Photothermal Attenuation of Cancer Cell Stemness, Chemoresistance, and Migration Using CD44-Targeted MoS2 Nanosheets.

Cancer stem-like cells (CSCs) play key roles in chemoresistance, tumor metastasis, and clinical relapse. However, current CSC inhibitors lack specificity, efficacy, and applicability to different cancers. Herein, we introduce a nanomaterial-based approach to photothermally induce the differentiation of CSCs, termed "photothermal differentiation", leading to the attenuation of cancer cell stemness, chemoresistance, and metastasis. MoS2 nanosheets and a moderate photothermal treatment were applied to target a CSC surface receptor (i.e., CD44) and modulate its downstream signaling pathway. This treatment forces the more stem-like cancer cells to lose the mesenchymal phenotype and adopt an epithelial, less stem-like state, which shows attenuated self-renewal capacity, more response to anticancer drugs, and less invasiveness. This approach could be applicable to various cancers due to the broad availability of the CD44 biomarker. The concept of using photothermal nanomaterials to regulate specific cellular activities driving the differentiation of CSCs offers a new avenue for treating refractory cancers.

Transmembrane MUC18 Targeted Polydopamine Nanoparticles and a Mild Photothermal Effect Synergistically Disrupt Actin Cytoskeleton and Migration of Cancer Cells.

Transmembrane MUC18 is highly expressed on most metastatic cancers. Herein, we demonstrate that targeting MUC18 with polydopamine nanoparticles (PDA NPs) and a mild photothermal effect can completely cease the migration of melanoma and breast cancer cells without killing the cells. The inhibited cell migration can be attributed to the altered actin cytoskeleton, cell stiffness, and cell morphology, as revealed by nanomechanical and super resolution fluorescence imaging techniques. Further mechanistic studies at the molecular level show that MUC18 targeted PDA NPs and a mild photothermal treatment produce a synergistic effect on the actin cytoskeleton by downregulating the transmembrane MUC18 and interrupting ezrin-radixin-moesin phosphorylation, thereby releasing the actin cytoskeleton from the cell membrane and compromising force transduction through the actin cytoskeleton to the transmembrane MUC18. Overall, the concept of targeting transmembrane metastatic markers and disrupting their downstream effectors (i.e., actin and actin-binding proteins) opens up a new avenue to cancer therapy.

Bioplasmonic paper-based assay for perilipin-2 non-invasively detects renal cancer.

Renal cell carcinoma (RCC) has poor survival prognosis because it is asymptomatic at an early, more curative stage. Recently, urine perilipin-2 (PLIN-2) was demonstrated to be a sensitive and specific biomarker for the noninvasive, early detection of RCC and an indispensable indicator to distinguish cancer from a benign renal mass. However, current Western blot or ELISA PLIN-2 assays are complicated, expensive, time-consuming or insensitive, making them unsuitable for routine analysis in clinical settings. Here we developed a plasmonic biosensor based on the high refractive index sensitivity of gold nanorattles for the rapid detection of PLIN-2 in patient urine. The paper-based plasmonic assay is highly sensitive and has a dynamic range of 50 pg/ml to 5 µg/ml PLIN-2. The assay is not compromised by variations in urine pH or high concentrations of interfering proteins such as albumin and hemoglobin, making it an excellent candidate for routine clinical applications. The urine PLIN-2 assay readily distinguished patients with pathologically proven clear cell carcinomas of various size, stage and grade (55.9 [39.5, 75.8] ng/ml, median [1st and 3rd quartile]) from age-matched controls (0.3 [0.3, 0.5] ng/ml), patients with bladder cancer (0.5 [0.4, 0.6] ng/ml) and patients with diabetic nephropathy (0.6 [0.4, 0.7] ng/ml). Urine PLIN-2 concentrations were roughly proportional to tumor size (Pearson coefficient 0.59). Thus, this cost-effective and label-free method represents a novel approach to conduct a non-invasive population screen or rapid differential diagnosis of imaged renal masses, significantly facilitating the early detection and diagnosis of RCC.

Single Molecule Force Spectroscopy to Compare Natural versus Artificial Antibody-Antigen Interaction.

