Current Topics in Medicinal Chemistry - Volume 14, Issue 6, 2014

In this work, we investigate the effect of chitosan hydrophobization on the internalization and cytotoxic effect of chitosan-based nanoparticles (NPs) on breast cancer cells (MDA-MB-231), cervical cancer cells (HeLa) and noncancer cells (Arpe-19). We also analyzed the interaction of NPs with a phospholipid (DPPC) membrane model at the airwater interface. An alkylation procedure to insert 8 carbon chains along the chitosan macromolecule with final 10 and 30 % substitution degrees was used. Nuclear magnetic resonance (NMR) and infrared spectroscopes (IR) were used to evaluate the success and extent of the hydrophobization procedure. Size, shape, and charge of NPs were evaluated by dynamic light scattering (DLS), atomic force microscope (AFM), and zeta potential, respectively. The effect of hydrophobicity on NPs was the reduction of the NPs average size, the formation of slightly elongated structures and the enhancing of the interaction of NPs with a DPPC monolayer at the air-water interface. By using fluorescence images on fluorescein-chitosan NPs, we observed a higher internalization of hydrophobic chitosan NPs in cancer cells in comparison with a low internalization of these NPs in normal cells. Even when non modified chitosan NPs were highly internalized in all cell lines, hydrophobized chitosan NPs showed a significantly higher cytotoxic effect on cancer cells in comparison with a lower effect showed by non-modified chitosan NPs on these cells. The cytotoxic effect on the normal cell line used was low for native chitosan NPs and negligible for hydrophobized chitosan NPs.

The aim of this work was to critically review recent results pertinent to fibrinogen adsorption at solid/electrolyte interfaces with the emphasis focused on a quantitative analysis of these processes in terms of the electrostatic interactions. Accordingly, in the first part, the primary chemical structure of fibrinogen is analyzed. Physicochemical data pertinent to the bulk properties derived from hydrodynamic, dynamic light scattering and micro-electrophoretic measurements aided by theoretical modeling are discussed. Possible conformations and the effective charge distribution over the fibrinogen molecule for various pH an ionic strength are defined, especially the semi-collapsed conformation prevailing at physiological conditions. Adsorption kinetics of fibrinogen at hydrophilic and hydrophobic (polymer modified) substrates determined by various techniques is described. Adsorption at polymeric carrier particles, pertinent to immunological assays, studied in terms of electrokinetic and concentration depletion methods, are also considered. The reversibility of adsorption, fibrinogen molecule orientations and maximum coverages are thoroughly discussed. The stability of fibrinogen monolayers formed at these carrier particles in respect to pH and ionic strength cyclic changes is also discussed. In the final section interactions and deposition of model colloid particles on fibrinogen monolayers are analyzed which allows one to derive valuable information about molecule orientations. Based on the physicochemical data, adsorption kinetics and colloid particle deposition measurements, probable adsorption mechanisms of fibrinogen on solid/electrolyte interfaces are defined.

Medicinal chemistry is intimately connected with basic science such as organic synthesis, chemical biology and biophysical chemistry among other disciplines. The reason of such connections is due to the power of organic synthesis to provide designed molecules; chemical biology to give tools to discover biological and/or pathological pathways and biophysical chemistry which provides the techniques to characterize and the theoretical background to understand molecular behaviour. The present review provides some selective examples of these research areas. Initially, template dsDNA organic synthesis and the spatio-temporal control of transcription are presenting following by the supramolecular entities used in drug delivery, such as liposomes and liquid crystal among others. Finally, peptides and protein self-assembly is connected with biomaterials and as an important event in the balance between health and disease. The final aim of the present review is to show the power of chemical tools not only for the synthesis of new molecules but also to improve our understanding of recognition and self-assembly in the biological context.

The process of self-assembly is universal and lies at the heart of biological structures and function. Peptide aggregation, while considered a nuisance in peptide chemistry, soon gained interest with the discovery of pore-forming peptide toxins and had been an area of intense research during last century and even to date. This has also resulted in the increasing use of the more respectable term peptide self-assembly. The discovery of amyloid forming peptides has rekindled the interest in peptide self-assembly since such aggregates are directly implicated in many debilitating diseases in human and animals. Amyloid aggregates have posed many fundamental questions to researchers. In addition, self-assembly of peptides has emerged as a bottom-up strategy for the fabrication of nanostructures owing to highly ordered nature of the process and considerable degree of flexibility and diversity provided by peptides as starting materials. This review provides a brief account of the progress in the field of peptide self-assembly from pore-forming toxins to amyloid forming peptides and those forming nanostructures.

