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122 Current Pharmaceutical Biotechnology, 2009, 10, 122-137
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Advances in Peptide Pharmaceuticals
Cynthia L. Stevenson*
Independent Pharmaceuticals Consultant, 100 W. El Camino Real, Mountain View, CA 94040, USA
Abstract: Drug delivery strategies for peptide pharmaceuticals have incorporated a wide range of structure activity rela-
tionships, analog generation to impart protease resistance and increased bioavailability, novel formulations, and delivery
systems to target optimal therapeutic dosing requirements. Advances in peptide pharmaceuticals have provided products
for the treatment of diabetes, obesity, Crohn’s disease, osteoporosis, cancer, cardiovascular disease, immunotherapy, ac-
romegaly, enuresis, pain, and antimicrobials. Here we review these marketed peptides and new peptidomimetic therapies
currently in clinical trials.
Keywords: Peptide, peptidomimetic, drug delivery.
INTRODUCTION
The cost of developing drugs has increased from $802
million in 2001 to $1,318 billion in 2006 [1]. The average
time to develop a drug is now over 10 years, where for every
5,000 compounds tested, 5 will make it to clinical trials and
only 1 will receive FDA approval. Of those compounds that
are approved, only 2 of 10 will ever produce revenues that
match or exceed R & D costs [1]. The pharmaceutical busi-
ness model could be characterized as long-term, high-risk.
Biopharmaceutical companies have made great progress
in treating rare diseases. Over the last decade (1995-2005),
160 drugs were approved to treat rare or orphan diseases that
affect <200,000 people in the US. Generic competition is
anticipated to increase as the patents expired and cost of
goods decrease. For example, the generic share of the overall
pharmaceutical market has increased from 51% in 2000 to
67% in 2007 [1]. These two drivers indicate that there is a
shift to cost-effective products, which are efficacious against
unmet medical needs in smaller patient populations based on
genetic makeup.
Therapeutic peptides contribute significantly to treatment
of diabetic, osteoporotic, oncologic, gastroenterologic, car-
diovascular, immunosuppression, acromegaly, enuresis, an-
tiviral, antibacterial and antifungal indications. However,
many biotechnology-derived products do not have ideal de-
livery profiles. The therapeutic profile can be improved by
generating novel peptidomimetics with improved stability
and permeability. In addition, drug delivery offers a way to
improve the delivery profile/efficacy of an already estab-
lished peptide, develop new indications, provide a line-
extension as the patents expire, improve patient quality of
life and remain competitive against generic competition.
Drug delivery platforms are more diverse (extended release,
pulsatile delivery, increased bioavailability) and available
(due to expiring patents) than ever before. Furthermore, they
have been established for the delivery of small molecules

*Address correspondence to this author at the 100 W. El Camino Real,
Mountain View, CA 94040, USA; Tel: (650) 248-4718;
E-mail: cynthialstevenson@gmail.com
(transdermal, pulmonary, nasal), and are gaining acceptance
for biotechnology products, where non-injection drug deliv-
ery technologies are starting to deliver biomolecules with
cost effective bioavailability values.
This article surveys the field of pharmaceutically relevant
peptides and peptidomimetics less than 40 amino acids in
length currently marketed or in clinical trials, their therapeu-
tic indications, mechanism of action and delivery innova-
tions.
DIABETES
The Centers for Disease Control and Prevention forecasts
a 4.3% annual growth of diabetes cases [2]. Despite evidence
for the need for tight glucose control, two-thirds of Ameri-
cans with Type 2 diabetes do not adequately control their
glucose levels [1]. Among 157,000 patients monitored na-
tionwide, 67% did not maintain hemoglobin A1C (HbA1C)
levels below 6.5% [2]. Mean change from baseline HbA1C,
fasting and postprandial glucose levels and body weight gain
are the usual markers utilized to test the efficacy of mole-
cules in this class.
Glucagon-Like Peptide 1
Glucagon-like peptide 1 (GLP-1) is derived from proglu-
cagon and is released by L-cells in the small intestine in re-
sponse to a meal [3,4]. When blood glucose levels are high,
GLP-1 stimulates the release of insulin from pancreatic beta
cells through the G-protein coupled GLP-1 receptor. This
"incretin effect," which accounts for 60% of postprandial
insulin secretion, is diminished in diabetes. GLP-1 also sup-
presses the release of glucagon from the pancreas, preventing
the dumping of glucose into the bloodstream by the liver,
and slows stomach emptying, leading to satiety. Therefore,
GLP-1 used as an adjunctive therapy does not cause hypo-
glycemia or weight gain, but facilitates weight loss. Weight
loss is a key competitive edge for incretin mimetics.
GLP-1 (7-36) demonstrates helix forming propensity
from Thr
7
-Lys
28
, where the N-terminal region provides high
affinity to the receptor, while the C-terminal region provides
Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 123
selectivity [5]. However, GLP-1 has a short half-life of about
2-5 minutes [6]. In circulation, GLP-1 is cleaved by dipepti-
dyl peptidase IV (DPP IV), resulting in inactivation [7,8].
DPP IV cleaves the N-terminal dipeptide His-Ala leaving
GLP-1 (9-36), which may be a specific antagonist, instead of
agonist [9]. Consequently, drug companies are searching for
GLP-1 analogs and drug delivery systems that provide a
longer circulating half life.
GLP-1 Delivery
Exenatide (Byetta

) is the first FDA approved incretin
mimetic and is indicated as an adjunct therapy to improve
glycemic control in patients with Type 2 diabetes. These
patients are usually failing to achieve adequate control with
metformin or sulfonylurea alone. Exenatide has approxi-
mately 50% sequence homology with GLP-1 and exendin-4,
and is derived from gila monster saliva. Exenatide contains a
Gly
2
instead of Ala
2
found in GLP-1, this modification in-
creased the half-life to ~4 hours (Table 1) [4]. This site spe-
cific substitution eliminates the DPP IV cleavage site. The
increase in half-life from minutes to hours allowed the de-
velopment of a twice daily injectable product [3]. However,
improvement to a daily injectable formulation, in a pen in-
jector, would be of benefit. Amylin currently has a sustained
release poly lactic/glycolic acid (PLGA) depot formulation
(Exenatide LAR) in Phase 2 trials that is projected in in-
crease the dosing from twice daily to once weekly, with no
dose limiting side effects [10].
Novo Nordisk is also developing a GLP-1 analog, Lira-
glutide, and has completed Phase 3 clinical trials. Liraglutide
contains several sequence alterations: Arg
28
replaces Lys
28
,
an additional Gly at the C-terminus and Lys
20
contains a C16
fatty acid chain (Arg
28
, Lys
20
-N

-(-Glu (N--
hexadacanoyl)) GLP-1) (Table 1) [11]. The fatty acid portion
binds to serum albumin, which extends its lifetime to a once
daily injection. Furthermore, Novo Nordisk has a once
weekly, extended release version (Liraglutide SR) in Phase 1
trials. A major side effect for incretin mimetics is nausea and
vomiting at high doses. Therefore, whatever sustained re-
lease format is utilized for a once weekly product will re-
quire the elimination of an initial burst. Novo Nordisk has
also partnered with Emisphere for oral delivery of GLP-1.
Conjuchem, Inc. is in Phase 2 trials, using their PC-DAC
technology to develop a subcutaneous injection with a novel
GLP analog. CJC-1131 has a D-Ala
8
and a C-terminal reac-
tive chemical linker, N

-(2-[2-[2-(3-maleimidopropylamido)
ethoxy] ethoxy] acetyl) Lys, bioconjugated to Cys
34
of hu-
man serum albumin (HSA) [12]. This covalent and irreversi-
ble bond to HSA extends the half life 30-fold relative to na-
tive exendin-4 (t
1/2
10-12 days), but with a reduction in bio-
activity [13]. Conjuchem has also applied their conjugation
technology to Exendin (CJC-1134) and completed Phase 2
trials.
Zealand Pharma and Sanofi-Aventis have entered Phase
3 trials with a GLP-1 analog (ZP10), which is modified by
attaching six Lys residues to the C-terminus [14]. Human
Genome Sciences is in Phase 2 with Albugon, a proprietary
fusion technology, which fuses the gene for human albumin
to the gene that expresses GLP-1. The half-life in monkeys is
3 days [15,16]. GlaxoSmithKline holds exclusive worldwide
rights to develop and commercialize Albugon. Beaufour Ip-
sen and Roche have finished Phase 2 trials with a once
weekly administered DPP IV resistant GLP-1 analog called
Taspoglutide [17]. Taspoglutide is an -aminoisobutyric
acid derivatized GLP-1 analog, Aib
8,35
GLP-1(7,37) NH
2
.
Nastech and Amylin are developing a nasal spray of Ex-
enatide. Finally, Intarcia has formulated GLP-1 for 6 months
of delivery from an implantable DUROS pump and plans to
enter Phase 1 in 2008 [18].
Other Peptides
Pramlintide (Symlin

