmacophores.

In vitro and in vivo studies on a group of chalcones find promising results as potential drugs against fascioliasis.

About a third of the world population is infected by helminth parasites implicated in foodborne trematodiasis. Fascioliasis is a worldwide disease caused by trematodes of the genus Fasciola spp. It generates huge economic losses to the agri-food industry and is currently considered an emerging zoonosis by the World Health Organization (WHO). The only available treatment relies on anthelmintic drugs, being triclabendazole (TCBZ) the drug of choice to control human infections. The emergence of TCBZ resistance in several countries and the lack of an effective vaccine to prevent infection highlights the need to develop new drugs to control this parasitosis. We have previously identified a group of benzochalcones as inhibitors of cathepsins, which have fasciolicidal activity in vitro and are potential new drugs for the control of fascioliasis. We selected the four most active compounds of this group to perform further preclinical studies. The compound's stability was determined against a liver microsomal enzyme fraction, obtaining half-lives of 34-169 min and low intrinsic clearance values (<13 µL/min/mg), as desirable for potential new drugs. None of the compounds were mutagenic or genotoxic and no in vitro cytotoxic effects were seen. Compounds C31 and C34 showed the highest selectivity index against liver fluke cathepsins when compared to human cathepsin L. They were selected for in vivo efficacy studies observing a protective effect, similar to TCBZ, in a mouse model of infection. Our findings strongly encourage us to continue the drug development pipeline for these molecules.

Tautomerism and Rotamerism of Favipiravir and Halogenated Analogues in Solution and in the Solid State.

Favipiravir is an important selective antiviral against RNA-based viruses, and currently, it is being repurposed as a potential drug for the treatment of COVID-19. This type of chemical system presents different carboxamide-rotameric and hydroxyl-tautomeric states, which could be essential for interpreting its selective antiviral activity. Herein, the tautomeric 3-hydroxypyrazine/3-pyrazinone pair of favipiravir and its 6-substituted analogues, 6-Cl, 6-Br, 6-I, and 6-H, were fully investigated in solution and in the solid state through ultraviolet-visible, 1H nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction techniques. Also, a study of the gas phase was performed using density functional theory calculations. In general, the keto-enol balance in these 3-hydroxy-2-pyrazinecarboxamides is finely modulated by external and internal electrical variations via changes in solvent polarity or by replacement of substituents at position 6. The enol tautomer was prevalent in an apolar environment, whereas an increase in the level of the keto tautomer was favored by an increase in solvent polarity and, even moreso, with a strong hydrogen-donor solvent. Keto tautomerization was favored either in solution or in the solid state with a decrease in 6-substituent electronegativity as follows: H ≫ I ≈ Br > Cl ≥ F. Specific rotameric states based on carboxamide, "cisoide" and "transoide", were identified for the enol and keto tautomer, respectively; their rotamerism is dependent on the tautomerism and not the aggregation state.

Exploring binding chemistry of alkali/alkaline earth cations in solution through modulation of intramolecular charge-transfer in an excited ambidentate organic fluorophore.

Studying the metal-ligand monoligation of alkali/alkaline earth metals (AMs) in solution represents a significant challenge due to the low stabilization of their complexes and the absence of an effective strategy to identify this type of weak binding. Herein, we show that the modulation of the intramolecular charge-transfer (ICT) in an excited ambidentate organic fluorophore is a convenient strategy to characterize the binding chemistry of AM cations in solution through simple steady-state fluorescence and fluorescence lifetime measurements. The key points of the fluorophore as a metal-binding probe were the location of diverse coordination functionalities with different binding abilities (ionic-, pseudo-covalent- and non-covalent-probes) along the donor-acceptor (D-A) chain and the occurrence of an intramolecular charge-transfer (ICT) mechanism upon excitation. The binding of these functionalities with AM-cations generated selective and specific fluorescence responses, which were quantifiable and allowed us to recognize the primary, secondary and tertiary interactions for all the AM cations in the solution. The relative binding affinities for each one of the functionalities with AM cations was estimated, and a general and consistent perspective of the binding of AMs as a function of their location in the Periodic Table, hardness property and ionic radius was established. The binding preferences of the AM cations were supported by DFT calculations. Our strategy allowed us to validate the binding dynamics of AMs in solution for three types of key ligations, which opens a new perspective to recognize weak intermolecular interactions derived from acidic species and rationally design selective AM-cation probes using an ICT-based ambidentate organic fluorophore.

