The growing significance of peptide therapeuticsSo what has happened in the last decade that indicatesthat peptides drugs have a long and secure future?

Well, first there is increasing amount of statisticalevidence to support this1. Forty years ago, back in theseventies, the average frequency of peptides enteringclinical trials was just over one per year. Ten andtwenty years on, it was 5 and 10 per year respectively,and as we approach the end of this decade, it lookslike the annual number will be close to 20. There arenow about 60 approved peptide drugs that willgenerate annual sales of approximately US$ 13 billionby the end of 2010. Although this only representsabout 1.5% of all drug product sales the numbers areincreasing dramatically with a current continuousannual growth rate (CAGR) between 7.5% and 10%.There are about 140 peptide candidates in the clinicand (our best guess) about another 500 – 600 inpre‐clinical development.

However it is more than just the numbers. Peptidetherapeutics are starting to show a maturity thatreflects their potential for addressing a growing rangeof medical challenges. While about half of thepeptides in clinical trials target indications inoncology, metabolic, cardiovascular and infectiousdiseases, the total range of therapeutic areasaddressed encompasses a wide assortment of medicaldisorders from endocrinological lesions through topain and hematology. A noticeable increase in thenumber of peptides targeting metabolic disorders hasheralded a move towards longer and more complexmolecules. There is also a willingness of both thepharmaceutical industry and its contract manufacturersto consider production scales of multi‐100 kg andeven tons using both solid‐ and solution‐phasesynthetic strategies.

Not that shorter peptides (<10 residues) are goingaway and the growing interest in peptide‐basedtherapeutic vaccines is currently opening up a wholenew market for such sequences. The manufacture ofshort sequences is significantly more economical thanfor longer peptides (>30 residues). Such sequences, ifrequired in large quantities, are also often amenableto solution‐phase approaches that offer scalabilityadvantages over solid‐phase chemistry.

The potential of peptides should be no surprise.Evolution has been honing the specificity of polypeptidesfor millions of years. Amino acid sequences –whether they are in peptides or in proteins – controland direct all aspects of cellular function and coordinatemost intercellular communication. No other class ofbiological molecules offers the range of chemicaldiversity that peptides and proteins possess. They arenature’s tool kit and the more we can use nativepeptides or closely related analogs, the safer andmore specific the drugs at the physician’s disposal.An advantage over small molecules is the fact that thestructural relationships between peptide drugcandidates and the physiologically active parentmolecules that they were derived from substantiallyreduces the risk of unforeseen side‐reactions. This isreflected in an over 20% probability of regulatoryapproval2, a rate which is double that of smallmolecules. In so far as they are composed of naturallyoccurring or metabolically tolerable amino acids, theyare generally non‐toxic and, as a result, toxicologystudies often consume vastly more peptide drugsubstance than the subsequent clinical trials. Whereside‐effects occur, these are often related to dosage orlocal reactions at the injection site. In general,peptides do not cause serious immune responses,although this must always be taken into consideration,particularly for longer sequences.

The impact of new technologiesPeptides have not always been the most popularcandidates for drugs and it is worth asking why andwhat might have occurred to change the bias againstpeptides as pharmaceutical agents. For many years,peptide‐based therapies were regarded as beinglimited to the treatment of hormonal lesions and laterhormone‐dependent cancer. Other indications werenot obvious at the time. In addition, peptides – dueto their chemical structure – were expensive andcomplicated pharmaceuticals to manufacture. Theyalso often had exceptionally short half‐lives makingchronic administration problematic and costly.However, the main downside was the lack of oralavailability. With a few notable exceptions, peptidesare degraded to their component amino acids in theupper gut. Given the lack of patient compliance withdrugs that require chronic self‐injection – theexception being drugs for life‐threatening diseases

The Future of Peptide Development in the Pharmaceutical IndustryRodney Lax, Ph.D., Senior Director of Business Development North America, PolyPeptide Group

A couple of weeks ago I was asked how long I thought the current interest in peptides as drug candidates would lastbefore another class of molecule replaces them. My answer, based on the potential for new leads from genomics and thelength of clinical evaluation, was “about another 20 years”. I realized almost immediately that I have been saying thatfor at least the last 10 years. Perhaps it is time to re‐think this one. Obviously, the interest in developing new peptidetherapeutics is going to be around a lot longer.

