A novel small molecule chaperone of rod opsin and its potential therapy for retinal degeneration.

Rhodopsin homeostasis is tightly coupled to rod photoreceptor cell survival and vision. Mutations resulting in the misfolding of rhodopsin can lead to autosomal dominant retinitis pigmentosa (adRP), a progressive retinal degeneration that currently is untreatable. Using a cell-based high-throughput screen (HTS) to identify small molecules that can stabilize the P23H-opsin mutant, which causes most cases of adRP, we identified a novel pharmacological chaperone of rod photoreceptor opsin, YC-001. As a non-retinoid molecule, YC-001 demonstrates micromolar potency and efficacy greater than 9-cis-retinal with lower cytotoxicity. YC-001 binds to bovine rod opsin with an EC50 similar to 9-cis-retinal. The chaperone activity of YC-001 is evidenced by its ability to rescue the transport of multiple rod opsin mutants in mammalian cells. YC-001 is also an inverse agonist that non-competitively antagonizes rod opsin signaling. Significantly, a single dose of YC-001 protects Abca4 -/- Rdh8 -/- mice from bright light-induced retinal degeneration, suggesting its broad therapeutic potential.

Measuring Drug-Induced Changes in Metabolite Populations of Live Bacteria: Real Time Analysis by Raman Spectroscopy.

Raman difference spectroscopy is shown to provide a wealth of molecular detail on changes within bacterial cells caused by infusion of antibiotics or hydrogen peroxide. Escherichia coli strains paired with chloramphenicol, dihydrofolate reductase propargyl-based inhibitors, meropenem, or hydrogen peroxide provide details of the depletion of protein and nucleic acid populations in real time. Additionally, other reproducible Raman features appear and are attributed to changes in cell metabolite populations. An initial candidate for one of the metabolites involves population increases of citrate, an intermediate within the tricarboxyclic acid cycle. This is supported by the observation that a strain of E. coli without the ability to synthesize citrate, gltA, lacks an intense feature in the Raman difference spectrum that has been ascribed to citrate. The methodology for obtaining the Raman data involves infusing the drug into live cells, then washing, freezing, and finally lyophilizing the cells. The freeze-dried cells are then examined under a Raman microscope. The difference spectra [cells treated with drug] - [cells without treatment] are time-dependent and can yield population kinetics for intracellular species in vivo. There is a strong resemblance between the Raman difference spectra of E. coli cells treated with meropenem and those treated with hydrogen peroxide.

A Combination of G Protein-Coupled Receptor Modulators Protects Photoreceptors from Degeneration.

Degeneration of retinal photoreceptor cells can arise from environmental and/or genetic causes. Since photoreceptor cells, the retinal pigment epithelium (RPE), neurons, and glial cells of the retina are intimately associated, all cell types eventually are affected by retinal degenerative diseases. Such diseases often originate either in rod and/or cone photoreceptor cells or the RPE. Of these, cone cells located in the central retina are especially important for daily human activity. Here we describe the protection of cone cells by a combination therapy consisting of the G protein-coupled receptor modulators metoprolol, tamsulosin, and bromocriptine. These drugs were tested in Abca4-/-Rdh8-/- mice, a preclinical model for retinal degeneration. The specificity of these drugs was determined with an essentially complete panel of human G protein-coupled receptors. Significantly, the combination of metoprolol, tamsulosin, and bromocriptine had no deleterious effects on electroretinographic responses of wild-type mice. Moreover, putative G protein-coupled receptor targets of these drugs were shown to be expressed in human and mouse eyes by RNA sequencing and quantitative polymerase chain reaction. Liquid chromatography together with mass spectrometry using validated internal standards confirmed that metoprolol, tamsulosin, and bromocriptine individually or together penetrate the eye after either intraperitoneal delivery or oral gavage. Collectively, these findings support human trials with combined therapy composed of lower doses of metoprolol, tamsulosin, and bromocriptine designed to safely impede retinal degeneration associated with certain genetic diseases (e.g., Stargardt disease). The same low-dose combination also could protect the retina against diseases with complex or unknown etiologies such as age-related macular degeneration.