99mTc-HYNIC/Cy7-Fab(Bevacizumab): su empleo como agente de imagen en mieloma múltiple / 99mTc-HYNIC/Cy7-Fab(Bevacizumab): its use as an imaging agent in Multiple Myeloma / 99mTc-HYNIC/Cy7-Fab (Bevacizumab): seu uso como agente de imagem em mieloma múltiplo

Introducción: el mieloma múltiple es un trastorno hematológico maligno y el segundo cáncer de la sangre más frecuente. El proceso de la angiogénesis tumoral es fundamental para el crecimiento y metástasis de muchos tipos de tumores, incluido en mieloma múltiple. Se sabe que la sobreexpresión del factor de crecimiento endothelial vascular se encuentra asociado a un mal pronóstico en esta patología, representando un blanco clave para la terapia anti-angiogénica en mieloma múltiple. El anticuerpo monoclonal Bevacizumab es capaz de unirse con gran afinidad al factor de crecimiento endothelial vascular bloqueando su acción. Objetivo: evaluar el Fab(Bevacizumab) marcado con 99mTc o Cy7 como potenciales agentes de imagen moleculares de la expresión de factor de crecimiento endothelial vascular en mieloma múltiple. Material y métodos: la expresión de factor de crecimiento endothelial vascular fue analizada mediante citometría de flujo en la línea celular huaman de mieloma múltiple, la MM1S. Fab(Bevacizumab) fue producido mediante digestión de Bevacizumab con papaína, conjugado a NHS-HYNIC-Tfa y radiomarcado con 99mTc. Se realizaron estudios de biodistribución y de tomografía computarizada por emisión del fotón simple. A su vez, Fab(Bevacizumab) fue marcado con Cy7 para obtener imágenes de fluorescencia in vivo hasta 96 horas. Resultados: el análisis por citometría de flujo en la línea celular MM1S reveló que la expresión de factor de crecimiento endothelial vascular es predominantemente intracelular. Los estudios de biodistribución y SPECT/CT del complejo 99mTc-HYNIC-Fab(Bevacizumab) mostraron una rápida eliminación sanguínea y una significativa captación a nivel renal y tumoral. Las imágenes por fluorescencia empleando Cy7-Fab(Bevacizumab) permitieron la visualización tumoral hasta 96 h p.i. Conclusiones: logramos visualizar la expresión de factor de crecimiento endothelial vascular in vivo en mieloma múltiple mediante el empleo del fragmento Fab del anticuerpo anti-VEGF (Bevacizumab) marcado con 99mTc y Cy7. Estos nuevos agentes de imagen molecular podrían ser empleados potencialmente en el ámbito clínico para la estadificación y el seguimiento de pacientes con mieloma múltiple, mediante la visualización radioactiva in vivo de la expresión de factor de crecimiento endothelial vascular en todo el cuerpo. La imagen óptica de estos trazadores mejoraría el muestreo tumoral y podría guiar la extirpación quirúrgica.

Introduction: Multiple myeloma is a hematologic malignancy and the second most common blood cancer. The process of tumor angiogenesis is central to the growth and metastasis of many types of tumors, including multiple myeloma. Overexpression of vascular endothelial growth factor is known to be associated with poor prognosis in this pathology, representing a key target for anti-angiogenic therapy in multiple myeloma. The monoclonal antibody Bevacizumab is able to bind with high affinity to vascular endothelial growth factor blocking its action. Objective: to evaluate 99mTc- or Cy7-labeled Fab(Bevacizumab) as potential molecular imaging agents of vascular endothelial growth factor expression in multiple myeloma. Methods: Vascular endothelial growth factor expression was analyzed by flow cytometry in the multiple myeloma huaman cell line, MM1S. Fab(Bevacizumab) was produced by digestion of Bevacizumab with papain, conjugated to NHS-HYNIC-Tfa and radiolabeled with 99mTc. Biodistribution and single photon emission computed tomography studies were performed. In turn, Fab(Bevacizumab) was labeled with Cy7 to obtain in vivo fluorescence images up to 96 hours. Results: Flow cytometry analysis in the MM1S cell line revealed that vascular endothelial growth factor expression is predominantly intracellular. Biodistribution and SPECT/CT studies of the 99mTc-HYNIC-Fab(Bevacizumab) complex showed rapid blood clearance and significant renal and tumor uptake. Fluorescence imaging using Cy7-Fab(Bevacizumab) allowed tumor visualization up to 96 h p.i. Conclusions: we were able to visualize vascular endothelial growth factor expression in vivo in multiple myeloma using the Fab fragment of the anti-VEGF antibody (Bevacizumab) labeled with 99mTc and Cy7. These new molecular imaging agents could potentially be employed in the clinical setting for staging and monitoring of patients with multiple myeloma by in vivo radioactive visualization of vascular endothelial growth factor expression throughout the body. Optical imaging of these tracers would improve tumor sampling and could guide surgical excision.

