Syntheses of D-Glucose Derivatives Emitting Blue Fluorescence through Pd-Catalyzed C-N Coupling

Synthesis and characterization of coumarin containing fluorescent sugar based gelators

Carbohydrate based self-assembling systems containing coumarin functional groups are interesting class of materials. The unique fluorescence properties can be useful for many practical applications especially as biological probes. Coumarin containing low molecular weight gelators are especially interesting compounds with great potentials for new advanced molecular systems with multiple functions. We have synthesized and characterized a series of eleven coumarin based glucose and glucosamine derivatives. The structures of these compounds are based on the existing good performing supramolecular gelators through rational designs. These include three coumarin derivatives linked to anomeric positons of per-acetylated D-glucose and D-glucosamine via 1,2,3-triazole linkage , and eight4,6-benzylidene acetal protected D-glucosamine derivatives with various coumarin moieties attached to the C-2 positions through several different linkers. The gelation properties and fluorescence properties of these novel coumarin derivatives are studied and several self-assembling coumarin derivatives are also molecular gelators, which may have wide range of applications.

Asymmetric cell division of ALDH1-positive cancer stem cells generates glycolytic metabolically diverse cell populations

Metabolic heterogeneity in various cancer cells within a tumor causes resistance to medical therapies and promotes tumor recurrence and metastasis. However, the mechanisms by which tumors acquire metabolic heterogeneity are poorly understood. Here, we revealed that PKCλ-dependent asymmetric division of ALDH1-positive cancer stem cells (CSCs) led to an uneven distribution of glycolytic capacity, which is crucial for understanding metabolic heterogeneity within a tumor. The rate-limiting enzyme PFKP and the metabolic probe CDG in glycolysis codistributed with the ALDH1A3 protein during the post-cell division phase, highlighting a mechanism for acquiring metabolic diversity. PKCλ deficiency reduced the asymmetric distribution of these proteins in ALDH1high cells with high ALDH1 activity, suggesting a fundamental role for PKCλ in metabolic heterogeneity. We identified 28 distinct distribution patterns combining PFKP and CDG distributions, demonstrating the complexity of glycolytic heterogeneity. Furthermore, validation and prediction of cell distribution patterns via a probabilistic model confirmed that PKCλ deficiency diminished glycolytic diversity in individual cells within a cancer cell colony generated from an ALDH1-positive CSC. These findings suggest that PKCλ-dependent asymmetric cell division of ALDH1-positive CSCs is crucial for glycolytic heterogeneity in cancer cells within a tumor, potentially offering new therapeutic targets against tumor resistance and metastasis.

BNCT pancreatic cancer treatment strategy with glucose-conjugated boron drug

Multidisciplinary therapy centered on radical surgery for resectable pancreatic cancer is expected to prolong prognosis, but relies on CA19-9 biomarker levels to determine treatment strategy. Boron neutron capture therapy (BNCT) is a chemoradiotherapy using tumor hyperaccumulator boron drugs and neutron irradiation. The purpose of this study is to investigate novel boron drug agents for BNCT for pancreatic cancer. Bioinformatics was used to evaluate the uptake of current boron amino acid (BPA) drugs for BNCT into pancreatic cancer. The expression of the amino acid transporter LAT1, a BPA uptake transporter, was low in pancreatic cancer and even lower in high CA19-9 pancreatic cancer. In contrast, the glucose transporter was high in high CA19-9 pancreatic cancers and inversely correlated with LAT1 expression. Considering the low EPR effect in pancreatic cancer, we synthesized a small molecule Glucose-BSH, which is boron BSH bound to glucose, and confirmed its specific uptake in pancreatic cancer. uptake of Glucose-BSH was confirmed in an environment compatible with the tumor microenvironment. The therapeutic efficacy and safety of Glucose-BSH by therapeutic neutron irradiation were confirmed with BNCT. We report Glucose-BSH boron drug discovery study of a Precision Medicine BNCT with application to high CA19-9 pancreatic cancer.