) is an injectable drug to control
blood glucose in adults with Type 1 and Type 2 diabetes.
Pramlintide is an analog of amylin, a neuroendocrine hor-
mone synthesized by pancreatic beta cells that contributes to
glucose control during the postprandial period. Pramlintide is
a 37 amino acid peptide with one disulfide bond [3]. It dif-
fers from amylin by substitution with Pro residues at Ala
35
,
Ser
38
and Ser
29
(Table 1). Pramlintide is prescribed in con-
junction with insulin and both are injected separately before
meals [3]. In humans, pramlintide suppresses glucagon se-
cretion, slows gastric emptying, reduces postprandial glucose
levels, and improves glycemic control while managing
weight loss [19]. As an adjunct to insulin, pramlintide mod-
estly reduced HbA1C levels by 0.3 to 0.67% [20] and re-
duced body weight 0.5 to 1.4 kg [21]. Amylin has also com-
pleted Phase 2a trials co-administering Leptin and Pramlin-
tide and observed a 25 lb weight loss over 24 weeks [10].
Nastech is in Phase 2 studies with Peptide YY [PYY (1-
36)] for obesity [22]. Amylin is in Phase 2 trials with in-
jectable PYY (3-36). 7TM Pharma is in Phase 2 trials with a
36 amino acid analog of PYY and Gln
34
pancreatic peptide.
Merck Serono has completed Phase 1 trials with PYY (3-36).
Eli Lilly and Bedford/Novo Nordisk both market gluca-
gon for severe hypoglycemia and emergency treatment of
insulin induced hypoglycemia. The crystal structure of glu-
cagon shows a highly helical conformation; however it
shows a propensity to random coil/aggregation in solution.
Glucagon has an isoelectric point of 7 and therefore exhibits
very low solubility (<0.1 mg/ml) under physiologic condi-
tions, presenting formulation and delivery challenges [23].
DiObex has received Fast Track Status for very low dose
glucagon (VLDG™), currently in Phase 2 trials [24]. The
therapy is an extended release formulation for the prevention
nocturnal hypoglycemia induced by insulin intensification.
GASTROINTEROLOGY
The elucidation of the role of gastrointestinal peptide and
proteins has allowed the treatment of gastrointestinal disor-
ders, such as Short Bowel Syndrome, Crohn’s disease, en-
terocolitis, pediatric disorders, mucositis associated with
cancer chemotherapy, inflammatory bowel disease and irri-
table bowel syndrome. Short Bowel Syndrome affect 10,000-
15,000 patients in the US, with a cost of $100,000 annually
[25]. Patients suffer from malnutrition, severe diarrhea, de-
hydration, fatigue, osteopenia, and weight loss due to a loss
in the ability to absorb adequate amounts of nutrients and
water. Similarly, irritable bowel syndrome is quite common
and accounts for up to 50% of the patients seeking a gastro-
enterologist.
124 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson
Table 1. Peptide Sequences
Name # aa Sequence
Diabetes
GLP-1 (7-37) 30
His-Ala-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys-Glu-Phe-Ile-Ala-Trp-Leu-Val-
Arg-Gly-Arg-Gly-NH2
Exenatide 39
His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-
Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2
Liraglutide 30
His-Ala-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys*-Glu-Phe-Ile-Ala-Trp-Leu-Val-
Arg-Gly-Arg-Gly-NH2, *Glu-C16 fatty acid
ZP10
His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-
Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Ser-Lys-Lys-Lys-Lys-Lys-Lys-NH2
Pramlinitide 37
Lys-Cys-Asn-Thr-Ala-Thr-Cys-Ala-Thr-Gln-Arg-Leu-Ala-Asn-Phe-Leu-Val-His-Ser-Ser-Asn-Asn-Phe-Gly-Pro-Ile-Leu-
Pro-Pro-Thr-Asn-Val-Gly-Ser-Asn-Thr-Tyr-NHEt
PYY 36
Tyr-Pro-Ile-Lys-Pro-Glu-Ala-Pro-Gly-Glu-Asp-Ala-Ser-Pro-Glu-Glu-Leu-Asn-Arg-Tyr-Tyr-Ala-Ser-Leu-Arg-His-Tyr-
Leu-Asn-Leu-Val-Thr-Arg-Gln-Arg-Tyr-NH2
Glucagon 29
His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-
Met-Asn-Thr-Lys-Arg
Gastrointestinal
Teduglutide 33
His-Gly-Asp-Gly-Ser-Phe-Ser-Asp-Glu-Met-Asn-Thr-Ile-Leu-Asp-Asn-Leu-Ala-Ala-Arg-Asp-Phe-Ile-Asn-Trp-Leu-Ile-
Gln-Thr-Lys-Ile-Thr-Asp-OH
Delmitide 10 NH2-D-Arg-D-Nle-D-Nle-D-Nle-D-Arg-D-Nle-D-Nle-D-Nle-D-Gly-D-Tyr-CONH2
Osteoporosis
Salmon Calcitonin 32
Cys*-Ser-Asn-Leu-Ser-Thr-Cys*-Val-Leu-Gly-Lys-Leu-Ser-Gln-Glu-Leu-His-Lys-Leu-Gln-Thr-Tyr-Pro-Arg-Thr-Asn-
Thr-Gly-Ser-Gly-Thr-Pro-NH2, *disulfide bond (1-6)
PTH (1-34) 34
Ser-Val-Ser-Glu-Ile-Gln-Leu-Met-His-Asn-Leu-Gly-Lys-His-Leu-Asn-Ser-Met-Glu-Arg-Val-Glu-Trp-Leu-Arg-Lys-
Lys-Leu-Gln-Asp-Val-His-Asn-Phe-OH
Oncology
Bortezomib 2 [(1R)–3–methyl–1–[[(2S)–1–oxo–3–phenyl–2–[(pyrazinylcarbonyl) amino] propyl] amino] butyl] boronic acid
Cilengitide 4 cyclo(L-arginylglycyl-L--aspartyl-D-phenylalanyl-N-methyl-L-valyl)
Leuprorelin 9 pGlu-His-Trp-Ser-Tyr-D-Leu-Leu-Arg-Pro-NH2
Histrelin 9 pGlu-His-Trp-Ser-Tyr-N-benzyl-D-His-Leu-Arg-Pro-NH2
Goserelin 10 pGlu-His-Trp-Ser-Tyr-D-Ser(But)-Leu-Arg-Pro-Azgly-NH2
Stimuvax 25
Ser-Thr-Ala-Pro-Pro-Ala-His-Gly-Val-Thr-Ser-Ala-Pro-Asp-Thr-Arg-Pro-Ala-Pro-Gly-Ser-Thr-Ala-Pro-Pro-
Leu(palmitoyl)-Gly
GV1001 16 Glu-Ala-Arg-Pro-Ala-Leu-Leu-Thr-Ser-Arg-Leu-Arg-Phe-Ile-Pro-Lys
Cardiovascular
Nesiritide 32
Ser-Pro-Lys-Met-Val-Gln-Gly-Ser-Gly-Cys*-Phe-Gly-Arg-Lys-Met-Asp-Arg-Ile-Ser-Ser-Ser-Ser-Gly-Leu-Gly-Cys*-
Lys-Val-Leu-Arg-Arg-His-OH, *disulfide bond (10-26)
Eptifibatide 7
N 6 -(aminoiminomethyl)-N 2 -(3-mercapto-1-oxopropyl-L- lysylglycyl-L--aspartyl-L-tryptophyl-L-prolyl*-L-
cysteinamide, * disulfide bond (1-6)
Bivalirudin 20 D-Phe-Pro-Arg-Pro-Gly-Gly-Gly-Gly-Asp-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-Tyr-Leu
Icatibant 10 D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH
Rotigaptide 6 Ac-D-Tyr-D-Pro-D-Hyp-L-Gly-D-Ala-L-Gly-NH2
Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 125
(Table 1) contd.....
Name # aa Sequence
Immunotherapy
Cyclosporin 11 Cyclic MeBmt-Abu-Sar-MeLeu-Val-MeLeu-Ala-D-Ala-MeLeu-MeLeu-MeVal
MPB8298 17 Asp-Glu-Asn-Pro-Val-Val-His-Phe-Phe-Lys-Asn-Ile-Val-Thr-Pro-Arg-Thr
Acromegaly
Octreotide 8 D-Phe-Cys*-Phe-D-Trp-Lys-Thr-Cys*-Thr-ol, *disulfide bond (2-7)
Lanreotide 8 [cyclo S-S]-3-(2-naphthyl)-D-Ala-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2
Enuresis
Desmopressin 9 1-(3-mercaptopropionic acid)*-Tyr-Phe-Gln-Asn-Cys*-Pro-D-Arg-Gly-NH2, *disulfide bond (1-6)
Lypressin 9 Cyclic Cys*-Tyr-Phe-Gln-Asn-Cys*-Pro-Lys-Gly-NH2, *disulfide bond
Terlipressin 6 Gly-Gly-Gly-Cys*-Tyr-Phe-Gln-Asn-Cys*-Pro-Lys-Gly-NH2, *disulfide bond
Labor
Oxytocin 9 Cys*Tyr-Ile-Gln-Asn-Cys*-Pro-Leu-Gly
Atosiban 9 Mpa*-D-Tyr(Et)-Ile-Thr-Asn-Cys*-Pro-Orn-Gly-NH2, * disulfide bond (1-6)
Antiviral
Enfuvirtide 36
CH3CO-Tyr-Thr-Ser-Leu-Ile-His-Ser-Leu-Ile-Glu-Glu-Ser-Gln-Asn-Gln-Gln-Glu-Lys-Asn-Glu-Gln-Glu-Leu-Leu-Glu-
Leu-Asp-Lys-Trp-Ala-Ser-Leu-Trp-Asn-Trp-Phe-NH2
Thymalfasin 28
Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-
Glu-Asn-OH
Antibacterial
Daptamycin 11
Cyclic N-decanoyl-L-tryptophyl-D-asparaginyl-L-aspartyl-L-threonylglycyl-L-ornithyl-L-aspartyl-D-alanyl-L-
aspartylglycyl-D-seryl-threo-3-methyl-L-glutamyl-3-anthraniloyl-L-alanine 1-lactone
Bacitracin 10 D-Orn*-Ile-D-Phe-His-D-Asp-Asn--Lys*-Ile-D-Glu-Leu, *disulfide bond (1-7)
Gramidicin 15 HCO-Val-Gly-Ala-(D-Leu)-Ala-(D-Val)-Val-(D-Val)-Trp-(D-Leu)-Trp-(D-Leu)-Trp-(D-Leu)-Trp-NHCH2CH2OH
Colistin 10 Dbu-Thr-Dbu-Dbu*-Dbu-Leu-Leu-Dbu-Dbu-Thr*, * disulfide bond (4-10)
Pexiganan 22 Gly-Ile-Gly-Lys-Phe-Leu-Lys-Lys-Ala-Lys-Lys-Phe-Gly-Lys-Ala-Phe-Val-Lys-Ile-Leu-Lys-Lys
Omiganan 12 Ile-Leu-Arg-Trp-Pro-Trp-Trp-Pro-Trp-Arg-Arg-Lys-NH2
Antifungal
Caspofungin 6
1-[(4R,5S)5-[(2-aminoethyl)amino] -N2-(10,12-dimethyl-1-oxotetradecyl)4-hydroxy-L-ornithine]5-[(3R) 3-
hydroxy-L-ornithine] pneumocandin B0
Micafungin 6
1-[(4R,5R)-4,5-dihydroxy-N2-[4-[5-[4-(pentyloxy)phenyl]-3-isoxazolyl]benzoyl]-L- ornithine]-4-[(4S)-4-hydroxy-4-[4-
hydroxy-3-(sulfooxy)phenyl]-L-threonine] pneumocandin A0
Anidulafungin 6 1-[(4R,5R)-4,5-Dihydroxy-N2-[[4"-(pentyloxy)[1,1':4',1"-terphenyl]-4-yl]carbonyl] -L-ornithine] echinocandin B
Histatin 12 Ala-Lys-Arg-His-His-Gly-Tyr-Lys-Arg-Lys-Phe-His-NH2
Lactoferrin 11 Gly-Arg-Arg-Arg-Arg-Ser-Val-Gln-Trp-Cys-Ala
CNS
Conotoxin 25
Cys*-Lys-Gly-Lys-Gly-Ala-Lys-Cys*-Ser-Arg-Leu-met-Tyr-Asp-Cys*-Cys*-Thr-Gly-Ser-Cys*-Arg-Ser-Gly-Lys-Cys*-
NH2, * 3 disulfide bonds
Nemifitide 5 4-fluoro-L-phenylalanyl-trans-4-hydroxy-L-prolyl-L-arginyl-glycyl-tryptophanamide



