Download come from?

ORIGINAL ARTICLE
P E E R-R EVI EW E D
L. Revers
An introduction to biologics
and biosimilars. Part I: Biologics:
What are they and where do they
come from?
Leigh Revers, MA, DPhil; Eva Furczon, HBSc, MBiotech
E. Furczon
We wrote this article
because we recognize
a need for today’s generation of pharmacists to
become better informed
about the history of biologics, and to learn how
they differ from the more
conventional small-molecule drugs that are prevalent in pharmacopeias.
Nous avons rédigé cet
article, car nous reconnaissons que les pharmaciens
d’aujourd’hui doivent
mieux connaître l’histoire
des produits biologiques
et savoir en quoi ils diffèrent des médicaments
traditionnels à petites
molécules, si fréquents
dans la pharmacopée
actuelle.
134
Introduction
In recent times, the term biologics has come to be
synonymous with a new class of protein-based
therapeutics that are produced using living organisms, including plants, animals and microorganisms such as yeast and bacteria. Compared to the
more traditional drugs, such as Aspirin, this new
class of medicine is inherently more complex and
cannot be synthesized in the laboratory by chemical means alone. Given the intricate nature of biologics, it is important that pharmacists become
well informed about the origins of these new
therapeutics and how they differ from conventional, small-molecule drugs. This review is the
first in a two-part series on biologics. In Part I, we
seek to define biologics and briefly examine their
heritage. In Part II, featured in the next issue, we
will explore the diversity of biologics and discuss
the challenges for “follow-on,” or generic, versions
known as biosimilars. The goal of both articles is
to introduce the fundamentals of biologics and to
explain how they are different and what these differences mean for pharmacists.
In search of a definition
The use of the expression biologics has become
commonplace in the language of the pharmaceutical industry.1 It is most often used (imprecisely)
to describe the new wave of protein-based therapeutics, predominantly the monoclonal antibodies (MAbs), which are among the fastest-growing
medicines today. But what exactly is a biologic?
The rather surprising answer is that even in 2010
there remains considerable confusion as to what
does or does not constitute a biologic. In this
article, we will present some of the plausible definitions. Furthermore, we maintain that the term
only really makes sense if you understand where
it comes from. Our brief survey of the history of
biologics in Part I will set the stage for a more indepth discussion in Part II of some of the unique
challenges faced by today’s major pharmaceutical
manufacturers, as well as by their rivals, the generic
drug manufacturers. In particular, an understanding of these challenges will illuminate the growing
debate surrounding the emerging class of drugs
known as biosimilars — a term coined to describe
generic, or “follow-on,” biologics that will compete
with the established big-name brands once their
patents expire.2
Our first inkling of a meaning for the term
biologics comes from the word itself: an adjectival
noun originating from biology, the science of living
organisms. In the narrower context of pharmaceuticals, this lends itself to the concept of biologic as a
way to describe any of a class of medicines in which
the active pharmaceutical ingredient (API) comes
from a living organism. This would include substances obtained from plants and animals as well as
from microorganisms such as yeast and bacteria. It
would also cover human blood products and even
tissue transplants. Such a simple demarcation is
rather broad, however. Plants, in particular, produce a myriad of molecules with well-established
pharmaceutical value — among them products as
diverse as salicin, the penicillins, quinine, digoxin
and paclitaxel — that are conventionally termed
“natural products,” and these are clearly not bioC P J / R P C • M AY / J U N E 2 0 1 0 • V O L 1 4 3 , N O 3
logics according to the industry’s accepted vernacular. The reasoning behind omitting natural products from the biologics roster is obvious when you
realize that commercialization of such medicines
relies on their bulk manufacture using industrialscale chemical synthesis, so, in that sense, they are
synthetic, not biologic. Indeed, the entire pharmaceutical business is built squarely on the capabilities of medicinal chemists to synthesize such drug
molecules with relative ease.
A tighter definition, then, is that biologics are
APIs derived from living organisms that cannot
reasonably be synthesized by chemical means. This
is far better, but it also begs the following question: Which molecules today are chemists unable
to make? The rather roundabout answer to that is
just about any biological molecule or mixture of
biological molecules that is too complex; for example, proteins or large pieces of DNA or even intact
whole cells and tissues from organisms. Hence, all
vaccines are biologics, as are insulin, blood factors
such as coagulation factor VIIa (NovoSeven RT)
and epoetin alfa (EPOGEN), and all of the therapeutic MAbs, such as trastuzumab (Herceptin)
and rituximab (Rituxan). These molecules of biological origin, sometimes called macromolecules,
are simply far too complicated to be prepared by
chemical synthesis alone; instead, we must farm
living organisms to produce them for us.
