Protein and Peptide Letters - Volume 21, Issue 11, 2014

Designing therapeutic agents requires receptor targeting and drug delivery for optimal medication to improve health. Although innovative strategies help drug delivery, many therapeutic agents have side effects due to nonspecific binding. Biomedical engineering aims to target the therapeutic agents in controlled release over an extended period of time at specific rate to a targeted location of the body. Generally, administering engineered particles affect organ locally and this process reduces or eliminates the side effects compared to systemic drug delivery [1, 2]. This thematic issue reports recent developments in the field along with the applications. These contemporary approaches provide readers an up to date summary of the current literature and future perspectives for the prospective researchers. Dr. Hamman explains non-invasive delivery methods of protein and peptide based therapeutics via the oral, transmucosal, and inhalation routes. The study indicates current efforts to stimulate this research area to overcome degradation and absorption problems. A diabetic patient may need 60000 insulin injections and this invasive method is associated with pain and discomfort. For this reason development of the non-invasive methods will definitely increase patient’s life quality and these promising efforts will also prevent potential infections due to injections. Nanoparticles offer a unique solution for non-invasive drug delivery routes especially for protein based therapeutics. Proteins physicochemical properties, their permeability across biological membrane, and susceptibility to degradation limit non-invasive protein delivery. Nanostructured polymeric particles demonstrate significant advantages and Dr. Mitra group reviews applications of polymeric nanocarriers for protein and peptide delivery by non-invasive administrations. Degradation of protein based therapeutics limits drug delivery to the target area of the body and therefore, drug and macromolecule delivery carriers have been designed. These carriers are serum albumin, transferrin, virus capsids, polyethyleneglycol, polyvinylpyrrolidone, polylactic co-glycolic acid, N-(2-hydroxypropyl) methacrylamide copolymer, polyglutamic acid. Dr. Mukherjee reviews current efforts on protein-polymer conjugates and their advantages, limitations, and clinical trials. These carriers provide potential formulations against several diseases. A totally different approach to macromolecular drug delivery is cell penetrating peptides. This approach enhances intracellular delivery of therapeutic agents. Currently macromolecular drugs administered by injection due to their liable and unstable nature. Further, cell membrane is also impermeable to the macromolecules and protein based therapeutics as therapeutic candidates must be inside the cell to exert their function. These candidates can be administered via cell penetrating peptides. Dr. Huang work describes how cell penetrating peptides carry their protein cargo with non-covalent interaction for protein therapy. Side effects of synthetic drugs directed drug designers to natural compounds. Pentacyclic tripeptide phytochemicals have several therapeutic effects however, these compounds have poor solubility and their pharmacokinetic properties must be improved to employ as therapeutic agents. Dr. Soica summarizes the methods to improve pentacyclic tripeptides physiochemical and pharmacokinetic properties by polymeric carriers. Therapeutic drug delivery to the target depends on physicochemical properties of the drug and its receptor. Several factors may be involved in inadequate drug delivery. A computational model between doxorubicin and solid tumor was studied by Dr. Yun group to elucidate factors involved in drug delivery. Rest of the thematic issue covers applications based on biological and polymeric carriers for therapeutic agent delivery. An anti-inflammatory effect of solid lipid nanoparticle loaded with fluorescently labeled cyclosporine A was investigated by Dr. Battaliga research group and Dr. Boateng group also employs a biological carrier, chitosan xerogels, for non-invasive delivery of insulin. Dr. Chavda’s studies show drug delivery by mucoadhesive superporous hydrogel hybrids and explain characterization of the carrier along with mathematical models of drug release mechanism.In the last work, Dr. Patel addressed novel thermo sensitive penta-block copolymers for protein delivery in the treatment of posterior segment diseases. These biodegradable and biocompatible polymers can be used as biomaterial for controlled release and drug delivery. Approaches to develop physiochemical and pharmacokinetic properties of therapeutic agents with carrier systems have been investigated for the past decades. Recent advances have spawned several approaches and these approaches are expected to improve current technologies.

Protein and peptide based therapeutics are typically administered by injection due to their poor uptake when administered via enteral routes of drug administration. Unfortunately, chronic administration of these drugs through multiple injections presents certain patient related problems and it is difficult to mimic the normal physiological release patterns via this mode of drug administration. A need therefore exists to non-invasively deliver these drugs by means of alternative ways such as via the oral, pulmonary, nasal, transdermal and buccal administration routes. Although some attempts of needle free peptide and protein drug delivery have progressed to the clinical stage, relatively limited success has been achieved in terms of commercially available products. Despite the low frequency of clinical breakthroughs with noninvasive protein drug delivery this far, it remains an active research area with renewed interest not only due to its improved therapeutic potential, but also due to the attractive commercial outcomes it offers. It is the aim of this review article to reflect on the main strategies investigated to overcome the barriers against effective systemic protein drug delivery in different routes of drug administration. Approaches based on chemical modifications and pharmaceutical technologies are discussed with reference to examples of drugs and devices that have shown potential, while attempts that have failed are also briefly outlined.

