The emergence of peptides in the pharmaceuticalbusiness: From exploration to exploitationThomas Uhliga, Themis Kyprianoua, Filippo Giancarlo Martinellia,Carlo Alberto Oppicia, Dave Heiligersa, Diederik Hillsa,Xavier Ribes Calvoa, Peter Verhaerta,b,∗aLaboratory for Analytical Biotechnology & Innovative Peptide Biology, Department of Biotechnology, DelftUniversity of Technology, Delft, NetherlandsbBiomedical Research Institute, University of Hasselt, Diepenbeek, Belgiuma r t i c l e i n f oArticle history:Available online 29 May 2014Keywords:Peptide drugsPharmaceutical industryDrug discoveryDrug developmenta b s t r a c tThis minireview touches upon the challenges and opportunities peptides experience on thetrack to become an approved pharmaceutical.Peptide attributes originally considered troublesome with respect to drug developmentmay now turn out to be more convenient rather than unfavourable.Besides characteristic high target affinity, biological peptides often exhibit higher thanexpected stability. Clearly natural selective pressure has optimised these biomoleculesbeyond what can be anticipated solely on the basis of their chemical nature. This conceptis gradually finding its way into the pharma and biotech industry, as illustrated by a rise inmedicinal peptide patent applications and developmental work.© 2014 The Authors. Published by Elsevier B.V. on behalf of European ProteomicsAssociation (EuPA). This is an open access article under the CC BY-NC-SA license(http://creativecommons.org/licenses/by-nc-sa/3.0/)

.1. IntroductionDrug development pipelines, which in the first century ofthe industry have been dominated by small molecules, arecharacterised by high attrition rates. The road to marketauthorisation has many obstacles and next to efficacy andtolerability, new drug candidates have to meet several otherrequirements. Besides essential pharmacodynamics, pharma-cokinetics, toxicity, and safety issues, also economic factorsare vital, including producibility, market competition, intel-lectual property, and others. This is why in a typical drug∗Corresponding author at: Laboratory for Analytical Biotechnology & Innovative Peptide Biology, Department of Biotechnology, DelftUniversity of Technology, Delft, Netherlands. Tel.: +31 15 278 2332.E-mail address: p.d.e.m.verhaert@tudelft.nl (P. Verhaert).development process of today, >90% novel drug candidates failbetween their identification and being put on the market.As peptides are readily degraded inside the human body,which is equipped with roughly 600 molecularly different pro-teases [37], this class of (bio)chemicals has long been heldineligible for drug development, and deemed widely inferiorto small molecules. Despite such neglect, a number of recenttechnological breakthroughs and advances have sparkedmajor interest in their usage both as diagnostics as well astherapeutics. In particular, modern-day analytical methods,which greatly excel in sensitivity, resolution and through-put over those available to the traditional pharmaceutical http://dx.doi.org/10.1016/j.euprot.2014.05.003 2212-9685/© 2014 The Authors. Published by Elsevier B.V. on behalf of European Proteomics Association (EuPA). This is an open access article under the CC BY-NC-SA license (http://creativecommons.org/licenses/by-nc-sa/3.0

industry, facilitate the discovery and identification of a wealthof novel peptides with pharmaceutical potential. Further-more, present combinatorial chemistry provides the meansto modify them and to create completely artificial variantsand alternatives. Some pharmacodynamic ‘weaknesses’ ofpeptides cannot be fully abolished this way, but clever formu-lations may mask or amend them. In combination with anin-depth study of the complete biology of peptides in theiroriginal natural sources, current (bio)technologies have thepotential to generate an ample spectrum of efficacious andsafe peptide drugs.Here, we review the steady rise of therapeutic peptideswhich is apparent in the pharmaceutical and biotech indus-try of today. We will focus on how a peptide drug candidatepasses the various phases in the traditional pharmaceuticaldevelopment pipeline and the differences herein to both smallmolecules and the larger biopharmaceuticals. With this, weaim to reveal that peptides are by far not ‘undrugable’, but,instead, offer immense medicinal potential.2. Concept/historyIn terms of chemical complexity, peptides fill a niche betweentypical small molecule chemicals and the larger proteins. Justas the latter, they feature a modular structure with aminoacids linked by peptide bonds as base units. Their size islimited, with arbitrary boundaries set at up to 100 residues[20]. Nonetheless, within these limits, peptides exhibit mul-tifarious structures with regard to amino