<br><h3> Chapter One </h3> <b>Challenges in Delivery of Biopharmaceuticals; the Need for Advanced Delivery Systems</b> <p> <i>Hanne Morck Nielsen and Lene Jorgensen</i> <p> <p> <b>1.1 Introduction</b> <p> Due to the advances in biotechnology, traditional biopharmaceuticals of biological origin are being replaced and supplemented by therapeutics developed by recombinant technologies and chemical synthesis. In addition, the rapid advances in molecular biology and genetics contribute to an in depth understanding of mechanisms involved in disease development, and generate possibilities for novel indications for biopharmaceuticals. Recent reviews list several hundred biopharmaceuticals either in development or undergoing clinical trials for treatment of a number of serious diseases. However, formulating biopharmaceuticals with the optimal therapeutic efficacy and the possibility of large scale production of the required formulation as well as optimal storage stability is highly challenging. Firstly, the unique structural characteristics of both amino acid-based as well as nucleic acid-based biopharmaceuticals make the formulation development more challenging than for more conventional drugs. The backbone and folding structure of the drug must be retained during processing and storage for the drug to exert its effect on for example a receptor. Secondly, upon administration to the patient the formulation must protect the drug under degradative conditions, such as the presence of enzymes, in order to ensure efficient delivery. Optimally, the formulation should ensure targeted delivery to the site of action and controlled release of the drug from the formulation at this site, thus enabling easy administration and high efficacy of the formulated drug. Thirdly, the structure-activity complexity of the active biopharmaceutical often requires that for each drug, an individualized delivery system is designed, meaning that what may work for one biopharmaceutical may not be feasible or optimal for another biopharmaceutical drug. <p> <p> <b>1.2 Overcoming Delivery Barriers <p> 1.2.1 Stabilization</b> <p> Due to the inherent instability towards hydrolysis and enzymatic degradation and fast clearance, the half-life of biopharmaceuticals is most often relatively short after administration. Ways to overcome this are to develop, for example, stabilized analogues or prodrugs by conjugation of different chemical groups or by physical stabilization of the biopharmaceutical drug by use of excipients. <p> An example of a way to increase the circulation lifetime is the acylation of peptides, for example C16-acylated glucagon-like peptide 1, which possesses satisfactory pharmacokinetic properties sufficient for a once-daily administration. Another approach is site-specific pegylation, for example that of coagulation factor VIII with poly(ethylene glycol) (PEG) with a molecular weight of more than 10kDa resulting in a significant longer <i>in vivo</i> half-life as compared to the native factor VIII. Likewise, it was shown that conjugation of a 20kDa PEG chain to aptamers significantly increased aptamer residence in circulation and thus facilitate distribution to highly perfused organs. Amino acid substitution in peptides and proteins and modification of the degree of glycosylation are other ways to enhance the therapeutic efficacy of the peptide or protein drugs. Regarding nucleic acid-based drugs, chemical modifications of the nucleic acid backbone are also used to obtain increased biological stability as well as increased target affinity; one eminent example being the locked nucleic acid (LNA) modifications of RNAs intended for antisense therapy. <p> Thus, overcoming the challenges of inactivation of the biopharmaceutical by (i) physical conformational changes, (ii) complexation or association to other (naturally occurring) compounds or (iii) chemical degradation can be achieved by modification of the drug molecule. <p> Complexing or encapsulation of the biopharmaceutical drug in order to physically shield against protease or nuclease degradation is another generally interesting approach to prolong the half-life of amino acid-based and nucleic acid drugs, respectively. Peptides and protein drugs have thus proven to be protected by particulate encapsulation. Polymers capable of condensing nucleic acids (both DNA and RNA), and thereby protect them from nuclease degradation, include polycations like chitosan, linear and branched poly(ethylene imine) (PEI) and dendrimers. Lipoplex formation or encapsulation in capsules such as liposomes or solid particles based on lipids or polymers is also a promising approach to shield and protect nucleic acid-based biopharmaceuticals. <p> For the above mentioned formulation approaches, it is a prerequisite that the drug is not only protected during storage and administration, but also that it is released, <i>delivered</i>, at the target site irrespective of whether invasive or non-invasive administration routes are applied. <p> <p> <b>1.2.2 Enhancing Delivery</b> <p> A prerequisite for the successful delivery for local as well as systemic delivery of peptides, proteins and nucleic acid derived drugs is the maximization of the delivery to the target site and a controlled and prolonged delivery time. Apart from the above mentioned strategies, one of the potential successful injectable sustained release lipid formulations for biomacromolecules is the Depofoam[TM] concept by SkyePharma. It differs from the conventional lipsomes in the increased surface area available, which makes the aqueous volume larger, and it has been shown to successfully encapsulate (60-85%) and sustain the release of insulin, luteinizing hormone-releasing factor and others. <p> The therapeutic applicability of biopharmaceuticals is hampered not only by their inherent instability, but also by their weight and polar surface characteristics. This is mainly a challenge for therapeutics that are to be administered by non-invasive techniques and intended for systemic absorption, since the drug must reach and pass the viscous mucosa lining, for example the oral and upper airway mucosa, and then permeate the tight cellular barrier in order for the drug to reach the circulation after administration by, for example, the gastrointestinal or airway routes. In theory, the drug in solution can permeate the epithelium by the para- or transcellular route. However, the size of peptides, proteins and nucleic acid-based drugs implies that the amount crossing the barrier