Introdução: O mieloma múltiplo é uma malignidade hematológica e o segundo câncer de sangue mais comum. O processo de angiogênese tumoral é fundamental para o crescimento e a metástase de muitos tipos de tumores, incluindo o mieloma múltiplo. Sabe-se que a superexpressão do fator de crescimento endotelial vascular está associada a um prognóstico ruim no mieloma múltiplo, representando um alvo importante para a terapia antiangiogênica no mieloma múltiplo. O anticorpo monoclonal Bevacizumab é capaz de se ligar com alta afinidade ao fator de crescimento endotelial vascular e bloquear sua ação. Objetivo: avaliar o Fab(Bevacizumab) marcado com 99mTc ou Cy7 como possíveis agentes de imagem molecular da expressão do fator de crescimento endotelial vascular no mieloma múltiplo. Métodos: A expressão do fator de crescimento endotelial vascular foi analisada por citometria de fluxo na linha celular de mieloma múltiplo MM1S. O Fab(Bevacizumab) foi produzido pela digestão do Bevacizumab com papaína, conjugado com NHS-HYNIC-Tfa e radiomarcado com 99mTc. Foram realizados estudos de biodistribuição e tomografia computadorizada por emissão de fóton único. Por sua vez, o Fab(Bevacizumab) foi marcado com Cy7 para geração de imagens de fluorescência in vivo por até 96 horas. Resultados: A análise de citometria de fluxo na linha celular MM1S revelou que a expressão do fator de crescimento endotelial vascular é predominantemente intracelular. Os estudos de biodistribuição e SPECT/CT do complexo 99mTc-HYNIC-Fab(Bevacizumab) mostraram uma rápida depuração sanguínea e uma captação renal e tumoral significativa. A imagem de fluorescência usando Cy7-Fab(Bevacizumab) permitiu a visualização do tumor até 96 horas p.i. Conclusões: Conseguimos visualizar a expressão do fator de crescimento endotelial vascular in vivo no mieloma múltiplo usando o fragmento Fab do anticorpo anti-VEGF (Bevacizumab) marcado com 99mTc e Cy7. Esses novos agentes de imagem molecular poderiam ser usados no cenário clínico para o estadiamento e o monitoramento de pacientes com mieloma múltiplo, visualizando radioativamente a expressão do fator de crescimento endotelial vascular in vivo em todo o corpo. A geração de imagens ópticas desses traçadores melhoraria a amostragem do tumor e poderia orientar a excisão cirúrgica.

One-step synthesis of favipiravir from Selectfluor® and 3-hydroxy-2-pyrazinecarboxamide in an ionic liquid.

Favipiravir is an important selective antiviral that emerged as an alternative against COVID-19 during the pandemic. Its synthesis has gained great interest and the conventional strategies proceed through multiple-step protocols (6-7 reaction steps), which involve, in addition, several drawbacks with global yields, lower than 34%. Herein, a simple, economical, eco-friendly and scalable (1 g) one-step protocol for the synthesis of favipiravir from the direct fluorination of the available 3-hydroxy-2-pyrazinecarboxamide with Selectfluor® is reported. The reaction proceeds easily in BF4-BMIM through a simple operational work-up, affording the favipiravir with a yield of 50% without the need of a special catalyst/additive. The key point of the present strategy was the use of the ionic liquid of BF4-BMIM, which helps to minimize the several chemical limitations derived from 3-hydroxy-2-pyrazinecarboxamide as a substrate for the direct Selectfluor-mediated fluorination. All these chemical reactivity aspects are also discussed in detail.

Morphological evidence of the protective effects of a synthetic chalcone against the striatal myelin damage induced by glutaric acid.

