Materials and methods for delivery of biological drugs

Journal name:
Nature Chemistry
Volume:
8,
Pages:
997–1007
Year published:
DOI:
doi:10.1038/nchem.2629
Received
Accepted
Published online

Abstract

Biological drugs generated via recombinant techniques are uniquely positioned due to their high potency and high selectivity of action. The major drawback of this class of therapeutics, however, is their poor stability upon oral administration and during subsequent circulation. As a result, biological drugs have very low bioavailability and short therapeutic half-lives. Fortunately, tools of chemistry and biotechnology have been developed into an elaborate arsenal, which can be applied to improve the pharmacokinetics of biological drugs. Depot-type release systems are available to achieve sustained release of drugs over time. Conjugation to synthetic or biological polymers affords long circulating formulations. Administration of biological drugs through non-parenteral routes shows excellent performance and the first products have reached the market. This Review presents the main accomplishments in this field and illustrates the materials and methods behind existing and upcoming successful formulations and delivery strategies for biological drugs.

At a glance

Figures

  1. Biodegradable organic polymers can be used to engineer implantable depots for controlled release of biological drugs over extended periods of time.
    Figure 1: Biodegradable organic polymers can be used to engineer implantable depots for controlled release of biological drugs over extended periods of time.

    a, PLGA and PCL provide opportunities to tune the degradation rate of the implants for as long as several years. bd, Technologically there is virtually no restriction on the size of substrates and degradable matrices can be produced as nanoparticles (b), microparticles (c), and macroscopic objects (d). Panel b reproduced with permission from ref. 10, c, ref. 11 and d, ref. 12, all are from the ACS.

  2. Assembly of surface coatings.
    Figure 2: Assembly of surface coatings.

    The sequential, layer-by-layer deposition of polymers, and incorporation of biological drugs into the assembled thin films presents a facile means to engineer controlled and site-specific presentation of biologics to the cells and tissues, specifically for applications in tissue engineering and regenerative medicine. a, Polymers adsorb from solutions onto an underlying surface primed with a complementary interacting partner (polycation–polyanion, hydrogen bonding donor–acceptor). This leads to reversal of the surface properties, priming the surface for the deposition of the next polymer. Deposition cycles are repeated as necessary to achieve the desired coating thickness and can be performed on virtually any substrate with no restriction on the materials' surface chemistry, object size, or topography of the surface. Biological drugs can be immobilized into these films through adsorption during film assembly or absorption into the preformed multilayered polymer film. b, Representative polymers used in these applications include biodegradable polyamido-ester 1; biodegradable pseudo-natural polypeptides poly(lysine) 2 and poly(glutamic acid) 3; charge shifting polymer 4; hydrogen bonding donor poly(acrylic acid) 5 and complementary acceptor poly(ethylene glycol) 6; and ionic polysaccharides hyaluronic acid 7, poly(alginate) 8, and chitosan 9. Figure adapted with permission from ref. 30, ACS.

  3. Conjugation of biological drugs with synthetic non-ionic water-soluble polymers.
    Figure 3: Conjugation of biological drugs with synthetic non-ionic water-soluble polymers.

    This technology is highly successful for protecting biologics from fast proteolysis in blood, preventing their rapid renal clearance, and also decreasing recognition of the administered protein by the immune system — resulting in a significantly extended half-life of the biological drug in humans and a drastically decreased frequency of drug administration. a-b, Examples of such polymers include PEG, PVA, and PVP (a), of which PEG remains the golden standard and the polymer of choice for all but one marketed product of this kind. Conjugation of polymers to the proteins is well established using diverse tools of bioconjugation (b, N-hydroxysuccinimide derivative of PEG for a one-step conjugation to the peptidic amine groups on for example, lysine or chain terminus). Resulting conjugates are administered via injection.

