Aikaterini Lalatsa

Amphiphilic poly(l-amino acids) - New materials for drug delivery

The formulation of drug compounds into medicines will increasingly rely on the use of specially tailored molecules, which fundamentally alter the drugs pharmacokinetics to enable its therapeutic activity. This is particularly true of the more challenging hydrophobic drugs or therapeutic biological molecules. The demand for such enabled medicines will translate into a demand for advanced highly functionalised drug delivery materials. Polymers have been used to formulate medicines for many decades and this is unlikely to change soon. Amphiphilic polymers based on amino acids are the subject of this review. These molecules, which present as either poly(L-amino acid) block copolymers or poly(L-amino acid) backbones with hydrophobic substituents, self assemble into micelles, vesicles, nanofibres and solid nanoparticles and such self assemblies, have drug delivery capabilities. The nature of the self-assembly depends on the chemistry of the constituent molecules, with the more hydrophilic molecules forming nanosized micellar aggregates including peptide nanofibres, molecules of intermediate hydrophobicity forming polymeric vesicles and the more hydrophobic variants forming amorphous polymeric nanoparticles of 100-1000 nm in diameter. The self-assemblies may be loaded with drugs or may present as micelle forming polymer-drug conjugates and the supramolecular aggregates have been employed as drug solubilisers, tumour targeting agents, gene delivery vectors and facilitators of intracellular drug uptake, with a more promising polymer-drug conjugate progressing to clinical testing.

Strategies to deliver peptide drugs to the brain

Neurological diseases such as neurodegeneration, pain, psychiatric disorders, stroke, and brain cancers would greatly benefit from the use of highly potent and specific peptide pharmaceuticals. Peptides are especially desirable because of their low inherent toxicity. The presence of the blood brain barrier (BBB), their short duration of action, and their need for parenteral administration limits their clinical use. However, over the past decade there have been significant advances in delivering peptides to the central nervous system. Angiopep peptides developed by Angiochem (Montreal, Canada), transferrin antibodies developed by ArmaGen (Santa Monica, USA), and cell penetrating peptides have all shown promise in delivering therapeutic peptides across the BBB after intravenous administration. Noninvasive methods of delivering peptides to the brain include the use of chitosan amphiphile nanoparticles for oral delivery and nose to brain strategies. The uptake of the chitosan amphiphile nanoparticles by the gastrointestinal epithelium is important for oral peptide delivery. Finally protecting peptides from plasma degradation is integral to the success of most of these peptide delivery strategies.

Delivery of peptides to the blood and brain after oral uptake of quaternary ammonium palmitoyl glycol chitosan nanoparticles.

The clinical development of therapeutic peptides has been restricted to peptides for non-CNS diseases and parenteral dosage forms due to the poor permeation of peptides across the gastrointestinal mucosa and the blood-brain barrier. Quaternary ammonium palmitoyl glycol chitosan (GCPQ) nanoparticles facilitate the brain delivery of orally administered peptides such as leucine(5)-enkephalin, and here we examine the mechanism of GCPQ facilitated oral peptide absorption and brain delivery. By analyzing the oral biodistribution of radiolabeled GCPQ nanoparticles, the oral biodistribution of the model peptide leucine(5)-enkephalin and coherent anti-Stokes Raman scattering microscopy tissue images after an oral dose of deuterated GCPQ nanoparticles, we have established a number of facts. Although 85-90% of orally administered GCPQ nanoparticles are not absorbed from the gastrointestinal tract, a peak level of 2-3% of the oral GCPQ dose is detected in the blood 30 min after dosing, and these GCPQ particles appear to transport the peptides to the blood. Additionally, although peptide loaded nanoparticles from low (6 kDa) and high (50 kDa) molecular weight GCPQ are taken up by enterocytes, polymer particles with a polymer molecular weight greater than 6 kDa are required to facilitate peptide delivery to the brain after oral administration. By examining our current and previous data, we conclude that GCPQ particles facilitate oral peptide absorption by protecting the peptide from gastrointestinal degradation, adhering to the mucus to increase the drug gut residence time and transporting GCPQ associated peptide across the enterocytes and to the systemic circulation, enabling the GCPQ stabilized peptide to be transported to the brain. Orally administered GCPQ particles are also circulated from the gastrointestinal tract to the liver and onward to the gall bladder, presumably for final transport back to the gastrointestinal tract.