Defining Molecular Details of the Chemistry of Biofilm Formation by Raman Microspectroscopy.

Two protocols that allow for the comparison of Raman spectra of planktonic cells and biofilm formed from these cells in their growth phase have been developed. Planktonic cells are washed and flash-frozen in <1 min to reduce the time for metabolic changes during processing, prior to freeze-drying. Biofilm is formed by standing cells in 50 µL indentations in aluminum foil in an atmosphere of saturated water vapor for 24-48 h. The results for Escherichia coli type K12 cells, which do not readily form biofilm, are compared to those for Staphylococcus epidermidis cells, which prolifically synthesize biofilm. For E. coli, the Raman spectra of the planktonic and biofilm samples are similar with the exception that the spectral signature of RNA, present in planktonic cells, could not be detected in biofilm. For S. epidermidis, major changes occur upon biofilm formation. In addition to the absence of the RNA features, new bands occur near 950 cm-1 and between 1350 and 1420 cm-1 that are associated with an increase in carbohydrate content. Unlike the case in E. coli biofilm, the intensity of G base ring modes is reduced in but A and T base ring signatures become more prominent. For S. epidermis in the biofilm's amide III region, there is evidence of an increase in the level of ß-sheet structure accompanied by a decrease in α-helical content. The presence of biofilm is confirmed by microscope-aided photography and, separately, by staining with methyl violet.

"Mind the Gap": Raman Evidence for Rapid Inactivation of CTX-M-9 ß-Lactamase Using Mechanism-Based Inhibitors that Bridge the Active Site.

CTX-M ß-lactamases are one of the fastest growing extended-spectrum ß-lactamase (ESBL) families found in Escherichia coli rendering this organism extremely difficult to treat with ß-lactam antibiotics. Although they are grouped in class A ß-lactamases, the CTX-M family possesses low sequence identity with other enzymes. In addition, they have high hydrolytic activity against oxyimino-cephalosporins, despite having smaller active sites compared to other ESBLs in class A. Similar to most class A enzymes, most of the CTX-M ß-lactamases can be inhibited by the clinical inhibitors (clavulanic acid, sulbactam, and tazobactam), but the prevalence of inhibitor resistance is an emerging clinical threat. Thus, the mechanistic details of inhibition pathways are needed for new inhibitor development. Here, we use Raman microscopy to study the CTX-M-9 inactivation reaction with the three commercially available inhibitors and compare these findings to the analysis of the S130G variant. Characterization of the reactions in CTX-M-9 single crystals and solution show the formation of a unique cross-linked species, probably involving Ser70 and Ser130, with subsequent hydrolysis leading to an acrylate species linked to Ser130. In solution, a major population of this species is seen at 25 ms after mixing. Support for this finding comes from the CTX-M-9 S130G variant that reacts with clavulanic acid, sulbactam, and tazobactam in solution, but lacks the characteristic spectroscopic signature for the Ser130-linked species. Understanding the mechanism of inactivation of this clinically important ESBL-type class A lactamase permits us to approach the challenge of inhibitor resistance using knowledge of the bridging species in the inactivation pathway.

New techniques in antibiotic discovery and resistance: Raman spectroscopy.

Raman spectroscopy can play a role in both antibiotic discovery and understanding the molecular basis of resistance. A major challenge in drug development is to measure the population of the drug molecules inside a cell line and to follow the chemistry of their reactions with intracellular targets. Recently, a protocol based on Raman microscopy has been developed that achieves these goals. Drug candidates are soaked into live bacterial cells and subsequently the cells are frozen and freeze-dried. The samples yield exemplary (nonresonance) Raman data that provide a measure of the number of drug molecules within each cell, as well as details of drug-target interactions. Results are discussed for two classes of compounds inhibiting either ß-lactamase or dihydrofolate reductase enzymes in a number of Gram-positive or Gram-negative cell lines. The advantages of the present protocol are that it does not use labels and it can measure the kinetics of cell-compound uptake on the time scale of minutes. Spectroscopic interpretation is supported by in vitro Raman experiments. Studying drug-target interactions in aqueous solution and in single crystals can provide molecular level insights into drug-target interactions, which, in turn, provide the underpinnings of our understanding of data from bacterial cells. Thus, the applicability of X-ray crystallographic-derived data to in-cell chemistry can be tested.

