Advanced Drug Delivery Reviews 54 (2002) 453–456
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`www.elsevier.com / locate / drugdeliv
`
`Preface
`I ntroduction and overview of peptide and protein pegylation
`
`I ntroduction
`
`It has long been a dream in medicine and phar-
`macy to use peptides and proteins as drugs. The
`driving force for this interest is the ability of these
`compounds to eliminate toxic or overproduced com-
`pounds in the body and to mimic endogenous
`hormones, cytokines and antibodies. Two major
`hurdles were apparent. First, there was the difficulty
`in obtaining sufficient quantities of the materials.
`Small peptides could be made by chemical synthesis,
`but
`larger molecules could only be obtained by
`laborious extraction and purification from natural
`sources. This problem has been overcome by the
`development of genetic engineering, so that now it is
`routine to prepare kilogram quantities of pure pro-
`teins. The second major hurdle, and one that remains
`a serious challenge, is to deliver the molecules to the
`desired bodily target. Oral delivery of proteins
`remains unavailable because proteins are routinely
`destroyed by the digestive system. Even injected
`proteins generally have poor pharmacokinetics be-
`cause of rapid renal excretion and proteolytic diges-
`tion. There can also be significant immunological
`reactions. Finally, proteins are difficult to formulate
`because of their intrinsic instability.
`Many approaches to enhancing protein delivery
`have been examined, including protein entrapment in
`insoluble matrices [1] and liposomes [2] and im-
`mobilization onto polymer resins for use with ex-
`tracorporeal shunts through which blood could flow
`[3]. By far the most successful approach has been to
`mask the protein surface by covalent coupling of
`soluble poly(ethylene glycol) (PEG) or, as it has
`become known, ‘‘pegylation’’.
`
`literature is available on
`A large amount of
`pegylation, including several books and reviews [1–
`10]. The prime purpose of the present volume is to
`present, for the first time, a review of the extensive
`human and animal data that have recently become
`available on pegylated proteins and peptides. Previ-
`ous reviews have focused on chemistry for pegyla-
`tion and on in vitro examination of pegylated
`molecules. Until recently only two proteins, PEG-
`asparaginase and PEG-adenosine deaminase, had
`been approved for human use, and little clinical
`information was available on other pegylated mole-
`cules. However,
`the past few years have seen a
`dramatic expansion of clinical trials, and applications
`for approval as drugs have been filed for two PEG-
`proteins (PEG-granulocyte colony stimulating factor
`from Amgen and PEG-human growth hormone
`antagonist
`from Pharmacia). Also two pegylated
`molecules with major commercial potential have
`been approved (PEG-alpha interferon 2b, Schering
`Plough’s PEG-Intron , and PEG-alpha-interferon 2a,
`Hoffman-La Roche’s Pegasys ). Results from these
`studies have revealed tremendously valuable infor-
`mation on strengths and weaknesses of pegylation,
`and it is clear that pegylation is well on its way to
`becoming a standard component of the pharmaceu-
`tical tool box.
`
`H istorical background
`
`The pioneering first steps in pegylation were taken
`in late 1970s in the laboratory of Professor Frank
`Davis of Rutgers University, and the Commentary in
`this volume is a reminiscence of these early days
`
`0169-409X / 02 / $ – see front matter
`P I I : S 0 1 6 9 - 4 0 9 X ( 0 2 ) 0 0 0 2 0 - 0
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`2002 Elsevier Science B.V. All rights reserved.
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`454
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`Preface
`
`written by Davis. It is important to remember that
`the technique of coupling polymers to proteins was
`originated in the 1950s and 1960s with investigations
`of protein structure and function by site-directed
`chemical modification. These studies led to so-called
`‘‘gentle chemistry’’ for protein manipulation. Im-
`portant also were discoveries made in the 1970s that
`enzymes could be covalently linked to insoluble
`matrices for biocatalytic applications. From such
`studies we came to understand that the delicate and
`complex protein molecules, under appropriate con-
`ditions, could be treated as a common chemical
`entity.
`Other soluble polymers, including polysaccharides
`[11] and albumin [12], have been used for protein
`conjugation, primarily to stabilize proteins toward
`proteolysis and to increase residence time in the
`body. One product, dextran-streptokinase, has been
`marketed in Russia for thrombolytic therapy [13].