Exploring uptake mechanisms of oral nanomedicines using multimodal nonlinear optical microscopy

Advances in pharmaceutical nanotechnology have yielded ever increasingly sophisticated nanoparticles for medicine delivery. When administered via oral, intravenous, ocular and transcutaneous delivery routes, these nanoparticles can elicit enhanced drug performance. In spite of this, little is known about the mechanistic processes underlying interactions between nanoparticles and tissues, or how these correlate with improved pharmaceutical effects. These mechanisms must be fully understood before nanomedicines can be rationally engineered to optimise their performance. Methods to directly visualise these particulates within tissue samples have traditionally involved imaging modalities requiring covalent labelling of fluorescent or radioisotope contrast agents. We present CARS, second harmonic generation and two photon fluorescence microscopy combined as a multi-modal label-free method for pinpointing polymeric nanoparticles within the stomach, intestine, gall bladder and liver. We demonstrate for the first time that orally administered chitosan nanoparticles follow a recirculation pathway from the GI tract via enterocytes, to the liver hepatocytes and intercellular spaces and then to the gall bladder, before being re-released into the gut together with bile.

A prodrug nanoparticle approach for the oral delivery of a hydrophilic peptide, leucine5-enkephalin, to the brain

The oral use of neuropeptides to treat brain disease is currently not possible because of a combination of poor oral absorption, short plasma half-lives and the blood-brain barrier. Here we demonstrate a strategy for neuropeptide brain delivery via the (a) oral and (b) intravenous routes. The strategy is exemplified by a palmitic ester prodrug of the model drug leucine(5)-enkephalin, encapsulated within chitosan amphiphile nanoparticles. Via the oral route the nanoparticle-prodrug formulation increased the brain drug levels by 67% and significantly increased leucine(5)-enkephalins antinociceptive activity. The nanoparticles facilitate oral absorption and the prodrug prevents plasma degradation, enabling brain delivery. Via the intravenous route, the nanoparticle-prodrug increases the peptide brain levels by 50% and confers antinociceptive activity on leucine(5)-enkephalin. The nanoparticle-prodrug enables brain delivery by stabilizing the peptide in the plasma although the chitosan amphiphile particles are not transported across the blood-brain barrier per se, and are excreted in the urine.

Peptide Self-Assemblies for Drug Delivery.

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.

Fundamentals of Pharmaceutical Nanoscience

The emerging discipline of nanoscience has resulted in a number of new technologies. These groundbreaking advances are firing the imagination of a generation of scientists and leading to new materials with a wealth of functionality. In the biomedical sciences these technological advances are finally translating into clinically relevant products and bringing patients exciting new therapies and diagnostics. This is the first book of its kind that seeks to present the application of nanoscience to medicines development - pharmaceutical nanoscience in one accessible volume. The nanotechnologies that derive from pharmaceutical nanoscience are just beginning to make their mark. The book spans the chemistries, which are harnessed to create the materials, the concepts upon which their application rests and model examples of the exploitation of this new knowledge to bring healthcare benefits. A final chapter on the commercialisation pathways taken by these new technologies provides a fitting end to the book as all science is geared towards new knowledge or an improved quality of life through the creation of new interventions, products or services. The book is designed to introduce undergraduates to the technologies underpinning these emerging and existing products, provide a reference volume for graduate scholars seeking an introduction to the fields of pharmaceutical nanoscience and pharmaceutical nanotechnology and provide the expert with accessible information on complementary areas satellite to their main areas of expertise.

