De novo design and utilization of photolabile caged substrates as probes of hydrogen tunneling with horse liver alcohol dehydrogenase at sub-zero temperatures: a cautionary note

Design, Synthesis, and Activity Evaluation of Novel N-benzyl Deoxynojirimycin Derivatives for Use as α-Glucosidase Inhibitors

To obtain α-glucosidase inhibitors with high activity, 19 NB-DNJDs (N-benzyl-deoxynojirimycin derivatives) were designed and synthesized. The results indicated that the 19 NB-DNJDs displayed different inhibitory activities towards α-glucosidase in vitro. Compound 18a (1-(4-hydroxy-3-methoxybenzyl)-2-(hydroxymethyl) piperidine-3,4,5-triol) showed the highest activity, with an IC₅₀ value of 0.207 ± 0.11 mM, followed by 18b (1-(3-bromo-4-hydroxy-5-methoxybenzyl)-2-(hydroxymethyl) piperidine-3,4,5-triol, IC₅₀: 0.276 ± 0.13 mM). Both IC₅₀ values of 18a and 18b were significantly lower than that of acarbose (IC₅₀: 0.353 ± 0.09 mM). According to the structure-activity analysis, substitution of the benzyl and bromine groups on the benzene ring decreased the inhibition activity, while methoxy and hydroxyl group substitution increased the activity, especially with the hydroxyl group substitution. Molecular docking results showed that three hydrogen bonds were formed between compound 18a and amino acids in the active site of α-glucosidase. Additionally, an arene–arene interaction was also modelled between the phenyl ring of compound 18a and Arg 315. The three hydrogen bonds and the arene–arene interaction resulted in a low binding energy (−5.8 kcal/mol) and gave 18a a higher inhibition activity. Consequently, compound 18a is a promising candidate as a new α-glucosidase inhibitor for the treatment of type Ⅱ diabetes.

Reversible optogenetic control of protein function and localization

Protein-protein interactions are highly dynamic biological processes that regulate various cellular reactions. They exhibit high specificity and spatiotemporal control in order to efficiently utilize finite resources in a cellular compartment. Photoactivatable chemically inducible dimerization (pCID) has emerged as an attractive technique in the scientific community, leading to the development of systems that can be activated with various wavelengths of light in order to manipulate processes on biologically relevant scales with molecular specificity. These systems can be modified to control various protein functions with unprecedented precision and spatiotemporal resolution. In this chapter, we describe an optogenetic platform that provides reversible control over dimerization of genetically tagged proteins using orthogonal wavelengths of light. We demonstrate photoactivation and photo-reversal of protein localization and transport. Mitosis is manipulated by activating and silencing the spindle assembly checkpoint through recruitment and release of proteins from kinetochores.

Quinazolinone-Based Anticancer Agents: Synthesis, Antiproliferative SAR, Antitubulin Activity, and Tubulin Co-crystal Structure

Quinazolinone-based anticancer agents were designed, decorated with functional groups from a 2-methoxyestradiol-based microtubule disruptor series, incorporating the aryl sulfamate motif of steroid sulfatase (STS) inhibitors. The steroidal AB-ring system was mimicked, favoring conformations with an N-2 substituent occupying D-ring space. Evaluation against breast and prostate tumor cell lines identified 7b with DU-145 antiproliferative activity (GI₅₀ 300 nM). A preliminary structure-activity relationship afforded compounds (e.g., 7j GI₅₀ 50 nM) with activity exceeding that of the parent. Both 7b and 7j inhibit tubulin assembly in vitro and colchicine binding, and 7j was successfully co-crystallized with the αβ-tubulin heterodimer as the first of its class, its sulfamate group interacting positively at the colchicine binding site. Microtubule destabilization by 7j is likely achieved by preventing the curved-to-straight conformational transition in αβ-tubulin. Quinazolinone sulfamates surprisingly showed weak STS inhibition. Preliminary in vivo studies in a multiple myeloma xenograft model for 7b showed oral activity, confirming the promise of this template.

Programmed activation of cancer cell apoptosis: A tumor-targeted phototherapeutic topoisomerase I inhibitor

We report here a tumor-targeting masked phototherapeutic agent 1 (PT-1). This system contains SN-38-a prodrug of the topoisomerase I inhibitor irinotecan. Topoisomerase I is a vital enzyme that controls DNA topology during replication, transcription, and recombination. An elevated level of topoisomerase I is found in many carcinomas, making it an attractive target for the development of effective anticancer drugs. In addition, PT-1 contains both a photo-triggered moiety (nitrovanillin) and a cancer targeting unit (biotin). Upon light activation in cancer cells, PT-1 interferes with DNA re-ligation, diminishes the expression of topoisomerase I, and enhances the expression of inter alia mitochondrial apoptotic genes, death receptors, and caspase enzymes, inducing DNA damage and eventually leading to apoptosis. In vitro and in vivo studies showed significant inhibition of cancer growth and the hybrid system PT-1 thus shows promise as a programmed photo-therapeutic ("phototheranostic").

Synthesis of FMRFaNV, a Photoreleasable Caged Transmitter Designed to Study Neuron-Glia Interactions in the Central Nervous System

Neuroscience studies require technologies able to deliver compounds with both scale and timing compatibility with morphological and physiological synaptic properties. In this light, two-photon flash photolysis has been extensively used to successfully apply glutamate or other neurotransmitters at the synaptic level. However, the set of commercially available caged compounds is restricted and incompatible with studies demanding high cell specificity. The gain in cell specificity is especially relevant and challenging when studying neuron-glia interactions in the central nervous system. Here we develop a system to mimic the metabotropic glutamate receptor-dependent response of astrocytes, a glial cell type, following synaptic glutamate release. For this, we expressed an exogeneous orphan Gq-coupled protein of the Mas-related-gene (Mrg) family in glial cells and generated an MrgR's agonist peptide (FMRFa) that was chemically caged with a nitroveratryl photolabile protecting group (NV). NV has an appropriate quantum yield and a high absorption maximum that makes it very adapted to experiments with very short irradiation time. This novel caged compound allowed the activation of MrgR with both single- and two-photon light sources. Indeed, MrgR activation induced calcium transients and morphological changes in astrocytes as described previously. Thus, FMRFaNV is a very promising tool to study neuron-glia interactions.

