Current Topics in Medicinal Chemistry - Volume 15, Issue 22, 2015

With a number of formulations currently in clinical trials, the interest in polymer micelles as drug carriers in unlikely to subside. Historically, linear diblock copolymers have been used as the building blocks for micelle preparation. Yet, recent advances in polymer chemistry have meant that a wider variety of polymer architectures and compositions have become available and been trialed for pharmaceutical applications. This mini-review aims to provide an overview of recent, exciting developments in triblock, graft and hyperbranched polymer chemistries that may change the way polymeric micelles drug formulations are prepared.

Three different amyloid targeting ligands, previously shown to exhibit amyloid specific properties, have been used to develop amyloid -targeted nanoliposomes (AT-NLs). For this a MAb against Aβ-peptides (Aβ-MAb) (immobilized on NLs at 0.015 and 0.05 mol %), and two different curcumin-lipid derivatives were attached to the surface of preformed NLs or incorporated in NL membranes during their formation. Following physicochemical characterization, these AT-NLs were studied for their ability to inhibit or delay amyloid peptide aggregation –using the thioflavin-T assay, and for their potential to reverse amyloid-induced (and Zn, or, amyloid + Zn) cytotoxicity, on wild type (N2aWT) and transformed (N2aAPP) neuroblastoma cells, applying the MTT assay. Experimental results reveal that all formulations were found to strongly delay amyloid peptide aggregation (with no significant differences between the different AT-NL types). However, although Aβ-MAb-NLs significantly reversed amyloid-induced cytotoxicity in all cases, both curcumin-NL types did not reverse Zn-induced, nor Zn+Aβ-induced cytotoxicity in N2aWT cells, suggesting lower activity against synthetic-Aβ peptides (compared to endogenous Aβ peptides); perhaps due to different affinity towards different (aggregation stages of) peptide species (monomers, oligomers, fibrils, etc). Taken into account that the aggregation stage of amyloid species is an important determinant of their toxicity, the importance of the affinity of each AT-NL type towards specific species, is highlighted.

Peptide amphiphiles (PAs) are novel engineered biomaterials able to self-assemble into supramolecular systems that have shown significant promise in drug delivery across the cell membane and across challenging biological barriers showing promise in the field of brain diseases, regenerative medicine and cancer. PAs are amino-acid block co-polymers, with a peptide backbone composed usually of 8-30 amino acids, a hydrophilic block formed by polar amino acids, a hydrophobic block which usually entails either non-polar or aromatic amino acids and alkyl, acyl or aryl lipidic tails and in some cases a spacer or a conjugated targeting moiety. Finely tuning the balance between the hydrophilic and hydrophobic blocks results in a range of supramolecular structures that are usually stabilised by hydrophobic, electrostatic, β-sheet hydrogen bonds and π-π stacking interactions. In an aqueous environment, the final size, shape and interfacial curvature of the PA is a result of the complex interplay of all these interactions. Lanreotide is the first PA to be licensed for the treatment of acromegaly and neuroendocrine tumours as a hydrogel administered subcutaneously, while a number of other PAs are undergoing preclinical development. This review discusses PAs architecture fundamentals that govern their self-assembly into supramolecular systems for applications in drug delivery.

Bone is a biologically and structurally sophisticated multifunctional tissue. It dynamically responds to biochemical, mechanical and electrical clues by remodelling itself and accordingly the maximum strength and toughness are along the lines of the greatest applied stress. The challenge is to develop an orthopaedic biomaterial that imitates the micro- and nano-structural elements and compositions of bone to locally match the properties of the host tissue resulting in a biologically fixed implant. Looking for the ideal implant, the convergence of life and materials sciences occurs. Researchers in many different fields apply their expertise to improve implantable devices and regenerative medicine. Materials of all kinds, but especially hierarchical nano-materials, are being exploited. The application of nano-materials with hierarchical design to calcified tissue reconstructive medicine involve intricate systems including scaffolds with multifaceted shapes that provides temporary mechanical function; materials with nano-topography modifications that guarantee their integration to tissues and that possesses functionalized surfaces to transport biologic factors to stimulate tissue growth in a controlled, safe, and rapid manner. Furthermore materials that should degrade on a timeline coordinated to the time that takes the tissues regrow, are prepared. These implantable devices are multifunctional and for its construction they involve the use of precise strategically techniques together with specific material manufacturing processes that can be integrated to achieve in the design, the required multifunctionality. For such reasons, even though the idea of displacement from synthetic implants and tissue grafts to regenerative-medicine-based tissue reconstruction has been guaranteed for well over a decade, the reality has yet to emerge. In this paper, we examine the recent approaches to create enhanced bioactive materials. Their design and manufacturing procedures as well as the experiments to integrate them into engineer hierarchical inorganic materials for their practical application in calcified tissue reparation are evaluated.

The development of nanocarriers able transport and release therapeutic agents in a controlled manner has provided a promising alternative in the oncology field due to the lack of selectivity of the conventional treatments. The encapsulation of cytotoxic compounds within nanoparticles improves the pharmacokinetic profile of the trapped drugs and allows their selective accumulation into the tumoral tissue owing to the enhance permeation and retention effect (EPR). In addition, the selectivity of the nanocarrier can be enhanced attaching targeting agents on their surface able to be specifically recognized by cancer cells or by the tumor microenvironment. Among the different materials which can be employed, mesoporous silica nanoparticles (MCM-41 type) constitutes a promising candidate due to their very interesting properties such as tuneable size, shape and porosity, high loading capacity, low toxicity, robustness and easiness fabrication and functionalization. This material presents a unique pore architecture which allows the synthesis of stimuliresponsive devices able to release the trapped drugs only in the presence of certain stimuli achieving a precise control on the drug dosage. This review presents some of the recent advances in the development of mesoporous silica nanocarriers for antitumoral therapy paying special attention on the stimuli-responsive systems able to release their load in response to external (light, magnetic field, temperature or ultrasounds) or internal stimulus (enzymes, pH, redox, among others).

The overall pharmaceutical market is changing. A more personalised medicine approach is replacing the concept of blockbuster drugs and the “one size fits all” model. The two main forces that fuel the growth of nano-enabled drug technologies are the low aqueous solubility of new chemical entities and the pharmaceutical market itself, as the development of novel drug delivery systems can extend the drug patent lifetime. Classical solubilisation techniques, such as salt formation and the use of cyclodextrins can only be applied to drugs with ionisable groups or specific molecular weight ranges in order to fit in the cavity of the cyclodextrin. However, drug nanonisation, or particle size reduction into the nanosize range, is a versatile technique that can be applied to a wide range of pharmaceutical compounds. Nano-drugs exhibit higher surface area per unit of volume, which leads to faster dissolution kinetics and hence potentially improved bioavailability. Marketed nano-drugs are mostly crystalline due to the improved physical stability afforded by the crystalline state whereas amorphous nano-drugs have been largely neglected in spite of generating higher saturation solubility compared to their crystalline counterparts. Due to the vast potential in the global pharmaceutical market, many technologies have been licensed to produce nano-drugs. Among them, the most successful by far is Nanocrystal^® Technology based on wet milling methods. In this review, the main methods to generate and characterise nano-drugs are covered and also, the biopharmaceutical characteristics of the marketed nano-drugs are discussed.