Michela Abrami

Polysaccharides for the Delivery of Antitumor Drugs

Among the several delivery materials available so far, polysaccharides represent very attractive molecules as they can undergo a wide range of chemical modifications, are biocompatible, biodegradable, and have low immunogenic properties. Thus, polysaccharides can contribute to significantly overcome the limitation in the use of many types of drugs, including anti-cancer drugs. The use of conventional anti-cancer drugs is hampered by their high toxicity, mostly depending on the indiscriminate targeting of both cancer and normal cells. Additionally, for nucleic acid based drugs (NABDs), an emerging class of drugs with potential anti-cancer value, the practical use is problematic. This mostly depends on their fast degradation in biological fluids and the difficulties to cross cell membranes. Thus, for both classes of drugs, the development of optimal delivery materials is crucial. Here we discuss the possibility of using different kinds of polysaccharides, such as chitosan, hyaluronic acid, dextran, and pullulan, as smart drug delivery materials. We first describe the main features of polysaccharides, then a general overview about the aspects ruling drug release mechanisms and the pharmacokinetic are reported. Finally, notable examples of polysaccharide-based delivery of conventional anti-cancer drugs and NABDs are reported. Whereas additional research is required, the promising results obtained so far, fully justify further efforts, both in terms of economic support and investigations in the field of polysaccharides as drug delivery materials.

Reduction of melting temperature and enthalpy of drug crystals: Theoretical aspects

This review deals with the mathematical models describing the reduction of melting temperature and enthalpy of solids in the nano-size range. In particular, the attention focuses on the thermodynamic based models that are theoretically solid and can be suitably used in the case of organic drugs. Indeed, while much effort has been put in the past to study the melting of metal nano-crystals, little work has been done for organic drug nano-crystals. However, due to the high potential of drug nano-crystals (their solubility increases with size reduction), this theme has become more and more important in the pharmaceutical field. Accordingly, this review, after illustrating the physical frame of drug melting, focuses on the thermodynamic aspects required to describe the melting of spherical and not spherical nano-crystals. Finally, the reliability of some models is tested against the results coming from X-rays analysis in the case of two organic drugs (griseofulvin and nifedipine). This test proved models strength.

Therapeutic Potential of Nucleic Acid-Based Drugs in Coronary Hyper- Proliferative Vascular Diseases

The thickening of the vessel wall (intimal hyperplasia) is a pathological process which often follows revascularization approaches such as transluminal angioplasty and artery bypass graft, procedures used to re-vascularize stenotic artery. Despite the significant improvements in the treatment of intimal hyperplasia obtained in the last years, the problem has not completely solved. Nucleic acid based-drugs (NABDs) represent an emergent class of molecules with potential therapeutic value for the treatment of intimal hyperplasia. NABDs of interest in the field of intimal hyperplasia are: ribozymes, DNAzymes, antisense oligonucleotides, decoy oligonucleotides, small interfering RNAs and micro interfering RNAs. These molecules can recognize, in a sequencespecific fashion, a target which, depending on the different NABDs, can be represented by a nucleic acid or a protein. Upon binding, NABDs can down-modulate the functions of the target (mRNA/proteins) and thus they are used to impair the functions of disease-causing biological molecules.In spite of the great therapeutic potential demonstrated by NABDs in many experimental model of intima hyperplasia, their practical use is hindered by the necessity to identify optimal delivery systems to the vasculature. In the first part of this review a brief description of the clinical problem related to intima hyperplasia formation after revascularization procedures is reported. In the second part, the attention is focused on the experimental evidences of NABD therapeutic potential in the prevention of intimal hyperplasia. Finally, in the third part, we will describe the strategies developed to optimize NABD delivery to the diseased vessel.

Novel Lipid and Polymeric Materials as Delivery Systems for Nucleic Acid Based Drugs.

Nucleic acid based drugs (NADBs) are short DNA/RNA molecules that include among others, antisense oligonucleotides, aptamers, small interfering RNAs and micro-interfering RNAs. Despite the different mechanisms of actions, NABDs have the ability to combat the effects of pathological gene expression in many experimental systems. Thus, nowadays, NABDs are considered to have a great therapeutic potential, possibly superior to that of available drugs. Unfortunately, however, the lack of effective delivery systems limits the practical use of NABDs. Due to their hydrophilic nature, NABDs cannot efficiently cross cellular membrane; in addition, they are subjected to fast degradation by cellular and extracellular nucleases. Together these aspects make the delivery of NABDs as naked molecules almost un-effective. To optimize NABD delivery, several solutions have been investigated. From the first attempts described in the beginning of the 1980s, a burst in the number of published papers occurred in the beginning of 1990 s reaching a peak in 2012-13. The extensive amount of work performed so far clearly witnesses the interest of the scientific community in this topic. In the present review, we will concentrate on the description of the most interesting advances in the field. Particular emphasis will be put on polymeric and lipid materials used alone or in combination with a promising delivery strategy based on the use of carbon nanotubes. The data presented suggest that, although further improvements are required, we are not far from the identification of effective delivery systems for NABDs thus making the clinical use of these molecules closer to reality.