New structure-activity relationships of chalcone inhibitors of breast cancer resistance protein: polyspecificity toward inhibition and critical substitutions against cytotoxicity

Adenosine triphosphate-binding cassette subfamily G member 2 (ABCG2) plays a major role in cancer cell multidrug resistance, which contributes to low eifficacy of chemotherapy. Chalcones were recently found to be potent and specific inhibitors, but unfortunately display a significant cytotoxicity. A cellular screening against ABCG2-mediated mitoxantrone efflux was performed here by flow cytometry on 54 chalcone derivatives from three different series with a wide panel of substituents. The identified leads, with submicromolar IC₅₀ (half maximal inhibitory concentration) values, showed that the previously identified 2′-OH-4′,6′-dimethoxyphenyl, as A-ring, could be efficiently replaced by a 2′-naphthyl group, or a 3′,4′-methylenedioxyphenyl with lower affinity. Such a structural variability indicates 3polyspecificity of the multidrug transporter for inhibitors. At least two methoxyl groups were necessary on B-ring for optimal inhibition, but substitution at positions 3, 4, and 5 induced cytotoxicity. The presence of a large O-benzyl substituent at position 4 and a 2′-naphthyl as A-ring markedly decreased the cytotoxicity, giving a high therapeutic ratio, which constitutes a critical requirement for future in-vivo assays in animal models.

Synthetic organic compounds with potential for bacterial biofilm inhibition, a path for the identification of compounds interfering with quorum sensing

New unconventional approaches to the development of antimicrobial drugs must target inhibition of infection stages leading to host colonisation or virulence itself, rather than bacterial viability. Amongst the most promising unconventional targets for the development of new antimicrobial drugs is bacterial adherence and biofilm formation as well as their control system, the quorum-sensing (QS) system, a mechanism of communication used to co-ordinate bacterial activities. Here we describe the evaluation of synthetic organic compounds as bacterial biofilm inhibitors against a panel of clinically relevant Gram-positive and Gram-negative bacterial strains. This approach has successfully allowed the identification of five compounds (GEt, GHex, GOctad, G19 and C33) active not only against bacterial biofilms but also displaying potential to be used as antagonists and/or inhibitors of bacterial QS.

Synthesis, biological evaluation, and molecular modeling of chalcone derivatives as potent inhibitors of Mycobacterium tuberculosis protein tyrosine phosphatases (PtpA and PtpB)

Tuberculosis (TB) is a major infectious disease caused by Mycobacterium tuberculosis (Mtb). According to the World Health Organization (WHO), about 1.8 million people die from TB and 10 million new cases are recorded each year. Recently, a new series of naphthylchalcones has been identified as inhibitors of Mtb protein tyrosine phosphatases (PTPs). In this work, 100 chalcones were designed, synthesized, and investigated for their inhibitory properties against MtbPtps. Structure-activity relationships (SAR) were developed, leading to the discovery of new potent inhibitors with IC(50) values in the low-micromolar range. Kinetic studies revealed competitive inhibition and high selectivity toward the Mtb enzymes. Molecular modeling investigations were carried out with the aim of revealing the most relevant structural requirements underlying the binding affinity and selectivity of this series of inhibitors as potential anti-TB drugs.

Antibacterial activity of chalcones, hydrazones and oxadiazoles against methicillin-resistant Staphylococcus aureus

The increase in antibiotic resistance due to multiple factors has encouraged the search for new compounds which are active against multidrug-resistant pathogens. In this context, chalcones, dihydrochalcones, hydrazones and oxadiazoles were tested against Staphylococcus aureus ATCC 25923 and methicillin-resistant S. aureus (MRSA) isolates, which were obtained from clinical laboratories and were characterized as MRSA using traditional and molecular methods. Among 65 tested compounds, two chalcones, one dihydrochalcone and two hydrazones were active against MRSA. Based on the minimal inhibitory concentration and cytotoxicity, hydrazones provided a better selectivity index than chalcones. Active hydrazones are promising antibiotic-like substances and they should be the subject of further microbiological studies.

An integrated model for enzyme catalysis emerges from studies of hydrogen tunneling

The origins of the enormous rate accelerations brought about by enzymes are discussed. The focus is on enzymatic C-H activation, which has been shown to take place via tunneling. Four enzyme systems illustrate the impact of site-specific mutagenesis, changes in temperature or changes in protein solvation on the tunneling properties. A model emerges in which conformational sampling is required to access a subset of protein conformers where the H-donor and acceptor undergo a close approach. The evidence for an inverse relationship between protein flexibility and active site compression is likely to extend to all classes of enzyme catalysts.

Making light work of enzyme catalysis: protochlorophyllide oxidoreductase

In the chlorophyll biosynthetic pathway, the enzyme protochlorophyllide oxidoreductase (POR) catalyses a key light-driven reaction that triggers a profound transformation in plant development. Because POR is activated by light, it can provide information on the way in which light energy can be harnessed to power enzyme reactions and it presents us with a unique opportunity to study catalysis at low temperatures and on ultrafast timescales that are not accessible for most analyses of enzyme function. Recent advances in our understanding of the catalytic mechanism of POR illustrate why it is an important generic model for studying enzyme catalysis and reaction dynamics.