126 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson

GLP-2
GLP-2 (Teduglutide) is derived from proteolytic cleavage
of proglucagon in the same process that yields glucagon and
GLP-1. GLP-2 acts in an opposite fashion to GLP-1, enhanc-
ing intestinal growth and metabolism with nutrient intake.
Native GLP-2 is susceptible to DPP-IV cleavage, similar to
GLP-1. However, NPS Pharmaceuticals has created an ana-
log [Gly
2
] GLP-2 (Teduglutide) that is resistance to protease
degradation (Table 1) [26]. NPS Pharmaceuticals received
Orphan Drug status and has completed Phase 3 trials on sub-
cutaneous delivery of 0.05 mg or 0.10 mg per kilogram of
body weight [25]. An NDA on Gattex
®
(Teduglutide) is an-
ticipated to be filed in 2008 for Short Bowel Syndrome.
Short Bowel Syndrome is a malabsorption disorder caused
by the surgical removal of more than two thirds of the small
intestine, where the primary endpoint is the reduction of in-
travenous or parenteral feeding [25].
Teduglutide is also in Phase 2 trials for Crohn’s disease.
Crohn's disease is a chronic, episodic, inflammatory bowel
disease and is generally classified as an autoimmune disease.
The main gastrointestinal symptoms are abdominal pain,
diarrhea, constipation, vomiting, weight loss or weight gain
caused by inflammation in the GI tract. Crohn's disease is a
chronic inflammatory bowel disease that affects approxi-
mately one million patients in the United States and Europe.
Zealand Pharma also has a GLP-2 analog in Phase 2 tri-
als for chemotherapy induced diarrhea [27].
Other Peptides
Delmitide (Genzyme) is a protease resistant D-amino
acid decapeptide in Phase 2 trials for irritable bowel syn-
drome (Table 1) [28]. Irritable bowel syndrome is a func-
tional bowel disorder characterized by abdominal pain and
changes in bowel habits. Delmitide in an anti-inflammatory
peptide that inhibits synthesis of proinflammatory cytokines
by disrupting cell signaling, specifically tumor necrosis fac-
tor, interferon and interleukins 2 and 12. The peptide is also
recovered unchanged in the feces after oral administration.
Sapphire Therapeutics also has a ghrelin analog (Aib-
His-D-2-Nal-D-Phe-Lys-NH
2
) in Phase 2 trials for post-
operative illeus [29]. Ipamorelin stimulates growth hormone
relase via a GHRP like receptor [30].
OSTEOPOROSIS
Over 10 million women and men in the United States
population have osteoporosis, and an addition 18 million
more have low bone mass.
The World Health Organization definition of osteoporo-
sis is a bone mineral density (BMD) 2.5 standard deviation
below the mean for normal women, plus fracturing [31, 32].
Post-menopausal women are at the highest risk and can lose
up to 5% of their total bone volume per year and following
menopause women can lose up to 20% of their bone mass in
5-7 years [32]. Annual sale projections for injectable PTH
vary from US $500 million to US $2 billion annually, where
an efficacious alternative to injections would significantly
expand the market due to patient acceptability and compli-
ance [33].
Calcitonin
Current anti-resorptive treatments do not cure osteoporo-
sis, since they do not replace previously lost bone mass. Cal-
citonin acts mainly to inhibit bone resorption and reduce
bone remodeling. Bone is a framework of supporting tissue,
bone cells, osteoblasts and osteoclasts. Osteoblasts are cells
that make bone, while the osteoclast cells break it down.
Osteoblasts and osteoclasts are normally in equilibrium with
normal bone remodeling. Therefore, many skeletal disease
states can be characterized by the uncoupling of bone resorp-
tion and formation processes [34].
Fish derived calcitonins, like salmon calcitonin (sCT),
are more potent than thyroidal calcitonins like human calci-
tonin (hCT) [35, 36]. Therefore, most pharmaceutical appli-
cations utilize the sequence for sCT. Salmon calcitonin is 32
amino acids in length with a disulfide between Cys
1
and
Cys
7
, and a stable -helix in the central region (Table 1) [35,
36]. Calcitonin is used in post menopausal women with low
bone mass, where primary clinical endpoints are bone bi-
opsy, radial bone mass and bone mineral density [3].
sCT Delivery
Currently, several calcitonin products are on the market
[3]. Micalcin
®
(Novartis) contains sCT in a refrigerated vial
for subcutaneous or intramuscular injection, and is indicated
for Paget’s disease, hypercalcemia and post-menopausal
osteoporosis [3]. Parenteral sCT can maintain bone density
and produce small increases in bone mass in the spine [37].
Injections are recommended every other day for osteoporo-
sis, and therefore, nasal products have been more acceptable
to some patients.
Local barriers to peptide absorption including permeabil-
ity, protease stability and bioavailability challenges increase
the dosage to achieve efficacy by the nasal route. Fortical
Nasal Spray (Upsher-Smith/Unigene) and Micalcin
®
Nasal
Spray (Novartis) contain sCT in a refrigerated product ad-
ministered daily, and are indicated for post-menopausal os-
teoporosis [3]. The average bioavailability of Micalcin
®
is
3%, with a wide range of variability (0.3-30.6%), when
compared to intramuscular injection. However, even with
low and variable bioavailability, nasal sCT can increase spi-
nal bone density 2-3% without an effect on proximal femur
bone mass [38]. Nastech filed an ANDA in 2004 for nasal
calcitonin. However, Nastech received a non-approvable
letter from the FDA in July 2006 due to potential immuno-
genicity concerns that might result from interactions between
salmon calcitonin and chlorobutanol, used as a preservative
[39].
Oral delivery of sCT has been difficult due to poor
bioavailability and in vitro intestinal degradation [40, 41].
However, Emisphere Technologies utilizes proprietary, syn-
thetic chemical compounds that facilitate the transport of
therapeutic macromolecules across biological membranes.
Specifically, non-acylated amino acids were evaluated as
carriers, where a non-covalent complex is formed, causing
partial unfolding of the protein [42]. They have hypothesized
that this conformational change results in exposure of hydro-
phobic side chains and facilitates passive diffusion through
the lipid bilayer. Once the complex crosses the intestinal
barrier via a passive transcellular transport process, it then
Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 127
dissociates and the protein refolds into its native conforma-
tion. Emisphere, in collaboration with Novartis, has reported
positive Phase 2 results on an oral formulation of sCT [43,
44]. The Phase 2 study was performed in Europe over a three
month period. Five doses were administered with a fixed
amount (200 mg) of N-acetylated amino acid delivery agent
(8-[N-2-hydroxy-5-chloro-benzoyl]-amino-caprylic acid) (4-
MOAC). A significant reduction in bone resorption markers
was observed for one of the doses (1 mg/day) [45]. The de-
livery agent forms a non-covalent complex, induces confor-
mational changes in sCT, exposing hydrophobic residues and
facilitating their transport across the intestinal tract [42, 43,
46]. Once the complex crosses the intestinal barrier via a
passive transcellular transport process, it then dissociates and
the protein refolds into its native conformation. Future trials
will need to assess the impact of long term administration on
changes in BMD and fracture risk. Novartis has informed
Emisphere that they have met with the FDA to discuss the
Phase 3 clinical plan. Bone Medical (Australia) has also
completed Phase 2a studies in the UK with oral calcitonin
(Capsitonin™) [47]. Nobex/Biocon have an oral form of
calcitonin in Phase 1 modified with amphiphilic oligomers.
Parathyroid Hormone
Human parathyroid hormone (hPTH) is an 84-amino acid
peptide hormone that plays a key role in the maintenance of
calcium homeostasis. hPTH binds to a target cell surface G-
protein-coupled hPTH/hPTHrP receptor, which results in
activation of adenylate cyclase and phospholipases and in-
creased intracellular levels of cyclic AMP and calcium.
hPTH increases the rate of bone remodeling and results in a
positive remodeling balance, leading to thicker osteons
(structural units of remodeled bone). New bone formation
occurs on quiescent surfaces and as a result, trabecular archi-
tecture comes to more closely resemble normal bone.
The active region resides in the N-terminal region, and
therefore, most development work has been executed on
hPTH (1-34) (Table 1). Furthermore, the region contains
three function domains responsible for receptor binding
(His
14
-Phe
34
), cAMP-cyclase activation (entire sequence) and
initiation of a cAMP independent signal transduction path-
way (Asp
30
-Phe
34
) [48, 49]. The structure of hPTH (1-34) in
water has been shown to consist of an -helical region be-
tween Glu
4
-Lys
13
, a turn at Asn
16
-Glu
19
, a globular hydro-
phobic core comprising Leu
15
, Leu
18
, Trp
23
, Val
31
and an -
helix from Val
21
-Gln
29
[48, 49].
PTH analogs represent a new class of anabolic therapies
for the treatment of severe osteoporosis, having the potential
to improve skeletal microarchitecture. Sustained high levels
of circulating PTH induces an increase in bone turnover and
a subsequent reduction in bone mass caused by stimulation
of osteoclastic resorption activity. Specifically, continuous
PTH promotes osteoclasts to demineralize bone; however
pulsatile delivery promotes osteoblasts to strengthen bone
[33, 50, 51]. Intermittant daily subcutaneous injections of
PTH stimulates the bone formation activity of osteoblasts,
replacing lost bone in both osteopenic, ovariectomized rats
and osteoporotic humans. PTH is used in post menopausal
women with high risk for fracture, where primary markers
are new vertebral and non-vertebral fractures, and bone min-
eral density [3].
PTH Delivery
Currently, only one PTH product is on the market [3].
Forteo
®
contains an emulsion of rhPTH(1-34) in a refriger-
ated disposable pen, and is indicated for post menopausal
osteoporosis [3]. Daily subcutaneous injections in the thigh
or abdominal wall result in bone formation and bone resorp-
tion markers increasing 55% and 25%, respectively. These
results indicate that bone turnover was successfully uncou-
pled, with an overall increase in bone formation [52, 53].
Allelix Biopharmaceuticals and NPS Pharmaceuticals
have just completed enrollment of Phase 3 for a PTH analog
(ALX 111) (PREOS
®
) for subcutaneous injection [45, 54].
Zelos Therapeutics is also in Phase 2 trials with in-
jectable Ostabolin-C
®
[33]. The Ostabolin-C analog [(Leu
27
)-
cyclo(Glu
22
-Lys
26
)-hPTH(1-31)NH
2
] retains bone formation
properties, but does not induce hypercalcaemia, which is a
side effect for PTH and Forteo. Unlike hPTH(1-34), the
truncated analog does not stimulate bone resorption or result
in elevated serum calcium levels [33, 55].
For chronic indications, injections are painful and patient
compliance is poor. To further optimize the therapeutic ef-
fect, PTH requires easily executed pulsatile delivery [50,51].
Most of the current delivery systems have been designed for
controlled/ sustained release and will not meet this need.
However, nasal and pulmonary PTH products, addressing
these needs, are currently in development. Zelos has ex-
plored pulmonary delivery with Nektar, and is currently in
collaboration with Aegis Therapeutics to develop a nasal
formulation [56]. Aegis’ Intravail
®
provides mild, non-
irritating absorption enhancing excipients for increased
bioavailability for nasal and other mucosal delivery.