  4. Recombinant techniques constitute a highly successful approach to engineer derivatives of biological drugs with markedly extended blood residence time.
    Figure 4: Recombinant techniques constitute a highly successful approach to engineer derivatives of biological drugs with markedly extended blood residence time.

    a, An expression plasmid can be engineered such that the therapeutic protein is expressed as a fused polypeptide containing the protein of interest and a non-structured polypeptide based on Pro, Ala, and/or Ser (termed PAS). Upon expression, the protein-encoding part of the polypeptide folds into the nominated therapeutic protein, whereas the PAS sequence forms a random coil. The latter serves to extend the circulation lifetime of the biological drug due to an increase in hydrodynamic volume of the conjugate (compared to the parent biological drug). aa, amino acid. b, Biological drugs can also be 'fused' through recombinant engineering (or alternatively through chemical ligation) to the XTEN protein, albumin or Fc fragment of the immunoglobulin. Of these, XTEN is a non-structured sequence and works similarly to PAS, whereas albumin and Fc extend the blood residence time of the conjugate due to physiological mechanisms of protein recycling.

  5. Physiological recycling of albumin and immunoglobulins.
    Figure 5: Physiological recycling of albumin and immunoglobulins.

    This natural mechanism to prevent degradation of and elimination of these proteins from the blood, has been adapted to become the highly successful platform for delivery of biological drugs. a, Physiological recycling upon internalization of albumin and immunoglobulins relies on the recognition of these proteins by the neonatal FcRn receptor in the lysosome upon acidification of this subcellular compartment during intracellular trafficking. Receptor bound proteins — together with the associated cargo — are exocytosed whereas all other solutes are trafficked further for processing. b, Albumin binding can be non-covalent, capitalizing on the natural propensity of albumin to bind hydrophobic solutes. Specifically, biological drugs such as peptide hormones and insulin can be functionalized with a hydrophobic (aliphatic) tail. The resulting conjugates spontaneously bind to albumin upon administration into humans.

  6. Examples of non-invasive drug administration routes.
    Figure 6: Examples of non-invasive drug administration routes.

    The routes are being developed to overcome the low bioavailability of biological drug upon administration per os, and to avoid the resulting necessity to administer biologics via injection. These routes include (but are not limited to) pulmonary, transdermal, nasal and buccal; which are schematically discussed herein together with the relative positives (in green) and negatives (in red) — specifically with regard to the delivery of biological drugs.

  7. Transdermal administration of biological drugs.
    Figure 7: Transdermal administration of biological drugs.

    This technique, specifically using transdermal microneedles penetrating the stratum corneum, is poised to be a highly versatile, non-invasive and pain-free route of administering biological drugs. Microneedles can be designed as solid miniaturized pins — to provide a temporary opening of the impermeable barrier created by the skin and allow diffusion of drugs. Coated microneedles contain the drug on their surface and deposit the payload upon contact. Dissolving microneedles contain the payload within the matrix material and release the drug upon needle dissolution. Hollow microneedles are true miniaturized analogues to serological needles for infusion of the drug. Figure adapted with permission from ref. 107, Elsevier.