Ultrastructural features of striatal white matter and cells in an in vivo model of glutaric acidemia type I created by intracerebral injection of glutaric acid (GA) were analyzed by transmission electron microscopy and immunohistochemistry. To test if the white matter damage observed in this model could be prevented, we administered the synthetic chemopreventive molecule CH38 ((E)-3-(4-methylthiophenyl)-1-phenyl-2-propen-1-one) to newborn rats, previous to an intracerebroventricular injection of GA. The study was done when striatal myelination was incipient and when it was already established (at 12 and 45 days post-injection [DPI], respectively). Results obtained indicate that that the ultrastructure of astrocytes and neurons did not appear significantly affected by the GA bolus. Instead, in oligodendrocytes, the most prominent GA-dependent injury defects included endoplasmic reticulum (ER) stress and nuclear envelope swelling at 12 DPI. Altered and reduced immunoreactivities against heavy neurofilament (NF), proteolipid protein (PLP), and myelin-associated glycoprotein (MAG) together with axonal bundle fragmentation and decreased myelin were also found at both ages analyzed. CH38 by itself did not affect striatal cells or axonal packages. However, the group of rats that received CH38 before GA did not show evidence neither of ER stress nor nuclear envelope dilation in oligodendrocytes, and axonal bundles appeared less fragmented. In this group, labeling of NF and PLP was similar to the controls. These results suggest that the CH38 molecule is a candidate drug to prevent or decrease the neural damage elicited by a pathological increase of GA in the brain. Optimization of the treatments and identification of the mechanisms underlying CH38 protective effects will open new therapeutic windows to protect myelin, which is a vulnerable target of numerous nervous system diseases.

A Potential Boron Neutron Capture Therapy Agent Selectively Suppresses High-Grade Glioma: In Vitro and in Vivo Exploration.

Glioblastoma (GBM), as the most central nervous system (CNS) intractable disease, has spoiled millions of lives due to its high mortality. Even though several efforts have been made, the existing treatments have had limited success. In this sense, we studied a lead compound, the boron-rich selective epidermal growth factor receptor (EGFR)-inhibitor hybrid 1, as a potential drug for GBM treatment. For this end, we analyzed the in vitro activity of hybrid 1 in a glioma/primary astrocytes coculture, studying cellular death types triggered by treatment with this compound and its cellular localizations. Additionally, hybrid 1 concentrated boron in glioma cells selectively and more effectively than the boron neutron capture therapy (BNCT)-clinical agent 10B-l-boronophenylalanine and thus displayed a better in vitro-BNCT effect. This encouraged us to analyze hybrid 1 in vivo. Therefore, immunosuppressed mice bearing U87 MG human GBM were treated with both 1 and 1 encapsulated in a modified liposome (recognized by brain-blood barrier peptide transporters), and we observed a potent in vivo per se antitumor activity (tumor size decrease and animal survival increase). These data demonstrate that 1 could be a promising new targeted therapy for GBM.

Targeted-Lymphoma Drug Delivery System Based on the Sgc8-c Aptamer.

Aptamers are emerging as a promising new class of functional nucleic acids because they can specifically bind to any target with high affinity and be easily modified chemically with different pharmacophoric subunits for therapy. The truncated aptamer, Sgc8-c, binds to tyrosine-protein kinase-like 7 receptor, a promising cancer therapeutic target, allowing the recognition of haemato-oncological malignancies, among others. We have previously developed aptamer-drug conjugates by chemical synthesis, hybridizing Sgc8-c and dasatinib, a drug proposed for lymphoma chemotherapy. One of the best-characterised Sgc8-c-dasatinib hybrids, namely Sgc8-c-carb-da, was capable of releasing dasatinib at an endosomal-pH. Herein, we probed the therapeutic potential of this aptamer-drug conjugate. Sgc8-c-carb-da specifically inhibited murine A20 B lymphocyte growth and produced cell death, mainly by late apoptosis and necrosis. In addition, Sgc8-c-carb-da generated an arrest in cell proliferation, with a cell cycle arrest in the Sub-G1-peak. The mitochondrial potential was altered accordingly to these pathways. Moreover, using an in vitro cell-targeting assay that mimics in vivo conditions, we showed that Sgc8-c-carb-da displayed higher (2.5-fold) cytotoxic effects than dasatinib. These findings provide proof-of-concept of the therapeutic value of Sgc8-c-carb-da for lymphoma, creating new opportunities for the chemical synthesis of targeted biotherapeutics.