by the paracellular route is strictly limited. The barrier properties might be affected by co-administration of chemical enhancers in the delivery system, but safe and reversible modulation of tight junction function might be achievable with co-excipients such as lipids and cationic peptides. As biopharmaceuticals are usually very potent, a low absorbed amount of drug might be sufficient and the use of such membrane destabilizing excipients is promising. However, the risk of side effects by modulating the barrier properties should not be neglected. Endocytotic transport mechanisms, such as macropinocytosis, are likely to comprise the primary flux mechanisms for transcellular flux of macromolecules larger than, for example, insulin. Also, the cellular uptake of complexes, aggregates or nanoparticles is expected to occur by endocytotic mechanisms. <p> Even though formulation advances are evident, the above mentioned barriers still imply that most biomacromolecular drugs are currently administered by injection, since the absorption and distribution properties are better due to that the capillary lining endothelia is more permeable than the mucosal epithelium. A crucial issue in formulating novel drug delivery systems is, therefore, also to consider how to overcome the biological barrier at the site of administration. <p> <b>1.3 Drug Delivery Technologies and Excipients</b> <p> As indicated above, longevity of the drugs and delivery systems is important for efficient delivery. However, targetability and triggerability of the system are issues that are addressed more efficiently as materials sciences develop. <p> Nanocarriers such as liposomes can be prepared at a certain size and with a shielding coating to prevent both aggregation and also facilitate passive targeting by the enhanced permeation and retention effect, and thereby accumulate in fenestrated tissue like cancer or inflamed tissue. Further, the vesicles can be tailored to trigger release upon changes in, for example, pH or temperature. Likewise, synthetic biomimetic pH sensitive polymersomes have shown successful intracellular delivery of macromolecules. Supramolecular structure synthesis on the basis of well-known chemical structures like cyclodextrins is becoming increasingly applicable, also in combination with other polymers and targeting ligands. Emerging materials such as carbon nanotubes can also be grafted with targeting ligands in order to obtain more efficient delivery. Several promising delivery systems based on polymers that partly consist of cell penetrating peptides are reported to show high cellular transfection efficiencies and low cytotoxicity and intracellular targeting, and thus be feasible as a non-viral delivery technology for, for example, antisense therapeutics. It has recently been shown in vivo that nasal and oral absorption of insulin in rats was markedly improved by the presence of L-penetratin or oligo-arginine, respectively, and without any detectable side effects; yet there is still a number of important factors to be addressed to elucidate the enhancing effect of co-administration of cell penetrating peptides with biopharmaceuticals. <p> Also, for vaccines, it is important not only to target the delivery system to the proper antigen presenting cells, but also to elicit an immune response. Since many excipients and drug delivery systems explored for systemic delivery of, for example, proteins used in substitution or replacement therapy in themselves show immunomodulatory effects, more and more of these advanced delivery systems are explored as adjuvants for vaccine formulations. As an example, alginate coated chitosan nanoparticels have proven effective as an adjuvant for subcutaneous administration of an antigen, and short peptides or nucleic acid-based immunomodulators are explored for a number of optimized vaccine formulations. In addition, non-injectable formulations for, for example, airway delivery of vaccines may also introduce the use of various well-known and novel excipients. <p> <p> <b>1.4 Risks</b> <p> All structures introduced to the patient should be biocompatible and biodegradable, so the direct effects of, for example, membrane interacting chemical enhancers or reactive degradation products of excipients must obviously be known and avoided when designing drug delivery systems. Apart from that, for many biologic pharmaceuticals, a major issue is the risk of inducing immunogenic side reactions towards the therapeutic molecule itself or towards the co-administered excipients or degradation products thereof. For all types of pharmaceutical formulations, the choice of excipients can be detrimental to the efficacy of the formulation, since minor changes in, for example, composition and purity can cause highly unwanted side effects. One example is the alteration in the glycosylation pattern of erythropoietin, which is thought to cause increased immunogenicity. Polymeric and lipid carrier molecules as well as their physical appearance as, for example, nanoparticles might induce significant toxicity issues that require resolution, since a number of toxicology reports have demonstrated that exposure to nanotechnology derived particles pose a serious risks to biological systems. Taking advantage of the technical advances in detection and prediction of unwanted side effects also helps to focus the attention on the long term effects of seemingly safe drug delivery systems. <p> <p> <b>1.5 Conclusion</b> <p> Successful formulation of delivery systems for biopharmaceuticals depends on a thorough understanding of the biopharmaceutical molecular structure, stability and biological activity and the effect of processing it into a pharmaceutical dosage form. A thorough understanding of the wanted and, especially, the unwanted effects caused by the excipients and the formulation appearance in relation to the administration and target site is equally important. Developing advanced drug delivery systems thus requires interdisciplinary science, and a successful formulation of a biotechnology-based drug is very likely to be individual for each drug due to their structural complexity. <p> <i>(Continues...)</i> <p> <!-- copyright notice --> <br></pre> <blockquote><hr noshade size='1'><font size='-2'> Excerpted from <b>Delivery Technologies for Biopharmaceuticals</b> Copyright © 2010 by John Wiley & Sons, Ltd. Excerpted by permission.<br> All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.<br>Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.