Mannkind Pharmaceuticals has published results from a
pilot study on pulmonary delivery of PTH (1-34) [57]. The
PTH is formulated in a drug delivery system called Techno-
spheres™, which utilizes a diketopiperazine derivative (3,6-
bis(N-fumaryl-N-(n-butyl) amino-2,5-diketopiperazine) [57].
At acidic pH, the diketopiperazine formulation self assem-
bles into an ordered lattice plate approximately 2 μm in di-
ameter. In the precipitation process, the diketopiperazine
microencapsulates the PTH in the solution. The precipitates
are either freeze dried or spray dried for pulmonary delivery.
Following lyophilization, the Technospheres have a MMAD
of 2-4 μm [58]. When administered by the pulmonary route,
Technospheres dissolved in the pH neutral environment of
the deep lung and facilitate the rapid and efficient absorption
of insulin into systemic circulation. The carrier molecules are
excreted as ammonium salts in the urine within hours of ad-
ministration and not metabolized [57]. Crystalline PTH (1-
34) (~1% w/w) in Technospheres was delivered from a pas-
sive Medtone Dry Powder Inhaler using a single use dispos-
able cartridge, and appeared in the serum with a faster con-
centration increase and higher maximal concentration when
compared to subcutaneous injection. Furthermore, the rela-
tive bioavailability was calculated to be ~48% [57].
Alkermes and Eli Lilly have also announced an agree-
ment to develop and commercialize inhaled PTH [59]. The
128 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson
Alkermes AIR
®
technology consists of large, porous parti-
cles (> 5 μm) of low density (< 0.4 g/cm
3
), containing di-
palmitoyl phosphatidylcholine (DPPC) [60]. Additional dry
powder formulation of PTH in albumin, lactose or trehalose,
and DPPC have been characterized and delivered to rats
[61,62]. The powders had a tap density of 0.06 g/cm
3
, pri-
mary particle size of 4.5 μm, MMAD of 3.9-5.9 μm and an
ED of up to 98%. The absolute PTH bioavailability after
intratracheal administration was 21%, when compared with
18% for subcutaneous injection. Removal of albumin for the
formulation increased the bioavailability to 34% [62].
Nastech has completed Phase 2 studies on PTH delivery
from a nasal spray [63]. In a Phase 1 clinical study, PTH (1-
34) nasal spray formulations had bioavailability relative to
the subcutaneous injection of up to 11% [64]. This is consis-
tent with 17.6% bioavailability in rats [65]. Nastech has also
published on a novel tight junction modulating (TJM) pep-
tide that causes a transient, reversible decrease in transepi-
thelial electrical resistance (TEER) and an increase in per-
meability across tight junctions in cultured nasal epithelial
tissue [66]. The TJM peptide is 18 amino acids in length,
polycationic, amphipathic and C-terminally amidated. The
presence of TJM peptide (100 μm) resulted in an increase in
PTH (1-34) and sCT permeability (P
app
) of 3-5 fold and 23-
47 fold, respectively [67]. This technology utilizes high
throughput screening of formulations for safety and perme-
ability through tight junctions.
Daiichi and Chugai have completed Phase 2 clinical trials
in Japan with nasal PTH [33,68]. Similarly peak serum con-
centration of hPTH (1-34) were obtained between 20 μg
subcutaneous injection and 1000 μg nasal delivery. After 3
months, the 1000 μg/day dose showed an increase of 2.4%
BMD [68].
Emisphere Technologies is also in collaboration with
Novartis to develop oral PTH using the eligen technology
[33]. Emisphere has published oral delivery of PTH utilizing
a different non-acylated amino acid, N-[8(2-hydroxy-4-
methoxy) bensoyl] amino caprylic acid (4-MOAC) [69]. The
relative bioavailability of oral PTH (1-34), administered as
an aqueous solution to monkeys, was 2.1% relative to subcu-
taneous injection. The biological activity of oral PTH was
also determined to be comparable to injection in rats [69].
However, much development will still be required due deg-
radation of PTH(1-34) by GI proteolytic enzymes [70].
Unigene has also partnered with GlaxoSmithKline to
develop oral delivery of PTH for osteoporosis. The PTH
analog (768974) has not been disclosed; however Unigene
utilizes enteric coated solid dosage forms that reduce intesti-
nal proteolytic activity and has shown bioavailability in dogs
[71]. Bone Medical, in Australia, have completed Phase 1
trials comparing oral PTH(1-34) (Perthoxal™) with Forteo
®