Turn-on Rhodamine Glycoconjugates Enable Real-Time GLUT Activity Monitoring in Live Cells and In Vivo

The direct relationship between facilitative glucose transporters (GLUTs) and metabolic diseases opens new avenues for sensing metabolic deregulations and drives the development of molecular probes for GLUT-targeted detection of metabolic diseases. Radiotracer-based molecular imaging probes have been effectively utilized in reporting alterations in sugar uptake as an indication of metabolic deregulations, cancer development, or inflammation. Progress in developing fluorophore-based tools facilitated GLUT-specific analyses using more accessible fluorescence-based instrumentation. However, restrictions on the emission range of fluorophores and the requirement for substantial post-treatments to reduce background fluorescence have brought to light the critical directions for improvement of the technology for broader use in screening applications. Here we present turn-on GLUT activity reporters activated upon cells' internalization. We demonstrate a specific delivery of a sizable rhodamine B fluorophore through GLUT5 and showcase a stringent requirement in conjugate structure for maintaining a GLUT-specific uptake. With the turn-on GLUT probes, we demonstrate the feasibility of high-throughput fluorescence microscopy and flow cytometry-based GLUT activity screening in live cells and the probes' applicability for assessing sugar uptake alterations in vivo.

Late-Stage Functionalization through Click Chemistry Provides GLUT5-Targeting Glycoconjugate as a Potential PET Imaging Probe

The targeting of facilitative sugar transporters (GLUTs) has been utilized in the development of tools for diagnostics and therapy. The interest in this area is promoted by the phenomenon of alterations in cellular metabolic processes that are linked to multitudes of metabolic disorders and diseases. However, nonspecific targeting (e.g., glucose-transporting GLUTs) leads to a lack of disease detection efficiency. Among GLUTs, GLUT5 stands out as a prominent target for developing specific molecular tools due to its association with metabolic diseases, including cancer. This work reports a non-radiolabeled fluoride (19F) coumarin-based glycoconjugate of 2,5-anhydro-D-mannitol as a potential PET imaging probe that targets the GLUT5 transporter. Inherent fluorescent properties of the coumarin fluorophore allowed us to establish the probe's uptake efficiency and GLUT5-specificity in a GLUT5-positive breast cell line using fluorescence detection techniques. The click chemistry approach employed in the design of the probe enables late-stage functionalization, an essential requirement for obtaining the radiolabeled analog of the probe for future in vivo cancer imaging applications. The high affinity of the probe to GLUT5 allowed for the effective uptake in nutrition-rich media.

Uptake of fluorescent D- and L-glucose analogues, 2-NBDG and 2-NBDLG, into human osteosarcoma U2OS cells in a phloretin-inhibitable manner

Mammalian cells take in d-glucose as an essential fuel as well as a carbon source. In contrast, l-glucose, the mirror image isomer of d-glucose, has been considered merely as a non-transportable/non-metabolizable control for d-glucose. We have shown that 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a d-glucose analogue combining a fluorophore NBD at the C-2 position, is useful as a tracer for monitoring d-glucose uptake through glucose transporters (GLUTs) into mammalian cells. To more precisely evaluate the stereoselectivity of 2-NBDG uptake, we developed an l-glucose analogue 2-NBDLG, the mirror-image isomer of 2-NBDG. Interestingly, 2-NBDLG was taken up into mouse insulinoma MIN6 cells showing nuclear heterogeneity, a cytological feature of malignancy, while remaining MIN6 cells only exhibited a trace amount of 2-NBDLG uptake. The 2-NBDLG uptake into MIN6 cells was abolished by phloretin, but persisted under blockade of major mammalian glucose transporters. Unfortunately, however, no such uptake could be detected in other tumor cell lines. Here we demonstrate that human osteosarcoma U2OS cells take in 2-NBDLG in a phloretin-inhibitable manner. The uptake of 2-NBDG, and not that of 2-NBDLG, into U2OS cells was significantly inhibited by cytochalasin B, a potent GLUT inhibitor. Phloretin, but neither phlorizin, an inhibitor of sodium-glucose cotransporter (SGLT), nor a large amount of d/l-glucose, blocked the 2-NBDLG uptake. These results suggest that a phloretin-inhibitable, non-GLUT/non-SGLT, possibly non-transporter-mediated yet unidentified mechanism participates in the uptake of the fluorescent l-glucose analogue in two very different tumor cells, the mouse insulinoma and the human osteosarcoma cells.