Exploring the cell death mechanisms of cytotoxic [1,2,3]triazolylcarborane lead compounds against U87 MG human glioblastoma cells.

Moving towards high-grade glioma drug discovery, this study aimed to detect the mechanism of cellular death (apoptosis, necrosis and/or autophagy) induced by three carboranyl-based lead compounds. For that, we performed in U87 MG cells, flow cytometry experiments, as the gold standard technique, as well as confocal microscopy and 1 H-NMR experiments as non-invasive assays. We selected three hybrid leads (1-3) from the in-house-library and the corresponding parent compounds, and recognized tyrosine kinase inhibitors (lapatinib, sunitinib and erlotinib) to put to the test in these experiments. Flow cytometry with Annexin V-FITC/DAPI staining showed that leads 1 and 3 and lapatinib mainly induced necrosis in U87 MG upon a 24 h treatment at IC50 dose; meanwhile, hybrid 2, sunitinib and erlotinib seem to induce apoptosis in such cells. In general, confocal microscopy studies were in agreement with flow cytometry observing loss of cell membrane integrity in necrotic cells and features of apoptosis, that is, chromatin condensation, in apoptotic cells. Finally, NMR results showed that glioblastoma cells treated with hybrid 1, 3 or lapatinib displayed changes in CH2 /CH3 signal ratio and choline signals that could indicate necrotic cell death mechanism: meanwhile, 2-, sunitinib- or erlotinib-treated cells showed apoptotic characteristic behaviors. Additionally, carboranyl-hybrid 2 also produced autophagy in U87 MG cells.

Aptamer-Based Immunotheranostic Strategies.

The escape from immune surveillance is a hallmark of cancer progression. The classic immune checkpoint molecules PD-1, PD-L1, CTLA-4, LAG-3, TIM-3 novel ones are part of a sophisticated system of up- and downmodulation of the immune system, which is unregulated in cancer. In recent years, there have been remarkable advances in the development of targeting strategies, focused principally on immunotherapies aiming at blocking those molecules involved in the evasion of the immune system. However, there are still challenges to predicting their efficacy due to the wide heterogeneity of clinical responses. Thus, there is a need to develop new strategies, and theranostics has much to contribute in this field. Besides that, aptamers have emerged as promising molecules with the potential to generate a huge impact in the immunotheranostic field. They are single-stranded oligonucleotides with a unique self-folding tridimensional structure, with high affinity and specificity for the target. In particular, their small size and physicochemical characteristics make them a versatile tool for designing theranostic strategies. Here, we review the progress in theranostic strategies based on aptamers against immune checkpoints, and highlight the potential of those approaches.

Synthesis and Antitrypanosomal and Mechanistic Studies of a Series of 2-Arylquinazolin-4-hydrazines: A Hydrazine Moiety as a Selective, Safe, and Specific Pharmacophore to Design Antitrypanosomal Agents Targeting NO Release.

Nitric oxide (NO) represents a valuable target to design antitrypanosomal agents by its high toxicity against trypanosomatids and minimal side effects on host macrophages. The progress of NO-donors as antitrypanosomal has been restricted by the high toxicity of their agents, which usually is based on NO-heterocycles and metallic NO-complexes. Herein, we carried out the design of a new class of NO-donors based on the susceptibility of the hydrazine moiety connected to an electron-deficient ring to be reduced to the amine moiety with release of NO. Then, a series of novel 2-arylquinazolin-4-hydrazine, with the potential ability to disrupt the parasite folate metabolism, were synthesized. Their in vitro evaluation against Leishmania and Trypanosoma cruzi parasites and mechanistic aspects were investigated. The compounds displayed significant leishmanicidal activity, identifying three potential candidates, that is, 3b, 3c, and 3f, for further assays by their good antiamastigote activities against Leishmania braziliensis, low toxicity, non-mutagenicity, and good ADME profile. Against T. cruzi parasites, derivatives 3b, 3c, and 3e displayed interesting levels of activities and selectivities. Mechanistic studies revealed that the 2-arylquinazolin-4-hydrazines act as either antifolate or NO-donor agents. NMR, fluorescence, and theoretical studies supported the fact that the quinazolin-hydrazine decomposed easily in an oxidative environment via cleavage of the N-N bond to release the corresponding heterocyclic-amine and NO. Generation of NO from axenic parasites was confirmed by the Griess test. All the evidence showed the potential of hydrazine connected to the electron-deficient ring to design effective and safe NO-donors against trypanosomatids.