[47].
TransPharma is currently partnered with Eli Lilly, and in
Phase 2 trials with PTH (1-34) delivered from a pen sized
transdermal patch (1 cm
2
) with microneedles. Phase 1 results
reported a relative bioavailability of 40% was observed when
compared with injection [72,73]. The ViaDerm System is a
transdermal patch with a solid state formulation on the back-
ing liner. A high frequency alternating current is transferred
through the microelectrodes, creating microchannels [73].
The microneedle array creates micrometer-scale holes in the
outer skin layer, thereby allowing drug delivery across the
skin [74,75].
Alza and Theratechnologies shared Phase 1 results for
PTH using the Macroflux
®
transdermal patch (2 cm
2
) [76].
In a cross-over study, patients received both a transdermal
patch and a subcutaneous injection of Forteo. Zosano’s Mac-
roflux technology incorporates a thin titanium screen with
microprojections that create superficial pathways in the skin.
In general, the microneedles penetration depth is less than
100 μm and penetrates only the stratum corneum (10-20 μm)
and epidermis (50-150 μm) layers. The microneedles are
painless because they do not penetrate to the nerve endings,
deeper in the skin, below the epidermis.
Similarly, Altea is in research with PTH and the Passport
patch [77]. The PassPort patch uses short bursts of focused
thermal energy to create hundreds of tiny channels in the
surface of the skin. When the patch is removed, the channels
close and the skin returns to a normal state. The patch con-
tains a reservoir of drug plus a tiny screen made of wafer-
thin metallic filaments. A small device is used to activate the
patch. One click of this battery-operated device rapidly de-
livers a short pulse of energy that passes through the metallic
film resulting in the creation of tiny channels in the skin sur-
face.
Other Peptides
Acologix is developing 23 amino acid peptide, Dentonin,
derived from matrix extracellular phosphoglycoprotein
(MEPE) found in bone and dental cells. Dentonin has com-
pleted Phase 2 trials for stimulating formation of new dentin
when applied directly to teeth [78]. Orthologic completed
Phase 1 trials with a 23 amino acid peptide, Chrysalin, for
acceleration of fracture repair [79].
ONCOLOGY
Worldwide, there were 10.9 million new cases, 6.7 mil-
lion deaths and 24.6 million persons living with cancer [80].
The most commonly diagnosed cancers are lung, breast and
colorectal, while the most common causes of death are lung,
stomach and liver. Of the cancers that are treated by the pep-
tide drugs listed below, lung, liver and prostate cancer were
most prevalent (Table 2) [80].
GnRH Agonists
Several GnRH (gonadotropin releasing hormone) ago-
nists are currently on the market for the palliative treatment
of prostate cancer and/or endometriosis and as an endo-
metrial-thinning agent prior to endometrial ablation for dys-
functional uterine bleeding [3]. Clinical markers include se-
rum testosterone levels (<50 ng/dL) and serum prostate spe-
cific antigen (PSA) score for prostate cancer. Markers for
endometriosis include pain relief and reduction of endo-
metriotic lesions.
Prostate cancer is commonly dependent on circulating
androgen levels. Testicular androgen ablation, or decreasing
serum testosterone levels to castrate level, is the standard of
Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 129
care advanced prostate cancer [81]. GnRH agonists, like le-
uprorelin, stimulate the pituitary testicular axis, resulting in a
temporary increase in serum testosterone levels. This is fol-
lowed by down regulation of the pituitary GnRH receptors,
resulting in decreased secretion of luteinizing hormone, and
suppression of serum testosterone levels to below castrate
level (50 ng/dl) [82].
Leuprorelin, or leuprolide, is the most commonly utilized
agonist in products today. The N-terminal residues, pGlu-
His-Trp, appear to be the region responsible for activity (Ta-
ble 1) [82]. The active conformation has been proposed to
consist of two -turns: a type II -turn centered at Tyr
5
-Arg
8

and a type III -turn perpendicular to the first centered at
pGlu
1
-Ser
4
[83].
Subcutaneous or intramuscular sustained release products
derived from leuprorelin, lasting 3-12 months, include
Lupron Depot
®
(Takeda/Abbott), Eligard
®
(Sanofi-Aventis),
Viadur
®
(Baxter), Leuprolide Acetate Injection
®
(Genzyme),
Prostap
®
(Wyeth), Atrigel
®
(Atrix). The products include
depot injections and sustained release implants. Subcutane-
ous implants containing the analog histrelin include Vantas
®

