Thermodynamic analysis of binding between drugs and glycosaminoglycans by isothermal titration calorimetry and fluorescence spectroscopy

Glycosaminoglycans and Contrast Agents: The Role of Hyaluronic Acid as MRI Contrast Enhancer

A comprehensive understanding of the behaviour of Glycosaminoglycans (GAGs) combined with imaging or therapeutic agents can be a key factor for the rational design of drug delivery and diagnostic systems. In this work, physical and thermodynamic phenomena arising from the complex interplay between GAGs and contrast agents for Magnetic Resonance Imaging (MRI) have been explored. Being an excellent candidate for drug delivery and diagnostic systems, Hyaluronic acid (HA) (0.1 to 0.7%w/v) has been chosen as a GAG model, and Gd-DTPA (0.01 to 0.2 mM) as a relevant MRI contrast agent. HA samples crosslinked with divinyl sulfone (DVS) have also been investigated. Water Diffusion and Isothermal Titration Calorimetry studies demonstrated that the interaction between HA and Gd-DTPA can form hydrogen bonds and coordinate water molecules, which plays a leading role in determining both the polymer conformation and the relaxometric properties of the contrast agent. This interaction can be modulated by changing the GAG/contrast agent molar ratio and by acting on the organization of the polymer network. The fine control over the combination of GAGs and imaging agents could represent an enormous advantage in formulating novel multifunctional diagnostic probes paving the way for precision nanomedicine tools.

Glypican-1 in human glioblastoma: implications in tumorigenesis and chemotherapy

Glioblastoma is one of the most common malignant brain tumors, with which patients have a mean survival of 24 months. Glypican-1 has been previously shown to be overexpressed in human glioblastoma and to be negatively correlated with patient’s survival. This study aimed to investigate how glypican-1 influences the tumoral profile of human glioblastoma using in vitro cell line models. By downregulating the expression of glypican-1 in U-251 MG cells, we observed that the cellular growth and proliferation were highly reduced, in which cells were significantly shifted towards G0 as opposed to G1 phases. Cellular migration was severely affected, and glypican-1 majorly impacted the affinity towards laminin-binding of glioblastoma U-251 MG cells. This proteoglycan was highly prevalent in glioblastoma cells, being primarily localized in the cellular membrane and extracellular vesicles, occasionally with glypican-3. Glypican-1 could also be found in cell-cell junctions with syndecan-4 but was not identified in lipid rafts in this study. Glypican-1-silenced cells were much more susceptible to temozolomide than in U-251 MG itself. Therefore, we present evidence not only to support facts that glypican-1 is an elementary macromolecule in glioblastoma tumoral microenvironment but also to introduce this proteoglycan as a promising therapeutic target for this lethal tumor.

Controlling methacryloyl substitution of chondroitin sulfate: injectable hydrogels with tunable long-term drug release profiles

Drug delivery systems capable of local sustained release of small molecule therapeutics remain a critical need in many fields, including oncology. Here, a system to create tunable hydrogels capable of modulating the loading and release of cationic small molecule therapeutics was developed. Chondroitin sulfate (CS) is a sulfated glycosaminoglycan that has many promising properties, including biocompatibility, biodegradation and chemically modifiable groups for both covalent and non-covalent bonding. CS was covalently modified with photocrosslinkable methacryloyl groups (CSMA) to develop an injectable hydrogel fabrication. Utilizing anionic groups, cationic drugs can be adsorbed and released from the hydrogels. This study demonstrates the synthesis of CSMA with a varying degree of substitution (DS) to generate hydrogels with varying swelling properties, maximum injection force, and drug release kinetics. The DS of the synthesized CSMA ranged from 0.05 ± 0.02 (2 h reaction) to 0.28 ± 0.02 (24 h reaction) with a DS of 1 representing 100% modification. The altered DS resulted in changes in hydrogel properties with the swelling of 20% CSMA hydrogels ranging from 42 (2 h reaction) to 13 (24 h reaction) and injection forces ranging from 18 N (2 h reaction) to 94 N (24 h reaction). The release of sunitinib, an oncology therapeutic that inhibits intracellular signaling by targeting multiple receptor tyrosine kinases, ranged from 18 μg per day (2 h reaction) to 9 μg per day (24 h reaction). While decreasing the DS increased the hydrogel swelling and rate of therapeutic release, it also limited the hydrogel fabrication range to only those containing 10% or higher CSMA. Blended polymer systems with poly(vinyl alcohol)-methacrylate (PVAMA) were fabricated to stabilize the resulting hydrogels via attenuating the swelling properties. Release profiles previously unattainable with the pure CSMA hydrogels were achieved with the blended hydrogel formulations. Overall, these studies identify a method to formulate tunable CSMA and blended CSMA/PVAMA hydrogels capable of sustained release of cationic therapeutics over six weeks with applications in oncology therapeutics.