Yet, we find that even this “beyond-chemicalreach” definition fails to address the underlying
molecular properties that distinguish biologics
from conventional medicines. Furthermore, biologics today have become
inextricably intertwined
• The application of biotechnology to produce
with biopharmaceuticals,
modern medicines or “biologics” began about
to the point where they are
40 years ago when the techniques of recomsynonymous. As an alterbinant technology were first put into practice.
native, then, you need only
• Since then a number of increasingly complex
consider 2 properties of an
biologic drugs have been approved for the
API when deciding from
treatment of patients worldwide.
first principles whether
• It is important for pharmacists to know the
or not it is a biologic: the
origins of these new therapeutics and how
first is the relative molecuthey differ from conventional, small-molecule
lar size of the API, and the
drugs.
second, its compositional
uniformity.
The relative molecular mass (Mr) is the molecular mass of a substance relative to 1/12 the mass
of an atom of carbon-12. The relative molecular
mass, and by direct relation, the size, is a primary
defining feature of any molecule, yet, amazingly,
this often goes unappreciated and is not specified
on drug labels. In a very real sense, size is everything in the world of molecular medicine. Why?
Because all APIs are information carriers. This
information takes the form of the drug’s unique
3-dimensional shape, a shape defined by its underlying molecular structure, and the complexity of
that information is size-dependent and, therefore, mass-dependent. The bigger the molecule,
the greater the number of atoms that make up its
structure and the more complex and information-
Key points
Molecular size comparison of a small molecule drug (Aspirin)
to 3 different classes of biologics*
FIGURE 1
*Relative molecular masses are shown in parentheses.
Images: Molecule of the month, adapted with permission from the RCSB Protein Data Bank website, with
attributions to David Goodsell.3
C P J / R P C • M AY / J U N E 2 0 1 0 • V O L 1 4 3 , N O 3
135
rich it becomes and hence the more biologically
sophisticated. The flipside of this coin is equally
significant: bigger, more complex APIs are less portable than their smaller cousins. In a patient, small
molecules administered intravenously can travel
just about anywhere unimpeded, almost always
unnoticed by the immune system. However, bulkier APIs encounter barriers, such as membranes,
that can block their entrance into cells or across the
blood-brain barrier, and they are much more likely
to trigger an immune response. To gain perspective on the relative sizes of different molecules, we
need only compare common Aspirin, with an Mr
of 180, to some archetypal biologics (Figure 1).3
Insulin, a simple biologic, has an Mr of 5808, over
30 times larger than Aspirin; the hormone erythropoietin has an Mr of 30,400, which is 5 times
larger again; and MAbs weigh in at an enormous
150,000, another 5 times larger. Biologics, then, are
molecular heavyweights — comparing Aspirin to
a MAb is like comparing a 2 kg bag of sugar to an
average-size family car. Thus, as a rule of thumb,
we suggest defining a biologic as any API that is
5 or more times larger than Aspirin (i.e., with an
Mr > 1000). There are provisos to this. First, we
must exclude synthetic biopolymers, molecules
with highly repetitive structures, because these
are readily manufactured by chemists. We also prefer to avoid including vaccines because, although
FIGURE 2
136
strictly falling under the biologics umbrella, the
field of vaccines, like that of natural products, is
already well established and has been reviewed
elsewhere.4,5
The second characteristic property of biologics
is the possibility of molecular diversity. Small APIs
are uniform in their composition because they are
chemically synthesized with precise control, and
any contaminants or unwanted side products
can be purified away. This is not true of biologics, which often comprise a wide range of closely
related variants or are intentionally a mixture of
different biomolecules. We will revisit this topic
of heterogeneity in greater detail later in Part II,
but now that we have some working definitions
for biologics, we will review some of the historical
milestones behind their rise to prominence.
A glimpse into the history of biologics
Biologics are a 20th-century development (Figure 2).6-10 The isolation of the first-ever biologic,
the hormone insulin, was achieved by Frederick
Banting and Charles Best in Toronto in 1921.11,12
Insulin (from the Latin insula) is named for the
islets of Langerhans in the pancreas, which secrete
the hormone. Banting and Best isolated the substance from the pancreatic ducts of dogs and later
used it to correct the inborn insulin deficiency in
type 1 diabetic patients. Several decades later, in
Timeline: Biologics development 6-10
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1955, it was identified by Frederick Sanger as a
protein composed of 51 amino acids, with an Mr
of 5808.13 The molecule is an archetype for the socalled replacement therapy category of biologics,
in that it is introduced into the body to correct a
physiological deficiency. While extraction of insulin from the pancreas of cattle and pigs quickly
became a commercial success,5 it was soon apparent that there were allergic complications in some
people, because insulin is large enough to be monitored by the immune system. In these cases, the
subtle difference between the human and animal
forms of insulin caused the latter to be recognized
as foreign.