Biorecognition is central to various biological processes and finds numerous applications in virtually all areas of chemistry, biology, and medicine. Artificial antibodies, produced by imprinting synthetic polymers, are designed to mimic the biological recognition capability of natural antibodies, while exhibiting superior thermal, chemical, and environmental stability compared to their natural counterparts. The binding affinity of the artificial antibodies to their antigens characterizes the biorecognition ability of these synthetic nanoconstructs and their ability to replace natural recognition elements. However, a quantitative study of the binding affinity of an artificial antibody to an antigen, especially at the molecular level, is still lacking. In this study, using atomic force microscopy-based force spectroscopy, the authors show that the binding affinity of an artificial antibody to an antigen (hemoglobin) is weaker than that of natural antibody. The fine difference in the molecular interactions manifests into a significant difference in the bioanalytical parameters of biosensors based on these recognition elements.

Investigation of the heparin-thrombin interaction by dynamic force spectroscopy.

BACKGROUND: The interaction between heparin and thrombin is a vital step in the blood (anti)coagulation process. Unraveling the molecular basis of the interactions is therefore extremely important in understanding the mechanisms of this complex biological process. METHODS: In this study, we use a combination of an efficient thiolation chemistry of heparin, a self-assembled monolayer-based single molecule platform, and a dynamic force spectroscopy to provide new insights into the heparin-thrombin interaction from an energy viewpoint at the molecular scale. RESULTS: Well-separated single molecules of heparin covalently attached to mixed self-assembled monolayers are demonstrated, whereby interaction forces with thrombin can be measured via atomic force microscopy-based spectroscopy. Further these interactions are studied at different loading rates and salt concentrations to directly obtain kinetic parameters. CONCLUSIONS: An increase in the loading rate shows a higher interaction force between the heparin and thrombin, which can be directly linked to the kinetic dissociation rate constant (koff). The stability of the heparin/thrombin complex decreased with increasing NaCl concentration such that the off-rate was found to be driven primarily by non-ionic forces. GENERAL SIGNIFICANCE: These results contribute to understanding the role of specific and nonspecific forces that drive heparin-thrombin interactions under applied force or flow conditions.

Real-Time Observation of Antimicrobial Polycation Effects on Escherichia coli: Adapting the Carpet Model for Membrane Disruption to Quaternary Copolyoxetanes.

Real-time atomic force microscopy (AFM) was used for analyzing effects of the antimicrobial polycation copolyoxetane P[(C12)-(ME2Ox)-50/50], C12-50 on the membrane of a model bacterium, Escherichia coli (ATCC# 35218). AFM imaging showed cell membrane changes with increasing C12-50 concentration and time including nanopore formation and bulges associated with outer bacterial membrane disruption. A macroscale bactericidal concentration study for C12-50 showed a 4 log kill at 15 µg/mL with conditions paralleling imaging (1 h, 1x PBS, physiological pH, 25 °C). The dramatic changes from the control image to 1 h after introducing 15 µg/mL C12-50 are therefore reasonably attributed to cell death. At the highest concentration (60 µg/mL) further cell membrane disruption results in leakage of cytoplasm driven by detergent-like action. The sequence of processes for initial membrane disruption by the synthetic polycation C12-50 follows the carpet model posited for antimicrobial peptides (AMPs). However, the nanoscale details are distinctly different as C12-50 is a synthetic, water-soluble copolycation that is best modeled as a random coil. In a complementary AFM study, chemical force microscopy shows that incubating cells with C12-50 decreased the hydrophobicity across the entire cell surface at an early stage. This finding provides additional evidence indicating that C12-50 polycations initially bind with the cell membrane in a carpet-like fashion. Taken together, real time AFM imaging elucidates the mechanism of antimicrobial action for copolyoxetane C12-50 at the single cell level. In future work this approach will provide important insights into structure-property relationships and improved antimicrobial effectiveness for synthetic amphiphilic polycations.

The effect of growth temperature on the nanoscale biochemical surface properties of Yersinia pestis.

Yersinia pestis, the causative agent of plague, has been responsible for several recurrent, lethal pandemics in history. Currently, it is an important pathogen to study owing to its virulence, adaptation to different environments during transmission, and potential use in bioterrorism. Here, we report on the changes to Y. pestis surfaces in different external microenvironments, specifically culture temperatures (6, 25, and 37 °C). Using nanoscale imaging coupled with functional mapping, we illustrate that changes in the surfaces of the bacterium from a morphological and biochemical standpoint can be analyzed simultaneously using atomic force microscopy. The results from functional mapping, obtained at a single cell level, show that the density of lipopolysaccharide (measured via terminal N-acetylglucosamine) on Y. pestis grown at 37 °C is only slightly higher than cells grown at 25 °C, but nearly three times higher than cells maintained at 6 °C for an extended period of time, thereby demonstrating that adaptations to different environments can be effectively captured using this technique. This nanoscale evaluation provides a new microscopic approach to study nanoscale properties of bacterial pathogens and investigate adaptations to different external environments.