References

  1. Brown, L. R. Commercial challenges of protein drug delivery. Expert Opin. Drug Deliv. 2, 2942 (2005).
  2. Desnick, R. J. & Schuchman, E. H. Enzyme replacement therapy for lysosomal diseases: lessons from 20 years of experience and remaining challenges. Annu. Rev. Genom. Hum. G. 13, 307335 (2012).
  3. Gu, Z., Biswas, A., Zhao, M. & Tang, Y. Tailoring nanocarriers for intracellular protein delivery. Chem. Soc. Rev. 40, 36383655 (2011).
  4. Torchilin, V. Intracellular delivery of protein and peptide therapeutics. Drug Discov. Today Technol. 5, e95e103 (2008).
  5. Pashuck, E. T. & Stevens, M. M. Designing regenerative biomaterial therapies for the clinic. Sci. Transl. Med. 4, 160sr4 (2012).
  6. Langer, R. & Folkman, J. Polymers for the sustained release of proteins and other macromolecules. Nature 263, 797800 (1976).
  7. Uhrich, K. E., Cannizzaro, S. M., Langer, R. S. & Shakesheff, K. M. Polymeric systems for controlled drug release. Chem. Rev. 99, 31813198 (1999).
  8. Greiner, A. & Wendorff, J. H. Electrospinning: a fascinating method for the preparation of ultrathin fibres. Angew. Chem. Int. Ed. 46, 56705703 (2007).
  9. Mundargi, R. C., Babu, V. R., Rangaswamy, V., Patel, P. & Aminabhavi, T. M. Nano/micro technologies for delivering macromolecular therapeutics using poly(d, l-lactide-co-glycolide) and its derivatives. J. Control. Release 125, 193209 (2008).
  10. Karnik, R. et al. Microfluidic platform for controlled synthesis of polymeric nanoparticles. Nano Lett. 8, 29062912 (2008).
  11. Enlow, E. M., Luft, J. C., Napier, M. E. & DeSimone, J. M. Potent engineered PLGA nanoparticles by virtue of exceptionally high chemotherapeutic loadings. Nano Lett. 11, 808813 (2011).
  12. Yang, C.-S., Wu, H.-C., Sun, J.-S., Hsiao, H.-M. & Wang, T.-W. Thermo-induced shape-memory PEG-PCL copolymer as a dual-drug-eluting biodegradable stent. ACS Applied Mater. Interf. 5, 1098510994 (2013).
  13. Mitragotri, S., Burke, P. A. & Langer, R. Overcoming the challenges in administering biopharmaceuticals: formulation and delivery strategies. Nat. Rev. Drug Discov. 13, 655672 (2014).
  14. Cawley, P., Wilkinson, I. & Ross, R. J. Developing long-acting growth hormone formulations. Clin. Endocrinol. 79, 305309 (2013).
  15. Seliktar, D. Designing cell-compatible hydrogels for biomedical applications. Science 336, 11241128 (2012).
  16. Slaughter, B. V., Khurshid, S. S., Fisher, O. Z., Khademhosseini, A. & Peppas, N. A. Hydrogels in regenerative medicine. Adv. Mater. 21, 33073329 (2009).
  17. Van Vlierberghe, S., Dubruel, P. & Schacht, E. Biopolymer-based hydrogels as scaffolds for tissue engineering applications: a review. Biomacromolecules 12, 13871408 (2011).
  18. Li, Y., Rodrigues, J. & Tomas, H. Injectable and biodegradable hydrogels: gelation, biodegradation and biomedical applications. Chem. Soc. Rev. 41, 21932221 (2012).
  19. Lin, C. C. & Anseth, K. S. PEG hydrogels for the controlled release of biomolecules in regenerative medicine. Pharm. Res. 26, 631643 (2009).
  20. Knop, K., Hoogenboom, R., Fischer, D. & Schubert, U. S. Poly(ethylene glycol) in drug delivery: pros and cons as well as potential alternatives. Angew. Chem. Int. Ed. 49, 62886308 (2010).
  21. Lozinsky, V. I. & Plieva, F. M. Poly(vinyl alcohol) cryogels employed as matrices for cell immobilization. 3. Overview of recent research and developments. Enzyme Microb. Technol. 23, 227242 (1998).
  22. Henderson, T. M. A., Ladewig, K., Haylock, D. N., McLean, K. M. & O'Connor, A. J. Cryogels for biomedical applications. J. Mater. Chem. B 1, 26822695 (2013).