The real breakthrough in insulin production
came with the advent of recombinant DNA technology, first described by Herbert Boyer and Stanley Cohen and colleagues in 1973.14 After hearing
about Boyer and Cohen’s breakthrough, a venture
capitalist by the name of Robert Swanson placed a
call to Boyer and requested a meeting.15 Famously,
Boyer agreed to give Swanson 10 minutes of his
time.16 Swanson’s enthusiasm for the technology
and his faith in its commercial viability was contagious, and the meeting extended from 10 minutes to 3 hours; by its conclusion, the world’s first
biotechnology company, Genentech, was born.
Using Boyer and Cohen’s techniques, a team at
Genentech was able to introduce the human
C P J / R P C • M AY / J U N E 2 0 1 0 • V O L 1 4 3 , N O 3
insulin gene into bacteria,
enabling the isolation of
biosynthetic insulin that
was indistinguishable from
human insulin. Though
• Le recours à la biotechnologie pour fabriquer
Swanson and Boyer faced
des médicaments modernes ou « produits
skepticism from both the
biologiques » a débuté il y a 40 ans avec
academic and business
l’utilisation des techniques de recombinaison
communities, by 1982, in
génétique.
partnership with pharma• Depuis lors, un certain nombre de médicaceutical giant Eli Lilly, they
ments biologiques de plus en plus complexes ont
had succeeded in obtainété approuvés pour le traitement de patients à la
ing the FDA’s approval for
grandeur de la planète.
the drug, which has been
• Il est important que les pharmaciens connaismarketed successfully ever
sent l’origine de ces nouvelles thérapies, ainsi que
since under the trade name
ce qui les distingue des médicaments traditionHumulin. In 2008, Lilly
nels à petites molécules.
reported collective sales of
US$2.8 billion17 for its family of recombinant insulin products, which includes both the Humulin
range and Humalog, a more recent insulin variant.
The second biologic essential to our story is
another hormone, erythropoietin (EPO). It too
is a replacement therapy. EPO is a blood factor
that regulates red blood cell production, and its
existence was first postulated in 1906 by Paul Carnot in Paris based on transfusion experiments he
conducted in rabbits.18 By the middle of the 20th
century, it was found that rats breathing a low-oxy-
Points clés
137
gen atmosphere had elevated levels of EPO in their
blood, and, by the 1960s, the hormone was discovered to originate from the kidneys. Human EPO
was first purified from human urine by Eugene
Goldwasser and his team at the University of Chicago in 1977.19 Subsequently, the limited quantities
available were used to successfully treat patients
with anemia. EPO has since been identified as a
glycoprotein — a protein with chains of sugar
molecules attached to it — with a molecular mass
of 30,400. It comprises a 165 amino acid polypeptide with 4 sugar side chains. EPO circulates in the
blood plasma at a very low concentration (about 5
picomolar). The presence of the sugar components
is of particular interest, because they are essential
to the molecule’s biological activity and because
they highlight that biologics can have added layers of complexity beyond just protein structure.20
Amgen Inc. became the first company to isolate
and patent the human gene responsible for making
EPO and to reproduce the drug in large quantities by inserting the gene into hamster ovary cells.
The company brought the resulting recombinant
drug to market in 1989 under the trade name Epogen, despite a bitter legal battle with rival Genetics
Institute, Inc., over alleged patent infringements.
Today, 3 main variants of EPO are available to
patients in North America: Amgen’s Epogen and
Aranesp, and Johnson & Johnson’s Procrit.
Amgen’s advances with Epogen and related
molecules such as the granulocyte colony-stimulating factor filgrastim (Neupogen) ran in parallel with the emergence of the second major
category of biologics, the MAbs. The first MAb,
Ortho Biotech’s muromonab-CD3 (Orthoclone),
was approved by the FDA in 1986.21 The original
concept of antibodies (more correctly termed
immunoglobulins) as molecules that bind to specific targets, or antigens, emerged at the turn of
the 19th century through the pioneering work of
Paul Ehrlich, Emil von Behring and Shibasaburo
Kitasato, and Karl Landsteiner.22 In the second
half of the 20th century, it became clear that antibodies consisted of an extremely diverse family of
glycoproteins circulating in blood with molecular masses of approximately 150,000. MAbs are
comprised of not 1, but 4 polypeptides — 2 heavy
and 2 light chains — interwoven into a Y-shaped
structure, as first postulated by Rodney Porter in
1962.23 Like EPO, antibodies are proteins with
sugar side chains, although in lesser proportion.