`However, it was the development of pegylation that
`provided the real breakthrough in enhancing the
`pharmaceutical properties of proteins and peptides.
`PEG possesses a unique set of properties, including
`absence of toxicity, immunogenicity and antigenici-
`ty; low, mass-dependent elimination via the kidney;
`high flexibility and high solubility in water and
`certain organic media. In turn, PEG-proteins possess
`reduced toxicity, immunogenicity and antigenicity,
`reduced rates of kidney clearance and proteolysis,
`and enhanced solubility and stability. Valuable im-
`provements in various pharmacokinetic kinetics pa-
`rameters (e.g., absorption rate and volume of dis-
`tribution) are also seen. Details of these various
`properties are provided in the reviews we have
`referenced and in the following sections.
`It is interesting that it has taken over 20 years for
`protein pegylation to approach becoming a standard
`technique. In part this was due to the time required
`to improve protein manufacturing, but also it has
`been necessary for the organic and polymer chemis-
`try of PEG activation to mature. Of course there has
`been tremendous advancement as well in understand-
`ing of protein structure and properties and of the
`effects of pegylation. Quite probably, various market
`forces have also played a role in slow adoption of the
`technology, as with any revolutionary new technolo-
`gy.
`
`A rticles in this issue (Parts One and Two)
`
`The seventeen chapters of these two issues of
`ADDR will review many major achievements of
`pegylation. As mentioned above, the Commentary in
`this first volume is a review by Davis of
`the
`discovery of pegylation and its benefits. It is indeed
`fascinating to read this first-hand accounting of the
`creative and the mundane forces that led to such an
`important invention. We see the professor’s eternal
`pursuit for funding, the delight and value of old-
`fashioned library detective work, the light-bulb flash
`of a good idea, the juxtaposition of the idea with
`protein availability and just
`the right polymer
`catalogue, and finally appreciation of unexpected
`laboratory results. We suspect it is just this type of
`experience that keeps most of us in science. Admit-
`tedly, however, Davis’ work has had far greater
`impact than most.
`The first chapter by Roberts and co-workers
`reviews the contributions from many different re-
`search groups on improving conjugation chemistry,
`analytical methods for conjugate characterization,
`and the influence of mass and shape of the polymer
`on conjugate properties.
`The second chapter by Kinstler and co-workers
`teaches how PEG may be specifically linked to the
`amine terminus of a protein. As noted here, site-
`specific conjugation chemistries are a critical need in
`protein pegylation because of the many isomers that
`can result from non-specific chemistries. Two im-
`portant applications of this chemistry to therapeu-
`tically useful proteins are reported also. The problem
`of specificity of conjugation is also faced by Sato in
`Chapter 3 where conjugation to glutamine residues is
`described.
`Hinds and Kim report specific conjugation of PEG
`to two of the three amino groups of insulin in
`Chapter 4. PEGs of low mass were shown in this
`work not to alter the conformation or activity of the
`hormone, but
`they did eliminate immunogenicity,
`antigenicity and allergenicity and lengthen circula-
`tion lifetime.
`In Chapter 5 Chapman and co-workers discuss
`results obtained in the pegylation of antibody frag-
`ments. Antibodies have remarkable potential as
`drugs, but their high production cost is a serious
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`Preface
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`455
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`barrier to commercial application. Antibody frag-
`ments are much less costly to manufacture, but their
`circulation life times in the body are quite short. The
`half-life problem can be solved by pegylation. Chap-
`man and co-workers describe this approach and show
`that PEG–antibody fragment conjugates have great
`therapeutic potential.
`The next two chapters present pivotal papers from
`groups at Schering-Plough and Hoffman-La Roche
`and Shearwater on pegylation of alpha-interferon.
`The scientific community is fortunate to receive
`these important papers on two very important com-
`(cid:210) (cid:210)
`mercial products (Pegasys
`and PEG-Intron ). This
`kind of
`information is frequently not published.
`These papers reveal chemical and clinical results for
`pegylated proteins
`in unprecedented detail. We
`believe the information will be used for years to
`design new PEG-protein pharmaceuticals. The
`pegylated alpha-interferons have been approved for
`treatment of hepatitis-C, a disease of great societal
`importance, and they are under investigation for
`other important indications.