  23. Lutolf, M. P. et al. Synthetic matrix metalloproteinase-sensitive hydrogels for the conduction of tissue regeneration: engineering cell-invasion characteristics. Proc. Natl Acad. Sci. USA 100, 54135418 (2003).
  24. Jensen, B. E. B., Edlund, K. & Zelikin, A. N. Micro-structured, spontaneously eroding hydrogels accelerate endothelialization through presentation of conjugated growth factors. Biomaterials 49, 113124 (2015).
  25. Fang, R. C. & Galiano, R. D. A review of becaplermin gel in the treatment of diabetic neuropathic foot ulcers. Biologics 2, 112 (2008).
  26. Rehfeldt, F., Engler, A. J., Eckhardt, A., Ahmed, F. & Discher, D. E. Cell responses to the mechanochemical microenvironment — implications for regenerative medicine and drug delivery. Adv. Drug Deliv. Rev. 59, 13291339 (2007).
  27. Wong, J. Y., Velasco, A., Rajagopalan, P. & Pham, Q. Directed movement of vascular smooth muscle cells on gradient-compliant hydrogels. Langmuir 19, 19081913 (2003).
  28. Discher, D. E., Sweeney, L., Sen, S. & Engler, A. Matrix elasticity directs stem cell lineage specification. Biophys. J. 32a32a (2007).
  29. Engler, A. J., Sen, S., Sweeney, H. L. & Discher, D. E. Matrix elasticity directs stem cell lineage specification. Cell 126, 677689 (2006).
  30. Zelikin, A. N. Drug releasing polymer thin films: new era of surface-mediated drug delivery. ACS Nano 4, 24942509 (2010).
  31. Shukla, A., Fang, J. C., Puranam, S., Jensen, F. R. & Hammond, P. T. Hemostatic multilayer coatings. Adv. Mater. 24, 492496 (2012).
  32. Chen, X. Y. et al. The influence of arrangement sequence on the glucose-responsive controlled release profiles of insulin-incorporated LbL films. Acta Biomater. 8, 43804388 (2012).
  33. Crouzier, T., Szarpak, A., Boudou, T., Auzely-Velty, R. & Picart, C. Polysaccharide-blend multi layers containing hyaluronan and heparin as a delivery system for rhBMP-2. Small 6, 651662 (2010).
  34. Dierich, A. et al. Bone formation mediated by synergy-acting growth factors embedded in a polyelectrolyte multilayer film. Adv. Mater. 19, 693697 (2007).
  35. Shah, N. J. et al. Surface-mediated bone tissue morphogenesis from tunable nanolayered implant coatings. Sci. Transl. Med. 5, 191ra83 (2013).
  36. Mendelsohn, J. D., Yang, S. Y., Hiller, J., Hochbaum, A. I. & Rubner, M. F. Rational design of cytophilic and cytophobic polyelectrolyte multilayer thin films. Biomacromolecules 4, 96106 (2003).
  37. Kocgozlu, L. et al. Selective and uncoupled role of substrate elasticity in the regulation of replication and transcription in epithelial cells. J. Cell Sci. 123, 2939 (2010).
  38. Saurer, E. M., Flessner, R. M., Sullivan, S. P., Prausnitz, M. R. & Lynn, D. M. Layer-by-layer assembly of DNA- and protein-containing films on microneedles for drug delivery to the skin. Biomacromolecules 11, 31363143 (2010).
  39. Saurer, E. M. et al. Polyelectrolyte multilayers promote stent-mediated delivery of DNA to vascular tissue. Biomacromolecules 14, 16961704 (2013).
  40. De Cock, L. J. et al. Layer-by-layer incorporation of growth factors in decellularized aortic heart valve leaflets. Biomacromolecules 11, 10021008 (2010).
  41. Thierry, B., Winnik, F. M., Merhi, Y. & Tabrizian, M. Nanocoatings onto arteries via layer-by-layer deposition: toward the in vivo repair of damaged blood vessels. J. Am. Chem. Soc. 125, 74947495 (2003).
  42. Kerdjoudj, H. et al. Small vessel replacement by human umbilical arteries with polyelectrolyte film-treated arteries in vivo behavior. J. Am. Coll. Cardiol. 52, 15891597 (2008).
  43. Shah, N. J. et al. Tunable dual growth factor delivery from polyelectrolyte multilayer films. Biomaterials 32, 61836193 (2011).
  44. Cezar, C. A. & Mooney, D. J. Biomaterial-based delivery for skeletal muscle repair. Adv. Drug Deliv. Rev. 84, 188197 (2015).