The first therapeutic antibodies were obtained by
von Behring as far back as 1890, in the form of
serum from animals that had been immunized
with a suitable antigen.9 The antisera contained
138
polyclonal antibodies — a mixture of immunoglobulins, only some of which were active against
the antigen — that were capable of neutralizing
invading pathogens in acute disease as well as
acting prophylactically. But the immune system’s
response to the antisera triggered a range of side
effects (called serum sickness) that were potentially
life-threatening.
The modern discovery that revolutionized antibody therapy came 85 years later, in 1975, when
César Milstein and Georges Köhler, working
together in Cambridge, UK, developed a relatively
simple method for custom-producing antibodies
in the laboratory.24 They fused together B lymphocytes, the white blood cells that generate antibodies, with immortal myeloma (cancer) cells from
bone marrow, inventing a new type of cell that
they called a hybridoma. The hybridoma inherited both the lymphocyte’s ability to produce antibodies and the cancer cell’s capacity for endlessly
dividing and proliferating. Careful segregation of
the hybridomas, so as to isolate only those individual cells capable of producing the most specific antibodies to a given antigen, allowed access
to an inexhaustible supply of antibodies that were
no longer a mixture of molecules with differing
antigen specificities. The monoclonal antibody, or
MAb, had arrived. Yet again, there were complications. The large size of these molecules and their
recognition as foreign invaders by the immune
system almost ended in premature disaster.25 This
stemmed from the fact that hybridoma technology relied on mouse cells to produce the desired
MAbs, which the human immune system could
discriminate as non-self molecules. More recent
advances in the technology have led to the development of part-mouse, part-human MAbs called
chimeras (e.g., rituximab [Rituxan] and cetuximab
[Erbitux]), as well as humanized antibodies (e.g.,
trastuzumab [Herceptin] and bevacizumab [Avastin]) that contain a bare minimum of non-human
amino acid sequences. In 2002, the first completely
human therapeutic MAb, Abbott’s adalimumab
(Humira), received market approval. Usually, the
more human the MAb, the better, although some
argue that immune reactions triggered by foreign
MAb components can be beneficial, particularly
in oncology.6 Today, there are over a dozen MAbs,
with collective oncology market sales in 2006 of
over US$7.8 billion and sharp growth predicted
over the next decade.6
We will only briefly mention the third and final
category of biologics. These are the “hybrid” biologics, such as MAb conjugates and protein fusions:
APIs that comprise 2 or more different molecules
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with different biological functions linked together.
Sometimes this approach can be as conceptually
straightforward as weaponizing an MAb by attaching a suitable “warhead,” such as a radioactive element (e.g., yttrium-90, iodine-131) that delivers a
deadly, short-range burst of radiation only to those
cells targeted by the antibody. Examples of such
radiolabelled MAbs include ibritumomab tiuxetan
(Zevalin) and tositumomab (Bexxar).26 Another
related strategy involves weaponizing the MAb by
chemical linkage to a bacterial toxin, such as calicheamicin, in order to specifically target antigenpresenting cancer cells, as in the case of Wyeth’s
gemtuzumab ozogamicin (Mylotarg). A more
sophisticated paradigm is Eisai Inc.’s denileukin
diftitox (ONTAK), which is an example of a protein
fusion between the enzymatically active portion of
the diphtheria toxin and the human cytokine interleukin-2 (IL-2).27 The resulting chimeric molecule
can bind to the IL-2 receptor and introduce the
diphtheria toxin into cancer cells that present these
receptors, killing the cells. These biologics are the
subject of most recent research and are expected to
be areas of considerable growth in the future.
End of Part I
We have chosen in this brief review to describe
what we believe the term biologics has come to
mean and to highlight a few of the most significant
advances that have defined this emerging field in
recent times. In Part II, we will explore the unique
diversity of biologics, where that diversity comes
from and why it is one of the foremost topics in the
present drug development climate. 
From the Master of Biotechnology Program, University of Toronto, Toronto, Ontario. Contact leigh.revers@
utoronto.ca.
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