L-Glucose: Another Path to Cancer Cells

Cancerous tumors comprise cells showing metabolic heterogeneity. Among numerous efforts to understand this property, little attention has been paid to the possibility that cancer cells take up and utilize otherwise unusable substrates as fuel. Here we discuss this issue by focusing on l-glucose, the mirror image isomer of naturally occurring d-glucose; l-glucose is an unmetabolizable sugar except in some bacteria. By combining relatively small fluorophores with l-glucose, we generated fluorescence-emitting l-glucose tracers (fLGs). To our surprise, 2-NBDLG, one of these fLGs, which we thought to be merely a control substrate for the fluorescent d-glucose tracer 2-NBDG, was specifically taken up into tumor cell aggregates (spheroids) that exhibited nuclear heterogeneity, a major cytological feature of malignancy in cancer diagnosis. Changes in mitochondrial activity were also associated with the spheroids taking up fLG. To better understand these phenomena, we review here the Warburg effect as well as key studies regarding glucose uptake. We also discuss tumor heterogeneity involving aberrant uptake of glucose and mitochondrial changes based on the data obtained by fLG. We then consider the use of fLGs as novel markers for visualization and characterization of malignant tumor cells.

A sustainable innovation for the tandem synthesis of sugar-containing coumarin derivatives catalyzed by lipozyme TL IM from Thermomyces lanuginosus in continuous-flow microreactors

We developed an efficient and environmentally friendly two-step tandem methodology for the synthesis of sugar-containing coumarin derivatives catalyzed by lipozyme TL IM from Thermomyces lanuginosus in continuous-flow microreactors. Compared to those observed for other methods, the salient features of this work including green reaction conditions, short residence time (50 min), and catalysts are more readily available and the biocatalysis reaction process is efficient and easy to control. This two-step tandem synthesis of coumarin derivatives using the continuous-flow technology is a proof of concept that opens the use of enzymatic microreactors in coumarin derivative biotransformations.

An effective and environmentally friendly two-step tandem protocol for the synthesis of sugar-containing coumarin derivatives catalyzed by lipozyme TL IM in continuous-flow microreactors has been developed.

Insights into Substrate and Inhibitor Selectivity among Human GLUT Transporters through Comparative Modeling and Molecular Docking

The solute carrier 2 family is composed of 14 transporters, which are members of the major facilitator superfamily. Despite their high physiological importance, there are still many open questions concerning their function and specificity, and in some cases, their physiological substrate is still unknown. To understand the determinants of the substrate and inhibitor specificity, we modeled all human glucose transport carriers (GLUTs) and simulated their interaction with known ligands. Comparative modeling was performed with the @TOME-2 pipeline, employing multiple templates and providing an ensemble of models for each GLUT. We analyzed models in both outward-occluded and inward-open conformations, to compare exofacial and endofacial binding sites throughout the family and understand differences in susceptibility of GLUTs to the inhibitor cytochalasin B. Finally, we employed molecular docking and bioinformatics to identify residues likely critical for recognition of myo-inositol by GLUT13 and urate by GLUT9. These results provide insights into the molecular basis for the specificity for these substrates. In addition, we suggested a potential recognition site of glucosamine by GLUT11 to be evaluated in future experiments.

Aberrant Uptake of a Fluorescent L-Glucose Analogue (fLG) into Tumor Cells Expressing Malignant Phenotypes