Measuring propargyl-linked drug populations inside bacterial cells, and their interaction with a dihydrofolate reductase target, by Raman microscopy.

We report the first Raman spectroscopic study of propargyl-linked dihydrofolate reductase (DHFR) inhibitors being taken up by wild type Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus cells. A novel protocol is developed where cells are exposed to the fermentation medium containing a known amount of an inhibitor. At a chosen time point, the cells are centrifuged and washed to remove the extracellular compound, then frozen and freeze-dried. Raman difference spectra of the freeze-dried cells (cells exposed to the drug minus cells alone) provide spectra of the compounds inside the cells, where peak intensities allow us to quantify the number of inhibitors within each cell. A time course for the propargyl-linked DHFR inhibitor UCP 1038 soaking into E. coli cells showed that penetration occurs very quickly and reaches a plateau after 10 min exposure to the inhibitor. After 10 min drug exposure, the populations of two inhibitors, UCP 1038 and UCP 1089, were ~1.5 × 10(6) molecules in each E. coli cell, ~4.7 × 10(5) molecules in each K. pneumonia cell, and ~2.7 × 10(6) in each S. aureus cell. This is the first in situ comparison of inhibitor population in Gram-negative and Gram-positive bacterial cells. The positions of the Raman peaks also reveal the protonation of diaminopyrimidine ring upon binding to DHFR inside cells. The spectroscopic signature of protonation was characterized by binding an inhibitor to a single crystal of DHFR.

Following drug uptake and reactions inside Escherichia coli cells by Raman microspectroscopy.

Raman microspectroscopy combined with Raman difference spectroscopy reveals the details of chemical reactions within bacterial cells. The method provides direct quantitative data on penetration of druglike molecules into Escherichia coli cells in situ along with the details of drug-target reactions. With this label-free technique, clavulanic acid and tazobactam can be observed as they penetrate into E. coli cells and subsequently inhibit ß-lactamase enzymes produced within these cells. When E. coli cells contain a ß-lactamase that forms a stable complex with an inhibitor, the Raman signature of the known enamine acyl-enzyme complex is detected. From Raman intensities it is facile to measure semiquantitatively the number of clavulanic acid molecules taken up by the lactamase-free cells during growth.

Raman spectra of interchanging ß-lactamase inhibitor intermediates on the millisecond time scale.

Rapid mix-rapid freeze is a powerful method to study the mechanisms of enzyme-substrate reactions in solution. Here we report a protocol that combines this method with normal (non-resonance) Raman microscopy to enable us to define molecular details of intermediates at early time points. With this combined method, SHV-1, a class A ß-lactamase, and tazobactam, a commercially available ß-lactamase inhibitor, were rapidly mixed on the millisecond time scale and then were flash-frozen by injection into an isopentane solution surrounded by liquid nitrogen. The "ice" was finally freeze-dried and characterized by Raman microscopy. We found that the reaction is almost complete in solution at 25 ms, giving rise to a major population composed of the trans-enamine intermediate. Between 25 and 500 ms, minor populations of protonated imine are detected that have previously been postulated to precede enamine intermediates. However, within 1 s, the imines are converted entirely to enamines. Interestingly, with this method, we can measure directly the turnover number of SHV-1 and tazobactam. The enzyme is completely inhibited at 1:4 ratio (enzyme:inhibitor) or greater, a number that agrees with the turnover number derived from steady-state kinetic methods. This application, employing non-intensity-enhanced Raman spectroscopy, provides a general and effective route to study the early events in enzyme-substrate reactions.