Morphological and mechanical imaging of Bacillus cereus spore formation at the nanoscale.

Bacteria from the genus Bacillus are able to transform into metabolically dormant states called (endo) spores in response to nutrient deprivation and other harsh conditions. These morphologically distinct spores are fascinating constructs, amongst the most durable cells in nature, and have attracted attention owing to their relevance in food-related illnesses and bioterrorism. Observing the course of bacterial spore formation (sporulation) spatially, temporally and mechanically, from the vegetative cell to a mature spore, is critical for a better understanding of this process. Here, we present a fast and versatile strategy for monitoring both the morphological and mechanical changes of Bacillus cereus bacteria at the nanoscale using atomic force microscopy. Through a strategy of imaging and nanomechanical mapping, we show the morphogenesis of the endospore and released mature endospore. Finally, we investigate individual spores to characterize their surface mechanically. The progression in elasticity coupled with a similarity of characteristic distributions between the incipient endospores and the formed spores show these distinct stages. Taken together, our data demonstrates the power of atomic force microscopy applied in microbiology for probing this important biological process at the single cell scale.

Mechanism of inhibition of the GluA1 AMPA receptor channel opening by the 2,3-benzodiazepine compound GYKI 52466 and a N-methyl-carbamoyl derivative.

2,3-Benzodiazepine derivatives, also known as GYKI compounds, represent a group of the most promising synthetic inhibitors of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Here we investigate the mechanism of inhibition of the GluA1 channel opening and the site of inhibition by GYKI 52466 and its N-3 methyl-carbamoyl derivative, which we term as BDZ-f. GluA1 is a key AMPA receptor subunit involved in the brain function. Excessive activity and elevated expression of GluA1, however, has been implicated in a number of neurological disorders. Using a laser-pulse photolysis technique, which provides ∼60 µs resolution, we measured the effect of these inhibitors on the rate of GluA1 channel opening and the amplitude of the glutamate-induced whole-cell current. We found that both compounds inhibit GluA1 channel noncompetitively. Addition of an N-3 methyl-carbamoyl group to the diazepine ring with the azomethine feature (i.e., GYKI 52466) improves the potency of the resulting compound or BDZ-f without changing the site of binding. This site, which we previously termed as the "M" site on the GluA2 AMPA receptor subunit, therefore favorably accommodates an N-3 acylating group. On the basis of the magnitude of the inhibition constants for the same inhibitors but different receptors, the "M" sites on GluA1 and GuA2 are different. Overall, the "M" site or the binding environment on GluA2 accommodates the same compounds better, or the same inhibitors show stronger potency on GluA2, as we have reported previously [ Wang et al. Biochemistry ( 2011 ) 50 , 7284 - 7293 ]. However, acylating the N-3 position to occupy the N-3 side pocket of the "M" site can significantly narrow the difference and improve the potency of a resulting compound on GluA1.

Spatial recognition and mapping of proteins using DNA aptamers.

Atomic force microscopy-based adhesion force measurements have emerged as a powerful tool for the biophysical analyses of biological systems. Such measurements can now be extended to detection and mapping of biomolecules on surfaces via integrated imaging and force spectroscopy techniques. Critical to these experiments is the choice of the biomolecular recognition probe. In this study, we demonstrate how oligonucleotide aptamers can be used as versatile probes to simultaneously image and spatially locate targets on surfaces. We focus on two structurally distinct proteins relevant to the clotting cascade - human α-thrombin and vascular endothelial growth factor. Via AFM-recognition mapping using specific DNA aptamers on a commercially available instrument, we show a clear consistency between height and force measurements obtained simultaneously. Importantly, we are able to observe changes in binding due to changes in the external microenvironment, which demonstrate the ability to study fluctuating biological systems in real time. The aptamer specificity and the ability to distinguish their targets are shown through positive and negative controls. It is therefore possible to generate high resolution maps to spatially and temporally identify proteins at the molecular level on complex surfaces.

N-Cadherin Targeted Melanin Nanoparticles Reverse the Endothelial-Mesenchymal Transition in Vascular Endothelial Cells to Potentially Slow the Progression of Atherosclerosis and Cancer.