High CT-Fluorophore Featuring a Basic Moiety into D-A Chain as a pKa Probe.

The determination of acidity represents a significant challenge within fluorometry, and no effective strategy has been developed successfully yet. It is attributed to the fact that acidity tends to be enhanced upon excitation, giving, in general, an overestimation of the ionization constant, pKa. Herein, we developed a strategy for pKa estimation of Brønsted acids in solution through fluorometry by using a convenient pKa probe, N1-aryl-7-methoxy-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one. It allowed us to obtain a linear log KSV versus pKa correlation derived from the selective quenching response of the probe by an interaction with different Brønsted acids. The key points of N1-aryl-7-methoxy-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one as a pKa probe were (i) the location of a weak basic moiety in the donor-acceptor chain of the fluorophore, which favors a selective quenching of the intramolecular charge-transfer process according to the acidity of acid, and (ii) the high CT character upon excitation that promotes higher quenching magnitudes and favors a wider pKa range (19.5pKa) for the log KSV versus pKa correlation. Other key principles were to delimit the study to pure proton transfer and nonfluorescent acids, which allowed restricting the quenching response to a process dependent mainly on the acid-base equilibrium. All these findings open a new perspective as a proof of concept to design effective fluorescent pKa probes.

Glycogen Synthase Kinase-3 Maleimide Inhibitors As Potential PET-Tracers for Imaging Alzheimer's Disease: 11C-Synthesis and In Vivo Proof of Concept.

Herein we present the evaluation of 11C-labeled-maleimides as radiotracers for positron emission tomography imaging of GSK-3 associated with Alzheimer's disease (AD). 3-Acetyl-4-(1-[11C]-methyl-1H-indol-3-yl)[1H]pyrrole-2,5-dione ([11C]-2) was obtained by direct methylation using [11C]-CH3I and Cs2CO3 in DMF with a 31 ± 4% radiochemical yield and a radiochemical purity of 97.7 ± 0.8%. [11C]-2 was stable both in its final formulation and in human plasma for 120 min and had a plasma protein binding of 70 ± 1% and a LogD7.4 value of 1.84 ± 0.04. [11C]-2 ex vivo biodistributions in healthy animals demonstrated significant brain uptake and retention, showing its ability to penetrate the intact blood-brain barrier. In vivo PET imaging in mice bearing AD showed, with respect to normal animals, significant differences in uptake in the hypothalamus, the striatum, and the amygdala and a significant increase in amygdala uptake in later stages of the pathology. These results are very promising, and further studies are being performed for a complete validation of this compound as novel tracer for AD.

Preclinical Studies and Drug Combination of Low-Cost Molecules for Chagas Disease.

Chagas disease is caused by the protozoan Trypanosoma cruzi (T. cruzi). It remains the major parasitic disease in Latin America and is spreading worldwide, affecting over 10 million people. Hundreds of new compounds with trypanosomicidal action have been identified from different sources such as synthetic or natural molecules, but they have been deficient in several stages of drug development (toxicology, scaling-up, and pharmacokinetics). Previously, we described a series of compounds with simple structures, low cost, and environmentally friendly production with potent trypanosomicidal activity in vitro and in vivo. These molecules are from three different families: thiazolidenehydrazines, diarylideneketones, and steroids. From this collection, we explored their capacity to inhibit the triosephosphate isomerase and cruzipain of T. cruzi. Then, the mechanism of action was explored using NMR metabolomics and computational molecular dynamics. Moreover, the mechanism of death was studied by flow cytometry. Consequently, five compounds, 314, 793, 1018, 1019, and 1260, were pre-clinically studied and their pharmacologic profiles indicated low unspecific toxicity. Interestingly, synergetic effects of diarylideneketones 793 plus 1018 and 793 plus 1019 were evidenced in vitro and in vivo. In vivo, the combination of compounds 793 plus 1018 induced a reduction of more than 90% of the peak of parasitemia in the acute murine model of Chagas disease.