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such as Type I diabetes and insulin – wherever thepharmaceutical industry saw an oral alternative theyopted against peptide (and protein‐based) drugcandidates.

In the late 1980s, the introduction of long‐actingrelease (LAR) forms of peptides such as GnRH andsomatostatin analogs encapsulated in biodegradablepolymers that only required injection at extendedintervals was a major step in increasing theacceptability of peptide drug substances. However,it was the advent of pharmaceuticals based on geneticengineering and recombinant technology thatgradually, but radically changed the mindset of theindustry. Paradoxically, these new technologies thatmany thought would make “peptide chemistry” ‐ asa strategy for manufacturing peptides ‐ redundant,actually succeeded in breaking down the main barrierto peptide drugs (lack of oral bioavailability) andcaused a surge of interest in the chemical manufactureof peptides. Genetically engineered proteins offereda window to previously untreatable medicalconditions and – with it – the industry accepted theneed to develop drugs that could not be orallyadministered. It also initiated a massive drive to findalternative drug delivery platforms (to injection) thatwould find patient acceptability and compliance.

Moreover, recombinant technology as a tool formanufacturing peptides has not made the chemicalsynthesis of peptides redundant – far from it. Thereare a number of reasons for this. The first has to dowith the nature of recombinant technology itself.Recombinant processes require substantial designand development before clinical manufacturing lotsbecome available. The use and control of biologicalorganisms and the associated genetic engineeringrequire extensive quality management and regulatorycontrol. Downstream processing is usually complexand customized to the specific product. In spite of thealmost negligible costs of starting materials, the priceof even the smallest scale GMP‐grade manufacturinglot using fermentation of a recombinant organism islikely to exceed US$ 1 million with a lead‐time of over1 year.

The second reason that chemical synthesis, in particularsolid‐phase procedures based on Fmoc‐chemistry, isstill the manufacturing procedure of choice forpeptides has to do with changes in the peptidemanufacturing industry. The last 15 years has seen aremarkable decrease in the cost of solid phasemanufacturing – partly due to the cost of raw materialsand economy of scale, and partly due to the technicalimprovements in chromatographic equipment andmedia. There is no doubt that solid‐phase chemistryapproaches are faster and less expensive for

manufacturing at up to a multi‐10 kg or 100‐kg scaleand are more su i ted to ear ly s tage c l in ica ldevelopment. In contrast to recombinant technology,solid phase chemical approaches require significantlyless process development, use mainly genericchemical and purification procedures, and are lesspersonnel intensive in terms of production, qualityassurance and regulatory affairs . Chemicalapproaches also allow significantly more flexibility indesign of analogs that require unnatural amino acidsor non‐proteogenic components.

However, there is no doubt that recombinanttechnology will play an increasingly important rolein peptide manufacturing in the future becauseof quantity requirements. A number of peptidessuch as salmon calcitonin, human glucagon, humanPTH (1‐34) and human brain natriuretic factor,manufactured by recombinant technology, arealready commercially available. Procedures arealready being developed that allow the use ofredundant codons to introduce unnatural aminoacids into proteins and pept ides , of fer ingsubstantially more flexibility in the peptide sequencesavailable to this technology.

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200‐litre Reactor for Solid Phase Peptide Synthesis

Although many costs of chemical manufacture ofpeptides have decreased significantly in recent years,local labor and some solvent costs continue to rise,and the unit cost of goods is still a major componentfor drug manufacturers. One needs to be aware thatthe manufacturing cost of some peptide drugsubstances – particularly those above 30 amino acidsin length – could represent significant challenges tothe final cost of goods of the drug product if they haveto be given chronically at a high dose (>100 mg/day).If this is where you plan to go, you would be welladvised to do some careful calculations beforecommitting to long‐term development. Economicalcommercial processes can be developed for mostpeptides, but significant, maybe multi‐million dollarinvestments may be required along the way toachieve that goal. Fortunately, many of the longersequence candidates under development areexceptionally potent with daily doses in themicrogram range.