Glucose, one of the most fundamental sugar elements, has either D- or L-conformation. Of these, most cells preferentially take up D-glucose as an essential energy/carbon source. Such stereoselective uptake of glucose has been explored by fluorophore-bearing D- and L-glucose analogues. 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), the most widely used fluorescent D-glucose analogue, was abundantly taken up into living Escherichia coli cells, whereas no detectable uptake was obtained for 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-L-glucose (2-NBDLG), the antipode of 2-NBDG developed as a fluorescent L-glucose analogue (fLG). Interestingly, we found three-dimensionally accumulating tumor cell aggregates taking up 2-NBDLG when they expressed nuclear heterogeneity, one of the major cytological criteria for cells suspected of high-grade malignancy in clinical diagnosis. 2-NBDLG uptake was not detected in aggregates consisting of homogeneous cells and was specifically abolished by phloretin, a broad-spectrum inhibitor against transporters/channels. Preliminary studies have suggested that a combined use of 2-NBDLG, which emits green fluorescence, with 13-[4-[(2-deoxy-D-glucopyranose-2-yl)aminosulfonyl]-2-sulfonatophenyl]-4,5-trimethylene-7,8-trimethylene-1,2,3,4,6,9,10,11-octahydro-4-aza-6-oxa-8-azoniapentacene (2-TRLG), a membrane-impermeable fLG bearing a large red fluorophore, is effective for discriminating malignant tumor from benign cells both in living biopsy specimens endoscopically dissected from patients with early-stage gastric cancer and in ascites fluid of patients with gynecological cancers. Confocal endomicroscopic imaging of a carcinogen-induced cancer in bile duct of hamsters indicated that the fLG uptake pattern well correlated with pathological diagnosis for carcinoma. Safety tests according to Good Laboratory Practice regulations have been successfully completed so far. fLGs are unique fluorescent glucose analogues for identifying and characterizing living cancer cells based on derangements in their transport function.

High Photostability in Nonconventional Coumarins with Far-Red/NIR Emission through Azetidinyl Substitution

Replacement of electron-donating N,N-dialkyl groups with three- or four-membered cyclic amines (e.g., aziridine and azetidine, respectively) has been described as a promising approach to improve some of the drawbacks of conventional fluorophores, including low fluorescent quantum yields (Φ_F) in polar solvents. In this work, we have explored the influence of azetidinyl substitution on nonconventional coumarin-based COUPY dyes. Two azetidine-containing scaffolds were first synthesized in four linear synthetic steps and easily transformed into far-red/NIR-emitting fluorophores through N-alkylation of the pyridine moiety. Azetidine introduction in COUPY dyes resulted in enlarged Stokes' shifts with respect to the N,N-dialkylamino-containing parent dyes, but the Φ_F were not significantly modified in aqueous media, which is in contrast with previously reported observations in other fluorophores. However, azetidinyl substitution led to an unprecedented improvement in the photostability of COUPY dyes, and high cell permeability was retained since the fluorophores accumulated selectively in mitochondria and nucleoli of HeLa cells. Overall, our results provide valuable insights for the design and optimization of novel fluorophores operating in the far-red/NIR region, since we have demonstrated that three important parameters (Stokes' shifts, Φ_F, and photostability) cannot be always simultaneously addressed by simply replacing a N,N-dialkylamino group with azetidine, at least in nonconventional coumarin-based fluorophores.

Multicolor GLUT5-permeable fluorescent probes for fructose transport analysis

The specificity of carbohydrate transporters towards their substrates poses a significant challenge for the development of molecular probes to monitor sugar uptake in cells for biochemical and biomedical applications. Herein we report a new set of coumarin-based fluorescent sugar conjugates applicable for the analysis of fructose uptake due to their free passage through the fructose-specific transporter GLUT5. The reported probes cover a broad range of the fluorescence spectrum providing essential tools for the evaluation of fructose transport capacity in live cells.

Metabolism-Driven High-Throughput Cancer Identification with GLUT5-Specific Molecular Probes

Point-of-care applications rely on biomedical sensors to enable rapid detection with high sensitivity and selectivity. Despite advances in sensor development, there are challenges in cancer diagnostics. Detection of biomarkers, cell receptors, circulating tumor cells, gene identification, and fluorescent tagging are time-consuming due to the sample preparation and response time involved. Here, we present a novel approach to target the enhanced metabolism in breast cancers for rapid detection using fluorescent imaging. Fluorescent analogs of fructose target the fructose-specific transporter GLUT5 in breast cancers and have limited to no response from normal cells. These analogs demonstrate a marked difference in adenocarcinoma and premalignant cells leading to a novel detection approach. The vastly different uptake kinetics of the analogs yields two unique signatures for each cell type. We used normal breast cells MCF10A, adenocarcinoma cells MCF7, and premalignant cells MCF10AneoT, with hepatocellular carcinoma cells HepG2 as the negative control. Our data indicated that MCF10AneoT and MCF7 cells had an observable difference in response to only one of the analogs. The response, observed as fluorescence intensity, leads to a two-point assessment of the cells in any sample. Since the treatment time is 10 min, there is potential for use in rapid on-site high-throughput diagnostics.