  45. Lam, J., Lu, S., Kasper, F. K. & Mikos, A. G. Strategies for controlled delivery of biologics for cartilage repair. Adv. Drug Deliv. Rev. 84, 123134 (2015).
  46. Bechler, S. L. et al. Reduction of intimal hyperplasia in injured rat arteries promoted by catheter balloons coated with polyelectrolyte multilayers that contain plasmid DNA encoding PKC delta. Biomaterials 34, 226236 (2013).
  47. Kontos, S. & Hubbell, J. A. Drug development: longer-lived proteins. Chem. Soc. Rev. 41, 26862695 (2012).
  48. Alconcel, S. N. S., Baas, A. S. & Maynard, H. D. FDA-approved poly(ethylene glycol)-protein conjugate drugs. Polym. Chem. 2, 14421448 (2011).
  49. Davis, F. F. The origin of pegnology. Adv. Drug Deliv. Rev. 54, 457458 (2002).
  50. Ravin, H. A., Seligman, A. M. & Fine, J. Polyvinyl pyrrolidone as a plasma expander. New Eng. J. Med. 247, 921929 (1952).
  51. Kojima, Y. & Maeda, H. Evaluation of poly(vinyl alcohol) for protein tailoring: improvements in pharmacokinetic properties of superoxide dismutase. J. Bioact. Comp. Polym. 8, 115131 (1993).
  52. Torchilin, V. P. et al. New synthetic amphiphilic polymers for steric protection of liposomes in vivo. J. Pharm. Sci. 84, 10491053 (1995).
  53. Yamaoka, T., Tabata, Y. & Ikada, Y. Fate of water-soluble polymers administered via different routes. J. Pharm. Sci. 84, 349354 (1995).
  54. Zelikin, A. N., Such, G. K., Postma, A. & Caruso, F. Poly(vinylpyrrolidone) for bioconjugation and surface ligand immobilization. Biomacromolecules 8, 29502953 (2007).
  55. Smith, A. A. A. et al. Macromolecular design of poly(vinyl alcohol) by RAFT polymerization. Polym. Chem. 3, 8588 (2012).
  56. Barz, M., Luxenhofer, R., Zentel, R. & Vicent, M. J. Overcoming the PEG-addiction: well-defined alternatives to PEG, from structure-property relationships to better defined therapeutics. Polym. Chem. 2, 19001918 (2011).
  57. Pelegri-O'Day, E. M., Lin, E.-W. & Maynard, H. D. Therapeutic protein–polymer conjugates: advancing beyond PEGylation. J. Am. Chem. Soc. 136, 1432314332 (2014).
  58. Matyjaszewski, K. & Xia, J. Atom transfer radical polymerization. Chem. Rev. 101, 29212990 (2001).
  59. Moad, G., Rizzardo, E. & Thang, S. H. Living radical polymerization by the RAFT process. Aus. J. Chem. 58, 379410 (2005).
  60. Rudmann, D. G., Alston, J. T., Hanson, J. C. & Heidel, S. High molecular weight polyethylene glycol cellular distribution and peg-associated cytoplasmic vacuolation is molecular weight dependent and does not require conjugation to proteins. Toxicol. Pathol. 41, 970983 (2013).
  61. Webster, R. et al. in PEGylated Protein Drugs: Basic Science and Clinical Applications Milestones in Drug Therapy (ed. Veronese, F.) 127146 (Birkhäuser Basel, 2009).
  62. Hadjichristidis, N., Iatrou, H., Pitsikalis, M. & Sakellariou, G. Synthesis of well-defined polypeptide-based materials via the ring-opening polymerization of alpha-amino acid N-carboxyanhydrides. Chem. Rev. 109, 55285578 (2009).
  63. Ulbricht, J., Jordan, R. & Luxenhofer, R. On the biodegradability of polyethylene glycol, polypeptoids and poly(2-oxazoline)s. Biomaterials 35, 48484861 (2014).
  64. Li, C. Poly(l-glutamic acid)–anticancer drug conjugates. Adv. Drug Deliv. Rev. 54, 695713 (2002).
  65. Schlapschy, M. et al. PASylation: a biological alternative to PEGylation for extending the plasma half-life of pharmaceutically active proteins. Prot. Eng. Des. Sel. 26, 489501 (2013).
  66. Morath, V. et al. PASylation of murine leptin leads to extended plasma half-life and enhanced in vivo efficacy. Mol. Pharm. 12, 14311442 (2015).