Endothelial-mesenchymal transition (EndoMT) of vascular endothelial cells has recently been considered as a key player in the early progression of a variety of vascular and nonvascular diseases, including atherosclerosis, cancer, and organ fibrosis. However, current strategies attempting to identify pharmacological inhibitors to block the regulatory pathways of EndoMT suffer from poor selectivity, unwanted side effects, and a heterogeneous response from endothelial cells with different origins. Furthermore, EndoMT inhibitors focus on preventing EndoMT, leaving the endothelial cells that have already undergone EndoMT unresolved. Here, we report the design of a simple but powerful nanoparticle system (i.e., N-cadherin targeted melanin nanoparticles) to convert cytokine-activated, mesenchymal-like endothelial cells back to their original endothelial phenotype. We term this process "Reversed EndoMT" (R-EndoMT). R-EndoMT allows the impaired endothelial barriers to recover their quiescence and intactness, with significantly reduced leukocyte and cancer cell adhesion and transmigration, which could potentially stop atheromatous plaque formation and cancer metastasis in the early stages. R-EndoMT is achieved on different endothelial cell types originating from arteries, veins, and capillaries, independent of activating cytokines. We reveal that N-cadherin targeted melanin nanoparticles reverse EndoMT by downregulating an N-cadherin dependent RhoA activation pathway. Overall, this approach offers a different prospect to treat multiple EndoMT-associated diseases by designing nanoparticles to reverse the phenotypical transition of endothelial cells.

Plasmonic biochips with enhanced stability in harsh environments for the sensitive detection of prostate-specific antigen.

Hollow and porous plasmonic nanomaterials have been demonstrated for highly sensitive biosensing applications due to their distinctive optical properties. Immunosensors, which rely on antibody-antigen interactions, are essential constituents of diverse biosensing platforms owing to their exceptional binding affinity and selectivity. The majority of immunosensors and conventional bioassays needs special storage conditions and cold chain systems for transportation. Prostate-specific antigen (PSA), a serine protease, is widely employed in the diagnosis of prostate cancer. In this study, we present the successful utilization of a biopolymer-preserved plasmonic biosensor with improved environmental stability for the sensitive detection of PSA. The preserved plasmonic biosensors exhibited sustained sensitivity in the detection of PSA, achieving a limit of detection of 10 pg mL-1. Furthermore, these biosensors exhibited remarkable stability at elevated temperatures for one week.

Self-decoupled porphyrin with a tripodal anchor for molecular-scale electroluminescence.

A self-decoupled porphyrin with a tripodal anchor has been synthesized and deposited on Au(111) using different wet-chemistry methods. Nanoscale electroluminescence from single porphyrin molecules or aggregates on Au(111) has been realized by tunneling electron excitation. The molecular origin of the luminescence is established by the vibrationally resolved fluorescence spectra observed. The rigid tripodal anchor not only acts as a decoupling spacer but also controls the orientation of the molecule. Intense molecular electroluminescence can be obtained from the emission enhancement provided by a good coupling between the molecular transition dipole and the axial nanocavity plasmon. The unipolar performance of the electroluminescence from the designed tripodal molecule suggests that the porphyrin molecule is likely to be excited by the injection of hot electrons, and then the excited state decays radiatively through Franck-Condon π*-π transitions. These results open up a new route to generating electrically driven nanoscale light sources.

Low-dose albumin-coated gold nanorods induce intercellular gaps on vascular endothelium by causing the contraction of cytoskeletal actin.

Cytotoxicity of nanoparticles, typically evaluated by biochemical-based assays, often overlook the cellular biophysical properties such as cell morphology and cytoskeletal actin, which could serve as more sensitive indicators for cytotoxicity. Here, we demonstrate that low-dose albumin-coated gold nanorods (HSA@AuNRs), although being considered noncytotoxic in multiple biochemical assays, can induce intercellular gaps and enhance the paracellular permeability between human aortic endothelial cells (HAECs). The formation of intercellular gaps can be attributed to the changed cell morphology and cytoskeletal actin structures, as validated at the monolayer and single cell levels using fluorescence staining, atomic force microscopy, and super-resolution imaging. Molecular mechanistic study shows the caveolae-mediated endocytosis of HSA@AuNRs induces the calcium influx and activates actomyosin contraction in HAECs. Considering the important roles of endothelial integrity/dysfunction in various physiological/pathological conditions, this work suggests a potential adverse effect of albumin-coated gold nanorods on the cardiovascular system. On the other hand, this work also offers a feasible way to modulate the endothelial permeability, thus promoting drug and nanoparticle delivery across the endothelium.