In passing, one should mention that there are stillsome peptides on the market that are isolated fromanimal sources, but their numbers are dwindling.There is also some re‐emerging interest in usingenzymatic procedures (reversed proteolysis) tosynthesize specific sequences. The use of free aminoacids as opposed to Fmoc‐derivatives as startingmaterials has great economic appeal.

Current challengesOne of the challenges facing the manufacturers ofboth peptide drug substances and peptide drugproducts today is the inability of regulatory authoritieson different continents to come up with a harmonizedset of guidelines that define what level of peptideimpurities can be present in peptide therapeutics. Itis a challenge for two reasons. First, no‐one in thebusiness is totally sure what is expected of them, and– secondly – designing manufacturing processes toproduce a higher quality product than is requiredadds significantly to the cost of goods, possibly to thepoint where an effective drug loses its economicviability.

The underlying issue is that the term “peptide” oreven “complex peptide” is too vague to havemeaningful regulatory usage. Peptides range fromsequences containing only 2 amino acids, which areobviously “small molecules”, to sequences of up to100 residues, where historically biochemists arbitrarilydecided that anything larger should be called aprotein. That delineation is even fuzzier today where– in deference to insulin as the long‐standing borderline between recombinant and chemical synthesis –sequences longer than 50 amino acids are oftenreferred to as “small proteins”.

The two extremes – dipeptides at one end and 50 to100‐meric polypeptides at the other – representpeptidic molecules of vastly different complexity withsignificantly divergent physical and chemicalproperties, as well as different abilities to adoptsecondary and tertiary structures. Small moleculesand biologics are justifiably treated as differentclasses of molecules by the regulatory authorities.Peptides, which span both categories, cannot beassigned in toto to either. Given the mainly non‐toxicnature of peptides, an impurity profile guideline thatis based on “dose” and “indication”, or on the factualdata generated in the tox studies, might be moreappropriate for those peptides that do not fulfill therequirements for small molecules. This is perhaps atoo simplistic approach, and certainly any extrapolationof data from tox studies can only be justified if theidentical manufacturing process is used for both toxand clinic. Nevertheless, the lack of harmonizedguidelines needs addressing.

An unfortunate spin‐off of the lack of clear guidancefor setting impurity profile specifications is that manydrug product manufacturers adopt the mostconservative and stringent limits for peptides(effectively using small molecule API guidelines forcomplex peptides) in order to ensure that “noregulatory issues” arise. If one considers that mostpeptide drugs have exceptionally low toxicity and areadministered at doses between 50 μg and 50 mg,requiring limits for individual, unidentifiedimpurities of less than 0.1% constitutes an element of“overkill”. While such caution may be warranted forsome products, for many it simply results in anunnecessary additional cost of goods.

While few companies can – at the start of productdevelopment – specify the final dose or will beprepared to commit decisively to the commercialquantities that will eventually be required , a “bestguess” of the commercial scale of manufacture, thetime‐line to achieve this and the anticipated cost ofgoods helps CMOs design appropriate manufacturingprocesses. As a project moves from the multi‐100gram to the multi‐10 kg scale and beyond, the processwill almost certainly have to evolve or change. Thefailure to recognize this early in a project may resultin progressing past a point of no return wherechanges are not acceptable from a regulatory oreconomic standpoint. The choice of counterion is anexample. The solubility and stability of peptides canbe influenced by their salt form and the initial choiceof counterion may be disadvantageous for large scalemanufacture. However, from a regulatory standpointdifferent salt forms of a peptide are considered to bedifferent drug substances and changing from one toanother may, therefore, be challenging.