  67. Podust, V. N. et al. Extension of in vivo half-life of biologically active peptides via chemical conjugation to XTEN protein polymer. Prot. Eng. Des. Sel. 26, 743753 (2013).
  68. Schellenberger, V. et al. A recombinant polypeptide extends the in vivo half-life of peptides and proteins in a tunable manner. Nat. Biotech. 27, 11861190 (2009).
  69. Sleep, D., Cameron, J. & Evans, L. R. Albumin as a versatile platform for drug half-life extension. Biochim. Biophys. Acta Gen. Subj. 1830, 55265534 (2013).
  70. Elsadek, B. & Kratz, F. Impact of albumin on drug delivery — new applications on the horizon. J. Control. Release 157, 428 (2012).
  71. Mullard, A. Maturing antibody-drug conjugate pipeline hits 30. Nat. Rev. Drug Discov. 12, 329332 (2013).
  72. Jiang, X. R. et al. Advances in the assessment and control of the effector functions of therapeutic antibodies. Nat. Rev. Drug Discov. 10, 101110 (2011).
  73. Czajkowsky, D. M., Hu, J., Shao, Z. F. & Pleass, R. J. Fc-fusion proteins: new developments and future perspectives. EMBO Mol. Med. 4, 10151028 (2012).
  74. Andersen, J. T. et al. Structure-based mutagenesis reveals the albumin-binding site of the neonatal Fc receptor. Nat. Commun. 3, 610 (2012).
  75. Madsen, K. et al. Structure − activity and protraction relationship of long-acting glucagon-like peptide-1 derivatives: importance of fatty acid length, polarity, and bulkiness. J. Med. Chem. 50, 61266132 (2007).
  76. Lau, J. et al. Discovery of the once-weekly glucagon-like peptide-1 (glp-1) analogue semaglutide. J. Med. Chem. 58, 73707380 (2015).
  77. Liu, H. et al. Structure-based programming of lymph-node targeting in molecular vaccines. Nature 507, 519522 (2014).
  78. Harrison, G. A. Insulin in alcoholic solution by the mouth. Brit. Med. J. 1923, 12041205 (1923).
  79. Brown, L. R. Commercial challenges of protein drug delivery. Expert Opin. Drug Deliv. 2, 2942 (2005).
  80. Goldberg, M. & Gomez-Orellana, I. Challenges for the oral delivery of macromolecules. Nat. Rev. Drug Discov. 2, 289295 (2003).
  81. Clement, S., Still, J. G., Kosutic, G. & McAllister, R. G. Oral insulin product hexyl-insulin monoconjugate 2 (HIM2) in type 1 diabetes mellitus: the glucose stabilization effects of HIM2. Diabetes Technol. Ther. 4, 459466 (2002).
  82. Lai, S. K., Wang, Y.-Y. & Hanes, J. Mucus-penetrating nanoparticles for drug and gene delivery to mucosal tissues. Adv. Drug Deliv. Rev. 61, 158171 (2009).
  83. Sosnik, A., das Neves, J. & Sarmento, B. Mucoadhesive polymers in the design of nano-drug delivery systems for administration by non-parenteral routes: a review. Prog. Polym. Sci. 39, 20302075 (2014).
  84. Khutoryanskiy, V. V. Advances in mucoadhesion and mucoadhesive polymers. Macromol. Biosci. 11, 748764 (2011).
  85. Bernkop-Schnurch, A. Thiomers: a new generation of mucoadhesive polymers. Adv. Drug Deliv. Rev. 57, 15691582 (2005).
  86. Russell-Jones, G. J. Use of vitamin B12 conjugates to deliver protein drugs by the oral route. Crit. Rev. Ther. Drug Carrier Syst. 15, 557586 (1998).
  87. Petrus, A. K., Fairchild, T. J. & Doyle, R. P. Traveling the vitamin B12 pathway: oral delivery of protein and peptide drugs. Angew. Chem. Int. Ed. 48, 10221028 (2009).
  88. Pridgen, E. M. et al. Transepithelial transport of Fc-targeted nanoparticles by the neonatal Fc receptor for oral delivery. Sci. Transl. Med. 5, 213ra167 (2013).
  89. Schulz, J. D., Gauthier, M. A. & Leroux, J. C. Improving oral drug bioavailability with polycations? Eur. J. Pharm. Biopharm. 97, 427437 (2015).
  90. Binkley, N. et al. A phase 3 trial of the efficacy and safety of oral recombinant calcitonin: the oral calcitonin in postmenopausal osteoporosis (ORACAL) trial. J. Bone Miner. Res. 27, 18211829 (2012).