"Non-cytotoxic" doses of metal-organic framework nanoparticles increase endothelial permeability by inducing actin reorganization.

Cytotoxicity of nanoparticles is routinely characterized by biochemical assays such as cell viability and membrane integrity assays. However, these approaches overlook cellular biophysical properties including changes in the actin cytoskeleton, cell stiffness, and cell morphology, particularly when cells are exposed to "non-cytotoxic" doses of nanoparticles. Zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs), a member of metal-organic framework family, has received increasing interest in various fields such as environmental and biomedical sciences. ZIF-8 NPs may enter the blood circulation system after unintended oral and inhalational exposure or intended intravenous injection for diagnostic and therapeutic applications, yet the effect of ZIF-8 NPs on vascular endothelial cells is not well understood. Here, the biophysical impact of "non-cytotoxic" dose ZIF-8 NPs on human aortic endothelial cells (HAECs) is investigated. We demonstrate that "non-cytotoxic" doses of ZIF-8 NPs, pre-defined by a series of biochemical assays, can increase the endothelial permeability of HAEC monolayers by causing cell junction disruption and intercellular gap formation, which can be attributed to actin reorganization within adjacent HAECs. Nanomechanical atomic force microscopy and super resolution fluorescence microscopy further confirm that "non-cytotoxic" doses of ZIF-8 NPs change the actin structure and cell morphology of HAECs at the single cell level. Finally, the underlying mechanism of actin reorganization induced by the "non-cytotoxic" dose ZIF-8 NPs is elucidated. Together, this study indicates that the "non-cytotoxic" doses of ZIF-8 NPs, intentionally or unintentionally introduced into blood circulation, may still pose a threat to human health, considering increased endothelial permeability is essential to the progression of a variety of diseases. From a broad view of cytotoxicity evaluation, it is important to consider the biophysical properties of cells, since they can serve as novel and more sensitive markers to assess nanomaterial's cytotoxicity.

Channel-opening kinetic mechanism of wild-type GluK1 kainate receptors and a C-terminal mutant.

GluK1 is a kainate receptor subunit in the ionotropic glutamate receptor family and can form functional channels when expressed, for instance, in HEK-293 cells. However, the channel-opening mechanism of GluK1 is poorly understood. One major challenge to studying the GluK1 channel is its apparent low level of surface expression, which results in a low whole-cell current response even to a saturating concentration of agonist. A low level of surface expression is thought to be contributed by an endoplasmic reticulum (ER) retention signal sequence. When this sequence motif is present as in the C-terminus of wild-type GluK1-2b, the receptor is significantly retained in the ER. Conversely, when this sequence is either lacking, as in wild-type GluK1-2a (i.e., a different alternatively spliced isoform at the C-terminus), or disrupted, as in a GluK1-2b mutant (i.e., R896A, R897A, R900A, and K901A), there is a higher level of surface expression and a greater whole-cell current response. Here we characterize the channel-opening kinetic mechanism for these three GluK1 receptors expressed in HEK-293 cells by using a laser-pulse photolysis technique. Our results show that wild-type GluK1-2a, wild-type GluK1-2b, and the GluK1-2b mutant have identical channel opening and channel closing rate constants. These results indicate that the amino acid sequence near or within the C-terminal ER retention signal sequence, which affects receptor trafficking and/or expression, does not affect channel gating properties. Furthermore, as compared with the GluK2 kainate receptor, the GluK1 channel is faster to open, close, and desensitize by at least 2-fold, yet the EC(50) value of GluK1 is similar to that of GluK2.

Potent and selective inhibition of a single alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit by an RNA aptamer.

Inhibitors of AMPA-type glutamate ion channels are useful as biochemical probes for structure-function studies and as drug candidates for a number of neurological disorders and diseases. Here, we describe the identification of an RNA inhibitor or aptamer by an in vitro evolution approach and a characterization of its mechanism of inhibition on the sites of interaction by equilibrium binding and on the receptor channel opening rate by a laser-pulse photolysis technique. Our results show that the aptamer is a noncompetitive inhibitor that selectively inhibits the GluA2Q(flip) AMPA receptor subunit without any effect on other AMPA receptor subunits or kainate or NMDA receptors. On the GluA2 subunit, this aptamer preferentially inhibits the flip variant. Furthermore, the aptamer preferentially inhibits the closed-channel state of GluA2Q(flip) with a K(I) = 1.5 µM or by ∼15-fold over the open-channel state. The potency and selectivity of this aptamer rival those of small molecule inhibitors. Together, these properties make this aptamer a promising candidate for the development of water-soluble, highly potent, and GluA2 subunit-selective drugs.