`The last chapter by Veronese and colleagues
`reviews
`the hundreds of
`laboratory studies of
`superoxide dismutase pegylation. This enzyme is
`involved in many pathological states, and it would
`seem reasonable to expect commercial development,
`but this has not occurred, and one is left to wonder
`why. Nonetheless these works have served as a
`proving ground for new chemical methods of PEG
`coupling and new analytical procedures for conjugate
`characterization, and they illustrate the influence of
`PEG molecular weight on clearance and activity.
`The ADDR issue following this one will report
`nine additional reviews regarding other products,
`including pegylated asparaginase, growth hormone
`releasing factor, growth hormone antagonist, tumor
`necrosis factor, a TPO-mimetic and staphylokinase,
`and a chapter on pharmacokinetic and immunologi-
`cal properties of conjugates.
`
`C onclusions
`
`In summary, protein pegylation has come a long
`way toward becoming a standard tool for the phar-
`maceutical sciences. We believe these volumes will
`
`the scientific community in applying the
`assist
`knowledge that is now available.
`
`Francesco M. Veronese
`(Theme Editor)
`
`Department of Pharmaceutical Science
`University of Padova
`Via Marzoilo 5
`Padova 35128, Italy
`E-mail: francesco.veronese@unipd.it
`
`J. Milton Harris
`(Theme Editor)
`
`Shearwater Corporation
`490 Discovery Drive
`Huntsville, AL 35806, USA
`E-mail: jmharris@shearwatercorp.com
`
`R eferences
`
`(Ed.), Poly(Ethylene Glycol) Chemistry,
`[1] J.M. Harris
`Biotechnical and Biomedical Applications, Plenum Press,
`New York, 1992.
`[2] J.M. Harris, S. Zalipsky (Eds.), Poly(Ethylene Glycol)
`Chemistry and Biological Applications, ACS Symposium
`Series No. 680, American Chemical Society, Washington,
`DC, 1997.
`[3] F.F. Davis, G.M. Kazo, M.L. Nucci, A. Abuchowski,
`Reduction of immunogenicity and extension of circulating
`half-life of peptide and protein, in: V.H.L. Lee (Ed.), Peptide
`and Protein Drug Delivery, Marcel Dekker, New York, 1990.
`[4] M.L. Nucci, R. Schorr, A. Abuchowski, The therapeutic
`value of poly(ethylene glycol) modified protein, Adv. Drug
`Deliv. Rev. 6 (1991) 133–151.
`[5] C. Delgado, G.E. Francis, D. Fisher, The uses and properties
`of PEG-linked proteins, Crit. Rev. Ther. Drug Carrier
`Systems 9 (1992) 249–304.
`[6] N.V. Katre, The conjugation of proteins with poly(ethylene
`glycol)and other polymers. Altering properties of proteins to
`enhance their therapeutic potential, Adv. Drug Deliv. Rev.
`10 (1993) 91–114.
`[7] Y. Inada, M. Furukawa, H. Sasaki, Y. Kodera, M. Hiroto, H.
`Nischimura, A. Matsushima, Biomedical and biotechnologi-
`cal application of PEG and PEG-modified proteins, Tibtech
`13 (1995) 86–91.
`[8] C. Monfardini, F.M. Veronese, Stabilization of substances in
`the circulation, Bioconj. Chem. 9 (1998) 418–450.
`
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`Preface
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`[9] P. Bailon, W. Berthold, Polyethylene glycol-conjugated phar-
`maceutical proteins, Pharm. Sci. Technol. Today (PSTT)
`(1998) 352–356.
`[10] F.M. Veronese, Peptide and protein PEGylation: a review of
`problems and solutions, Biomaterials 22 (2001) 405–417.
`[11] R.G. Melton, C.N. Wiblin, R.F. Sherwood, Covalent linkage
`of carboxypeptidase to soluble dextran. Properties of conju-
`gates and effects on plasma persistence in mice, Biochem.
`Pharmacol. 36 (1987) 105–112.
`
`[12] K. Wong, L.G. Cleland, M.J. Poznanski, Enhanced anti-
`inflammatory effects and reduced immunogenicity of bovine
`liver superoxide dismutase by conjugation with homologous
`albumin, Agent Action 10 (1980) 231–239.
`[13] V.P. Torchilin, J.I. Voronkov, A.V. Mazoev, The use of
`immobilised streptokinase (Strptodekaza) for the therapy of
`thromboses, Ther. Arch. 54 (1982) 21–28.
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