Diels-Alder Hydrogels for Controlled Antibody Release: Correlation between Mesh Size and Release Rate.

Eight-armed PEG, molecular mass 10 kDa, was functionalized with furyl and maleimide groups, respectively; the obtained macromonomers were cross-linked via Diels-Alder chemistry. The mesh size (ξ) of the prepared hydrogels was determined by swelling studies, rheology, and low field NMR spectroscopy. The in vitro release of fluorescein isothiocyanate labeled dextrans (FDs) and bevacizumab was investigated. The average mesh size (ξavg) increased from 5.8 ± 0.1 nm to 56 ± 13 nm during degradation, as determined by swelling studies. The result of the rheological measurements (8.0 nm) matched the initial value of ξavg. Low field NMR spectroscopy enabled the determination of the mesh size distribution; the most abundant mesh size was found to be 9.2 nm. In combination with the hydrodynamic radius of the molecule (Rh), the time-dependent increase of ξavg was used to predict the release profiles of incorporated FDs applying an obstruction-scaling model. The predicted release profiles matched the experimentally determined release profiles when Rh < ξavg. However, significant deviations from the theoretical predictions were observed when Rh ≥ ξavg, most likely due to the statistical distribution of ξ in real polymer networks. The release profile of bevacizumab differed from those of equivalently sized FDs. The delayed release of bevacizumab was most likely a result of the globular structure and rigidity of the protein. The observed correlation between ξ and the release rate could facilitate the design of controlled release systems for antibodies.

Insight into the ionotropic gelation of chitosan using tripolyphosphate and pyrophosphate as cross-linkers

Ionotropic gelation of chitosan by means of opposite charged ions represents an efficient alternative to covalent reticulation because of milder condition of use and, in general, higher biocompatibility of the resulting systems. In this work 90° light scattering (turbidimetry), circular dichroism (CD) and 1H NMR measurements have been performed to study the interactions between the biopolymer and ionic cross-linkers tripolyphosphate (TPP) and pyrophosphate (PPi) in dilute solutions. Thereafter, a dialysis-based technique was exploited to fabricate tridimensional chitosan hydrogels based on both polyanions. Resulting matrices showed a different mechanical behavior because of their peculiar mesh-texture at micro/nano-scale: in the present contribution we demonstrate that TPP and PPi favor the formation of homogeneous and inhomogeneous systems, respectively. The different texture of networks could be exploited in future for the preparation of systems for the controlled release of molecules.

Potential applications of nanocellulose-containing materials in the biomedical field

Because of its high biocompatibility, bio-degradability, low-cost and easy availability, cellulose finds application in disparate areas of research. Here we focus our attention on the most recent and attractive potential applications of cellulose in the biomedical field. We first describe the chemical/structural composition of cellulose fibers, the cellulose sources/features and cellulose chemical modifications employed to improve its properties. We then move to the description of cellulose potential applications in biomedicine. In this field, cellulose is most considered in recent research in the form of nano-sized particle, i.e., nanofiber cellulose (NFC) or cellulose nanocrystal (CNC). NFC is obtained from cellulose via chemical and mechanical methods. CNC can be obtained from macroscopic or microscopic forms of cellulose following strong acid hydrolysis. NFC and CNC are used for several reasons including the mechanical properties, the extended surface area and the low toxicity. Here we present some potential applications of nano-sized cellulose in the fields of wound healing, bone-cartilage regeneration, dental application and different human diseases including cancer. To witness the close proximity of nano-sized cellulose to the practical biomedical use, examples of recent clinical trials are also reported. Altogether, the described examples strongly support the enormous application potential of nano-sized cellulose in the biomedical field.

Synthesis and characterization of UV photocrosslinkable hydrogels with poly(N-vinyl-2-pyrrolidone): Determination of the network mesh size distribution

ABSTRACT Hydrogels of poly(n-vinyl-2-pyrrolidone) were produced by UV irradiation of aqueous solutions of the polymer in presence of hydrogen peroxide, used as initiator. The mechanical and the nanostructural properties of the gels were characterized by a combination of experimental techniques including rheology, low field nuclear magnetic resonance spectroscopy (LF-NMR), and small angle X-ray scattering. Different irradiation doses as well as polymer and initiator concentrations were tested in the characterization. The study elucidates the relationship between different methods to estimate the mesh size of the gel polymeric network. Moreover, a novel correlation model was developed based on Chui and Scherer theories for the interpretation of LF-NMR dataset of polymer solutions and networks. GRAPHICAL ABSTRACT