Reversing the Epithelial-Mesenchymal Transition in Metastatic Cancer Cells Using CD146-Targeted Black Phosphorus Nanosheets and a Mild Photothermal Treatment.

Cancer metastasis leads to most deaths in cancer patients, and the epithelial-mesenchymal transition (EMT) is the key mechanism that endows the cancer cells with strong migratory and invasive abilities. Here, we present a nanomaterial-based approach to reverse the EMT in cancer cells by targeting an EMT inducer, CD146, using engineered black phosphorus nanosheets (BPNSs) and a mild photothermal treatment. We demonstrate this approach can convert highly metastatic, mesenchymal-type breast cancer cells to an epithelial phenotype (i.e., reversing EMT), leading to a complete stoppage of cancer cell migration. By using advanced nanomechanical and super-resolution imaging, complemented by immunoblotting, we validate the phenotypic switch in the cancer cells, as evidenced by the altered actin organization and cell morphology, downregulation of mesenchymal protein markers, and upregulation of epithelial protein markers. We also elucidate the molecular mechanism behind the reversal of EMT. Our results reveal that CD146-targeted BPNSs and a mild photothermal treatment synergistically contribute to EMT reversal by downregulating membrane CD146 and perturbing its downstream EMT-related signaling pathways. Considering CD146 overexpression has been confirmed on the surface of a variety of metastatic, mesenchymal-like cancer cells, this approach could be applicable for treating various cancer metastasis via modulating the phenotype switch in cancer cells.

Spectral characterization of cell surface motion for mechanistic investigations of cellular mechanobiology.

Understanding the specific mechanisms responsible for anabolic and catabolic responses to static or dynamic force are largely poorly understood. Because of this, most research groups studying mechanotransduction due to dynamic forces employ an empirical approach in deciding what frequencies to apply during experiments. While this has been shown to elucidate valuable information regarding how cells respond under controlled provocation, it is often difficult or impossible to determine a true optimal frequency for force application, as many intracellular complexes are involved in receiving, propagating, and responding to a given stimulus. Here we present a novel adaptation of an analytical technique from the fields of civil and mechanical engineering that may open the door to direct measurement of mechanobiological cellular frequencies which could be used to target specific cell signaling pathways leveraging synergy between outside-in and inside-out mechanotransduction approaches. This information could be useful in identifying how specific proteins are involved in the homeostatic balance, or disruption thereof, of cells and tissue, furthering the understanding of the pathogenesis and progression of many diseases across a wide variety of cell types, which may one day lead to the development of novel mechanobiological therapies for clinical use.

Mechanism of inhibition of the GluA2 AMPA receptor channel opening: consequences of adding an N-3 methylcarbamoyl group to the diazepine ring of 2,3-benzodiazepine derivatives.

2,3-Benzodiazepine derivatives are AMPA receptor inhibitors, and they are potential drugs for treating some neurological diseases caused by excessive activity of AMPA receptors. Using a laser-pulse photolysis and rapid solution flow techniques, we characterized the mechanism of action of a 2,3-benzodiazepine derivative, termed BDZ-f, by measuring its inhibitory effect on the channel-opening and channel-closing rate constants as well as the whole-cell current amplitude of the homomeric GluA2Q AMPA receptor channels. We also investigated whether BDZ-f competes with GYKI 52466 for binding to the same site on GluA2Q(flip). GYKI 52466 is the prototypic 2,3-benzodiazepine compound, and BDZ-f is the N-3 methylcarbamoyl derivative. We found that BDZ-f is a noncompetitive inhibitor with a slight preference for the closed-channel state of both the flip and the flop variants of GluA2Q. Similar to other 2,3-benzodiazepine compounds that we have previously characterized, BDZ-f inhibits GluA2Q(flip) by forming an initial, loose intermediate that is partially conducting; however, this intermediate rapidly isomerizes into a tighter, fully inhibitory receptor-inhibitor complex. BDZ-f binds to the same noncompetitive site as GYKI 52466 does. Together, our results show that the addition of an N-3 methylcarbamoyl group to the diazepine ring with the azomethine feature (i.e., GYKI 52466) is what makes BDZ-f more potent and more selective toward the closed-channel conformation than the original GYKI 52466. Our results have useful implications for the structure-activity relationship of the 2,3-benzodiazepine series.