  91. Maggio, E. T. & Pillion, D. J. High efficiency intranasal drug delivery using Intravail alkylsaccharide absorption enhancers. Drug Deliv. Transl. Res. 3, 1625 (2013).
  92. Heinemann, L. & Jacques, Y. Oral insulin and buccal insulin: a critical reappraisal. J. Diab. Sci. Technol. 3, 568584 (2009).
  93. Whitehead, K., Karr, N. & Mitragotri, S. Safe and effective permeation enhancers for oral drug delivery. Pharm. Res. 25, 17821788 (2008).
  94. Whitehead, K., Karr, N. & Mitragotri, S. Discovery of synergistic permeation enhancers for oral drug delivery. J. Control. Release 128, 128133 (2008).
  95. Malkov, D. et al. Oral delivery of insulin with the eligen technology: mechanistic studies. Curr. Drug Deliv. 2, 191197 (2005).
  96. Heubner, W., de Jongh, S. E. & Laquer, E. Über Inhalation von Insulin. Klinische Wochenschrift 3, 23422343 (1924).
  97. Siekmeier, R. & Scheuch, G. Systemic treatment by inhalation of macromolecules — principles, problems, and examples. J. Physiol. Pharmacol. 59, 5379 (2008).
  98. Patton, J. S. et al. The particle has landed-characterizing the fate of inhaled pharmaceuticals. J. Aerosol Med. Pulm. Drug Deliv. 23, S71S87 (2010).
  99. Forbes, B. et al. Challenges in inhaled product development and opportunities for open innovation. Adv. Drug Deliv. Rev. 63, 6987 (2011).
  100. Pilcer, G. & Amighi, K. Formulation strategy and use of excipients in pulmonary drug delivery. Int. J. Pharm. 392, 119 (2010).
  101. Chow, A. H. L., Tong, H. H. Y., Chattopadhyay, P. & Shekunov, B. Y. Particle engineering for pulmonary drug delivery. Pharm. Res. 24, 411437 (2007).
  102. Johnson, K. A. Preparation of peptide and protein powders for inhalation. Adv. Drug Deliv. Rev. 26, 315 (1997).
  103. Edwards, D. A., Ben-Jebria, A. & Langer, R. Recent advances in pulmonary drug delivery using large, porous inhaled particles. J. Appl. Physiol. 85, 379385 (1998).
  104. Patton, J. S. & Byron, P. R. Inhaling medicines: delivering drugs to the body through the lungs. Nat. Rev. Drug Discov. 6, 6774 (2007).
  105. Angelo, R., Rousseau, K., Grant, M., Leone-Bay, A. & Richardson, P. Technosphere insulin: defining the role of Technosphere particles at the cellular level. J. Diabetes Sci. Technol. 3, 545554 (2009).
  106. Siekmeier, R. & Scheuch, G. Treatment of systemic diseases by inhalation of biomolecule aerosols. J. Physiol. Pharmacol. 60, 1526 (2009).
  107. Kim, Y. C., Park, J. H. & Prausnitz, M. R. Microneedles for drug and vaccine delivery. Adv. Drug Deliv. Rev. 64, 15471568 (2012).
  108. Haq, M. I. et al. Clinical administration of microneedles: skin puncture, pain and sensation. Biomed. Microdevices 11, 3547 (2009).
  109. Chu, L. Y. & Prausnitz, M. R. Separable arrowhead microneedles. J. Control. Release 149, 242249 (2011).

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Affiliations

  1. Department of Chemistry, Aarhus University, Aarhus C 8000, Denmark

    • Alexander N. Zelikin
  2. iNano Interdisciplinary Nanoscience Centre, Aarhus University, Aarhus C 8000, Denmark

    • Alexander N. Zelikin
  3. School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin 2, Ireland

    • Carsten Ehrhardt &
    • Anne Marie Healy
  4. Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland

    • Carsten Ehrhardt
  5. Synthesis and Solid State Pharmaceutical Centre, School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin 2, Ireland

    • Anne Marie Healy
  6. Advanced Materials and Bioengineering Research (AMBER) Centre, Trinity College Dublin, Dublin 2, Ireland

    • Anne Marie Healy

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