(Valera) and Supprelin LA
®
(Indevus). AstraZeneca also
provides a subcutaneous depot formulation of another ana-
log, goserelin, called Zoladex
®
. In addition, Debio-
Pharm/Beaufor Ipsen, Ferring, Ambrilia and Spectrum all
have GnRH products currently in clinical trials. Therefore,
influx of multiple generic versions has made this market very
competitive, where consumers are loyal to the Takeda prod-
uct line.
Other Peptides
Bortezomib (Velcade
®
) marketed by Millenium for man-
tle cell lymphoma and multiple myeloma in patients who
have received at least 1 prior therapy. Bortezomib is a modi-
fied dipeptidyl boronic acid, which exists as a cyclic anhy-
dride (trimeric boroxine) (Table 1). An intravenous bolus
dose is injected twice weekly for 2 weeks. Bortezomib is a
proteasome inhibitor. The boron atom in bortezomib binds
the catalytic site of the 26S proteasome with high affinity
and specificity [84]. The 26S proteasome is a large protein
complex that degrades ubiquitinated proteins and cleanses
the cell of misfolded proteins. Inhibition of the 26S protea-
some disrupts the normal homeostatic mechanisms, leading
to cell death. Bortezombic is metabolized by cytochrome
P450, where the major metabolic pathway is deboronation.
The deboronated metabolites show no activity. A follow on
subcutaneous weekly injection would minimize dosing in-
conveniences.
Merck KGaA and Oncothyreon have been granted Fast
Track Status for Stimuvax
®
and are currently in Phase 3 tri-
als [85]. Stimuvax
®
(L-BLP 25) is palmitoylated peptide
vaccine, formulated as a liposome (Table 1). The liposomal
formulation enhances recognition of the cancer antigen and
induces T-cell response to cancer cells expressing MUC1.
Stimuvax is indicated for non-small cell lung cancer, where
the median survival in Stage IIIB cancer patients was 30.6
months compared to control of 13.3 months in Phase 2b tri-
als [86].
Pharmexa also has a peptide cancer vaccine in Phase 3
trials [87]. Primovax
®
(GV1001 in combination with gemcit-
abine) has been granted Orphan Drug status for the treatment
of advanced unresectable pancreatic cancer. GV1001 is a 16
amino acid peptide that activates the immune system so that
it recognizes and kills cancer cells. GV1001 targets telom-
erase, which is seldom found in normal cell types, but over
expressed in most cancer cells. GV1001 is also in Phase 2
trials for liver cancer.
Merck KGaA and Integra have another oncology peptide in
Phase 2 for glioblastoma, or head and neck cancer. Cilengi-
tide is a cyclic RGD peptide, and a highly selective integrin
inhibitor that inhibits blood vessel formation in tumors (Ta-
ble 1) [88]. In Phase 2 trials, Cilengitide is dosed twice a
week in combination with temozolomide, where 69% of pa-
tients showed progression free survival for 6 months, com-
pared to 54% for the control group [89]. In addition, 92% of
patients in a subgroup with a methylated MGMT gene pro-
moter in the tumor tissue were progression free at 6 months.
Cilengitide is a small, cyclic peptide, and may have adequate
bioavailability for an oral dosage form could be useful.
Melanotan
®
(Clinuvel) has started Phase 3 trials with a topi-
cal application for pre-cancerous actinic keratosis and poly-
morphous light eruptions [90,91]. Melanotan is a 13 amino
acid analog of -melanocyte stimulating hormone, [Nle
4
, D-
Phe
7
] -MSH [91]. The product is a subcutaneous dissolving
implant the size of a grain of rich. After implantation, skin
pigmentation appears in 2 days and lasts for 2 months [90].
CARDIOVASCULAR
Integrilin
®
(Millenium) is an IV infusion indicated for
acute coronary syndrome in percutaneous coronary interven-
Table 2. Incidence and Mortality of Worldwide Cancer in 2002 [77]
Cancer Incidence Mortality
Lung 1,352,000 1,179,000
Liver 626,000 598,000
Prostate 679,000 221,000
Pancreas 232,000 227,000
Brain 189,000 142,000
Multiple Myeloma 86,000 62,000
130 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson
tion (PCI), myocardial infarction. Eptifibatide is a cyclic
heptapeptide, derived from rattlesnake venom, with an inter-
chain disulfide bridge is formed between the cysteine amide
and the mercaptopropionyl moieties (Table 1) [3]. Eptifi-
batide reversibly inhibits platelet aggregation by preventing
the binding of fibrinogen and von Willebrand factor. When
administered intravenously, eptifibatide inhibits platelet ag-
gregation in a dose- and concentration-dependent manner.
Natrecor
®
(J&J/Scios) is human recombinant B-type na-
triuretic peptide (Nesiritide), which is produced by the ven-
tricular myocardium (Table 1) [3]. Nesiritide is used for pa-
tients with acutely decompensated congestive heart failure
who have dyspnea at rest or with minimal activity to reduce
pulmonary capillary wedge pressure and improve dyspnea.
Clinical endpoints include pulmonary capillary wedge pres-
sure, right atrial pressure, cardiac index mean pulmonary
artery pressure, system vascular resistance, and systolic
blood pressure. Nesiritide promotes vasodilation, natriuresis,
and diuresis. Nesiritide may also offer tolerability and practi-
cal advantages over currently used vasodilators, inodilators
and inotropes in this condition; in particular, nesiritide does
not appear to have proarrhythmic effects [92]. The product is
supplied as a refrigerated, sterile single-use vial containing
1.5 mg lyophilized powder for reconstitution. Nesiritide has
a half life of 18 minutes; therefore a longer acting analog or
delivery format might be useful in enabling new indications,
such as congestive heart failure or heart attack. Scios
has explored delivering nesiritide from Medtronic’s implant-
able infusion systems.
Angiomax
®
(The Medicines Company) is indicated for
use as an anticoagulant in unstable angina and percutaneous
transluminal coronary angioplasty. Bivalirudin is indicated to
reduce the risk of acute ischemic complications, death due to
myocardial infarction or need for urgent revascularization
procedures, in patients with unstable angina pectoris under-
going percutaneous coronary intervention. Bivalirudin is
found (with hirudin) in the saliva of the medicinal leech (Ta-
ble 1). The pharmacological difference between bivalirudin
and hirudin, is that hirudin is an irreversible inhibitor of
thrombin while bivalirudin is a reversible one. Both peptides
directly inhibit thrombin by specifically binding to the cata-
lytic site and to the anion-binding exosite of circulating and
clot-bound thrombin [3].
Icatibant
®
(Jerini) is an effective and specific antagonist
of bradykinin B2 receptors, with sequence homology to
bradykinin (Table 1) [93]. Jerini obtained Orphan Drug
Status and has finished Phase 3 trials for hereditary angioe-
dema (HEA), and is in Phase 2 and Phase 1 trials for drug
induced angioedema and capillary leakage, respectively.
They have received a positive CHMP opinion from the
European Medicines Agency (EMEA), but received a not
approval letter from the FDA for HEA [94], and have re-
cently partnered with Shire Ltd to market Firazyr
®
.
Rotigaptide
®
(Zealand/Wyeth) is in Phase 2 trials in pa-
tients with large myocardial infarcts. Rotigaptide was devel-
oped for prevention of ventricular arrhythmia by reestablish-
ing heart tissue conductance and function by modifying gap-
junction communication. Rotigaptide also incorporates D
amino acids to provide improved proteolytic stability [95].
Finally, Affymax has generated a peptidomimetic of
erythropoietin (EPO) called Hematide
®
. Hematide
®
is a PE-
Gylated peptide with no sequence homology to EPO, and is
anticipated to be dosed monthly. It is in Phase 3 trials for the
treatment of anemia associated with chronic renal failure and
is in Phase 2 clinical trials for the treatment of anemia in
cancer patients [96]. Similarly, Aplagen has an EPO pepti-
domimetic called HemoMer
®
in preclinical development
[97].
IMMUNOTHERAPY
With the technological improvements in medicine, im-
munosuppressive and immunomodulator therapies have in-
creased.
Cyclosporine
Cyclosporine is used in immunosuppression for prophy-
lactic treatment of organ transplants (liver, kidney, heart),
rheumatoid arthritis and severe psoriasis. Patients are rou-
tinely monitored for serum cyclosporine levels. Cyclosporine
exerts specific and reversible inhibition of immunocompe-
tent lymphocytes in the G0-or G1-phase of the cell cycle. T-
lymphocytes are preferentially inhibited. The T1-helper cell
is the main target, although the T1-suppressor cell may also
be suppressed. Sandimmune also inhibits lymphokine pro-
duction and release including interleukin-2.
Cyclosporine is a hydrophobic cyclic peptide containing
only four amide groups (Table 1). Three of the amide hydro-
gen bonds stabilize the antiparallel -sheet structure, and the
fourth hydrogen bond stabilizes the -loop [98-101]. There-
fore, all of the amide groups are rotated inwards and in-
tramolecularly bonded to stabilize the -sheet and -turn,
making the molecule essentially insoluble in water.
However, the active conformation, from receptor binding
studies with cyclophilin, is characterized by rotation of the
four amide groups outwards to bond with the solvent or the
active site [102-104]. The overall effect is complete disrup-
tion of the secondary structure, including the -sheet and -
turn conformations. The cyclosporine/cyclophilin complex
then inhibits calcineurin, which is normally responsible for
activating transcription of interleukin 2. Cyclosporine also
inhibits lymphokine production and interleukin release.
Cyclosporine Delivery
Cyclosporine is essentially insoluble in water, which
makes formulation difficult [105]. For example, many of the
current marketed products are suspensions or emulsions.
Sandimmune
®
(Sandoz/Novartis) Injection is formulated in
Cremophor and alcohol; not an optimal IV infusion formula-
tion. Oral capsule forms (Neoral
®
, Sandimmune
®
) are formu-
lated in alcohol [3]. Gengraf
®
(Abbott) is an oral capsule
microsuspension in castor oil and propylene glycol. Similar
solubility challenges were encountered in developing Pulmi-
niq
®
(Chiron/Novartis) for lung transplant and Restasis
®
(Al-
lergan) for chronic dry eye [3].
Oral bioavailability of peptides is often low and variable.
Sandimmune provides <10% bioavailability in liver trans-
plant patients and >89% oral bioavailability in renal trans-
plant patients. Improvements in next generation analogs
Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 131
would benefit from classical structure/activity relationships,
but also structure/permeability and solubility relationships.
Other Peptides
Copaxone
®
(Teva) is a copolymer (5,000-9,000 mw) of
composed of four amino acids in myelin basic protein: Glu
(0.141), Lys (0.427), Ala(0.095), and Tyr (0.338) [2].
Glatiramer acetate modifies the immune processes responsi-
ble for the pathogenesis of Multiple Sclerosis, and is indi-
cated for reduction of the frequency of relapses in patients
with Relapsing-Remitting Multiple Sclerosis. Glatiramer
acetate is refrigerated solution for subcutaneous daily injec-
tion.
BioMS Medical is in Phase 3 trials with MBP8298, a 17
amino acid peptide derived from myelin basic protein, for
secondary progressive Multiple Sclerosis (Table 1) [106].
MBP8298 is a molecular replicate of the site of attack that is
dominant in MS patients with HLA haplotypes DR-2 or DR-
4. High doses of antigen, delivered intravenously every 6
months, induces immunological tolerance and suppresses
immune responses to the administered substance [106].
Peptimmune is in Phase 1 trials with a random copolymer
(PI-2301) of Phe, Lys, Ala and Tyr for relapsing Multiple
Sclerosis [107]. It was discovered that substitution of Glu for
Phe resulted in better binding of the peptide with the MHC
Class II complex on the surface of antigen presenting cells
and T-cells. Neurovax
®
(Orchestra) is also in Phase 2 trials
with a combination vaccine of three T-cell receptor peptides
(BV5S2, BV6S5 and BV13S1) [108].
Peptimmune is also in Phase 2 trials for pemphigus vul-
garis. PI-2301 is a 19 amino acid peptide derived from the
immunodominant T-cell epitope of DSg3 (desmoglein 3).
Patients are currently treated with high doses of steroids and
drugs that suppress the immune system in an effort to de-
crease the production of antibodies. Therefore, PI-2301 im-
munotherapy selectively suppresses the production of anti-
DSg3 antibodies, the pathogenic agent in pemphigus vul-
garis. Wyeth (TRU-015) is also in clinical trials with immu-
nosuppressant peptides for rheumatoid arthritis [109].
ACROMEGALY
Acromegaly occurs in approximately 60 people per mil-
lion of population [110]. Acromegaly is caused by the over-
production of growth hormone by the anterior pituitary
gland. The excess growth hormone in the blood stream trig-
gers the liver to produce IGF-1, which in turn directly stimu-
lates bone and tissue growth.
Somatostatin Analogs
The two most prevalent somatostatin analogs success-
fully developed into products are octreotide and lanreotide
(Table 1). Structure/activity relationships for somatostatin
analogs are similar. For example, octreotide is a cyclic oc-
tamer assumes an antiparallel -sheet and a type II -turn
[111]. Furthermore, an equilibrium between -sheet and 3
10