Development of fluorescent- and radio-traceable T1307-polymeric micelles as biomedical agents for cancer diagnosis: biodistribution on 4T1 tumor-bearing mice

Abstract In recent years, nanocarriers have been studied as promising pharmaceutical tools for controlled drug-delivery, treatment-efficacy follow-up and disease imaging. Among them, X-shaped amphiphilic polymeric micelles (Tetronic®, poloxamines) display great potential due to their biocompatibility and non-toxic effects, among others. In the present work, polymeric micelles based on the T1307 copolymer were initially decorated with a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-fluorophore in order to determinate its in vivo biodistribution on 4T1 tumor-bearing mice. However, unfavorable results with this probe led to two different strategies. On the one hand, the BODIPY-micelle-loaded, L-T1307-BODIPY, and on the other hand, the 99mTc-micelle-radiolabeled, L-T1307- 99m Tc, were analyzed separately in vivo. The results indicated that T1307 accumulates mainly in the stomach, the kidneys, the lungs and the tumor, reaching the maximum organ-accumulation 2 hours after intravenous injection. Additionally, and according to the results obtained for L-T1307- 99m Tc, the capture of the polymeric micelles in organs could be observed up to 24 hours after injection. The results obtained in this work were promising towards the development of new radiotracer agents for breast cancer based on X-shaped polymeric micelles.

Metastatic and non-metastatic melanoma imaging using Sgc8-c aptamer PTK7-recognizer.

Melanoma is one of the most aggressive and deadly skin cancers, and although histopathological criteria are used for its prognosis, biomarkers are necessary to identify the different evolution stages. The applications of molecular imaging include the in vivo diagnosis of cancer with probes that recognize the tumor-biomarkers specific expression allowing external image acquisitions and evaluation of the biological process in quali-quantitative ways. Aptamers are oligonucleotides that recognize targets with high affinity and specificity presenting advantages that make them interesting molecular imaging probes. Sgc8-c (DNA-aptamer) selectively recognizes PTK7-receptor overexpressed in various types of tumors. Herein, Sgc8-c was evaluated, for the first time, in a metastatic melanoma model as molecular imaging probe for in vivo diagnostic, as well as in a non-metastatic melanoma model. Firstly, two probes, radio- and fluorescent-probe, were in vitro evaluated verifying the high specific PTK7 recognition and its internalization in tumor cells by the endosomal route. Secondly, in vivo proof of concept was performed in animal tumor models. In addition, they have rapid clearance from blood exhibiting excellent target (tumor)/non-target organ ratios. Furthermore, optimal biodistribution was observed 24 h after probes injections accumulating almost exclusively in the tumor tissue. Sgc8-c is a potential tool for their specific use in the early detection of melanoma.

Photo-Induced Partially Aromatized Intramolecular Charge Transfer.

Diverse models of intramolecular charge transfer (ICT) have been proposed for interpreting the origin of the charge-transfer (CT) state in donor-acceptor (D-A) dyes. However, a large variety of fused-heterocyclic dyes containing a pseudo-aromatic ring in the rigid structure have shown to be incompatible with them. To approximate a solution within the ICT concept, we reported a novel ICT model called partially aromatized intramolecular charge transfer (PAICT). PAICT involves the generation of a CT state from an ICT that occurred within a pre-excited D-A fused-heterocyclic structure possessing a pseudo-aromatic or unstable aromatic ring as the acceptor moiety. The model was proposed from the multiple-emissive mesomeric D-A N1-aryl-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one, whose excited mesomeric states, which are defined by the aromatic and pseudo-aromatic forms of the pyrindin-4(1H)-one ring, led to a common partial aromatized CT state upon excitation via PAICT. The latter was supported through theoretical calculations on the excited mesomeric states, one-dimensional (1D) and two-dimensional (2D) excitation-emission measurements in different solvents, and the detection of three excited states by lifetime measurements upon 370 nm excitation. The existence of mesomerism was supposed from: (i) two overlapping bands at 370-390 (or 400-420 nm) in UV-vis spectra, (ii) the direct interaction between the pyridinic nitrogen of one molecule and the carbonylic oxygen of the other found in the solid state and, (iii) the detection of three excited states by lifetime measurements. The PAICT opens new perspectives for interpreting the charge-transfer phenomenon in fused-heterocyclic dyes, in particular, those containing a pseudo-aromatic or unstable aromatic ring as an acceptor moiety.