Novel synthesis and in vitro drug release of polymeric prodrug: Chitosan–O-isopropyl-5′-O-d4T monophosphate conjugate

Biomacromolecules as carriers in drug delivery and tissue engineering

Natural biomacromolecules have attracted increased attention as carriers in biomedicine in recent years because of their inherent biochemical and biophysical properties including renewability, nontoxicity, biocompatibility, biodegradability, long blood circulation time and targeting ability. Recent advances in our understanding of the biological functions of natural-origin biomacromolecules and the progress in the study of biological drug carriers indicate that such carriers may have advantages over synthetic material-based carriers in terms of half-life, stability, safety and ease of manufacture. In this review, we give a brief introduction to the biochemical properties of the widely used biomacromolecule-based carriers such as albumin, lipoproteins and polysaccharides. Then examples from the clinic and in recent laboratory development are summarized. Finally the current challenges and future prospects of present biological carriers are discussed.

RTG-loaded nanomicelles (CS–VES–NAC) for oral anti-HIV drug delivery

An acetylcysteine–chitosan–vitamin E succinate copolymer (CVN) was synthesized from chitosan (CS), vitamin E succinate (VES) and N-acetyl-l-cysteine (NAC) as self-assembled nanomicelles for multifunctional delivery of anti-HIV drug Raltegravir (RTG).

A facile method for synthesizing water-soluble and superior sustained release anti-HIV prodrug SCs-d4T

To efficiently deliver stavudine (d4T) for AIDS therapy, chitosan-stavudine conjugate (Cs-d4T) was synthesized. However, its poor water-solubility limited its clinical application. In this study, a sulphonated chitosan-stavudine conjugate (SCs-d4T) was synthesized with a mild SO3·Py complex sulphonation strategy. Chemical characteristics and morphology of Cs-d4T and SCs-d4T were performed by NMR, XRD, FTIR, ICP-AES and SEM. SCs-d4T demonstrated satisfactory solubility (106-bold of Cs-d4T solubility), good anti-HIV activity (6-fold of d4T anti-HIV activity), and well sustained release ability. The major release product O-isopropyl-5'-H-phosphonate of d4T (d4T-P-H) showed higher anti-HIV activity than d4T. For further evaluating the influence of linker and sulphonation strategy on anti-HIV activity, chitosan grafted with d4T by succinyl linker (Cs-sd4T) and SCs-d4T sulphonated by oleum were also prepared. The result showed that the O-isopropyl monophosphate linker of Cs-d4T and SO3·Py complex sulphonation strategy revealed higher anti-HIV activity than succinyl linker of Cs-sd4T and oleum sulphonation strategy, respectively.

Atherton-Todd reaction: mechanism, scope and applications

Initially, the Atherton-Todd (AT) reaction was applied for the synthesis of phosphoramidates by reacting dialkyl phosphite with a primary amine in the presence of carbon tetrachloride. These reaction conditions were subsequently modified with the aim to optimize them and the reaction was extended to different nucleophiles. The mechanism of this reaction led to controversial reports over the past years and is adequately discussed. We also present the scope of the AT reaction. Finally, we investigate the AT reaction by means of exemplary applications, which mainly concern three topics. First, we discuss the activation of a phenol group as a phosphate which allows for subsequent transformations such as cross coupling and reduction. Next, we examine the AT reaction applied to produce fire retardant compounds. In the last section, we investigate the use of the AT reaction for the production of compounds employed for biological applications. The selected examples to illustrate the applications of the Atherton-Todd reaction mainly cover the past 15 years.

Advances in chitosan-based drug delivery vehicles

Within the past few years, chitosan-based drug delivery vehicles have become some of the most attractive to be studied. In contrast to all other polysaccharides, chitosan has demonstrated its unique characteristics for drug delivery platforms, including its active primary amino groups for chemical modification, simple and mild preparation methods for the encapsulation of biomolecules or drugs, mucoadhesion to facilitate transport across mucosal barriers and so on. In this review, an overview of the various types of chitosan-based drug delivery systems is provided, with special focus on polymeric drug conjugates and drug nanocarriers. The first part of the review is concerned with the development and applications of polymeric chitosan-drug conjugates. Then the chitosan-based nanocarrier systems as well as their preparation methods and applications are further discussed.

Synthesis, nanosizing and in vitro drug release of a novel anti-HIV polymeric prodrug: chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate

A novel approach to improve the antiviral efficacy of nucleoside reverse transcriptase inhibitors (NRTIs) and reduce their side effects was developed by constructing a nanosized NRTI monophosphate-polymer conjugate using d4T as a model NRTI. Firstly, a novel chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate with a phosphoramidate linkage was efficiently synthesized through Atherton-Todd reaction under mild conditions. The anti-HIV activity and cytotoxicity of the polymeric conjugate were evaluated in MT4 cell line. Then the conjugate nanoparticles were prepared by the process of ionotropic gelation between TPP and chitosan-d4T conjugate to improve their delivery to viral reservoirs, and their physicochemical properties were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) techniques and X-ray diffraction (XRD). In vitro drug release studies in pH 1.1 and pH 7.4 suggested that both chitosan-d4T conjugate and its nanoparticles prefer to release d4T 5'-(O-isopropyl) monophosphate than free d4T for prolonged periods, which resulted in the enhancement of anti-HIV selectivity of the polymeric conjugate relative to free d4T due to bypassing the metabolic bottleneck of monophosphorylation. Additionally, the crosslinked conjugate nanoparticles can prevent the coupled drug from leaking out of the nanoparticles before entering the target viral reservoirs and provide a mild sustained release of d4T 5'-(O-isopropyl) monophosphate without the burst release. The results suggested that this kind of chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate nano-prodrugs may be used as a targeting and sustained polymeric prodrugs for improving therapy efficacy and reducing side effects in antiretroviral treatment.