helix is possible.
Octreotide exerts pharmacologic actions similar to the
natural hormone, somatostatin. It is an even more potent
inhibitor of growth hormone, glucagon, and insulin than so-
matostatin. Like somatostatin, it also suppresses leuteinizing
hormone (LH) response to GnRH, decreases splanchnic
blood flow, and inhibits release of serotonin, gastrin, vasoac-
tive intestinal peptide, secretin, motilin, and pancreatic poly-
peptide. Octreotide has been used to treat the symptoms as-
sociated with metastatic carcinoid tumors (flushing and diar-
rhea), and Vasoactive Intestinal Peptide (VIP) secreting ade-
nomas (watery diarrhea). Octreotide substantially reduces
and in many cases can normalize growth hormone and/or
IGF-1 (somatomedin C) levels in patients with acromegaly.
Octreotide and lanreotide are indicated for treatment of
acromegaly and reduction of side effects from cancer chemo-
therapy. It is a long term therapy for patients where surgery
is not possible or surgery was not effective. The clinical
markers are serum growth hormone levels and serum IGF-1
levels [3].
Octreotide and Lanreotide Delivery
Several products are on the market, currently, with more
generic competition expected [3]. Sandostatin
®
(Novartis)
contains is available as a refrigerated sterile octreotide solu-
tion in 1 and 5 mL vials for subcutaneous or intravenous
injection. Sandostatin LAR
®
(Novartis) is a 1 month sus-
tained release depot formulated in PLGA for intramuscular
injection. Similarly, Somatuline
®
(Tercica) provides a refrig-
erated 1 month depot as a supersaturated suspension of lan-
reotide. Lanreotide has a longer half life than octreotide,
providing a better drug substance for a sustained release
formulation. Novartis has developed another analog, pasireo-
tide, which is in Phase 3 trials for Cushing’s disease and
Phase 2 trials for acromegaly and gastroentero pancreatic
neuroendocrine tumors [112]. Ambrilla/Mallinckrodt are in
Phase 3 trials with a sustained release formulation of octreo-
tide [113]. Generic competition will benefit from improve-
ments in storage stability (room temperature), ease of prepa-
ration and less pain on injection.
ENURESIS
Analogs of vasopressin have been very effective at treat-
ing urinary incontinence or enuresis [3]. Clinical endpoints
include total urine and maximum urine osmolality.
The peptide analogs are used as an antidiuretic replace-
ment therapy for management of central diabetes insipidus
and temporary prevention polyria/polydipsia and dehydration
following head trauma or surgery. They are also indicated to
increase the plasma levels of Factor VIII in patients with
mild hemophilia A and von Willebrands disease (Type 1).
For example, desmopressin will often maintain hemostasis in
patients with hemophilia A during surgical procedures and
will also stop bleeding in patients with episodes of spontane-
ous or trauma- induced injuries, such as intramuscular hema-
tomas or mucosal bleeding.
Desmopressin
The analogs most commonly found in marketed products
are Arg vasopressin, Lys vasopressin (lypressin), desmo-
pressin, felypressin and terlipressin [114]. Like all members
of the vasopressin/oxytocin family, they contain an internal
disulfide loop. Desmopressin (DDAVP) contains a D-Arg at
position 8 and deamination of the hemicysteine in position 1
132 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson
(Table 1) [115]. These modifications yielded an analog with
a higher antidiurectic to vasopressor ratio and a prolonged
biological halflife.
Desmopressin Delivery
Many products are on the market, as generic competition
has become prevalent. Sanofi-Aventis provides DDAVP
Injection
®
, DDAVP
®
Tablet and DDAVP
®
Nasal Spray [3].
DDAVP Injection is available as a refrigerated sterile solu-
tion in 1 mL single-dose ampules and in 10 mL multiple-
dose vials and the DDAVP Nasal spray is a room tempera-
ture aqueous formulation delivered from a spray pump.
Cyclic peptides usually have better bioavailability and
protease stability than their longer linear analogs, like soma-
tostatin, tachykinin, enkephalin and melanotropin analogs
[116]. The bioavailability of DDAVP oral tablets is about
5% compared to intranasal DDAVP, and about 0.16% com-
pared to intravenous DDAVP. The bioavailability of Sti-
mate
®
Nasal Spray (ZLB Berhing) when administered by the
intranasal route as a 1.5 mg/mL solution is between 3.3-
4.1%.
Other marketed products include injectable desmopressin
products from Ferring and hospira, oral desmopressin prod-
ucts from Teva and Barr, and nasal desmopressin/lypressin
from Ferring/Novartis, respectively. A peptidomimetic with
increased bioavailability would decrease the cost of goods,
and possibly recapture some of the generic market.
LABOR INDUCTION/RETARDATION
Oxytocin
Oxytocin and Vasopressin have very similar cyclic se-
quences, where modification of the sequences can yield ago-
nist and antagonists of diurectic and pressor activity (Table
1). For example, basic amino acids, such as Lys or Arg in
position 8 favored vasopressin activity, while Ile in place of
Phe at position 3 favored oxytocin activity [114]. The C-
terminal amide was also determined to be critical for agonist
activities.
Oxytocin agonists are used to induce labor and support
labor in case of non-progression of parturition, while oxyto-
cin antagonists are used to retard premature labor. Oxytocin
promotes contractions by increasing the intracellular Ca
2+
.
Oxytocin has specific receptors in the myometrium and the
receptor concentration increases greatly during pregnancy,
reaching a maximum in early labor.
The oxytocin antagonist, Atosiban, retards premature
labor. Structure/activity relationships resulted in analogs
where alkylating the hydroxyl group on Tyr
2
and adding al-
kyl groups to position 1 resulted in altering the activity from
agonist to antagonist [114].
Oxytocin Analog Delivery
Pitocin
®
(Monarch) is a sterile solution for intravenous or
intramuscular delivery to initiate or improve uterine contrac-
tions. Oxytocin has a half life of 1-6 minutes in the blood.
Syntocinon
®
(Novartis) is provided as an injectable (labor
induction) or nasal spray (lactation induction).
Tractocile
®
(Ferring) is an oxytocin antagonist, called
atosiban, used to retard premature labor (Table 1). Ferring
has an additional oxytocin antagonist, called barusiban, in
Phase 2 trials.
CNS
Peptides used for treatment of the central nervous system
include indications such as pain management, depression,
autism and neurodegenerative diseases such as Alzheimer’s
disease.
Ziconotide
Prialt
®
(Elan) is a polybasic peptide with three disulfide
bonds, characterized by a triple stranded antiparallel -sheet
(Table 1) [117]. Ziconotide is a neurotoxin derived from the
genus Conus snails, that bind to presynaptic voltage gated,
N-Type, Ca
+2
channels, causing inhibition of neurotransmit-
ter release. Prialt
®
is indicated for the management of severe
chronic pain in patients for whom intrathecal therapy is war-
ranted, and who are intolerant of or refractory to other treat-
ment, such as systemic analgesics, adjunctive therapies, or
intrathecal morphine. Ziconotide does not bind to opioid
receptors and its pharmacological effects are not blocked by
opioid antagonists. Ziconotide intrathecal infusion is used in
the Medtronic SynchroMed
®
EL, SynchroMed
®
II Infusion
System and Cadd-Micro
®
ambulatory infusion pump.
Other Peptides
Nemifitide
®
(Tetragenex) is in Phase 3 trials for major
depressive disorder (Table 1) [118]. The peptide is adminis-
tered subcutaneously, with a rapid (3-5 days) onset of action
and symptomatic relief with few side effects.
Alzheimer’s disease therapeutics have utilized peptides to
help break down amyloid plaque formation, modulate pep-
tide processing enzymes (secretases) and degrade Abeta
toxic peptides [119]. Eli Lilly, Allon and Elan are in clinical
trials with peptides to treat Alzheimer’s disease.
ANTIBACTERIAL
An antimicrobial is a substance that kills or inhibits the
growth of microbes such as bacteria (antibacterial activity),
and fungi (antifungal activity) and viruses (antiviral activity).
Antibacterial and antifungal peptides are commonly fermen-
tation products; however, many are also made synthetically.
Peptide antimicrobials fall into two classes, non-ribosomally
synthesized peptides (gramicidin, bacitracin) and ribo-
somally synthesized peptides (pexiganan, histatin). Non-
ribosomally synthesized peptides are often constrained in
structure and may contain macrolactones, macrolactams, D-
amino acids, N-methylated residues, glycosylation, fatty
acids and heterocyclic elements [120,121].
Daptomycin
Cubicin
®
(Cubist) is indicated for patients with compli-
cated skin and skin structure infections, and Staphylococcus
aureus bloodstream infections (bacteremia), including right-
sided infective endocarditis [3]. Daptomycin is a lipopeptide
antibiotic effective against gram positive infections, and is

Advances in Peptide Pharmaceuticals Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 133
effective against methicillin-resistant Staphylococcus aureus
(MRSA). The peptide binds to the cell membrane and causes
rapid depolarization, resulting in a loss of membrane poten-
tial, which results in bacterial cell death (Table 1) [122]. The
product is supplied as a refrigerated, sterile, lyophilized, sin-
gle use vial (500 mg/vial), and is reconstituted in 0.9% NaCl
solution (refrigerated) for intravenous infusion. Infusion
times are short (30 minutes), which allows the use in outpa-
tient settings. Cubist has investigated an oral formulation,
but development was discontinued.
Other Peptides
Synercid
®
(Monarch/King Pharma) is an intravenous
infusion indicated for the treatment of patients with serious
or life-threatening infections associated with vancomycin-
resistant Enterococcus faecium (VREF) bacteremia, and
complicated skin and skin structure infections caused by
Staphylococcus aureus (methicillin susceptible) or Strepto-
coccus pyogenes [3]. Synercid is a streptogramin antibacte-
rial agent for intravenous administration containing two
semisynthetic pristinamycin derivatives, quinupristin and
dalfopristin. Streptogramin derived peptides work by inhibit-
ing protein synthesis [121]. Specifically, dalfopristin inhibits
the early phase protein synthesis and quinupristin inhibits the
late phase of protein synthesis.
Several peptide antibiotics are routinely formulated in
over the counter products or generic products [3]. For exam-
ple, bacitracin is used as an intramuscular injection for in-
fants with pneumonia and emphysema caused by staphylo-
cocci (Table 1). Neosporin
®
(J&J) is an antimicrobial oint-
ment containing two peptides (polymixin and bacitracin) and
neomycin. Bacitracin works by inhibiting the transfer of pep-
tidoglycan precursors to bactoprenol pyrophsphate [121].
Gramicidin (Bausch & Lomb) is formulated as an oph-
thalmic solution (Table 1). Coly-Mycin
®
(King Pharma) is a
polymixin parenteral indicated for the treatment of acute or
chronic infections due to sensitive strains of certain gram-
negative bacilli.
XOMA 629 (Xoma) is a peptide derived from bacteri-
cidal/permeability-increasing protein (BPI) currently in
Phase 1 studies for Staphylococcus aureus, MRSA, and su-
perficial skin infections, such as impetigo [123]. Pexiganan
(Genaera), a helical peptide related to magainin (derived
from frog skin) had failed to gain FDA approval for diabetic
foot ulcers [121,124]. However, Genaera has licensed pexi-
ganan to MacroChem [125]. Omigard
®
(Cadence/Migenix) is
in Phase 3 for prevention of local catheter site infections
[126]. Omiganan is related to bactolysins and is formulated
as a topical gel. Migenix has also partnered omiganan with
Cutanea for dermatologic indications, and are in Phase 2 for
papulopustular rosacea [127].