Proteins and peptides are widely indicated in many diseased states. Parenteral route is the most commonly em- ployed method of administration for therapeutic proteins and peptides. However, requirement of frequent injections due to short in vivo half-life results in poor patient compliance. Non-invasive drug delivery routes such as nasal, transdermal, pulmonary, and oral offer several advantages over parenteral administration. Intrinsic physicochemical properties and low permeability across biological membrane limit protein delivery via non-invasive routes. One of the strategies to improve protein and peptide absorption is by delivering through nanostructured delivery carriers. Among nanocarriers, polymeric nanoparticles (NPs) have demonstrated significant advantages over other delivery systems. This article summarizes the application of polymeric NPs for protein and peptide drug delivery following oral, nasal, pulmonary, parenteral, transder- mal, and ocular administrations.

In the last few decades, novel drug delivery strategies have been a big priority to the formulation scientists. Peptides and proteins have drawn a special attention for their wide scope in the area. Serum albumin, transferrin, recom- binant proteins, virus capsids etc. are used as carrier for drug and biomolecules. Conjugates of polymers with proteins have also shown strong potency in the field of drug delivery. Polyethylene glycol is one of the most successful polymers that has been used extensively to develop protein conjugated formulations. Besides, polyvinyl pyrrolidone, polylactic-co- glycolic acid, N-(2-hydroxypropyl) methacrylamide copolymer, polyglutamic acid have also been investigated. In this re- view, we will highlight on the most recent overview of various advantages, limitations and marketed products of proteins, peptides and protein/peptide-polymer conjugates as drug carriers, such products in clinical trials and their various uses in the field of modern drug delivery. Understanding the key features of these materials and the vigorous research in this field will develop new drug formulations that will combat various types of life-threatening diseases.

Macromolecular drugs (e.g., proteins and nucleic acids) are highly environmentally liable and unstable, and their administration is strictly limited to injection. Moreover, a vast majority of macromolecules are cell membrane- impermeable, and it is a critical issue to enhance the cellular uptake efficiency for improving the treatment outcomes. Cell-penetrating peptide (CPP)-assisted strategy is promising for effective macromolecular delivery. As a case in point, CPP-mediated protein delivery has been considered as a revolutionary breakthrough. With aid of CPP, virtually all pro- teins can become cell-permeable. Generally, CPP-protein delivery works in a covalent delivery pattern, by which CPP and its cargo are linked via covalent bond. Recently, noncovalent delivery has also attracted attention for its potential application for protein delivery. In the presented work, the noncovalent pattern was demonstrated for its feasibi lity in percutaneous and nose-to-brain delivery with TAT/GFP as model drug, in comparison with the covalent method. Noncovalent CPP/protein delivery and its noninvasive application may provide a facile method for protein therapy.

Phytochemicals are becoming more and more interesting in the field of therapeutic research, mainly in the treatment of chronic illnesses, due to the fact that many synthetic drugs cause important side effects that impact on pa- tient’s life quality. Pentacyclic triterpenes are a class of compounds with several therapeutic effects and increasing impor- tance in cancer therapy; however, a major disadvantage is their low water solubility and bioavailability which leads to rather poor therapeutic results in vivo.Technological attempts to improve the pharmacokinetic profile of the main repre- sentatives of this class include the use of cyclodextrins, micro- and nanoemulsions, liposomes, polymeric nanoparticles, and nanocapsules. This paper is aimed to briefly summarize the most significant achievements in this field.

Effective delivery of therapeutic agents to tumour cells is essential to the success of most cancer treatment therapies except for surgery. The transport of drug in solid tumours involves multiple biophysical and biochemical proc- esses which are strongly dependent on the physicochemical properties of the drug and biological properties of the tumour. Owing to the complexities involved, mathematical models are playing an increasingly important role in identifying the factors leading to inadequate drug delivery to tumours. In this study, a computational model is developed which incorpo- rates real tumour geometry reconstructed from magnetic resonance images, drug transport through the tumour vasculature and interstitium, as well as drug uptake by tumour cells. The effectiveness of anticancer therapy is evaluated based on the percentage of survival tumour cells by directly solving the pharmacodynamics equation using predicted intracellular drug concentrations. Computational simulations are performed for the delivery of doxorubicin through different administration modes and doses. Our predictions show that continuous infusion is far more effective than bolus injection in maintaining high levels of intracellular drug concentration, thereby increasing drug uptake by tumour cells. On the other hand, bolus injection leads to higher extracellular concentration in both tumour and normal tissues compared to continuous infusion, which is undesirable as high drug concentration in normal tissues may increase the risk of associated side effects.

