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Schmallegger, M. ; Barbon, A. ; Bortolus, M. ; Chemelli, A. ; Bilkis, I. ; Gescheidt, G. ; Weiner, L. Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters. LANGMUIR 2020, 36, 10429-10437.Abstract
In this report, we present a method to characterize the kinetics of electron transfer across the bilayer of a unilamellar liposome composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The method utilizes synthetic phospholipids containing noninvasive nitroxide spin labels having the >N-O center dot moiety at well-defined distances from the outer surface of the liposome to serve as reporters for their local environment and, at the same time, permit measurement of the kinetics of electron transfer. We used 5-doxyl and 16-doxyl stearic acids. The paramagnetic >N-O center dot moiety is photo-oxidized to the corresponding diamagnetic oxoammonium cation by a ruthenium electron acceptor formed in the solution. Electron transfer is monitored by three independent spectroscopic methods: by both steady-state and time-resolved electron paramagnetic resonance and by optical spectroscopy. These techniques allowed us to differentiate between the electron transfer rates of nitroxides located in the outer leaflet of the phospholipid bilayer and of those located in the inner leaflet. Measurement of electron transfer rates as a function of temperature revealed a low-activation barrier (Delta G double dagger similar to 40 kJ/mol) that supports a tunneling mechanism.
Kohay, H. ; Bilkis, I. ; Mishael, Y. Effect of polycation charge density on polymer conformation at the clay surface and consequently on pharmaceutical binding. Journal of Colloid and Interface Science 2019, 552, 517-527. Publisher's VersionAbstract
Polycation conformation upon adsorption to a negatively charged surface can be modulated by its charge density. At high charge density monomers directly interact with the surface in a ‘trains’ conformation and as charge density decreases a high degree of monomers dangle into solution in a ‘loops and tails’ conformation. In this study, the conformations of polycations upon adsorption to montmorillonite, as a function of polycation charge (20, 50 and 100% of the monomers, denoted as P-Q20, P-Q50 and P-Q100) were characterized and in accordance with their conformation, the adsorption of non-ionic and anionic molecules by the composite was tested. As expected, the adsorption of the nonionic pharmaceuticals increased to a composite with a ‘loops and tails’ conformation, due to both conformation and chemical properties. On the other hand, the anionic molecules, gemfibrozil and diclofenac, preferably adsorbed to composites with higher charge density (Q50 or Q100 composites). However, they showed different tendency toward the composites, i.e. higher adsorption of diclofenac by Q100 composite vs. higher adsorption of gemfibrozil by Q50 composite. To elucidate the differences in adsorption between these two pharmaceuticals, density functional theory calculations were employed. Both gemfibrozil and diclofenac were found to be better stabilized by methyl pyridinium sites (prevail in Q100 composite). The preferable adsorption of gemfibrozil by Q50 composite was explained by the presence of ‘loops and tails’ conformation enabling additional adsorption sites and diverse monomer-target molecule orientations. © 2019
Bilkis, I. ; Silman, I. ; Weiner, L. Generation of reactive oxygen species by photosensitizers and their modes of action on proteins. Current Medicinal Chemistry 2018, 25, 5528-5539. Publisher's VersionAbstract
In this review, we first survey the mechanisms underlying the chemical modification of amino acid residues in proteins by singlet oxygen elicited by photosensitizers. Singlet oxygen has the capacity to cause widespread chemical damage to cellular proteins. Its use in photodynamic therapy of tumors thus requires the development of methodologies for specific addressing of the photosensitizer to malignant cells while sparing normal tissue. We describe three targeting paradigms for achieving this objective. The first involves the use of a photosensitizer with a high affinity for its target protein; in this case, the photosensitizer is methylene blue for acetylcholinesterase. The second paradigm involves the use of the hydrophobic photosensitizer hypericin, which has the capacity to interact selectively with partially unfolded forms of proteins, including nascent species in rapidly dividing or virus-infected and cancer cells, acting preferentially at membrane interfaces. In this case, partially unfolded molten globule species of acetylcholinesterase serve as the model system. In the third paradigm, the photodynamic approach takes advantage of a general approach in ‘state-of-the-art’ chemotherapy, by coupling the photosensitizer emodin to a specific peptide hormone, GnRH, which recognizes malignant cells via specific GnRH receptors on their surface. © 2018 Bentham Science Publishers.
Polyakov, N. ; Leshina, T. ; Fedenok, L. ; Slepneva, I. ; Kirilyuk, I. ; Furso, J. ; Olchawa, M. ; Sarna, T. ; Elas, M. ; Bilkis, I. ; et al. Redox-Active Quinone Chelators: Properties, Mechanisms of Action, Cell Delivery, and Cell Toxicity. Antioxidants and Redox Signaling 2018, 28, 1394-1403. Publisher's VersionAbstract
Significance: Chemotherapy is currently the principal method for treating many malignancies. Thus, the development of improved antitumor drugs with enhanced efficacy and selectivity remains a high priority. Recent Advances: Anthracycline antibiotics (AAs), for example, doxorubicin, daunomycin, and mitomycin C, belong to an important family of antitumor agents widely used in chemotherapy. These compounds are all quinones. They are, thus, capable of being reduced by appropriate chemicals or reductases. One of their important properties is that under aerobic conditions their reduced forms undergo oxidation, with concomitant generation of reactive oxygen species (ROS), namely, superoxide anion radicals, hydrogen peroxide, and hydroxyl radicals. The presence of metal ions is essential for the generation of ROS by AAs in biological systems. Critical Issues: A fundamental shortcoming of the AAs is their high cardiotoxicity. We have proposed, and experimentally realized, a new type of quinones that is capable of coordinating metal ions. We have demonstrated in vitro that they can be reduced by electron transfer chains and glutathione with concomitant generation of ROS. They can also produce ROS under photo-excitation. The mechanisms of these reactions have been characterized by using nuclear magnetic resonance and electron paramagnetic resonance. Future Directions: To enhance their therapeutic effectiveness, and decrease cardiotoxicity and other side effects, we intend to conjugate the quinone chelators with monoclonal antibodies and peptide hormones that are specifically targeted to receptors on the cancer cell surface. Some such candidates have already been synthesized. An alternative approach for delivery of our compounds involves the use of specific peptide-based nanoparticles. In addition, our novel approach for treating malignancies is also suitable for photodynamic therapy. Antioxid. Redox Signal. 28, 1394-1403. © 2018, Mary Ann Liebert, Inc.