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For biotech and emerging pharmaceutical companieswith their limited budgets, one of the most challengingissues today must be finding the correct balance betweenexpediency and due diligence. Many small biotechcompanies do not have quality assurance or regulatoryaffairs departments with adequate experience withpeptides. Every CMO knows customers that expecttheir products to be delivered shortly after the purchaseorder is issued, if not before. Right quality, right time andright price (equating to high purity, expedited deliveryand low unit cost respectively) are commonly cited goalsat the start of most projects. Unfortunately these threedemands are not mutually compatible and one usuallyhas to be sacrificed to achieve the other two. In the hurryto move forward, it is often easy to lose sight of theultimate goals, which should be (a) an expedient approval,(b) a robust, scalable and economic process, and (c) aprofitable drug product. Particularly for longer peptides,the urge to push forward quickly, without duly diligentcharacterization of the active pharmaceutical ingredient,can result in disaster. Typical issues are the failure todetect impurit ies which cannot be removedchromatographically and then, as a consequence, mayrequire an alternative synthetic approach. Manyanalytical HPLC systems fail to resolve enantiomericforms or other isomers (e.g. β‐aspartyl transformations)of peptides, particularly if the sequences are long. Ifsuch co‐eluting impurities arise due to degradation ofthe peptide during storage, the peptide may continueto appear to meet the HPLC purity specifications, butlose its pharmaceutical potency. Such impurities areoften missed unless the analytical method isspecifically designed to detect them.

For peptide API manufacturers one of the currentchallenges is matching equipment and otherresources to meet customer requirements. Most clinicaltrials of peptide APIs involve annual quantitiesbetween 10 grams and 10 kilograms. While most ofthe larger CMOs are equipped to handle severalparallel campaigns at this scale, they are not all sowell equipped to make annual quantities of 100kilograms to a ton. There are very few projects thatroutinely exceed 100 kg per year at a single site, themost commonly cited being those of Fuzeon,Eptifibitide and Bivalirudin. The acquisition andmaintenance of equipment for this scale ofmanufacture is difficult to justify if it is sitting idle formost of the year.

The use of large equipment does not alwaysequate to economy of scale and certainly exposesboth sponsor and contract manufacturingorganization (CMO) to enhanced risk if equipmentfails. Working at larger scale is usually associatedwith longer hold times during or between processsteps, conditions which can favor degradation oraggregation. It is not difficult to make a case for theuse of more modest equipment organized in tandemor parallel configuration. Whatever the process thatis eventually chosen to manufacture at a multi‐10 kgor multi‐100 kg scale, it will probably have beenthrough significant development and may notresemble the process of the first GMP lots at all.It may not even be based on the same technology,e.g. if the switch to recombinant fermentation ismade.

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Large‐capacity Liquid Phase Synthesis

Perspective for the futureSo what can we expect from peptide therapeutics inthe future?

We can expect the number of peptides enteringclinical trials to grow. We can expect the overallcomplexity of peptide APIs, their potency (by design)and their specificity (including the ability to targetspecific organs and cells) to increase. The use ofpeptides conjugated to PEGs, carbohydrates, antibod‐ies and other proteins will become more frequent.Peptides will not only be used as the active ingredientof new drugs, but as “add‐ons” to other pharmaceu‐tical agents to direct them to their targets, to ferrythem across cellular membranes, and to modify theirbiological action.

We can expect the range of medical indications thatpeptides address to grow. We can expect peptide‐based antimicrobial peptides to find commercial use.Almost certainly peptides will find increased usageto treat obesity, metabolic syndromes and Type 2 diabetes.The use of membrane‐penetrating peptides will increasethe number of intracellular targets. Peptides will beused to address currently “undruggable” targets.

We can expect a massive upsurge of interest in peptidetherapeutics to occur once a delivery platform, thatcan deliver short‐acting peptides efficiently into thebloodstream, has been developed. This is not a questionof “if it happens”, but “when”. While an oral routeto obtain maximum compliance would be most desirable,there are a number of non‐invasive (pulmonary,nasal) or minimally invasive (transdermal) devices indevelopment that might provide suitable and, interms of efficicacy, more attractive alternatives.

We can expect the introduction of novel formulationsand excipients to stabilize peptides at room temperature.We can expect the efficacy of long‐acting formulationsto improve and to enable smaller quantities of peptidedrug products in the body to maintain activity overlonger periods of time. At the same time we shouldnot forget that many peptides do not exert theirpharmacological action only when maintained abovea threshold concentration in the body. Indeed, mostpeptides exert their biological function by acting assignals; “switching off” can be as important as“switching on”. This requires a combination ofpulsatile administration and the ability of the bodyto degrade the peptide. One can anticipate thatcomputerized transdermal or implanted deliverydevices may eventually be able to fulfill this function.Coupled with physical or chemical targeting devices,the concept of total temporal and chemical repair ofhormonal and other “signal function” lesions maybecome a reality.