Novacta has several lantibiotic
analogs in pre-clinical development for C. difficile, skin in-
fections and MRSA [127]. Nisin, a 34 amino acid peptide, is
another member of the lantibiotic family and is a ubiquitous
antibacterial in foods. The majority of cationic antimicrobial
peptides act by the same mechanism: intercalation or uptake
across either the bacterial cell membrane and/or cytoplasmic
membrane followed by degradation of the membrane stabil-
ity [118,128].
ANTIFUNGAL
Echinocandins
Three echinocandins are currently on the market for can-
didemia. Unlike azole, allylamine and polyene fungal thera-
pies that target ergosterol synthesis, echinocandins have a
novel mechanism of action. These cyclic lipopeptides inhibit
the synthesis of (1,3)-D-glucan, which an integral polysac-
charide specific to fungal cell walls [128]. Chains of (1,3)-
D-glucan provide a solid matrix that gives the cell was its
shape and mechanical strength. Without this structural integ-
rity, osmotic lysis of the cell occurs. Because these lipopep-
tides are specific to fungal cells (mammalian cells do not
contain (1,3)-D-glucan) and target an entirely different
fungal pathway, they have less side effects and little to no
resistance to therapy.
Cancidas
®
(Merck), or caspofungin, was first to market in
2001 as an empirical therapy for fungal infections in febrile
neutropenic patients, candidemia, intra-abdominal abscesses,
peritonitis and pleural space candida infections, and eso-
phageal candidiasis, Cancidas
®
is also the only echinocandin
approved for invasive aspergillosis in patients who are re-
fractory to or intolerant of other therapies [3]. Mycamine
®

(Astellas) and Eraxis
®
(Pfizer) obtained similar indications
for candidemia, esophageal candidiasis, acute disseminated
candidiasis, peritonitis and abscesses (Table 1). Mycamine
®
,
or Micafungin, obtained an additional indication for prophy-
laxis of candida infections in patients undergoing hema-
topoietic stem cell transplantation. Furthermore, Mycamine
®

can be used in immunocompromised patients taking cy-
closporine, unlike Cancidas
®
. All three products are reconsti-
tuted sterile lyophilized powders for intravenous infusion.
Therefore, delivery of echinocandins by other routes
would allow treatment of additional indications. However,
efforts to develop oral products have not been successful.
Caspofungin and anidulafungin oral bioavailabilities are
<1% and ~7%, respectively [128-130].
Other Peptides
A fragment from human saliva, histatin, has shown anti-
bacterial activity (Table 1). Histatins form -helices and
work by binding to a receptor on the fungal cell membrane,
entering the cytoplasm and targeting the mitocondria
[124,131]. Histatin (PacGen/Demegen) is an oral wash in
Phase 2b trials for oral flush (candida albicans) in HIV [132].
A D-amino acid version is also in preclinical development.
Target patient populations, besides HIV, include asthma,
diabetes and xerostomia.
HLF1-11 (AM Pharma) is an injectable in Phase 2a trials
for hematopoietic stem cell transplant infections, MRSA
infection, and systemic candidiasis. HLF1-11 is an N-
terminal fragment of lactoferrin, with both antibacterial and
antifungal activity (Table 1) [124,133]. Helix Biomedix is
also developing a family of lipohexapeptides with both anti-
bacterial and antifungal activity.
NovaBiotics is in Phase 2a trials with a novel cationic
peptide for the treatment of onychomycosis [134]. The pep-
tide is delivered via a topical lacquer.

134 Current Pharmaceutical Biotechnology, 2009, Vol. 10, No. 1 Cynthia L. Stevenson
ANTIVIRAL
Many of the HIV protease inhibitors are di-or tripeptide-
like analogs that bind to the protease active site and inhibit
the activity of the enzyme. Class of small molecules with
peptide like characteristics (HIV protease inhibitors, ACE
inhibitors) is beyond the scope of this paper. However, there
are several larger peptide sequences marketed for the treat-
ment of AIDS and hepatitis.
Fuzeon
®
(Roche) is the brand name for enfuvirtide, an -
helical inhibitor of the fusion of HIV-1 with CD4+ cells
[3,135]. Enfuvirtide interferes with the entry of HIV-1 into
cells by inhibiting fusion of viral and cellular membranes
[3]. Enfuvirtide binds to the first heptad-repeat in the viral
envelope glycoprotein and prevents the conformational
changes required for the fusion of viral and cellular mem-
branes. Both the N- and C-terminal residues are required for
antiviral activity. Fuzeon
®
is used combination with other
antiretroviral agents for the treatment of HIV-1 infection in
treatment experienced patients with evidence of HIV-1 repli-
cation despite ongoing antiretroviral therapy. Clinical mark-
ers are mean log change in HIV-1 RNA and mean change in
CD4+ cell count.
Fuzeon
®
is injected subcutaneously twice per day with
the aid of the Biojector
®
2000. The product is a lyophilized
sterile product that is reconstituted prior to use. Enfuvirtide
has a short half life (3.8 hr) and undergoes hydrolysis to
form a deamidated metabolite at the C-terminal Phe residue
(Table 1) [3]. The most prevalent clinical side effect (98% of
patients) was local injection site reactions, including e-
rythema, induration, the presence of nodules or cysts, and
mild to moderate pain. Therefore, the development a sus-
tained release formulation or an analog with increased half
life would greatly improve the acceptability of this product.
Zadaxin
®
(SciClone) or thymalfasin is an immunomodu-
lator that augments (differentiation and maturation) T-cell
function. Zadaxin
®
is indicated as a monotherapy or combi-
nation (with interferon, ribavirin) therapy for the treatment of
chronic hepatitis B and C. Clinical endpoints are sustained
viral response at 72 weeks and normalization of the liver
enzyme ALT (at weeks 48 and 72), absence of HCV RNA
(at week 48), and an improvement in the liver biopsy. Zad-
axin
®
is also indicated as an adjuvant for influenza and hepa-
titis B vaccination in elderly and immunocompromised pa-
tients and in chronic hemodialysis patients who failed to
achieve adequate antibody titers from previous immuniza-
tion, respectively [3]. Zadaxin
®
is supplied as a sterile ly-
ophilized product for reconstitution, and is injected subcuta-
neously twice a week for 6 to 12 months. A product that pro-
vided a weekly injection would be a marked improvement,
similar to enfuvirtide.
SciClone has another dipeptide (-D-Glu-L-Trp) called
SCV-07 currently in Phase 2 trials for hepatitis C [136].
SCV-07 has shown efficacy in treating both viral and bacte-
rial infections, and is orally bioavailable. In addition, SCV-
07 has been approved in Russia for the treatment of tubercu-
losis.
CONCLUSION
Peptide pharmaceuticals have utilized D-amino acids,
novel amino acids and structure/activity relationships to gen-
erate analog that impart protease resistance and increased
bioavailability. Further improvements in novel formulation
strategies and delivery platforms have made it possible to
target optimal therapeutic dosing requirements. However,
additional innovations in technology will be required to op-
timize the next generation of successful peptidomimetics.
Companies are taking fresh approaches to modifying the
peptide backbone to impart efficacy, bioavailability and pro-
tease stability [127]. Other efforts are creating analogs from
structural families. For example, Amunix is making non-
immnogenic peptides with structures constrained by multiple
disulfide bonds (cysteine knots) [137]. These peptides are
similar to toxins/venoms found in nature (conotoxin, hi-
rudin), and often form ion channels in cell membranes. Ai-
leron is exploring the use of hydrocarbon peptide staples to
stabilize -helical structure [138]. These molecules can also
enter cells, and are being utilized for intracellular targets,
such as oncology [139]. Peptx is developing peptidomimetic
drugs from larger therapeutic proteins, specifically antimi-
crobials and oncology [140]. Key functional residues from
the active sites of proteins are incorporated in -sheet form-
ing peptides (bpep) [141]. The stable -sheet conformation
provides good structural stability under physiologic condi-
tions. If these strategies prove viable, new chemical entities
targeted to unmet needs and orphan disease states will be
able to successfully compete for efficacy, safety profiles and
cost of goods.
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Received: August 05, 2008 Revised: September 08, 2008 Accepted: October 23, 2008