acid sequence,post-translational modifications and resultant spatial shape.Starting about a century ago (World War I), the adventof the modern drug era came with pioneering therapeuticcompounds like the opiate morphine and the cyclic peptidepenicillin, followed in the early 1920s by the (poly)peptideinsulin. These drugs introduced a new standard in diseasetreatment. Although peptides thus held their place amongthe initial therapeutic discoveries [50], small molecules rapidlytook preference in the drug development industry, primarilydue to their ease of production, simplicity of administra-tion (as oral ‘pill’) and superior pharmacodynamic properties.Meanwhile, the rapid enzymatic breakdown of peptides inbiological systems and the consequently more challengingadministration routes (e.g. injection such as for insulin) ledto more and more neglect of this biochemical class in thetraditional drug development process.In the 21st century, the pharmaceutical business is expe-riencing dramatic changes. Stringent safety regulations,lengthy compound development processes and massivefinancial efforts (Vlieghe, Lisowski et al., 2010) all incur con-cern that, despite the increasing investment into research anddevelopment, medicinal innovation is declining. Especiallythe last decade has seen a major paradigm shift in the scopeof the pharmaceutical sector, focusing more on orphan orrepurposed drugs and reducing production costs, as to endurethe high expenses associated with drug development. Fewernew drugs make it to the market and the patent protectionof current blockbuster drugs is deteriorating, with a result-ing drainage of the drug pipelines. All this may ultimatelypush the pharmaceutical industry towards a new frontier inmodern drug development. Fresh strategies are needed torevive pharma’s lost momentum and we agree with Vliegheand coauthors (Vlieghe, Lisowski et al., 2010) that the sector’shope (partly) lies in peptides.3. Peptide discovery3.1. Natural sourcesNature harbours an impressive variety of biologically activepeptides expressed in virtually all living species and, therefore,represents one of the most promising sources for peptide drugdiscovery (see also www.NP2D.com).Within the multicellular body, peptides exert diversebiological roles, most prominently as signalling/regulatorymolecules in a broad variety of physiological processes,including defence, immunity, stress, growth, homeostasis,and reproduction [24].Through evolution, numerous peptides have evolved toexhibit their ‘natural’ bioactivity outside of the producingorganism. Many of these have been isolated and characterisedfrom the skin of frogs and toads [49,55]. These geneticallyencoded compounds have been shown to protect and defendtheir manufacturers against many foes, both predators andpathogens [13]. Hitherto, over 300 antimicrobial peptides havebeen identified from amphibians that hold promise for futureantibiotic research and development [33].Intriguingly, many externally active peptides have evolvedas means of active predation, especially in venomous animalssuch as spiders, snails and snakes (see [64]). While the toxicityarises from interfering with neuronal transmission (blockingsynaptic signalling, ion channel; e.g. conotoxins) or, in general,disrupting critical biochemical signalling networks within theprey’s body [61], low doses of these peptides can actually coun-teract disturbances from diverse disorders. Accordingly, toxicpeptides may aid in treating pain [41], neurological and car-diovascular diseases, diabetes and cancer [32]. A prominentexample is the type 2 diabetes drug Exenatide, a synthetic ver-sion of a glucagon-like peptide-1 analogue found in the venomof the Gila monster Heloderma suspectum [7].As bioactive peptides obtained from natural sources havebeen subject to aeons of selective pressure, they showconsiderable plusses over artificially/chemically conceivedpeptide-like compounds. Namely, they excel in stabilityand target affinity, both of which are extremely chal-lenging to achieve or reproduce through rational peptidedesign, screening of libraries of randomly composed peptidesor peptidomimetics. Although we appreciate the intelli-gence of peptide medicinal chemists, and other traditional(bio)chemistry based pharmacologists, we believe that muchis still to be discovered from the natural bioactive peptidesused all over the biological taxonomy (from microorganismsover plants to animals). With so many of these being used asdrugs by so many different species for so many different pur-poses, it is clear that mankind can still learn a lot from theimplied biology. We would, therefore, wholeheartedly supportan adjustment of the name of the ‘Natural Peptides to Drugs’NP2D discussion forum to ‘NP4D’ (Natural Peptides for Drugs