Although one can never rule out the introduction ofnew chemistry, solid phase peptide synthesis basedon Fmoc‐chemistry will probably continue to be the“first choice” for the manufacture of most peptidesfor some time to come. Changing establishedapproaches of manufacturing is significantly moredifficult in a GMP environment than in the researchlaboratory. Manufacturers’ raw materials need to beeconomically affordable commodities available for allscales of production. It is also difficult to draftcontingency (back‐up, secondary supplier) plans forproprietary manufacturing technologies. We willcontinue to see a steady increase of new amino acidderivatives, of “exotic” amino acids and reagents.New strategies for coupling peptide fragments maycontribute to peptide chemistry advancing regularlyinto the territory of pharmaceutical manufacture ofsmall proteins without the risk of uncontrollableimpurity profiles. Perhaps even more likely, wewill see the borders between peptide chemistry,recombinant fermentation, enzymatic synthesis andbio‐organic chemistry overlap and merge, andbecome one set of tools for the design of large scalemanufacturing processes rather than being differentbranches of contract manufacturing.

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One would hope that, as experience with peptidesgrows, the regulatory directives will provide moreguidance to industry as to how specifications forimpurity limits should be set. Without that guidance,many potential peptide drugs may fall by the waysidedue to the technical or economical inability to meetspecifications that are excessively tight.

There are also many peptide‐associated issues wherenew regulatory approaches are needed. Vaccine“cocktails” is one. It is difficult to conceive how thecurrent regulatory expectations for peptide APIs fortherapeutic usage (e.g. limits for impurities) can beapplied to small gram quantities of the severalpeptide components of a vaccine product, which isnot administered chronically, and still be economicallyviable. Others include polydispersed peptides (e.g.poly‐lysine) or peptides attached to polymers whichcurrently pose significant challenges to analyticalcharacterization. However, one should not forget thatCopaxone, which has the highest current sales for anypeptide therapeutic, with worldwide sales of overUS$ 3 billion, falls into the category of polydispersehetero‐polypeptides, and is clear proof that a gooddrug can “make it” whatever the analytical orregulatory challenges.

As a final comment, we should mention that we– as peptide contract manufacturers – often takea retrospective look at those peptide therapeuticcandidates that have made it and those that havenot. There is really no way of knowing at the startwhich ones will be successful. The only facts weknow for sure are that peptide therapeutics arecontinuing to flourish and that their foreseeablefuture is secure.

1 For anyone wanting to view statistics about peptidetherapeutics in more detail, the Peptide TherapeuticsFoundation publishes a bi‐annual report “DevelopmentTrends for Peptide Therapeutics” and you shouldvisit their website at http://www.peptidetherapeutics.org/peptide‐therapeutics‐foundation.html

2 There is a 10 ‐ 12 year lag between a peptide drugcandidate entering clinical trials and its potentialapproval. The probability of regulatory approval canbe obtained by analyzing the individual approvals ina fixed time period and comparing that with thenumber of peptide drug candidates entering clinicaltrials 12 years earlier. By analysing consecutive timeperiods an extrapolated probability can be calculated1.

Acknowledgement I would like to thank PharManufacturing for lettingme offer some personal views on the future of peptidetherapeutics and peptide manufacturing. I wouldalso like to thank a number of my colleagues in thePolyPeptide Group for their support reviewing thisdocument and providing suggestions.

About the AuthorRodney Lax is Senior Director of Business Developmentat PolyPeptide Laboratories in Torrance (California).He has a B.Sc. in Biochemistry from the University ofBirmingham (UK) and obtained his Ph.D. at theInstitute of Cancer Research (London, UK).Post‐graduate studies were in Germany at theUniversity of Ulm before moving to the University ofEssen, where he became Associate Professor ofPhysiological Chemistry. He has been in the peptidemanufacturing industry since 1986. He moved to hiscurrent position in the USA in 2003.

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