FMOC-isocyclosporine A, a fluorescent labeled cyclosporine A, was encapsulated in solid lipid nanoparticles (SLN) prepared by the coacervation technique, and its anti-inflammatory activity was evaluated. The anti-inflammatory activity of the fluorescent labelled molecule, measured as inhibition of TNF-α secretion, is similar to the native one. SLN were compared to commercial formulations, through measurement of cytokine release and drug uptake in rat peripheral blood mononuclear cells. Drug-loaded SLN inhibit TNF-α secretion in a lower extent than commercial formulations, probably due to a lower uptake by the cells, but the increase of IL-10 secretion caused by the lipid matrix itself makes this formulation interesting for its anti-inflammatory activity.

Stable and mucoadhesive, lyophilised, thiolated chitosan xerogels, loaded with insulin for buccal mucosa deliv- ery, in place of the currently used parenteral route have been developed. The xerogels were backed with impervious ethyl- cellulose laminate to ensure unidirectional release and also loaded with enzyme inhibitor to enhance insulin permeability across the buccal mucosa. Characterisation of xerogels using 1 HNMR confirmed the degree of deacetylation of the syn- thesised thiolated chitosan. The amount of thiol groups immobilised on the modified chitosan was quantified by Ellman’s reaction and molecular weight monitored by gel permeation chromatography. The stability of the secondary structure of insulin was examined by attenuated total reflectance Fourier transform infra-red spectroscopy and circular dichroism. In vitro and ex vivo permeation studies were undertaken by using EpiOral ™ and sheep buccal membrane respectively. Insu- lin released from thiolated chitosan xerogels, loaded with aprotinin (enzyme inhibitor and permeation enhancer) showed a 1.7-fold increase in permeation through EpiOral ™ buccal tissue construct compared to the pure drug. However, permea- tion was decreased for xerogels containing the enzyme inhibitor glutathione. Further, aprotinin containing xerogels en- hanced insulin permeation through sheep buccal membrane and demonstrated good linear correlation with the permeation data from the EpiOral ™ study. The results show the potential application of lyoph ilised thiolated chitosan xerogels con- taining aprotinin with improved mucoadhesion, penetration enhancing and enzyme inhibition characteristics for buccal mucosa delivery of macromolecules such as insulin.

In this investigation a novel approach based on mucoadhesive superporous hydrogel hybrids (SPHHs) for topi- cal vaginal drug delivery for Metronidazole was tried. Method: SPHHs were synthesized by solution polymerization tech- nique. The synthesized SPHHs were characterized for tensile strength, swelling behavior, porosity, density, mucoadhesion time, SEM, DSC and FT-IR studies. In vitro drug release study from prepared vaginal formulation based on SPHH was performed in simulated vaginal fluid. Different mathematical models were applied to ascertain the drug release mecha- nism. SPHHs have shown good tensile strength, mucoadhesion time and drug release for 24 hour. SEM images reflected the formation of pores and interconnected capillary channels. The release kinetic of drug from the prepared system was best explained by Korsmeyer-Peppas and Higuchi models and shown anomalous transport. The proposed novel drug de- livery system based on SPHH was successfully prepared and SPHH-DDS might be promising candidate for topical vagi- nal delivery of Metronidazole.

Biodegradable and injectable in situ thermosensitive hydrogels were investigated for sustained delivery of pro- tein therapeutics in the treatment of ocular posterior segment neovascular diseases. A series of triblock (TB, polycaprolac- tone-polyethylene glycol-polycaprolactone (PCL-PEG-PCL), B-A-B) and pentablock copolymers (PBCs) (polylactic acid (PLA)-PCL-PEG-PCL-PLA (C-B-A-B-C) and PEG-PCL-PLA-PCL-PEG (A-B-C-B-A)) were synthesized and evaluated for their thermosensitive behavior. Effects of molecular weight, hydr ophobicity and block arrangement on polymer crys- tallinity, sol-gel transition, micelle size, viscosity and in vitro drug release were examined. Results from sol-gel transition studies demonstrated that aqueous solutions of block copolymers can immediately transform to hydrogel upon exposure to physiological temperature. PBC provide significantly longer sustained release (more than 20 days) of IgG relative to TB copolymers. Moreover, kinematic viscosity of aqueous solution at 25°C for A-B-C-B-A type of PBCs was noticeably lower than the TB (B-A-B) copolymers and other PBCs with C-B-A-B-C block arrangements suggesting desired syringe- ability. The presence of PLA blocks in PBCs (C-B-A-B-C and A-B-C-B-A) significantly reduces crystallinity. Hence, it is anticipated that PBCs will have a faster rate of degradation relative to PCL-PEG-PCL based TB c opolyme rs. PBCs also exhibited excellent cell viability and biocompatibility on ARPE-19 (human retinal pigment epithelial cell line) and RAW- 264.7 (mouse macrophage cells), likely rendering it safe for ocular applications. Owing to biodegradability, thermosensi- tivity, ease of handling and biocompatibility PBC hydrogels can be considered as promising biomaterial for sustained de- livery of protein therapeutics to the back of the eye.