Rheology of Laponite-scleroglucan hydrogels

Both Laponite and scleroglucan can find several applications in various fields (from industrial to biomedical one) in virtue of their peculiar features and rheological properties displayed in aqueous phases. Structural states of Laponite dispersions strongly depend on concentration and ionic strength. When attractive and repulsive interparticle interactions are so effective that they lead to arrested states (attractive gel or repulsive glass), the rheological behavior of the dispersion undergoes a sharp transition, from quasi-Newtonian to markedly shear thinning and viscoelastic. Conversely, scleroglucan solutions gradually change to weak gels with increasing polymer concentration. The present work is concerned with aqueous Laponite-scleroglucan mixed systems, obtained according to different preparation modes, and is aimed at examining how much the content and proportion of both components affect the viscoelastic and flow properties of the mixed system.

Role of sonication pre-treatment and cation valence in the sol-gel transition of nano-cellulose suspensions

Sol-gel transition of carboxylated cellulose nanocrystals has been investigated using rheology, SAXS, NMR and optical spectroscopies to unveil the distinctive roles of ultrasound treatments and addition of various cations. Besides cellulose fiber fragmentation, sonication treatment induces fast gelling of the solution. The gelation is independent of the addition of cations, while the final rheological properties are highly influenced by the type, concentration and sequence of the operations since the cations must be added prior to sonication to produce stiff gels. The gel elastic modulus was found to increase proportionally to the ionic charge rather than the cationic size. In cases where ions were added after sonication, SAXS analysis of the Na+ hydrogel and Ca2+ hydrogel indicated the presence of structurally ordered domains in which water is confined, and 1H-NMR investigation showed the dynamics of water exchange within the hydrogels. Conversely, separated phases containing essentially free water were characteristic of the hydrogels obtained by sonication after Ca2+ addition, confirming that this ion induces irreversible fiber aggregation. The rheological properties of the hydrogels depend on the duration of the ultrasound treatments, enabling the design of programmed materials with tailored energy dissipation response.Sol-gel transition of carboxylated cellulose nanocrystals is investigated using rheology, SAXS, NMR and optical spectroscopies to unveil the distinctive roles of ultrasounds treatment and ions addition. Besides cellulose fibers fragmentation, sonication treatment induces fast gelling of the solution. Gelation is induced independently on the addition of cations, while the final rheological properties are highly influenced by the type, the concentration as well as on the sequence of the operations since salts must be added before sonication to produce stiff gels. Cations with various charge and dimension have been associated to ultrasounds to induce gelation and the gel elastic modulus increase proportionally with the charge over the ion size ratio. SAXS analysis of the Na + hydrogel and Ca 2+ hydrogel to which the ion was added after sonication shows the presence of structurally ordered domains where water is confined as indicated by 1H-NMR investigation of the dynamic of water exchange in the hydrogels. Conversely, separated phases containing essentially free water, characterize the hydrogels obtained by sonication after Ca 2+ addition, confirming that this ion induces irreversible fiber aggregation. The rheological properties of the hydrogels depend on the duration of the ultrasound treatment and it enables the design of materials programmed with tailored energy dissipation response. INTRODUCTION Nanocellulose (NC) is a renewable and biocompatible material with interesting and versatile properties which allow its integration in a huge number of applications, as has been extensively reviewed [1,2]. The procedures to break natural cellulose and obtain nano-sized structures are usually based on the combination of chemical modification or enzymatic hydrolysis with mechanical refinement [3,4]. Fine changes of these procedures give rise to different nanostructure morphology: branched nanofibrils with amorphous regions (CNF) and rod-like rigid nanocrystals (CNC) [5]. TEMPO-mediated oxidation of cellulose followed by sonication provides well dispersed, negatively charged CNC [6]. Despite the large interest on NC and its applications, several basic aspects regulating NC properties and its interaction with the environment are still unclear. Concerning the structure investigation, the effort has been addressed mainly toward the understanding of the liquid crystalline self-assembly resulting in ordered helical structures with peculiar mechanical and optical properties [7-9]. The self-assembly of NC or NC-composites into soft hydrogels [10,11] has been characterized in terms of macroscopic parameters such as mesh size, charge density, gelation rate, mechanical performances, or stability [12-15]. In this context, rheology experiments have been performed and a gel-like behavior of NC suspensions with an elastic response even at a low concentration [16] has been reported. In general, the rheological behaviour of NC suspensions is strongly dependent on NC production: mechanical fibrillation without chemical modification produces suspensions with flocculated structure while NC which underwent chemical processes, produces suspensions with better colloidal stability [17]. The static and dynamic rheological behavior of