The Effect of Dextran Sulfate-as Model Glycosaminoglycan Analogue-on Membrane Lipids: DPPC, Cholesterol, and DPPC-Cholesterol Mixture. The Monolayer Study

Glycosaminoglycans (GAGs) are essential components of the extracellular matrices (ECMs) located on the outer surface of cellular membranes. They belong to the group of polysaccharides involved in diverse biological processes acting on the surface and across natural lipid membranes. Recently, particular attention has been focused on possible role of GAGs in the amyloid deposits. The amyloid formation is related to a disorder in protein folding, causing that soluble-in normal conditions-peptides become deposited extracellularly as insoluble fibrils, impairing tissue structure and its function. One of the hypothesis holds that GAGs may inhibit amyloid formation by interacting with the lipid membrane by blocking the accumulation of protein aggregates on the membrane surface. Although the biophysical properties of GAGs are described rather well, little is known about the nature of association between these polysaccharides and components of natural cell membranes. Therefore, a study of GAGs influence on membrane lipids is of particular importance. The aim of the present work is to get insight into the effect of hydrophilic dextran sulfate (DS)-that can be considered as GAG analogue-on membrane lipids organization. This study was based on examining interactions between DS sodium salt of molecular weight equal to about 40 kDa (DS40), dissolved in water subphase, and a model membrane, mimicked as Langmuir monolayer, formed by representative natural membrane lipids: cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as well as their mixtures. Due to the fact that calcium ions in excess may accumulate in the lipid membrane, attracting high molecular weight molecules to their surface, the influence of calcium ions present in the subphase on the DS40 activity has also been examined. It has been found that negatively charged DS, forming a sublayer underneath the monolayer, barely interacts with membrane lipids; however, in the presence of calcium ions the electrostatic interactions between DS40 and lipid membrane are significantly enhanced, leading to the formation of network-like crystalline structures at the surface of model membrane, which can prevent incorporation and interaction with other extracellular molecules, e.g., proteins.

Interaction of hexadecylbetainate chloride with biological relevant lipids

The present work investigates the interaction of hexadecylbetainate chloride (C(16)BC), a glycine betaine-based ester with palmitoyl-oleoyl-phosphatidylcholine (POPC), sphingomyelin (SM), and cholesterol (CHOL), three biological relevant lipids present in the outer leaflet of the mammalian plasma membrane. The binding affinity and the mixing behavior between the lipids and C(16)BC are discussed based on experimental (isothermal titration calorimetry (ITC) and Langmuir film balance) and molecular modeling studies. The results show that the interaction between C(16)BC and each lipid is thermodynamically favorable and does not affect the integrity of the lipid vesicles. The primary adsorption of C(16)BC into the lipid film is mainly governed by a hydrophobic effect. Once C(16)BC is inserted in the lipid film, the polar component of the interaction energy between C(16)BC and the lipid becomes predominant. Presence of CHOL increases the affinity of C(16)BC for membrane. This result can be explained by the optimal matching between C(16)BC and CHOL within the film rather by a change of membrane fluidity due to the presence of CHOL. The interaction between C(16)BC and SM is also favorable and gives rise to highly stable monolayers probably due to hydrogen bonds between their hydrophilic groups. The interaction of C(16)BC with POPC is less favorable but does not destabilize the mixed monolayer from a thermodynamic point of view. Interestingly, for all the monolayers investigated, the exclusion surface pressures are above the presumed lateral pressure of the plasma membranes suggesting that C(16)BC would be able to penetrate into mammalian plasma membranes in vivo. These results may serve as a useful basis in understanding the interaction of C(16)BC with real membranes.