Liquid systems containing droplets with size in the nanoscale range are attractive from both scientific and technological points of view as they have many current and potential applications in several industries and products. The formation and stabilization of nano-droplet systems are mostly based on the self-assembly of surfactant (amphiphilic) molecules at interfaces, driven by the solvophobic effect. Surfactants are involved in both top-bottom (high energy) and bottom- up (low energy) methods. Several devices have also been developed to aid in liquid fragmentation down to the nanometer scale. Nano-droplet systems can be both thermodynamically stable (microemulsions) or metastable (nanoemulsions), and appropriate formulation is a key for optimum product design in terms of droplet size, maximum solubilization, colloidal stability, and optical and rheological properties, among others. Such characteristics are determined by molecular packing, interfacial curvature, droplet-droplet interactions, film elasticity and nature of the dispersed and continuous phase. These properties can be engineered by proper understanding of the molecular structure and phase behavior of the multicomponent systems involved and by a range of experimental characterization techniques. Nano-droplet systems can help to solve specific issues in pharmaceutical products such as processing, limitations in drug solubility or stability, control on drug release, drug targeting and absorption; there are many examples to prove that. However, several practical aspects should be considered for preclinical and clinical tests and product development.

In this review we summarize and discuss the different methods we can use to achieve reversible DNA compaction in vitro. Reversible DNA compaction is a natural process that occurs in living cells and viruses. As a result these process long sequences of DNA can be concentrated in a small volume (compacted) to be decompacted only when the information carried by the DNA is needed. In the current work we review the main artificial compacting agents looking at their suitability for decompaction. The different approaches used for decompaction are strongly influenced by the nature of the compacting agent that determines the mechanism of compaction. We focus our discussion on two main artificial compacting agents: multivalent cations and cationic surfactants that are the best known compacting agents. The reversibility of the process can be achieved by adding chemicals like divalent cations, alcohols, anionic surfactants, cyclodextrins or by changing the chemical nature of the compacting agents via pH modifications, light induced conformation changes or by redox-reactions. We stress the relevance of electrostatic interactions and self-assembly as a main approach in order to tune up the DNA conformation in order to create an on-off switch allowing a transition between coil and compact states. The recent advances to control DNA conformation in vitro, by means of molecular self-assembly, result in a better understanding of the fundamental aspects involved in the DNA behavior in vivo and serve of invaluable inspiration for the development of potential biomedical applications.

The formation of reverse micelles by nonionic alcohol ethoxylates surfactants in two “dry” non polar solvents, heptane and dibutoxymethane (DBM), has been studied. These surfactants are formed by a linear hydrocarbon chain consisting of i carbons, and a poly(ethylene oxide) chain with j ethoxylate units (EO) ending with a hydroxyl group, CiEOj. The study is focused on the determination of the critical micelle concentration CMC and the size and morphology of the formed aggregates. The CMC was obtained from the decreasing of interfacial tension with increasing surfactant concentration and by using pyrene sulfonic acid sodium salt as fluorescence probe. The results show that the CMC in heptane is one order of magnitude higher than in DBM and two orders of magnitude higher than those determined in aqueous solution. The self-diffusion coefficients D of C8EO5, C8EO4 and C10EO6 in heptane, were obtained by diffusion ordered spectroscopy (DOSY 1H-NMR). The experimental values of D were then fitted to four different configurations to determine the most probable morphology of the formed aggregates. In all cases the presence of large and compact aggregates, with aggregation numbers going from a few dozens of monomers to a hundred of them, was shown.

Recent advances in synthesis of functional poly-ε-caprolactone (PCL) and its self-assembly behavior, as well as application in drug delivery have been reviewed. Three strategies including end group functionalization, postpolymerization modification and new monomer preparation have been summarized to show possibilities for PCL derivatives. Complex architectures like cyclic and multi-arm PCL have been emphasized. Both chemical composition and topology have coordinately affected the property of PCL-based materials on the molecular level. A large variety of PCLs with sophisticated topology like block, graft, cyclic, and star have displayed versatile morphologies in solutions. These selfassembly aggregates have been applied as nano-scaled drug carries either to physically encapsulate or covalently conjugate drugs for controlled release. In particular, PCL with pendant groups has been extensively studied to illustrate the noncovalent interaction with drugs and the influence on the release profile. In general, functional PCL has shown great potential in construct of complicated supramolecular structures, and thus as ideal drug carriers for sustainable and targeted delivery.

The emergence of the new scientific field known as nanomedicine is being catalyzed by multiple improvements in nanoscience techniques and significant progress in materials science, especially as regards the testing of novel and sophisticated biomaterials. This conjuncture has furthered the development of promising instruments in terms of detection, bioanalysis, therapy, diagnostics and imaging. Some of the most innovative new biomaterials are protein-inspired biomimetic materials in which modern biotechnology and genetic-engineering techniques complement the huge amount of information afforded by natural protein evolution to create advanced and tailor-made multifunctional molecules. Amongst these protein-based biomaterials, Elastin-like Recombinamers (ELRs) have demonstrated their enormous potential in the fields of biomedicine and nanoscience in the last few years. This broad applicability derives from their unmatched properties, particularly their recombinant and tailor-made nature, the intrinsic characteristics derived from their elastin-based origin (mainly their mechanical properties and ability to self-assemble as a result of their stimuli-responsive behavior), their proven biocompatibility and biodegradability, as well as their versatility as regards incorporating advanced chemical or recombinant modifications into the original structure that open up an almost unlimited number of multifunctional possibilities in this developing field. This article provides an updated review of the recent challenges overcome by using these recombinant biomaterials in the fields of nano- and biomedicine, ranging from nanoscale applications in surface modifications and self-assembled nanostructures to drug delivery and regenerative medicine.