Drug delivery across the blood-brain barrier

Brain diseases are a leading cause of disability, morbidity, and mortality. However, the treatment of brain diseases (e.g., neurodegenerative diseases, psychiatric disorders, pain, and brain cancers) is hampered by the blood–brain barrier (BBB). The BBB is a unique membranous barrier formed by the endothelial cells of the brain capillaries. This barrier tightly segregates the brain from the circulating blood maintaining a constant internal environment for optimal neuronal function. Despite the relative impermeability of the BBB, the BBB is associated with a number of specific transport processes from blood to brain, primarily aimed at the transport of glucose and amino acids into the brain and is also permeable to some low-molecular-weight lipid molecules. However, in essence, an estimated 95% of drugs are excluded from the brain. To deliver drugs across the BBB and, thus, treat central nervous system disorders, specific delivery approaches must be adopted. The approaches may be divided into four separate categories: (1) direct injection and implantation; (2) a temporary opening of the BBB using chemical means; (3) the modification of drugs to make them either lipophilic or substrates of endogenous transporters; and (4) the use of nanosystems, which may be either plain nanoparticles, nanoparticles decorated with ligands for specific transporters or nanoparticles coated with water-soluble surfactants. An additional area of interest is delivery via the nasal route. Although some of the brain delivery approaches used to date are indeed promising, it is clear that further work is needed in the area of brain medicine development if we are to meet the global demand for these therapies.

Chitosan amphiphile coating of peptide nanofibres reduces liver uptake and delivers the peptide to the brain on intravenous administration

The clinical development of neuropeptides has been limited by a combination of the short plasma half-life of these drugs and their ultimate failure to permeate the blood brain barrier. Peptide nanofibres have been used to deliver peptides across the blood brain barrier and in this work we demonstrate that the polymer coating of peptide nanofibres further enhances peptide delivery to the brain via the intravenous route. Leucine(5)-enkephalin (LENK) nanofibres formed from the LENK ester prodrug - tyrosinyl(1)palmitate-leucine(5)-enkephalin (TPLENK) were coated with the polymer - N-palmitoyl-N-monomethyl-N,N-dimethyl-N,N,N-trimethyl-6-O-glycolchitosan (GCPQ) and injected intravenously. Peptide brain delivery was enhanced because the GCPQ coating on the peptide prodrug nanofibres, specifically enables the peptide prodrug to escape liver uptake, avoid enzymatic degradation to non-active sequences and thus enjoy a longer plasma half life. Plasma half-life is increased 520%, liver AUC0-4 decreased by 54% and brain AUC0-4 increased by 47% as a result of the GCPQ coating. The increased brain levels of the GCPQ coated peptide prodrug nanofibres result in the pharmacological activity of the parent drug (LENK) being significantly increased. LENK itself is inactive on intravenous injection.

Carbohydrate nanoparticles for brain delivery

Many brain tumors and neurological diseases can greatly benefit from the use of emerging nanotechnologies based on targeted nanomedicines that are able to noninvasively transport highly potent and specific pharmaceuticals across the blood-brain barrier. Carbohydrates have received considerable interest as materials for drug carriers due to their natural origin and inherent biodegradability and biocompatibility, as well as due to their hydrophilic character and ease of chemical modification combined with low cost and the possibility for large-scale manufacturing. This chapter provides an overview of the latest research involving the use of carbohydrate-based nanoparticles for drug delivery to the central nervous system. After reviewing the challenges posed by delivering drugs into the brain, the current state-of-the-art approaches for delivery of actives across the blood-brain barrier, including invasive and noninvasive strategies, are presented. A particular focus has been placed on chitosan polymers as they are among the most promising carbohydrate nanocarriers for the preparation and testing of chitosan-based nanomedicines that led, in preclinical proof-of-concept studies, to enhanced brain drug levels and increased pharmacodynamics responses after intravenous, nasal, and oral administration. While chitosan nanoparticles are to date among the most studied and most promising carriers, approaches based on other polysaccharides such as dextran, pullulan, and cellulose warrant further research in the attempt to advance the existing technologies for overcoming the blood-brain barrier.