Molecular recognition at protein surface in solution and gas phase: Five VEGF peptidic ligands show inverse affinity when studied by NMR and CID-MS

Protein-protein interactions comprise of collection of molecular recognition events that take place at protein surfaces. A better understanding of the mechanism behind these interactions would provide deeper insight into the nature of many diseases, caused by the malfunction of protein networks, and contribute to design of molecules for efficient modulating of these interactions. One major factor in molecular recognition mechanism is interaction of reacting species with aqueous media. Thus, comparative study of noncovalent complex behavior in solution and gas phase can provide valuable information about the role of the solvent. Here examined interactions of vascular endothelial growth factor (VEGF) protein with five peptidic ligands of the same molecular weight but with different affinities. Interactions of VEGF with ligands in solution were studied by ITC and NMR, and K(D)s were determined. Gas phase stability was addressed using CID-MS approach. The energy transfer model was taken and adapted for the calculation of binding energy. Peptides were ranked on the basis of both solution and gas phase affinity to VEGF. The results indicate that the ranking of peptides in terms of affinity in solution is reversed compared with the gas phase ranking. This observation opens up a vast field for the future study of the system, and the determination and characterization of factors, responsible for the change of stability of noncovalent protein-ligand complexes upon complete or partial removal of the solvent.

A survey of the year 2007 literature on applications of isothermal titration calorimetry

Elucidation of the energetic principles of binding affinity and specificity is a central task in many branches of current sciences: biology, medicine, pharmacology, chemistry, material sciences, etc. In biomedical research, integral approaches combining structural information with in-solution biophysical data have proved to be a powerful way toward understanding the physical basis of vital cellular phenomena. Isothermal titration calorimetry (ITC) is a valuable experimental tool facilitating quantification of the thermodynamic parameters that characterize recognition processes involving biomacromolecules. The method provides access to all relevant thermodynamic information by performing a few experiments. In particular, ITC experiments allow to by-pass tedious and (rarely precise) procedures aimed at determining the changes in enthalpy and entropy upon binding by van't Hoff analysis. Notwithstanding limitations, ITC has now the reputation of being the "gold standard" and ITC data are widely used to validate theoretical predictions of thermodynamic parameters, as well as to benchmark the results of novel binding assays. In this paper, we discuss several publications from 2007 reporting ITC results. The focus is on applications in biologically oriented fields. We do not intend a comprehensive coverage of all newly accumulated information. Rather, we emphasize work which has captured our attention with originality and far-reaching analysis, or else has provided ideas for expanding the potential of the method.

New challenges for pharmaceutical formulations and drug delivery systems characterization using isothermal titration calorimetry

Long viewed as the 'method of choice' for characterizing thermodynamics and stoichiometry of molecular interactions, with high sensitivity, isothermal titration calorimetry (ITC) has been applied to many areas of pharmaceutical analysis. This review highlights ITC employment to measure binding thermodynamics and their use for pharmaceutical formulations and drug delivery system characterization particularly cyclodextrin-guest interactions, investigation of micellar-based systems, polyelectrolytes, nucleic acid interactions with multivalent cations and the optimization of DNA targeting and delivery. Furthermore, the potential of ITC for the characterization of different functionalities carried by nanoparticles as well as their interaction with living systems was outlined.